Abstract

Maritime Antarctica is one of the major terrestrial ecosystems dominated by lichens and mosses, which represent important ecological indicators. Thus, we aimed to evaluate the changes in associated communities of mosses-lichens diversity and coverage along a pedoenvironmental gradient on Half Moon Island, Maritime Antarctica. We focused on how patterns in associated communities of mosses-lichens species diversity (richness, species composition and beta diversity) and coverage are associated with soil properties using plant inventory data from 174 plots across 14 contrasting pedoenvironments. The results clearly show marked differences in soil properties along the pedoenvironmental gradient, which determine variations in species composition, richness and coverage. We presumed that these variations are common in Maritime Antarctica owing to varying periglacial processes, weathering degree, parent material and biological influence (especially by penguins and other birds). The community species richness and coverage along the pedoenvironmental gradient differ, nevertheless share common species present in most pedoenvironments, despite differences in coverage. We assume that most of the pedoenvironments are habitats to rare species that occur only under specific soil conditions, additionally promotes high β-diversity between pedoenvironments and low species similarity.

Key words
beta diversity; community composition; mosses; lichens; plant-soil relationships; soil filters

INTRODUCTION

Understanding how soil gradients shape plant community diversity and structure represents an important question in ecology (Pekin et al. 2012PEKIN BK, BOER MM, WITTKUHN RS, MACFARLANE C & GRIERSON PF. 2012. Plant diversity is linked to nutrient limitation of dominant species in a world biodiversity hotspot. J Veg Sci 23: 745-754., Hernández-Hernández et al. 2017HERNÁNDEZ-HERNÁNDEZ R, BORGES PA, GABRIEL R, RIGAL F, AH-PENG C & GONZÁLEZ-MANCEBO JM. 2017. Scaling α- and β-diversity: bryophytes along an elevational gradient on a subtropical oceanic Island (La Palma, Canary Islands). J Veg Sci 28: 1209-1219.). Plant-soil relationships have constituted an important approach in ecology studies to address diversity patterns at both large and fine spatial scales in different ecosystems worldwide (e.g. Pekin et al. 2012PEKIN BK, BOER MM, WITTKUHN RS, MACFARLANE C & GRIERSON PF. 2012. Plant diversity is linked to nutrient limitation of dominant species in a world biodiversity hotspot. J Veg Sci 23: 745-754., Schmitz et al. 2020SCHMITZ D, SCHAEFER CERG, PUTZKE J, FRANCELINO MR, FERRARI FR, CORREA GR & VILLA PM. 2020. How does the pedoenvironmental gradient shape non-vascular species assemblages and community structures in Maritime Antarctica? Ecol Indic 108: 105726.). Soil gradients may determine plant community assembly by selecting species from a regional species pool into a local habitat (e.g. Pekin et al. 2012PEKIN BK, BOER MM, WITTKUHN RS, MACFARLANE C & GRIERSON PF. 2012. Plant diversity is linked to nutrient limitation of dominant species in a world biodiversity hotspot. J Veg Sci 23: 745-754., Villa et al. 2018VILLA PM, MARTINS SV, OLIVEIRA NETO SN, RODRIGUES AC, MARTORANO L, DELGADO L, CANCIO NM & GASTAUERG M. 2018. Intensification of shifting cultivation reduces forest resilience in the northern Amazon. For Ecol Manag 430: 312-320.). These patterns in plant community assembly reflected changes in species diversity (i.e. species richness, community composition), and structure (e.g. plant coverage) along soil properties gradients (i.e. soil fertility and depth filtering) based on multivariate analyses (e.g. Pekin et al. 2012PEKIN BK, BOER MM, WITTKUHN RS, MACFARLANE C & GRIERSON PF. 2012. Plant diversity is linked to nutrient limitation of dominant species in a world biodiversity hotspot. J Veg Sci 23: 745-754., Villa et al. 2018VILLA PM, MARTINS SV, OLIVEIRA NETO SN, RODRIGUES AC, MARTORANO L, DELGADO L, CANCIO NM & GASTAUERG M. 2018. Intensification of shifting cultivation reduces forest resilience in the northern Amazon. For Ecol Manag 430: 312-320., Schmitz et al. 2020SCHMITZ D, SCHAEFER CERG, PUTZKE J, FRANCELINO MR, FERRARI FR, CORREA GR & VILLA PM. 2020. How does the pedoenvironmental gradient shape non-vascular species assemblages and community structures in Maritime Antarctica? Ecol Indic 108: 105726.). Thus, diversity patterns are highly scale-dependent, and particularly high species diversity often matches habitat patchiness and promotes high species turnover (e.g. beta diversity) along environmental gradients (e.g. Hernández-Hernández et al. 2017HERNÁNDEZ-HERNÁNDEZ R, BORGES PA, GABRIEL R, RIGAL F, AH-PENG C & GONZÁLEZ-MANCEBO JM. 2017. Scaling α- and β-diversity: bryophytes along an elevational gradient on a subtropical oceanic Island (La Palma, Canary Islands). J Veg Sci 28: 1209-1219., Schmitz et al. 2020SCHMITZ D, SCHAEFER CERG, PUTZKE J, FRANCELINO MR, FERRARI FR, CORREA GR & VILLA PM. 2020. How does the pedoenvironmental gradient shape non-vascular species assemblages and community structures in Maritime Antarctica? Ecol Indic 108: 105726.).

Beta diversity (β-diversity) measures temporal and spatial variation in species composition (Baselga 2012BASELGA A. 2012. The relationship between species replacement and dissimilarity derived from turnover and nestedness. Glob Ecol Biogeogr 21: 1223-1232.). Taxonomic β-diversity corresponds to the percentage of dissimilarity in species composition between two distinct communities (Baselga 2010BASELGA A. 2010. Partitioning the turnover and nestedness components of beta diversity. Glob Ecol Biogeogr 19(1): 134-143.). For instance, a high β-diversity can result from a low proportion of shared species between two communities with a similar number of species, leading to a high contribution of the turnover (Baselga 2010BASELGA A. 2010. Partitioning the turnover and nestedness components of beta diversity. Glob Ecol Biogeogr 19(1): 134-143., 2012). Most studies on β-diversity along environmental gradients have emphasised vascular plant communities in different ecosystems of the world. However, the relative importance of spatial dissimilarities in associated communities of mosses-lichens species composition (β-diversity) as ecological indicators along soil gradients remains poorly understood. In this context, changes in mosses-lichens species diversity along soil gradients can be significantly given ongoing climate change, affecting their response to rising global temperatures (e.g. Robinson et al. 2018ROBINSON SA ET AL. 2018. Rapid change in East Antarctic terrestrial vegetation in response to regional drying. Nat Clim Change 8: 879-884.).

Antarctica’s main terrestrial ecosystems are dominated by lichens and mosses (Ochyra et al. 2008OCHYRA R, LEWIS-SMITH RI & BEDNAREK-OCHYRA H. 2008. The Illustrated Moss Flora of Antarctic. Cambridge: Cambridge University Press, p. 709., Poelking et al. 2015POELKING EL, SCHAEFER CEGR, FERNANDES FILHO EI, DE ANDRADE AM & SPIELMANN AA. 2015. Soil-landform-plant-community relationships of a periglacial landscape on Potter Peninsula, maritime Antarctica. Solid Earth 6: 583-594., Rodriguez et al. 2018RODRIGUEZ JM, PASSO A & CHIAPELLA JO. 2018. Lichen species assemblage gradiente in South Shetlands, Antarctica: relationship to deglaciation and microsite conditions. Polar Biol 41: 2523-2531.), and it is considered a key bioregion for the monitoring of environmental changes (Vieira et al. 2010VIEIRA G ET AL. 2010. Thermal State of permafrost and active-layer monitoring in the Antarctic: advances during the International Polar Year 2007–09. Permafr Periglac Process 21: 182-197., Michel et al. 2014MICHEL RFM, SCHAEFER CEGR, LÓPEZ-MARTINEZ J, SIMAS FNB, HAUS NW, SERRANO E & BOCKHEIM JG. 2014. Soils and landforms from Fildes Peninsula and Ardley Island, Maritime Antartica. Geomorphology 225: 76-86.). Antarctic vegetation is restricted to ice-free areas, such as the coastal zone, debris slopes or nunataks (Putzke & Pereira 2001PUTZKE J & PEREIRA AB. 2001. The Antarctic Mosses with special reference to the South Shetlands Islands. 1a Ed. Canoas: Editora da Ulbra, p. 196., Ochyra et al. 2008OCHYRA R, LEWIS-SMITH RI & BEDNAREK-OCHYRA H. 2008. The Illustrated Moss Flora of Antarctic. Cambridge: Cambridge University Press, p. 709.). Relatedly, there are different community types, which can be dominated by mosses, forming carpets and turfs, or lichens with different life forms or forming mosses-lichens associations, modeled according to landforms and soil properties (Francelino et al. 2011FRANCELINO MR, SCHAEFER CEGR, SIMAS FNB, FILHO EIF, SOUZA JJLL & COSTA LM. 2011. Geomorphology and soils distribution under paraglacial conditions in an ice-free area of Admiralty Bay, King George Island, Antarctica. Catena 85: 194-204., Poelking et al. 2015POELKING EL, SCHAEFER CEGR, FERNANDES FILHO EI, DE ANDRADE AM & SPIELMANN AA. 2015. Soil-landform-plant-community relationships of a periglacial landscape on Potter Peninsula, maritime Antarctica. Solid Earth 6: 583-594.). However, differences in soil properties along the pedoenvironment gradient concerning to moss and lichen diversity and community structure remain poorly understood in Antarctica (Leishman & Wild 2001LEISHMAN M & WILD C. 2001. Vegetation abundance and diversity in relation to soil nutrients and soil water content in Vestfold Hills, East Antarctica. Antarct Sci 13(2): 126-134., Schmitz et al. 2020SCHMITZ D, SCHAEFER CERG, PUTZKE J, FRANCELINO MR, FERRARI FR, CORREA GR & VILLA PM. 2020. How does the pedoenvironmental gradient shape non-vascular species assemblages and community structures in Maritime Antarctica? Ecol Indic 108: 105726.).

In this study, we aimed to evaluate the changes species composition, diversity and coverage in mosses-lichens communities along a pedoenvironmental gradient on Half Moon Island, Maritime Antarctica. We focused on how patterns in mosses-lichens species composition and richness, and coverage with soil properties using species inventory data from 174 plots across 14 contrasting pedoenvironments. In order to evaluate the community species diversity and coverage, we posed the following two research questions: 1) How do community species richness and coverage change along the pedoenvironmental gradient? 2) Do the community composition and β-diversity change across pedoenvironments? Based on the premise that soil filters shape mosses-lichens associated communities’ distributions (e.g. soil chemistry, depth, elevation), we sought to determine the following hypotheses: 1) The pedoenvironmental conditions by soil properties determine differences in community species richness and coverage; 2) The community composition of mosses and lichens species diminishes in similarity with increased soil properties differences and depth vartion along the pedoenvironment gradient. These differences in community composition are driven by soil properties variables directly related to the pedoenvironment gradient; 3) Differences in soil properties along the pedoenvironment gradient promote high β-diversity.

MATERIALS AND METHODS

Study area

This study was performed on Half Moon island (62°35’42.94”S 59°55’8.41”W), one of the smallest of the South Shetland archipelago, Maritime Antarctica (Figure 1). Its total surface area is 171 hectares, of which 19.17% is covered by vegetation (Schmitz et al. 2018SCHMITZ D, PUTZKE J, ALBUQUERQUE MP DE, SCHÜNNEMAN AL, VIEIRA FCB, VICTORIA FC & PEREIRA AB. 2018. Description of plants communities from Half Moon Island, Antarctica. Polar Res 37(1): 1523663.). There are three main hills on the island, Gabriel Hill (101 m.a.s.l) being the highest point (Schmitz et al. 2018SCHMITZ D, PUTZKE J, ALBUQUERQUE MP DE, SCHÜNNEMAN AL, VIEIRA FCB, VICTORIA FC & PEREIRA AB. 2018. Description of plants communities from Half Moon Island, Antarctica. Polar Res 37(1): 1523663.) followed by Xenia hill (≈ 90 m.a.s.l) and La Morenita Hill (≈ 85 m.a.s.l. behind Camara Base). Penguin rookeries are concentrated on Baliza Point and are frequently visited by tourists during the summer. The island was intensively studied during the 32^nd and 33^rd Brazilian Antarctic Expeditions in the austral summers of 2013/2014 and 2014/2015.

Selection of pedoenvironments

We selected 14 pedoenvironments with contrasting pedogenetic characteristics (Table I). We recognised that differents environmental processes (i.e. pedogenetic and landform processes) determine the 14 pedoenvironments along Half Moon island (Figure 2, Supplementary Material - Text S1 and Table SIa of Appendix). Given the marked differences between pedoenvironments, we considered the habitat filtering approach for soil-species relationship analysis (Poelking et al. 2015POELKING EL, SCHAEFER CEGR, FERNANDES FILHO EI, DE ANDRADE AM & SPIELMANN AA. 2015. Soil-landform-plant-community relationships of a periglacial landscape on Potter Peninsula, maritime Antarctica. Solid Earth 6: 583-594., Benavent-González et al. 2018BENAVENT-GONZÁLEZ A, DELGADO-BAQUERIZO M, FERNÁNDEZ-BRUM L, SINGH BK, MAESTRE FT & SANCHO LG. 2018. Identity of plant, lichen and moss species connects with microbial abundance and soil functioning in maritime Antarctica. Plant Soil 429(1-2): 35-52., Schmitz et al. 2020SCHMITZ D, SCHAEFER CERG, PUTZKE J, FRANCELINO MR, FERRARI FR, CORREA GR & VILLA PM. 2020. How does the pedoenvironmental gradient shape non-vascular species assemblages and community structures in Maritime Antarctica? Ecol Indic 108: 105726.). Thus, the possibility of a separating boundary between pedoenvironments provided an opportunity to study the effects of habitat filtering on species assemblages at a local scale in Maritime Antarctica (Poelking et al. 2015POELKING EL, SCHAEFER CEGR, FERNANDES FILHO EI, DE ANDRADE AM & SPIELMANN AA. 2015. Soil-landform-plant-community relationships of a periglacial landscape on Potter Peninsula, maritime Antarctica. Solid Earth 6: 583-594.).

Soil properties collection

According to Bockheim et al. (2006)BOCKHEIM JG, BALKS MR & MCLEOD M. 2006. ANTPAS Guide for Describing, Sampling, Analyzing, and Classifying Soils of the Antarctic Region, ANTPAS 1-12. recommendations, each soil profile was dug and sampled, facilitating their classification using the World Reference Base for Soil Resources (IUSS Working Group WRB 2015IUSS WORKING GROUP WRB. 2015. World Reference Base for Soil Resources 2014, update 2015 International soil classification system for naming soils and creating legends for soil maps. World Soil Resources reports no. 106. FAO, Rome.). To measure the soil properties within each plot, a composite sample of the surface soil (0-10 cm) was collected. All soil samples were analysed at the Soil Laboratory of the Federal University of Viçosa, following international standard protocols (EMBRAPA 1997EMBRAPA. 1997. Manual de Métodos de Análise de Solo. 2. ed. ver. atualiz. Centro Nacional de Pesquisa de Solos, Rio de Janeiro (212 pp. il., EMBRAPA/CNPS-RJ. Documentos, 1).). The following parameters were assessed: available P; exchangeable K, Ca, Na, Mg, Fe, Cu, Mn, Zn; exchangeable acidity (H + Al); pH (H₂O); organic matter (OM); sum of exchangeable bases (BS); effective cation exchange capacity (t); potential effective cation exchange capacity (T); bases saturation percentage (V); Al saturation (m); and remaining phosphorus (Prem). Due to the limited sample size, physical analyses could not be performed for all environments, so they were not included in the statistical analyszes.

Associated communities of mosses-lichens sampling

The pedoenvironments presented different mosses-lichens coverage areas; hence the number of plots was sufficient sampling representation in Half Moon. The number of plots ranged from five to 21 plots measuring 20×20 cm in differents pedoenvironments (Table I). A total of 174 plots across the 14 studied pedoenvironments were sampled using the Braun-Blanquet (1932)BRAUN-BLANQUET J. 1932. Plant Sociology: The study of plant communities. New York: McGraw-Hill, p. 439. square method and adapted to Antarctic vegetation conditions to measure the coverage of species in each plot. Within each plot, the majority of mosses and lichens were identified to the species level. Moss species were identified using the taxonomy keys presented by Ochyra et al. (2008)OCHYRA R, LEWIS-SMITH RI & BEDNAREK-OCHYRA H. 2008. The Illustrated Moss Flora of Antarctic. Cambridge: Cambridge University Press, p. 709. and Putzke & Pereira (2001)PUTZKE J & PEREIRA AB. 2001. The Antarctic Mosses with special reference to the South Shetlands Islands. 1a Ed. Canoas: Editora da Ulbra, p. 196., and lichen species using the keys presented by Øvstedal & Lewis-Smith (2001)ØVSTEDAL DO & LEWIS-SMITH RI. 2001. Lichens of Antactica and South Georgia: a guide to their identification and ecology. Cambridge: Cambridge University Press, p. 453. and Olech (2004)OLECH M. 2004. Lichens of King George Island Antarctica. The Institute of Botany of The Jagiellonian University, Cracow, p. 391.. The species were deposited in the herbarium at the Universidade de Santa Cruz do Sul (HCB).

The types of plant communities were named according to Schmitz et al. (2018)SCHMITZ D, PUTZKE J, ALBUQUERQUE MP DE, SCHÜNNEMAN AL, VIEIRA FCB, VICTORIA FC & PEREIRA AB. 2018. Description of plants communities from Half Moon Island, Antarctica. Polar Res 37(1): 1523663. and the landform classification provided by López-Martínez et al. (2012)LÓPEZ-MARTÍNEZ J, SERRANO E, SCHMID T, MINK S & LINÉS C. 2012. Periglacial processes and landforms in the South Shetland Islands (northern Antarctic Peninsula region). Geomorphology 155-156: 62-79.. Other characteristics such as elevation, depth and soil drainage levels and face of exposure were measured in the field (Table I).

Data analyses

All analyses were carried out in R Environment (R Core Team 2018R CORE TEAM. 2018. R: A language and environment for statistical computing. R Foundation for Statistical Computing. Vienna: Austria. https://www.R-project.org/.
https://www.R-project.org/... ). We tested normal distribution for all variables, using the Shapiro-Wilk test and evaluating the Q-Q plot, and the homogeneity of variances by Bartlett’s test. In order to compare soil properties (non-normally distributed data), species richness and coverage between pedoenvironments sites, we used Kruskal-Wallis’ test followed by a posterior Dunn’s test performed with the ‘dunn.test’ package (Dinno 2017DINNO A. 2017. “dunn.test” package: Dunn’s test of multiple comparisons using rank sums. http://CRAN.R-project.org/package=dunn.test. RStudio package version 1.0.14.
http://CRAN.R-project.org/package=dunn.t... ).

Soil variables were summarized using principal components analysis (PCA) to identify a possible pedoenvironmental gradient and to reduce the number of redundant soil properties; all variables were centred and standardized. We also calculated Pearson correlations among soil properties and the PCA ordination axes. The PCA was performed using the ‘FactoMineR’ package (Husson et al. 2017HUSSON F, JOSSE J, LE S & MAZET J. 2017. “FactoMineR” package Multivariate: Exploratory Data Analysis and Data Mining. http://CRAN.R-project.org/package=FactoMineR. RStudio package version 1.0.14.
http://CRAN.R-project.org/package=FactoM... )

Species richness in the 14 contrasting pedoenvironments’ sample areas was evaluated using both sample-based data to estimate rarefaction and extrapolation curves using the first Hill number (Chao et al. 2014CHAO A, GOTELLI NJ, HSIEH TC, SANDER EL, MA KH, COLWELL RK & ELLISON AM. 2014. Rarefaction and extrapolation with Hill numbers: a framework for sampling and estimation in species diversity studies. Ecol Monogr 84(1): 45-67.). Extrapolations were made based on presence/absence in the plot data of species by pedoenvironment (e.g. Colwell et al. 2012COLWELL RK, CHAO A, GOTELLI NJ, LIN SY, MAO CX, CHAZDON RL & LONGINO JT. 2012. Models and estimators linking individual-based and sample based rarefaction, extrapolation and comparison of assemblages. J Plant Ecol 5(1): 3-21.). Sample-based rarefaction/extrapolations with 95% confidence intervals were computed using the ‘iNEXT’ package (Hsieh et al. 2016HSIEH TC, MA KH & CHAO A. 2016. ‘iNEXT’: iNterpolation and EXTrapolation for species diversity.). Rarefaction was estimated as the mean of 100 replicate bootstrapping runs to estimate 95% confidence intervals. Whenever the 95% confidence intervals did not overlap, species numbers differed significantly at P < 0.05 (Colwell et al. 2012COLWELL RK, CHAO A, GOTELLI NJ, LIN SY, MAO CX, CHAZDON RL & LONGINO JT. 2012. Models and estimators linking individual-based and sample based rarefaction, extrapolation and comparison of assemblages. J Plant Ecol 5(1): 3-21.). These estimates were obtained using the “iNEXT” package (Hsieh et al. 2016HSIEH TC, MA KH & CHAO A. 2016. ‘iNEXT’: iNterpolation and EXTrapolation for species diversity.).

We performed non-metric multidimensional scaling (NMDS) to analyse differences between pedoenvironments in terms of species composition using Euclidean distance, specifically the ‘metaMDS’ function of the “vegan” package (Oksanen et al. 2018OKSANEN J ET AL. 2018. Vegan: Community Ecology Package. R package version 2.0-7.). We used permutational multivariate analysis of variance (PERMANOVA, 9999 permutations) to determine differences in species composition by using the adonis routine available within the “vegan” package (Oksanen et al. 2018OKSANEN J ET AL. 2018. Vegan: Community Ecology Package. R package version 2.0-7.). We undertook two way cluster analyses using Sorensen measures dissimilarity based on presence/absence data to identify pattern dissimilarity in species between pedoenvironments.

We used the multivariate homogeneity analysis to assess β-diversity along pedoenvironments (Anderson 2006ANDERSON MJ. 2006. Distance-based tests for homogeneity of multivariate dispersions. Biometrics 62: 245-253.). We calculated β-diversity as distance to group centroid based on Euclidean distance by using the R function betadisper in ‘vegan’ (Monte-Carlo, 999 permutations). We tested for differences in β-diversity between pedoenvironments for each site using the permutation test of homogeneity of multivariate dispersion (PERMDISP), which avoids problems of lack of independence among pairwise site comparisons (Anderson 2006ANDERSON MJ. 2006. Distance-based tests for homogeneity of multivariate dispersions. Biometrics 62: 245-253.). We subsequently used TukeyHSD.betadisper to create a set of confidence intervals on the differences between the mean distance-to-centroid of the levels of the grouping factor (Anderson 2006ANDERSON MJ. 2006. Distance-based tests for homogeneity of multivariate dispersions. Biometrics 62: 245-253.). We used the vegdist function to calculate Euclidean distance, and the betadisper and permutest functions to test for homogeneity of multivariate dispersion in the vegan package in R software 3.4.2. (Oksanen et al. 2018OKSANEN J ET AL. 2018. Vegan: Community Ecology Package. R package version 2.0-7., R Development Core Team 2018).

RESULTS

Soil fertility descriptors

The first two axes of the soil fertility PCA explained 52.7 % of the data variance (Figure 3). The biplot scores of the soil fertility descriptors were significantly correlated with the first axis (PCA1) and explained 34.3 % of the variance. The first axis was positively correlated (Figure S1 of Appendix ) with pH (R = 0.70 p < 0.05), the percentage of base saturation (R = 0.48, p < 0.05) and nutrients such as Mn (R = 0.60, p < 0.05), and Mg (R = 0.58, p < 0.05), distinguishing different pedoenvironments. Conversely, the PCA₁ was negatively correlated with organic matter (R = -0.87, p < 0.05), Al saturation (R = -0.63, p < 0.05) and potential cation exchange capacity (R = -0.86, p < 0.05). The second axis explained 18.4% of the variation and was negatively correlated with soil depth (R = 0.88, p <0.05), elevation (R = 0.70, p <0.05) and phosphorus (R = 0.67, p<0.05) along the pedoenvironmental gradient.

Species richness and plant coverage pattern

Twenty-one bryophyte species (20 mosses and one liverwort), 42 lichen species and one macroscopic algae (Prasiola crispa (Lightfoot) Kützing) were identified in the 14 pedoenvironments of Half Moon Island (Table SIb). The number of sampled plots reached the asymptote in most pedoenvironments, i.e. the extrapolation did not differ significantly from the interpolation (Figure 4a). The exceptions were P2, P5 and P6, suggesting that these environments could have presented more species with a greater sampling effort. Given that plots were set along transects over the vegetation patches, in some cases sampling was limited. The pedoenvironments revealed similar patterns of richness, but with different species. P12 had the lowest number of species (six), while P1, P2, P3, P9, P10 and P11 had similar numbers (ranging from 10 to 20 species) (Table I). The highest numbers were recorded for P4, P5, P6, P7, P8, P13 and P14 (22 to 30 species). The community coverage also presented significant differences (chi-squared = 79.53, df = 13, p-value = 0.001) among pedoenvironments (Figure 4b).

Community composition and beta diversity pattern

The pedoenvironments differed significantly in their species composition, forming 14 groups on the first and second axis (Figure 5). Although some species were present in various pedoenvironments, their spatial distribution was concentrated in pedoenvironments such as P4, P6, P8, P9 and P13 (Figure 6). Others were restricted to specific environments with particular soil conditions, such as Buellia racovitzae CW rodeio and B. russa (Hue) Darb. in P4; Ceratodon purpureus (Hedw.) Brid. in P5; Bartramia patens Brid., Bryum sp., Bacidia sp. in P6; Physconia muscigena (Ach.) Poelt and Pohlia nutans (Hedw.) Lindb. in P7; Candelaria murrayi Poelt, Lecania brialmontii (Vain). Zahlbr., Ramalina terebrata Hook. f. & Taylor, Syntrichia magellanica (Mont.) RH Zander and Xantoria elegans (Link) Th. Fr. in P10; Bryum nivale Müll. Hal. in P12; Bryum dichotomum Hedw. and Scapania sp in P13; and Sanionia spp, despite its absence in P10, was dominant in the other pedoenvironments. Differences in β-diversity among pedoenvironments (PERMDISP: F₁₃,₁₇₃ = 8.12, p < 0.001) were observed (Figure 7). β-diversity, measured as the distance to the group centroid, was higher in the P13 and P14 pedoenvironments than in the P11 and P12 pedoenvironments.

DISCUSSIONS

Our study area clearly presented marked differences in soil properties along the pedoenvironmental gradient. These variations are common in Maritime Antarctica (Thomazini et al. 2018THOMAZINI A, FRANCELINO MR, PEREIRA AB, SCHÜNEMANN AL, MENDONÇA ES & SCHAEFER CEGR. 2018. The spatial variability structure of soil attributes using a detailed sampling grid in a typical periglacial area of Maritime Antarctica. Environ Earth Sci 77: 637.) due to varying periglacial processes, weathering degree, parent material and biological influence (especially by penguins and other birds) (Simas et al. 2007SIMAS FNB, SCHAEFER CEGR, MELO VF, ALBUQUERQUE-FILHO MR, MICHEL RFM, PEREIRA VV, GOMES MRM & DA COSTA LM. 2007. Ornithogenic Cryosols from Maritime Antarctica: phosphatization as a soil forming process. Geoderma 138: 191-203., Schaefer et al. 2008SCHAEFER CEGR, SIMAS FNB, GILKES RJ, MATHISON C, COSTA LM & ALBUQUERQUE MA. 2008. Micromorphology and microchemistry of selected Cryosols from Maritime Antarctica. Geoderma 144: 104-115.). On Half Moon Island, the discontinuous permafrost affects sites located above the marine terraces, where landforms are mainly periglacial and include till. Many different landforms occur on this tiny island, such as patterned ground, stone stripes, gelifluction sheets, gelifluction lobes, debris slopes and debris cones (López-Martínez et al. 2012LÓPEZ-MARTÍNEZ J, SERRANO E, SCHMID T, MINK S & LINÉS C. 2012. Periglacial processes and landforms in the South Shetland Islands (northern Antarctic Peninsula region). Geomorphology 155-156: 62-79.).

This study showed marked differences in species richness and coverage due to differences in soil properties along the pedoenvironmental gradient, corroborating our first hypothesis. Accordingly, we note that community similarity decreases as differences in soil properties between pedoenvironments increases, supporting our second hypothesis. These changes in soil properties along the pedoenvironmental gradient promote a high degree of species turnover between pedoenvironments (β-diversity) despite a fine spatial scale, confirming our third hypothesis. Therefore, differences observed in β-diversity can be related to differences in the soil properties evaluated through a direct gradient analysis.

Direct gradient analysis: community diversity and coverage pattern

The 14 pedoenvironments are distributed throughout the entire length of Half Moon Island and show substantial soil variability. The different pedoenvironments studied probably have different levels of ornithogenic influence, where the formation and variability of soil chemical properties are shaped by penguins’ activity (Simas et al. 2007SIMAS FNB, SCHAEFER CEGR, MELO VF, ALBUQUERQUE-FILHO MR, MICHEL RFM, PEREIRA VV, GOMES MRM & DA COSTA LM. 2007. Ornithogenic Cryosols from Maritime Antarctica: phosphatization as a soil forming process. Geoderma 138: 191-203.). Penguins incorporate organic matter into the soil through their excreta (known as guano), which is dependent on the long-term permanence of penguins at each specific pedoenvironment, thereby altering the nutrient cycling process at a fine scale (Zhu et al. 2014ZHU R, WANG Q, DING W, WANG C, HOU L & MA D. 2014. Penguins significantly increased phosphine formation and phosphorus contribution in maritime Antarctic soils. Sci Rep 4: 7055.). In this way, we assume that most differences in soil properties between pedoenvironments owe to the temporal and spatial variation of penguin activity in the study area, resulting in contrasting values of available P and acidity (pH and H + Al) in the different pedoenvironments (Tatur 1989TATUR A. 1989. Ornithogenic soils of the Maritime Antarctic. Pol Polar Res 4: 481-532., Tatur & Myrcha 1989TATUR A & MYRCHA A. 1989. Soils and vegetation in abandoned penguin rookeries (Maritime Antarctic). NIPR, Symp, Polar Biol 2: 181-189., Tatur & Keck 1990TATUR A & KECK A. 1990. Phosphates in ornithogenic soils of the maritime Antarctic. NIPR, Symp. Polar Biol 3: 133-150., Tatur et al. 1997TATUR A, MYRCHA A & NIEGODZISZ J. 1997. Formation of abandoned penguin rookery ecosystems in the maritime Antarctic. Polar Biol 17: 405-417., Michel et al. 2006MICHEL RFM, SCHAEFER CEGR, DIAS L, SIMAS FNB, BENITES V & MENDONÇA ES. 2006. Ornithogenic Gelisols (Cryosols) from Maritime Antarctica: pedogenesis, vegetation and carbon studies. Soil Sci Soc Am J 70: 1370-1376., Simas et al. 2007SIMAS FNB, SCHAEFER CEGR, MELO VF, ALBUQUERQUE-FILHO MR, MICHEL RFM, PEREIRA VV, GOMES MRM & DA COSTA LM. 2007. Ornithogenic Cryosols from Maritime Antarctica: phosphatization as a soil forming process. Geoderma 138: 191-203.). According to Simas et al. (2007)SIMAS FNB, SCHAEFER CEGR, MELO VF, ALBUQUERQUE-FILHO MR, MICHEL RFM, PEREIRA VV, GOMES MRM & DA COSTA LM. 2007. Ornithogenic Cryosols from Maritime Antarctica: phosphatization as a soil forming process. Geoderma 138: 191-203., guano is initially alkaline, but rapid progressive acidification occurs with greater microbial degradation of organic matter. Ornithogenic soils are well-known in the Maritime Antarctic region, where phosphatisation is the main soil formation process (Michel et al. 2006MICHEL RFM, SCHAEFER CEGR, DIAS L, SIMAS FNB, BENITES V & MENDONÇA ES. 2006. Ornithogenic Gelisols (Cryosols) from Maritime Antarctica: pedogenesis, vegetation and carbon studies. Soil Sci Soc Am J 70: 1370-1376., Simas et al. 2007SIMAS FNB, SCHAEFER CEGR, MELO VF, ALBUQUERQUE-FILHO MR, MICHEL RFM, PEREIRA VV, GOMES MRM & DA COSTA LM. 2007. Ornithogenic Cryosols from Maritime Antarctica: phosphatization as a soil forming process. Geoderma 138: 191-203., Pereira et al. 2013PEREIRA TTC, SCHAEFER CEGR, KER JC, ALMEIDA CC, ALMEIDA ICC & PEREIRA AB. 2013. Genesis, mineralogy and ecological significance of ornithogenic soils from a semi-desert polar landscape at Hope Bay, Antarctic Peninsula. Geoderma 209-210: 98-109., Daher et al. 2019DAHER M, SCHAEFER CEGR, THOMAZINI A, NETO EL, SOUZA CD & LOPES DV. 2019. Ornithogenic soils on basalts from maritime Antarctica. Catena 173: 367-374.).

Despite their proximity, some pedoenvironments showed differences in species composition, associated with large variations in soil properties at a fine scale. For example, even though the adjacent P1 and P2 areas located on the eastern side of Xenia Hill were covered by a similar moss carpet in terms of species composition, they exhibited large differences in soil chemical properties. In this example, P2 presented soils with low acidity (pH 6.5) and P, K and Ca values twice as high as P1, whereas P1 showed the highest content of Na (1551.41 cmol/dm³, Table SIb) due to its exposure to marine saline sprays and local aridity (Michel et al. 2006MICHEL RFM, SCHAEFER CEGR, DIAS L, SIMAS FNB, BENITES V & MENDONÇA ES. 2006. Ornithogenic Gelisols (Cryosols) from Maritime Antarctica: pedogenesis, vegetation and carbon studies. Soil Sci Soc Am J 70: 1370-1376.). This finding can be corroborated by the presence of Verrucaria sp., which is associated with saline environments and wind exposure (Olech 2004OLECH M. 2004. Lichens of King George Island Antarctica. The Institute of Botany of The Jagiellonian University, Cracow, p. 391.). Although we mainly focused here on the species distribution patterns and types of communities along with a complex pedoenvironmental gradient system, presumably other environmental factors (e.g. sea spray, drainage and biotic interactions) may also influence plant community diversity and structure. On the other hand, P2 is located in a poorly drained and small depression pedoenvironment where a high water table and substantial organic matter content favor the growth of a thick moss carpet. However, along with P3, these two pedoenvironments exhibited the highest organic matter content associated with abundant available P, suggesting that a former penguin colony inhabited the area (Michel et al. 2006MICHEL RFM, SCHAEFER CEGR, DIAS L, SIMAS FNB, BENITES V & MENDONÇA ES. 2006. Ornithogenic Gelisols (Cryosols) from Maritime Antarctica: pedogenesis, vegetation and carbon studies. Soil Sci Soc Am J 70: 1370-1376.) and created a phosphatized environment (Simas et al. 2007SIMAS FNB, SCHAEFER CEGR, MELO VF, ALBUQUERQUE-FILHO MR, MICHEL RFM, PEREIRA VV, GOMES MRM & DA COSTA LM. 2007. Ornithogenic Cryosols from Maritime Antarctica: phosphatization as a soil forming process. Geoderma 138: 191-203.).

Soils P3 and P7 have a muscicolous lichen community, and both showed similar soil patterns, only differing significantly to OM and Mn. These soils are well-developed, with lichens growing on moribund or living mosses, confirming their advanced succession and favorable status for the coexistence of some species, as suggested for similar soils from King George Island (Tatur & Myrcha 1993TATUR A & MYRCHA A. 1993. Ornithogenic soils. In: Rakusa-Suszczewski, S (Ed), The Antarctic Coastal Ecosystem of Admiralty Bay. Polish Academy of Sciences, Warsaw, p. 161-165.). However, P7 has higher species richness (29 species), and P3 only 10, nine of which share (Figure 6).

P4 (moss carpet community) and P5 (moss turf community) are located at Gabriel Hill, at more elevated sites. They followed similar soil fertility patterns, except for micronutrients (Fe and Zn), but presented different plant compositions. However, these pedoenvironments exhibited different textural classes (Table SIa), P4 being sandy-loam and P5 sandy, i.e. P4 has a higher percentage of clay, probably there is a significant effect on species composition (e.g. Schmitz et al. 2020SCHMITZ D, SCHAEFER CERG, PUTZKE J, FRANCELINO MR, FERRARI FR, CORREA GR & VILLA PM. 2020. How does the pedoenvironmental gradient shape non-vascular species assemblages and community structures in Maritime Antarctica? Ecol Indic 108: 105726.).

In P9, high phosphorus (P), calcium (Ca) and magnesium (Mg) content combined with high effective cation exchange capacity levels, and greater depth characterize an ornithogenic cryosol (Michel et al. 2006MICHEL RFM, SCHAEFER CEGR, DIAS L, SIMAS FNB, BENITES V & MENDONÇA ES. 2006. Ornithogenic Gelisols (Cryosols) from Maritime Antarctica: pedogenesis, vegetation and carbon studies. Soil Sci Soc Am J 70: 1370-1376.), indicating a former penguin rookery. Located on an elevation escarpment (64 m a.s.l.) with a moss carpet cover, it is certainly an abandoned penguin colony that with glacio-isostatic uplift migrated to lower parts of the island. There is ample evidence that due to deglaciation and resultant glacio-isostatic uplift during the Holocene (Fretwell et al. 2010FRETWELL PT, HODGSON DA, WATCHAM EP, BENTLEY MJ & ROBERTS SJ. 2010. Holocene isostatic uplift of the South Shetland Islands, Antarctic Peninsula, modelled from raised beaches. Quat Sci Rev 29: 1880-1893.), a large number of penguin rookeries moved from upland areas to newly exposed marine terraces (Rodrigues et al. 2019RODRIGUES WF, OLIVEIRA FS, SCHAEFER CEGR, LEITE MGP, GAUZZI TG, BOCKHEIM JG & PUTZKE J. 2019. Soil-landscape interplays at Harmony Point, Nelson Island, Maritime Antarctica: Chemistry, mineralogy and classification. Geomorphology 336: 77-94.), closer to the emerging coast and into adjacent rock outcrops (Michel et al. 2006MICHEL RFM, SCHAEFER CEGR, DIAS L, SIMAS FNB, BENITES V & MENDONÇA ES. 2006. Ornithogenic Gelisols (Cryosols) from Maritime Antarctica: pedogenesis, vegetation and carbon studies. Soil Sci Soc Am J 70: 1370-1376., Daher et al. 2019DAHER M, SCHAEFER CEGR, THOMAZINI A, NETO EL, SOUZA CD & LOPES DV. 2019. Ornithogenic soils on basalts from maritime Antarctica. Catena 173: 367-374.). These highland areas thus became inaccessible for penguins, while the newly emerged land became occupied by new populations (Daher et al. 2019DAHER M, SCHAEFER CEGR, THOMAZINI A, NETO EL, SOUZA CD & LOPES DV. 2019. Ornithogenic soils on basalts from maritime Antarctica. Catena 173: 367-374., Rodrigues et al. 2019RODRIGUES WF, OLIVEIRA FS, SCHAEFER CEGR, LEITE MGP, GAUZZI TG, BOCKHEIM JG & PUTZKE J. 2019. Soil-landscape interplays at Harmony Point, Nelson Island, Maritime Antarctica: Chemistry, mineralogy and classification. Geomorphology 336: 77-94.), resulting in pedoenvironments with higher plant coverage, such as P9 (Figure 4b).

This is consistent with known glacio-isostatic uplift rates, between 16 and 20 m (Fretwell et al. 2010FRETWELL PT, HODGSON DA, WATCHAM EP, BENTLEY MJ & ROBERTS SJ. 2010. Holocene isostatic uplift of the South Shetland Islands, Antarctic Peninsula, modelled from raised beaches. Quat Sci Rev 29: 1880-1893.) with the highest beach ridge is located 16.8 m above the present-day beach (P12). Contemporary periglacial processes in a warming scenario seem less intense, corroborating the widespread presence of lichens over debris slopes and patterned ground, like P11 (López-Martínez et al. 2012LÓPEZ-MARTÍNEZ J, SERRANO E, SCHMID T, MINK S & LINÉS C. 2012. Periglacial processes and landforms in the South Shetland Islands (northern Antarctic Peninsula region). Geomorphology 155-156: 62-79.). P11 is a high marine terrace in the Holocene, at an elevation of 20 m.a.s.l. (Table I) and located in the central tombolo formed by marine graves connecting the northern and southern parts of the island. It presented the lowest P and OM amounts recorded in the study, with sparse coverage of crustose lichens on cobbles and gravels at the soil surface, under similar areas from the South Shetland Islands (Kim et al. 2007KIM JH, AHN I, LEE KS, CHUNG H & CHOI H. 2007. Vegetation of Barton Peninsula in the neighbourhood of King Sejong Station (King George Island, maritime Antarctic). Polar Biol 30: 903-916., Simas et al. 2008SIMAS FNB, SCHAEFER CEGR, ALBUQUERQUE FILHO MR, FRANCELINO MR, FERNANDES FILHO EI & COSTA LM. 2008. Genesis, properties and classification of cryosols from Admiralty Bay, maritime Antarctica. Geoderma 144: 116-122., Rodrigues et al. 2019RODRIGUES WF, OLIVEIRA FS, SCHAEFER CEGR, LEITE MGP, GAUZZI TG, BOCKHEIM JG & PUTZKE J. 2019. Soil-landscape interplays at Harmony Point, Nelson Island, Maritime Antarctica: Chemistry, mineralogy and classification. Geomorphology 336: 77-94.). Despite the intermediary species richness observed (Figure 4a, Table I), this pedoenvironment showed the lowest community coverage (Figure 4b) due to its recent exposure and relative lack of local bird activity.

P10 is located in the extreme south of the island, in an area called Baliza Point near an active penguin colony, and can be classified as a crustose lichens community (Schmitz et al. 2018SCHMITZ D, PUTZKE J, ALBUQUERQUE MP DE, SCHÜNNEMAN AL, VIEIRA FCB, VICTORIA FC & PEREIRA AB. 2018. Description of plants communities from Half Moon Island, Antarctica. Polar Res 37(1): 1523663.). Some rare species, such as C. murrayi, R. terebrata and X. elegans, which only occur in this pedoenvironment, are ornitocoprophilous (Olech 2004OLECH M. 2004. Lichens of King George Island Antarctica. The Institute of Botany of The Jagiellonian University, Cracow, p. 391.), capable of surviving under the high phosphorus and nitrogen levels present in penguin guano. As it is a dry and stony pedoenvironment, it was the only one where Sanionia spp. was not detected, even though this is a genus of wide distribution on this island and elsewhere in Maritime Antarctica. It is usually absent in dry habitats dominated by crustose lichens (Ochyra et al. 2008OCHYRA R, LEWIS-SMITH RI & BEDNAREK-OCHYRA H. 2008. The Illustrated Moss Flora of Antarctic. Cambridge: Cambridge University Press, p. 709., Schmitz et al. 2018SCHMITZ D, PUTZKE J, ALBUQUERQUE MP DE, SCHÜNNEMAN AL, VIEIRA FCB, VICTORIA FC & PEREIRA AB. 2018. Description of plants communities from Half Moon Island, Antarctica. Polar Res 37(1): 1523663.).

P12 is located on current beaches on the northern side of Half Moon Island that receives meltwater from the highest parts. Scattered bone and egg shell fragments, nest remains and bird droppings indicate nesting activity by skuas, with weak ornithogenic influence (Simas et al. 2007SIMAS FNB, SCHAEFER CEGR, MELO VF, ALBUQUERQUE-FILHO MR, MICHEL RFM, PEREIRA VV, GOMES MRM & DA COSTA LM. 2007. Ornithogenic Cryosols from Maritime Antarctica: phosphatization as a soil forming process. Geoderma 138: 191-203.). A discontinuous vegetation community composed of moss carpet Sanionia ssp is present (Table I), and only six species were identified, the lowest level of richness (Figure 4a). The moss Bryum nivale is a rare species that only occurred in this pedoenvironment, which is often flooded or covered by snow, and recorded the highest values of V, P Rem and Mn. The B. nivale record for the South Shetland Islands is rare and recent, indicating that this species may currently be colonizing areas after glacier retreat, as postulated by Wierzgoń et al. (2018)WIERZGÓN M, SUCHAN T & RONIKIER M. 2018. Two additions to the moss flora of the South Shetland Islands in the maritime Antarctic. Acta Soc Bot Pol 87: 4..

P6 and P14 are located at La Morenita Hill, at different elevations (40 and 85 m.a.s.l., respectively), although some of their soil properties followed similar patterns (Figure 2, Table SIa). Indeed, they showed plant coverage with distinct communities: whereas P6 has a moss carpet, P14 has a fruticose lichen community (Table I). Both are closely related to drainage and landform, as P6 is a flat area in the lower part of La Morenita Hill, classified as a debris slope and cone (López-Martínez et al. 2012LÓPEZ-MARTÍNEZ J, SERRANO E, SCHMID T, MINK S & LINÉS C. 2012. Periglacial processes and landforms in the South Shetland Islands (northern Antarctic Peninsula region). Geomorphology 155-156: 62-79.), whereas P14 at the top of the hill is classified as a middle platform. Some rare species were found in P6 (B. patens, Bacidia sp. and Bryum sp.) that did not occur in any other pedoenvironment of this study, and may be related to water logging and high Fe content. Species such as Caloplaca cinericola (Hue) Darb., Cladonia furcata (Huds.) Schrad., Dicranoweisia (Hymenoloma) grimmiacea (Müll. Hal.) Broth, Leptogium puberulum Hue, Schistidium antarctici (Card.) L.I. Savicz & Smirnova and Schistidium urnulaceum (Müll. Hal.) BG Sino were only recorded in P14 (Figure 6), where the highest levels of Cu were noted (Figure 2). According to Schaefer et al. (2004)SCHAEFER CEGR, PEREIRA SB, FRANCELINO MR, FERNANDES FILHO EI, SIMAS FNB, COSTA LM & OLIVEIRA AC. 2004. Comunidades vegetais na Peninsula Keller: Ecologia e padrões de distribuição. In: Schaefer CEGR et al. (Eds.), Ecossistemas Costeiros e Monitoramento Ambiental da Antártica marítima, Baía do Almirantado, ilha Rei George. NEPUT – Dep. de Solos, Viçosa, p. 65-72., the presence of Usnea spp as common fruticose lichen (P14) generally indicates a more stable, rocky and drained landscape. This species has a tendency to occur in locations with greater exposure, less snow cover and high altitude (Kim et al. 2007KIM JH, AHN I, LEE KS, CHUNG H & CHOI H. 2007. Vegetation of Barton Peninsula in the neighbourhood of King Sejong Station (King George Island, maritime Antarctic). Polar Biol 30: 903-916.). On the other hand, bryophytes, which are positively associated with higher water content and waterlogging (Leishman & Wild 2001LEISHMAN M & WILD C. 2001. Vegetation abundance and diversity in relation to soil nutrients and soil water content in Vestfold Hills, East Antarctica. Antarct Sci 13(2): 126-134.), are found in moister, more sheltered habitats (Kim et al. 2007KIM JH, AHN I, LEE KS, CHUNG H & CHOI H. 2007. Vegetation of Barton Peninsula in the neighbourhood of King Sejong Station (King George Island, maritime Antarctic). Polar Biol 30: 903-916.). This was the case of Sanionia spp., which often occurs in hydromorphic soils (Thomazini et al. 2018THOMAZINI A, FRANCELINO MR, PEREIRA AB, SCHÜNEMANN AL, MENDONÇA ES & SCHAEFER CEGR. 2018. The spatial variability structure of soil attributes using a detailed sampling grid in a typical periglacial area of Maritime Antarctica. Environ Earth Sci 77: 637.), probably regardless of their chemical attributes.

P8 is located at a slightly higher landscape position than P13, and both have moss carpet communities. The soil fertility patterns and species composition of these pedoenvironments are very similar, but the number of species in P13 is much higher, reaching 30 species, the most in this study. The species that appeared in P13 but were absent in P8 were mostly fruticose lichens (Himantormia lugubris (Hue) Cordeiro IM, Sphaerophorus globosus (Huds.) Vain.) and crustose lichens (Acarospora macrocyclos Vain., Haematomma eryhtromma (Nyl.) Zahlbr.) with a preference for growing on pebbles and boulders (Kim et al. 2007KIM JH, AHN I, LEE KS, CHUNG H & CHOI H. 2007. Vegetation of Barton Peninsula in the neighbourhood of King Sejong Station (King George Island, maritime Antarctic). Polar Biol 30: 903-916.), in places of better soil drainage, such a stable Felsenmeer surfaces, and platforms with high wind exposure and desiccation (Francelino et al. 2011FRANCELINO MR, SCHAEFER CEGR, SIMAS FNB, FILHO EIF, SOUZA JJLL & COSTA LM. 2011. Geomorphology and soils distribution under paraglacial conditions in an ice-free area of Admiralty Bay, King George Island, Antarctica. Catena 85: 194-204.). Despite P13’s ornithogenic influence, it showed a neutral/alkaline pH (7.2) and lower values of Fe, which is associated with the presence of Scapania sp., Bryum dichotomum and Ceratodon grossiretis Cardot, indicating that these mosses are limited by soil acidity. This pattern is consistent with previous reports that bryophyte diversity increases with soil pH (e.g. Stephenson et al. 1995STEPHENSON SL, STUDLAR SM, MCQUATTIE CJ & EDWARDS PJ. 1995. Effects of acidification on bryophyte communities in West Virginia Mountain Streams. Plant and Environment Interactions 24: 116-125.). Hence, this environment with higher soil fertility also presented higher β-diversity, probably because favorable soil conditions and considerable availability of resources enable greater species coexistence (Laliberté et al. 2014LALIBERTÉ E, ZEMUNIK G & TURNER BL. 2014. Environmental filtering explains variation in plant diversity along resource gradients. Science 345: 1602.), while environmental filtering has less importance than in other pedoenvironments with lower fertility.

We found higher β-diversity in P13 and P14, where higher pH and Mg²⁺ respectively occur. Lower β-diversity was recorded in P12 and P11, with CEC, P and OM contents. We predicted that the β-diversity pattern was also influenced by changes in species richness along the pedoenvironmental gradient. For example, where higher β-diversity was observed, higher richness was also found, and vice-versa (P12) with lower species richness. However, there is limited information available regarding the abiotic and biotic processes and drivers to explain how resource availability (i.e. nutrients) in these pedoenvironments directly influence β-diversity in non-vascular communities in Maritime Antarctica.

A similar β-diversity pattern has been observed in numerous studies from other locations where the plant coverage of dryland vegetation is discontinuous by forming a patchy mosaic of grasses and shrubs in a more or less bare soil matrix (Rietkerk & van de Koppel 2008RIETKERK M & VAN DE KOPPEL J. 2008. Regular pattern formation in real ecosystems. Trends Ecol Evol 23: 169-175.). This patchy mosaic is assumed to be the result of close feedback on the availability of resources (nutrients and water) and associated communities of mosses-lichens dynamics (Rietkerk & van de Koppel 2008RIETKERK M & VAN DE KOPPEL J. 2008. Regular pattern formation in real ecosystems. Trends Ecol Evol 23: 169-175.). On the other hand, species coexistence in these patchy mosaics may be crucial to increasing species richness by facilitation (Molina-Montenegro et al. 2016MOLINA-MONTENEGRO MA, OSES R, ACUÑA-RODRÍGUEZ IS, FARDELLA C, BADANO EI, TORRES-MORALES P, GALLARDO-CERDA J & TORRES-DÍAZ C. 2016. Positive interactions by cushion plants in high mountains: fact or artifact? J Plant Ecol 9: 117-123.). Thus, we presumed that different community types and plant coverage levels between different soil conditions reported for Maritime Antarctica (i.e. Schmitz et al. 2018SCHMITZ D, PUTZKE J, ALBUQUERQUE MP DE, SCHÜNNEMAN AL, VIEIRA FCB, VICTORIA FC & PEREIRA AB. 2018. Description of plants communities from Half Moon Island, Antarctica. Polar Res 37(1): 1523663.) can also promote higher species turnover along the pedoenvironmental gradient. Previous studies have shown that high vegetation density produces a niche differentiation, and promotes species coexistence and niche facilitation processes between rare and common species (e.g. Sanaei et al. 2018SANAEI A, ALI A, CHAHOUKI MAS & JAFARI M. 2018. Plant coverage is a potential ecological indicator for species diversity and aboveground biomass in semi-steppe rangelands. Ecol Indic 93: 256-266.).

CONCLUSIONS

1. Our study has revealed differences in environmental conditions (elevation, depth and chemical soil properties) between 14 contrasting pedoenvironments of Half Moon Island, a small island in Maritime Antarctica.

2. Newly exposed pedoenvironments (P10, P11 and P12) have lower species richness and coverage. Thus, species richness and coverage along the pedoenvironmental gradient differed, yet some species were present in the majority of the pedoenvironments. Nevertheless, most pedoenvironments recorded rare species that occurred only under specific soil conditions, thereby contributing to the high species turnover between pedoenvironments and low floristic similarity, which promoted high β-diversity.

ACKNOWLEDGMENTS

We acknowledge the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) for concession the scholarship of the first author and CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico, process no. 574018/2008 and 556794/2009-5) and PDJ to the second author. This work is a contribution of INCT-Criosfera TERRANTAR group and INCT_APA. We would like to say thanks to the crew of the Argentinean Camara Station. We thank researcher Camila Ditmar for her assistance in collecting soil samples.

REFERENCES

SUPPLEMENTARY MATERIAL

Appendix.

Table SIa.

Table SIb.

Figure S1.

Publication Dates

History