Local environmental context drives heterogeneity of early succession dynamics in alpine glacier forefields

Glacier forefields have long provided ecologists with a model to study patterns of plant succession following glacier retreat. While plant-survey-based approaches applied along chronosequences provide invaluable information on plant communities, the “space-for-time” approach assumes environmental uniformity and equal ecological potential across sites and does not account for spatial variability in initial site conditions. Remote sensing provides a promising avenue for assessing plant colonization dynamics using a so-called “real-time” approach. Here, we combined 36 years of Landsat imagery with extensive field sampling along chronosequences of deglaciation for eight glacier forefields in the southwestern European Alps to investigate the heterogeneity of early plant succession dynamics. Based on the two complementary and independent approaches, we found strong variability in the time lag between deglaciation and colonization by plants and in subsequent growth rates and in the composition of early plant succession. All three parameters were highly dependent on the local environmental context, i.e., neighboring vegetation cover and energy availability linked to temperature and snowmelt gradients. Potential geomorphological disturbance did not emerge as a strong predictor of succession parameters, which is perhaps due to insufficient spatial resolution of predictor variables. Notably, the identity of pioneer plant species was highly variable, and initial plant community composition had a much stronger influence on plant assemblages than elapsed time since deglaciation. Overall, both approaches converged towards the conclusion that early plant succession is not stochastic as previous authors have suggested but rather determined by local ecological context. We discuss the importance of scale in deciphering the complexity of plant succession in glacier forefields and provide recommendations for improving botanical field surveys and using Landsat time series in glacier forefield systems. Our work demonstrates complementarity between remote sensing and field-based approaches for both understanding and predicting future patterns of plant succession in glacier forefields.</p

Data from: Riders in the sky (islands): using a mega-phylogenetic approach to understand plant species distribution and coexistence at the altitudinal limits of angiosperm plant life

Aim: Plants occurring on high-alpine summits are generally expected to persist due to adaptations to extreme selective forces caused by the harshest climates where angiosperm life is known to thrive. We assessed the relative effects of this strong environmental filter and of other historical and stochastic factors driving plant community structure in very high-alpine conditions. Location: European Alps, Écrins National Park, France. Methods: Using species occurrence data collected from floristic surveys on 15 summits (2,791–4,102 m a.s.l.) throughout the Écrins range, along with existing molecular sequence data obtained from GenBank, we used a mega-phylogenetic approach to evaluate the phylogenetic structure of high-alpine plant species assemblages. We used three nested species pools and two null models to address the importance of species-specific and species-neutral processes for driving coexistence. Results: Compared with the entire species pool of the study region, alpine summits exhibited a strong signal of phylogenetic clustering. Restricting statistical sampling to environmentally and historically defined species pools reduced the significance of this pattern. However, we could not reject a model that explicitly incorporates neutral colonization and local extinction in shaping community structure for dominant plant orders. Between summits, phylogenetic turnover was generally lower than expected. Environmental drivers did not explain overall phylogenetic patterns, but we found significant geographical and climatic structure in phylogenetic diversity at finer taxonomic scales. Main conclusions: Although we found evidence for strong phylogenetic clustering within alpine summits, we were not able to reject models of species-neutral processes to explain patterns of floristic diversity. Our results suggest that plant community structure in high-alpine regions can also be shaped by neutral processes, and not through the sole action of environmental selection as traditionally assumed for harsh and stressful environments

Colocalization analysis to understand Yttrium uptake in Saxifraga paniculata using complementary imaging technics

International audienceOver the last decades, yttrium (Y) has gained importance inhigh tech applications. Due to its chemical similarities with thelanthanides, Y is often considered a rare earth element (REE).Despite their increased usage, the environmental behaviour ofREEs remains poorly understood. Especially regarding theirinteractions with plants many uncertainties exist as both, positiveand negative effects on plant development have been observed[1]. In order to understand these phenomena a precise knowledgeis necessary about how Y is absorbed by the plant and how it ishandled once inside the organism. Contradictory studies exist,stating that due to similar ionic radius, Y and the other REEsmight be absorbed through Ca2+-channels while others suspect ashared pathway with Al3+ [2].In this study, we used laser ablation coupled ICP-MS andsynchrotron-based micro-X-ray fluorescence spectroscopy(μXRF, beamline Nanoscopium, SOLEIL, France) to localise Ywithin the plant tissue and identify colocalized elements. Theplant used in this study is Saxifraga paniculata, a rugged alpineplant that has shown an affinity for Y in a previous study (inprep.). The results show that after growing on a Y-doped soil(500mg/kg), Y is mainly concentrated in the roots of Saxifragapaniculata and only a small amount is translocated to the aerialparts.μXRF analysis indicates that within the roots the majority of Yremains in the outer cortex and epidermis and hardly penetratesthe stele. Laser ablation coupled ICP-MS confirms this findingand shows a colocalization between Y, Fe and Al and to a lesserextent Ca. In the stem and the leaves Ca disappears from thisgroup of correlated elements while especially in Y-hotspots, Feand Al remain strongly associated. Accordingly, a relationbetween Ca and Y during root uptake remains possible whereasthe correlation to Fe and Al appears to be dominant in the aerialparts, indicating the formation of complexes or a shared pathwayduring translocation

EcrinsCommunityMatrix

Species list for the Écrins National Park, France. Columns show alien origin, endemic status, GenBank accession numbers for each gene region that were used to estimate phylogenetic relationships, and the presence/absence of each species in the three species pools (Regional, All Summits, LGM), and across each alpine summit sampled in this study

Discovery of cryptic plant diversity on the rooftops of the Alps

High elevation temperate mountains have long been considered species poor owing to high extinction or low speciation rates during the Pleistocene. We performed a phylogenetic and population genomic investigation of an emblematic high-elevation plant clade (Androsace sect. Aretia, 31 currently recognized species), based on plant surveys conducted during alpinism expeditions. We inferred that this clade originated in the Miocene and continued diversifying through Pleistocene glaciations, and discovered three novel species of Androsace dwelling on different bedrock types on the rooftops of the Alps. This highlights that temperate high mountains have been cradles of plant diversity even during the Pleistocene, with in-situ speciation driven by the combined action of geography and geology. Our findings have an unexpected historical relevance: H.-B. de Saussure likely observed one of these species during his 1788 expedition to the Mont Blanc and we describe it here, over two hundred years after its first sighting

genetrees.zip

Tree files for gene trees estimated for each gene region (ITS, atpB, matK, rbcL, and trnTLF). Bootstrap support values are labeled on the nodes

alignments.zip

DNA alignments of each gene region (ITS, atpB, matK, rbcL, and trnTLF) and the concatenated alignment (.phy)

phy.Alpes

Time calibrated community phylogeny of the Écrins National Park, France. Bootstrap support values are labeled on the nodes