Biology subjects

Bokhorst, S.

Publications and source records attributed to Bokhorst, S..

5 recordsLinked to original sources

bioRxiv2026

Lichen Growth Form Effects on Rock Weathering in Cold Biomes

Rock surface weathering is a critical element in the process of early soil formation, in which lichens are thought to play a significant role. Crustose lichens, with a large area of rock-surface contact, are generally considered more influential in rock weathering, while foliose and fruticose growth forms, with more developed three-dimensional structure and less rock-surface contact, are rarely considered in this context. Here, we test the extent to which all three growth forms contribute to granitic rock surface weathering in Maritime Antarctic ecosystems, by quantifying rock hardness beneath foliose (n = 2 species), fruticose (n = 2) and crustose lichens (n= 5). Our data confirm that foliose lichens reduced rock surface hardness by 9%, to a lesser extent than crustose and foliose lichens (40% and 31% reduction, respectively). To disentangle whether these effects result from lichen-induced weathering or lichen preference for pre-weathered rock, we also analyzed a dated deglaciation sequence on granitic rocks from the Morteratsch Glacier forefield in the Swiss Alps. At this location, the impact of crustose lichens on rock substrate hardness generally increased with time since exposure from glacial retreat and with lichen thallus size. We conclude that lichen presence on rock surfaces significantly reduces rock hardness, with crustose lichens having a greater impact than foliose and fruticose forms, highlighting the potential role of lichens of all three growth forms in driving substrate breakdown and shaping early-stage ecosystem processes in polar and alpine regions.

ecology↗

bioRxiv2024

Greening rates are sensitive to methodology and biology; comment to Sustained greening of the Antarctic Peninsula observed from satellites

Roland et al.1 claim to provide evidence for a greening trend throughout the Antarctic Peninsula region over the last four decades, based on satellite remote sensing data. However, the early period vegetation cover estimates do not match with the likely extent of vegetated areas in this region at that time, raising doubts about the magnitude of any greening trend. Furthermore, growth rates of mosses and higher plants in Antarctica are insufficient to explain the 14-fold green cover expansion claimed, and neither have such changes been observed at long-term monitoring sites or from field warming studies. The reported satellite time series analyses of the presented trend seems biased by satellite image availability, lack of consistency in the areas covered by imagery and processing pitfalls. Antarctic terrestrial ecosystems are indeed predicted to become greener with climate change, but at much slower rates than reported by Roland et al.1.

ecology↗

bioRxiv2024

Increases in Arctic extreme climatic events are linked to negative fitness effects on the local biota

1.The Arctic harbours uniquely adapted biodiversity and plays an important role in climate regulation. Strong warming trends in the terrestrial Arctic have been linked to an increase in aboveground biomass (Arctic greening) and community-wide shifts such as the northwards-expansion of boreal species (borealisation). Whilst considerable efforts have been made to understand the effects of warming trends in average temperatures on Arctic biota, far fewer studies have focused on trends in extreme climate events and their biotic effects, which have been suggested to be particularly impactful during the Arctic winter months. Here, we present an analysis of trends in two ecologically-relevant winter extreme events -extreme winter warming and rain-on-snow, followed by a meta-analysis on the evidence base for their effects on Arctic biota. We show a strong increase in extreme winter warming across the entire Arctic and high variability in rain-on-snow trends, with some regions recently experiencing rain-on-snow for the first time whilst others seeing a decrease in these events. Ultimately, both extreme events show significant changes in their characteristics and patterns of emergence. Our meta-analysis -encompassing 178 effect sizes across 17 studies and 49 species- demonstrates that extreme winter warming and rain-on-snow induce negative impacts on Arctic biota, with certain taxonomic groups -notably angiosperms and chordates (mostly vertebrates)- exhibiting higher sensitivity than others. Our study provides evidence for both emerging trends in Arctic winter extreme climate events and significant negative biotic effects of such events -which calls for attention to winter weather variability under climate change in the conservation of Arctic biodiversity, whilst highlighting important knowledge gaps.

ecology↗

bioRxiv2024

Macro-environment strongly interacts with warming in a global analysis of decomposition

Empirical studies worldwide show substantial variability in plant litter decomposition responses to warming, leaving the overall impact of climate change on this process uncertain. We conducted a meta-analysis of 109 experimental warming studies across seven continents, utilizing natural and standardized plant material, to assess the overarching effect of warming on decomposition and identify potential moderating factors. Warming influences decomposition differently across macro-environmental gradients of moisture and temperature. Negative warming effects on decomposition in warmer, low-moisture areas were counterbalanced by the positive, though not significant, warming effects in colder areas, resulting in an overall non-significant effect. We determine that at least 5.2 degrees of warming is required for a significant increase in decomposition. This is particularly relevant given the past decades global warmth in higher latitudes, holding a significant proportion of terrestrial carbon. Low-quality plant litter was more sensitive to warming. Therefore, future vegetation changes toward low-quality, temperature-sensitive plants could increase carbon release and reduce the net supply of stored organic matter in the soil by increasing the decomposition of low-quality litter with warming. Our findings emphasize the connection between warming responses, macro-environment, and litter characteristics, refining predictions of climate changes consequences on key ecosystem processes and its contextual dependencies.

ecology↗

bioRxiv2022

Globally invariant metabolism but density-diversity mismatch in springtails

Soil life supports the functioning and biodiversity of terrestrial ecosystems1, 2. Springtails (Collembola) are among the most abundant soil animals regulating soil fertility and flow of energy through above- and belowground food webs3-5. However, the global distribution of springtail diversity and density, and how these relate to energy fluxes remains unknown. Here, using a global dataset collected from 2,470 sites, we estimate total soil springtail biomass at 29 Mt carbon (threefold higher than wild terrestrial vertebrates6) and record peak densities up to 2 million individuals per m{superscript 2} in the Arctic. Despite a 20-fold biomass difference between tundra and the tropics, springtail energy use (community metabolism) remains similar across the latitudinal gradient, owing to the increase in temperature. Neither springtail density nor community metabolism were predicted by local species richness, which was highest in the tropics, but comparably high in some temperate forests and even tundra. Changes in springtail activity may emerge from latitudinal gradients in temperature, predation7, 8, and resource limitation7, 9, 10 in soil communities. Contrasting temperature responses of biomass, diversity and activity of springtail communities suggest that climate warming will alter fundamental soil biodiversity metrics in different directions, potentially restructuring terrestrial food webs and affecting major soil functions.

ecology↗