Quist, C. | bioRxiv Science

bioRxiv2026

Top predators in soil food webs increase carbon cycling efficiency

Soil microbes are considered central in litter decomposition and soil carbon formation. Microbial activity and abundance are controlled by microbivores, which are themselves preyed upon by top predators. However, the role of top predators in carbon cycling is rarely studied, especially in bacterivore-dominated food webs. Here we tested how trophic cascades, consisting of microbes, microbivores (bacterivore-dominated nematode communities) and top predators (nematode-feeding mites) impact carbon cycling and associated microbial pools and processes. We found that our model top predator decreased the abundance of fungivorous nematodes and had cascading effects on microbiome composition, notably increasing Gram-positive bacterial biomass, thus promoting the bacterial energy channel. These trophic cascades propagated to carbon cycling, decreasing heterotrophic respiration by 10 % while maintaining litter decomposition rates. Taken together, our results suggest that top predators increase carbon cycling efficiency and highlight the importance of complex trophic interactions, including trophic cascades, in determining soil carbon cycling.

ecology↗

bioRxiv2025

Scarcity of flowering plants on Sedum roofs limits pollinator diversity

Green roofs can provide suitable habitats for pollinating insects in urban areas. Pollinators are a large and diverse group with high economic and ecological relevance to society. Yet their populations are in decline, highlighting the need for new habitats such as green roofs. An understanding of how local and landscape factors of green roofs shape pollinator communities is crucial to optimize the design and development of green roofs. This study aimed to identify how the surrounding landscape and green roof characteristics influence pollinator diversity and abundance. Pollinators - such as bees, wasps, hoverflies and butterflies - were sampled using pan traps and hand netting on 25 green roofs that were categorized into three types based on functionality and vegetation structure: sedum roofs, nature roofs, and roof gardens. To assess pollinator communities, we examined species richness, abundance, and functional diversity--defined here as the range of ecological roles or traits. Roof characteristics (e.g., flower diversity, microrelief, vegetation cover, roof height, size, and age) and landscape factors (e.g. percentage of surrounding green, distance to surrounding green) were analysed in relation to these diversity metrics. We show that a continuous supply of flowers throughout the year, flower abundance and the type of green roof significantly influence pollinator diversity and abundance. Sedum roofs supported lower pollinator diversity compared to the other roof types. Furthermore, our models indicated a decrease in pollinator diversity on higher green roofs, and when honeybee hives are present, while the presence of bee hotels increased pollinator abundance. The study highlights the value of nature roofs and roof gardens, compared to sedum roofs for supporting pollinator diversity. This is linked to the importance of constant forage availability, especially in early spring, which is absent on most sedum roofs. The results from this study offer guidelines to green roof designers on how to design pollinator friendly roofs in urban areas. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=171 SRC="FIGDIR/small/676189v1_ufig1.gif" ALT="Figure 1"> View larger version (34K): org.highwire.dtl.DTLVardef@dfb4caorg.highwire.dtl.DTLVardef@d6478eorg.highwire.dtl.DTLVardef@1f3e725org.highwire.dtl.DTLVardef@1cc4ef0_HPS_FORMAT_FIGEXP M_FIG C_FIG Pollinator species: Macropis europea (Hymenoptera: Melittidae), Helophilus pendulus (Diptera: Syrhidae) and Polyommatus icarus (Lepidoptera: Lycaenidae). All three species were observed on green roofs during the authors fieldwork. Image created using biorender.com and personal drawings. HighlightsO_LIBiodiverse roofs and roof gardens support higher pollinator diversity compared to sedum roofs. C_LIO_LIA continuous supply of flowers throughout the year, along with a higher abundance of flowers, are key factors influencing pollinator diversity and abundance on green roofs. C_LIO_LIRoof height affects the diversity and abundance of different pollinator groups in distinct ways, a novel finding that needs further investigation. C_LIO_LIWe provide guidelines for green roof designers, emphasizing the importance of selecting roof types and designs that ensure constant flower availability. C_LI

ecology↗

bioRxiv2023

Soil legacies of extreme droughts enhance the performance of invading plants

Extreme droughts can weaken the biotic resistance of native plant communities against the establishment of invading plants. However, we know little about the underlying mechanisms. Using a plant-soil feedback approach, we tested how an extreme drought event alters the soil-mediated biotic resistance of resident native plant communities against invading plant species from native and non-native ranges, namely non-resident natives, native range-expanders, and alien plants. We show that all three types of invading plants performed better in soils with a legacy of extreme drought independent of resident native plant diversity. Path models revealed that extreme drought effects on non-resident natives were mediated by the root biomass of resident native plants and endophytic fungal pathogens during drought, whereas alien plant performance was mediated only via the root biomass of resident native plants also during drought. Our results highlight that the performance of resident native plants during extreme drought and subsequent effects on soil fungi determine the performance of invading plants from native and non-native origins after extreme droughts.

ecology↗