Yunhui Liu

Urbanization can act as a powerful ecological filter, restructuring biodiversity through species loss, replacement, and altered resource pathways. While urban green spaces (UGS) are recognized as potential biodiversity refuges, the effectiveness and mechanisms for conserving insect diversity across the urban-to-natural gradient remain poorly understood. Here, we combine full-season Malaise trapping (April–November) with MinION-based DNA barcoding to test two predictions about how urbanization reshapes Diptera communities across five sites in Haidian District, Beijing, ranging from residential areas and urban parks to a nearby shallow mountain reserve (BWM). Based on 5528 barcoded individuals, we identified 686 putative species from 39 families. As predicted, β-diversity between urban and mountain sites was overwhelmingly driven by species turnover rather than nestedness, demonstrating that cities do not simply receive subsets of the surrounding fauna but actively reassemble communities. This filtering effect was, however, trophic-guild specific. Detritivores showed the highest replacement, consistent with a shift from natural to anthropogenic resource subsidies, while predators/parasitoids exhibited significant nested loss, aligning with their hypothesized sensitivity at higher trophic levels. Vegetation structure further clarified these patterns: vegetation density, not plant species richness, was the primary bottom-up driver for herbivore and predator/parasitoid diversity, whereas detritivores were decoupled from living plant biomass. These findings demonstrate that urban and near-natural habitats maintain distinct species pools via guild-specific assembly pathways, highlighting the need for guild-specific conservation strategies for urban biodiversity conservation. Extending beyond compositional analysis, we propose a temporal-abundance framework, classifying species by persistence and abundance, as a diagnostic tool for assessing ecological integrity and guiding conservation in urbanizing landscapes.

Apple is one of the most important pollinator‐dependent fruit crops worldwide. To secure high‐quality yields, it is crucial to know which, and to what extent, pollinating insects contribute to its pollination success as measured by fruit set, fruit weight and seed set. We perform a meta‐analysis of field studies conducted across multiple orchards on insect‐mediated pollination in apple cultivation, using raw data from 29 studies, totalling 532 orchard replicates. We assessed the extent of pollen limitation on different pollination outcomes and assessed the contribution of honeybees, wild bees and bee species richness to apple pollination. Across all studies, we detected strong evidence of pollen limitation for fruit set and seed set, but not for fruit weight. Honeybees were the most abundant flower visitors (average relative visitation of 71.9%) compared to wild bees; but when correcting for their pollination efficiency, the relative pollination contribution of honeybees was lower compared to their relative visitation (vice versa for solitary bees). We conclude that honeybee visitation rate did not influence fruit or seed set; yet increasing honeybee visitation had a small, negative effect on fruit weight. Fruit set was not influenced by wild bee visitation rate, whereas wild bee visitation had a small, but clear positive effect on fruit weight and seed set. Bee species richness had a small, positive effect on seed set; whereas it did not affect fruit set and fruit weight. Syntheses and applications. Our study highlights that pollen limitation is common in this global crop. While managed honeybees are dominant pollinators, a diverse community of wild bees contributes significantly to apple pollination and high‐quality yield. The positive effect of wild bees and species richness on fruit weight and seed set demonstrates that wild bee pollination results in better‐quality fruit production (increased weight & seed set). Therefore, our synthesis highlights the importance of conserving pollinator diversity to maintain pollination services. The absence of a clear effect of honeybee visitation rate on fruit and seed set, coupled with its negative impact on fruit weight, suggests a need for further optimisation of honeybee management to improve the cost‐efficiency of pollination management.

Nitrogen (N) deposition is known to strongly modify biogeochemical cycles and trophic interactions, in turn altering ecosystem functioning and plant diversity around the globe. However, our understanding of N deposition effects on arthropod diversity remains limited. Here, we investigate how N deposition impacts the diversity of arthropods by combining biodiversity data from the PREDICTS database with data on global N deposition and land cover using mixed-effects models. We then explore the potential for semi-natural and natural habitats (‘SNH’) to buffer against potential N deposition-linked biodiversity losses. N deposition has a negative effect on arthropod biodiversity. Both, species richness and abundance are significantly reduced in areas of high levels of N deposition when compared to areas of low N deposition, with responses varying across different land-use types. The strongest negative effects of N deposition on arthropod diversity were observed in locations where the local land use entails the least anthropogenic modification. At the same time, with the exception of cropland-dominated landscapes, increases in the amount of SNH in the surrounding landscape reduced arthropod biodiversity losses associated with N deposition. We conclude that SNH can play an important role in mitigating the negative effects of N deposition on arthropod diversity, with the conservation and creation of these habitats promoting arthropod diversity even under high levels of N deposition.

Cover crop mixtures have been increasingly adopted across agroecosystems worldwide due to their potential to improve soil health and ecosystem functioning. However, it is not clear whether and how cover crop mixtures vs. single cover crops might influence different ecosystem functions. Here, we selected 1895 paired data from 61 studies worldwide to evaluate the role of cover crop mixtures in affecting biomass production, soil properties and subsequent main crop yields in comparison with single cover crops. We also assessed whether the number of plant species in cover crop mixtures, crop field types and cover crop combinations could affect ecosystem functioning. Multi‐species mixtures increased cover crop above‐ground biomass by 21.7%, carbon and nutrient accumulation (C: +27.7%, N: +27.7%, P: +22.8%, K: +24.1%), and subsequent crop yields by 4.9% compared to single cover crops. These benefits were most pronounced in paddy fields (e.g. a 35.3% increase in biomass), as well as in specific species combinations such as milk vetch‐rapeseed (32.8%) and milk vetch‐ryegrass (36.0%). Also, multi‐species cover crop mixtures increased subsequent soil moisture content (+1.5%), soil total nitrogen (+5.8%), soil microbial carbon (+37.8%), soil microbial nitrogen (+37.6%), Chao1 index of fungi (+12.6%), decreased soil bulk density (−7.0%), soil electrical conductivity (−9.5%) and polyphenol oxidase activity (−7.0%). However, effects on soil pH, organic matter, and most nutrients were neutral unless specific combinations. Synthesis and applications. Multi‐species cover crop mixtures significantly enhance agroecosystem productivity and soil health, particularly in paddy systems and when combining functionally complementary species (e.g. legumes with Cruciferae, legumes with Gramineae). Farmers and policymakers should prioritize tailored mixtures over monocultures to optimize biomass production, nutrient cycling and yield resilience. For maximum impact, mixtures should align with local conditions—such as using milk vetch‐rapeseed or milk vetch‐ryegrass in humid regions—to advance sustainable agriculture and climate adaptation goals globally.

Honeybees (Apis mellifera) are increasingly used in commercial crop production, while wild bees are also important pollinators. Few studies have investigated the relative importance of honeybees and wild bees for apple pollination and whether the contribution of wild bees is affected by increasing numbers of honeybees. Here, we conducted experiments in 52 commercially important Fuji apple orchards across three apple production areas in China, to investigate how wild bees, honeybees and their interaction influences apple quantity (fruit set, weight) and quality (seed number). Both honeybees and wild bees contributed to apples production, resulting in an overall 996%, 26% and 64% increase of apple fruit set, fruit weight and seed number, respectively. We found a hump‐shaped relationship between bee density and fruit set and fruit weight with the maximum fruit set at intermediate bee density, but honeybees reached the maximum only with one and a half times higher numbers than wild bees. Furthermore, when honeybee activity density was low, an increase in wild bee activity density and species richness led to enhanced pollination contribution. Conversely, when honeybee activity density was high, increased wild bee activity density and species richness were associated with reduced pollination contribution. Additionally, the highest fruit set was observed at high densities of wild bees and intermediate densities of honeybees. These results indicate that high honeybee activity density may interfere with the pollination services provided by wild bees in apple orchards. Synthesis and applications. Both honeybees and wild bees contribute to apple pollination and production, but wild bees evidenced much higher pollination efficiency than honeybees. Importantly, introducing high density of honeybee colonies appeared to enhance competition with wild bees, decreasing their contribution to pollination. As highest fruit set was found with high wild bee densities, but only intermediate levels of honeybee densities, it is important to carefully assess the number of honeybee colonies before possible introduction of hives for apple production, in particular when wild bee diversity and density are high. Conserving wild bee diversity is of priority to harness pollination services in apple production, given their high diversity and pollination efficiency.

Land use change threatens global biodiversity and compromises ecosystem functions, including pollination and food production. Reduced taxonomic α‐diversity is often reported under land use change, yet the impacts could be different at larger spatial scales (i.e., γ‐diversity), either due to reduced β‐diversity amplifying diversity loss or increased β‐diversity dampening diversity loss. Additionally, studies often focus on taxonomic diversity, while other important biodiversity components, including phylogenetic diversity, can exhibit differential responses. Here, we evaluated how agricultural and urban land use alters the taxonomic and phylogenetic α‐, β‐, and γ‐diversity of an important pollinator taxon—bees. Using a multicontinental dataset of 3117 bee assemblages from 157 studies, we found that taxonomic α‐diversity was reduced by 16%–18% in both agricultural and urban habitats relative to natural habitats. Phylogenetic α‐diversity was decreased by 11%–12% in agricultural and urban habitats. Compared with natural habitats, taxonomic and phylogenetic β‐diversity increased by 11% and 6% in urban habitats, respectively, but exhibited no systematic change in agricultural habitats. We detected a 22% decline in taxonomic γ‐diversity and a 17% decline in phylogenetic γ‐diversity in agricultural habitats, but γ‐diversity of urban habitats was not significantly different from natural habitats. These findings highlight the threat of agricultural expansions to large‐scale bee diversity due to systematic γ‐diversity decline. In addition, while both urbanization and agriculture lead to consistent declines in α‐diversity, their impacts on β‐ or γ‐diversity vary, highlighting the need to study the effects of land use change at multiple scales.

The negative impact of agricultural land on biodiversity is widely recognized. However, there remains a knowledge gap regarding the role of different crop types in maintaining biodiversity within the agricultural landscape. By extracting biodiversity data from global datasets and classifying different crop types, we quantified the contribution of different crop types to biodiversity. Our results indicate that biodiversity levels vary widely among crop types. We found a general loss of biodiversity when natural vegetation is converted to agricultural land, and highest losses in fiber crops, cereals and oil crops, and least in other crops (such as coffee or cocoa) and in mixed crops. In general, perennial crops retain more biodiversity than annual crops. Losses of biodiversity can be mitigated through mixed cropping of multiple crop types, especially by combining annual and perennial crops. The negative impact of converting natural vegetation to agriculture is greater in tropical than in nontropical areas, and hence, the import of commodities from these biodiversity‐rich regions may be particularly detrimental. Given the ongoing increase in biodiversity losses from global intensification and expansion of agricultural land, maintaining or restoring natural vegetation, rating the crop‐type‐specific biodiversity, diversifying crops, and preferring perennial over annual crops, particularly in the tropics, need to be better considered and implemented in global agri‐environmental schemes.