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Management of biodiversity and ecosystem services requires a better understanding of the factors that influence soil biodiversity. We characterized the species (or genera) richness of 10 taxonomic groups of invertebrate soil animals in replicated monocultures of 14 temperate tree species. The focal invertebrate groups ranged from microfauna to macrofauna: Lumbricidae, Nematoda, Oribatida, Gamasida, Opilionida, Araneida, Collembola, Formicidae, Carabidae, and Staphylinidae. Measurement of invertebrate richness and ancillary variables occurred ~34 years after the monocultures were planted. The richness within each taxonomic group was largely independent of richness of other groups; therefore a broad understanding of soil invertebrate diversity requires analyses that are integrated across many taxa. Using a regression-based approach and ~125 factors related to the abundance and diversity of resources, we identified a subset of predictors that were correlated with the richness of each invertebrate group and richness integrated across 9 of the groups (excluding earthworms). At least 50% of the variability in integrated richness and richness of each invertebrate group was explained by six or fewer predictors. The key predictors of soil invertebrate richness were light availability in the understory, the abundance of an epigeic earthworm species, the amount of phosphorus, nitrogen, and calcium in soil, soil acidity, and the diversity or mass of fungi, plant litter, and roots. The results are consistent with the hypothesis that resource abundance and diversity strongly regulate soil biodiversity, with increases in resources (up to a point) likely to increase the total diversity of soil invertebrates. However, the relationships between various resources and soil invertebrate diversity were taxon-specific. Similarly, diversity of all 10 invertebrate taxa was not high beneath any of the 14 tree species. Thus, changes to tree species composition and resource availability in temperate forests will likely increase the richness of some soil invertebrates while decreasing the richness of others.

Plant diversity strongly influences ecosystem functions and services, such as soil carbon storage. However, the mechanisms underlying the positive plant diversity effects on soil carbon storage are poorly understood. We explored this relationship using long-term data from a grassland biodiversity experiment (The Jena Experiment) and radiocarbon ((14)C) modelling. Here we show that higher plant diversity increases rhizosphere carbon inputs into the microbial community resulting in both increased microbial activity and carbon storage. Increases in soil carbon were related to the enhanced accumulation of recently fixed carbon in high-diversity plots, while plant diversity had less pronounced effects on the decomposition rate of existing carbon. The present study shows that elevated carbon storage at high plant diversity is a direct function of the soil microbial community, indicating that the increase in carbon storage is mainly limited by the integration of new carbon into soil and less by the decomposition of existing soil carbon.

© 2015 US Government Tree species interact with soil biota to impact soil organic carbon (C) pools, but it is unclear how this interaction is shaped by various ecological factors. We used multiple regression to describe how ~100 variables were related to soil organic C pools in a common garden experiment with 14 temperate tree species. Potential predictor variables included: (i) the abundance, chemical composition, and decomposition rates of leaf litter and fine roots, (ii) species richness and abundance of bacteria, fungi, and invertebrate animals in soil, and (iii) measures of soil acidity and texture. The amount of organic C in the organic horizon and upper 20 cm of mineral soil (i.e. the combined C pool) was strongly negatively correlated with earthworm abundance and strongly positively correlated with the abundance of aluminum, iron, and protons in mineral soils. After accounting for these factors, we identified additional correlations with soil biota and with litter traits. Rates of leaf litter decomposition, measured as litter mass loss, were negatively correlated with size of the combined soil organic C pool. Somewhat paradoxically, the combined soil organic C pool was also negatively related to the ratio of recalcitrant compounds to nitrogen in leaf litter. These apparent effects of litter traits probably arose because two independent components of litter “quality” were controlling different aspects of decomposition. Leaf litter mass loss rates were positively related with leaf litter calcium concentrations, reflecting greater utilization and depolymerization of calcium-rich leaf litter by earthworms and other soil biota, which presumably led to greater proportional losses of litter C as CO2 or dissolved organic C. The fraction of depolymerized and metabolized litter that is ultimately lost as CO2 is an inverse function of microbial C use efficiency, which increases with litter nutrient concentrations but decreases with concentrations of recalcitrant compounds (e.g. lignin); thus, high ratios of recalcitrant compounds to nitrogen in leaf litter likely caused a greater fraction of depolymerized litter to be lost as CO2. Existing conceptual models of soil C stabilization need to reconcile the effects of litter quality on these two potentially counteracting factors: rates of litter depolymerization and microbial C use efficiency.

Rapid biodiversity losses under global climate change threaten forest ecosystem functions. However, our understanding of the patterns and drivers of multiple ecosystem functions across biodiversity gradients remains equivocal. To address this important knowledge gap, we measured simultaneous responses of multiple ecosystem functions (nutrient cycling, soil carbon stocks, organic matter decomposition, plant productivity) to a tree species richness gradient of 1, 4, 8, 16, and 32 species in a young subtropical forest. We found that tree species richness had negligible effects on nutrient cycling, organic matter decomposition, and plant productivity, but soil carbon stocks and ecosystem multifunctionality significantly increased with tree species richness. Linear mixed‐effect models showed that soil organisms, particularly arbuscular mycorrhizal fungi (AMF) and soil nematodes, elicited the greatest relative effects on ecosystem multifunctionality. Structural equation models revealed indirect effects of tree species richness on ecosystem multifunctionality mediated by trophic interactions in soil micro‐food webs. Specifically, we found a significant negative effect of gram‐positive bacteria on soil nematode abundance (a top‐down effect), and a significant positive effect of AMF biomass on soil nematode abundance (a bottom‐up effect). Overall, our study emphasizes the significance of a multitrophic perspective in elucidating biodiversity‐multifunctionality relationships and highlights the conservation of functioning soil micro‐food webs to maintain multiple ecosystem functions. [ABSTRACT FROM AUTHOR]

It is well known that biodiversity positively affects ecosystem functioning, leading to enhanced ecosystem stability. However, this knowledge is mainly based on analyses using single ecosystem functions, while studies focusing on the stability of ecosystem multifunctionality (EMF) are rare. Taking advantage of a long‐term grassland biodiversity experiment, we studied the effect of plant diversity (1–60 species) on EMF over 5 years, its temporal stability, as well as multifunctional resistance and resilience to a 2‐year drought event. Using split‐plot treatments, we further tested whether a shared history of plants and soil influences the studied relationships. We calculated EMF based on functions related to plants and higher‐trophic levels. Plant diversity enhanced EMF in all studied years, and this effect strengthened over the study period. Moreover, plant diversity increased the temporal stability of EMF and fostered resistance to reoccurring drought events. Old plant communities with shared plant and soil history showed a stronger plant diversity–multifunctionality relationship and higher temporal stability of EMF than younger communities without shared histories. Our results highlight the importance of old and biodiverse plant communities for EMF and its stability to extreme climate events in a world increasingly threatened by global change. [ABSTRACT FROM AUTHOR]

Plant monocultures growing for extended periods face severe losses of productivity. This phenomenon, known as 'yield decline', is often caused by the accumulation of above‐ and below‐ground plant antagonists. The effectiveness of plant defences against antagonists might help explain differences in yield decline among species. Using a trait‐based approach, we studied the role of 20 physical and chemical defence traits of leaves and fine roots on yield decline of 4‐ and 18‐year‐old monocultures of 27 grassland species. We hypothesized that yield decline is lower for species with high defences, that root defences are better predictors of yield decline than leaf defences, and that in roots, physical defences better predict yield decline than chemical defences, while the reverse is true for leaves. We additionally hypothesized that the relationship between defences and yield decline increases with time and that species increasing the expression of defence traits after long‐term monoculture growth would suffer less yield decline. We summarized leaf and fine root defence traits using principal component analyses and analysed the relationship between the most informative components along with their temporal changes and monoculture yield decline. The significant predictors of yield decline were traits related to the so‐called collaboration gradient of the root economics space (specific root length and root diameter) as well as their temporal changes and traits related to the leaf physical vs chemical defence tradeoff (leaf dry matter, silicon and cellulose content, toughness and phytochemical diversity). We were unable to unequivocally identify the mechanisms relating the effect of those traits to yield decline as they could mediate plant responses to several stressors such as antagonist accumulation, nutrient depletion or drought. Further studies are needed to differentiate between these alternative mechanisms and to gain a comprehensive understanding of the drivers of yield decline in relation to root and leaf defence traits. [ABSTRACT FROM AUTHOR]

Biological invasions have major impacts on a variety of ecosystems and threaten native biodiversity. Earthworms have been absent from northern parts of North America since the last ice age, but non‐native earthworms were recently introduced there and are now being spread by human activities. While past work has shown that plant communities in earthworm‐invaded areas change towards a lower diversity mainly dominated by grasses, the underlying mechanisms related to changes in the biotic interactions of the plants are not well understood. Here, we used a trait‐based approach to study the effect of earthworms on interspecific plant competition and aboveground herbivory. We conducted a microcosm experiment in a growth chamber with a full‐factorial design using three plant species native to northern North American deciduous forests, Poa palustris (grass), Symphyotrichum laeve (herb) and Vicia americana (legume), either growing in monoculture or in a mixture of three. These plant community treatments were crossed with earthworm (presence or absence) and herbivore (presence or absence) treatments. Eight out of the fourteen above‐ and belowground plant functional traits studied were significantly affected by earthworms, either by a general effect or in interaction with plant species identity, plant diversity level and/or herbivore presence. Earthworms increased the aboveground productivity and the number of inflorescences of the grass P. palustris. Further, earthworms and herbivores together affected root tissue density of P. palustris and the specific leaf area of V. americana. In this study, earthworm presence gave a competitive advantage to the grass species P. palustris by inducing changes in plant functional traits. Our results suggest that invasive earthworms can alter competitive and multitrophic interactions of plants, shedding light on some of the mechanisms behind invasive earthworm‐induced plant community changes in northern North America forests. [ABSTRACT FROM AUTHOR]

Biodiversity–ecosystem functioning (BEF) research has provided strong evidence and mechanistic underpinnings to support positive effects of biodiversity on ecosystem functioning, from single to multiple functions. This research has provided knowledge gained mainly at the local alpha scale (i.e. within ecosystems), but the increasing homogenization of landscapes in the Anthropocene has raised the potential that declining biodiversity at the beta (across ecosystems) and gamma scales is likely to also impact ecosystem functioning. Drawing on biodiversity theory, we propose a new statistical framework based on Hill–Chao numbers. The framework allows decomposition of multifunctionality at gamma scales into alpha and beta components, a critical but hitherto missing tool in BEF research; it also allows weighting of individual ecosystem functions. Through the proposed decomposition, new BEF results for beta and gamma scales are discovered. Our novel approach is applicable across ecosystems and connects local‐ and landscape‐scale BEF assessments from experiments to natural settings. [ABSTRACT FROM AUTHOR]

Ecosystem management aims at providing many ecosystem services simultaneously. Such ecosystem service multifunctionality can be limited by tradeoffs and increased by synergies among the underlying ecosystem functions (EF), which need to be understood to develop targeted management. Previous studies found differences in the correlation between EFs. We hypothesised that correlations between EFs are variable even under the controlled conditions of a field experiment and that seasonal and annual variation, plant species richness, and plot identity (identity effects of plots, such as the presence and proportion of functional groups) are drivers of these correlations. We used data on 31 EFs related to plants, consumers, and physical soil properties that were measured over 5 to 19 years, up to three times per year, in a temperate grassland experiment with 80 different plots, constituting six sown plant species richness levels (1, 2, 4, 8, 16, 60 species). We found that correlations between pairs of EFs were variable, and correlations between two particular EFs could range from weak to strong or negative to positive correlations among the repeated measurements. To determine the drivers of pairwise EF correlations, the covariance between EFs was partitioned into contributions from species richness, plot identity, and time (including years and seasons). We found that most of the covariance for synergies was explained by species richness (26.5%), whereas for tradeoffs, most covariance was explained by plot identity (29.5%). Additionally, some EF pairs were more affected by differences among years and seasons, showing a higher temporal variation. Therefore, correlations between two EFs from single measurements are insufficient to draw conclusions on tradeoffs and synergies. Consequently, pairs of EFs need to be measured repeatedly under different conditions to describe their relationships with more certainty and be able to derive recommendations for the management of grasslands. [ABSTRACT FROM AUTHOR]