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Plant–soil feedbacks (PSFs) involve changes to the soil wrought by plants, which change biotic and abiotic properties of the soil, affecting plants that grow in the soil at a later time. The importance of PSFs for understanding ecosystem functioning has been the focus of much recent research, for example, in predicting the consequences for agricultural production, biodiversity conservation, and plant population dynamics. Here, we describe an experiment designed to test PSFs left by plants with contrasting traits under field conditions. This is one of the first, large-scale field experiments of its kind. We removed the existent plant community and replaced it with target plant communities that conditioned the soil. These communities consisted of contrasting proportions of grass and forb cover and consisted of either fast- or slow-growing plants, in accordance with the plant economics spectrum. We chose this well-established paradigm because plants on opposite ends of this spectrum have developed contrasting strategies to cope with environmental conditions. This means they differ in their feedbacks with soil abiotic and biotic factors. The experimental procedure was repeated in two successive years in two different subplots in order to investigate temporal effects on soils that were conditioned by the same plant community. Our treatments were successful in creating plant communities that differed in their total percentage cover based on temporal conditioning, percentage of grasses versus forbs, and percentage of fast- versus slow-growing plants. As a result, we expect that the influence of these different plant communities will lead to different PSFs. The unique and novel design of this experiment allows us to simultaneously test for the impacts of temporal effects, plant community composition and plant growth strategy on PSFs. Here, we describe the experimental design and demonstrate why this effective design is ideal to advance our understanding of PSFs in the field. [ABSTRACT FROM AUTHOR]

Trait-based approaches have recently been employed to develop a more mechanistic understanding of plant community effects on the assembly and functioning of terrestrial ecosystems. Despite the broad consensus that soils provide essential ecosystem services, plant community effects on soil communities and functions have rarely been linked to aboveground and belowground plant traits. Here, we studied the effects of plant species richness, plant trait diversity, and single plant functional traits related to spatial and temporal resource acquisition on soil microbial properties over five years in a grassland biodiversity experiment. The main response variables were soil basal respiration and microbial biomass. Above- and belowground plant traits associated with spatial (plant height, leaf area, rooting depth, and root length density) and temporal resource acquisition (growth start, flowering start) were selected to design communities with different levels of functional diversity as well as to calculate realized community means weighted by plant species cover. Plant species richness and trait diversity effects on soil microbial properties were nonsignificant over the course of the five-year experiment. After four years, however, we found significantly higher soil basal respiration in plant communities with smaller leaves and both denser and shallower root systems than in plant communities with taller plants and sparse root systems. One year later, these effects were significant for both soil basal respiration and soil microbial biomass. Structural equation modeling revealed that plant community effects on soil microbial properties were mostly due to differences in rooting depth, although the explanatory power of our models was low. Our findings highlight the importance of incorporating plant traits, particularly root traits, in analyses of plant community effects on soil biota and functions. Selecting for particular plant traits in communities and considering interactive effects of specific plant traits may facilitate the targeted management of grasslands to maintain essential ecosystem services. [ABSTRACT FROM AUTHOR]

Abstract: Anthropogenic nitrogen (N) deposition is a serious threat to biodiversity and the functioning of many ecosystems, particularly so in N-limited systems, such as many forests. Here we evaluate the associations between soil nitrate and changes in plant community structure and soil biota along nitrate gradients from croplands into closed forests. Specifically, we studied the composition of the understory plant and earthworm communities as well as soil microbial properties in two deciduous forests (Echinger Lohe (EL) and Wippenhauser Forst (WF)) near Munich, Germany, which directly border on fertilized agricultural fields. Environmental variables, like photosynthetically active radiation, distance to the edge and soil pH were also determined and used as co-variates. In both forests we found a decrease in understory plant coverage with increasing soil nitrate concentrations. Moreover, earthworm biomass increased with soil nitrate concentration, but this increase was more pronounced in EL than in WF. Soil microbial growth after addition of a nitrogen source increased significantly with soil nitrate concentrations in WF, indicating changes in the composition of the soil microbial community, although there was no significant effect in EL. In addition, we found changes in earthworm community composition along the soil nitrate gradient in WF. Taken together, the composition and functioning of forest soil communities and understory plant cover changed significantly along soil nitrate gradients leading away from fertilized agricultural fields. Inconsistent patterns between the two forests however suggest that predicting the consequences of N deposition may be complicated due to context-dependent responses of soil organisms. [Copyright &y& Elsevier]

Abstract: In a grassland plant diversity experiment, we studied if plant species richness induces transgressive overyielding in soil microbial biomass, the definition of which is greater microbial biomass with a plant mixture than in each of the plant monocultures. In June and November of 2012 soil microbial biomass increased significantly with plant species richness. Overyielding occurred in more than 61% of 24 plots containing six species, and transgressive overyielding occurred in 13–21% of the plots depending on season. Plots with nine species showed overyielding in all cases, and 25–50% showed transgressive overyielding. Transgressive underyielding occurred in a few plots with six species in June. Our results indicate plant complementarity effects on soil microbial biomass in diverse plant communities across seasons and stress the relevance of simplification of plant communities for soil processes. [Copyright &y& Elsevier]

Ecological communities are increasingly confronted with multiple global change factors, which can have wide-ranging consequences for ecosystem structure and functions. Yet, we lack studies on the interacting effects of multiple global change factors on ecological communities – particularly long-term studies in field settings. Here, using a grassland field experiment in temperate North America, we report the interactive effects of four of the most common and pressing global change factors of the Anthropocene (elevated CO 2 , elevated nitrogen, warming, and summer drought) on soil microbial and free-living soil nematode communities, which together form an extensive share of terrestrial biodiversity. In addition, we measured microbial mass-specific soil enzyme activities related to carbon, nitrogen, and phosphorus cycles. Our results showed that mass-specific soil enzyme activities and their stoichiometry were strongly affected by higher-order interactions among the global change factors. In particular, the three-way interaction among elevated CO 2 , reduced precipitation, and warming decreased the ratio of carbon-to phosphorus-acquiring enzymes as well as nitrogen-to phosphorus-acquiring enzymes in the soil, indicating a relative increase in the breakdown of organic phosphorus in the soil. We also found that the three-way interaction among elevated CO 2 , reduced precipitation, and warming altered the predominant decomposition pathway in the soil (towards a bacterial-dominated energy channel in future environments), indicated by the Channel Index of nematode communities. Further, the three-way interaction among nitrogen fertilization, reduced precipitation, and warming enhanced acid phosphatase (related to the P cycle). Nematode density increased at elevated nitrogen and ambient CO 2 as well as at ambient nitrogen and elevated CO 2, whereas it did not differ from controls at elevated nitrogen and elevated CO 2. Changes in microbial biomass were mainly driven by the additive effects of elevated CO 2 and temperature. Our results reveal various ways in which global change factors affect (both additively and interactively) soil biotic responses mainly via altering nutrient demands of soil microorganisms and changing soil community structure and energy channels. • Effects of CO 2 , nitrogen, warming and drought on soil biota and processes were investigated. • Higher-order interactions among global change drivers changed soil enzyme production. • Elevated CO 2 and warming changed microbial biomass C over the four year period. • Nematode density increased at elevated nitrogen and ambient CO 2. • Elevated CO 2 , precipitation, and temperature altered the decomposition pathway. [ABSTRACT FROM AUTHOR]

Soil legacies mediated by plant species-specific microbial communities are major drivers of plant community dynamics. Most soil legacy studies focus on the role of pathogens and mutualists in driving these processes, while much less is known about plant litter-mediated changes to the soil microbial community. Here, we used an existing plant-soil feedback field experiment in which plant communities with different growth strategies (i.e., fast versus slow) and different proportions of functional groups (i.e., grasses versus forbs) were allowed to condition the soil over contrasting temporal scales (i.e., one versus two years) in a natural grassland. In the feedback phase, we removed the existent plant community, and replaced it with a standardized response plant community. We then tested the legacy effects of these different soil conditioning treatments on decomposition processes, nutrient cycling and soil decomposer community composition. Soil legacy effects on decomposition and the soil decomposer community composition were most evident right after the start of the feedback phase, but disappeared soon after the new community established. The soil conditioning time and years since disturbance affected most of the soil functions consistently, while no strong effects of plant functional group and plant growth strategy were found. We conclude that after disturbance, it is recovery time, not soil legacy effects, that is the most important factor driving soil functions. • Litter decomposition is faster in soils conditioned by fast-growing forbs. • Soil legacy effects on nutrient cycling and decomposition are transient. • Time since disturbance, not soil legacy effects, is key in affecting soil functions. [ABSTRACT FROM AUTHOR]

Rapid ecosystem assessments are needed for large-scale ecotoxicological studies and coordinated distributed experiments. Bait-lamina stripes are commonly used as a standardized method to assess decomposer activity, but it is often difficult to distinguish bait substrate from soil. In the present study our aim was to identify a dyeing method that improves the precision of visual assessment of decomposition rates, while having negligible side effects. We compared five different dyes (food dye, Easter Grass, organic textile dye, ink, and wall paint) with control substrate in microcosms containing either acidic or alkaline soil with two introduced Collembola species (Folsomia candida and Sinellacoeca). Organic textile dye showed the highest precision of visual assessment, and had no detectable side effects on decomposition rates, soil microbial activity (biomass and respiration), or Collembola densities. We recommend using organic textile dye to improve the bait-lamina test due to the high precision and the ease of preparation. [ABSTRACT FROM AUTHOR]