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The magnitude of plant–soil feedback (PSF) can depend on the time of conditioning as well as the length of feedback. Understanding the temporal variation in PSF requires insight in the response of both soil characteristics and the plant. We examined how conspecific PSF varies with the length of conditioning and the size of the response plant using Jacobaea vulgaris, a species known to experience negative conspecific PSF. Together with reanalysis of an existing microbial sequence dataset, we tested whether the temporal variation in PSF is due to size‐dependent plant sensitivity to conditioned soil or due to compositional changes in microbial communities of conditioned soil. Further, by reanalysing another existing dataset, we examined temporal dynamics of the relative growth rates (RGR) of J. vulgaris during the feedback phase. Testing varying conditioning lengths, uncovered that J. vulgaris exhibited the strongest negative PSF at 5 weeks of conditioning, after which PSF gradually attenuated. Plant sensitivity to conditioned soil decreased with increasing plant age/size of the response plant. In the feedback phase, the RGR of J. vulgaris was first higher, then lower and at the end similar in ‘away’ soil compared to ‘home’ soil. The dissimilarity in bacterial and fungal communities in ‘home’ and ‘away’ soil significantly decreased during the feedback phase. When J. vulgaris grew in ‘away’ soil, the relative abundance of 10 (out of 80) bacterial OTUs that positively correlated with plant growth decreased over time, while 5 (out of 86) OTUs that negatively correlated with plant growth the relative abundance increased over time. Additionally, only one (out of 10) fungal OTU that negatively associated with plant growth increased over time in ‘away’ soil. Synthesis. Our findings illustrate that PSF varies with the duration of soil conditioning and of the feedback phase. During the feedback phase, changes in PSF can be attributed to both the size‐dependent plant sensitivity to conditioned soil and temporal changes in the microbial community of conditioned soil. This highlights the importance of considering the reconditioning of soil microbial communities by the test plants during the feedback phase for understanding temporal variation in PSF. [ABSTRACT FROM AUTHOR]

Plants influence numerous soil biotic factors that can alter the performance of later growing plants—defined as plant‐soil feedback (PSF). Here, we investigate whether PSF effects are linked with the temporal changes in root exudate diversity and the rhizosphere microbiome of two common grassland species (Holcus lanatus and Jacobaea vulgaris). Both plant species were grown separately establishing conspecific and heterospecific soils. In the feedback phase, we determined plant biomass, measured root exudate composition, and characterised rhizosphere microbial communities weekly (eight time points). Over time, we found a strong negative conspecific PSF on J. vulgaris in its early growth phase which changed into a neutral PSF, whereas H. lanatus exhibited a more persistent negative PSF. Root exudate diversity increased considerably over time for both plant species. Rhizosphere microbial communities were distinct in conspecific and heterospecific soils and showed strong temporal patterns. Bacterial communities converged over time. Using path models, PSF effects could be linked to the temporal dynamics of root exudate diversity, whereby shifts in rhizosphere microbial diversity contributed to temporal variation in PSF to a lesser extent. Our results highlight the importance of root exudates and rhizosphere microbial communities in driving temporal changes in the strength of PSF effects. Summary Statement: The direction and magnitude of plant‐soil feedbacks (PSF) depend on plant growth stages. Temporal shifts in PSFs effects could be linked to temporal dynamics of root exudate diversity whereas temporal changes of soil bacterial and fungal diversity effects contributed to a lesser extent. [ABSTRACT FROM AUTHOR]

The importance of plant–soil feedbacks (PSF) for above‐ground and below‐ground multitrophic interactions is well recognized. However, most studies only condition soil for a short time before testing the feedback response. Here we investigate the influence of time of conditioning on soil microbiome composition, plant growth and metabolomics, and plant–insect interactions. We used soil collected from large outdoor mesocosms with monocultures of six species and investigated the temporal changes in the soil over a full year.Every 2 months, we assessed the legacy effects of the soils on plant growth of one of the species (Jacobaea vulgaris) in a climate‐controlled chamber. Each time we used tissue culture plants that were genetically identical. We also measured leaf herbivore performance and leaf metabolomes, as well as the abiotic and biotic soil properties.We show that the monoculture soils harboured different microbiomes, but that these varied over time. Growth of the test plants also varied over time and plants grew consistently less well in their own soil. The soil legacy effects on the leaf metabolome were less consistent and varied strongly over time. Networking analysis showed that soil bacteria had stronger effects on the leaf metabolome than fungi early on. However, after 12 months of conditioning, only soil fungal community composition explained the metabolomic profiles of the leaves. Insect herbivory was not affected by soil conditioning, but decreased with increasing time of conditioning.Synthesis. Our results show that the biomass response of the test plants to soil conditioning remained consistent throughout the year, even though both the soil microbiome and leaf metabolomic responses to conditioned soil varied greatly over time. These soil‐induced changes in the metabolome of plants over time can be an important driver of above‐ground multitrophic interactions in nature. Our study demonstrates that the duration of conditioning has a strong impact on plant and soil properties, which highlights that temporal variation is an important aspect to consider in future studies investigating plant–soil interactions. [ABSTRACT FROM AUTHOR]

Plants leave legacy effects in the soil they grow in, which can drive important vegetation processes, including productivity, community dynamics and species turnover. Plants at the same time also face continuous pressure posed by insect herbivores. Given the intimate interactions between plants and herbivores in ecosystems, plant identity and herbivory are likely to interactively shape soil legacies. However, the mechanisms that drive such legacy effects on future generations of plants and associated herbivores are little known.In a greenhouse study, we exposed 10 common grasses and non‐leguminous forbs individually to insect herbivory by two closely related noctuid caterpillars, Mamestra brassicae and Trichoplusia ni (Lepidoptera: Noctuidae) or kept them free of herbivores. We then used the soil legacies created by these plant individuals to grow a plant community composed of all 10 plant species in each soil and exposed these plant communities to M. brassicae. We measured conditioning plant biomass, soil respiration and chemistry of the conditioned soils, as well as individual plant, plant community and herbivore biomass responses.At the end of the conditioning phase, soils with herbivore legacies had higher soil respiration, but only significantly so for M. brassicae. Herbivore legacies had minimal impacts on community productivity. However, path models reveal that herbivore‐induced soil legacies affected responding herbivores through changes in plant community shoot: root ratios. Soil legacy effect patterns differed between functional groups. We found strong plant species and functional group‐specific effects on soil respiration parameters, which in turn led to plant community shifts in grass: forb biomass ratios. Soil legacies were negative for the growth of plants of the same functional group.Synthesis. We show that insect herbivory, plant species and their functional groups, all incur soil microbial responses that lead to subtle (herbivory) or strong (plants and their functional group) effects in response plant communities and associated polyphagous herbivores. Hence, even though typically ignored, our study emphasizes that legacies of previous insect herbivory in the soil can influence current soil–plant–insect community interactions. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

In response to environmental conditions, plants can alter the performance of the next generation through maternal effects. Since plant–soil feedbacks (PSFs) influence soil conditions, PSFs likely create such intergenerational effects. We grew monocultures of three grass and three forb species in outdoor mesocosms. We then grew one of the six species, Hypochaeris radicata, in the conditioned soils and collected their seeds. We measured seed weight, carbon and nitrogen concentration, germination and seedling performance when grown on a common soil. We did not detect functional group intergenerational effects, but soils conditioned by different plant species affected H. radicata seed C to N ratios. There was a relationship between parent biomass in the differently conditioned soils and the germination rates of the offspring. However, these effects did not change offspring performance on a common soil. Our findings show that PSF effects changed seed quality and initial performance in a common grassland forb. We discuss the implications of our findings for multi‐generational plant–soil interactions, and highlight the need to further explore how PSF effects shape plant community dynamics over different generations and across a broad range of species and functional groups. [ABSTRACT FROM AUTHOR]

Plant–soil feedbacks of plants that are exposed to herbivory have been shown to differ from those of plants that are not exposed to herbivores. Likely, this process is mediated by jasmonic acid (JA) and salicylic acid (SA) defense pathways, which are induced by aboveground herbivory. Furthermore, exogenous application of these phytohormones to plants alters belowground communities, but whether this changes plant–soil feedbacks in natural systems is unknown. We applied exogenous sprays of JA and SA individually and in combination to field plots in a restored grassland. Control plots were sprayed with demineralized water. After three repeated application rounds, we transplanted seedlings of the plant–soil feedback model plant Jacobaea vulgaris as phytometer plants to test the effects of potential phytohormone-mediated changes in the soil, on plant performance during the response phase. We further measured how exogenous application of phytohormones altered plant-related ecosystem characteristics (plot-level); soil chemistry, plot productivity, insect communities and predation. Biomass of the phytometer plants only co-varied with plot productivity, but was not influenced by phytohormone applications. However, we did observe compound-specific effects of SA application on insect communities, most notably on parasitoid attraction, and of JA application on soil nitrogen levels. Although we did not find effects on plant–soil feedbacks, the effects of exogenous application of phytohormones did alter other ecosystem-level processes related to soil nutrient cycling, which may lead to legacy effects in the longer term. Furthermore, exogenous application of phytohormones led to altered attraction of specific insect groups. [ABSTRACT FROM AUTHOR]

Changes in plant community composition can have long‐lasting consequences for ecosystem functioning. However, how the duration of plant growth of functionally distinct grassland plant communities influences abiotic and biotic soil properties and thus ecosystem functions is poorly known. In a field experiment, we established identical experimental subplots in two successive years comprising of fast‐ or slow‐growing grass and forb community mixtures with different forb:grass ratios. After one and two years of plant growth, we measured above‐ and belowground biomass, soil abiotic characteristics (pH, organic matter, soil nutrients), soil microbial properties (respiration, biomass, community composition), and nematode abundance. Fast‐ and slow‐growing plant communities did not differ in above‐ and belowground biomass. However, fast‐ and slow‐growing plant communities created distinct soil bacterial communities, whereas soil fungal communities differed most in 100% forb communities compared to other forb:grass ratio mixtures. Moreover, soil nitrate availability was higher after two years of plant growth, whereas the opposite was true for soil ammonium concentrations. Furthermore, total nematodes and especially bacterial‐feeding nematodes were more abundant after two years of plant growth. Our results show that plant community composition is a driving factor in soil microbial community assembly and that the duration of plant growth plays a crucial role in the establishment of plant community and functional group composition effects on abiotic and biotic soil ecosystem functioning under natural field conditions. [ABSTRACT FROM AUTHOR]

Soil legacy effects are commonly highlighted as drivers of plant community dynamics and species co‐existence. However, experimental evidence for soil legacy effects of conditioning plant communities on responding plant communities under natural conditions is lacking. We conditioned 192 grassland plots using six different plant communities with different ratios of grasses and forbs and for different durations. Soil microbial legacies were evident for soil fungi, but not for soil bacteria, while soil abiotic parameters did not significantly change in response to conditioning. The soil legacies affected the composition of the succeeding vegetation. Plant communities with different ratios of grasses and forbs left soil legacies that negatively affected succeeding plants of the same functional type. We conclude that fungal‐mediated soil legacy effects play a significant role in vegetation assembly of natural plant communities. [ABSTRACT FROM AUTHOR]

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]

Flooding frequency is predicted to increase during the next decades, calling for a better understanding of impacts on terrestrial ecosystems and for developing strategies to mitigate potential damage. Plant diversity is expected to buffer flooding effects by providing a broad range of species’ responses. Here we report on the response of soil processes to a severe summer flood in 2013, which affected major parts of central Europe. We compared soil microbial respiration, biomass, nutrient limitation and enzyme activity in a grassland biodiversity experiment in Germany before flooding, one week and three months after the flood. Microbial biomass was reduced in the severely flooded plots at high, but not at low plant functional group richness. Flooding alleviated microbial nitrogen limitation, presumably due the input of nutrient-rich sediments. Further, the activity of soil enzymes including 1,4-β-N-acetylglucosaminidase, phenol oxidase and peroxidase increased with flooding severity, suggesting increased chitin and lignin degradation as a consequence of the input of detritus in sediments. Flooding effects were enhanced at higher plant diversity, indicating that plant diversity temporarily reduces stability of soil processes during flooding. The long-term impacts, however, remain unknown and deserve further investigation. [ABSTRACT FROM AUTHOR]

Higher plant diversity is often associated with higher soil microbial biomass and diversity, which is assumed to be partly due to elevated root exudate diversity. However, there is little experimental evidence that diversity of root exudates shapes soil microbial communities. We tested whether higher root exudate diversity enhances soil microbial biomass and diversity in a plant diversity gradient, thereby negating significant plant diversity effects on soil microbial properties. We set up plant monocultures and two- and three-species mixtures in microcosms using functionally dissimilar plants and soil of a grassland biodiversity experiment in Germany. Artificial exudate cocktails were added by combining the most common sugars, organic acids, and amino acids found in root exudates. We applied four different exudate cocktails: two exudate diversity levels (low- and high-diversity) and two nutrient-enriched levels (carbon- and nitrogen-enriched), and a control with water only. Soil microorganisms were more carbon- than nitrogen-limited. Cultivation-independent fingerprinting analysis revealed significantly different soil microbial communities among exudate diversity treatments. Most notably and according to our hypothesis, adding diverse exudate cocktails negated the significant plant diversity effect on soil microbial properties. Our findings provide the first experimental evidence that root exudate diversity is a crucial link between plant diversity and soil microorganisms. [ABSTRACT FROM AUTHOR]

Background: Several studies have examined the effects of plant colonization on aboveground communities and processes. However, the effects of plant colonization on soil microbial communities are less known. We addressed this gap by studying effects of plant colonization within an experimental plant diversity gradient in subplots that had not been weeded for 2 and 5 years. This study was part of a long-term grassland biodiversity experiment (Jena Experiment) with a gradient in plant species richness (1, 2, 4, 8, 16, and 60 sown species per plot). We measured plant species richness and productivity (aboveground cover and biomass) as well as soil microbial basal respiration and biomass in non-weeded subplots and compared the results with those of weeded subplots of the same plots. Results: After 2 and 5 years of plant colonization, the number of colonizing plant species decreased with increasing plant diversity, i.e., low-diversity plant communities were most vulnerable to colonization. Plant colonization offset the significant relationship between sown plant diversity and plant biomass production. In line with plant community responses, soil basal respiration and microbial biomass increased with increasing sown plant diversity in weeded subplots, but soil microbial properties converged in non-weeded subplots and were not significantly affected by the initial plant species richness gradient. Conclusion: Colonizing plant species change the quantity and quality of inputs to the soil, thereby altering soil microbial properties. Thus, plant community convergence is likely to be rapidly followed by the convergence of microbial properties in the soil. [ABSTRACT FROM AUTHOR]

Soil microbial biomass is a key determinant of carbon dynamics in the soil. Several studies have shown that soil microbial biomass significantly increases with plant species diversity, but it remains unclear whether plant species diversity can also stabilize soil microbial biomass in a changing environment. This question is particularly relevant as many global environmental change ( GEC) factors, such as drought and nutrient enrichment, have been shown to reduce soil microbial biomass. Experiments with orthogonal manipulations of plant diversity and GEC factors can provide insights whether plant diversity can attenuate such detrimental effects on soil microbial biomass. Here, we present the analysis of 12 different studies with 14 unique orthogonal plant diversity × GEC manipulations in grasslands, where plant diversity and at least one GEC factor (elevated CO2, nutrient enrichment, drought, earthworm presence, or warming) were manipulated. Our results show that higher plant diversity significantly enhances soil microbial biomass with the strongest effects in long-term field experiments. In contrast, GEC factors had inconsistent effects with only drought having a significant negative effect. Importantly, we report consistent non-significant effects for all 14 interactions between plant diversity and GEC factors, which indicates a limited potential of plant diversity to attenuate the effects of GEC factors on soil microbial biomass. We highlight that plant diversity is a major determinant of soil microbial biomass in experimental grasslands that can influence soil carbon dynamics irrespective of GEC. [ABSTRACT FROM AUTHOR]

Anthropogenic changes in biodiversity and atmospheric temperature significantly influence ecosystem processes. However, little is known about potential interactive effects of plant diversity and warming on essential ecosystem properties, such as soil microbial functions and element cycling. We studied the effects of orthogonal manipulations of plant diversity (one, four, and 16 species) and warming (ambient, +1.5°C, and +3°C) on soil microbial biomass, respiration, growth after nutrient additions, and activities of extracellular enzymes in 2011 and 2012 in the BAC (biodiversity and climate) perennial grassland experiment site at Cedar Creek, Minnesota, USA. Focal enzymes are involved in essential biogeochemical processes of the carbon, nitrogen, and phosphorus cycles. Soil microbial biomass and some enzyme activities involved in the C and N cycle increased significantly with increasing plant diversity in both years. In addition, 16-species mixtures buffered warming induced reductions in topsoil water content. We found no interactive effects of plant diversity and warming on soil microbial biomass and growth rates. However, the activity of several enzymes (1,4-ß-glucosidase, 1,4-ß-N-acetylglucosaminidase, phosphatase, peroxidase) depended on interactions between plant diversity and warming with elevated activities of enzymes involved in the C, N, and P cycles at both high plant diversity and high warming levels. Increasing plant diversity consistently decreased microbial biomass-specific enzyme activities and altered soil microbial growth responses to nutrient additions, indicating that plant diversity changed nutrient limitations and/or microbial community composition. In contrast to our expectations, higher plant diversity only buffered temperature effects on soil water content, but not on microbial functions. Temperature effects on some soil enzymes were greatest at high plant diversity. In total, our results suggest that the fundamental temperature ranges of soil microbial communities may be sufficiently broad to buffer their functioning against changes in temperature and that plant diversity may be a dominant control of soil microbial processes in a changing world. [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]

Plant diversity has been shown to determine the composition and functioning of soil biota. Although root-derived organic inputs are discussed as the main drivers of soil communities, experimental evidence is scarce. While there is some evidence that higher root biomass at high plant diversity increases substrate availability for soil biota, several studies have speculated that the quantity and diversity of root inputs into the soil, i.e. though root exudates, drive plant diversity effects on soil biota. Here we used a microcosm experiment to study the role of plant species richness on the biomass of soil bacteria and fungi as well as fungal-to-bacterial ratio via root biomass and root exudates. Plant diversity significantly increased shoot biomass, root biomass, the amount of root exudates, bacterial biomass, and fungal biomass. Fungal biomass increased most with increasing plant diversity resulting in a significant shift in the fungal-to-bacterial biomass ratio at high plant diversity. Fungal biomass increased significantly with plant diversity-induced increases in root biomass and the amount of root exudates. These results suggest that plant diversity enhances soil microbial biomass, particularly soil fungi, by increasing root-derived organic inputs. [ABSTRACT FROM AUTHOR]

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]

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]

Global warming and precipitation extremes (drought or increased precipitation) strongly affect plant primary production and thereby terrestrial ecosystem functioning. Recent syntheses show that combined effects of warming and precipitation extremes on plant biomass are generally additive, while individual experiments often show interactive effects, indicating that combined effects are more negative or positive than expected based on the effects of single factors. Here, we examined whether variation in biomass responses to single and combined effects of warming and precipitation extremes can be explained by plant growth form and community type. We performed a meta-analysis of 37 studies, which experimentally crossed warming and precipitation treatments, to test whether biomass responses to combined effects of warming and precipitation extremes depended on plant woodiness and community type (monocultures versus mixtures). Our results confirmed that the effects of warming and precipitation extremes were overall additive. However, combined effects of warming and drought on above- and belowground biomass were less negative in woody- than in herbaceous plant systems and more negative in plant mixtures than in monocultures. We further show that drought effects on plant biomass were more negative in greenhouse, than in field studies, suggesting that greenhouse experiments may overstate drought effects in the field. Our results highlight the importance of plant system characteristics to better understand plant responses to climate change.

Microorganisms are found everywhere and have critical roles in most ecosystems, but compared to plants and animals, little is known about their temporal dynamics. Here, we investigated the temporal stability of bacterial and fungal communities in the soil and how their temporal variation varies between grasses and forb species. We established 30 outdoor mesocosms consisting of six plant monocultures and followed microbial communities for an entire year in these soils. We demonstrate that bacterial communities vary greatly over time and that turnover plays an important role in shaping microbial communities. We further show that bacterial communities rapidly shift from one state to another and that this is related to changes in the relative contribution of certain taxa rather than to extinction. Fungal soil communities are more stable over time, and a large part of the variation can be explained by plant species and by whether they are grasses or forbs. Our findings show that the soil bacterial community is shaped by time, while plant group and plant species-specific effects drive soil fungal communities. This has important implications for plant-soil research and highlights that temporal dynamics of soil communities cannot be ignored in studies on plant-soil feedback and microbial community composition and function. IMPORTANCE Our findings highlight how soil fungal and bacterial communities respond to time, season, and plant species identity. We found that succession shapes the soil bacterial community, while plant species and the type of plant species that grows in the soil drive the assembly of soil fungal communities. Future research on the effects of plants on soil microbes should take into consideration the relative roles of both time and plant growth on creating soil legacies that impact future plants growing in the soil. Understanding the temporal (in)stability of microbial communities in soils will be crucial for predicting soil microbial composition and functioning, especially as plant species compositions will shift with global climatic changes and land-use alterations. As fungal and bacterial communities respond to different environmental cues, our study also highlights that the selection of study organisms to answer specific ecological questions is not trivial and that the timing of sampling can greatly affect the conclusions made from these studies., (Copyright © 2019 Hannula et al.)