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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. The mechanisms driving soil carbon storage, one of the largest stores of terrestrial carbon, remain poorly understood. Here, the authors present data from the long-term Jena Experiment on grassland biodiversity, showing that elevated carbon storage at high plant diversity is a direct function of increased soil microbial activity.

1. The temporal and spatial dynamics of soil water are closely interlinked with terrestrial ecosystems functioning. The interaction between plant community properties such as species composition and richness and soil water mirrors fundamental ecological processes determining above-ground-below-ground feedbacks. Plantwater relations and water stress have attracted considerable attention in biodiversity experiments. Yet, although soil scientific research suggests an influence of ecosystem productivity on soil hydraulic properties, temporal changes of the soil water content and soil hydraulic properties remain largely understudied in biodiversity experiments. Thus, insights on how plant diversity—productivity relationships affect soil water are lacking. 2. Here, we determine which factors related to plant community composition (species and functional group richness, presence of plant functional groups) and soil (organic carbon concentration) affect soil water in a long-term grassland biodiversity experiment (The Jena Experiment). 3. Both plant species richness and the presence of particular functional groups affected soil water content, while functional group richness played no role. The effect of species richness changed from positive to negative and expanded to deeper soil with time. Shortly after establishment, increased topsoil water content was related to higher leaf area index in species-rich plots, which enhanced shading. In later years, higher species richness increased topsoil organic carbon, likely improving soil aggregation. Improved aggregation, in turn, dried topsoils in species-rich plots due to faster drainage of rainwater. Functional groups affected soil water distribution, likely due to plant traits affecting root water uptake depths, shading, or water-use efficiency. For instance, topsoils in plots containing grasses were generally drier, while plots with legumes were moister. 4. Synthesis. Our decade-long experiment reveals that the maturation of grasslands changes the effects of plant richness from influencing soil water content through shading effects to altering soil physical characteristics in addition to modification of water uptake depth. Functional groups affected the soil water distribution by characteristic shifts of root water uptake depth, but did not enhance exploitation of the overall soil water storage. Our results reconcile previous seemingly contradictory results on the relation between grassland species diversity and soil moisture and highlight the role of vegetation composition for soil processes.

Biodiversity ensures ecosystem functioning and provisioning of ecosystem services, but it remains unclear how biodiversity–ecosystem multifunctionality relationships depend on the identity and number of functions considered. Here, we demonstrate that ecosystem multifunctionality, based on 82 indicator variables of ecosystem functions in a grassland biodiversity experiment, increases strongly with increasing biodiversity. Analysing subsets of functions showed that the effects of biodiversity on multifunctionality were stronger when more functions were included and that the strength of the biodiversity effects depended on the identity of the functions included. Limits to multifunctionality arose from negative correlations among functions and functions that were not correlated with biodiversity. Our findings underline that the management of ecosystems for the protection of biodiversity cannot be replaced by managing for particular ecosystem functions or services and emphasize the need for specific management to protect biodiversity. More plant species from the experimental pool of 60 species contributed to functioning when more functions were considered. An individual contribution to multifunctionality could be demonstrated for only a fraction of the species. Analysis of 82 indictors of ecosystem functioning at the Jena grassland biodiversity experiment shows that multifunctionality increases strongly with diversity, but depends on the number and identity of the functions considered.

Plant diversity drives changes in the soil microbial community which may result in alterations in ecosystem functions. However, the governing factors between the composition of soil microbial communities and plant diversity are not well understood. We investigated the impact of plant diversity (plant species richness and functional group richness) and plant functional group identity on soil microbial biomass and soil microbial community structure in experimental grassland ecosystems. Total microbial biomass and community structure were determined by phospholipid fatty acid (PLFA) analysis. The diversity gradient covered 1, 2, 4, 8, 16 and 60 plant species and 1, 2, 3 and 4 plant functional groups (grasses, legumes, small herbs and tall herbs). In May 2007, soil samples were taken from experimental plots and from nearby fields and meadows. Beside soil texture, plant species richness was the main driver of soil microbial biomass. Structural equation modeling revealed that the positive plant diversity effect was mainly mediated by higher leaf area index resulting in higher soil moisture in the top soil layer. The fungal-to-bacterial biomass ratio was positively affected by plant functional group richness and negatively by the presence of legumes. Bacteria were more closely related to abiotic differences caused by plant diversity, while fungi were more affected by plant-derived organic matter inputs. We found diverse plant communities promoted faster transition of soil microbial communities typical for arable land towards grassland communities. Although some mechanisms underlying the plant diversity effect on soil microorganisms could be identified, future studies have to determine plant traits shaping soil microbial community structure. We suspect differences in root traits among different plant communities, such as root turnover rates and chemical composition of root exudates, to structure soil microbial communities.

In the circular economy framework, municipal wastes are seen as secondary raw materials that can be used to fertilize agricultural soils. This study assessed the effect of different biowaste and green waste treatment schemes on P fertilizer value to learn about the optimal valorization of these feedstocks. The wastes were used either fresh, after composting or anaerobic digestion, or as biochars produced at various pyrolysis conditions. The fertilizer value was determined from the change in soil concentration of plant-available P (PCAL) in incubation experiments with different soils and the temporal dynamics of fertilizer-induced growth and P accumulation of ryegrass in a pot experiment with eight harvests. The mode of waste treatment significantly influenced the P fertilizer value in the incubation and in the pot experiment. In the incubation experiment, the amendment-induced PCAL increase varied between 22% and 33% of applied P on low-P acidic soil and between 55% and 88% of applied P on high-P acidic soil, whereby the amendment effects were mainly determined by their effects on soil pH. In the pot experiment with low-P acidic soil, the apparent P recovery in the plant biomass (APR) varied between 2% of applied P for fresh green waste and 42% for fluid digestate. The amendment effects on APR were not related to soil pH but to the PCAL supply with the amendments and amendment effects on soil P supply. Our data show great potential for increasing the P fertilizer value of organic municipal waste materials through appropriate processing prior to application.

In the original article [...]

Background: Organic amendments are often used for the phytostabilization of heavy metal-contaminated soils. This study investigated the suitability of different municipal waste processing methods for phytostabilization. Methods: The two feedstocks, biowaste, and green waste, were tested without pretreatment after composting or after pyrolysis at different temperatures and atmosphere compositions. The suitability of the differently pretreated amendments for phytostabilization was tested on sewage farm soil contaminated with Cd, Cu, Ni, and Zn by measurement of maize growth, mineral content, and mobile heavy metal concentrations in the bulk and rhizosphere soil. Results: In contaminated soils, shoot and root growth increased markedly due to the soil amendments. Shoot concentrations of all four heavy metals were significantly higher in contaminated than non-contaminated soil, whereas Fe concentrations were lower in contaminated soil. The amendments increased shoot Cd concentrations and did not significantly affect the other elements. In contaminated soil, concentrations of heavy metals were generally lower in the rhizosphere than in the bulk soil. The soil amendments markedly lowered soil heavy metal concentrations, whereby the decrease was significantly influenced by feedstock and pretreatment. The differences in the amendments’ ability to reduce the soil mobile heavy metals were primarily, but not exclusively, determined by their effect on soil pH. Conclusion: The feedstock processing conditions significantly influenced the phytostabilization performance of green waste and biowaste. Optimal processing for phytostabilization depends on the heavy metal most important in the contamination of a specific site.

One of the most significant consequences of contemporary global change is the rapid decline of biodiversity in many ecosystems. Knowledge of the consequences of biodiversity loss in terrestrial ecosystems is largely restricted to single ecosystem functions. Impacts of key plant functional groups on soil biota are considered to be more important than those of plant diversity; however, current knowledge mainly relies on short-term experiments. We studied changes in the impacts of plant diversity and presence of key functional groups on soil biota by investigating the performance of soil microorganisms and soil fauna two, four and six years after the establishment of model grasslands. The results indicate that temporal changes of plant community effects depend on the trophic affiliation of soil animals: plant diversity effects on decomposers only occurred after six years, changed little in herbivores, but occurred in predators after two years. The results suggest that plant diversity, in terms of species and functional group richness, is the most important plant community property affecting soil biota, exceeding the relevance of plant above- and belowground productivity and the presence of key plant functional groups, i.e. grasses and legumes, with the relevance of the latter decreasing in time. Plant diversity effects on biota are not only due to the presence of key plant functional groups or plant productivity highlighting the importance of diverse and high-quality plant derived resources, and supporting the validity of the singular hypothesis for soil biota. Our results demonstrate that in the long term plant diversity essentially drives the performance of soil biota questioning the paradigm that belowground communities are not affected by plant diversity and reinforcing the importance of biodiversity for ecosystem functioning.

Recent studies assessing the role of biological diversity for ecosystem functioning indicate that the diversity of functional traits and the evolutionary history of species in a community, not the number of taxonomic units, ultimately drives the biodiversity-ecosystem-function relationship. Here, we simultaneously assessed the importance of plant functional trait and phylogenetic diversity as predictors of major trophic groups of soil biota (abundance and diversity), six years from the onset of a grassland biodiversity experiment. Plant functional and phylogenetic diversity were generally better predictors of soil biota than the traditionally used species or functional group richness. Functional diversity was a reliable predictor for most biota, with the exception of soil microorganisms, which were better predicted by phylogenetic diversity. These results provide empirical support for the idea that the diversity of plant functional traits and the diversity of evolutionary lineages in a community are important for maintaining higher abundances and diversity of soil communities.

BackgroundPhosphorus (P) is an essential plant nutrient that has continued to depreciate in most soils in sub-Saharan Africa, mostly due to adsorption, leaching, and crop uptake.ObjectiveThis study was carried out to determine the effect of phosphorus forms and its absence on P uptake, root traits, and growth of leafy vegetables.MethodsFive African indigenous vegetable species alongside one exotic vegetable were grown in pots. Each pot was supplied with 49 milligrams of P in the form of KH2PO4, Phytate, rock P, and FePO4 with the control having no P. The P fertilizers were mixed with 1220 g of soil in a ratio of 60:1, sand and loam, to fill the pots before planting. Vegetable seeds were randomly planted and replicated four times, giving rise to 120 pots under investigation.ResultsAll vegetable species actively utilized KH2PO4 and Phytate to grow and form the highest shoot and root biomass. Spider plants absorbed high levels of P from all the P treatments, but could not convert more of it to biomass formation. African nightshade performed well in KH2PO4 and Phytate, but poorly in the rock P and FePO4. Cowpeas performed well by yielding high-shoot biomass in all the treatments. Cowpea and Ethiopian kale had high biomass when grown in rock P and FePO4.ConclusionVegetable species require P for optimal growth, although various species were seen to have different levels of P uptake and utilization efficiency on soluble and slightly soluble fertilizers as well as their ability to grow in P-absent or adsorbed soils.