Previous studies on biodiversity and soil food web composition have mentioned plant species identity, as well as plant species diversity as the main factors affecting the abundance and diversity of soil organisms. However, most studies have been carried out under limitations of time, space, or appropriate controls. In order to further examine the relation between plant species diversity and the soil food web, we conducted a three-year semi-field experiment in which eight plant species (4 forb and 4 grass species) were grown in monocultures and mixtures of two, four and eight plant species. In addition there were communities with 16 plant species. We analyzed the abundance and identity of the nematodes in soil and roots, including feeding groups from various trophic levels (primary and secondary consumers, carnivores, and omnivores) in the soil food web. Plant species diversity and plant identity affected the diversity of nematodes. The effect of plant diversity was attributed to the complementarity in resource quality of the component plant species rather than to an increase in total resource quantity. The nematode diversity varied more between the different plant species than between different levels of plant species diversity, so that plant identity is more important than plant diversity. Nevertheless the nematode diversity in plant mixtures

Plant species identity and diversity effects on different trophic levels of nematodes in the soil food web

1. Evidence is growing that leaf litter generally decomposes faster than expected in its environment of origin, owing to specialization of litter and topsoil decomposer communities to break down li ...

https://besjournals.onlinelibrary.wiley.com/doi/epdf/10.1111/j.1365-2745.2011.01943.x

Multiple mechanisms for trait effects on litter decomposition: moving beyond home‐field advantage with a new hypothesis

Spiders have been suspected to be one of the most important groups of natural enemies of insects worldwide. To document the impact of the global spider community as insect predators, we present estimates of the biomass of annually killed insect prey. Our estimates assessed with two different methods suggest that the annual prey kill of the global spider community is in the range of 400–800 million metric tons (fresh weight), with insects and collembolans composing >90% of the captured prey. This equals approximately 1‰ of the global terrestrial net primary production. Spiders associated with forests and grasslands account for >95% of the annual prey kill of the global spider community, whereas spiders in other habitats are rather insignificant contributors over a full year. The spider communities associated with annual crops contribute less than 2% to the global annual prey kill. This, however, can be partly explained by the fact that annual crop fields are “disturbed habitats” with a low buildup of spider biomass and that agrobiont spiders often only kill prey over short time periods in a year. Our estimates are supported by the published results of exclusion experiments, showing that the number of herbivorous/detritivorous insects and collembolans increased significantly after spider removal from experimental plots. The presented estimates of the global annual prey kill and the relative contribution of spider predation in different biomes improve the general understanding of spider ecology and provide a first assessment of the global impact of this very important predator group.

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An estimated 400-800 million tons of prey are annually killed by the global spider community.

Soil microorganisms are key to biological diversity and many ecosystem processes in terrestrial ecosystems. Despite the current alarming loss of plant diversity, it is unclear how plant species diversity affects soil microorganisms. By conducting a global meta-analysis with paired observations of plant mixtures and monocultures from 106 studies, we show that microbial biomass, bacterial biomass, fungal biomass, fungi:bacteria ratio, and microbial respiration increase, while Gram-positive to Gram-negative bacteria ratio decrease in response to plant mixtures. The increases in microbial biomass and respiration are more pronounced in older and more diverse mixtures. The effects of plant mixtures on all microbial attributes are consistent across ecosystem types including natural forests, planted forests, planted grasslands, croplands, and planted containers. Our study underlines strong relationships between plant diversity and soil microorganisms across global terrestrial ecosystems and suggests the importance of plant diversity in maintaining belowground ecosystem functioning.

/pdf/meta-analysis-shows-positive-effects-of-plant-diversity-on-301wfz2u75.pdf

Meta-analysis shows positive effects of plant diversity on microbial biomass and respiration

The ‘home-field advantage (HFA) hypothesis’ predicts that plant litter is decomposed faster than expected in the vicinity of the plant where it originates from (i.e. its ‘home’) relative to some other location (i.e. ‘away’) because of the presence of specialized decomposers. Despite growing evidence for the widespread occurrence HFA effects, what drives HFA is not understood as its strength appears highly variable and context-dependent. Our work advances current knowledge about HFA effects by testing under what conditions HFA is most important. Using published data on mass loss from 125 reciprocal litter transplants from 35 studies, we evaluated if HFA effects were modulated by macroclimate, litter quality traits, and the dissimilarity between ‘home’ and ‘away’ of both the quality of reciprocally exchanged litters and plant community type. Our results confirmed the occurrence of an overall, worldwide, HFA effect on decomposition with on average 7.5% faster decomposition at home. However, there was considerable variation in the strength and direction (sometimes opposite to expectations) of these effects. While macroclimate and average litter quality had weak or no impact on HFA effects, home-field effects became stronger (regardless of the direction) when the quality of ‘home’ and ‘away’ litters became more dissimilar (e.g. had a greater dissimilarity in N:P ratio; F1,42 = 6.39, p = 0.015). Further, home-field effects were determined by the degree of difference between the types of dominant plant species in the ‘home’ versus ‘away’ communities (F2,105 = 4.03, p = 0.021). We conclude that home-field advantage is not restricted to particular litter types or climate zones, and that the dissimilarity in plant communities and litter quality between the ‘home’ and ‘away’ locations, are the most significant drivers of home-field effects.

/pdf/litter-quality-and-environmental-controls-of-home-field-aqznl4w1hn.pdf

Litter quality and environmental controls of home-field advantage effects on litter decomposition

Scheu, S., Albers, D., Alphei, J., Buryn, R., Klages, U., Migge, S., Platner, C. andSalamon, J.-A. 2003. The soil fauna community in pure and mixed stands of beechand spruce of different age: trophic structure and structuring forces. – Oikos 101:225–238.This study investigates the response of the soil fauna community to replacement ofbeech by spruce or by mixed stands of beech and spruce. Stands of different age wereinvestigated in a factorial design with the factors tree species (beech and spruce) andstand age (30 and 120 years). The input of leaf/needle litter did not differ signiﬁcantlybetween the study sites. By contrast, the amount of organic matter in upper soillayers (L/F, H/Ah) of spruce forests strongly exceeded that of beech forests particu-larly in mature stands. The increase in organic matter in spruce stands was notassociated by an increase in the amount of microbial biomass. Biomass of eight(bacterivorous, fungivorous and omnivorous nematodes, enchytraeids, earthworms,isopodes, mycetophilid and cecidomyiid Diptera) of the twelve microbi-detritivoroussoil animal groups studied was signiﬁcantly increased in beech forests; only that ofone group (elaterid beetles) was increased in spruce forests and three groups did notrespond signiﬁcantly (collembolans, oribatid mites, sciarid Diptera). This indicatesthat in the forests studied neither habitat space (amount of organic matter in L/FandH/Ah layers) nor the amount of microbial biomass controlled microbi-detritivores.Rather, the quality of litter materials and the concentration of microbial biomasstherein appeared to be most important. Herbivores and predators also were favouredby beech: the biomass of one (rhizophagous nematodes) of the three herbivorousgroups studied were signiﬁcantly increased in beech stands and none in spruce stands;the biomass of four (predatory nematodes, centipedes, carabid and cantharid beetles)of the seven carnivorous groups studied were increased in beech stands, none inspruce stands. Generally, the biomass ratio between prey and predators was at aminimum in mature beech and mixed stands indicating more intense top-downcontrol in these forests. Overall, the study documents that replacement of beech byspruce strongly alters the soil food web. Mixed stands were more similar to sprucestands in respect to the biomass of soil animal groups but predator–prey interactionsappeared to be more similar in mature beech and mixed stands. Differences betweentree species usually were more pronounced in 120 compared to 30 years old standsindicating that the development of stand characteristics is slow.

Joern Alphei

Papers

The soil fauna community in pure and mixed stands of beech and spruce of different age: trophic structure and structuring forces