Water stress and insect herbivory interactively reduce crop yield while the insect pollination benefit is conserved.

Climate change is predicted to hamper crop production due to precipitation deficits and warmer temperatures inducing both water stress and increasing herbivory due to more abundant insect pests. Consequently, crop yields will be impacted simultaneously by abiotic and biotic stressors. Extensive yield losses due to such climate change stressors might, however, be mitigated by ecosystem services such as insect pollination. We examined the single and combined effects of water stress, insect herbivory and insect pollination on faba bean yield components and above- and belowground plant biomass under realistic field conditions. We used rainout shelters to simulate a scenario in line with climate change projections, with adequate water supply at sowing followed by a long period without precipitation. This induced a gradually increasing water stress, culminating around crop flowering and yield formation. We found that gradually increasing water stress combined with insect herbivory by aphids interactively shaped yield in faba beans. Individually, aphid herbivory reduced yield by 79% and water stress reduced yield by 52%. However, the combined effect of water stress and aphid herbivory reduced yield less (84%) than the sum of the individual stressor effects. In contrast, insect pollination increased yield by 68% independently of water availability and insect herbivory. Our results suggest that yield losses can be greatly reduced when both water stress and insect herbivory are reduced simultaneously. In contrast, reducing only one stressor has negligible benefits on yield as long as the crop is suffering from the other stressor. We call for further exploration of interactions among ecosystem services and biotic and abiotic stressors that simulate realistic conditions under climate change.

Relative importance of local- and large-scale drivers of alpine soil microarthropod communities.

Nitrogen (N) deposition and climate are acknowledged drivers of change in biodiversity and ecosystem function at large scales. However, at a local scale, their impact on functions and community structure of organisms is filtered by drivers like habitat quality and food quality/availability. This study assesses the relative impact of large-scale factors, N deposition and climate (rainfall and temperature), versus local-scale factors of habitat quality and food quality/availability on soil fauna communities at 15 alpine moss-sedge heaths along an N deposition gradient in the UK. Habitat quality and food quality/availability were the primary drivers of microarthropod communities. No direct impacts of N deposition on the microarthropod community were observed, but induced changes in habitat quality (decline in moss cover and depth) and food quality (decreased vegetation C:N) associated with increased N deposition strongly suggest an indirect impact of N. Habitat quality and climate explained variation in the composition of the Oribatida, Mesostigmata, and Collembola communities, while only habitat quality significantly impacted the Prostigmata. Food quality and prey availability were important in explaining the composition of the oribatid and mesostigmatid mite communities, respectively. This study shows that, in alpine habitats, soil microarthropod community structure responds most strongly to local-scale variation in habitat quality and food availability rather than large-scale variation in climate and pollution. However, given the strong links between N deposition and the key habitat quality parameters, we conclude that N deposition indirectly drives changes in the soil microarthropod community, suggesting a mechanism by which large-scale drivers indirectly impacts these functionally important groups.

Northward range expansion of rooting ungulates decreases detritivore and predatory mite abundances in boreal forests.

In the last few decades wild boar populations have expanded northwards, colonizing boreal forests. The soil disturbances caused by wild boar rooting may have an impact on soil organisms that play a key role in organic matter turnover. However, the impact of wild boar colonization on boreal forest ecosystems and soil organisms remains largely unknown. We investigated the effect of natural and simulated rooting on decomposer and predatory soil mites (total, adult and juvenile abundances; and adult-juvenile proportion). Our simulated rooting experiment aimed to disentangle the effects of (i) bioturbation due to soil mixing and (ii) removing organic material (wild boar food resources) on soil mites. Our results showed a decline in the abundance of adult soil mites in response to both natural and artificial rooting, while juvenile abundance and the relative proportion of adults and juveniles were not affected. The expansion of wild boar northwards and into new habitats has negative effects on soil decomposer abundances in boreal forests which may cascade through the soil food web ultimately affecting ecosystem processes. Our study also suggests that a combined use of natural and controlled experimental approaches is the way forward to reveal any subtle interaction between aboveground and belowground organisms and the ecosystem functions they drive.

Type of organic fertilizer rather than organic amendment per se increases abundance of soil biota.

Addition of organic amendments is a commonly used practice to offset potential loss of soil organic matter from agricultural soils. The aim of the present study was to examine how long-term addition of organic matter affects the abundance of different soil biota across trophic levels and the role that the quality of the organic amendments plays. Here we used a 17-year-old fertilization experiment to investigate soil biota responses to four different organic fertilizers, compared with two mineral nitrogen fertilizers and no fertilization, where the organic fertilizers had similar carbon content but varied in their carbon to nitrogen ratios. We collected soil samples and measured a wide range of organisms belonging to different functional groups and trophic levels of the soil food web. Long-term addition of organic and mineral fertilizers had beneficial effects on the abundances of most soil organisms compared with unfertilized soil, but the responses differed between soil biota. The organic fertilizers generally enhanced bacteria and earthworms. Fungi and nematodes responded positively to certain mineral and organic fertilizers, indicating that multiple factors influenced by the fertilization may affect these heterogeneous groups. Springtails and mites were less affected by fertilization than the other groups, as they were present at relatively high abundances even in the unfertilized treatment. However, soil pH had a great influence on springtail abundance. In summary, the specific fertilizer was more important in determining the numerical and compositional responses of soil biota than whether it was mineral or organic. Overall, biennial organic amendments emerge as insufficient, by themselves, to promote soil organisms in the long run, and would need to be added annually or combined with other practices affecting soil quality, such as no or reduced tillage and other crop rotations, to have a beneficial effect.