Joseph C. Blankinship

Ecosystems are projected to experience altered precipitation patterns associated with climate change, with some areas becoming wetter and others drier. Both above‐ and belowground communities will be impacted by such rainfall changes, yet research has predominantly focused on the flora and fauna aboveground. Still, there is a growing body of literature for the effects of altered precipitation on soil fauna. Nematodes are diverse and abundant in most soils, represent multiple trophic levels, and influence essential soil processes, making this group a good proxy for broader impacts on soil food webs. Hence, we assessed the effects of increased and reduced rainfall amount on total and trophic‐level abundances of nematodes using a meta‐analytical approach based on 46 independent observations from 37 field studies and tested whether effects differed among ecosystem types and with treatment duration (<1 year, short term; >1 year, long term). Overall, total and trophic group's abundances, except fungal feeders, were negatively impacted by reduced rainfall irrespectively of treatment duration. Increased rainfall had a positive effect on total abundances and plant parasitic nematodes, but only in longer term studies (>1 year). The impacts of altered rainfall were consistent across the ecosystems studied; however, most studies focus on grasslands and deserts, making it difficult to draw broad generalizations. Reductions in rainfall are therefore likely to decrease soil nematode abundance, with less pronounced effects on fungal feeders. Increased rainfall, on the other hand, may favor plant parasites, likely due to increased plant productivity. Hence, projections of reduced rainfall will have significant negative impacts on nematode abundances, at least in grasslands and deserts, with cascading effects on soil processes.

Up to half of the world's drylands have degraded, dysfunctional soils that lower success rates of restoration efforts to reestablish lost vegetation. Because soil amendments of organic matter have the potential to improve multiple ecosystem functions and overall soil health, we added a mulch of whole mesquite ( Prosopis velutina ) branches—both alone and in combination with 3 and 6 cm of compost—to a degraded semiarid rangeland. We then measured effects of these organic amendments on a suite of soil health indicators as well as plant cover and abundance. We found that surface applications of these amendments improved several indicators of soil health after two summer growing seasons. Soil temperature decreased and soil moisture increased in all treatments with organic amendments. However, during drier times of the year and in response to smaller rain events, mulch alone increased soil moisture more so than when combined with compost. As expected, total soil nitrogen was greatest with compost addition. Soil organic carbon, water‐stable aggregate size, and microbial abundance did not respond significantly to any treatment. Mesquite mulch increased native plant cover and abundance when applied without compost and increased plant cover when combined with 3 cm of compost, but it did not increase plant abundance or cover when combined with 6 cm of compost. Collectively, these results suggest that a thin layer of compost—but particularly woody branches used as mulch—can improve success rates of revegetation in dryland ecosystems by moderating the soil microclimate.