Climate change and intensive land use reduce soil animal biomass through dissimilar pathways

Global change drivers, such as climate and land use, may profoundly influence body size, density, and biomass of organisms. It is still poorly understood how these concurrent drivers interact in affecting ecological communities. We present results of an experimental field study assessing the interactive effects of climate change and land-use intensification on body size, density, and biomass of soil microarthropods. We found that both climate change and intensive land use decreased their total biomass. Strikingly, this reduction was realized via two dissimilar pathways: climate change reduced mean body size, while intensive land use decreased population size. These findings highlight that two of the most pervasive global change drivers operate via different pathways when decreasing soil animal biomass. These shifts in soil communities may threaten essential ecosystem functions like organic matter turnover and nutrient cycling in future ecosystems. Significance Many important ecosystem functions are determined by the biomass of soil animal, however, how their biomass may respond to climate change and land-use intensification still remains unknown. We conducted a large field study to investigate the potential interaction between these two pervasive global change drivers, and disentangle the pathways where they contribute to the changes in soil animal biomass. Our findings are exceptionally novel by showing detrimental, but largely independent, effects of climate change and land-use intensity on soil animal biomass, and that these independent effects can be explained by two dissimilar pathways: climate change reduced mean body size, while intensive land use decreased population size. Notably, consistent climate change effects under different land-use regimes suggest that (1) the identified pathways may apply to a wide range of environmental conditions, and (2) current extensive land-use regimes do not mitigate detrimental climate change effects on ecosystems.

an experimental field study assessing the interactive effects of climate change and 23 land-use intensification on body size, density, and biomass of soil microarthropods. 24 We found that both climate change and intensive land use decreased their total 25 biomass. Strikingly, this reduction was realized via two dissimilar pathways: climate 26 change reduced mean body size, while intensive land use decreased population size. 27 These findings highlight that two of the most pervasive global change drivers operate 28 via different pathways when decreasing soil animal biomass. These shifts in soil 29 communities may threaten essential ecosystem functions like organic matter turnover 30 and nutrient cycling in future ecosystems. extensively-used pasture (grazed by sheep). Half of the main-plots are subjected to an 153 ambient climate scenario, the other half to a future climate scenario (Fig. S1b, 1c).
Croplands and intensive meadows were established on the respective sub-plots in 156 summer and autumn of 2013. The intensive meadow is a conventionally used mixture 157 of forage grasses (20% Lolium perenne, 50% Festulolium, 20% Dactylis glomerata, 158 and 10% Poa pratensis). Within the study period, winter wheat (2015) and winter 159 barley (2016) were grown in these two croplands. In extensively-used meadow and 160 pasture, we repeatedly sowed target plant seeds (legumes, grasses and 161 non-leguminous dicots) during spring and autumn of 2014. For detailed description 162 see Table S1. 163

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The climate treatment is based on a consensus scenario for Central Germany in the 165 period from 2070 to 2100, which was derived from 12 climate simulations based on 166 four different emission scenarios using three established regional climate models:  closing during these periods increased the mean daily air temperature at 5 cm-height 180 by 0.55°C, as well as the mean daily soil temperature in 1 cm-and 15 cm-depth by 181 0.62°C and 0.50°C, respectively. By using an irrigation system, we added rain water 182 to achieve ~110% of ambient rainfall to the main-plots with future climate in spring 183 and autumn. Additionally, the rain sensors associated with the irrigation system were 184 used to regulate precipitation on the future climate main-plots to ~80% of ambient 185 rainfall in summer. As a result, precipitation was increased by 9.2% to 13.6% in 186 spring and autumn and decreased by 19.7% to 21.0% in summer in both years,  Table S4a).

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Intensive land use reduces the density of soil microarthropods 263 Land-use intensification dramatically decreased the density of microarthropods by 264 ~47% from the extensively-used meadow to conventional farming ( Fig. 2a; Table 1b), which was driven by the decreased density of Acari ( Fig. 2b; Table 1b). All observed 266 Acari orders, i.e., Oribatida, Mesostigmata and Prostigmata decreased their population 267 density in response to land-use intensification from meadows to croplands (Fig. S3a-c; 268 Table S4b). However, climate effects on microarthropods were negligible, specifically, 269 future climate only marginally decreased the density of Collembola ( Fig. 2c; Table   270 1b), which was caused by a significant decrease in the density of Isotomidae ( Fig. S3d; 271 Table S4b).  (Table 1). Specifically, climate change significantly reduced the 277 biomass of microarthropods by ~17% ( Fig. 3a; Table 1c). The same decreasing 278 pattern was found for the biomass of Acari ( Fig. 3b; Table 1c) Table S4c); whereas the total 281 biomass of Collembola was only marginally decreased by future climate (Table 1c), 282 which was driven by a significant decrease in total biomass of Isotomidae ( Fig. S4c; 283 Table S4c). Additionally, the total biomass of microarthopods sharply decreased by 284 ~37% from the extensively-used meadow to conventional farming ( Fig. 3d; Table 1c), 285 which was driven by the decreased biomass of Acari ( Fig. 3e Pathways of biomass decrease in soil microarthropods 296 SEM results revealed that climate change and intensive land use reduced the biomass 297 of soil microarthropods via two different pathways. While biomass loss caused by 298 future climate was mediated by reduced body size, biomass loss caused by intensive 299 land use was mediated by decreased density (Fig. 2b, Table S2).       A typical regional crop rotation consisting of winter rape, winter wheat and winter barley with the application of mineral fertilizers and pesticides.

Organic farming (OF)
A crop rotation aiming to maintain soil fertility, minimize measures of pest and weed control, and provide an environmentally friendly management of agro-ecosystems with mechanical weed control, organic fertilization, non-stained seeds and restricted use of pesticides.
Intensively-used meadow (IM) Conventional used mixture of forage grasses with moderate fertilization and frequent mowing (3-4 times per year).

Extensively-used meadow (EM)
A wide range of native common grasses, herbs and legumes (totally consisting 50 plant species, for each species seeds were sampled from different local populations to reflect to local gene pool and to introduce genetic variability) with moderate mowing (2-3 times per year) and no fertilization.

Extensively-used pasture (EP)
Plant species composition and land management as the same as extensively used meadows (see above), but with sheep grazing (2-3 grazing periods per year with a group of 20 sheep grazing for 24 hours).