Ecosystem multifunctionality is more related to the indirect effects than to the direct effects of human management in China's drylands.

Drylands provide a wide range of important ecosystem functions but are sensitive to environmental changes, especially human management. Two major land use types of drylands are grasslands and croplands, which are influenced by intensive grazing activities and agricultural management, respectively. However, little is known about whether the ecosystem functioning of these two land use types is predominated affected by human management, or environmental factors (intrinsic environmental factors and factors modified by human management). This limits our understanding of the ecosystem functions under intensive human management in drylands. Here we reported a study where we collected data from 40 grassland and 30 cropland sites along an extensive aridity gradient in China's drylands to quantify the effects of human management intensity, intrinsic environmental factors (i.e., aridity), and environmental factors modified by human management (i.e., soil bulk density and plant density) on specific ecosystem functions (ecosystem multifunctionality, productivity, carbon storage, soil water, and soil nutrients). We found that the relative importance of each function differed between croplands and grasslands. Ecosystem functions varied with human management intensity, with lower productivity and plant carbon storage in grasslands under high grazing intensity than un-grazed, while multifunctionality and carbon storage increased with greater fertilization only in arid croplands. Furthermore, among environmental factors, soil bulk density had the greatest negative effects, which directly reduced multifunctionality in grasslands and indirectly reduced multifunctionality in croplands via suppressing crop density. Crop density was the major environmental factor that positively related to multifunctionality in croplands. However, these effects would be exacerbated with increasing aridity. Our study demonstrated that compared with the direct impacts of human management, environmental factors modified by human management (e.g., soil bulk density) are the major drivers of ecosystem functions, indicating that improving soil structure by alleviating human interferences (e.g., reducing livestock trampling) would be an effective way to restore ecosystem functions in drylands under global warming and drying.