Vegetation type and aridity modulate the role of soil organic carbon fractions in shaping dryland ecosystem services

Soil organic carbon (SOC) supports multiple ecosystem services in drylands. However, the influence of the two main fractions of SOC −particulate organic carbon (POC) and mineral-associated organic carbon (MAOC)- on ecosystem services, and whether vegetation type and aridity shape this relationship, remains to be explored in global drylands. Here we used a global database of 251 dryland ecosystems to assess the association of POC and MAOC contents with seven ecosystem services (biomass production, nutrient cycling, pest control, mutualism, C storage, water regulation, and organic matter decomposition). We found positive associations between both SOC fractions and all ecosystem services, except mutualism and pest control, with the strength of these relationships varying across vegetation types. Specifically, POC was positively associated with C storage, water regulation, and organic matter decomposition in forests, with C storage and organic matter decomposition in shrublands, and with biomass production and C storage in grasslands, while MAOC was positively associated with nutrient cycling and C storage in forests and with biomass production and C storage in grasslands. Aridity (1 − mean annual precipitation/mean annual potential evapotranspiration) also shaped the magnitude of these associations, with consistently weaker links under high aridity (> 0.8). Overall, our results highlight that the potential POC and MAOC losses with ongoing aridification threaten not only soil C storage but also the maintenance of other fundamental ecosystem services which rely on both SOC fractions.