Meta-analysis of global soil data identifies robust indicators for short-term changes in soil organic carbon stock following land use change.

The restoration of degraded lands and minimizing the degradation of productive lands are at the forefront of many environmental land management schemes around the world. A key indicator of soil productivity is soil organic carbon (SOC), which influences the provision of most soil ecosystem services. A major challenge in direct measurement of changes in SOC stock is that it is difficult to detect within a short timeframe relevant to land managers. In this study, we sought to identify suitable early indicators of changes in SOC stock and their drivers. A meta-analytical approach was used to synthesize global data on the impacts of arable land conversion to other uses on total SOC stock, 12 different SOC fractions and three soil structural properties. The conversion of arable lands to forests and grasslands accounted for 91 % of the available land use change datasets used for the meta-analysis and were mostly from Asia and Europe. Land use change from arable lands led to 50 % (32-68 %) mean increase in both labile (microbial biomass C and particulate organic C - POC) and passive (microaggregate, 53-250 µm diameter; and small macroaggregate, 250-2000 µm diameter) SOC fractions as well as soil structural stability. There was also 37 % (24-50 %) mean increase in total SOC stock in the experimental fields where the various SOC fractions were measured. Only the POC and the organic carbon stored in small macroaggregates had strong correlation with total SOC: our findings reveal these two SOC fractions were predominantly controlled by biomass input to the soil rather than climatic factors and are thus suitable candidate indicators of short-term changes in total SOC stock. Further field studies are recommended to validate the predictive power of the equations we developed in this study and the use of the SOC metrics under different land use change scenarios.

Plant diversity and root traits benefit physical properties key to soil function in grasslands.

Plant diversity loss impairs ecosystem functioning, including important effects on soil. Most studies that have explored plant diversity effects belowground, however, have largely focused on biological processes. As such, our understanding of how plant diversity impacts the soil physical environment remains limited, despite the fundamental role soil physical structure plays in ensuring soil function and ecosystem service provision. Here, in both a glasshouse and a long-term field study, we show that high plant diversity in grassland systems increases soil aggregate stability, a vital structural property of soil, and that root traits play a major role in determining diversity effects. We also reveal that the presence of particular plant species within mixed communities affects an even wider range of soil physical processes, including hydrology and soil strength regimes. Our results indicate that alongside well-documented effects on ecosystem functioning, plant diversity and root traits also benefit essential soil physical properties.