The effect of land-use change on soil C, N, P, and their stoichiometries: A global synthesis

Land-use change (LUC) can lead to the uptake or release of carbon (C), nitrogen (N) and phosphorus (P). Here we summarize and statistically analyze available observations on changes in soil organic C (SOC), total N (TN), total P (TP), and their stoichiometries (C:N, C:P, and N:P) after LUC and try to identify any controlling factors. We analyzed 1110 published data sets of changes in SOC, TN, and TP and their stoichiometries. Conversion of forest to cropland greatly decreased SOC (-33.1%) and TN (-27.8%), but forest to grassland conversion increased both slightly (SOC: 5.6%, TN: 15.9%). Conversion of cropland to forest increased SOC (193%) and TN (102%). Conversion of grassland to forest did not change SOC but decreased TN (-17.0%). Converting forest to cropland or grassland increased TP by 10.6% and 14.9%, respectively, and forestation of cropland or grassland decreased TP by 39.7% and 48.3%, respectively. Across all LUCs, changes in SOC and TN were generally linearly correlated, with a ratio close to 1, except after forestation, when large SOC increases sometimes exceeded TN increases. Changes in TP following LUC were positively correlated with changes in P fertilizer application rates. Following some LUCs, changes in SOC, TN, and TP and their stoichiometries were correlated with temperature or rainfall, but few generalities emerged. Forestation with deciduous trees increased SOC (29.9%), TN (22.2%), and TP (14.4%), but forestation with conifers reduced SOC (-27.0%), TN (-35.5%), and TP (-6.7%). After converting forest to cropland or grassland, C:N, C:P, and N:P all decreased, whereas forestation of cropland or grassland increased C:N, C:P, and N:P. This suggests that SOC enhancements following LUC could be constrained by TN and TP availability, which might need to be overcome through extra nutrient additions to achieve maximal C storage.