Soil nutrients and stoichiometric ratios as affected by land use and lithology at county scale in a karst area, southwest China

Soil carbon (C), nitrogen (N), and phosphorus (P) are the main soil nutrients required for plant development and their stoichiometric ratios are important indicators of ecosystem functions. However, there have been few studies on the effects of land use and lithology on soil nutrients and stoichiometric ratios, especially in karst areas with extremely fragile geology and intensive human disturbance. To evaluate the synergistic effect of land use and lithology, soil samples at depth of 0–15 cm were collected from five land-use types (arable land, plantation forest, grassland, shrubland, and secondary forest) over three lithologies (karst dolomite and limestone and non-karst clasolite) in a typical karst area in southwest China. For natural succession, grassland, shrubland, and secondary forest corresponded to the early, middle, and late successional stage after agricultural abandonment, while from arable land to plantation forest can be treated as a manual reversion after agricultural abandonment. The results showed that, in dolomite, soil organic C (SOC) and total N (TN) increased continuously with natural succession and increased in plantation forest compared to arable land. Total P (TP) continued to decrease from arable land to grassland and then to shrubland. In limestone, SOC and TN did not follow the same pattern because SOC and TN were slightly higher in grassland than shrubland, while TN was slightly lower in plantation forest compared to arable land. TP was remarkably higher in arable land than the other land-use types. For clasolite, SOC was highest in grassland, while TN was not significantly different among land-use types. Compared to arable land, TP was lower in other types of land use. These soil nutrient characteristics led to various stoichiometric ratios under the five land-use types over different lithologies. Therefore, ecological restoration projects based on land use conversion should consider differences in regional lithology and human disturbance.