Response of soil nutrients and stoichiometric ratios to short-term land use conversions in a salt-affected region, northeastern China

Abstract

Soil organic carbon (SOC), nitrogen (N), phosphorus (P) and potassium (K) are essential soil nutrients needed for plant growth and their stoichiometric ratios are important indicators of the elemental balance in soil ecosystem. However, changes in contents and stoichiometric ratios of SOC, N, P and K under different land uses in salt-affected region remain poorly understand. Soils from five land use treatments, including corn cropland (CL), alfalfa perennial forage (AF), monoculture Lyemus chinensis grassland (AG), monoculture Lyemus chinensis grassland for hay (AG + M) and successional regrowth grassland (RG) were used to assess the influences of land use conversion on the contents and stoichiometric ratios of SOC, N, P and K in a salt-affected region, northeastern China. Results showed that conversion of cropland to forage and grasslands increased by 40.42%, 17.66%, 15.71% and 11.5% for SOC, total N, total P and total K contents in 0–20 cm depth, while the effects of land use conversion on these soil nutrients in 20–50 cm depth were very limiting. Similar with these soil nutrients, the influences of land use conversion on soil stoichiometric ratios were higher in topsoil (0–20 cm) than that in the subsoil (20–50 cm), and re-vegetation increased most of the soil stoichiometric ratios due to the increase of soil nutrient contents. The average C:N, C:P and N:P ratios in the study site were 7.4, 21.3 and 3.0, respectively, in 0–20 cm depth, which were relatively lower than the average values in China and global. The C:K, N:K and P:K ratios were relatively consistent in Songnen grassland, which were 2.0, 0.3 and 0.1, respectively. These findings suggested that land-use type is a major factor that affect the contents and stoichiometric ratios of soil nutrients, and re-vegetation on the cropland improves the soil nutrients in northeastern China.