Imbalanced Variation of Soil C, N, P Pool Following Artificial Vegetation Restoration in Loess Hilly Region of China.

Artificial vegetation restoration has dramatically positively driven the variation of soil C, N, and P pool in Loess Hilly region of China. However, the interaction effect of these nutrients and their dynamic relationship are still poor understood. Thus, we reported the contents, storages, stratification ratios (SRs) and stoichiometry ratios of soil total carbon (TC), total nitrogen (TN), total phosphorus (TP) at three 30 year re-vegetation lands converted from cropland (namely Robinia pseudoacacia L., RP, Caragana Korshinskii Kom., CK and abandoned cropland) and one slope cropland (SC) as a control for three soil profiles(0-20 cm, 20-40 cm and 40-60 cm) from June 2009 to June 2013.  Significantly higher levels of soil C, N and P were observed at re-vegetation lands, and the storages of TC, TN and TP in 0-60 cm increased by 7.9%-14.0%, 8.0%-15.5% and 8.8%-12.4% from 2009 to 2013. The SRs for C, N and P were significantly promoted following vegetation restoration, and in each soil profile at re-vegetation land were mostly >2 and increased with increasing restoration age (P<0.01). The C:P, N:P and C:N ratios increased by 34.1%-80.1%, 3.0%-33.7% and 3.2%-62.8% from SC to re-vegetation land, and increased from 2009 to 2013(P<0.01), except for C:N ratios in RP and CK are decreased. Land use type and soil depth were identified as the most influential factors for the SRs and soil C:N:P stoichiometry. The improved SRs indicated that the soil quality was significantly enhanced through vegetation restoration in Loess Hilly region. Moreover, the artificial vegetation restoration result in the disproportionate increase of soil C, N, and P, thereby causing in changes of soil C:N:P stoichiometry, and ultimately lead to the nutrition imbalance . This imbalance should be concerned for it may lead to potential nutrition limitations and other negative consequence in artificial vegetation restoration ecosystems.