| 英文摘要： |
Purpose Forest recovery from disturbance can alter soil nitrogen (N) status as a result of complex interactions in plant-soil system. The delta N-15 and delta O-18 are indicators that integrate complex soil N processes and can help elucidate changes in soil N status. Our objectives were to evaluate differences in soil N status among different forest recovery stages in karst plateau in southwestern China. Methods We established a forest recovery gradient with sites in cropland, abandoned cropland, shrub land, and early- and late-successional forests. We measured concentrations and isotopic compositions of soil total N, ammonium (NH4+), and nitrate (NO3-), and delta N-15 of plant tissue. Results With increased levels of recovery, concentrations of soil total N increased, and delta N-15 of soil total N (delta N-15(STN)) decreased at 0 similar to 10 cm depth. A positive relationship between delta N-15(STN) in surface soil and delta N-15 of plant (P < 0.05) suggested that recovery of plant biomass was the main contributor to soil N recovery. A large difference between delta N-15 of litter and delta N-15(STN) demonstrated an important dependence of plants on mycorrhizal fungi for N acquisition. delta N-15 of NH4+ was lower than delta N-15(STN), and a significant correlation between delta N-15 and delta O-18 of NO3- was observed only in late-successional forest (slope = l.4), indicating that gas N emission had a minor contribution to N loss. Ratio of ammonium N to nitrate N was < 1 (except in cropland), suggesting low risk of leaching. Conclusions Forest recovery promoted soil N recovery, and reduced soil N loss in karst plateau. However, N limitation persisted throughout forest recovery stages. |
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