关键词: 嘎啦苹果, 有机无机肥, 分次配施, 利用, 吸收, 损失, ¹⁵N-尿素

Abstract: Variation of N and P characteristics induced by hydrologic process of forest canopy rainfall plays an important role in nutrient cycling, community succession and biodiversity conservation in forests. In 2015, eight dominant tree species in secondary forests of Shennongjia Mountain were selected. Rainfall in open area, throughfall and stemflow of each species were collected monthly. The N and P characteristics of water samples, including nitrate, nitrite, ammonium,total nitrogen, total P and pH, were measured. Intensities of N and P deposition and the impacts of speciesspecific canopy hydrology on N and P concentrations and pH were analyzed. Ourresults showed that  N and P depositions in Shennongjia Mountain were 11.89 kg N·hm^-2·a^-1 and 1.98 kg P·hm^-2·a^-1, respectively. Nitrate, nitrite and ammonium accounted for 40.75%, 15.19%, and 44.08% of the total N in rainfall, respectively.  Annual mean concentrations of N and P in throughfall and stemflow of eight species were significantly higher than those of the atmospheric rainfall, indicating that N and P leaching occurred when rainfall dropped through tree canopy and stem. Meanwhile, we observed significant interspecific differences of N and P in both stemflow and throughfall. Interestingly, nitrate, ammonium, total N and total P of stemflow and throughfall of native speciesAbies fargesii were the highest among the eight species.  pH of stemflow and throughfall were slightly higher than that of atmospheric rainfall. Specifically, pH of stemflow of eight species ranged from 5.42 to 6.82, and those of throughfall varied from 6.23 to6.83. Furthermore, pH of stemflow and throughfall of introduced species was significantly lower than that of the native ones. In contrast, there were no significant differences of N and P between introduced and native tree groups. Therefore, more attention should be paid on the impacts of secondary forest succession on forest N and P cycling in Shennongjia Mountain.

Key words: Gala apple, organic-inorganic fertilizer, split combined application, utilization, absorption, loss, ¹⁵N-urea