模拟氮沉降对中亚热带森林土壤中可溶性氮含量的影响

Effects of Simulated Nitrogen Deposition on Soluble Nitrogen in Subtropical Forest Soils

通过野外模拟试验,研究CK〔对照,0 kg(hm2.a)〕、LN〔低氮,30 kg(hm2.a)〕和HN〔高氮,100 kg(hm2.a)〕处理3个氮沉降水平对亚热带针叶(杉木)和阔叶(浙江桂、罗桴栲)森林土壤中可溶性氮含量的影响.结果表明:施氮后3 d,土壤中的w(SIN)(可溶性无机氮含量)在CK和LN处理之间差异不显著,仅发现HN处理与LN及CK处理之间的差异显著.施氮后3个月,各处理之间差异不显著;与施氮后3 d相比,土壤中的w(NH4+-N)在CK处理显著增加了42%～68%(P<0.05),而HN处理则显著降低了45%～58%(P<0.05);土壤中的w(NO3--N)平均降低了24%～88%,其中HN处理降幅最大也最显著;杉木林土壤降幅最大.施氮后3 d,随着施氮水平的提高土壤尤其是杉木林土壤中的w(SON)(可溶性有机氮含量)增加,其占w(TSN)(可溶性总氮含量)的比例降低.然而3个月后,施氮影响趋缓甚至相反;与施氮后3 d比较,HN处理下w(SON)降低,而其占w(TSN)的比例却有所升高,表明SON损失仍低于SIN.阔叶天然林土壤中的w(SON)显著高于杉木人工林,表明凋落物性质差异造成的影响与w(SON)变化有关.

A field-simulated nitrogen deposition experiment was conducted to investigate the effects of added nitrogen on soil soluble inorganic nitrogen（SIN） and soluble organic nitrogen（SON） in two adjacent natural broad-leaved forests（Cinnamomum chekiangense,CIC and Castanopsis fabric,CAF） and a nearby coniferous plantation（Cunninghamia lanceolata,CUL）.Three treatments were set as the control（CK） of 0 kg/（hm^2·a）,low nitrogen（LN） treatment of 30 kg/（hm^2·a） and high nitrogen（HN） treatment of 100 kg/（hm^2·a）.The results showed that after three days of nitrogen addition,significant effects were only found from the high nitrogen treatment,and there were no significant differences between the effects of CK and LN.After three months of N addition,there were no significant differences among all treatments.Compared with the data after three days of N addition,NH4^＋-N content in the three forest soils after three months of N addition was significantly increased by 42%-68%（P〈0.05） under CK,and decreased by 45%-58%（P〈0.05） under HN.NO3^——N content was decreased on average by 24%-88% in the three treatments,with the effects most significant in the HN treatment and in the coniferous forest soil.After three days of N addition,soil SON in the three forest soils increased,with the proportion of SON in total soluble nitrogen（TSN） decreasing with increased N addition level,especially in the coniferous forest soil.However,three months of N addition had little or even the reverse effect on SON.The content of SON was decreased,and the proportion of SON to TSN was increased,after three months of N addition compared with that after three days.This indicated that SON loss was still lower than that of inorganic nitrogen.The content of SON in the broad-leaved forest soils,which was significantly higher than that in coniferous forest soil,which suggests that the chemical characteristics of litters play an important role in SON content variation.