氮沉降增加对青藏高原林地氮淋溶通量的影响

Effect of Increased Nitrogen on Nitrogen Leaching Fluxes in Spruce Forests on the Tibetan Plateau

森林生态系统对大气氮沉降升高的响应机制是国内外学者研究的热点问题之一,近年来中国学者相继在温带森林和热带森林建立了氮沉降增加影响的野外实验平台,但关于氮沉降增加对青藏高原地区森林土壤氮素淋溶通量影响的野外原位研究匮乏。基于此,该研究于2012-2013年生长季,在青藏高原林芝地区云冷杉林通过野外模拟试验,研究了3种水平(0、15和30 kg/(hm^(2)·a)(以N为计,下同))及3种形态((NH_(4))_(2)SO_(4)、NH_(4)Cl和KNO_(3))氮沉降增加对土壤可溶性氮素淋溶通量的影响。结果表明:林芝地区不同形态氮素的淋溶通量均存在显著的季节和年际变化特征,铵态氮(NH_(4)^(+)-N)、硝态氮(NO_(3)^(-)-N)的生长季月淋溶通量为0.02~0.6 kg/hm^(2),可溶性总氮(TDN)、可溶性总有机氮(DON)月淋溶通量为0.07~2.0 kg/hm^(2),不同形态氮淋溶通量峰值均出现在7-9月;森林穿透雨中硝态氮沉降通量的增加,对氮素淋溶通量具有明显的促进作用,造成NO_(3)^(-)-N显著淋失(p<0.05),且这种促进作用在施加低剂量硝态氮肥的处理上更为明显(p<0.01);大气氮沉降增加对DON和TDN淋溶通量有显著的抑制作用,且随着氮沉降量的增加其抑制作用也随之增加。

The response mechanism of forest ecosystems to increased atmospheric nitrogen deposition is the most of focus studied by researchers.Recently,Chinese researchers have successively established field experiment platforms for the effects of increased nitrogen deposition in temperate forests and tropical forests.However,there are few in situ studies on the effects of increased nitrogen deposition on soil nitrogen leaching fluxes in the Tibetan Plateau.Therefore,in the growing season of 2012-2013,the effect of increased nitrogen deposition on soil nitrogen leaching flux in spruce forest in Nyingchi area of the Qinghai-Tibet Plateau was studied,by field simulation tests which designed three levels(0,15 and 30 kg/(hm^(2)·a))and three forms((NH_(4))_(2)SO_(4),NH_(4)Cl,KNO_(3))nitrogen deposition.The results showed that there are significant seasonal and annual changes in different forms of nitrogen leaching fluxes.The monthly nitrogen leaching flux of ammonium(NH_(4)^(+)-N)and nitrate nitrogen(NO_(3)^(-)-N)is 0.02~0.6 kg/hm^(2),total nitrogen(TDN),organic nitrogen(DON)leaching flux is 0.07~2.0 kg/hm^(2) monthly,and the peaks of different forms of nitrogen leaching fluxes all appeared from July to September.The increase of nitrate nitrogen deposition flux in forest throughfall has a significant promotion effect on nitrogen leaching flux,and has caused significant NO_(3)^(-)-N leaching(p<0.05).In addition,the promotion was more obvious in low nitrogen treatments(p<0.01).However,the increase of ammonium nitrogen deposition has a different effect on soil nitrogen leaching.The increase of atmo⁃spheric nitrogen deposition has a significant negative effect on the leaching flux of DON and TDN,and with the increase of nitrogen deposition,its negative effect also increases.