增温对湿润亚热带杉木幼林和成熟林土壤无机氮的影响

Effects of warming on soil inorganic nitrogen in the young and mature Cunninghamia lanceolata plantations in humid subtropical region,China

全球变暖可能加快或抑制森林土壤氮循环,进而影响森林生态系统生产力,而且这种影响随时间的持续而更加复杂。本研究以亚热带杉木幼林和成熟林土壤为对象,通过土壤电缆增温模拟未来气候变化情景,分析土壤无机氮含量对模拟增温的响应。结果表明:经过持续3年的增温试验(4℃),亚热带地区增温显著降低了杉木幼林和成熟林土壤总无机氮和铵态氮含量。其中杉木幼林土壤的降幅更大,其0~10、10~20、20~40、40~60 cm土层土壤铵态氮含量的降幅分别为32.1%、37.1%、20.8%、19.9%。增温导致2种林分土壤可溶性有机氮减少和N_2O排放加快,土壤矿化基质输入减少和气态氮损失增大是土壤中现存无机氮含量减少的原因。杉木幼林土壤矿化基质降幅和气态氮排放升高幅度均比成熟林土壤大,杉木幼林土壤对增温更为敏感。3年的增温造成杉木幼林和成熟林土壤无机氮含量下降,可能对杉木人工林生产力产生不利的影响。

Soil nitrogen cycling in forests may be accelerated or inhibited by global warming,with consequences on forest productivity.Such an impact will be more complicated with extending period of warming.We examined the effects of warming on soil inorganic nitrogen content in the young and mature Cunninghamia lanceolata plantations.Warming was simulated by means of soil cable warming,simulating a future climate change scenario of 4℃warming.The results showed that after three years warming,both total soil inorganic nitrogen and ammonium contents in the young and mature plantations were significantly reduced.The sharp decline occurred in the young plantation,with soil ammonium content in 0-10,10-20,20-40,40-60 cm soil layers decreased by 32.1%,37.1%,20.8%and 19.9%,respectively.Dissolved organic nitrogen was reduced and N2O emission was accelerated in the both plantations.The main reasons for the reduction of soil inorganic nitrogen concentration were lower input of organic nitrogen substrate and higher gaseous nitrogen loss.The decrease in soil organic nitrogen substrate and increase in gaseous nitrogen emissions in the young plantation were larger than those in the mature plantation,indicating that soils in the young plantation were more sensitive to increasing temperature.The 3-year warming decreased soil inorganic nitrogen contents in the two C.lanceolata plantations,which might negatively affect productivity of the C.lanceolata plantations in subtropic China.