增温和氮添加对杉木不同序级细根形态和化学性状的影响

Effects of soil warming and nitrogen addition on the morphological and chemical characteristics of fine roots in different order classes of the Chinese fir

全球气候变暖与氮(N)沉降是两个同时存在的全球变化主要因素,但目前关于二者的研究多以单因子为主。细根形态和化学性状等功能性状在促进植物养分获取和森林生物地球化学循环方面起着关键作用,但目前气候变暖、N沉降以及两者交互对细根形态和化学性状的影响尚不清楚。在福建三明森林生态系统国家野外科学观测研究站陈大观测点开展土壤增温与N添加双因子试验,包括对照(无增温,无氮添加)、低氮(+4gN m^(-2)a^(-1))、高氮(+8gN m^(-2)a^(-1))、增温(+5℃)、增温+低氮(+5℃,+4gN m^(-2)a^(-1))、增温+高氮(+5℃,+8gN m^(-2)a^(-1))六个处理,探讨增温与N添加对杉木(Cunninghamia Lanceolata)细根形态和化学性状的影响。结果表明:(1)增温显著增加了细根直径(D)。增温和N添加的交互作用对细根比根长(SRL)、比表面积(SRA)及组织密度(RTD)均存在显著影响,与对照相比,增温处理及增温+高氮处理均降低了细根SRL和SRA;不同处理间细根RTD无显著差异。N添加与序级交互作用对细根SRA存在显著影响,仅低氮添加显著增加了1级根SRA。(2)增温和N添加交互作用对细根碳(C)含量存在显著影响,与对照相比,仅增温+高氮处理显著增加了细根C含量。N添加与序级交互作用对细根C含量存在显著影响,仅在1级细根中,高氮添加的细根C含量要显著高于低氮添加。增温、N添加以及序级三者交互作用对细根N含量及碳氮比(C∶N)存在显著影响,与对照相比,低氮和高氮处理对细根N含量及C∶N影响因序级而异;增温处理、增温+低氮处理以及增温+高氮处理均显著提高了细根N含量,降低了细根C∶N;与高阶根相比,低阶根N含量和C∶N对单独增温处理及增温+低氮处理响应要更为敏感。以上结果表明,不同细根功能性状对增温、N添加及两者交互的响应存在差异,这种差异主要与细根序级和N添加水平有关;增温和N添加抑制了细根SRL和SRA,但促进了细根N含量并降低了细根C∶N,这将有助于理解亚热带地区森林地下养分循环以及C固存对全球环境变化的响应。

Global warming and nitrogen deposition are two main global change drivers, often occurring simultaneously. However, most of related studies referred to only single factor. Fine root functional traits such as morphology and chemical properties play a key role in promoting plant nutrient acquisition and forest biogeochemistry cycling. The effects of climate warming, N deposition and their interactions on fine root morphology and chemical properties remain unclear. To explore the effects of warming and N addition on the morphological and chemical characteristics of fine roots of Cunninghamia Lanceolata. We conducted a two-factor experiment of soil warming and nitrogen addition, which consisted control(CT), low nitrogen treatment(LN), high nitrogen treatment(HN), warming treatment(W), warming and low nitrogen treatment(WLN), warming and high nitrogen treatment(WHN), at the Forest Ecosystem and Global Change Research Station of Fujian Normal University, Chenda, Sanming, Fujian Province. The results showed that:(1) the warming significantly increased fine root diameter(D). The interaction of warming and N addition had significant effects on the specific root length(SRL), specific surface area(SRA) and root tissue density(RTD) of fine roots. Compared with CT, the W and WHN reduced fine root SRL and SRA;there was no significant difference in RTD of fine roots among different treatments. The interaction of N addition and order had significant effects on fine root SRA. Low nitrogen addition only increased SRA of first order root significantly.(2) The interaction of warming and N addition had a significant effect on fine root C concentration, and only WHN significantly increased fine root C concentration. The interaction of N addition and order had significant effects on fine root concentration. The fine root C concentration of high N addition was significantly higher than that of low N addition. The interaction of warming, N addition and order had significant effects on fine root N concentration and C∶N. Compared with CT, the effects of LN and HN on fine root N content and C∶N varied with the order;The W, WLN and WHN significantly increased the fine root N concentration and decreased the fine root C∶N. Compared with high-order root, low-order root N concentration and C∶N were more sensitive to the effects of W and WLN. The results showed that the responses of fine root morphology and chemical characteristics to warming, N addition and their interaction were different, and the differences were mainly regulated by fine root branch order and N addition level;The warming and N addition promoted fine root N concentration and decreased fine root C∶N, which would contribute to understand the subsurface nutrient cycling and the response of C sequestration to global environmental change in subtropical forests.