川西高海拔增温和加氮对红杉凋落物有机组分释放的影响

对川西高山树线红杉新鲜凋落物中有机组分于11月进行自然条件(对照)、加氮(2 g N·m^-2)、增温(顶开式培养室)、加氮+增温4个处理的原位培养,并监测凋落物中有机组分的分解动态.结果表明: 在试验开始后4个月内,增温、加氮以及加氮+增温处理比对照显著促进了红杉凋落物中水溶性糖、水溶性酚和多酚的分解,但随着培养时间的延长,累积分解量的差异逐渐缩小.与对照相比,增温、加氮和增温+加氮处理均抑制红杉凋落物中CH₂Cl₂提取组分、酸溶碳水化合物、酸溶木质素和非酸溶木质素分解,其中增温处理抑制作用最强,加氮处理抑制效果最弱,增温+加氮处理介于二者之间;增温处理对非酸溶木质素和CH₂Cl₂提取组分的半分解周期延长1倍以上,热水溶组分的半分解周期延长50%以上.在原位培养条件下,红杉新鲜凋落物中水溶性糖、水溶性酚、多酚、酸溶碳水化合物、酸溶木质素是较容易分解的有机组分,半分解周期分别为182、159、127、154和190 d;热水溶组分、CH₂Cl₂提取组分和非酸溶木质素是较难分解的有机组分,半分解周期分别是209、302和318 d;尽管低温季节(11月至次年3月)极其寒冷,气温均低于0 ℃,常被认为是微生物活性最弱、有机物分解最慢的时期,但结果显示低温季节期间红杉凋落物各有机组分却分解最快.因此,氮沉降和升温将迟滞该区域高寒红杉林凋落物的分解.这将有利于高寒森林生态系统的土壤碳固持.

Impacts of warming and nitrogen addition on organic fraction release in fresh litter of Larix potaninii in alpine zone of the western Sichuan Province,China

The decomposition dynamics of organic components in fresh litter of Larix potaninii were monitored by in situ litter-bag incubation under four treatments, i.e., field condition (CK), nitrogen addition (AN, 2 g N·m^-2), warming by top-open chamber (OTC), nitrogen addition with warming by top-open chamber (OTC+AN), from November to next September. Decomposition of water-soluble sugar, water-soluble phenol and total polyphenol were stimulated significantly under the treatment OTC, AN and OTC+AN during the first four months compared with the CK, but the difference of these components release narrowed with the extension of incubation time. Compared with CK, releases of dichloromethane-extractable fraction, acid soluble carbohydrates, acid soluble lignin, and acid insoluble lignin, were inhibited significantly under OTC, AN, and OTC+AN treatments, and the significance of inhibitory effect under the treatments was: OTC > OTC+AN > AN. Especially, in the treatment of OTC, half-life of dichloromethane-extractable fraction and acid inso-luble lignin in fresh litter were doubled, and that of hot-water soluble component was prolonged by more than 50% compared with CK. Half-life of water-soluble sugar, water-soluble phenol, total polyphenol, acid-soluble carbohydrate and acid-soluble lignin in fresh litter were respectively 182, 159, 127, 154 and 190 d in CK, and these components seem to be easily mineralized organic fraction. Meanwhile, half-life of hot-water soluble components, dichloromethane-extractable fraction, and acid insoluble lignin was 209, 302 and 318 d, respectively, indicating these fractions recalcitrant to decomposing in the fresh litter. Decomposition of all components in L. potaninii litter occurred in cold season from November to next March, which suggested that cold season was the most important period for litter decay in the alpine conifer. Generally it was assumed that microorganisms were inactive and decomposition of organic matters was slow in alpine soil during harsh winter, while the results of fresh litter incubation in situ showed that all components decomposed very fast during the period. Therefore, in alpine treeline, nitrogen deposition and warming would inhibit rather than promote decomposition of fresh litter, which would be conducive to carbon sequestration for the alpine soil ecosystem.