杉木人工林剔除林下植被对凋落层养分循环的短期影响

Short-term effects of understory vegetation removal on nutrient cycling in litter layer of Chinese fir plantation

通过湖南会同杉木人工林3个试验地点的林下植被去除试验,研究了林下植被剔除对凋落物分解的影响.结果表明:杉木人工林未分解凋落层、半分解层和已分解层的凋落物现存量分别为(123.7±46.3)、(204.2±79.1)和(187.1±94.8)g·m-2,相应的C浓度为(447.51±16.75)、(418.89±35.75)和(376.11±47.33)g·kg-1,N浓度为(4.87±1.24)、(6.4±2.38)和(4.66±2.64)g·kg-1,P浓度为(0.14±0.01)、(0.16±0.03)和(0.16±0.02)g·kg-1.在试验点DL87和MS90中,林下植被剔除对半分解层凋落物的现存量和养分储量有显著影响,且不同试验地点的结果不一致,DL87的C、N、P储量降低55%以上,而MS90则上升约1倍,但对未分解层和已分解层的现存量和养分储量基本没有影响.林下植被剔除对凋落物分解早期阶段没有显著影响,处理150d后则有明显的抑制效应,剔除组分解速率下降了20.8%.因此,林下植被对凋落物养分循环的短期效应受其所处环境条件和作用时间的影响.

A short-term understory vegetation removal experiment was conducted at three experimental sites of Chinese fir （Cunninghamia lanceolata） plantation in Huitong of Hunan Province, South-central China to examine the short-term effects of the absence of understory vegetation on litter decomposition. In the plantation, the standing stock of the litter in L layer （un-decomposed litter）, F layer （semi-decomposed litter）, and H layer （decomposed litter） under understory intact condition was （123.7±46.3） g·m-2, （204.2±79.1） g·m-2, and （187.1±94.8） g·m-2, and the corresponding nutrient storage was （447.51±16.75） g·kg-1, （418.89±35.75） g·kg-1, and （376.11±47.33） g·kg-1 for carbon, （4.87±1.24） g·kg-1, （6.4±2.38） g·kg-1, and （4.66±2.64） g·kg-1 for nitrogen, and （0.14±0.01） g·kg-1, （0.16±0.03） g·kg-1, and （0.16±0.02） g·kg-1 for phosphorus, respectively. At sites DL87 and MS90, understory vegetation removal had significant effects on the standing stock of litter and the corresponding storage of carbon, nitrogen, and phosphorus in F layer, though the effects varied with sites （e.g., the storage of litter carbon, nitrogen, and phosphorus decreased by more than 55% at DL87 while increased by about 1 time at MS90）. Across the three sites, understory vegetation removal had little effects on the standing stock and nutrient storage of the litter in L layer and H layer. In addition, the removal had little effects on the litter decomposition at its early stage, but showed significant inhibitory effects after 150 days elapsed, with the decomposition rate decreased by 20.8%. These results suggested that the short-term effects of understory vegetation removal on the litter nutrient cycling could be depended on the forest site condition and the duration after the understory vegetation removal.