亚热带常绿阔叶林6个常见树种凋落叶在不同降雨期的分解特征

地处长江上游的四川盆地亚热带常绿阔叶林具有典型雨热同季的气候特点,季节性干湿交替可能显著影响凋落物分解,但迄今缺乏相应的报道。因此,采用凋落物分解袋法,研究了常绿阔叶林区最具代表性的马尾松(Pinus massoniana)、柳杉(Cryptomeria fortunei)、杉木(Cunninghamia lanceolata)、香樟(Cinnamomum camphora)、红椿(Toona ciliata)、麻栎(Quercus acutissima)等6种凋落叶在第1年不同雨热季节的分解特征。结果表明,经历1a的分解,6种凋落叶质量残留率大小顺序依次为:红椿(27.90%)柳杉(41.39%)杉木(48.93%)麻栎(49.62%)马尾松(68.82%)香樟(72.23%),6种凋落叶在不同干湿季节质量损失差异显著(P0.05)。阔叶树种在旱季(MRS、SRS和WRS)的质量损失显著高于针叶树种。雨季(ERS和LRS)对6种凋落叶质量损失的贡献率(69.73%—89.68%)均明显大于旱季(10.32%—30.27%)。6种凋落叶在不同时期中质量损失速率差异显著(P0.05),且6种凋落叶在雨季的质量损失速率明显高于旱季。相关分析结果表明,凋落叶质量损失及其速率均与降雨量和温度呈极显著(P0.01)正相关关系。凋落叶质量损失与初始C、木质素含量及C/N、木质素/N极显著(P0.01)负相关,与N含量极显著(P0.01)正相关。这些结果表明亚热带地区森林凋落物分解的质量损失主要发生在雨季,雨季温湿度的改变可显著影响凋落物分解过程。

Litter decomposition of six common tree species at different rainy periods in the subtropical region

Litter decomposition is an essential process of material cycling in the terrestrial ecosystem that can be the primary source of nutrients for plant growth, and of both nutrients and energy for soil biota. The present consensus is that climate-related precipitation and temperature patterns determine the rate of litter decomposition at the regional scale, while the substrate quality related to plant species manipulates the process of litter decomposition at the ecosystem level. Consequently, much more attention has been focused on litter decomposition as affected by climate, substrate quality, and soil biota in past decades. Theoretically, precipitation, temperature, biological activity, and their combined effects control the process of litter decomposition at different critical periods. As yet, little information has been available on the process of litter decomposition in different rainy and dry periods. Therefore, in order to understand the process of litter decomposition in seasonal rainy and dry periods, a field litterbag experiment was conducted in the Chongzhou Modern Agricultural Research & Development Base of Sichuan Agricultural University, which is located in the subtropical humid climate zone of Sichuan Basin at the upper reaches of the Yangtze River. Foliar litter was selected from Pinus massoniana, Cryptomeria fortunei, Cunninghamia lanceolata, Cinnamomum camphora, Toona ciliata, and Quercus acutissima, which are widely distributed in the subtropical evergreen broadleaved forest. Litterbags were sampled in the dry season, spring minor rainy season, early rainy season, later rainy season, and winter minor rainy season as litter decomposition proceeding from January 18, 2013 to January 18, 2014. In turn, the mass loss rates of foliar litter were measured, and rainfall and temperature were investigated at the same time. The results indicated that the litter mass loss of all six tree species increased as decomposition proceeded. Over one year''s decomposition, the remaining litter mass of six tree species was in the order T. ciliata (27.90%) < C. fortunei (41.39%) < C. lanceolata (48.93%) < Q. acutissima (49.62%) < P. massoniana (68.82%) < C. camphora (72.23%). Seasonal rainfall had significant (P < 0.05) effects on the litter mass loss of the six species. Compared with needle litter, broad-leaved litter had higher mass loss in the dry season (MRS, SRS, and WRS). The mass loss in the rainy season (ERS and LRS) accounted for 69.73%-89.68% of the mass loss of the entire first decomposition year, while that in the dry season accounted for only 10.32%-30.27%. Meanwhile, the rates of foliar litter mass loss in the rainy season were significantly (P < 0.05) higher than those in the dry season regardless of tree species. Pearson correlation analysis results revealed that the litter mass loss rate was significantly (P < 0.01) and positively correlated with precipitation and temperature. In addition, mass loss was significantly (P < 0.01) and negatively related to the initial concentrations of C, lignin, C/N, and lignin/N in foliar litter, but significantly (P < 0.01) and positively related to the initial N concentration in foliar litter. In conclusion, the mass loss of foliar litter occurred mainly in the rainy season in the subtropical humid region, so changes in seasonal rainfall patterns and the corresponding changes in temperature and humidity would significantly affect the process of litter decomposition.