草地利用方式对土壤呼吸和凋落物分解的影响

Effects of grassland-use on soil respiration and litter decomposition

草地利用方式影响植被群落结构和土壤微环境,制约草地生态系统碳循环。该文通过测定温带草原在放牧、割草、围封3种利用方式下湿润年(2012年)和干旱年(2011年)的凋落物产量、质量及其分解速率和土壤碳通量,分析了草地利用方式对土壤呼吸和凋落物的影响,探讨了凋落物对土壤呼吸的贡献机制。结果表明:在干旱年份,放牧样地土壤呼吸最大,分别达到割草和围封样地的1.5倍和1.29倍;在湿润年份,割草样地土壤呼吸最大,为309 g C·m–2·a–1,明显高于放牧样地和围封样地。不论干旱年还是湿润年,围封样地凋落物产量都大于放牧样地和割草样地。3种利用方式下湿润年土壤呼吸和凋落物分解均比干旱年增强。因此,水分是温带草原植物生长和生态系统碳循环的主要限制因子,草地利用方式则显著影响凋落物生产和分解。进一步分析表明,经过两年的分解,同一样地内凋落物质量C:N下降,N含量和木质素:N升高,土壤呼吸与凋落物产量、凋落物分解速率以及木质素:N正相关,而与凋落物C:N负相关。

Aims Land use change affects ecosystem carbon dynamics by changing the plant community structure and soil micro-environment in grassland ecosystems. The aims of this study were to determine the effects of land use on soil respiration and litter decomposition in the temperate grasslands of Nei Mongol and to identify the effects of litter quantity, quality and decomposition on soil respiration during growing season. Methods We measured soil respiration during growing season in 2011 and 2012 under three land use types, i.e. grazing, mowing, and grazing exclusion, by using an automatic infrared gas analyzer（LI-8100） that was connected to a multiplexer system（LI-8150）. Quadrat surveys and litter bags were utilized to measure litter production and decomposition. Several chemical indicators of litter quality were measured to calculate the litter decay rates. All data were analyzed with ANOVA and Pearson correlation procedures of SPSS. Important findings Soil respiration and litter decomposition differed greatly among the three land-use types. In the drought year, the total soil respiration at the grazing site was 1.5 times greater than at the mowing site and 1.29 times greater than at the grazing-exclusion site. However, in the wet year, the total soil respiration at the mowing site reached 309 g C·m–2·a–1 and was greater than at both the grazing site and the grazing-exclusion site. Precipitation increased soil respiration and litter decomposition, indicating that soil water availability was a primary constraint on plant growth and ecosystem C processes. Also, the responses of soil respiration and litter composition to rainfall differed among the land-use types. Further analysis showed that the litter C：N decreased and the litter N content and lignin：N increased after 2-years of decomposition. In addition, soil respiration was significantly correlated to litter production（r = 0.78, p〈0.01）, decay rates, C：N（r = –0.84, p〈0.01）, and lignin：N（r = 0.62, p〈0.05）.