内蒙古草甸草原与典型草原地下生物量与生产力季节动态及其碳库潜力

地下根系是草原生态系统的重要组成部分,其生物量及其净生产力对地下碳库具有直接与间接作用,分析地下生物量季节动态与周转对深入揭示草原生态系统碳库动态及其固碳速率与潜力具有重要意义。应用钻土芯法对不同利用方式或管理措施下内蒙古草甸草原、典型草原地下生物量动态及其与温度、降水的相关性研究表明:草甸草原和典型草原地上生物量季节动态均为单峰型曲线,与上月降水显著正相关(P0.05),但地下生物量季节动态表现为草甸草原呈"S"型曲线,典型草原则是双峰型曲线,与温度、降水相关性均不显著(P0.05);两种草原根冠比和地下生物量垂直分布均为指数函数曲线,根茎型草原地下生物量集中在土壤0—5 cm,丛生型草原地下生物量集中于土壤5—10 cm,根冠比值在生长旺季(7—8月份)最小。草甸草原地下净生产力及碳储量范围分别为2167—2953 g m-2a-1和975—1329 gC m-2a-1,典型草原为2342—3333 g m-2a-1和1054—1450 gC m-2a-1,地下净生产力及其碳储量约为地上净生产力及其碳储量的10倍,具有较大的年固碳能力,且相对稳定;地下净生产力与地上净生产力呈显著负相关性(P0.05);地下生物量碳库是地上生物量碳库的10倍左右,适度放牧可增加地下生产力,但长期过度放牧显著降低其地下生物量与生产力,并使其垂直分布趋向于浅层化。

Seasonal dynamics of belowground biomass and productivity and potential of carbon sequestration in meadow steppe and typical steppe, in Inner Mongolia, China

Belowground root system is an important part of the prairie ecosystem. Its biomass and net primary productivity have both direct and indirect effects on belowground carbon pool; therefore understanding the seasonal dynamic and turnover of belowground biomass is essential for further understanding of the dynamics, rate and potential of carbon sequestration in grassland ecosystems. Using soil coring method, we studied the dynamics of belowground biomass in relation to temperature and precipitation in meadow steppe and typical steppe grasslands under different land use and management regimes. For the studied grasslands, seasonal dynamic patterns of the aboveground biomass were characterized by unimodal curves. The aboveground biomass was significantly and positively correlated with the previous monthly precipitation (P < 0.05). The seasonal patterns of belowground biomass were characterized by "S" shaped curves in the meadow steppe grasslands, and bimodal curves in the typical steppe grasslands. There were no significant correlations between belowground biomass and temperature or precipitation in either meadow steppe or typical steppe (P > 0.05). Root to shoot ratio decreased throughout the growing season in both meadow steppe and typical steppe grasslands. The vertical distribution of belowground biomass can best be described as exponential curves. Belowground biomass was concentrated at the depth of 0-5 cm in the grasslands dominated by rhizomatous grasses and at 5-10 cm in grasslands dominated by bunch grasses. Belowground net primary productivity ranged from 2167 to 2953 g m^-2 a^-1 in the meadow steppe grasslands; whereas it ranged from 2342 to 3333 g m^-2 a^-1 in the typical steppe grasslands. Carbon storage ranged from 975 to 1329 g m^-2 a^-1 in the meadow steppe grasslands and 1054 to 1450 g m^-2 a^-1 in the typical steppe grasslands. Belowground net primary productivity and carbon storage were 10 times greater than those of aboveground, therefore the belowground system had a larger annual carbon sequestration capacity and was relatively stable. Moreover, net primary productivity was significantly and negatively correlated between above- and belowground (P < 0.05). We conclude that moderate grazing can increase the belowground productivity and carbon storage, however, the long-term overgrazing would significantly reduce the belowground biomass and productivity, and modify their vertical distributions. Belowground biomass and productivity tended to be higher at the upper layer of soil.