草地植物根系碳储量和碳流转对CO2浓度升高的响应

植物根系是陆地生态系统重要的碳汇和矿质养分库,也是土壤中碳及养分的主要来源,只有深入认识CO2浓度升高下根系的碳汇功能和根系周转对土壤碳库的影响,才能准确预测生态系统对全球变化的响应与反馈调节作用.介绍了CO2浓度升高对草地植物根系生物量、根系凋落物的数量和品质以及根系周转速率的影响,指出研究植物体内碳向根分配格局的变化趋势必须考虑CO2浓度升高的直接和间接两方面作用;在预测根系碳库储量的动态变化时,需要区分不同功能根系组分的生物量;为更准确估算根系周转速率,有必要确立草地植物根系直径与其寿命之间的关系;CO2浓度升高普遍提高根系凋落物的C/N,但以此判定其在土壤中的分解速率快慢并不可靠,需要进一步从机理上探究根系凋落物分解的控制因素.

Responses of root carbon reserves and root turnover to experimental CO2 enrichment in grasslands

Plant roots act as an important carbon pool, as well as a nutrient pool in terrestrial ecosystems. Roots also provide the main sources of soil C and mineral nutrients. Understanding the effects of elevated CO2 on root C reserve and turnover is necessary to predict the response and feedback of terrestrial ecosystems to global change. This article reviews the responses of root biomass, the quantity and quality of root-derived organic matter, and root turnover rate in grassland ecosystems under the conditions with experimental elevation of air CO2. We conclude that both the direct and indirect effects of CO2 enrichment should be considered when studying the change of carbon allocation among plant organs. Measuring separately the biomass for roots with different functions is recommended to predict precisely the effects of elevated CO2 on the root carbon-reserve. In order to gain more accurate grassland root turnover rate also depends on sorting measured roots by diameter. The C/N of root-derived organic matter generally increases under elevated CO2, but it should be careful to use the C/N only for qualifying carbon decomposition process under elevated CO2. Further studies are needed to clarify the mechanisms controlling the decomposition rate of root litter and organic matter through rhizodeposition.