长期开垦与放牧对内蒙古典型草原地下碳截存的影响

Variation of Below-Ground Carbon Sequestration Under Long Term Cultivation and Grazing in the Typical Steppe of Nei Monggol in North China

以围封26 a草地（E26）为对照,研究了内蒙古典型草原区长期开垦与放牧对土壤-植物根系系统碳截存的影响.结果表明,0-40 cm土壤和根系中的C贮量,E26（7307.59和950.32 g·m^-2）≈连续放牧草地（LG）（7834.01和843.43 g·m^-2）〉开垦35a耕地（LC）（4537.04和277.35 g·m^-2）.E26、LG和LC中,0-40 cm土壤贮存的C分别占各自土壤-根系系统C总贮量的88.49%、90.28%和94.24%.长期开垦完全破坏了草地原生的植被-土壤系统,造成严重的土壤风蚀：相对于E26,LC中0-10cm和10-20 cm砂粒含量分别增加了81%和39%,0-40 cm土层中根系生物量减少了71%;长期开垦导致草地土壤及根系碳截存分别降低了37.9%和70.8%.因此,在草原地区,若将长期开垦的耕地恢复为天然草地,土壤和植物根系将会有较大的固碳潜力.放牧对该区土壤有机碳含量及根系生长的影响较小;但长期放牧样地土壤表层容重显著增加,预示目前放牧压力已达到或接近草地的承载阈值,应及时减小放牧压力以避免草地的进一步退化.

Human activities have changed the earth surface mostly, which caused many environment issues now. We aimed to detect the process that human activities exert on ecosystem by investigating and analyzing the changes of plant community, especially underground soil and root carbon sequestration under long term cultivation and grazing in typical steppe area of Nei Monggol, North China. The carbon sequestration on the root and soil in three plots of typical steppe area： 26-year exclosure grassland （E26）, continuous grazing grassland （LG） and 35-year cultivated tillage （LC） were measured. The carbon storage in the layer of 0-40 cm showed a trend that E26 （7 307.59 g·m^-2 and 950.32 g·m^-2） ≈ LG （7834.01 g·m^-2 and 843.43 g·m^-2） 〉 LC （4537.04 g·m^-2 and 277.35 g·m^-2）, occupied 88.49%, 90.28% and 94.24% of total soil-root carbon respectively. The original composition structure of plant-soil system was completely destroyed by human cultivation, and it also led to sever soil erosion as well. The sand content in soil of LC at layers 0-10 cm, 10-20 cm were increasing by 81% and 39% compared to E26. On the other hand, the root biomass of LG at 0-40 cm decreased by 71% . Cuhivation resulted in significant decrease of the carbon storages in soil and root. Therefore, the present cultivation should be ceased and the optimum measurements should be taken to make the tillage restore to natural grassland condition. Continuous grazing led to the significantly changes of the above-ground vegetation characteristics such as community height, coverage and biomass. While the changes of soil organic content and root biomass was not remarkable under grazing. However, the bulk density of surface soil （0-10 cm） exhibited significant increase in LG compared to E26, which indicated that the present grazing pressure have been reaching the threshold of grassland capacity. Therefore, the present grazing pressure should be decreased properly in order to avoid more serious degradation.