短期牧压梯度下高寒杂草类草甸植被/土壤碳氮分布特征

Distribution patterns of vegetation-and soil carbon and nitrogen density in an alpine forb meadow under short-term grazing gradient

讨论了牧压梯度下高寒杂草类草甸植被／土壤碳氮密度，以期构建草地固碳作用与放牧管理的平衡模式，为草地生态系统固碳技术的管理提供科学依据。结果表明：牧压梯度下，植被现存总碳量为对照（SCK）〉轻牧（SL）〉中牧（SM）〉重牧（SH），表现出随放牧强度的增大而减小。年净初级生产碳量表现为SM〉SL〉SH〉SCK，说明适度放牧能促进植被碳素的积累，过度放牧或禁牧不利于碳素的积累。0～40cm土壤总有机碳密度和全氮密度分布状况相同，由大到小依次为SCK、SH、SM、SL。其中0～10cm层次，土壤有机碳密度为SH〉SM〉SL〉SCK，全氮密度为SH〉SCK〉SM〉SL。在10～20cm、20—30cm和30—40cm各层次，土壤有机碳密度和土壤全氮密度由大到小均为SCK〉SH〉SL〉SM。0～10cm与10～40cm各层次的土壤碳氮密度变化趋势略有不同，说明短期放牧对土壤表层和深层的碳氮密度影响不同。牧压梯度下，0—40cm各层次的土壤碳氮比和变化趋势不尽相同。总体来看，牧压梯度下的碳氮比适合微生物的矿化。回归分析表明，牧压梯度下，不同层次的土壤碳氮密度之间呈极显著正相关（P〈0．01）。

In order to obtain the equilibrium mode of grassland carbon sequestration and grazing management to provide a scientific basis for carbon sequestration management of grassland ecosys tem, this paper studied the vegetation-and soil carbon and nitrogen density under a short-term grazing gradient in an alpine forb meadow ecosystem on the northeastern Qinghai-Tibetan Plat eau, China. Under the grazing gradient, the existing total vegetation carbon storage decreased with increasing grazing intensity, i. e. , no grazing （SCK） 〉 light grazing （SL） 〉 moderate graz- ing （SM） 〉 heavy grazing （SH）. The annual net primary carbon production was in the order of SM 〉SL 〉SH 〉 SCK, indicating that moderate grazing could promote vegetation carbon storage, while overgrazing or no grazing was in reverse. In the soil layers of 0-40 cm, the total organic carbon density and total nitrogen density had the same variation pattern, i. e. , SCK 〉 SH〉 SM 〉 SL. However, in topsoil （0-10 cm） , the organic carbon density was in the order of SH 〉 SM 〉 SL 〉 SCK, while the total nitrogen density was of SH 〉 SCK 〉 SM 〉 SL. In 10-20 cm, 20-30 cm, and 30-40 cm soil layers, both the organic carbon density and the total nitrogen density de-clined in the order of SCK 〉 SH 〉 SL 〉 SM. A slight difference was observed in the soil carbon and nitrogen density between 0-10 cm and 10-40 cm layers, indicating that short-term grazing had different effects on the soil carbon and nitrogen between surface layer and deeper layers. Under the grazing gradient, soil C/N in different layers of 0-40 cm had somewhat difference. Overall, the soil C/N under the grazing gradient except CK was suitable for microbial mineraliza tion. Regression analysis showed that under the grazing gradient, soil carbon density in all layers was positively correlated with soil nitrogen density （P〈0.01）.