Abstract:

Soil carbon and nitrogen are important nutrient and energy substances for alpine vegetation to respond to the changes of ecological environment in permafrost regions. However， their surveys are still based on single-pass sampling during the growing season， and there is a lack of researches on seasonal changes， which is very important but exists obvious limitation for accurately grasping contents and estimating storages of soil carbon and nitrogen in permafrost area. Thus， in the study， the alpine meadow， located at the permafrost regions of Shule River headwaters in the western part of the Qilian Mountains and the northeast margin of the Qinghai-Tibet Plateau， was selected as the study area. The vertical （0-50 cm profile） and seasonal variations of soil organic carbon （SOC）， total nitrogen （TN） contents and carbon to nitrogen ratio （C/N）， as well as their influencing factors were analyzed. The results showed that： （1） The profile distribution of SOC and TN are consistent as， SOC and TN in the 0-10 cm soil layer were significantly higher than those in the 10-50 cm （P<0.05）. However， the SOC and TN decreased gradually from 0 to 50 cm only in autumn， while 0-30 cm in spring， summer and winter； （2） Seasonal changes were found in SOC and TN contents， and SOC showed summer > winter > spring > autumn， while TN was consistent in spring， autumn and winter， but slightly lower in summer； （3） The seasonal variation of C/N was remarkable （P<0.05）， which highest in summer and lowest in autumn； 4） Soil moisture content and vegetation biomass were key factors for vertical and seasonal changes in the SOC content， TN content and C/N； （5） The soil carbon and nitrogen density in summer were higher than the annual average. It can be seen that only the survey of a single node （mainly in the growing season） indicates that there is an overvalued trend of the annual soil carbon and nitrogen storage.

Key words: permafrost regions, alpine meadow, soil carbon and nitrogen, vertical change, seasonal pattern