Chin J Plant Ecol ›› 2018, Vol. 42 ›› Issue (1): 6-19.DOI: 10.17521/cjpe.2017.0266

• Research Articles • Previous Articles     Next Articles

CO2 flux dynamics and its limiting factors in the alpine shrub-meadow and steppe-meadow on the Qinghai-Xizang Plateau

CHAI Xi1,3,LI Ying-Nian2,DUAN Cheng1,3,ZHANG Tao4,ZONG Ning1,SHI Pei-Li1,3,*(),HE Yong-Tao1,3,ZHANG Xian-Zhou1,3   

  1. 1 Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China

    2 Northwest Institute of Plateau Biology, Chinese Academy of Sciences, Xining 810001, China

    3 College of Resources and Environment, University of Chinese Academy of Sciences, Beijing 100190, China

    4 College of Agronomy, Shenyang Agricultural University, Shenyang 110866, China
  • Online:2018-01-20 Published:2018-03-08
  • Contact: SHI Pei-Li, ORCID: 0000-0002-1120-0003
  • Supported by:
    Supported by the National Natural Science Foundation of China(41703079);Supported by the National Natural Science Foundation of China(41271067);the National Key Research and Development Project of China(2016YFC0502001);the National Key Research and Development Project of China(2017YFA0604801)

Abstract:

Aims Alpine shrub-meadows and steppe-meadows are the two dominant vegetation types on the Qinghai-Xizang Plateau, and plays an important role in regional carbon cycling. However, little is known about the temporal-spatial patterns and drivers of CO2 fluxes in these two ecosystem types.

Methods Based on five years of consecutive eddy covariance measurements (2004-2008) in an eastern alpine shrub-meadow at Haibei and a hinterland alpine steppe-meadow at Damxung, we investigated the seasonal and annual variation of net ecosystem productivity (NEP) and its components, i.e. gross primary productivity (GPP) and ecosystem respiration (Re).

Important findings The CO2 fluxes (NEP, GPP and Re) were larger in the shrub-meadow than in the steppe-meadow during the study period. The shrub-meadow functioned as a carbon sink through the five years, with the mean annual NEP of 70 g C·m -2·a -1. However, the steppe-meadow acted as a carbon neutral, with mean annual NEP of -5 g C·m -2·a -1. The CO2 fluxes of steppe-meadow exhibited large variability due to the inter-annual and seasonal variations in precipitation, ranging from a carbon sink (54 g C·m -2·a -1) in 2008 to a carbon source (-88 g C·m -2·a -1) in 2006. The differences in carbon budget between the two alpine ecosystems were firstly attributed to the discrepancy of normalized difference vegetation index (NDVI) because NDVI was the direct factor regulating the seasonal and inter-annual NEP. Secondly, the shrub-meadow had higher carbon use efficiency (CUE), which was substantially determined by annual precipitation (PPT) and NDVI. Our results also indicated that the environmental drivers of CO2 fluxes were also different between these two alpine ecosystems. The structure equation model analyses showed that air temperature (Ta) determined the seasonal variations of CO2 fluxes in the shrub-meadow, with NEP and GPP being positively correlated with Ta. By contrast, the seasonal CO2 fluxes in the steppe-meadow were primarily co-regulated by soil water content (SWC) and Ta, and increased with the increase of SWC and Ta. In addition, the changes of Re during the growing season in two ecosystems were directly affected by GPP and soil temperature at 5 cm depth (Ts), while Re during non-growing season were determined by Ts. These results demonstrate that the synergy of soil water and temperature played crucial roles in determining NEP and GPP of the two alpine meadows on the Qinghai-Xizang Plateau.

Key words: Qinghai-Xizang Plateau, alpine meadow ecosystems, CO2 fluxes, temperature, soil water content, eddy covariance