Key Laboratory of Arid Climatic Change and Reducing Disaster of Gansu Province, Key Open Laboratory of Arid Climatic Change and Disaster Reduction of China Meteorological Administration-CMA, Institute of Arid Meteorology, CMA, Lanzhou, China.
PLoS One. 2013;8(2):e55418. doi: 10.1371/journal.pone.0055418. Epub 2013 Feb 5.
Arid grassland ecosystems have significant interannual variation in carbon exchange; however, it is unclear how environmental factors influence carbon exchange in different hydrological years. In this study, the eddy covariance technique was used to investigate the seasonal and interannual variability of CO₂ flux over a temperate desert steppe in Inner Mongolia, China from 2008 to 2010. The amounts and times of precipitation varied significantly throughout the study period. The precipitation in 2009 (186.4 mm) was close to the long-term average (183.9±47.6 mm), while the precipitation in 2008 (136.3 mm) and 2010 (141.3 mm) was approximately a quarter below the long-term average. The temperate desert steppe showed carbon neutrality for atmospheric CO₂ throughout the study period, with a net ecosystem carbon dioxide exchange (NEE) of -7.2, -22.9, and 26.0 g C m⁻² yr⁻¹ in 2008, 2009, and 2010, not significantly different from zero. The ecosystem gained more carbon in 2009 compared to other two relatively dry years, while there was significant difference in carbon uptake between 2008 and 2010, although both years recorded similar annual precipitation. The results suggest that summer precipitation is a key factor determining annual NEE. The apparent quantum yield and saturation value of NEE (NEE(sat)) and the temperature sensitivity coefficient of ecosystem respiration (R(eco)) exhibited significant variations. The values of NEE(sat) were -2.6, -2.9, and -1.4 µmol CO₂ m⁻² s⁻¹ in 2008, 2009, and 2010, respectively. Drought suppressed both the gross primary production (GPP) and R(eco), and the drought sensitivity of GPP was greater than that of R(eco). The soil water content sensitivity of GPP was high during the dry year of 2008 with limited soil moisture availability. Our results suggest the carbon balance of this temperate desert steppe was not only sensitive to total annual precipitation, but also to its seasonal distribution.
干旱草原生态系统的碳交换具有显著的年际变化，但环境因素如何影响不同水文年的碳交换尚不清楚。本研究利用涡度相关技术，于 2008-2010 年对中国内蒙古温带荒漠草原生态系统进行了为期 3 年的 CO₂通量季节和年际变化观测。整个研究期间，降水量的多少和时间变化都很大。2009 年的降水量（186.4mm）接近多年平均水平（183.9±47.6mm），而 2008 年（136.3mm）和 2010 年（141.3mm）的降水量约为多年平均水平的四分之一。在整个研究期间，温带荒漠草原对大气 CO₂表现为碳中性，2008、2009 和 2010 年的净生态系统二氧化碳交换量（NEE）分别为-7.2、-22.9 和 26.0 g C m⁻² yr⁻¹，与零值无显著差异。与其他两个相对干旱的年份相比，2009 年生态系统吸收了更多的碳，而 2008 年和 2010 年的碳吸收量存在显著差异，尽管这两年的年降水量相似。结果表明，夏季降水是决定年 NEE 的关键因素。NEE 的表观量子产量和饱和值（NEE(sat)）以及生态系统呼吸的温度敏感性系数（R(eco)）均表现出显著变化。2008、2009 和 2010 年的 NEE(sat)值分别为-2.6、-2.9 和-1.4µmol CO₂ m⁻² s⁻¹。干旱抑制了总初级生产力（GPP）和 R(eco)，且 GPP 的干旱敏感性大于 R(eco)。在 2008 年干旱的一年中，由于土壤水分有限，GPP 对土壤水分含量的敏感性较高。本研究结果表明，该温带荒漠草原的碳平衡不仅对年总降水量敏感，而且对其季节性分布也敏感。
