Biophysical controls on net ecosystem CO2 exchange over a semiarid shrubland in northwest China
Biophysical controls on net ecosystem CO2 exchange over a semiarid shrubland in northwest China
复制标题
中国西北半干旱灌丛生态系统二氧化碳净交换的生物物理控制
DOI：
10.5194/bg-11-4679-2014
复制
发表时间：
2014-01-01
期刊：
影响因子：
4.9
通讯作者：
Peltola, H.
中科院分区：
文献类型：
--
作者：
Jia, X.;Zha, T. S.;Peltola, H.
半干旱和干旱地区的碳（C）循环在很大程度上仍未得到探索，尽管旱地在全球分布广泛。许多荒漠化地区已经开展了恢复植被的工作，但有关恢复植被的能力的资料仍然很缺乏。利用涡度相关技术，对中国西北地区一个恢复中的灌木生态系统2012年全年的净生态系统CO2交换（NEE）进行了测量，目的是：（1）量化NEE及其分量;（2）考察穆尔多时间尺度上C通量对生物物理因子的依赖性。年度预算表明，总生态系统生产力（GEP）为456 g C m 2 yr 1（90%预测区间为449 - 463 g C m 2 yr 1）和生态系统呼吸（Re）为379 g C m 2 yr 1（90%预测区间为370 - 389 g C m 2 yr 1），导致净碳汇为77 g C m 2 yr 1（90%预测区间为68 - 87 g C m 2 yr 1）。最大日NEE，GEP和Re分别为4.7，6.8和3.3克C米2第1天。最大C同化率（即，在最适光照条件下），量子产率随生长期的变化而变化，夏季较高，春秋季较低。在半小时尺度上，水分亏缺对白天的NEE产生了主要控制作用，并与其他压力（例如，热和光抑制），限制植被固碳。低土壤湿度也降低了Re（Q10）的温度敏感性。在天气尺度上，降雨事件触发了生态系统释放C的即时脉冲，随后在1 - 2天后出现CO2吸收峰值。在整个生长季节，叶面积指数分别占NEE和GEP季节变化的45%和65%。每日Re对GEP呈线性依赖关系，斜率为0.34。这些结果突出了非生物胁迫及其缓解在极端气候事件频率和强度增加的情况下调节碳循环的作用。
The carbon (C) cycling in semiarid and arid areas remains largely unexplored, despite the wide distribution of drylands globally. Rehabilitation practices have been carried out in many desertified areas, but information on the C se- questration capacity of recovering vegetation is still largely lacking. Using the eddy-covariance technique, we measured the net ecosystem CO2 exchange (NEE) over a recovering shrub ecosystem in northwest China throughout 2012 in or- der to (1) quantify NEE and its components and to (2) exam- ine the dependence of C fluxes on biophysical factors at mul- tiple timescales. The annual budget showed a gross ecosys- tem productivity (GEP) of 456 g C m 2 yr 1 (with a 90 % prediction interval of 449-463 g C m 2 yr 1 ) and an ecosys- tem respiration (Re) of 379 g C m 2 yr 1 (with a 90 % pre- diction interval of 370-389 g C m 2 yr 1 ), resulting in a net C sink of 77 g C m 2 yr 1 (with a 90 % prediction interval of 68-87 g C m 2 yr 1 ). The maximum daily NEE, GEP and Re were 4.7, 6.8 and 3.3 g C m 2 day 1 , respectively. Both the maximum C assimilation rate (i.e., at the optimum light intensity) and the quantum yield varied over the growing sea- son, being higher in summer and lower in spring and autumn. At the half-hourly scale, water deficit exerted a major control over daytime NEE, and interacted with other stresses (e.g., heat and photoinhibition) in constraining C fixation by the vegetation. Low soil moisture also reduced the temperature sensitivity of Re (Q10). At the synoptic scale, rain events trig- gered immediate pulses of C release from the ecosystem, fol- lowed by peaks of CO2 uptake 1-2 days later. Over the entire growing season, leaf area index accounted for 45 and 65 % of the seasonal variation in NEE and GEP, respectively. There was a linear dependence of daily Re on GEP, with a slope of 0.34. These results highlight the role of abiotic stresses and their alleviation in regulating C cycling in the face of an in- creasing frequency and intensity of extreme climatic events.