Carbon dioxide exchange above a Mediterranean C3/C4 grassland during two climatologically contrasting years
Carbon dioxide exchange above a Mediterranean C3/C4 grassland during two climatologically contrasting years
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DOI：
10.1111/j.1365-2486.2007.01507.x
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发表时间：
2008-03-01
影响因子：
11.6
通讯作者：
Pereira, Joao Santos
中科院分区：
文献类型：
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作者：
Aires, Luis Miguel Igreja;Pio, Casimiro Adriao;Pereira, Joao Santos
在2004-2005年和2005-2006年两个水文年期间，对葡萄牙南部一个放牧的地中海C3/C4草地上的净生态系统碳交换（NEE）进行了涡旋协方差测量。在此，我们从相关生物物理控制的角度研究了新能源经济及其主要成分——初级生产总值（GPP）和生态系统呼吸（R-eco）的季节和年际变化。第一个水文年干旱，总降水量比长期平均值（669 mm）低45%；第二个水文年正常，总降水量仅比长期平均值高12%。干旱年冬季和早春的干旱条件限制了草产量，叶面积指数（LAI）很低。因此，在生长期的高峰期，新能源经济的最大日增长率以及光利用和水利用效率约为正常年份的一半。2006年夏季，暖季C4草Cynodon dactylon L.在强降雨事件后将生态系统转化为碳汇，并在C3草衰老结束后将碳固存延长数天，对NEE产生了明显的正向影响。在年基础上，干旱年的GPP和NEE分别为524和49 g C m(-2)，正常年的GPP和NEE分别为1261和-190 g C m（-2）。因此，在干旱年，草原是一个中等的净碳源，在正常年，草原是一个相当大的净碳汇。在这2年的试验中，降水总量是决定东北东东线年际变化的主要因素。相关对照方面，GPP和NEE在短期时间尺度上与入射光合光子通量密度密切相关。LAI的变化分别解释了GPP和NEE变化的84%和77%。R-eco的变化主要受冠层光合作用的控制。在每次放牧后，LAI的减少对NEE的影响呈负相关。
Eddy-covariance measurements of net ecosystem carbon exchange (NEE) were carried out above a grazed Mediterranean C3/C4 grassland in southern Portugal, during two hydrological years, 2004-2005 and 2005-2006, of contrasting rainfall. Here, we examine the seasonal and interannual variation in NEE and its major components, gross primary production (GPP) and ecosystem respiration (R-eco), in terms of the relevant biophysical controls. The first hydrological year was dry, with total precipitation 45% below the long-term mean (669 mm) and the second was normal, with total precipitation only 12% above the long-term mean. The drought conditions during the winter and early spring of the dry year limited grass production and the leaf area index (LAI) was very low. Hence, during the peak of the growth period, the maximum daily rate of NEE and the light-use and water-use efficiencies were approximately half of those observed in the normal year. In the summer of 2006, the warm-season C4 grass, Cynodon dactylon L., exerted an evident positive effect on NEE by converting the ecosystem into a carbon sink after strong rain events and extending the carbon sequestration for several days, after the end of senescence of the C3 grasses. On an annual basis, the GPP and NEE were 524 and 49 g C m(-2), respectively, for the dry year, and 1261 and -190 g C m(-2) for the normal year. Therefore, the grassland was a moderate net source of carbon to the atmosphere, in the dry year, and a considerable net carbon sink, in the normal year. In these 2 years of experiment the total amount of precipitation was the main factor determining the interannual variation in NEE. In terms of relevant controls, GPP and NEE were strongly related to incident photosynthetic photon flux density on short-term time scales. Changes in LAI explained 84% and 77% of the variation found in GPP and NEE, respectively. Variations in R-eco were mainly controlled by canopy photosynthesis. After each grazing event, the reduction in LAI affected negatively the NEE.