Interseasonal comparison of CO2 concentrations, isotopic composition, and carbon dynamics in an Amazonian rainforest (French Guiana)
Interseasonal comparison of CO2 concentrations, isotopic composition, and carbon dynamics in an Amazonian rainforest (French Guiana)
复制标题
DOI：
10.1007/s004420050140
复制
发表时间：
1997-03-01
期刊：
影响因子：
2.7
通讯作者：
Ehleringer, JR
中科院分区：
文献类型：
--
作者：
Buchmann, N;Guehl, JM;Ehleringer, JR
在1994年旱季和1995年雨季，在法属圭亚那的热带雨林冠层CO2浓度进行了连续5天的测量。整个冠层（0.02-38米）的二氧化碳浓度（[CO2]）表现出明显的日变化模式，分层良好，并随着进入冠层的高度增加而降低。在这两个季节，白天[CO2]在上层和中层冠层平均下降7-10 μ mol mol（-1）低于对流层基线值在巴巴多斯测量。在冠层的主要部分（大于或等于0.7米），[CO2]没有不同的雨季和旱季。相反，在旱季，低于0.7米的[CO2]一般较高，导致较大的[CO2]梯度。支持这一观察结果，土壤CO2排放量平均较高，在旱季比在雨季，无论是由于扩散限制和/或缺氧的根和微生物呼吸。强降雨事件后土壤呼吸速率下降了40%，导致森林地面上方的冠层[CO2]迅速下降约50 μ mol mol（-1）。δ（13）C（冠层）和δ（18）O（冠层）值的变化反映了[CO2]（冠层）的时空变化。两个季节冠层CO2的δ（13）C和δ（18）O之间存在密切的相关关系（r（2）> 0.86）。在森林地面上方测量到的δ（13）C（冠层）和δ（18）O（冠层）值最低（δ（13）C = -16.4 ‰; δ（18）O = 39.1 ‰ SMOW）。在林冠顶部和森林地面之间的CO2同位素比值中，δ（13）C的颗粒介于2.0 ppm和6.3 ppm之间，δ（18）O的颗粒介于1.0 ppm和3.5 ppm之间。3个不同位置叶片的δ（13）C（叶）和计算的c（i）/c（a）在旱季和雨季相似，表明冠层维持恒定的光合作用与气孔导度的比值。林冠内δ（13）C（叶）的差异中约千分之二十是由源气效应引起的，其余80%是由c（i）/c（a）的变化引起的。绘制1/[CO2]与相应的δ（13）C比率的曲线图，得到非常紧密的线性关系（r（2）= 0.99），两个季节之间没有显著差异，表明湍流混合相对于生态系统气体交换的季节性变化可以忽略不计。这些关系的截距应指示呼吸源的Δ（13）C接近土壤呼吸CO2的实测Δ（13）C和凋落物和土壤有机质的Δ（13）C。整个生态系统的碳同位素差别估计数Delta（e）在旱季为千分之20.3，在雨季为千分之20.5。
Canopy CO2 concentrations in a tropical rainforest in French Guiana were measured continuously for 5 days during the 1994 dry season and the 1995 wet season. Carbon dioxide concentrations ([CO2]) throughout the canopy (0.02-38 m) showed a distinct daily pattern, were well-stratified and decreased with increasing height into the canopy. During both seasons, daytime [CO2] in the upper and middle canopy decreased on average 7-10 mu mol mol(-1) below tropospheric baseline values measured at Barbados. Within the main part of the canopy (greater than or equal to 0.7 m), [CO2] did not differ between the wet and dry seasons. In contrast, [CO2] below 0.7 m were generally higher during the dry season, resulting in larger [CO2] gradients. Supporting this observation, soil CO2 efflux was on average higher during the dry season than during the wet season, either due to diffusive limitations and/or to oxygen deficiency of root and microbial respiration. Soil respiration rates decreased by 40% after strong rain events, resulting in a rapid decrease in canopy [CO2] immediately above the forest floor of about 50 mu mol mol(-1). Temporal and spatial variations in [CO2](canopy) were reflected in changes of delta(13)C(canopy) and delta(18)O(canopy) values. Tight relationships were observed between delta(13)C and delta(18)O of canopy CO2 during both seasons (r(2) > 0.86). The most depleted delta(13)C(canopy) and delta(18)O(canopy) values were measured immediately above the forest floor (delta(13)C = -16.4 parts per thousand; delta(18)O = 39.1 parts per thousand SMOW). Grandients in the isotope ratios of CO2 between the top of the canopy and the forest floor ranged between 2.0 parts per thousand and 6.3 parts per thousand for delta(13)C, and between 1.0 parts per thousand, and 3.5 parts per thousand, for delta(18)O. The delta(13)C(leaf) and calculated c(i)/c(a) of foliage at three different positions were similar for the dry and wet seasons indicating that the canopy maintained a constant ratio of photosynthesis to stomatal conductance. About 20 parts per thousand of the differences in delta(13)C(leaf) within the canopy was accounted for by source air effects, the remaining 80% must be due to changes in c(i)/c(a). Plotting 1/[CO2] vs. the corresponding delta(13)C ratios resulted in very tight, linear relationships (r(2) = 0.99), with no significant differences between the two seasons, suggesting negligible seasonal variability in turbulent mixing relative to ecosystem gas exchange. The intercepts of these relationships that should be indicative of the delta(13)C of respired sources were close to the measured delta(13)C of soil respired CO2 and to the delta(13)C of litter and soil organic matter. Estimates of carbon isotope discrimination of the entire ecosystem, Delta(e), were calculated as 20.3 parts per thousand during the dry season and as 20.5 parts per thousand, during the wet season.