Interannual variability of net carbon exchange is related to the lag between the end-dates of net carbon uptake and photosynthesis: Evidence from long records at two contrasting forest stands
Interannual variability of net carbon exchange is related to the lag between the end-dates of net carbon uptake and photosynthesis: Evidence from long records at two contrasting forest stands
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DOI：
10.1016/j.agrformet.2012.05.002
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发表时间：
2012-10
影响因子：
6.2
通讯作者：
Chaoyang Wu;J. Chen;A. Gonsamo;D. Price;T. A. Black;W. Kurz
中科院分区：
文献类型：
--
作者：
Chaoyang Wu;J. Chen;A. Gonsamo;D. Price;T. A. Black;W. Kurz
落叶林地和常绿林地都有长期(15年)连续的二氧化碳涡旋协方差数据，这使得能够对年度净生态系统生产量(NEP)与总初级生产量(GPP)和净碳吸收(CU)转变之间的时间间隔(例如，GPP的开始和结束日期和净碳吸收)之间的关系进行年代际分析。春季GPP开始日期(GPP Start)和CU开始日期(CU−)之间的间隔与年净生产力之间没有关系(因此CUStart GPP Start被称为“春季间隔”)。相反，我们发现NEP的年际变化与秋季GPP(GPPend)和CU(CUEnd)的结束日期之间的间隔密切相关(因此GPPend−Cuendis被称为“秋季间隔”)。在秋季较晚的年份发生的延长的生态系统呼吸不能单独解释落叶地点NEP与秋季间隔之间的相关性，但与年度GPP的归一化有助于理解两个地点秋季间隔较长的年份NEP下降的情况。根据站点一级气象变量对秋季间隔的解释表明，秋季温度(无论是气温还是土壤温度)不能单独用来解释这两个站点的秋季间隔变化。秋季全球短波辐射对这两个地点的秋季间隔造成了不同的影响。秋季高辐射缩短了落叶部位的秋季间隔(即增加NEP)，但延长了常绿部位的秋季间隔(即降低了NEP)。据我们所知，这是第一个评估可测量的总光合作用和净碳吸收发生日期之间的滞后影响的分析，并将这些影响与年度净净额联系起来。我们的结果表明，与以前报道的对春季物候的重视不同，秋季物候可能也在调节年度NEP方面发挥重要作用，即使在温度被认为是主要限制因素的北方森林生态系统中也是如此。此外，其他变量，特别是辐射和土壤湿度，似乎对确定净碳交换的年际变异性至关重要。
The availability of long-term (15 years) continuous CO2eddy-covariance data at both deciduous and evergreen forest sites has allowed decadal analysis of the relationship between annual net ecosystem production (NEP) and the time intervals between gross primary production (GPP) and net carbon uptake (CU) transitions (e.g., start and end dates of GPP and net carbon uptake). No relationships were observed between annual NEP and the interval between the start-dates of GPP (GPPstart) and CU (CUstart) in spring (hence CUstart−GPPstartis termed the “spring interval”). Conversely, we found that interannual variability of annual NEP was strongly related to the interval between the end-dates of GPP (GPPend) and CU (CUend) in autumn (hence GPPend−CUendis termed the “autumn interval”). Extended ecosystem respiration occurring in years with late autumns could not alone explain the correlation between NEP and the autumn interval at the deciduous site, but normalization with annual GPP facilitated understanding of decreased NEP during years with longer autumn intervals at both sites. Interpretation of the autumn interval based on site-level meteorological variables showed that autumn temperature (either air temperature or soil temperature) alone cannot be used to interpret autumn interval variations for either site. Autumn global shortwave radiation caused contrasting impacts on the autumn intervals at these two sites. High autumn radiation shortened the autumn interval at the deciduous site (i.e., it increased NEP) but lengthened it at the evergreen site (i.e., it decreased NEP). To our knowledge, this is the first analysis to assess the impacts of the lag between the dates when measurable gross photosynthesis and net carbon uptake occur, and to relate these to annual NEP. Our results suggest that in contrast to previously reported emphasis on spring phenology, autumn phenology may also have a major role in regulating annual NEP, even in northern boreal forest ecosystems where temperature is considered a major limiting factor. Further, it appears that other variables, notably radiation and soil moisture, are critical for determining interannual variability in net carbon exchange.