Birmingham Institute of Forest Research, University of Birmingham, Edgbaston, B15 2TT, UK.
School of Biological Sciences, University of Birmingham, Edgbaston, B15 2TT, UK.
Tree Physiol. 2022 Jan 5;42(1):130-144. doi: 10.1093/treephys/tpab090.
Current carbon cycle models attribute rising atmospheric CO2 as the major driver of the increased terrestrial carbon sink, but with substantial uncertainties. The photosynthetic response of trees to elevated atmospheric CO2 is a necessary step, but not the only one, for sustaining the terrestrial carbon uptake, but can vary diurnally, seasonally and with duration of CO2 exposure. Hence, we sought to quantify the photosynthetic response of the canopy-dominant species, Quercus robur, in a mature deciduous forest to elevated CO2 (eCO2) (+150 μmol mol-1 CO2) over the first 3 years of a long-term free air CO2 enrichment facility at the Birmingham Institute of Forest Research in central England (BIFoR FACE). Over 3000 measurements of leaf gas exchange and related biochemical parameters were conducted in the upper canopy to assess the diurnal and seasonal responses of photosynthesis during the 2nd and 3rd year of eCO2 exposure. Measurements of photosynthetic capacity via biochemical parameters, derived from CO2 response curves, (Vcmax and Jmax) together with leaf nitrogen concentrations from the pre-treatment year to the 3rd year of eCO2 exposure, were examined. We hypothesized an initial enhancement in light-saturated net photosynthetic rates (Asat) with CO2 enrichment of ≈37% based on theory but also expected photosynthetic capacity would fall over the duration of the study. Over the 3-year period, Asat of upper-canopy leaves was 33 ± 8% higher (mean and standard error) in trees grown in eCO2 compared with ambient CO2 (aCO2), and photosynthetic enhancement decreased with decreasing light. There were no significant effects of CO2 treatment on Vcmax or Jmax, nor leaf nitrogen. Our results suggest that mature Q. robur may exhibit a sustained, positive response to eCO2 without photosynthetic downregulation, suggesting that, with adequate nutrients, there will be sustained enhancement in C assimilated by these mature trees. Further research will be required to understand the location and role of the additionally assimilated carbon.
当前的碳循环模型将大气中 CO2 的增加归因于陆地碳汇增加的主要驱动因素，但存在很大的不确定性。树木对大气中 CO2 升高的光合作用反应是维持陆地碳吸收的必要步骤，但不是唯一步骤，它会随时间、季节和 CO2 暴露时间而变化。因此，我们试图量化在英国中部伯明翰森林研究所（BIFoR FACE）的一个长期自由空气 CO2 富集设施的前 3 年中，树冠主导物种栎树（Quercus robur）对升高的 CO2（eCO2）（+150 μmol mol-1 CO2）的光合作用反应。在 eCO2 暴露的第 2 年和第 3 年，对树冠上层进行了超过 3000 次叶片气体交换和相关生化参数的测量，以评估光合作用的日变化和季节变化。通过生化参数（Vcmax 和 Jmax）从 CO2 响应曲线推导得出的光合作用能力测量值，以及从预处理年到第 3 年 eCO2 暴露的叶片氮浓度，都进行了检查。我们假设根据理论，在 CO2 富集的情况下，光饱和净光合速率（Asat）最初会增强约 37%，但我们也预计光合作用能力会随着研究的进行而下降。在 3 年的时间里，与在大气 CO2（aCO2）中生长的树木相比，生长在 eCO2 中的树冠上层叶片的 Asat 高 33±8%（平均值和标准误差），并且光合作用增强随光照的减少而降低。CO2 处理对 Vcmax 或 Jmax 以及叶片氮均无显著影响。我们的结果表明，成熟的栎树可能对 eCO2 表现出持续的积极响应，而不会出现光合作用下调，这表明，在有足够养分的情况下，这些成熟树木对碳的同化能力将持续增强。需要进一步的研究来了解额外同化的碳的位置和作用。
