Center of Functional and Evolutionary Ecology, CNRS 1919 Route de Mende, 34293, Montpellier Cedex 5, France.
Tree Physiol. 2012 Apr;32(4):464-77. doi: 10.1093/treephys/tps020. Epub 2012 Apr 3.
Leaves of Mediterranean evergreens experience large variations in gas exchange rates over their life span due to aging and seasonally changing environmental conditions. Accounting for the changing respiratory physiology of leaves over time will help improve estimations of leaf and whole-plant carbon balances. Here we examined seasonal variations in light-saturated net CO(2) assimilation (A(max)), dark respiration (R(d)) and the proportional change in R(d) per 10 °C change in temperature (Q(10) of R(d)) in previous-year (PY) and current-year (CY) leaves of the broadleaved evergreen tree Quercus ilex L. A(max) and R(d) were lower in PY than in CY leaves. Differences in nitrogen between cohorts only partly explained such differences, and rates of A(max) and R(d) expressed per unit of leaf nitrogen were still significantly different between cohorts. The decline in A(max) in PY leaves did not result in the depletion of total non-structural carbohydrates, whose concentration was in fact higher in PY than CY leaves. Leaf-level carbon balance modeled from gas exchange data was positive at all ages. Q(10) of R(d) did not differ significantly between leaf cohorts; however, failure to account for distinct R(d) between cohorts misestimated canopy leaf respiration by 13% across dates when scaling up leaf measurements to the canopy. In conclusion, the decline in A(max) in old leaves that are close to or exceed their mean life span does not limit the availability of carbohydrates, which are probably needed to sustain new growth, as well as R(d) and nutrient resorption during senescence. Accounting for leaf age as a source of variation of R(d) improves the estimation of foliar respiratory carbon release at the stand scale.
地中海常绿植物的叶子由于衰老和季节性变化的环境条件，在其寿命过程中经历了气体交换率的巨大变化。随着时间的推移，考虑到叶片呼吸生理的变化，将有助于提高叶片和整个植物碳平衡的估算。在这里，我们研究了宽叶常绿树种 Quercus ilex L. 去年（PY）和当年（CY）叶片的最大饱和净 CO2 同化速率（A(max)）、暗呼吸（R(d)）以及温度每升高 10°C 暗呼吸（R(d)）的比例变化（R(d)的 Q10）的季节性变化。与 CY 叶片相比，PY 叶片的 A(max)和 R(d)较低。队列之间的氮差异只能部分解释这种差异，并且每单位叶片氮的 A(max)和 R(d)的速率在队列之间仍然存在显著差异。PY 叶片中 A(max)的下降并没有导致非结构性碳水化合物的耗尽，事实上，PY 叶片的非结构性碳水化合物浓度高于 CY 叶片。从气体交换数据建模的叶片水平碳平衡在所有年龄都是正值。R(d)的 Q10 在叶片队列之间没有显著差异；然而，如果不考虑队列之间的 R(d)差异，在将叶片测量值扩展到冠层时，将叶片呼吸的估算值高估了 13%。总之，接近或超过其平均寿命的老叶中 A(max)的下降并不会限制碳水化合物的可利用性，这些碳水化合物可能是维持新生长以及衰老过程中 R(d)和养分再吸收所必需的。将叶片年龄作为 R(d)变化的来源考虑在内，可以提高林分尺度上叶片呼吸碳释放的估算精度。
