Yu Liyao, Fujiwara Kazuhiro, Matsuda Ryo
Department of Geography, National University of Singapore, 1 Arts Link, Kent Ridge, 117568, Singapore.
Department of Biological and Environmental Engineering, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo, Tokyo, 113-8657, Japan.
BMC Plant Biol. 2025 Apr 3;25(1):426. doi: 10.1186/s12870-025-06378-0.
Plant leaves adjust their properties under changing photosynthetic photon flux density (PPFD) through acclimation. Accurate estimation of leaf photosynthetic properties (e.g., maximum photosynthetic rate, A) using experienced PPFD helps to estimate canopy photosynthesis. So far, A and its underlying properties could reportedly be estimated using a simple average PPFD (Q) in recent days or weeks. We have recently proposed a time-weighted average PPFD (Q), which improved the estimation of leaf mass per area but not that of photosynthetic properties of cucumber leaves. Results on cucumber leaves exposed to a one-day increase or decrease in PPFD at different timings suggested that responses of photosynthetic properties to an increase or decrease in PPFD were asymmetrical, with different extents and lengths of time lag.
To incorporate these asymmetrical responses, we calculated a Q', in which Q was calibrated by time-weighting the change of PPFD from the previous day, ΔQ(t). A test using measurement data under random day-to-day PPFD showed that this method using Q' achieved more accurate estimations (determination coefficient, R = 0.77) of photosynthetic properties than those using Q or Q (R = 0.68). Moreover, the optimal weight trends of ΔQ(t) were asymmetrical, consistent with those suggested by our previous independent measurement data. This asymmetry was also confirmed by experiments, where photosynthetic properties acclimated faster to a decrease in PPFD than to an increase in PPFD.
Our results indicate that these asymmetrical responses to changes in PPFD should be incorporated to improve the estimation of photosynthetic properties.
植物叶片通过适应性调节在不断变化的光合光子通量密度（PPFD）下调整其特性。利用经验性PPFD准确估计叶片光合特性（例如最大光合速率，A）有助于估算冠层光合作用。到目前为止，据报道，在最近几天或几周内，可以使用简单的平均PPFD（Q）来估计A及其潜在特性。我们最近提出了一种时间加权平均PPFD（Q），它改善了对单位面积叶质量的估计，但对黄瓜叶片光合特性的估计没有改善。在不同时间点暴露于PPFD一天增加或减少情况下黄瓜叶片的结果表明，光合特性对PPFD增加或减少变化的响应是不对称的，具有不同的程度和时间滞后长度。
为了纳入这些不对称响应，我们计算了一个Q'；其中Q通过对前一天PPFD变化量ΔQ(t)进行时间加权来校准。使用随机每日PPFD下测量数据进行的测试表明，与使用Q或Q（R = 0.68）相比，使用Q'；的这种方法对光合特性的估计更准确（决定系数，R = 0.77）。此外，ΔQ(t)的最佳权重趋势是不对称的，与我们之前独立测量数据所表明的一致。这种不对称性也通过实验得到证实，即光合特性适应PPFD降低比适应PPFD增加更快。
我们的结果表明应纳入这些对PPFD变化量的不对称响应，以改进光合特性的估计。
