Matsuda Ryo, Ito Hiroki, Fujiwara Kazuhiro
Department of Biological and Environmental Engineering, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, Japan.
Front Plant Sci. 2021 Jun 15;12:675810. doi: 10.3389/fpls.2021.675810. eCollection 2021.
The effects of photosynthetic photon flux density (PPFD) fluctuations in sunlight have already been investigated; however, the spectral photon flux density distribution (SPD) has hardly been considered. Here, sunlight SPD fluctuations recorded for 200 min in October in Tokyo, Japan were artificially reproduced using an LED-artificial sunlight source system. The net photosynthetic rate ( ) of cucumber leaves under reproduced sunlight was measured and compared with the estimated from a steady-state PPFD- curve for the same leaves. The measured and estimated agreed except when the PPFD was low, where the measured was lower than the estimated . The ratio of measured to estimated was 0.94-0.95 for PPFD ranges of 300-700 μmol m s, while the value was 0.98-0.99 for 900-1,300 μmol m s, and the overall ratio was 0.97. This 3% reduction in the measured compared with the estimated from a steady-state PPFD- curve was significantly smaller than the approximately 20-30% reduction reported in previous experimental and simulation studies. This result suggests that the loss of integral net photosynthetic gain under fluctuating sunlight can vary among days with different fluctuation patterns or may be non-significant when fluctuations in both PPFD and relative SPD of sunlight are taken into consideration.
太阳光中光合光子通量密度（PPFD）波动的影响已经得到了研究；然而，光谱光子通量密度分布（SPD）几乎未被考虑。在此，利用LED人工太阳光源系统人工再现了日本东京10月份记录的200分钟太阳光SPD波动情况。测量了再现阳光下黄瓜叶片的净光合速率（ ），并将其与根据相同叶片的稳态PPFD- 曲线估算的 进行比较。实测值和估算值在PPFD较低时除外，实测值低于估算值，二者一致。对于300 - 700 μmol m s的PPFD范围，实测 与估算 的比值为0.94 - 0.95，而对于900 - 1300 μmol m s，该值为0.98 - 0.99，总体比值为0.97。与根据稳态PPFD- 曲线估算的 相比，实测 降低3%，这明显小于先前实验和模拟研究报告的约20 - 30%的降低幅度。该结果表明，在波动阳光下积分净光合增益的损失可能因波动模式不同的日期而异，或者当同时考虑PPFD和太阳光相对SPD的波动时可能并不显著。
