Key message

Seasonal variations in the leaf photosynthetic traits of an urban tree, Ginkgo biloba, were almost synchronized with the photoperiod. Non-stomatal limitations were a cue for photosynthesis in Ginkgo biloba.

Photosynthetic functions, which are key traits in determining the carbon uptake of urban trees, exhibit significant seasonal variations in temperate zones. It is essential to clarify the seasonal dynamics of photosynthesis to evaluate the CO₂ uptake in urban areas. We investigated seasonal variations in the photosynthetic traits of Ginkgo biloba, which is a major urban deciduous tall tree often planted in Japan. Seasonal variations in the leaf photosynthetic traits, including the maximum photosynthesis rate, maximum carboxylation rate, and mesophyll and stomatal conductance, were well fitted to quadratic models, in which they peaked around the summer solstice and then declined with time. Seasonal variations in the environmental variables, such as photoperiod, temperature, and solar radiation, were compared to those of the leaf photosynthetic traits, in which the photoperiod explained well variations in the leaf photosynthetic traits. Seasonal variations in photosynthesis were largely governed by non-stomatal limitations, i.e., mesophyll and biochemical limitations. The high synchrony of the photoperiod and photosynthetic traits during leaf maturation may cause an enhancement in the daily carbon uptake of G. biloba leaves around the summer solstice, which has the longest photoperiod, and thus, will lead to an increase in the annual carbon uptake.

中文翻译：

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城市景观树种银杏的光合功能的季节性变化：光周期是关键特征

关键信息

城市树木银杏叶片光合特性的季节性变化几乎与光周期同步。非气孔限制是银杏叶片光合作用的提示。

光合功能是决定城市树木碳吸收的关键特征，在温带地区表现出明显的季节性变化。阐明光合作用的季节动态以评估城市地区的CO ₂吸收至关重要。我们调查了银杏光合特性的季节性变化是日本经常种植的一种主要的城市落叶高大乔木。叶片光合特性的季节性变化，包括最大光合作用率，最大羧化率以及叶肉和气孔导度，与二次方模型非常吻合，在夏至前后达到峰值，然后随时间下降。将环境变量（例如光周期，温度和太阳辐射）的季节性变化与叶片光合特性的季节变化进行比较，其中光周期可以很好地说明叶片光合特性的变化。光合作用的季节性变化主要由非气孔限制（即叶肉和生化限制）控制。银杏叶在夏至前后有较长的光周期，因此将导致每年的碳吸收量增加。