苹果叶片气体交换日变化动态模拟

The dynamic diurnal simulation of gas exchange in apple leaves

根据苹果叶片气体交换模型可模拟不同小气候条件下光合速率(Pn)、气孔导度(Gs)、蒸腾速率(Tr)和水分利用效率(WUE)的日变化。Pn和Gs在晴天呈现出不对称双峰曲线:上午增加,约8:00前后达到最大值,然后下降,到16:00左右时再升高到第2个峰值,最后再下降。Tr晴天的日变化与Pn和Gs相似,在晴天呈"n"字形曲线,但是Tr的午休现象较Pn和Gs轻,并且最大值出现在午后。晴天时WUE在太阳出来不久就达到了最大值,并迅速下降到一个比较稳定的水平,傍晚前后降到0。模型模拟表明气体交换的日变化主要是由太阳辐射驱动的,而午休现象主要是由叶水势和湿度的减少引起。根据在富士苹果园观测数据(Maluspumila Mill.Fuji;北纬40°13′,东经116°13′,海拔79m)对模型进行了验证。结果表明在不同的有效光合辐射、温度、湿度和CO2浓度下Pn的观测值和模拟值非常吻合,树冠上层叶片Pn和Gs日变化的实测值和模拟值也基本一致。Tr的模拟值略有高估,可能是由叶片的相互遮荫及Pn和有效光合辐射之间的非线性关系引起。

The diurnal responses of photosynthetic rates（Pn）,stomatal conductance（Gs）,transpiration rates（Tr）and water use efficiency（WUE）to the daily march of microclimatic conditions were simulated by the coupled model of apple leaves gas exchange.Values of Pn and Gs increased in the morning,reached a maximum about 8：00 AM,decreased to lower values in the midday,recovered to the second maximum about 4：00 PM,and decreased in late afternoon,creating an asymmetrical double-peak curve on sunny days.The diurnal change of Tr was similar to that of Pn and Gs,following ＂n＂ shape curves on clear days,reached the maximum after midday.But the midday depressions of Pn and Gs were more strongly expressed than Tr.On clear days,the peak of WUE was reached early after sunrise;it then decreased to a stable level maintained through most of the day until falling to zero at sunset.The mathematical simulation showed the diurnal course of gas exchange was driven mainly by radiation and midday depressions mostly caused by the reduction of leaf water potential and relative humidity.These established models were tested by the observation data in an apple（Malus pumila Mill.＇Fuji＇）orchard（latitude 40°13＇ north,longitude 116°13＇ east,altitude 79 m）.There was a satisfactory correspondence between measured and simulated values of Pn in different photosynthetically active radiation（PAR）,air relative humidity（RH）,air temperature（Ta）,air CO2 concentration.The diurnal variations of Pn and Gs in upper layers of canopy,compared with the model predictions,showed a good general agreement.Only a slight overestimation of Tr was in our study,which might be caused by leaves shading and non-linear relationship between Pn and PAR.