基于CO_2传输阻力解析的土壤水分调控番茄光合生理机制

Mechanism of Soil Moisture Regulating Photosynthesis Rate of Tomato Based on Resistance of CO_2 Transport along Pathway

利用盆栽试验控制土壤含水率,基于叶绿素荧光、气体交换和响应曲线拟合相结合的方法解析番茄光合作用中CO_2由大气传输至叶绿体羧化位点的系列阻力构成,揭示了土壤水分胁迫限制番茄光合速率的关键步骤及位点。结果表明:番茄光合速率(Pn)、最大羧化速率(Vc,max)、最大电子传递速率(Jmax)及初始羧化效率(CE)随土壤含水率变化呈"S"形变化曲线,初期缓慢增长,中期迅速增长,土壤水分充分时达到最大值并趋于稳定,可用logistic函数模拟。气孔和叶肉对CO_2的传输导度及总传输导度随土壤含水率变化均呈明显的"S"形变化曲线,各支段CO_2导度及总传输导度在土壤水分充分时趋于稳定并达到最大值;随着土壤水分胁迫的增大,各CO_2传输导度逐渐降低并在重度土壤水分胁迫下达到最低值,可用logistic函数模拟。气孔导度与叶肉导度对光合速率限制的相对贡献率变化趋势相似,随着水分胁迫的加重,其贡献率逐渐增大,可以用指数函数模拟;羧化反应对光合速率限制的相对贡献率与气孔和叶肉导度相反,随着水分胁迫的增大,其贡献率逐渐减小,可以用对数函数模拟;在土壤水分充分时,羧化反应限速光合速率的相对贡献率最大,是限制光合速率的主导因子;在水分胁迫状况下,气孔限制和叶肉限制占主导地位,羧化反应的相对贡献率较低。气孔对CO_2的传输导度与叶水势呈正相关,随叶水势的下降,气孔导度也呈线性下降趋势;叶肉导度与比叶重呈线性负相关关系,叶肉导度随比叶重的增大而线性减小,比叶重随土壤水分胁迫程度的加剧而逐渐增大。因此,水分胁迫状况下,气孔与叶肉对CO_2的传输是水分胁迫限制光合速率的关键位点,气孔限速与保卫细胞水分失衡相关,而叶肉限速则由叶片厚度和组织疏松程度决定。

Soil moisture was closely linked to plant photosynthesis rate and plant productivity. Water stress was important factors for photosynthetic depression and yield decrease. However, the key limiting step and underlying mechanism was highly uncertain. The resistance distribution along the pathway of CO 2 transport from the atmosphere surrounding the leaf to the site of carboxylation inside the chloroplast stroma of tomato under different soil water content gradients was explored. Soil moisture was maintained by a standardized gravimetric approach. Stomatal and mesophyll conductance were estimated from simultaneous measurement of leaf gas exchange and chlorophyll fluorescence. The results showed that the photosynthesis rate ( P n ), rubisco carboxylation capacity ( V c ,max ), maximum electron transport capacity ( J max ) and carboxylation efficiency ( C E ) were increased with the increase of soil moisture, which showed as "S" curves and can be described in logistic models. Stomatal conductance, mesophyll conductance and the total conductance for CO 2 transport were decreased with water stress. The proportions of stomatal and mesophyll conductance limitations imposed on photosynthetic depression were increased with soil water stress, which were the dominant limiting factors; in contrast to stomatal and mesophyll limitation, biochemical limitations were increased with the increase of soil moisture and performed as predominant limiting factors when soil moisture was sufficient. Stomatal conductance showed positive linear relationship with leaf water potential, which was declined with soil water stress; mesophyll conductance showed negative linear relationship with leaf mass area, which was increased with soil water stress. The research result demonstrated that stomatal and mesophyll resistance for CO 2 uptake were key limiting step for photosynthesis rate. The greatest resistance of stomata under water stress was determined by the turgor loss of guard cells while the mesophyll conductance was determined by the leaf anatomical structure.