Influence of some interrelated physiological factors on the net photosynthetic rate of apple leaves

摘要

In order to study the photosynthetic characteristics of center-open form apple trees, net photosynthetic rate (Pn), CO_2 concentration in the intercellular space (Ci), CO_2 concentration in atmosphere (Ca), stomatal conductance (Cs), vapor pressure deficit (VPD), photosynthetically active radiation (PAR), leaf temperature (Tl) of apple (Malus domestica Borkh. cv.Fuji) leaves were measured under the field conditions. The results showed that: 1) Mesophyll resistance (Rm) of leaves from east side of a tree was low at 8:30, then increased at the daytime, and Ci / Ca changed in the similar way as Rm. The diurnal changes of Rm and Ci / Ca were negatively correlated with the change of Pn ; the Rm of leaves from west side of a tree was high at 8:30, then decreased with the increase of Pn, and kept a reverse change at the day, while Cs changed gently. It was suggested that the diurnal changes of Pn was mainly caused by the increase of mesophyll resistance to CO_2 at the daytime. 2) The response of Pn to PAR at 26℃ showed that the Rm of leaves from both east and west sides of a tree was high at 100 μ mol m~(-2)s~(-1), then decreased with the increase of Pn. Rm reached its minimum at 1200 μ mol m~(-2)s~(-1) and Pn got to its maximum at the same time, and keeping a reverse change. From 800 μ mol m~(-2)s~(-1) to 2000 μmol m~(-2)s~(-1), Cs decreased gently. The response of Pn to PAR was mainly caused by the increase of Rm. 3) The response of Pn to Tl at PAR 1050μ molm~(-2)s~(-1) showed that when the Tl changed from 20 to 28 ℃, the Cs of leaves increased gently, and it decreased greatly when the Tl changed from 32 to 40℃. During the experiment, Tl and Pn changed in the similar way, and both Rm and Ci/Ca were in the opposite way with Pn. The response of Pn to Tl was mainly caused by Rm and Cs.