Institute of Botany, Chinese Academy of Sciences, 100093 Beijing, China.
Tree Physiol. 2010 Mar;30(3):313-25. doi: 10.1093/treephys/tpp114. Epub 2010 Jan 12.
Gas exchange, chlorophyll fluorescence, photosynthetic end products and related enzymes in source leaves in response to low sink demand after girdling to remove the root sink were assessed in young apple trees (Malus pumila) grown in two greenhouses with different air temperatures for 5 days. Compared with the non-girdled control in the low-temperature greenhouse (diurnal maximum air temperature <32 degrees C), low sink demand resulted in lower net photosynthetic rate (P(n)), stomatal conductance (g(s)) and transpiration rate (E) but higher leaf temperature on Day 5, while in the high-temperature greenhouse (diurnal maximum air temperature >36 degrees C), P(n), g(s) and E declined from Day 3 onwards. Moreover, gas exchange responded more to low sink demand in the high-temperature greenhouse than in the low-temperature greenhouse. Decreased P(n) at low sink demand was accompanied by lower intercellular CO(2) concentrations in the low-temperature greenhouse. However, decreased maximal photochemical efficiency, potential activity, efficiency of excitation capture, actual efficiency and photochemical quenching, with increased minimal fluorescence and non-photochemical quenching of photosystem II (PSII), were observed in low sink demand leaves only in the high-temperature greenhouse. In addition, low sink demand increased leaf starch and soluble carbohydrate content in both greenhouses but did not result in lower activity of enzymes involved in metabolism. Thus, decreased P(n) under low sink demand was independent of a direct effect of end-product feedback but rather depended on a high temperature threshold. The lower P(n) was likely due to stomatal limitation in the low-temperature greenhouse, but mainly due to non-stomatal limitation in the high-temperature greenhouse.
在两个具有不同空气温度的温室中，对 5 天内去根库环割以去除根库后的源叶的气体交换、叶绿素荧光、光合终产物和相关酶进行了评估。与低温温室（日最高空气温度<32°C）中非环割对照相比，低库需求导致净光合速率（Pn）、气孔导度（gs）和蒸腾速率（E）降低，但第 5 天叶片温度升高，而在高温温室（日最高空气温度>36°C）中，Pn、gs 和 E 从第 3 天开始下降。此外，在高温温室中，气体交换对低库需求的响应比对低温温室更为敏感。低库需求下 Pn 的降低伴随着低温温室中胞间 CO2浓度的降低。然而，在高温温室中，低库需求下最大光化学效率、潜在活性、激发捕获效率、实际效率和光化学猝灭降低，而最小荧光和光系统 II（PSII）的非光化学猝灭增加。此外，在两个温室中，低库需求都会增加叶片淀粉和可溶性碳水化合物含量，但不会导致参与代谢的酶活性降低。因此，低库需求下 Pn 的降低与终产物反馈的直接影响无关，而是取决于高温阈值。较低的 Pn 可能是由于低温温室中的气孔限制，但主要是由于高温温室中的非气孔限制。
