彰武松、樟子松光合生产与蒸腾耗水特性

本文采用Li-6400光合测定系统对性成熟(18a)阶段彰武松(Pinus densiflora var.zhangwuensis)和樟子松(Pinus sylvestris var.mongolica)光合及蒸腾指标不同季节日变化进行了测定，并采用切枝蒸腾法对两个树种叶片气孔蒸腾和角质层蒸腾进行对比测定，评价了气孔开闭敏感性，探讨了两个树种光合生产与蒸腾耗水特性。结果表明：在同样生境条件下，彰武松比樟子松有较大的光合速率(Pn)和较小的蒸腾速率(Tr)。在5月和7月，彰武松的Pn和Tr日变化呈现明显双峰型，其Pn和Tr“午休”现象均主要受气孔限制；在10月呈单峰型。樟子松的Pn和Tr日变化在整个生长季均呈单峰型，而且，彰武松日光合量(DAP)均高于樟子松，是樟子松的163.4%(5月)、211.1%(7月)和183.6%(10月)。光响应曲线参数表明：在不同月份，彰武松最大光合速率(Pmax)均大于樟子松，且光饱和点(LSP)较高，光补偿点(LCP)较低。在任意被测时刻，彰武松气孔导度(Gs)和Tr都小于樟子松。彰武松具有较小气孔和角质层蒸腾速度，并且在同样干旱条件下，彰武松气孔下陷，其气孔的开闭反应更加敏感。彰武松水分利用效率(WUE)较高，约是樟子松的2.29倍。这些结果暗示，彰武松以其高的光合速率和低的蒸腾耗水特性，提高水分利用效率，以其敏感的气孔开闭机制和旱生叶片结构进而实现在干旱半干旱地区的速生特性。

Characteristics of photosynthetic productivity and water-consumption for transpiration in Pinus densiflora var. zhangwuensis and Pinus sylvestris var. mongolica

In order to photosynthesize, land plants must open their stomata to exchange small amounts of CO2 at the cost of losing a lot of water vapor through transpiration. This gas exchange is unequal in that more water is lost than CO2 is taken in. In general, fast growing species are characterized by their high photosynthetic capacity, most of which is achieved at the expense of consuming large amounts of water. This trade-off poses a serious challenge to forestry in the selection of fast-growing tree species in arid and semiarid areas. The ideal forestry species for drier climates should maintain a high photosynthetic capacity as well as low water consumption for transpiration, but such species are very rare. In this study, the LI-6400 (LICOR, Inc. Lincoln, NE, USA) portable photosynthesis system was employed to measure diurnal changes in photosynthetic and transpiration indices in sexually mature Pinus densiflora var. zhangwuensis and P, sylvestris var. mongolica (18 years old). In addition, the cut-branch transpiration method was used to compare stomatal and cuticular transpiration in order to evaluate the sensitivity of stomatal opening and closing and to characterize the photosynthetic productivity and water consumption for transpiration in these two species in different growing seasons. P. densiflora var. zhangwuensis had a higher photosynthesis rate (Pn) and a lower transpiration rate (Tr) than P. sylvestris var. mongolica under the same conditions. In May and July, the diurnal changes of Pn and Tr in P. densiflora var. zhangwuensis formed double-peaked curve as a result of mid-day stomatal limitation, while it formed single-peaked curve in October. The daily variation of Pn and Tr in P. sylvestris var. mongolica exhibited a monopeak curve throughout the growing season. The net photosynthesis per day in P. densiflora var. zhangwuensis was higher than in P. sylvestris var. mongolica; values for the former were 163.4 (May), 211.1 (July), and 183.6 (October) percent of the latter. The photoresponse parameter measurements showed that, in different months, the maximum rate of photosynthesis of P. densiflora var. zhangwuensis was greater than that of P. sylvestris var. mongolica, and the former also had a higher light saturation point and a lower light compensation point. The stomatal conductivity (Gs) and Tr of P. densiflora var. zhangwuensis were lower than those of P. sylvestris var. mongolica when measured at random times. The stomatal and cuticular Tr of P. densiflora var. zhangwuensis were lower, and in the same drought conditions, its stomata were deeper and had a higher sensitivity for opening and closing. Water use efficiency (WUE) of P. densiflora var. zhangwuensis was 2.29 times that of P. sylvestris var. mongolica. Analysis of the correlation between Gs and WUE showed that P. densiflora var. zhangwuensis could maintain high WUE when Gs levels were high. In May and July, when P. densiflora var. zhangwuensis exhibited midday photosynthetic depression, its Gs level was low, usually in the 90-200 mmol ? m-2 ? s-1 range. At the same time, its WUE was higher than that of P. sylvestris var. mongolica, indicating that P. densiflora var. zhangwuensis could effectively conserve water by closing its stomata rapidly at midday, so as to maintain its high WUE. These results implied that P. densiflora var. zhangwuensis can improve its WUE, yielding its higher Pn and lower Tr, and achieves its fast growth in arid and semiarid regions through its sensitive stomatal response and leaf xeromorphism.