巨桉与5种木本植物幼树的耗水特性及水分利用效率的比较

巨桉因生长迅速且经济效益高,在我国南方被广泛用于营造短周期工业原料林,但其蒸腾耗水状况与其他常见或乡土树种存在怎样的差异,大面积种植是否会改变栽培区原有的水分平衡,是一个尚未明确的问题。利用LI-6400光合作用仪测定了巨桉与其他5种木本植物在不同光强、温度、湿度下的净光合速率(Pn)、蒸腾速率(Tr)和水分利用效率(WUE),用称重法测定了参试植物载叶量、生物量和耗水量,并对这些树种的蒸腾耗水特性进行了评价。结果表明:(1)相同环境条件下,巨桉的Tr最大,WUE最低,单位质量耗水量最多,单株蒸腾耗水量远高于其他树种,其明显较大的叶面积可能是重要原因之一,虽然其Pn仅次于杨树,生物量积累最大,因此为高光合、高蒸腾、低水分利用效率植物。(2)阔叶树种的Pn和Tr明显高于针叶树种,而WUE低于针叶树种。(3)环境因子(光照强度、温度和湿度)对植物Pn、Tr和WUE的影响较大,其中Pn主要受光照强度影响,Tr对湿度最为敏感,一般情况下WUE随湿度的增大而升高。在试验设置的温度范围(24—32℃)内,光合作用变化幅度不大。光照强度800μmol.m-.2s-1和温度28℃最有利于参试植物的光合作用。(4)巨桉等速生树种较强的光合作用使其生长迅速,固碳潜力大,但其高蒸腾和低水分利用效率的特点意味着在栽培区替代原有植被进行大规模造林时,可能会消耗更多的水资源而对生态环境造成一定的不利影响,因此在发展巨桉人工林时应选择水分条件好的区域(尤其是年降雨量充沛且季节间分配相对均匀的地区),并进行科学的经营管理。

The water consumption and water use efficiency of the seedlings of Eucalyptus grandis and other five tree species in Sichuan Province

Eucalyptus grandis,a fast-growing timber species with outstanding economic efficiency,has been extensively planted as short-term industrial material in southern China.But what′s the difference of features in relation to water consumption between E.grandis and common or native tree species of Sichuan Province,whether or not the amount of water consumption of E.grandis would change the original water balance in its cultivation area remains to be answered.In this paper,the net photosynthetic rate(Pn),the transpiration rate(Tr) and the water use efficiency(WUE) of seedlings of E.grandis and other five tree species under different light intensities,air temperatures and atmosphere humidities were determined with the help of LI-6400 photosynthesis meter,the plant total leaf weight,biomass and the water consumption were measured using weighing method,then the water consumption characteristics of these species were evaluated and compared based on the indicators mentioned above.The results were showed as follows:(1) Of all the tested species,E.grandis possessed the highest Tr and the lowest WUE under the same condition,in addition the maximum water consumption per unit biomass,so the water consumption per plant of which was significantly larger than the others,its largest total leaf area was probably one of the important reasons.Its Pn was lower than that of P.× R270,but its biomass accumulation was the largest.We drew a conclusion that E.grandis was a tree species with strong photosynthesis,high transpiration,and low water use efficiency.(2) The Pn and the Tr of the broad-leaved tree species were obviously higher than those of the coniferous tree species,while the WUE of the former was lower than that of the latter.(3) Environmental factors(the light intensity,the air temperature and the atmosphere humidity) influenced the Pn,the Tr and the WUE of plants to a large extent.Particularly,the Pn was mainly affected by the light intensity,the Tr was most sensitive to the atmosphere humidity,and generally the WUE rose with the increase of the atmosphere humidity.In the range of variation temperature(24—32℃),which was set in the experiment,the photosynthesis of these tree species did not changed to a large extent.The light intensity of 800 μmol · m-2 · s-1 and the temperature of 28 ℃ in this study were observed most conducive to plant photosynthesis.(4) Fast-growing tree species such as E.grandis,grew more rapidly and were more potential to fix considerable carbon because of its comparatively stronger capability of photosynthesis,thus higher economic benefit could be obtained.However,in terms of the higher transpiration and lower water use efficiency,replacing the former vegetation(mainly composed by indigenous tree species) with large-scale plantations of E.grandis was more likely to be adverse to the environment of introduction areas because of more water consumption.Therefore,the area for E.grandis plantation should be in a good water condition,especially where abundant annual rainfall and uniform rainfall distribution were seen.Moreover,adequate attention should be paid to the scientific and rational water management.