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

Abstract

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.