| Based on the measurements of vegetation structure, stable carbon isotope, dendrometer,sap flow and tree ring width, we measured the leaf13C, biomass, productivity, transpirationand evapotranspiration of dominant tree species to calculate water use efficiency (WUE) atleaf-, tree-and stand scales in2010in the south (Xiangshuihe Watershed, semi-humid area)and north (Diediegou Watershed, semi-arid area) of Liupanshan Mountain, Ningxia. Thevariations in temporal and spatial heterogeneity of WUE were analyzed, we also analyzed howWUE responds to climate change at different scales. This study is helpful to systematicunderstand the variation characteristics of WUE, and to select tree species for the afforestaionand recovery of forest vegetation in the semi-arid and semi-humid area, and to offer scientificguidance for the harmonious and integrated management of forest and water. The mainconclusions were as follows:1. Leaf level of water use efficiencyLeaf WUE of Larix principris-rupprechtii, Betula platyphylla, Pinus tablaeformisincreased with increasing canopy height, but the leaf WUE in the low canopy of Pinusarmandii and Quercus liaotungensis were higher compared with those of the mid-and upperparts in the canopy. The range of leaf WUE values was3.62～7.09mmol/mol, with the average5.35(±0.66)mmol/mol in Xiangshuihe Watershed, and10.42～13.14mmol/mol, with average11.47(±0.88)mmol/mol in Diediegou Watershed. The order of mean WUE of each treespecies is as P. tablaeformis＞Prunus davidiana＞Hippophae rhamnoides＞Q. liaotungersis＞L. principis-rupprechtii＞P. armandii＞Tilia panciostata＞B. Platyphylla. The leaf WUEfor life forms were significantly different, with a sequence of shrubs＞evergreen trees＞leavedtrees.The leaf WUE of species flucutated with the time during the growing season, beingrelatively higher WUE in the early stage than that in the middle and late phases. The leaf WUEamong individual trees of L. principris-rupprechtii, P. davidiana and H. rhamnoides in twodifferent water-environmental regions were significantly different during the growing season,IV and semi-arid area with the higher values. It showed that the ability of water use efficiency ofthe same tree species could be improved through long-term adaptation to drought.2. Individual level of water use efficiencyThe seasonal pattern of WUE value of individual tree of L. principis-rupprechtii exhibitedan initial increase and a subsequent decrease, the value ranged from0.88to9.73g/kg duringgrowing season in2010, having the maximum in June. The growing season WUE is4.85g/kg.Individual level of water use efficiency of L. principis-rupprechtii was mainly affected by solarradiation and the potential evaporation. WUE exhibited positive associations with precipitation,temperature and wind speed, except air humidity.3. Estimation of water use efficiency at stand level1) The WUETr(Productivity/Transpiration) and WUEET(Productivity/Evapotranspiration)of L.principis-rupprechtii plantation had higher values in the early stage of growing seasonthan that in the middle and late phases. The RUE(Productivity/Precipitation) values ofL.principis-rupprechtii plantation exhibited an initial increase and a subsequent decrease. TheWUETrvalues ranged from0.016to14.373g·m-2·mm-1, and the WUEETvalues ranged from0.008to10.718g·m-2·mm-1, and the RUE values ranged from0.002to5.126g·m-2·mm-1.2) The interannual changes of RUE of P.armandii natural forest exhibited "fast increase-slow increase-slow decrease", but variation amplitude was different. The interannual changesof RUE of L.principis-rupprechtii and P.tablaeformis plantations showed rapid rising trendwith fluctuations, and the greater fluctuations in L.principis-rupprechtii plantation. The RUEof two artificial forests and natural forest had extremely remarkable difference, with the orderof L.principis-rupprechtii plantation(1.12t· hm-2·a-1)＞P.tablaeformis plantation(0.97t·hm-2·a-1)＞P.armandii Natural Forest(0.45t·hm-2·a-1). The coefficient of variation in RUEwas as L.principis-rupprechtii plantation(0.54)＞P.armandii natural forest(0.45)＞P.tablaeformis plantation(0.41).The RUE of P.armandii natural forest was significantly positively correlated withprecipitation in August of the previous year and that from September to November of thecurrent year, but the RUE of two artificial forests was significantly positively correlated with precipitation in September of the previous year and negatively correlated with precipitation inApril of the current year, and the productivity of L.principis-rupprechtii plantation was alsosignificantly positively correlated with precipitation in September of the current year. So theRUE of the three forests was affected by the distribution pattern of precipitation during theyear.Most of monthly temperature negatively affected the RUE of P.armandii natural forest,but positively affected the RUE of two artificial forests, and the RUE values of three forestswas significantly correlated with temperature in June of the previous year and that in Marchand June of the current year. There were significantly negative correlations between RUE ofP.armandii Natural Forest and mean and minimum temperature in February, and the RUE ofL.principis-rupprechtii plantation was also significantly correlated with mean-and minimum-temperature in April and May of the current year, but P.tablaeformis plantation wassignificantly correlated with mean temperature in April and minimum temperature from May toAugust of the current year.There were significantly correlations between RUE of P.armandiinatural forest and mean humidity in March, and that between productivity of artificial forestand mean humidity in April.4. Some innovative viewpoint in the WUE research1) we showed that RUE of P.armandii forest decreases as mean annual precipitationincreases, but RUE of L.principis-rupprechtii and P.tablaeformis plantation increased at firstand then decreased. During the driest years, there was convergence to common RUE that wastypical of three coniferous tree plantions, but in most moisture years, all forests exhibited thesame minimum rate of biomass production per unit rainfall.2) With the expansion of the research scale, the WUE of trees showed a decreasing trend,and was affected by different environmental factors. In forest management, we shouldcomprehensive analysis the WUE and its impact factors at different scales to select suitabletree species in the afforestaion and recovery of forest vegetation.3) The L. principis-rupprechtii, P. tablaeformis, P. davidiana and H. rhamnoides that hadhigher WUE values whether they were in dry condition or wet conditions, were ecologicalwater-saving species, having high drought tolerance, so they can be chosen as the main afforestation tree for vegetation restoration and construction in arid and semi-arid regions.Secondly, the WUE values of shrubs and small trees were more than trees in different waterconditions, so we could rationally configure the proportion of different tree species. The WUEof trees had the characteristics of conservative and variability, so moderate drought exercisemeasures could be taken to improve the WUE of tree species in afforestations. |
PDF Full Text Request