不同疏伐强度下黄土丘陵区刺槐林的水分利用特征

Water use characteristics of Robinia pseudoacacia plantations under different thinning intensities in the loess hilly region

造林是生态恢复的重要措施,但由于种植密度过高,导致土壤干燥化,林木生长衰退,严重制约其生态功能的提升。疏伐是人工林改造的重要手段,水分利用特征是确定适宜疏伐密度的关键因素,但目前缺少疏伐对人工林水分利用特征影响的系统研究。基于此,以黄土丘陵区刺槐林为研究对象,设置疏伐55%(P1)、28%(P2)、16%(P3)和对照(P4)四个处理,通过0—500 cm深度的土壤水与茎秆水δ^(2)H和δ^(18)O、叶片δ^(13)C的采样分析并利用MixSIAR模型,比较了不同疏伐强度下刺槐林水分来源和水分利用效率的差异,建立了水分来源比例与叶片δ^(13)C的定量关系。结果表明:(1)疏伐样地在不同深度的土壤含水量均高于对照样地,表明疏伐对缓解土壤水分胁迫具有重要作用。(2)随着疏伐强度的增大,浅、中层(0—100 cm、100—300 cm)土壤水对刺槐的贡献比例呈增加趋势(P1:80.4%;P2:78.1%;P3:76.3%;P4:67.8%),而深层土壤水分(300—500 cm)的贡献比例相对降低,表明疏伐促进了刺槐对浅层及中层土壤水的吸收利用,减少了对深层土壤水的过度消耗。(3)疏伐样地的叶片δ^(13)C均大于对照样地,表明疏伐提高刺槐了的水分利用效率,且刺槐叶片δ^(13)C与浅层土壤水分贡献比例呈线性正相关(P<0.01),而与中深层土壤水贡献比例呈线性负相关(P<0.05)。研究结果初步反映了疏伐对刺槐林水分利用特征的影响,可为黄土高原刺槐林改造和功能提升提供科学依据,未来需开展疏伐后长时间序列的观测研究。

Afforestation is an important measure for ecological restoration.Due to the high planting density,the soil becomes dry,the growth of trees declines,and the improvement of ecological function is restricted seriously.Thinning is an important means of the artificial forest reconstruction,and water use characteristic is the key factor to determine suitable thinning density.However,there is few systematic studies about the effects of thinning on water use characteristics.This study set up four treatments including thinning 55%(P1),28%(P2),16%(P3)and control(P4)for Robinia pseudoacacia plantation in the loess hilly region.Theδ^(2)H andδ^(18)O values in soil water and stem water at 0-500 cm depth and leafδ^(13)C value were measured.The differences of water source and water use efficiency of R.pseudoacacia among different thinning intensities were compared.The quantitative relationships between water source ratio andδ^(13)C were established.The results showed that the soil water content of the thinned plots at different depths was higher than that of the control plot,which indicated that thinning played an important role in alleviating soil water stress.The contribution proportion of soil water in shallow(0-100 cm)and middle layers(100-300 cm)to R.pseudoacacia increased with the thinning intensity(P1:80.4%;P2:78.1%;P3:76.3%;P4:67.8%),and the contribution proportion of soil water in deep layer(300-500 cm)decreased relatively.The leafδ^(13)C of the thinned plots was higher than that of the control plot,which indicated that thinning improved water use efficiency of R.pseudoacacia.There was a positive linear correlation betweenδ^(13)C value of R.pseudoacacia and the contribution proportion of soil water in shallow layer(P<0.01),while a negative linear correlation was found betweenδ^(13)C value and the contribution proportion of soil water in the middle and deep layers(P<0.05).These findings gave a preliminary understanding about the effects of thinning on the water use characteristics of R.pseudoacacia plantation,and provided the scientific basis for the reconstruction of artificial R.pseudoacacia plantations and the improvement of ecological function in the Loess Plateau.It is necessary to carry out long-term observation after thinning in the future.