基于林龄的黄河三角洲白蜡人工林细根分布与活力研究

Fine root distribution and activity of Fraxinus velutina plantations based on the forest stand age in the Yellow River Delta

为研究黄河三角洲盐碱区白蜡人工林的细根空间分布与生长特征,选取5a、12a和18a典型白蜡人工林为研究对象,采用分层挖掘法和图像扫描分析法,对细根(≤2mm)的生物量密度(RBD)、根长密度(RLD)、根表面积密度(SAD)、比根长(SRL)、比表面积(SSA)根尖数、分支数、交叉数以及根系活力等9个指标进行了研究。结果表明:不同林龄白蜡人工林细根RBD随林龄的增大而增加,随土层深度的增加而降低。3种林龄的细根多集中在0~40cm的表层土和亚表层土中,RBD在总RBD中所占的比例为70.91%~81.39%,而在深层土中细根RBD所占的比例为1.16%~3.71%,细根有随林龄增大而向土壤深层延伸的趋势,且表层土根系生物量与次深层土和深层土均差异显著(P<0.05);随着林龄和土壤深度的增加,RLD、SAD、细根根尖数、分支数和交叉数分别呈增加和下降趋势,细根平均直径在土层垂直结构上则呈相反的变化趋势,而SRL与SSA的变化规律有所差异;根系活力在表层土和亚表层土中的变化趋势相似,主要表现为12a>5a>18a,而在次深层土和深层土中则表现为12a>18a>5a,且随着土层深度增加而减小;相关分析表明,3种林龄细根生物量密度与土壤含盐量、容重呈极显著负相关,除12a林龄细根生物量密度与土壤总孔隙度呈显著正相关外,其它林龄均与土壤总孔隙度、有机质、铵态氮、速效磷、有效钾及根系活力呈极显著正相关。

To determine the distribution and growth characteristics of fine roots of Fraxinus velutina plantations of different forest stand age(5 a,12 a,and 18 a)in saline-alkali soils of the Yellow River Delta,we studied the fine root(≤2 mm)biomass density,root length density,surface area density,specific root length,specific surface area,root tip number,branch number,cross number and root activity by layered digging and image-scanning analysis.The results showed that the fine root biomass density of Fraxinus velutina plantations of different forest stand age increased with the increase of forest stand age and decreased with the increase of soil depth.The fine root of 3 kinds of forest stand ages were mostly distributed in surface soil and subsurface soil of 0-40 cm,and the proportion of root biomass density in this layer was 70.91%~81.39%in the total root biomass density,while the proportion of root biomass density in the deep soil layer was 1.16%~3.71%.The fine root extended from topsoil to deep soil with the increase of forest age,and fine root biomass in the surface soil had significantly difference with that of subdeep soil and deep soil(P<0.05).Root length density,surface area density,fine root tip number,branch number and cross number increased with the increase of forest age and decreased with the increase of soil depth,the average diameter of fine roots showed an opposite trend in vertical structure of soil layer,and the variation rules of specific root length and specific surface area were different.The variation of root activity in surface soil and subsurface soil was similar with the sequences of 12 a>5 a>18 a,but the sequences in subdeep soil and deep soil were 12 a>18 a>5 a.Besides the root activity decreased with the increase of soil depth.The correlation analysis indicated that there was a significant negative correlation between fine root biomass density of three kinds of forest stand age and soil salinity and soil bulk density,and significantly positively correlation with total soil porosity,organic matter,ammonium nitrogen,available phosphorus,available potassium and root activity except that there was a positive correlation between the fine root biomass density of 12 a plantations and the total soil porosity.