功能性状和立地条件与树木根系NO_(3)^(-)吸收能力的关系

Relationship of functional traits and site conditions with NO_(3)^(-) uptake capacity of tree root

【目的】养分是干旱瘠薄立地中树木生长的重要限制因素,树木对干旱瘠薄立地中养分的吸收利用方式决定其生态适应对策。本研究通过野外原位测定,探究根系氮吸收动力学及其与根系形态性状间的耦合关系,为揭示林木根系在干旱瘠薄环境中的生理功能奠定基础。【方法】以北京市百望山森林公园内的山桃、栓皮栎和元宝枫为对象,采用以硝态氮(NO_(3)^(-))为唯一氮源的改良型梯度霍格兰营养液,在一般程度的干旱瘠薄立地和极端程度的干旱瘠薄立地中分别开展野外原位测定根系NO_(3)^(-)吸收动力学研究,并通过Pearson相关性分析和通径分析研究根系NO_(3)^(-)吸收速率与根系功能性状间的关系。【结果】树种、立地条件和两者的交互效应对NO_(3)^(-)吸收速率和动力学参数均有显著或极显著的影响。3个树种对氮的亲和性均较高,元宝枫根系对NO_(3)^(-)的吸收速率偏低,在2种立地条件中均显著低于山桃和栓皮栎。生长在更加干旱瘠薄立地中的速生树种对NO_(3)^(-)的吸收具有补偿性。根系功能性状与NO_(3)^(-)的吸收速率有很好的耦合关系,比根长和比根表面积对根系NO_(3)^(-)吸收速率有显著正效应,根直径和根组织密度则相反。分支结构性状中,分支强度和链接数对根系NO_(3)^(-)吸收速率的作用较弱。【结论】生长速度较快的山桃和栓皮栎根系的NO_(3)^(-)吸收速率在极端干旱瘠薄立地胁迫下显著降低,元宝枫则相反。采取提高最大吸收速率和降低氮亲和力的“速度策略”可保障速生树种根系对NO_(3)^(-)的补偿性吸收。高比根长、高比根表面积、低根直径和低根组织密度的形态性状组合,可有效提高根系在干旱瘠薄立地中对NO_(3)^(-)的吸收速率。

[Objective]Nutrient is an important limiting factor for tree growth in drought and barren sites,and the way trees absorbing and using nutrients in drought and barren sites determines their ecological adaptation strategies.In this paper,the kinetics of root nitrogen uptake and the coupling relationship between root morphological traits were measured in situ in the field,which laid a foundation for revealing the physiological function of trees in drought and barren environments.[Method]We took Prunus davidiana,Acer truncatum and Quercus variabilis in Baiwangshan Forest Park of Beijing as the research objectives.NO_(3)^(-)We used modified Hogland nutrient solution with concentration gradients to carry out in-situ NO_(3)^(-)measurement of root uptake kinetics in generally and extremely drought and barren site conditions,NO_(3)^(-)respectively.The relationship between root uptake rate and root functional traits was analyzed by Pearson correlation and path analysis.[Result]Tree species,site conditions and the interaction of above NO_(3)^(-)two factors all had an significant or extremely significant effect on root uptake rate and kinetic NO_(3)^(-)parameters.Three tree species all had high nitrogen affinity.The uptake rate of in the root of A.truncatum was lower,and it was significantly lower than that of P.davidiana and Q.variabilis under the above two site conditions.Under the site conditions of more drought and barren,fast growing tree species NO_(3)^(-) NO_(3)^(-)had compensatory absorption of.Root functional traits and the uptake rate of had a good coupling relationship.The result showed that the morphological traits of specific root length(SRL)and specific root NO_(3)^(-)surface area(SRA)had significantly positive effects on uptake rate of roots,while root diameter(RD)and root tissue density(RTD)had negative effects.In terms of branching structure traits,branching intensity NO_(3)^(-) NO_(3)^(-)and number of links had weak effects on uptake rate.[Conclusion]The uptake rate of P.davidiana and Q.variabilis with a faster growth rate decreases significantly under the extremely drought and barren site stress,while A.truncatum is the opposite.The“speed strategy”of increasing the maximum NO_(3)^(-)absorption rate and reducing nitrogen affinity ensures the compensatory absorption of by the roots of fast-growing tree species.The combination of morphological traits with higher SRL,higher SRA,lower RD NO_(3)^(-)and lower RTD can effectively improve the uptake rate of by roots in drought and barren sites.