摘要
高大树木木质部水分运输阻力和叶片蒸腾速率随树高的增加导致高度梯度水分供需矛盾.量化分析相关功能性状随高度的变异与性状协同关系,有助于深入理解植物的水分供需机制.该研究选取了生长在湿生同质园中的落羽杉(Taxodium distichum)及其变种池杉(T.distichum var.imbricatum),采用回归分析、单因素方差分析、通径分析等方法探究其水力(枝比导率(Ks)、叶比导率(K1)、导水率损失50％时的水势(P50)、最大蒸腾速率(Tr)、正午叶水势(ΨMD)、胡伯尔值(Hv)等)、光合(最大净光合速率(Pn))和碳经济性状(比叶质量(LMA)、木质部密度(WD))随高度的变异规律、协同关系以及种间性状差异.结果发现:(1)落羽杉和池杉K1、Hv、Pn和LMA随高度增加,其中Pn的增加可能与中冠层的Tr和最大气孔导度(Gs)下降有关.(2)种内性状间协同关系:落羽杉和池杉Ks与Hv显著负相关,落羽杉WD与Ks显著正相关,池杉WD与Hv极显著负相关.(3)落羽杉和池杉高冠层存在水分限制,由达西定律和Tr计算的理论水分供需比(r)量化了水分供需能力的下降,且它们r=0时的理论最大高度(落羽杉:32 m(95％置信区间上限:57 m);池杉:21 m(95％置信区间上限:27 m))在历史记载的最大高度范围内.(4)池杉各个冠层高度K1、Hv和LMA显著高于落羽杉,而Pn、Tr和Gs显著更低;池杉中、高冠层水力安全边界(HSM)显著更高,P50显著更低:池杉保守的水力策略与低资源获取能力导致其最大理论高度较低,而落羽杉激进的水力策略与高资源获取能力导致其最大理论高度较高.
Abstract
Aims The xylem water transport resistance and leaf transpiration rate of tall trees increased with tree height,resulting in a water supply-demand paradox along the tree height gradient.Quantitative analysis of the variation and coordination of related functional traits along tree height will be conducive to deeply understanding the water supply and demand mechanism of plants.Methods Here,Taxodium distichum and its variety T.distichum var.imbricatum grown in a mesic common garden were studied,with hydraulic(sapwood-specific hydraulic conductivity(Ks),leaf specific conductivity(Kl),the water potential causing 50％ loss of conductivity(P50),maximum transpiration rate(Tr),midday leaf water potential(ΨMD),Huber value(Hv),etc.),photosynthetic(maximum photosynthetic rate(Pn))and carbon economic traits(leaf mass per unit area(LMA),wood density(WD))measured.Traits variation and coordination along the tree height and traits differences between the same canopy of T.distichum and T.distichum var.imbricatum were analyzed by a series of methods,including regression analysis,one-way ANOVA,and path analysis.Important findings We found that:(1)K1,Hv,Pn and LMA in T.distichum and T distichum var.imbricatum increased along the height,and the increase of Pn may be related to the decrease of Tr and maximum operational stomatal conductance(Gs)in the middle canopy.(2)Coordination relationships between intraspecific traits:Ks in T.distichum and T.distichum var.imbricatum was significantly negatively related to Hv,WD in T.distichum was significantly positively related to Ks,and WD in T.distichum var.imbricatum was significantly negatively related to Hv.(3)There was water limitation in the higher canopy of T.distichum and T.distichum var.imbricatum.The theoretical water supply and demand ratio(r)calculated by Darcy's Law and Tr confirmed this limitation.The theoretical maximum height when r=0:T.distichum:32 m(upper bound of 95％ confidence interval:57 m);T.distichum var.imbricatum:21 m(upper bound of 95％ confidence interval:27 m),was consistent with the maximum height recorded historically.(4)K1,Hv and LMA in canopies of T.distichum var.imbricatum were significantly higher than those of T.distichum,while Pn,Tr and Gs were significantly lower;hydraulic safety margin(HSM)in the middle and higher canopies of T.distichum var.imbricatum was significantly higher,and P50 was significantly lower:The conservative hydraulic strategy of T.distichum var.imbricatum corresponded to lower resource acquisition capacity,which in turn resulted in lower maximum growth height.The radical hydraulic strategy of T.distichum corresponded to higher resource acquisition capacity,which in turn resulted in higher maximum growth height.
维普
万方数据