湿润地区3种松属植物枝和根导水系统的效率-安全关系

Efficiency-Safety Relationships of Hydraulic Conducting System for Branch and Root of Three Pinus Species Growing in Humid Area

【目的】干旱导致的树木衰退甚至死亡并不局限于干旱地区,湿润区树木干旱适应能力弱,更易因水力失效而死亡。建立湿润区树木器官水平上的木质部结构与水力功能性状(包括输水效率和安全)的数量关系,是解答湿润区树木干旱致死机制的关键。【方法】以湿润地区马尾松、日本五针松和湿地松为对象,测定其枝条、根的木质部水力功能性状(导水率与栓塞抗性)和结构性状(管胞、纹孔特征等)。结合已发表的其他松属树种相关数据,检验了松属枝条与根的水力效率-水力安全权衡;定量分析了木质部输水效率(K_(s),单位边材面积的导水率)和栓塞抗性(P_(50),导水率损失50%时的木质部水势)的结构基础。【结果】1)对所研究的松属3个种,根比导率(K_(sr),根单位边材面积的导水率)>枝条比导率(K_(ss),枝条单位边材面积的导水率),根P_(50)>枝条P_(50);K_(ss)与K_(sr)正相关,枝条P_(50)与根P_(50)也呈正相关;3个种均属低效率低安全性树种。2)相关分析表明:K_(ss)与枝条P_(50)负相关,枝条存在效率-安全权衡;K_(sr)与根P_(50)的决定系数接近0(R^(2)=0.01,P=0.94),即根无效率-安全权衡。这种功能权衡关系由其解剖结构决定:K_(ss)与枝条P_(50)对结构的需求趋异(枝条有效率-安全权衡),而K_(sr)与根P_(50)对结构的需求趋同(根无效率-安全权衡)。3)冗余分析表明,枝条纹孔膜面积对K_(ss)解释度最高,枝条纹孔塞面积对枝条P_(50)解释度最高;根木材密度对K_(sr)解释度最高,根塞缘面积对根P_(50)解释度最高。【结论】枝条和根的输水效率、栓塞抗性主要由木质部结构决定,其中纹孔结构影响最大,木材密度与管胞壁厚度次之。马尾松、日本五针松和湿地松的枝条存在效率-安全权衡,而根不存在这种权衡,其相关的结构性状解释为:效率与安全的结构需求趋异存在权衡,趋同则无权衡。

【Objective】The decline and even death of vegetation caused by drought are not limited to arid areas.Species growing in humid areas have weak adaptation to drought,and thus are more likely to die from hydraulic failure.Establishing quantitative relationship between xylem anatomy and hydraulic function(including hydraulic efficiency and safety)at organ level of vascular plants is the key to understand the drought-induced mortality mechanism for plants growing in humid areas.【Method】Pinus massoniana,P.parviflora and P.elliottii were sampled to determine the hydraulic function(hydraulic conductivity,embolism resistance)and anatomical structures(tracheid traits,pit traits,etc.)of branch and root xylem.Combined with data from published studies,the trade-offs between hydraulic efficiency and hydraulic safety of branch and root for Pinus were examined;And the structural basis of xylem hydraulic efficiency(Ks,sapwood-specific hydraulic conductivity)and embolism resistance(P_(50),xylem water potential causing 50%loss of hydraulic conductivity)were analyzed quantitatively.【Result】1)For the three Pinus species,K_(sr)(root K_(s))>K_(ss)(branch Ks),root P_(50)>branch P_(50);K_(ss) was positively correlated with K_(sr),branch P_(50) and root P_(50) were also positively correlated;All the three species showed low efficiency and low safety.2)Correlation analysis revealed that:K_(ss) was negatively correlated with branch P_(50),branch exhibited an efficiency-safety trade-off.The correlation coefficient between K_(sr) and root P_(50) was close to 0(R2=0.01,P=0.94),there was no trade-off in root.Functional trade-off was determined by anatomical structure:K_(ss) and branch P_(50) had different structural requirements(there was an efficiency-safety trade-off in branch),while K_(sr) and root P_(50) had similar structural requirements(there was no trade-off in root).3)Redundancy analysis revealed that:K_(ss) was best interpreted by branch pit membrane area;Branch pit torus area had the highest interpretation for branch P_(50);K_(sr) was best interpreted by root wood density;Root pit margo area had the highest interpretation to root P_(50).【Conclusion】Hydraulic efficiency and embolism resistance of branch and root were mainly determined by anatomical structure,of which pit had the greatest influence,followed by wood density and tracheid wall thickness.This study demonstrated that there was an efficiency-safety trade-off in branch,but not in root.The anatomical structural bases behind this are:If the structural requirements are different,there is a trade-off between efficiency and safety,while the structural requirements are similar,then no trade-off.