摘要
通过分析具不同水力结构的马占相思、荷木和粉单竹液流变化格局的偏度和时滞,探讨液流的空间分布特征及对冠层蒸腾的影响。结果表明:荷木的液流格局偏度和时滞随树木胸径的增加呈减小的趋势,但马占相思由于冠层开阔和林分分化程度高而规律不明显,粉单竹液流偏度随胸径减少,由于冠幅较小,接受的光照较均匀,个体间的时滞差异不明显,但时滞值比胸径近似的荷木小。树干水分传输过程中存在液流再分配的现象,边材的导水效率可能是影响时滞的重要原因。冠层蒸腾的空间异质性与树木储存水有关,大树储存水较多,冠层蒸腾的异质性小;小树储存水较少,液流被优先分配到光照充足的东南方位,导致冠层蒸腾较高的异质性。旱季受土壤水分的限制,大树储存水对蒸腾的贡献大于湿季,而小树蒸腾由于受到储水容量的制约,储存水对蒸腾的贡献小于湿季。冠层接受光照的迟或早以及辐射量的大小是引起蒸腾时间变化格局和树干不同方位液流格局差异的重要原因,但液流的横向交换弱化了这种现象,往往是个体间的差异掩盖了方位的差异。湿季较小胸径的树木比偏值(枝下高与胸高处液流偏度的比值)大于旱季,而较大胸径的树木比偏值恰好相反,总体而言,比偏值随着胸径的增加而逐渐下降。
In this article the skewness of sap flow pattern and the time lag between stem sap flow and canopy transpiration in Acacia mangium,Schima superba and Bambusa chungii which were characterized with different hydraulic structures were analyzed.The spatial variation in sap flow within tree trunk and its effect on transpiration were also investigated.The results showed that both skewness and time lag in S.superba decreased with the increment of stem diameter at breast height（DBH）.However,similar changes in A.maingum were not significant because of open canopy of the stand and differentiation among individuals.The skewness of sap flow pattern in B.chungii increased with DBH,but no significant relation between time lag and DBH was observed because of its smaller canopy that evenly received radiation.However the time lag in B.chungii was smaller than in S.superba with similar DBH.Re-allocation of sap flow within stem during water transport implied that hydraulic conductivity was an important factor affecting time lag.The spatial heterogeneity of canopy transpiration was related to water storage.Larger tree had relative more water storage and therefore lower heterogeneity.In smaller trees that normally had less water storage,sap flow was preferentially allocated to the east and south branches where more sunlight was received than in the other directions,which leaded to higher heterogeneity in canopy transpiration.Being restricted by soil moisture during dry season,the water storage in larger trees contributed more contribution to transpiration than in wet season.In contrast,contribution of water storage to transpiration in smaller trees was less in dry season than in wet season,since the transpiration was more restricted by the quantity of stored water.Being radiated earlier or later and the intensity of radiation on canopy may have caused differences in time pattern of sap flow and its azimuthal difference in tree stem.However,the transversal exchange of sap flow attenuated this difference and among-trees difference
出处
《生态学报》
CAS
CSCD
北大核心
2012年第22期7018-7026,共9页
Acta Ecologica Sinica
基金
国家基金项目(30871998
41030638
31170673)
关键词
蒸腾
液流密度
偏度
时滞
transpiration
sap flux density
skewness
time lag
