夏季干旱期新老毛竹水分传输和水分竞争研究

[Objective]As a giant woody bamboo species distributing widely,Moso bamboo(Phyllostachys edulis)has high ecological and economic values to the local communities.Extreme events with high temperature and intensive drought occurred frequently in recent years,which had led to significantly higher mortality rate of newly sprouted culms,posing a threat to the post-disaster recovery and succession of Moso bamboo forests.To deeply understand the mechanism of differential age-specific drought-induced mortalities on Moso bamboos,This study focused on exploring the age-specific water-use and hydraulic response of newly sprouted and established culms,and the water share and competition via physiological integration of rhizomes between the newly sprouted and established culms.[Method]During summer(July to September)in 2020,we conducted a drought treatment by setting up a manipulated throughfall exclusion plot within a bamboo forest of approximately 10 ha in Lin'an city(30°14′N,119°42′E),Zhejiang Province,China.To improve the measurement accuracy of Thermal Dissipation Probe(TDP),we calibrated the original empirical formulas for Moso bamboo with different ages in laboratory before applying TDP.In the field we have continuously monitored the environmental factors and sap flow rates in newly sprouted and established culms and rhizomes between them,and periodically measured the light response curves of leaves and the percentage loss of xylem conductivity of culms,branches and leaves.[Result]The results showed that:(1)There are significant differences on the empirical formulas of TDP on bamboo culms with different ages,and it is necessary to build age-specific correction for different ages.(2)By applying corrected age-specific TDP formulas,we found that sap flow densities and daily water use of the newly sprouted culms were higher than that of the established culms.But the water consumption of bamboos was significantly reduced with the progressing and intensifying of the summer drought.(3)Radiation and soil moisture were the two main factors limiting sap flow of established culms and newly sprouted culms in the ambient condition.However,drought changed the limiting factors from radiation to soil moisture for established culms,but no change appeared in those newly sprouted culms.At the same time,soil moisture was also the main limiting factor of physiological indexes of Moso bamboos under drought,which significantly decreased photosynthesis and increased percentage loss of conductivity of both newly sprouted and established culms.(4)During drought,the rhizome provided water sources for the transpiration of Moso bamboo and provided water to refill the culms through nighttime sap flow for the newly sprouted culms,but this support mechanism to alleviate drought is limited.[Conclusion]In summary,compared to established culms,the newly sprouted culms have stronger competition for water in the rhizome system under drought conditions,but their higher transpiration demand led to more susceptible hydraulic structures.Thus,previously observed higher mortality of the newly sprouted bamboos may be attributed the increasing xylem embolism and eventually hydraulic failure that could not recover during a continuous severe drought.This study will provide theoretical support for drought-coping management of Moso bamboo forests under climate change.