Effects Of Spring Phenology On Water Use And Stem Photosynthesis Of Phyllostachys Pubescens

Moso bamboo(Phyllostachys edulis)is one of the most widely naturally distributed and artificially cultivated bamboo species in China.Therefore,Moso bamboo is of great economic and ecological importance for China.In spring,Moso bamboo takes only 3 months to finish sprouting,growing height,flushing branches and leaves,and this period is thus usually called as fast growing period.Because culms are connected via underground rhizome system,water and carbon transfer from old established culms is thought to be one important way to meet the growing need for the newly sprouted culms with few leaves.However,the water and carbon transfer may impact their own need of the old established culms,especially those changing leaves during spring.Additionally,chlorophyll was found in stems of the Moso bamboo culms,which thus indicates a photosynthesis potential for newly sprouted culms.The culm photosynthesis may be another way to facilitate their own height growing,but it is not explored and verified yet.Therefore,to deepen our insight on the fast growing mechanism of Moso bamboo,it is crucial to explore the water and carbon acquirement ways of newly sprouted culms and the induced water and carbon redistribution among culms of different ages in a stand.This study was conducted in a bamboo stand in Ping-shan experimental base of Zhejiang A&F university in Lin'an district,Hangzhou,China.During the fast growing period of newly sprouted culms(April 6,2018-June 30,2018),thermal dissipation probe(TDP)method was applied to measure sap flow densities of bamboos of three different culm ages.At the end of the fast growing period and the leaf spreading stage of freshly sprouted bamboo,sap flow densities and photosynthesis intensities were measured simultaneously.This study aims to explore the age effect in early spring phenology of bamboo on its water use characteristics and water redistribution in stand and the coordination of carbon and water in newly sprouted culms in its fast growing period.The results indicated that:(1)Age has a significant impact on culm water use amount during the growing season of spring.In the early spring periods(Period ? and Period ?),when freshly sprouted culms start their height growth,the culm transpiration rate ranked as two-year-old culms(A2)> one-year-old culms(A1)>three-year-old culms(A3).Water use amount of A1 started to increase significantly in the middle of Period ? and was close to that of A2.In the later spring,when the newly established culms started togrow branches(Period ?)and leaves(Period ?),and finish leaf growth(Period ?),culm water use amount ranked as A1 > A2 > A3.In addition,during Period ?,? and ?,water use amount of A1,A2 and A3 culms showed different changing patterns,with a consistently increasing trend for A1,a consistently decreasing trend for A2 and relatively stable for A3.(2)The water use of Moso bamboo is affected by soil humidity,radiation,water vapor pressure deficit and other environmental factors.Under the condition of sufficient soil moisture,the water use of bamboo is mainly influenced by radiationand water vapor pressure deficit.(3)The water use of Moso bamboo is also affected by age.For the culms of A1 and A3,both of which changed leaves during the studies period,they showed different water use.The potential reason for the water use difference may lay in lacking ability to renew conducting tissues in stems by secondary growth.Therefore,water conduction tissue in older culms may be embolized more and thus water use is less.(4)The stems of newly sprouted culms can perform photosynthesis and provide some carbohydrates for self-own growth.However,at different periods,the culm photosynthesis intensities varied greatly.The photosynthetic intensity of the stem in the period before flushing leaves was about 10 times higher than that in the period before flushing leaves.The potential reason could be that,before spreading branches and leaves,only the stem of new bamboo can carry out photosynthesis,and thus,exert its full photosynthesis ability for carbon sequestration.After spreading branches and leaves,the leaves of new bamboo replaced the stem as the main photosynthetic tissue,which reduced the dependence on stem photosynthesis.Finally,the intensity of photosynthesis was weakened.(5)There was a strong correlation between photosynthesis and light intensity,atmospheric relative humidity,stem temperature and stem sap flow density.Among them,there was a strong positive correlation with light intensity and stem temperature,and a strong negative correlation with atmospheric relative humidity.The correlation with stem sap flow density was different in different periods.In the early stage of branch and leaf flushing of newly sprouted culms,the daily pattern of sap flow density was opposite in newly sprouted and established culms.Because newly sprouted culms could not pull the stem sap flow by the transpiration of leaves,the water supply to them during the daytime was small.In contrast,old established culms consumed a lot of water due to their strong transpiration.However,at night,the transpiration of established culms is very small,they can supply more water than duringdaytime to newly sprouted culms.The correlation analysis showed a strong negative correlation between stem sap flow density and stem photosynthesis after flushing branches and leaves.