| This paper selected three typical tree species (Quereus aeutissima, Chinese fir,Phyllostachys edulis) located in the Yangtze River Delta region, analyzed the change rules ofthe transpiration based on the observation of leaf transpiration rate and the continuous locatingobservation of the sap flow rate and environment factors by using LI-6400, sap flow meter andmini weather station. The main results are as follows:(1)The transpiration rate and net photosynthetic rate of Q.aeutissima, Chinese fir,Phyllostachys edulis showed distinct diurnal change rhythms in different seasons.The diurnalchange characteristic of water use efficiency had difference among the three trees. Stomatalconductance and solar radiation had bigger influence on the transpiration rate.(2)The sap flow rate showed distinct diurnal change rhythms both in sunny and cloudydays in different seasons. The leading environmental factors that influenced the sap flow rateexisted seasonal differences. The leading environmental factors of Q.aeutissima in spring,autumn and winter were vapor pressure deficiency (VPD), which was air temperature in summer.The leading environmental factors of Chinese fir in spring, summer, autumn and winter wereVPD, air relative humidity, VPDand solar radiation. The leading environmental factors ofPhyllostachys edulis in spring, summer were solar radiation, which were VPDin autumn andwinter. Air temperature and solar radiation were the important environment factors thatinfluence the average daily sap flow rate of Q.aeutissima, which were soil temperature thatinfluenced the average daily sap flow rate of Chinese fir and Phyllostachys edulis.(3)The relationship between sap flow of Q.aeutissima and diameter at breast, sapwoodarea, radius of canopy breadth showed logarithmic function relationship. The relationshipbetween sap flow of Chinese fir and diameter at breast, tree height, sapwood area, radius ofcanopy breadth showed exponential function relationship. The same with the tree height and theradius of canopy breadth of Q.aeutissima. The multiple linear regression models between sapflow rate, daily sap flow and impact factors were established by stepwise regressionanalysis.These models was all significant that could explain the change characteristics of sapflow rate and daily sap flow.(4)The nocturnal sap flow density showed the values of before midnight were bigger thanthat of after midnight. The nocturnal sap flow density of Chinese fir was bigger than Q.acutissima. At the temporal scale of an hour, vapor pressure deficiency could better explain thechange of nocturnal sap flow of Q. acutissima of mostly months. The leading environmentalfactor of Chinese fir nocturnal sap flow was soil water content. At the temporal scale of a day, the correlation between nocturnal sap flow and diurnal sap flow, temperature showed asignificant correlation. The monthly nocturnal sap flow of Q. acutissima and Chinese firshowed significantly difference. The nocturnal sap flow of Q. acutissima and Chinese fir washighest in April and July, with the values of73.62kg and77.23kg. Tree characteristics couldbetter explain the change of monthly Q. acutissima nocturnal sap flow. The sapwood area couldbetter explain the change of monthly Chinese fir nocturnal sap flow. The impact caused bynocturnal sap flow on whole-tree transpiration in not deciduous period of Q. acutissima and allthe time of Chinese fir was not significantly.(5)Individual tree canopy transpiration model based on Penman-Monteith method couldmore accurate simulate the variation characteristics of tree canopy transpiration of the typicaltrees. The relationships between DBH and sapwood area of Q. acutissima and Chinese fir wererespectively power function and index function. The forest canopy transpirations of Q.acutissima, Chinese fir and Phyllostachys edulis were respectively273.54mm,333.15mm and563.04mm. |
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