the hourly transpiration rate of Cinnamomum camphora was measured from June 2019 to October 2020 using the Grainer-type thermal dissipation probes. Meteorological factors and soil water content were simultaneously monitored during the study period. To deepen the understanding of the relationship between plant physiological changes and environmental changes
and to provide a basis for improving the accuracy of transpiration predicting model
this study analyzed the relationship between the transpiration of C. camphora and the main meteorological factors at different periods during the day. The variation characteristics of time lag and the change of hysteresis correction on the predicting model of transpiration were also investigated. The results showed that the time lag between transpiration and solar radiation is counterclockwise
and that between transpiration and saturated water vapor pressure or temperature is clockwise during the growing seasons (from June to October). Based on Gauss equations
it was found that on average transpiration in the growing seasons of 2019 and 2020 lagged behind solar radiation by 0.94 hours
and advanced by 2.60 and 2.61 hours on saturated vapor pressure difference and temperature. This time-lag effect was caused by the different responses of transpiration to meteorological factors at different stages of the day. In the rising stage (7:00-11:00)
transpiration was more sensitive to changes of solar radiation than that in the descending stage (17:00-21:00). On the contrary
in the rising stage
transpiration was less sensitive to variation in saturated vapor pressure and temperature than that in the descending stage. The time-lag effects between transpiration and solar radiation or saturated vapor pressure or temperature had obvious seasonal variation. There were certain differences in the hysteresis loop area between the growing seasons of 2019 and 2020
but the maximum area appeared in October and the minimum area appeared in August or September. On the hourly scale
when soil moisture was sufficient
the hysteresis added with the increase of the main daily mean meteorological factors
but under soil moisture stress
the time lag did not change significantly with the increase of the major daily mean meteorological factors. After correcting time lag
the determinants of the regression equations of transpiration and solar radiation increased by 4% and 9%
and the coefficient of determination of the regression equations of transpiration and integrated meteorological factors constructed by principal component analysis increased by 7%. Therefore
eliminating time lag could improve the accuracy of transpiration predicting model.
Phillips N, Oren R, Zimmermann R, et al. Temporal patterns of water flux in trees and lianas in a Panamanian moist forest[J]. Trees, 1999, 14(3):116-123.
Zhang R F, Xu X L, Liu M X, et al. Hysteresis in sap flow and its controlling mechanisms for a deciduous broad-leaved tree species in a humid karst region[J]. Science China Earth Sciences, 2019, 62(11):1744-1755.
Liu H, Guo J B, Liu Z B, et al. Time-Lag effect between sap flow and environmental factors of Larix principis-rupprechtii Mayr[J]. Forests, 2019, 10(11):642-650.
O'Grady A P, Eamus D, Hutley L B. Transpiration increases during the dry season:Patterns of tree water use in eucalypt open-forests of northern Australia[J]. Tree Physiology, 1999, 19(9):591-597.
Zeppel M J B, Murray B R, Barton C, et al. Seasonal responses of xylem sap velocity to VPD and solar radiation during drought in a stand of native trees in temperate Australia[J]. Functional Plant Biology, 2004, 31(5):461-470.
Granier A. Evaluation of transpiration in a Douglas-fir stand by means of sap flow measurements[J]. Tree Physiology, 1987, 3(4):309-320.
Dingman S L. Physical hydrolog[M]. Illinois:Waveland Press, 2015:28-86.
Oishi A C, Hawthorne D A, Oren R. Baseliner:An open-source, interactive tool for processing sap flux data from thermal dissipation probes[J]. SoftwareX, 2016, 18(5):139-143.
Wang H L, Doerthe T, Chris S. Hysteretic response of sap flow in Scots pine (
Pinus sylvestris
) to meteorological forcing in a humid low-energy headwater catchment[J]. Ecohydrology, 2019, 12(6):1-31.
Bai Y, Li X Y, Liu S M, et al. Modelling diurnal and seasonal hysteresis phenomena of canopy conductance in an oasis forest ecosystem[J]. Agricultural and Forest Meteorology, 2017, 246:98-110.
Chen L X, Zhang Z Q, Li Z D, et al. Biophysical control of whole tree transpiration under an urban environment in Northern China[J]. Journal of Hydrology, 2011, 402(3/4):388-400.
Bai Y, Zhu G F, Su Y H, et al. Hysteresis loops between canopy conductance of grapevines and meteorological variables in an oasis ecosystem[J]. Agricultural and Forest Meteorology, 2015, 214/215:319-327.