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Azimuthal variation in nighttime sap flow and its mainly influence factors of Populus tomentosa |
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| Affiliation: | Ministry of Education Key Laboratory of Silviculture and Conservation, Beijing Forestry University, Beijing 100083, China School of Ecology and Environment, Inner Mongolia University, Hohhot 010021, China Beijing Academy of Forestry and Pomology sciences, Beijing 100093, China Faculty of Agriculture, Forestry and Medicine, the Open University of China, Beijing 100039, China |
| Abstract: | Aims To clarify the azimuthal regularity of nocturnal sap-flow activities of Populus tomentosa, which includes nocturnal transpiration (Nt) and stem water refilling (Sr), and explore the main impact factors of Nt and Sr in different orientations. Methods The thermal dissipation method was used to monitor the nocturnal sap flow of P. tomentosa planted in wide and narrow rows patterns. The image method was used to distinguish Nt and Sr. An automatic weather station measured global solar radiation (Rs, kW·m-2), air temperature (Ta, ℃), relative humidity (RH, %), wind speed (v, m·s-1) and other environmental factors. Mechanical tensiometers measured soil water potential (ψ, kPa). The differences of nocturnal sap-flow among orientations and their main impact factors were determined by comparing the magnitudes of Nt and Sr and their correlations with the impact factors. Important findings The results showed that, for trees on the east-wide-row, the west orientation has the largest Nt and Sr. The Sr in the west orientation was significantly larger than that in the other three orientations. In contrast, north oriented Nt was significantly smaller than that in the other three orientations. There was no significant difference in Nt and Sr among other orientations and the proportion of Sr accounted for the nighttime sap flow (Sr/Q) in all orientations. For trees on the west-wide-row, Nt and Sr in the west orientation were also the largest, and the Sr in the west orientation was significantly larger than that in the east and south. The Nt in the south orientation was the smallest and significantly smaller than that in the west and north. There was no significant difference in Nt and Sr among other orientations. The Sr/Q in the south orientation was significantly larger than that in the other three orientations. The Nt and Sr had significantly positive correlations with vapor pressure deficiency (VPD), and Nt and Sr in some orientations had significant correlations with Ta and RH, but Nt and Sr in all orientations had no significant correlation with v and ψ. The variation coefficient of Nt and Sr among the four orientations (NtCV and SrCV) had no significant correlation with VPD, Ta, RH, v and ψ. In addition, the Sr was significantly affected by the daytime sap flow. In conclusion, there were significant differences in nocturnal sap flow of P. tomentosa such as Nt and Sr, with west being the most dominant. VPD was the mainly meteorological impact factor of Nt and Sr in all orientations at night. |
| Keywords: | Populus tomentosa')" >Populus tomentosa, orientation, nighttime transpiration')" >nighttime transpiration, stem refilling')" >stem refilling |
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