| Thermal dissipation method and ICT-2000TE (Transpiration-Environment) automatic measuring system for tree transpiration and environmental factors were applied to study comparatively the stem sap flow dynamics of main tree species (Quercus mongolica, Fraxinus mandshurica, Pinus koraiensis, Phellodendron amurense, Juglans mandshurica, Betula platyphylla, Tilia amurensis and Pinus sylvestris) in field under the consistent tree status and environmental factors. The tree biological and environmental factors influencing the diurnal and seasonal stem sap flow were discussed, and mathematical models on the responses of the diurnal sap flow to the related environmental factors were developed during the growing season.Diurnal course of each tree stem sap flow density exhibited mostly mono-peak patterns during clear sky days in the growing season, except that Betula platyphylla, Fraxinus mandshurica (big), Pinus sylvestris and Phellodendron amurense showed unregular diurnal course, there was significant peak value during day time, but sap flow quantity in the night higher than any other measurement in the middle of October in the following species: Tilia amurensis, Juglans mandshurica, Quercus mongolica, Pinus koraiensis, Fraxinus mandshurica (small). Maximum value of all tree sap flow density occurred mostly in 9a.m.-14p.m. (69%-91%) in diurnal course. Maximum value of ring-porous species-Frawzus mandshurica (big), Fraxinus mandshurica (small), Phellodendron amurense, Quercus mongolica; semi ring-porous Juglans mandshurica; diffuse-porous Betula platyphylla, Tilia amurensis and non-porous Pinus sylvestris, Pinus koraiensis were as following: 430.53, 516.36, 234.00, 625.93, 945.83, 199.49,507.93, 142.43, 286.21cm3cm"V in diurnal course during the growing season. The sap flow persisted after leaf senescence until the mid-October.Each tree sap flow density had significant seasonal change. Betula platyphylla, Fraxinus mandshurica (big), Pinus sylvestris showed two-peak curve pattern during growing season. Maximum value occurred in July and at the end of August. There is low value in the middle of August due to soil water deficient. Seasonal sap flow change of Juglans mandshurica, Tilia amurensis, Phellodendron amurense were one-peak curve patter, maximum value 119.64, 83.36, 44.57cm3cm-2h-1 respectively; Pinus koraiensis, Quercus mongolica, Fraxinus mandshurica (small) showed two-peak pattern during growing season, the maximum value was 42.32, 73.62, 65.39cm3cm-2h-1 respectively, occurred at the beginning and middle of September. Seasonal average sap flow density (cm3cm-2h-1) in the fine day during growing season was in the following order: Juglans mandshurica (29A4)>Fraxinus mandshurica (small)(17.97)>2wercus mongolica (17.68)>Fraxinus mandshurica (big) (\5.50)>Phellodendron amurense (\5.21)>Tilia amurensis (14.91)>Pinus koraiensis (12.10)> Pinus sylvestris (7.59)> Betula platyphylla (7.27).Result of statistical analysis indicated that PAR and VPD were the major factors(71%-92%) affecting each tree sap flow density on clear sky days in different growth period. Results of relation between seasonal sap flow and environmental factors showed that seasonal sap flow of Quercus mongolica, Fraxinus mandshurica (small), Fraxinus mandshurica (big), Tilia amurensis, Phellodendron amurense were not impacted by any environmental factors. Stepwise regression of seasonal sap flow of Betula platyphylla, Pinus sylvestris, Juglans mandshurica, Pinus koraiensis and related significantly environmental factors showed that: only soil minimum temperature was selected in the equation of Pinus koraiensis, Pinus sylvestris and Juglans mandshurica (Adjust R2=0.47-0.67); Seasonal sap flow of Betula platyphylla was determined by air minimum temperature (Adjust R2=0.49).Diurnal sap flow course changed from mono-peak curve to two-peak curve or mono-peak curve's maximum value was not corresponding to PAR maximum value after natural reduced leaf area of Betula platyphylla in July during full growing season. Sap flow quantity in the nigh...
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