The influence of air temperature and relative humidity on dynamics of water potential in Betula pendula (Betulaceae) trees

Linear multiple models were developed to describe diurnal and seasonal dynamics of water potential (Ψ) of the foliated shoots in the plants of Betula genus related to air temperature and relative humidity in the middle taiga (southern Karelia). The results of the study revealed unidirectional changes, but different effect strength of air temperature and relative humidity on Ψ of the foliated shoots of common silver birch (Betula pendula Roth) and curly (Karelian) birch (Betula pendula Roth var. carelica). It was shown that increasing air temperature 1°С results in similar decreasing of Ψ value equal to 0.037–0.038 MPa in both of the birches (p > 0.05). Since the diurnal air temperature range achieves 10–15 °С, the contribution of this factor may be up to 0.57 MPa. On the contrary, the contribution of relative air humidity to Ψ value differs significantly in distinct birch forms (p < 0.05). In this case the change range of Ψ value in silver birch and curly birch may be up to 0.46 (0.015 MPa/1 % RH) and 0.52 МПа (0.017 MPa/1 % RH), respectively. The results indicate that curly birch responds to the increase of relative air humidity with higher magnification of Ψ in comparison with common silver birch