Effects of air humidity and soil nitrogen source on diurnal water flux in hybrid aspen and silver birch

P. Kupper, G. Rohula-Okunev, M. Sell, O. Kangur, A. Sellin
A growing body of evidence suggests that water uptake of plants depends on available N forms. The objective of this study was to investigate tree water flux at different levels of relative humidity (RH) of air, soil N source (ammonium, nitrate), and N contents. Aspen saplings demonstrated lower (pKLEINERDAN0.05) night-time and daytime sap flux densities (F) under high-RH treatment (diurnal RH ~80%) compared with a moderate-RH treatment (RH ~80 and 65% during night and day, respectively). The soil-to-leaf hydraulic conductance (GT) declined toward the end of the night, whereas the late-night and daytime GT did not differ between the RH treatments. The soil N source and content did not affect diurnal F and GT in aspen. In birch saplings, daytime measurements showed the lowest F, GT, stem hydraulic conductance, specific and leaf-specific conductivity of xylem in the high-RH treatment. No significant differences were observed in F and GT between the RH treatments in birch at night. In contrast with aspen, the late-night GT was lower (pKLEINERDAN0.05) than the daytime GT in both high and moderate-RH treatments. In birch, the daytime F was higher (p<0.05) in nitrate compared to ammonium-fed plants, whereas the night-time F did not depend on the N source. Although GT was not affected by the N source, the hydraulic conductance of the root system and the whole-plant hydraulic conductance were higher (p<0.05) in nitrate-fed plants. The results suggest that RH and soil N source modify F and hydraulic efficiency of trees, whereas the trees' responses evidently depend on water and N-use strategies of particular species.
Kupper, P., Rohula-Okunev, G., Sell, M., Kangur, O. and Sellin, A. (2020). Effects of air humidity and soil nitrogen source on diurnal water flux in hybrid aspen and silver birch. Acta Hortic. 1300, 153-160
DOI: 10.17660/ActaHortic.2020.1300.20
ammonium, hydraulic conductance, night-time, nitrate, transpiration

Acta Horticulturae