Does soil nutrient availability influence night-time water flux of aspen saplings?

Abstract

Previous investigations have been demonstrated that night-time water flux may increase or remain unchanged at low mineral nutrient availability. At the same time, it is a well-known fact that night-time water flux is relatively high in fast-growing species, which typically grow in fertile soil. To test the impact of soil nutrient deficiency on night-time water flux and fine-root acclimation in saplings of hybrid aspen (Populus tremula L.×Populus tremuloides Michx.), a growth chamber experiment was carried out. We set up a hypothesis that night-time sap flux density (F) and night-time water use percentage from daytime water use (NWU) are more intense in fertile conditions, in order to enhance or sustain the high intrinsic growth potential of hybrid aspen. The main limiting element in the low nutrient availability treatment (low-n) was nitrogen. The nitrogen concentrations of leaves and fine-roots exhibited the strongest (R2=0.95; P<0.001) positive relationship with NWU and foliar biomass. Both the night-time F and NWU were several times higher in the case of fertilized soil (high-n treatment) compared to low-n treatment (P<0.01). The differences in nocturnal (and in diurnal) F disappeared at the end of the period of sap flow measurements, when the foliage area of trees was almost full-grown. Endogenous increase in water flux during predawn hours was observable only in the high-n treatment. Significantly greater NWU (P<0.01) and specific fine-root length (P<0.05), but smaller fine-root biomass (P<0.05) in saplings of the high-n treatment potentially allow plants to use mass flow in soil more efficiently for transportation nutrients towards roots and to decrease construction costs for fine-root biomass production. Our results suggest that decreased night-time water flux as a result of strong nutrient (especially nitrogen) deficit could be characteristic to fast-growing tree species, which are adapted to grow in fertile soil.