Abstract:

Objective: This study aims to accurately quantify the transpiration characteristics of typical plantations in the semi-arid area and their response to meteorological factors and soil moisture, and to explore the differences in water use strategies among tree species, so as to provide a theoretical basis for integrated forest-water management in this area. Method: From May to October in 2022, the plantations of main afforestation tree species of Larix principis-rupprechtii and Betula platyphylla were selected for this study in the small watershed of Diediegou in the semi-arid area of Liupan Mountains. A fixed sample plot was set up for each type of plantation with the size of 30 m × 30 m. A total of 12 sample trees with different diameters at breath height (DBH) in each plot were chosen for monitoring the sap flow density of trunk. Meanwhile, the meteorological parameters and soil moisture of 0–60 cm soil layers were measured continuously. The differences in transpiration response of the two plantations to the daily potential evapotranspiration (PET) and relative extractable soil water (REW) were analyzed. Result: 1) From July to October, the daily transpiration of L. principis-rupprechtii and B. platyphylla plantations was 0.63 and 0.54 mm·d^?1, respectively, with the transpiration for the former being 0.09 mm·d^?1 higher than that for the latter. The daily transpiration of both plantations firstly increased and then decreased with changing month, and reached their maximum values in July, at 1.38 and 1.45 mm·d^?1, respectively. 2) The responses of daily transpiration of both plantations to PET exhibited an exponential function relationship, that is, the daily transpiration increased gradually with rising PET and finally tended to be stable, but the response trends were different among different REW levels. The increase rate of daily transpiration of L. principis-rupprechtii plantation with rising PET was relatively low when the REW was < 0.3, and rapidly increased after the REW was > 0.3, but the difference in the rates among REW levels was small. In contrast, the daily transpiration of B. platyphylla plantation continued to increase at a relatively uniform rate with rising PET in the whole variation range of REW. 3) The responses of daily transpiration of both plantations to REW also followed an exponential function relationship. However, there was a significant difference in the response trend of daily transpiration between the two plantations, that is, the increase rate of daily transpiration of L. principis-rupprechtii plantation increased with rising REW was low when PET < 2 mm·d^?1, but it rapidly increased when PET > 2 mm·d^?1, and showed little difference among the PET levels. In contrast, the increase rate of daily transpiration of B. platyphylla plantation with rising REW was more uniform and showed a continuous increase in the whole variation range of PET. Conclusion: The response of daily transpiration of L. principis-rupprechtii plantation to PET and REW is more sensitive than that of B. platyphylla plantation to PET and REW. When PET < 2 mm·d^?1 or REW < 0.3, the daily transpiration of L. principis-rupprechtii plantation is significantly higher than that of B. platyphylla plantation. When PET > 2 mm·d^?1 or REW > 0.3, the daily transpiration of L. principis-rupprechtii plantation increases rapidly to its maximum and then remains stable with the increase of PET or REW, while the daily evapotranspiration of B. platyphylla plantation tends to its maximum in a relatively uniform manner. Therefore, in the semi-arid areas with limited water, the water consumption for the transpiration of L. principis-rupprechtii plantation is higher than that of B. platyphylla plantation, and the transpiration of B. platyphylla plantation is more obviously restricted by the soil drought stress.

Key words: transpiration, soil water, potential evapotranspiration, Larix principis-rupprechtii plantations, Betula platyphylla plantations