Responses of Sap Flow of Deciduous and Conifer Trees to Soil Drying in a Subalpine Forest

Chunhua Yan,Guo Qiu,Xiaonan Zhang,Yang Zhang,Bei Wang,Shinichi Takeuchi

doi:10.3390/f9010032

Abstract

Co-occurring species may adopt different water-use strategies to adapt to limited soil water. In Jiuzhaigou Valley, a continuous decline in soil water after an initial recharge from the thawing of snow and frozen soil in early spring was observed, but its effects on the sap flow dynamics of co-occurring species are not well understood. To clarify the species-specific water-use strategy, variations in sap flow and environmental conditions were investigated for two co-occurring species (Betula albosinensis Burk. and Pinus tabuliaeformis Carr.) in a mixed forest during a transition from the wet to dry period in 2014. Sap flow was measured using Granier-type thermal dissipation probes, and the soil-water content was measured using time-domain reflectometry probes for a successive period. Our study showed that B. albosinensis maintained relatively high transpiration until late into the season regardless of soil moisture, while the transpiration of P. tabuliformis showed a continuous decrease in response to seasonal soil drying. Sap flow for both species exhibited a marked hysteresis in response to meteorological factors and it was conditioned by the soil-water status, especially in the afternoon. We found that P. tabuliformis was sensitive to soil-water conditions, while for B. albosinensis, the sap flow was not very sensitive to changes in soil-water conditions. These results indicate that B. albosinensis could manage the water consumption conservatively under both dry and wet conditions. These results may have implications for evaluating the species-specific water-use strategy and carrying out proper reforestation practices.

Highlights

Jiuzhaigou Valley (JZG), located in the upper reach of the Jialing River, is a typical subalpine river valley in the transition zone between the northeast Qinghai-Tibet Plateau and the Sichuan Basin.Jiuzhaigou Valley has been rated as a World Heritage, National Nature Reserve and a world-class place of interest, due to the so-called “color forests” in fall and the fantastic beauty of the water
The saturation values for B. albosinensis were almost the same under different different soil‐water conditions, while for P. tabuliformis a higher saturation value was observed under soil-water conditions, while for P. tabuliformis a higher saturation value was observed under wet wet conditions. These results further indicated that the stomata for B. albosinensis showed little conditions
≥0.4 and the relative extractable water (REW)

Summary

Introduction

Jiuzhaigou Valley (JZG), located in the upper reach of the Jialing River, is a typical subalpine river valley in the transition zone between the northeast Qinghai-Tibet Plateau and the Sichuan Basin.Jiuzhaigou Valley has been rated as a World Heritage, National Nature Reserve and a world-class place of interest, due to the so-called “color forests” in fall and the fantastic beauty of the water. It was mainly the color forests that formed and the ratio between the deciduous and conifer species greatly changed after the forest harvest from 1966 to 1978 [1] Betula albosinensis Burk. In JZG is one of the main broadleaved species forming the color forests. The local administration is greatly concerned with the succession trend and the rate at which the broadleaved species (e.g., B. albosinensis) are replaced by the conifers (e.g., Pinus tabuliaeformis Carr.) [2]. With runoff decreasing and streams drying up, the water landscape of Jiuzhaigou Valley has been affected [6,7,8,9]. For proper reforestation practices and landscape management, common species in JZG need to be investigated to understand their water-use strategies under different climatic and soil-water conditions and to determine whether they are suitable for developing a sustainable color forest landscape

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Conclusion