Sap flow and responses to meteorological about the Larix principis-rupprechtii plantation in Gansu Xinlong mountain, northwestern China

The transpiration of trees plays a decisive role in the water balance of forest stands and in water yields from forested catchments, especially an artificial forest planted for the purpose of soil and water conservation in semiarid mountain ecosystem regions. For proper management of watershed ecosystems, quantification of water use, sensitivity and adaptation for artificial forest is needed. This study were monitored the sap flow for Larix principis-rupprechtii plantation by thermal dissipation probes (TDP), analyzed the correlation between the sap flow and the meteorological factors on daily and seasonal scale, and upscaled stand transpiration from individual sap flow measurements. Within a daily timescale, the net radiation (Ra), air temperature (AT), air humidity (AH), vapor pressure deficit (VPD) and wind speed (WS) showed a significantly positive correlation with sap flow velocity in day-time, but in the night-time sap flow had no significant correlation. Within a monthly timescale, the Ra, AT, WS, and VPD showed a significantly positive correlation with stand water use, whereas precipitation (Pr) showed a significantly negative correlation with stand water use. Our results also showed that the daily transpiration of L. principis-rupprechtii continued to increase with the increase of net radiation (Ra), until the late stages of growth season (except rainy and cloudy days), and the sap flow velocity showed an obvious hysteresis response to meteorological factors to alleviate plant water stress from June to October, while there was no significant correlation between day-time and night-time water use during the stage of germination and rapid growth in May. Besides, due to the relatively low temperature, the water consumption of forest stands was only about 151.05 mm during the whole growing season, and there was no obvious 'noon break' phenomenon in the whole growing season. These results indicated that L. principis-rupprechtii could manage the water consumption conservatively, and were appropriate for afforestation in the mountains ecosystem with high altitude and low temperature.