Effects of influencing factors on stem sap flow in Larix gmelinii in northern Da Hinggan Mountains, northeastern China.

In this study, by Granier thermal dissipation probe (TDP) method, Larix gmelinii transpiration was continuously observed in northern Da Hinggan Mountains, northeastern China from May to September in 2012. Integrated with simultaneous environmental factors, transpiration of L. gmelinii and its relationship with influencing factors were investigated. The results showed that: 1) L. gmelinii transpiration rate showed significant diurnal variations, which presented unimodal curves in sunny and cloudy days, and bimodal or multimodal curves in rainy days, respectively. Transpiration rates of sunny and cloudy days were higher than those of rainy days. The ratio list of night sap flow flux accounting for a full day's flow flux was: sunny day(5.91%) rainy day (4.88%) cloudy day(2.57%). In the case of high temperature and no rain, the sap flow presented a decreasing trend with the rainless and hot days increasing. 2) Daily peak of L. gmelinii sap flow rate was high in June to August, and it reached the highest value of 23.6 cm3 / (cm2·h) in July, the transpiration in June to August accounted for 80% of the total water consumption during observation period. The daily peak in May was less and it got the lowest value of 2.03 cm3 / (cm2·h) in September. 3) Good correlation existed between sap flow rate and environmental factors, just as the coefficient of determination of their multiple regression model was 0.79. Further correlation analyses indicated that main environmental factors influencing sap flow density in the growing season were vapor pressure deficit and photosynthetic active radiation. 4) The total transpiration of L. gmelinii stand during the growing season was 566.49 t/ hm2, i. e. 56.65 mm, accounted for 12% of rainfall in the same period.