JOURNAL OF NANJING FORESTRY UNIVERSITY ›› 2021, Vol. 45 ›› Issue (1): 131-140.doi: 10.12302/j.issn.1000-2006.202001025

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Stand transpiration characteristics of Larix principis-rupprechtii plantation and their influencing factors in Liupan Mountain

YU Songping1,2(), LIU Zebin2, GUO Jianbin1,*(), WANG Yanhui2, YU Pengtao2, WANG Lei1   

  1. 1. College of Soil & Water Conservation,Beijing Forestry University, Beijing 100083, China
    2. Institute of Forest Ecology, Environment and Protection, Chinese Academy of Forestry, Key Laboratory of Forestry Ecology and Environment of National Forestry and Grassland Administration, Beijing 100091, China
  • Received:2020-01-09 Accepted:2020-05-13 Online:2021-01-30 Published:2021-02-01
  • Contact: GUO Jianbin E-mail:m18342800419@163.com;jianbinguo@bjfu.edu.cn

Abstract:

【Objective】Stand transpiration, a key process in the soil-plant-atmosphere continuum, is an important water output item in the forest ecosystem, accounting for more than 50% of the total forest evapotranspiration. Therefore, exploring the stand transpiration response to environmental factors can provide a theoretical basis and data support for the scientific guidance of afforestation and integrated management of forest and water.【Method】At the Ningxia Liupan Mountain positioning station of the National Forestry and Grassland Administration, the sap flow of a Larix principis-rupprechtii plantation during the growing season (May-September) of 2016 was observed in the semi-humid area of Liupan Mountain and scaled-up for an estimation of stand transpiration. Meanwhile, the atmospheric factors outside the forest and the soil water content under the forest were simultaneously observed and the response of stand transpiration to atmospheric factors and root-zone (0-60 cm soil layer) soil water content was analyzed.【Result】 ① During the study period, the daily stand transpiration ranged from 0.005 to 1.866 mm/d, with a mean of 1.042 mm/d. The daily stand transpiration in different months was: June (1.325 mm/d) >May (1.099 mm/d) >July (1.077 mm/d) >August (1.009 mm/d) >September (0.717 mm/d). ② According to the correlation coefficient matrix of atmospheric factors and daily stand transpiration, the main atmospheric factors affecting daily stand transpiration were solar radiation intensity (Rn), saturated water vapor pressure deficit (DVPD) and relative air humidity (HRH). The order of correlation was: Rn (0.784) >DVPD (0.754) >HRH (-0.704). ③ The atmospheric factors could be reduced to three comprehensive indicators based on the factor analysis were climate fluctuation factor (44.9%), transpiration driving factor (35.2%) and air mobility factor (15.7%). The relevant analysis showed that transpiration driving factors (Rn, DVPD and HRH) and stand transpiration were significantly correlated. Also, the fitting effect of transpiration driving factors and stand transpiration (R2 = 0.688) was better than the fitting effect of potential evapotranspiration and daily stand transpiration TPET (R2 = 0.649). ④ The contribution rate of Rn and DVPD to the daily stand transpiration could reach 93%, of which 54.2% came from Rn,and 38.8% came from DVPD. ⑤ The diurnal variation of decoupling coefficient and stand transpiration showed that the time of Rn controlling transpiration occurred from sunrise to the highest net radiation (at 11:00 am), while the time of DVPD controlling transpiration occurred in the afternoon and at night. ⑥ Under humid soil conditions [root-zone relative extract water (WREW)>0.38], the daily stand transpiration was significantly positively correlated with WREW in the 40-60 cm soil layers (P<0.01), but there was no significant correlation or significant negative correlation with WREW in other soil layers. Under soil drought conditions (root-zone WREW≤0.38), the daily stand transpiration was significantly positively correlated with WREW of ≥20-40 cm and ≥40-60 cm soil layers (P<0.01), and was not significantly negatively correlated with WREW of 0-10 cm and ≥10-20 cm soil layers.【Conclusion】The main atmospheric factors affecting stand transpiration were Rn and DVPD, and in the intra-day scale, the period dominating transpiration was different between the two factors. The transpiration driving factor was better than TPET in reflecting the comprehensive effect of atmospheric factors on stand transpiration. Under humid soil conditions, the water source for transpiration in Larix principis-rupprechtii was mainly from the ≥40-60 cm soil profile layers, while under soil drought conditions, the water source of transpiration was mainly from the ≥20-60 cm soil profile layers.

Key words: stand transpiration, atmospheric factor, transpiration driving factor, soil relative extract water, response characteristics

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