| For serious soil erosion and arid ecological condition on the loess plateau, the ecological construction mainly on vegetation restoration were carried out for many years in the region of Loess Plateau of China. To adapt to arid environments, The trees planted in the area should have strong ability of drought tolerance and high water use efficiency. In this paper, the comparative study on the photosynthesis and transpiration characteristics of three tree species for soil protecting on the Loess Plateau area of west Shanxi were done by using Li—6400(LI-COR. Lincoln, Nebraska, USA) portable photosynthesis system and Thermal Dissipation Probe, the water consumption of three stand in the growing season were estimated, the correlation analysis between the net photosynthetic rate, Sap flow velocity and related physiological factors were researched respectively, and based on which, the prediction model of the net photosynthetic rate, Sap flow velocity and related physiological factors were created, the main results are as follows:1. The photosynthetic capacity, carbon consumption capacity of R. pseudoacacia are the greatest among three trees whose apparent quantum yield, maximum photosynthetic rate and respiration rate is respectively:0.052mol·mol-1,18.04μmol·m-2vs-1,1.50μmol·m-2·s-1, R. pseudoacacia have strong ability to use strong light with light saturation point567.26μmol·m-2·s-1and average ability to use weak light with light compensation point31.98μmol·m-2·s-1so that it is suitable for planting in the sunny slopes of loess plateau with better light conditions; The photosynthetic capacity, carbon consumption capacity of P. tabulaeformis are the greatest among three trees whose apparent quantum yield, maximum photosynthetic rate and respiration rate is respectively:0.034mol·mol-1,9.12μmol·m-2·s-1,1.12μmol·m-2·s-1.P. tabulaeformis have average ability to use strong light with light saturation point460.04μmol·m-2·s-1and strong ability to use weak light with light compensation point38.00μmol·m-2·s-1so that it is suitable for planting in the half shaded slopes and the half sunny slopes; The photosynthetic capacity, carbon consumption capacity of Q. liaotungensis are smallest among three trees whose apparent quantum yield, maximum photosynthetic rate and respiration rate is respectively:0.044mol·mol-1、10.01μmol·m-2·s-1、1.37μmol·m-2·s-1, Q. liaotungensis have weak ability to use strong light with light saturation point339.67μmol·m-2·s-1and strong ability to use weak light with light compensation point21.86μmol·m-2·s-1so that it is suitable for planting in the shaded slopes.The light use efficiency and respiration rate of three tree species are in the following descending order:R. pseudoacacia, Q. liaotungensis, P. tabulaeformis; The light saturated point of three tree species are in the following descending order:R. pseudoacacia, P. tabulaeformis, Q. liaotungensis; The light compensation points of three tree species are in the following descending order:P. tabulaeformis, R. pseudoacacia, Q. liaotungensis. The photosynthetic capacity and carbon consuming capacity of R. pseudoacacia are biggest, which have strong ability to use strong light and average ability to use weak light; The photosynthetic capacity and carbon consuming capacity of Q. liaotungensis are smallest, which have strong ability to use weak light and weak ability to use strong light so that it is most suitable for growth in the shade environment in tree species. The photosynthetic capacity and carbon consuming capacity of P. tabulaeformis are moderate, which have average ability to use strong light and weak ability to use weak light.2. The photosynthesis diurnal courses of the three trees species were bimodal curve or single-peak curve during clear days of the growing season. Trees had a more significant photosynthetic midday depression phenomenon in the months with highest light. And high light intensity, high temperature and high vapor pressure difference are the major environment factors for this depression, The environment factors had effect on the variation of photosynthetic rate major by influencing stomatal conductance and intercellular CO2concentration. photosynthetic rate was decreased caused by the interaction of stomatal factor and mesophyll assimilation capacity decreases when photosynthetic midday depression phenomenon is significant, However, mesophyll assimilation capacity decreases is main reason when photosynthetic midday depression phenomenon is not significant. The daily average photosynthetic rate and the assimilation were less with photosynthetic midday depression phenomenon is more significant in June and July.3. The diurnal courses of sap flow velocity of three trees species generally were single and broad-peak curve, and the minority were single and narrow-peak curve or bimodal curve during growing season:The diurnal courses of transpiration rate of leaves generally were single and narrow-peak curve or bimodal curve during growing season, the average transpiration rate of leaves during growing season from big to small was Robinia pseudoacacia (1.17mmol·m-2·s-1), Quercus liaotungensis (0.97mmol·m-2·s-1), Pinus tabulaeformis (0.76mmol·m-2·s-1). Therefore, the transpiration water consumption of trees from high to low was Robinia pseudoacacia, Quercus liaotungensis, Pinus tabulaeformis. Trees had a photosynthetic midday depression phenomenon because of the highest solar radiation and temperature in June and July, which can decrease the transpiration. So sap flow velocity is lower in June and July than other months, the total water consumption of R. pseudoacacia, Q. liaotungensis, P. tabulaeformis was respectively70.14mm、44.29mm、38.70mm。4. The diurnal courses of water use efficiency of three trees species were single-peak curve, bimodal curve or multi-peak curve, the average water use efficiency of leaves during growing season from big to small was Pinus tabulaeformis (2.68mmol·m-2·s-1) Robinia pseudoacacia (2.55μmol·mmol-1), Quercus liaotungensis (1.34μmol·mmol-1). Although both the average photosynthetic rate and the average transpiration rate of trees were decreased due to strong photosynthetic midday depression phenomenon in June and July, the decreased degree of the average transpiration rate of trees was more obvious, so water use efficiency of trees were higher in June and July.5. Sap flow was affected by various environmental factors, such as solar irradiation, vapor pressure deficit, stomatal conductance, wind speed, soil moisture and so on, but each factor has different influence degree on it in different months. It was found that sap flow was mainly affected by wind speed because the wind is stronger in may; In June and July, solar irradiation is stronger, soil water content is lower while soil evaporation is higher, at this time the physiological regulation function is strengthened which induce stomatal closure then make transpiration weaken, so Sap flow is mainly affected by stomatal conductivity and The environment factors including air humidity, soil moisture, had effect on the transpiration of trees by influencing stomatal conductance; in other months sap flow was affected by solar irradiation or vapor pressure deficit mainly. |
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