Study On Transpiration Characteristics Of Major Tree Species For Soil Conservation In Loess Plateau Of West Shanxi

Based on the theory of " Soil-Plant-Atmosphere Continuum", daily and seasonal changes of water consumption by transpiration of chief species for soil protecting in Semi-arid Area such as Populus spp, Robinia pseudoacacia, Pinus tabulaeformis and Platycladus orientalis of 15 years and the major determinant factors were studied on account of planting-design patterns and water use statusquo of Semi-arid Area in Loess Plateau in Ji Country, Shanxi province. Integrated model of transpiration and meteorological factors and water consumption amount by transportation on unit leaf area (by 1cm2) were concluded.Primary achievements are listed as follows:1. Under the same climatic conditions, it took 19h,41h,49h and 77h respectively before the leaf-weight of Platycladus orientalis, Pinus tabulaeformis, Robinia pseudoacacia and Populus spp did not decrease.2. Daily average and amplitude of leaf water potential can be ordered as Pinus tabulaeformis> Robinia pseudoacacia>Platycladus orientalis>Populus spp and Populus spp>Robinia pseudoacacia>Platycladus orientalis>Pinus tabulaeformis respectively. Leaf water potential rises with increasing leaf water content, and the relationship between them can be fitted by logarithmic curve.3. According to leaf water potential of unitwatercontent,16 kinds of commen herbaceous can be divided into delay dehydration by developing high leaf water potential and delay dehydration by developing low leaf water potential by the demarcation point of-5Mpa,26 kinds of commen shrubs can be divided into four types such as delay dehydration by developing high leaf water potential, less higher leaf water potential, low leaf water potential and less lower leaf water potential by the demarcation points of-5Mpa,-10Mpa and-15Mpa, and 34 kinds of commen macrophanerophytes can also be divided into four types as above by the demarcation points of-10Mpa,-15Mpa and-20Mpa.4. Diurnal variation of transpiration rate of different tree species are similar, meaning that the curves take on " single peak", " double peak" and" tribble peak" with the value lower in the early morning and late afternoon and higher at noontime. On typical sunny day, daily average transportation can be ordered as follows:Populus spp> Robinia pseudoacacia>Pinus tabulaeformis>Platycladus orientalis, and transportation of the same specie in different months can be ordered as August>July> September> June>May.5. The relationship between transpiration and leaf water potential can be fitted by exponential curve. That means, reaction to drought stress of each specie various with phases, specifically is transportation changes slowly with leaf water content when it is higher and quickly when it is lower.6. The relationship between transportation and single meteorological factor can be fitted by exponential function or power function. Influention to Populus spp by single factor is the most obvious(slope of the curve is the sharpest), while Robinia pseudoacacia is the second, and Pinus tabulaeformis and Platycladus orientalis are the third and forth.7. Transpiring water consumption amount (by 12h/d) on unit leaf area (by 1cm2) of the four tree species in growing season can be ordered as:Populus spp (103.42mm)> Robinia pseudoacacia (67.47 mm)> Pinus tabulaeformis (27.26 mm)> Platycladus orientalis (24.41 mm). The relationship between unique water consumption and DBH of Robinia pseudoacacia and Pinus tabulaeformis is Wlocust= 61.1481Dlocust-136.8292 (Dlocust>3), r2=0.8582;Wpitch pine=7.5565 Dpitch pine+10.0998, r2=0.9799.8. Diurnal variation of transpiration curves changed from " double peak" style to " single peak" with increasing stand densities. Daily average transpiration rate wasρ1800>ρ1600>ρ1400>ρ2000>ρ2200·9. Difference between leaf and root water potential was negatively related with transpiration rate, and such relationship can be fitted by logarithmic curve, and the regression coefficients were within the range of 0.26-0.30.10. From the respectives of monthly transpiration water consumption of Robinia pseudoacacia stand with different density (1400-2200 strains/hm2) on unit leaf area(cm2) and the best growth vigor, 1800 strains/hm2 is the reasonable stand density.