Study On Photosynthesis, Transpiration And Drought Tolerance Of The Seedlings Of Ten Provenances Of Chinese Pine (Pinus Tabulaeformis Carr.)

1. Measurements of photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Gs) and intercellular CO₂ concentration (Ci) were made on the seedlings of ten provenances (PRs) of Chinnese pine (Pinus tabulaeformis Carr.) by using Li-6400 portable photosynthesis system. The photosynthetically active radiation (PAR), air temperature (T_air) and relative humidity (RH) were recorded synchronously during the growth season in 2005. The diurnal courses of Pn and Tr, the difference of Pn or Tr among these provenances were analysed. The correlation analysis was performed between Pn or Tr and PAR, T_air or RH, and between Pn or Tr and Gs or Ci.2. At the same time these physiological perameters (Pn, Tr, Gs and Ci) were measured on the seedlings of same provenances in soil water treatment conditions, and a comparison of their drought resistance was made.3. The results showed that the diurnal courses of Pn and Tr generally showed patterns of single and double peaks. The daily mean net photosynthetic rates (wmolCO₂ m^-2s^-1) had following order in July: PR 8(3.50) > PR 2(3.03) > PR 3(2.81) > PR 7(2.73) > PR 11(2.48) > PR 12(2.11) > PR 5(1.98) > PR 4(1.95) > PR 10(1.91) > PR 6(1.00) and in August: PR 8(2.86) > PR 7(2.75) > PR 11(2.47) > PR 4(2.30) > PR 12(2.25) > PR 6(2.07) > PR 10(1.89) > PR 5(1.83) > PR 3(1.65) > PR 2(0.99). The daily mean transpiration rates (mmol H₂O m^-2s^-1) could be ordered as follows: PR 8(2.06) > PR 2(1.69) > PR 7(1.68) > PR 4(1.53) PR 3(1.51) > PR 11(1.44) > PR 12(1.30) > PR 10(1.28) > PR 5(1.12) > PR 6(0.61) in July and PR 7(2.11) > PR 3(1.68) > PR 8(1.62) > PR 11(1.49) > PR 12(1.39) > PR 4(1.33) > PR 6(1.32) > PR 10(1.13) > PR 5(0.99) > PR 2(0.72) in August. The daily mean net photosynthetic rates were significantly different of the ten PRs of Chinnese pine, and the daily mean transpiration rates of them were significant difference inJuly.4. The relationship between Pn, Tr, Gs, Ci and the soil water content can been simulated by the binomial y=a+bx+cx2. The Pn in PR 5 and PR 6 decreased quickly as soil water content droped, indicating their lower drought resistance. PR 2, PR 3, PR 4 and PR 10 had a highter Pn compared with other PRs. PR 8 had the strongest drought resistance, and it can maintain a high Pn at when soil water content was in 5%. The WUE had following order when soil water content was7%⁹%: PR 12 > PR 7 > PR 11 > PR 8 > PR 2 > PR 4 > PR 3 > PR 10 > PR 6 > PR 5.