在高CO_2浓度下四种亚热带幼树光合作用对水分胁迫的响应

Response of photosynthesis to water stress in four saplings from subtropical forests under elevated atmospheric CO_2 concentration

在较高 CO2 浓度 ( 70 0 μl/L)下 ,随着光强 ( PAR)增高 ,来自高林密度林地植物罗伞的光合速率 ( Pn)增高 ,当叶片水势 ( Ψ)从 -0 .92 k Pa降低至 -2 .0 k Pa,Pn/PAR斜率从 0 .0 37降至 0 .0 1 7,即表观量子产率 ( αA)降低 54.0 % ;而来自林密度中等林地的九节和荷木 ,当叶片水势分别从 -0 .80 k Pa降至 -2 .0 0和 -1 .2 0 k Pa,αA分别降低 2 2 .2 %和 1 9.4 % ;来自开阔林地的桃金娘叶片水势降低时 ,αA亦见明显降低。当叶片水势降低 1 k Pa,罗伞叶片的光能转换效率 (δ)降低 0 .1 0电子 /量子或 39.2 % ,九节和荷木 ,以及桃金娘相应降低 0 .0 33至 0 .0 5电子 /量子。来自高林密度林地罗伞叶片水势从-0 .92 k Pa降低至 -2 .0 0 k Pa,最大羧化速率 ( Vcmax)降低 2 4 .3% ,来自林密度中等林地的九节叶片水势低 1 k Pa,Vcmax降低 7.0 8μmol/m2 s,荷木和疏林桃金娘则有明显高的 Vcmax。叶片水势降低 ,Vcmax亦受明显抑制 ( P<0 .0 1 )。结果表明 ,来自林密度中等林地的荷木和来自开阔林地的桃金娘有着高的 Rubisco激活特性 ,叶片水势降低明显影响 Rubisco的激活特性。来自较稀疏林地的荷木和桃金娘有较高电子传递速率 ( J) ,叶片水势降低 1 k Pa,J分别降低 52 .5和58.1μmol m2 /s。

Photosynthetic rate ( Pn ) in the leaf of Ardisia quinquegone with high density increased as enhancement of irradiation ( PAR ) in high CO 2 concentration (700μl/L).The initial slope of Pn / PAR decreased from 0.037 to 0.017 as leaf water potential ( Ψ ) decreased from -0.92kPa to -2.00kPa,or apparent quantum yield ( α A ) decreased by 54.0%. α A decreased by 22.2% and 19.4% in the leaves of Phychotria rubra and Schima superba with moderate stand density,respectively when leaf water potential decreased from 0 8kPa to -2.00 and -1.20kPa. α A in the leaves of Rhodomyrtus tementose also decreased considerably as leaf water potential decreased.The efficiency of light energy conversion ( δ ) decreased by 0 10 electrons/quanta or 39.2% in Ardisia as leaf water potential fell by 1kPa.And the values of 0.033 to 0.05 electrons/quanta decreased in leaves of Psychotria and Schima from the sites with moderate density and Rhodomyrtus from the open sites.The maximum rate of carboxylation ( Vc max) decreased by 24.3% in Ardisia as Ψ decreased from -0.92kPa to -2.00kPa.And Vc max decreased by 7.08μ/mol/m 2 ·s in leaf of Psychotria from the sites with moderate stand density.The results imply that higher kinetic properties of Rubisco was occurred in plants from the open and sparse site.And these properties have been modified as leaf water potential decreased.Higher potential electron transport rates ( J ) were observed in leaves of Schima and Rhodomyrtus . And those values decreased by 52.5 and 58.1μmol/m 2 ·s as water potential fell by 1kPa,while the relative values ony decreased by 8.9 to 9.0μmol/m 2 ·s in leaves of Ardisia and Psychotria .The response of J to leaf water potential was sensitive for the saplings from the open and sparse sites,in comparison with that of saplings from the sites with higher density of forest.Higher Vc max, J,δ and Γ * were found in leaves of sapling from the open and sparse sites.It may take advantage of maintaining the domination of species of trees as those exposed to rising air CO 2 concentration and decreased leaf water potential by water stress.