水分胁迫对重庆石灰岩地区不同龄级柏木(Cupressus funebris Endl.)幼苗气体交换的影响

Influence of drought stress on the gas exchange of Cupressus funebris Endl. seedlings of different ages in the limestone area of Chongqing,China

通过盆栽水分胁迫试验,采用美国Li-COR公司生产的Li-6400便携式光合测定分析仪,对比研究了水分胁迫对重庆石灰岩地区不同龄级柏木幼苗气体交换的影响。结果表明:水分胁迫降低了两种年龄柏木幼苗的净光合速率、蒸腾速率和气孔导度,1年生幼苗的净光合速率下降的幅度大于5年生幼苗。1年生幼苗的胞间CO2浓度随着水分胁迫强度的增加而升高,而气孔限制值下降,5年生幼苗在重度干旱前,胞间CO2浓度随着水分胁迫强度的增加而降低,气孔限制值上升,但重度干旱后,趋势与1年生幼苗相同,由这些指标的变化趋势分析得出,1年生幼苗的净光合速率的下降是由非气孔限制因素引起的,而5年生幼苗在重度干旱前净光合速率的下降是由气孔限制因素引起,而在重度干旱后转为非气孔因素。1年生幼苗的水分利用效率随着水分胁迫的加剧而降低,5年生幼苗水分利用效率呈上升趋势,说明5年生幼苗更能适应干旱胁迫。干旱胁迫降低了一年生柏木幼苗的表观量子产额、羧化效率以及最大净光合速率即光合能力,但光补偿点、CO2补偿点、光呼吸和暗呼吸却随着水分胁迫的加剧而升高。对于5年生幼苗,干旱胁迫对其表观量子效率、光补偿点、光呼吸及光合能力的影响基本与一年生幼苗一致。但羧化效率、CO2补偿点呈先降后升的趋势,而暗呼吸却先升后降,说明适度的干旱(未遭受重度干旱之前)提高了柏木的CO2利用能力,但因呼吸消耗较多的光合产物还是导致了其光合能力的降低,但降低的程度较一年生幼苗小,表现为对干旱环境更好的适应能力。

The influences of experimentally imposed drought stress on, photosyhthesis , photo-parameters and CO2-parameters of potted Cupressus funebris Endl. seedlings of two different ages in the limestone area of Chongqing, were studied using a Li-6400 portable photosynthesis system. Net photosynthetic rate （Pn）, transpiration （E）, and stomatal conductance （Gs） of the seedlings generally decreased under drought stress, but 1-year old seedlings decreased more than 5-year old seedlings. Intercellular concentration （Ci） of 1-year seedlings increased with aggravating drought stress while the stomatal limitation value （Ls） decreased. In contrast, Ci of 5-year seedlings decreased and Ls increased before they suffered serious drought stress, but they had the same trend as 1-year seedlings under serious stress. These results implied that the photosynthetic depression of 1-year seedlings was caused by non-stomatal limitation, while the depression of Pn in 5-year seedlings was predominantly due to stomatal limitation before suffering serious stress, but transferred to non-stomatal limitation after suffering serious stress. Water use efficiency （WUE） in 1-year seedlings decreased with the aggravation of drought stress, but 5-year seedlings showed the reversed trend, indicating that 5-year seedlings had greater drought resistance. Under drought stress apparent quantum yield （AQY）, carboxylation efficiency （CE） and photosynthetic ability （A0） of 1-year seedlings decreased, while light compensation point（ LCP）, CO2 compensation point（ F）, light respiration rate（Rp） and dark respiration rate（Rd） increased. For 5-year seedlings, AQY, LCP, Rp and A0showed similar trends, but CE and F decreased at first, then increased at the end, while Rd followed the reversed pattern. This also indicates that 5-year seedlings could cope better with drought stress.