干旱胁迫对拉萨半干旱河谷主要灌木树种耗水及光合的影响

Effects of drought stress on characteristics of water consumption and photosynthesis of the main shrub species in Lhasa semi-arid valley

采用盆栽苗木直接称量和Li-6400光合系统测定法,研究了拉萨半干旱河谷5种灌木在不同水分条件下的耗水及光合特性变化规律。结果表明:1)随着干旱胁迫加剧,细叶小红柳、江孜沙棘和小叶醉鱼草的耗水量均下降,江孜沙棘和小叶醉鱼草在轻度干旱时降幅最大,细叶小红柳在重度干旱时的耗水量较中度干旱时下降了71.8%。香柏和砂生槐则在轻度干旱时耗水量最大。重度干旱时各苗木的耗水量均最小。2)在正常供水条件下,细叶小红柳、香柏和小叶醉鱼草的耗水速率日变化为明显的双峰曲线,细叶小红柳峰值出现在10:00—12:00和14:00—16:00,香柏和小叶醉鱼草峰值出现在12:00—14:00和16:00—18:00;江孜沙棘和砂生槐均为单峰曲线,江孜沙棘在12:00—14:00耗水速率最大,砂生槐峰值出现在14:00—16:00。其他3种在干旱条件下,5个树种的耗水速率日变化为单峰曲线;轻度干旱下香柏和小叶醉鱼草的峰值出现在12:00—14:00,其余3个树种最大值出现在14:00—16:00;中度和重度干旱下各树种的耗水速率均在14:00—16:00达到最大值。3)在正常供水时小叶醉鱼草、细叶小红柳和江孜沙棘的净光合速率达到各自最大值,分别为19.67μmol/(m^2·s)、17.1μmol/(m^2·s)和18.06μmol/(m^2·s),显著高于香柏;香柏和砂生槐在轻度干旱下净光合速率达到最大值,分别为18.52μmol/(m^2·s)和21.99μmol/(m^2·s)。随着干旱加剧,细叶小红柳、江孜沙棘、小叶醉鱼草的蒸腾速率呈下降趋势。而香柏和砂生槐在轻度干旱胁迫下蒸腾速率最大,重度干旱时各树种的蒸腾速率均达到最小值。4)砂生槐的水分利用效率在正常供水条件下的最大值达到6.0μmol/mmol,其在各水分条件下均显著高于其他树种近50%。随干旱胁迫加剧,小叶醉鱼草的水分利用效率递增。香柏、细叶小红柳和江孜沙棘均在轻度干旱时达到最大水分利用效率。

Vegetation restoration and reconstruction in Lhasa semi-arid valley is an important part of the Tibetan plateau national ecological security barrier construction.Water remains a major limiting factor in the area of vegetation restoration.Considering the climatic characteristics of the region,the less types of species and difficult to introduction,it is very important to carry out water research about native tree species and screen low-water drought-resistant species.This paper observed the water consumption and photosynthesis of the main shrub species in Lhasa semi-arid valley.The selected five species were Salix microstachya,Hippophae gyantsensis,Sabina pingii var.wilsonii,Sophora moorcroftiana and Buddleja minima.The water consumption（WC）and water consumption rate（WCR）of all seedlings under different drought stresses were measured by pot seedling mass method,and net photosynthetic rate（Pn）,transpiration rate（Tr）and water use efficiency（WUE）of them were measured by an Li-6400 photosynthetic system.The results showed that：1）With the intensification of drought stress,the WCs of Salix microstachya,H.gyantsensis and B.minima were all gradually declined.The WC of H.gyantsensis and B.minimahad the steepest decline under light drought stress.Compared with the moderate drought stress,the WC of Salix microstachya under heavy drought stress was decreased by 71.8%.The WCs of Sabina pingii var.wilsonii and Sophora moorcroftiana were the largest under light drought stress.WC for each seedling was minimal under heavy drought stress.The day-and-night WCs of Sophora moorcroftiana and B.minima were only 208.3g/m2 and 173.8g/m2,respectively.2）Under normal water supply,the WCRs of Salix microstachya,Sabina pingii var.wilsonii and B.minima were clearly bimodal curve.The peak of Salix microstachyaappeared in 10：00—12：00and 14：00—16：00,and those of Sabina pingii var.wilsonii and B.minima were in 12：00—14：00and 16：00—18：00.The WCRs of H.gyantsensis and Sophora moorcroftiana were single-peak curve.The largest WCR of H.gyantsensis appeared in 12：00—14：00and that of Sophora moorcroftiana was in 14：00—16：00.The WCRs of all species were single peak curve under light,moderate and heavy drought stress.But under light drought stress,the peaks of Sabina pingii var.wilsonii and B.minima appeared in 12：00—14：00,and the maximum values of WCRs of the other three species appeared in 14：00—16：00.The maximum WCR of each species was in 14：00—16：00under moderate and heavy drought stress.3）Under normal water supply,the Pn of Salix microstachya,H.gyantsensis and B.minima was significantly higher than that of Sabina pingii var.wilsonii,reached their maximum.The Pn of Sabinapingiivar.wilsonii and Sophora moorcroftiana reached the maximum under light drought stress.With increased drought stress,the Tr of Salix microstachya,H.gyantsensis and B.minima was declined.The maximum Tr of Sabina pingii var.wilsonii and Sophora moorcroftiana appeared under light drought stress.Tr of each species had reached the minimum under heavy drought stress.4）The WUEs of Sophora moorcroftiana under various water stress were significantly higher than that in other species.With increased drought stress,the WUE of B.minima was increasing.The WUE of Salix microstachya,H.gyantsensis and Sabina pingii var.wilsonii reached the maximum in light drought stress.