模拟降水和氮沉降对准噶尔盆地南缘梭梭光合生理的影响

氮沉降和降水格局变化是目前全球气候变化背景备受关注的热点研究课题,也是荒漠生态系统的两个主要限制因子。因此,研究两者对荒漠植物的效应有助于深入了解荒漠生态系统对全球变化的响应。本文选择准噶尔盆地南缘荒漠地区的建群种梭梭(Haloxylon ammodendron)作为研究对象,设置自然降水(W0)与增加降水30%(W1)两个水分条件和自然氮沉降(N0)、增加氮素30 kg(N)·hm~(-2)·a~(-1)(N1)与增加氮素60kg(N)·hm~(-2)·a~(-1)(N2)3个施氮水平,连续处理2年,以探究降水、氮沉降及其交互作用对梭梭光合日变化及生理生态特征的影响。结果表明:降水、氮沉降及其交互作用对梭梭的净光合速率(Pn)日变化产生极显著正相关影响;同时根据梭梭Pn、胞间CO2浓度(Ci)及气孔限制值(Ls)的变化方向,推测梭梭光合"午休"主要由非气孔因素引起。此外,W0条件下,梭梭丙二醛(MDA)含量、抗氧化酶(POD、CAT、SOD)活性、可溶性蛋白(Pr)和可溶性糖(SS)含量均随施氮量增加而显著降低,脯氨酸(Pro)含量则呈先降低后增加的趋势;而W1条件下,梭梭MDA含量、抗氧化酶(POD、CAT、SOD)活性及渗透调节物质(Pro、Pr、SS)含量均随施氮量增加呈显著先增加后降低的趋势。两种水分条件下,除W1N1处理梭梭的Pro含量高于对照组外,其余处理均显著低于对照组;同时梭梭的MDA含量、抗氧化酶活性、Pr及SS含量也均显著低于对照组。综合分析结果表明:降水、增氮及其交互作用均有利于梭梭的生长,但其交互作用效应的强弱则取决于二者间的比例。

Combined effect of simulated precipitation and nitrogen deposition on photo-synthetic physiology of Haloxylon ammodendron in southern margin of Junggar Basin, China

Precipitation and nitrogen deposition are two of the most investigated factors of global climate change which also are the controlling factors of desert ecosystems. This study examined the combined effects of precipitation and nitrogen deposition on arid ecosystems in order to provide insight into the responses of ecosystems to global climate change. We selected plantation of Haloxylon ammodendron in the southern margin of Junggar Basin. Two precipitation conditionsnatural precipitation (W₀) and 30% increased precipitation (W₁)] and three levels of nitrogen depositionsnatural nitrogen deposition (N₀), 30 kg(N)·hm^-2·a^-1 (N₁) and 60 kg(N)·hm^-2·a^-1 (N₂) increased natural nitrogen deposition] were randomly added to simulate nitrogen deposition and precipitation for two years to explored the effects of precipitation, nitrogen deposition and the combined effects on diurnal change in photosynthetic and physio-ecological traits of H. ammodendron. The results showed that precipitation, nitrogen deposition and the combined effects had direct significant correlation with diurnal change in net photosynthetic rate of H. ammodendron. Based on the variation in net photosynthetic rate, intercellular CO₂ concentration and stomatal limitation of H. ammodendron, "midday depression" of photosynthesis was mainly caused by non-stomatal factors. Moreover, with increased nitrogen deposition, there were decreasing physiological indexes (MDA content, POD activity, CAT activity, SOD activity, soluble protein content and soluble sugar content) under W₀ precipitation condition. However, proline content initially decreased before eventually increasing. There were initial increases followed by decreases in physiological indexes (MDA content, POD activity, CAT activity, SOD activity, soluble protein content, proline content and soluble sugar content) under W₁ precipitation condition. With the exception of W₁N₁, proline content was lower under nitrogen deposition increase treatments than under the natural deposition treatment. Also MDA content, antioxidant enzymes activities, soluble protein content and soluble sugar content of H. ammodendron were also significantly lower under the other water/nitrogen treatments than under the control regimes. The results from the comprehensive analysis indicated that precipitation, nitrogen deposition and the combined effects benefited the growth of H. ammodendron, but the strength of the combined effect depended on the ratio between the nitrogen deposition and precipitation.