CO_2浓度倍增条件下土壤干旱对两种沙生灌木碳氮含量及其适应性的影响

Responses of two dominated desert shrubs to soil drought under doubled CO_2 condition

研究利用大型环境生长箱模拟了两种沙地优势灌木柠条和羊柴对 CO2 浓度倍增和土壤干旱交互作用的响应。 CO2 浓度倍增使柠条和羊柴的生物量分别增加了 6 2 .90 %和 5 0 .0 0 % ,使植株叶面积分别增加了 4 1.86 %和 4 5 .84 %。 CO2 浓度的倍增效应随着土壤干旱的增加而下降。 CO2 浓度倍增和土壤干旱都增加单位叶面积质量 (L MA) ,但 CO2 浓度倍增主要增加了水分充足时的 L MA。 CO2 倍增使柠条和羊柴叶片含氮量分别降低了 10 .4 0 %和 5 .0 6 %。柠条叶片含氮量在所有土壤干旱条件下均呈现出增加的趋势 ,而羊柴叶片的含氮量仅在严重干旱条件下增加。 CO2 倍增使叶片的碳氮比显著增加 ,但土壤干旱使之降低。CO2 浓度倍增降低叶肉细胞质膜的过氧化产物丙二醛 (MDA )的含量 ,干旱使之增加。叶片含氮量与 MDA呈显著正相关。研究表明 CO2 倍增有保护叶片免受严重土壤干旱的作用 ,但干旱的负面影响是 CO2

CO_2 concentration in the atmosphere is expected to increase continuously in the future and would be doubled around the middle part of the 21^(th) century. CO_2 enrichment may take advantage of pant growth, but water stress is a common stress for plant growth and productivity. At present, only a few studies on the combined effects of CO_2 enrichment and drought on plant eco-physiology have been done. This experiment was conducted to investigate that the responses of two dominant desert shrubs (Caragana intermedia Kuanget H.c.Fu and Hedysarum mongolicum Turcz.) in western China to the interaction of doubled CO_2 and soil drought in a large environmental growth chambers (19 m^2). Compared with ambient CO_2 concentration, doubled CO_2 would increase the plant biomass by 62.90% and 50.00%, and the plant leaf area by 41.86% and 45.84%, of Caragana intermedia Kuanget H.c.Fu and Hedysarum mongolicum Turcz., respectively. The CO_2 fertilizer effect would decrease with the increase of soil drought. Both doubled CO_2 and soil drought would result in the increase of leaf mass per area unit (LMA). The increase of the LMA under doubled CO_2 would be more obvious under soil water sufficiency than under soil drought. Doubled CO_2 reduced leaf nitrogen concentration by 10.40% and 5.06%, of Caragana intermedia Kuanget H.c.Fu and Hedysarum mongolicum Turcz., respectively. Generally, the leaf nitrogen concentration of Caragana intermedia Kuanget H.c.Fu would increase under soil drought, but leaf nitrogen concentration of Hedysarum mongolicum Turcz. would increase only under severe soil drought. Both CO_2 enrichment and drought would not affect significantly leaf carbon concentration. Leaf C: N would be increased from 6.98 at ambient CO_2 concentration to 8.20 at doubled CO_2 for Caragana intermedia Kuanget H.c.Fu, and from 8.34 to 9.01 for Hedysarum mongolicum Turcz.; however, it would be affected significantly only under severe soil droughts, and this response for Caragana intermedia Kuanget H.c.Fu is more obvious than that for Hedysarum mongolicum Turcz. Double CO_2 decreased root nitrogen concentration, increased root C: N, but would not obviously affect root carbon concentration of Caragana intermedia Kuanget H.c.Fu; while it did not significantly affect root nitrogen and carbon concentration as well as C: N of Hedysarum mongolicum Turcz. Malondialdehyde (MAD) is a marker for lipid peroxidation as plant tissue is subjected to stress. The results also showed that the effects of double CO_2 on MAD concentration varied with different soil water conditions and plant species. Double CO_2 apparently decreased leaf MDA concentration under severe soil drought for Caragana intermedia Kuanget H.c.Fu, but did not affect significantly for Hedysarum mongolicum Turcz., suggesting that CO_2 enrichment may protect plant leaf against the damage of severe soil drought. Leaf nitrogen concentration has close relationship with MDA concentration. The slope of the linear equation of Hedysarum mongolicum Turcz. was greater than that of Caragana intermedia Kuanget H.c.Fu. Leaf nitrogen concentration has also close relationship with LMA, implicating that increasing leaf thickness did not lead to a decrease in leaf nitrogen concentration. Moreover, LMA also had linear relationship with MDA, implying the increase in leaf thickness and MDA accumulation occurred simultaneously under the present experimental conditions. Thus, doubled CO_2 might protect leaf against severe drought damage, but the adverse effect of soil drought may outweigh this advantage due to doubled CO_2. The results indicated that a no higher tolerance to severe water deficit under double CO_2 condition is of great physiological significance for Caragana intermedia Kuanget H.c.Fu and Hedysarum mongolicum Turcz. In view of global change, the decrease in precipitation and the increase in atmospheric CO_2 concentration might happen in the future in the region dominated by Caragana intermedia Kuanget H.c.Fu and Hedysarum mongolicum Turcz., suggesting the distributing ranges of Caragana intermedia Ku