沙柳和柠条灌丛分枝生长对模拟降雨改变的响应

Responses of the shoot growth in Salix psammophila and Caragana korshinskii to manipulated precipitation variation

利用模拟降雨操纵试验(对照、降雨增加45%和减少50%),研究第2年沙柳和柠条灌丛不同径级分枝生长对模拟降雨改变的响应。结果表明:1)沙柳10~15 mm径级的分枝基径、枝长和生物量对降雨改变有一定响应,15~20 mm径级分枝枝长和生物量对降雨改变有响应;干旱显著降低了10~15 mm径级枝长和生物量的增加量,而增水增加了15~20 mm径级枝长和生物量的增加量,其他径级对降雨改变无显著响应。2)柠条<20 mm径级的基径生长对降雨改变均有显著的响应,但只有<10 mm径级枝长对降雨改变有显著响应,小径级分枝对降雨改变的响应更敏感。增水增加了<10 mm径级生物量,而干旱并未导致该径级生物量显著降低;增水对10~20 mm径级生长季生物量并未产生影响,但干旱导致该径级生物量显著降低。3)增水导致沙柳和柠条每丛生物量增加量分别为11.3%和35.5%,而干旱导致每丛生物量增加量分别下降14.2%和36.8%,降水改变对柠条生长的影响要大于沙柳。该研究可为未来降雨格局改变下,2种灌木的生长动态和生产力预测提供理论依据。

[ Background] Water is the major factor limiting plant growth on the water-wind erosion crisscross region of the Loess Plateau, which is being exacerbated by the precipitation reduction related to global climate change and the decline of groundwater level due to large-scale energy development such as coal mining and oil exploitation. How local vegetation respond to this decreased water availability is important for the understanding of their adaptation and survival in the future. [ Methods ] Using precipitation manipulation experiment （the contrast, ＋45% of precipitation by irrigation and -50% of precipitation （Dry） by partial exclusion） , the growths of different classes of branching shoots to varied simulated precipitations in Salix psammophila and Caragana korshinskii were studied during the second year of precipitation manipulation. [ Results] 1 ） For S. psammophila, the basal diameter, length and aboveground biomass of branching shoots within 10 - 15 mm class showed some responses to varied precipitation, the length and aboveground biomass of shoots with 15 -20 mm class also presented certain responses, drought decreased the length and aboveground biomass of 10- 15 mm class, and irrigationincreased the length and aboveground biomass of 15 - 20 mm class. No responses for other classes of shoots were found. 2） For Caragana korshinskii, the radial growth of shoots with basal diameter 〈 20 mm presented significant responses to precipitation variation, but the responses of height growth of shoots were only found for shoots with basal diameter 〈 10 mm, suggesting a more sensitive response in smaller classes of shoots. Irrigation significantly increased aboveground biomass in shoots with basal diameter 〈 10 mm whereas drought did not decrease aboveground biomass of this class. For shoots with basal diameter of 10 - 20 mm, irrigation did not increase the biomass but drought significantly decreased the biomass. 3） Irrigation increased aboveground biomass per plant by 11.3% in S. psammophila and 35.5% in C. korshinskii, drought decreased aboveground biomass per plant by 14.2% in S. psammophila and 36. 8% in C. korshinskii. [ Conclusions ] The results suggest that precipitation variation caused a greater effect on the growth of C. korshinskii than that of S. psammophila, and the growth of C. korshinskii showed a greater flexibility to varied precipitation, the reasons may be related with the differences of root water extraction source, soil infiltration properties and internal plant water redistribution, etc. These results may not only provide the insight of the adaptative mechanism how two shrubs cope with drought but also be conducive to forecast the growth dynamics and productivity of these two shrubs under future projected precipitation variation.