沿土壤水分梯度黄囊苔草碳同位素组成及其适应策略的变化

VARIATIONS IN FOLIAR CARBON ISOTOPE COMPOSITION AND ADAPTIVE STRATEGIES OF CAREX KORSHINSKYI ALONG A SOIL MOISTURE GRADIENT

选取了内蒙古锡林河流域 6个水分条件不同的典型植物群落 ,测定了各群落中黄囊苔草 (Carexkorshin skyi)叶片δ13 C值、叶片含水量 (LWC)及其种群特征的变化。结果表明 :1)不同生境下 ,黄囊苔草叶片的碳同位素组成发生明显变化 (变幅为 1.8‰ )。沿土壤水分梯度 ,随着土壤含水量的降低 ,黄囊苔草叶片δ13 C值显著增大 ,水分利用方式更加保守。 2 )虽然不同生境下 ,黄囊苔草叶片含水量变化不大 ,但其叶片δ13 C值与LWC表现出显著的负相关关系 (p=0 .0 5 1)。这表明黄囊苔草水分利用效率对其叶片水分状况变化的反应非常敏感。 3)在不同生境下 ,黄囊苔草种群的植株高度、密度、地上生物量及其在群落中的出现频度明显不同。具有较高δ13 C值的黄囊苔草种群在群落中出现的频度和地上生物量所占比例都显著增加。以上结果表明 ,生长在不同生境下的黄囊苔草种群能够通过改变其水分利用效率适应不同的土壤水分状况 。

The carbon isotope composition (δ 13C value) of plants is a useful index for assessing intrinsic water use efficiency (WUE) and can also provide information on long term WUE, because the δ 13C value integrates photosynthetic activity throughout the entire life span of the leaf tissue. Water is the limiting environmental factor for growth and reproduction of steppe plants in the Xilin River Basin, Inner Mongolia. Carex korshinskyi, a perennial forb, is widely distributed throughout the Xilin River Basin and shows strong adaptive characteristics enabling it to survive in habitats with widely varying nutrient and water conditions. In this study, six plant communities were selected which differed in floristic composition and soil water status but had similar climatic conditions, such as temperature and precipitation. Foliar δ 13C values, leaf water content (LWC) and population characteristics (including height, density and aboveground biomass) of C. korshinskyi were measured in each of the six communities. Our objectives were to study the variations in foliar δ 13C values, LWC and population characteristics of C. korshinskyi along a soil water gradient to better understand the adaptive strategies of C. korshinskyi to water stress. Results showed that: 1) There were significant variations in foliar δ 13C values of C. korshinskyi in different habitats (changing range 1.8‰). The foliar δ 13C values of different C. korshinskyi populations tended to increase with decreasing soil water content (SWC). A significant negative correlation was found between foliar δ 13C values and SWC in different soil layers, indicating that C. korshinskyi populations could change WUE in response to water availability. 2) A significantly negative correlation was found between foliar δ 13C values and LWC of C. korshinskyi. Only small variations in LWC were found among the six different C. korshinskyi populations indicating that the WUE of C. korshinskyi was sensitive to changes in leaf water status. 3) There were significant differences in height, density, aboveground biomass and frequency of occurrence among C. korshinskyi communities along the soil water gradient. The C. korshinskyi populations with higher δ 13C values had higher occurrences in the plant community and contributed more to total aboveground biomass and community productivity. Our results suggest that C. korshinskyi can adjust its water use pattern (such as enhancing WUE) to adapt to habitats with different soil water availability increasing its competitive ability across a wide range of habitats.