| 其他摘要 | Moisture is one of the limiting environmental factors for growth of plants in the karst area. Taking the foliar δ13C values as the indicator of plant water-use efficiency (WUE), and combining stable hydrogen and oxygen isotope ratios of xylem water in plants, we determined the foliar δ13C, δD and δ18O values of several local plant species in Wangjiazhai catchments, in order to discuss the impact of karst desertification on plant water use in micro-habitat, population, community levels, get insight into the impact of use of different waters on the long term patterns of plant water use, provide new information on plant water competition and water use strategy in karst peculiar habitat, and improve our understanding to water balance in karst ecosystem. The following conclusions were drawn:
1. Temporal and spatial distribution of foliar δ13C values in karst rocky desertification areas
(1) The average foliar δ13C values, i.e. WUE increase obviously (p<0.01) with increase of karst rocky desertified degrees in both yellow soil and rendzina area, which indicates that the effects of different karst rocky desertification degrees on WUE are obvious. Correlation analysis between the foliar δ13C values of plant species and environmental factors indicates that moisture and light are the main factors which affect the foliar δ13C values of plants.The average foliar δ13C values, i.e. WUE in yellow soil area are lower than those in rendzina area, which could be caused by the thicker yellow soil.
(2) Slope positions have little effect on the foliar δ13C values along the hillslope in study area, which could be caused by the particular complex topography and physiognomy in the karst region.
(3) The foliar δ13C values differ among the species tested, Pyracantha fortuneana is most negative, Viburnum utile most positive, the others medium. The foliar δ13C values of plants is significantly different throughout the growing season (p<0.01), the foliar δ13C values are significantly higher in April than in July, September and December (p<0.05), there is no significant difference in July, September and December (p>0.05). Correlation analysis between soil moisture indicates that the foliar δ13C values decrease with increase of soil moisture.
(4) The types of micro-habitat include stony surface, soil surface, stony gully and stony crevice in study area. The foliar δ13C values in various micro-habitat almost increase with the karst rocky desertification. The foliar δ13C values are more negative in the soil surface than the other micro-habitats, which indicates that the thicker soil could provide the plants sufficient water and nutrients, avoid or alleviate plant water stress. Correlation analysis between the foliar δ13C values and environmental factors of various micro-habitat indicates that moisture, soil thickness and light are important factors which affect the foliar δ13C values of plants in micro-habitat.
(5) There exist significant differences in the anatomical structures of plant leaves, including the thickness of palisade and spongy tissues, palisade tissue thickness/sponge tissue thickness, upper cuticle thickness, lower cuticle thickness, the plant maximum conduit diameter and plant stomata density with karst rocky desertification(p<0.05). All tissues tend to increase in thickness along with the karst rocky desertification, except for sponge tissue of plant leaves. All other anatomical structures have obviously positive correlation with the foliar δ13C values(p<0.05), except that the lower cuticle thickness have no significant correlation with the foliar δ13C values.
2. Temporal and spatial distribution of plant water source in karst rocky desertification areas
(1) δD and δ18O values of subcutaneous in 2007 were more negative than 2006 obviously beacause there had more abundant rainfall in 2007 than in 2006, δD and δ18O values of subcutaneous in 2006 were steady and changed little during 2006, which could be caused by the scarce rainfall in 2006. There was 721mm rainfall in 2006, just 60% of the normal year, which caused the piston effect insignificantly. δD and δ18O values of soil water and plant xylem water were enricher in December than in July and September. In rainy season (July), most of plants in strong and medium rocky desertification areas (S, M) mainly used soil water, whereas plants in no and slight rocky desertification areas (N, SL) use both soil water and subcutaneous water. In September, after half a month without rain, most plants in all plots used subcutaneous water to certain extent.
(2) δD and δ18O values of soil waters in different micro-habitat are different. δD and δ18O values of soil water in stony crevice are most negative, those of soil water in stony surface are most positive. Soil water δD、δ18O values of different soil layer in no karst desertification plot are obviously more negative than karst desertification plots, which indicats evaporation become stronger with the process of karst rocky desertification. Overall, plants in stony crevice are inclined to use more subcutaneous water than micro-habitats; plants in no rocky desertification plots use more subcutaneous water than slight, medium, strong desertification plots; and the evergreen species use more subcutaneous water than deciduous species.
3.coupling water sources and carbon metabolism by stable isotope
Based on the analysis the relationship between carbon isotope discrimination and the hydrogen isotope ration of xylem water for the study species, the results are as follow: the plants in non-desertification plots have the more negative δ13C values than desertification plots, the plants in non-desertification plots utilizing the steady subcutaneous water are associated with less water use efficiency and more negative δ13C values. The deciduous species show higher foliar δ13C values than the evergreen species. Evergreen species utilizing more subcutaneous water that is stable are associated with less water use efficiency and more negative δ13C values. The plants in soil surface show lower foliar δ13C values than in other micro-habitat. Soil surface could provide more stable water source as its thicker soil than other micro-habitat, avoiding or alleviating plant water stress. |
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