| 其他摘要 | The unique ground surface-underground dualistic structure of the karst rocky desertification area would make the structure and function of its ecosystem become very fragile. Once the ecosystem, especially the plant system is destroyed, it is extremely hard to rehabilitate. Although only at the end of the 1990s was common attention paid to research on karst rocky desertification, and work was carried out at the state level on the eco-rehabilitation and control of karst rocky desertification, rapid development in economy and strong demands of the local people in the karst area for the development of production and alleviating poverty and becoming prosperous made the contradiction between the growth of people and the reduction of farming land become more serious in the area, thereby leading to advance in eco-construction and backwardness in basic theoretical research and policy orientation. Moreover, different modes of artificial disturbance will lead to further deterioration of the original fragile karst rocky desertification eco-environment. As viewed from the above features, this paper, starting with basic theoretical research, takes the karst and non-karst background areas which are both located in a small karst catchment basin as the background of study, so as to eliminate some environmental affecting factors and both soil and plant as the main object of study, in combination with the employment of the international popular stable carbon isotope (δ13C) technique to determine the plant water utilization efficiency (WUE), and describes in detail the covariation relations of soil-vegetation systems in the process of degradation and the effects of different factors on the distinguishing of δ13C values of plant leaves in different background areas. Comparative studies of two different types of background areas were conducted with an attempt to provide certain reference for the eco-rehabilitation of karst rocky desertification area and the more scientific establishment of a model for the utilization of local moisture by plants，and the selection and collocation of plant species in vegetation restoration process in the area. So, the following conclusions have been drawn:
1. δ13C values of plant leaves in different background areas
The δ13C values of plant leaves studied in this paper vary between -25.60‰～-32.68‰, indicating that the plants studied belong to the typical C3 plants. The highest WUE（δ13C= -25.60‰）is produced in Rosa cymosa Tratt from the kast rocky desertification sample plot while the lowest WUE （δ13C= -32.65‰）is noticed in Cyperus rotundus from the non-karst background area undegraded sample plot. In the process from non-degradation to degradation in the karst background area, the δ13C values of plant leaves are within the ranges of -28.52‰～-30.74‰ and -25.60‰～-29.77‰, respectively, while in the process from non-degradation to degradation in the non-karst background area the δ13C values of plant leaves are within the ranges of -27.68‰～-32.68‰ and -26.17‰～-30.11‰, respectively. In the kast rocky desertification and non-karst background area degraded sample plots, the δ13C values of plant leaves are obviously higher than those of plant leaves in the kast non-rocky desertification and non-karst background area undegraded sample plots. This also indicates that the WUE of plants tends to intensify continuously with the process from non-degradation to degradation, and there is no significant difference in WUE of plants between the kast rocky desertification and non-karst background area degraded sample plots and between the kast non-rocky desertification and non-karst background area undegraded sample plots, On the whole, the WUE of plants in the karst background area is higher than that in the non-karst background area.
2. Physical and chemical properties of soil in different background areas
The study has indicated that either in the karst background area or in the non-karst background area, in the process from non-degradation to degradation, the physical structure of soil is obviously compressed, and as viewed from the contents of soil particle size fractions and the variation of fractal dimensions with the development of degradation, in both background areas the large particles of soil tend to increase and the small particles, especially the fine silt particles, tend to decrease. As can be seen from changes in water-stable aggregates in the karst background area, when soil is degraded to the extent of rocky desertification, the macro-aggregates in soil will be seriously destroyed and their erosion-resistance was a decisive factor for strong soil degradation once the surface vegetation is destroyed. But in the non-karst background area, the percentage of macro-aggregates will be far higher than in the karst background area, and the capability of soil to resist environmental degradation will also be intensified.
As for the chemical properties of soil in different background areas, the contents of organic matter and total nitrogen in soil tend to decrease obviously with the development of degradation. In the karst background area the easily moving nutrient elements in soil show a tendency of decreasing steadily, while the nutrient elements that are hard to move show a tendency of increasing. In the non-karst background area undegraded sample plot experienced long-term, remarkable desilicification and allitization at the stage of development of yellow soil, thus leading to the accumulation of the nutrient elements that are hard to move in large amounts. Therefore, the nutrient elements that are easier to move in soil tend to decrease progressively with intensifying soil degradation, while those nutrient elements that are hard to move also tend to decrease. As for the effective contents of nutrient elements in soil in different background areas, the contents of P and K are commonly lower than the critical level, and the variation tendency of other nutrient elements is roughly the same as their total contents variation tendency. And in the karst background area the contents of aforementioned nutrient elements are usually higher than those in the non-karst background area.
In the study of the relations between the contents of nutrient elements in soil and the δ13C values of plant leaves, although there are some differences between the results recently obtained from the analysis of the correlations between the contents of nutrient elements in soil and the δ13C values of plant leaves in the process from non-degradation to degradation in different background areas and the previous research results, a macroscopic comparison between the karst and non-karst background areas showed that the contents of nutrient elements in soil show significant positive correlations with the δ13C values of plant leaves, i.e., the WUE of plants in the sample plots where the contents of nutrient elements are high tended to increase.
3. The covariation relations of the soil-vegetation systems in the process of degradation in different background areas
The focus of this study is put on the analysis of the correlations between the physical and chemical properties of soil and the contents of nutrient elements in plant leaves of soil-vegetation systems in the process of degradation in different background areas. In the process of degradation in the karst background area, the physical properties of soil have so many affecting factors related to the element P in plant leaves. In the karst background area the element P is an important affecting factor. In the process of degradation in the non-karst background area, the physical properties of soil have no obvious correlations with the contents of nutrient elements in plant leaves. In the process of degradation in different background areas the chemical properties of soil, in most cases, show no correlations with the contents of nutrient elements in plant leaves.
It is seen from the bio- absorption coefficients of plant leaves, the contents of nutrient elements in plant leaves and those of soil in the process from non-degradation to degradation in different background areas that in the process of degradation in the karst background area, the absorption coefficients of nutrient elements in plant leaves are affected jointly by the contents of nutrient elements in plant leaves and those of soil, while in the process of degradation in the non-karst background area the impact on the absorption coefficients of nutrient elements in plant leaves is closely related to the contents of nutrient elements in plant leaves themselves, and the background values of nutrient elements in soil are of little influence on the absorption coefficients.
4. Relations between the contents of nutrient elements in plant leaves and the δ13C values of plant leaves in different background areas
Correlative analysis of the contents of nutrient elements in plant leaves in different background areas indicated that either in the karst background area or in the non-karst background area the nutrient elements N, K, Ca, Mg and Fe in plant leaves are all relatively high, with the exception of P whose contents are lower than the critical value. The contents of nutrient elements in plant leaves are characterized by Ca＞K＞Mg, and the contents of Ca in plant leaves are all higher than 10000μg/g. In the process of degradation in the karst background area the contents of nutrient elements N, Na, Ca, Mg, Mn, Cu and Zn in plant leaves are positive correlations with the δ13C values of plant leaves, whereas the contents of nutrient elements P, K and Fe are negative correlations with the δ13C values of plant leaves. In the process of degradation in the non-karst background area the contents of nutrient elements N, K, Ca, Mg and Cu are negative correlations with the δ13C values of plant leaves, whereas the contents of nutrient elements Mn and Na are positive correlations with the δ13C values of plant leaves, though the contents of nutrient elements P, Fe and Zn are not significant correlations with the δ13C values of plant leaves. Additionally, in the karst background area, w(N)／w(P) ratios in plant leaves are positive correlations with the δ13C values of plant leaves, whereas in the non-karst background areas w(N)／w(P) ratios in plant leaves are negative correlations with the δ13C values of plant leaves. These differences appear to be more or less related to the conditions of micro-habitats and the types of plant for various sample plots in different background areas.
5. Relations between the variation tendency of soil moisture and the δ13C values of plant leaves in different background areas
The correlations between soil moisture (on the 7th day following 30 mm precipitation ) and the δ13C values of plant leaves in different background areas indicated that the rate of water loss from soil in the kast rocky desertification sample plot within 7 days reached the maximum, especially within the soil layer at the 0-20cm depth which is in close relation to the growth of plants in the sample plot. This indicates that due to the limitation of eco-environmental conditions in the sample plot, water in soil is highly evaporated, so soil moisture is relatively low. In the kast non-rocky desertification sample plot, due to the limitation of soil thickness, soil moisture is lower than the non-karst background area undegraded sample plot. Soil moisture in the non-karst background area degraded sample plot is relatively variable, and soil moisture in the upper slope, middle slope and foot slope tends to increase progressively, though there is no significant difference. Soil moisture in the non-karst background area undegraded sample plot is least variable, indicating that the superior eco-environmental conditions are favorable to the soil moisture retention. With increasing soil moisture, soil moisture shows a significant negative correlation with the δ13C values of plant leaves, i.e., the higher the soil moisture is, the smaller the WUE of plants will be.
6. Relations between the anatomical structures of plant leaves and the δ13C values plant leaves in different background areas
This paper analyzed the anatomical structures of plant leaves in different background areas and the results showed that in the anatomical structures of plant leaves in different background areas degraded sample plots there exist significant differences in 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 stomatal density with those in the undegraded sample plots. With the development from non-degradation to degradation, with the exception of sponge tissue in the anatomical structures of plant leaves which tends to decrease progressively in thickness, the other tissues tend to increase in thickness, and the above indices for the anatomical structures of plant leaves in the kast rocky desertification sample plot are precisely higher than those in other sample plots. No significant difference is noticed in anatomical structures of the same kind of plants in karst and non-karst background areas. In the process of degradation in different background areas, the aforementioned anatomical structure indices for the main plants are all positive correlations with the δ13C values of plant leaves, indicating that in the different background areas within the small kast catchment basin studied, due to the consistency in external affection factors such as light, heat, water and air, there is a consistent tendency for the response of anatomical structures produced by plants themselves, for the plants adjust themselves to the environment. |
修改评论