| Gramineous plants are considerable distributed in the whole world. They can tolerate some extreme physical and chemical conditions in the copper tailings wasteland, such as the droughty conditions, extremely changed temperature, extreme pH, high salinity and high concentrations of harmful substances. They are also commonly survived from the nutrition stress in the barren habitat of the copper tailings. According to these ecological adaptive characteristics, gramineous plants become the mainly dominant vegetation group in the copper mine tailings. In this study, the nutritional strategy of Imperata cylindrica (Linn.) Beauv living in the copper tailings wasteland was explored. And the effect of Ⅰ. cylindrica growth metabolic process on nutrient level of copper tailings soil ecosystem was studied. The main research contents and conclusions are as follows:1. The nutrients conditions and other physicochemical properties of the copper tailings had more severe spatial heterogeneity. The number of the ground cloning seedlings and the rhizome length of Ⅰ. cylindrica increase significantly with the rich content of total nitrogen (r=0.513, p<0.05; r=0.687, p<0.01) and effective phosphorus (r=0.695,p<0.01; r=0.486, p<0.05) in the copper tailings. But the difference of the nutrients content in the stems and roots of Ⅰ. cylindrica between barren tailings and rich tailings was not significant. This indicated that Ⅰ. cylindrica was to adapt the barren environment of the tailings by reducing the physiological plasticity and improving its morphological plasticity. To increase the chances of looking for and absorbing nutrients, the roots of I. cylindrica were distributed in different nutrients level microhabitat in the copper tailings.2. P dynamics from rhizosphere of Ⅰ. cylindrica and other five plants in the copper tailings were studied. The results indicated that the plant growth decreased the rhizosphere pH by0.16-1.40pH units significantly. The difference of contents of soil inorganic P (Pi) and organic P between the rhizosphere and no-plant tailings were significant (p<0.05). The alkali-phosphatase activity in the rhizosphere was significant higher than in the no-plant tailings (p<0.05). The mean concentration of Ca2-bound Pi, Al-bound Pi and Fe-bound Pi in all the rhizosphere was significantly enhanced compared with the no-plant tailings, with the increase range from86.56%to147.58%, from5.46%to88.86%and from49.22%to214.20%respectively. All the other forms of phosphorus except Ca8-bound Pi and Caio-bound Pi, were shown to be negatively correlated with pH in the rhizosphere (r=-0.586, p<0.01; r=-0.487, p<0.05; r=-0.417, p<0.05). Among the studied species included the study, this capability of Indigofera pseudotinctoria on enhancing available P content was the most significant. Among three graminaceous plants, the relative content of available P in Ⅰ. cylindrica rhizosphere was the highest.3. The impacts of the roots activities of Ⅰ. cylindrica on its rhizosphere inorganic nitrogen dynamic were studied and with the five associated plants as control in the copper tailings. The results showed that the growth of plants influenced effectively the contents of total nitrogen and bioavailable nitrogen, and the contents of inorganic nitrogen and total nitrogen in all the plants rhizosphere were significantly higher than that in no-plant tailings (p<0.05). The percontages of all the forms inorganic nitrogen in the total nitrogen in the gramineous rhizosphere were slightly higher than that of other plants. The percontage of nitrate nitrogen in total nitrogen was significantly higher than in leguminous and compositae communities (p<0.05). The percontage of ammonium nitrogen in total nitrogen was also significantly higher than that of compositae rhizosphere (p<0.05). These indicated that Ⅰ. cylindrica could increase the ratio of bioavailable nitrogen in total nitrogen by roots activity in order to improve the absorption efficiency of nitrogen nutrition around the root system.4. N and P distributions, N:P, nutrient resorption rate, nitrate reductase and acidic phosphatase activities of Ⅰ. cylindrica organs in the copper tailings and the farmlands as control were investigated. The results showed that N and P in both populations were mainly in the rhizomes in the growth initial stage. At bud and mature times, N and P concentrations were highest in leaves and lowest in roots and rhizome. At the decay period, N and P concentrations in senescent leaves were9.19±0.80and0.05±0.03mg·g-1,respectively, which were significantly lower than for the control farmlands (p<0.05). The N and P resorption efficiencies of Ⅰ, cylindrica leaves in the tailings were49.54%-65.22%and74.71%-98.71%, respectively, with P in senescent leaves resorbed completely. Nitrate reductase activity of Ⅰ. cylindrica leaves in the tailings was significantly higher than in the farmlands (p<0.05), and this is useful to regulate Ⅰ. cylindrica nitrogen metabolism activities. But with plant growth, the differences gradually disappeared. At the same growth period, acidic phosphatase activity of Ⅰ. cylindrica leaves between the tailings and the farmlands were not significantly significant (p>0.05). With the plant growth, the acidic phosphatase activities increased, which was conducive to decompose organophosphate in senescent leaves and increase P resorption efficiencies. In short,Ⅰ. cylindrica might reduce the nutrition stress from the copper tailings by the timely distribution of N, P in its tissues, the enhancing resorption efficiencies of nutritions and the adjusting nutrition metabolism enzymatic activities.5. The soil and tissue litter of Gramineae (I. cylindrica and Zoysia sinica Hance) and Cryptogam (Hippochaete ramosissmium and algal-moss crusts) in the copper tailings were collected as experimental material. The differences and relationships of C, N contents, carbon isotope ratio (δ13C) and nitrogen isotope ratio (δ15N) between litter and soil were analyzed. The soil δ13C and δ15N in all community areas were lower than those in no-plant tailings. The correlation of C content between the litter and soil was significant in Gramineae community (r=0.998, p<0.01), but the relationship in Cryptogam community was not found. The effects ofⅠ. cylindrica and algal-moss on soil13C enrichment were significant, and the microbial biomass C (r=0.729, p<0.01), water content (r=0.716, p<0.01) and pH (r=0.529, p<0.05) also effectively affected soil813C. In contrast, the significant correlation was observed only between microbial biomass N and soil δ15N (r=0.935, p<0.01), and the other factors had no obvious effects on soil815N in the tailings. |
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