| Nutrient resorption of plants has a profound influence on the development of population, the nutrient cycle of ecosystem and the maintenance of ecological environment. Eucalyptus grandis is currently one of the main tree species planted in the hilly region of Sichuan Basin. Due to the characteristic of fast-growing, nutrient has been one of the most important factors restricting the growth of population. Therefore, it is very vital to explore the characteristics of the nutrient resorption of E. grandis population. In order to know the characteristics of nitrogen (N), phosphorus (P) and potassium (K) resorption and the relationship between nutrient resorption and soil fertility so as to enrich the ecosystem theory about E. grandis population and direct the management of E. grandis plantation in Sichuan, we researched the characteristics of N, P and K resorption, including resorption efficiency (RE) and resorption proficiency (RP), of the leaves of3-year E. grandis population located in different slope locations (i.e. the upper slope:U, the middle slope:M, the lower slope:L) in Yibin through monthly sampling from May2011to April2012and compared the differences of the characteristics of nutrient resorption based on two methods, i.e. per unit mass and per unit leaf area, meanwhile investigated the soil pH, the entire and available N, P and K in the soil, and discussed the relationship between the N, P and K resorption abilities and the N, P and K contents in soil. The results were as follows:(1) The mean values of12samplings of N, P and K resorption efficiency based on per unit mass in three slope locations were:U,42.45%,56.87%,48.40%, respectively; M,42.13%,56.35%,41.53%respectively; L,44.37%,60.54%,36.90%, respectively, and the monthly mean values of N, P and K resorption proficiency based on per unit mass were: U,6.05mg/g,251.51μg/g,3.12mg/g, respectively; M,5.74mg/g,256.05μg/g,4.17mg/g, respectively; L,5.57mg/g,244.53μg/g,4.49mg/g, respectively.(2) The mean values of12samplings of N, P and K resorption efficiency based on per unit leaf area in three slope locations were:U,46.01%,63.26%,53.01%, respectively; M,46.15%,63.23%,47.33%, respectively; L,46.37%,64.96%,41.39%, respectively, and the monthly mean values of N, P and K resorption proficiency based on per unit leaf area were:U,625.03mg/m2,25.94mg/m2,320.5lmg/m2, respectively; M,563.55mg/m2,24.97mg/m2,409.97mg/m2, respectively; L,547.19mg/m2,22.06mg/m2,444.73mg/m2, respectively.(3) According to the mean value of resorption efficiency based on12samplings and the differences of resorption efficiencies in three slope locations that repeated most, it was found that the resorption efficiencies based on both the methods of per unit mass and per unit leaf area had the same trend, being that the resorption efficiencies of N and P had bigger values in the L than that in the U and the M, while the resorption efficiency of K was U>M>L. Meanwhile, according to the mean value of resorption proficiency based on12samplings and the differences of resorption proficiencies in three slope locations that repeated most, it was found that the resorption proficiencies of N based on both methods were U>M>L, while the resorption proficiency of P had different trends among three slope locations by using different methods, showing M>U slightly based on per unit mass and U>M slightly based on per unit leaf area, and the resorption proficiencies of K based on both methods were U<M<L.(4) There was less difference for slope locations in N, P and K resorption proficiency monthly dynamics based on the same method. For mean resorption proficiency of three slope locations based on different methods, the difference of resorption proficiency monthly dynamics among U, M and L only existed in N in months of small variation amplitude. N and P resorption proficiencies based on leaf mass and area in this E. grandis plantation mostly showed that all of them firstly decreased slowly and then increased slowly from May to November, rose sharply in January, reached the peak in February, began to fall back in March, and were the level in April which were slightly higher than that in May. There were differences for N and P resorption proficiency dynamics in December, i.e. N resorption proficiency dropped to the lowest, while P increased sharply. Except for June, K resorption proficiency gradually rose to the peak from May to November, but obviously declined in December, and then fluctuated gently from January to April. Monthly dynamics of N, P and K of E. grandis population is closely related to climate, phenology, transfer properties and functions of mineral elements.(5) Partial physicochemical properties of soil in three slope locations of this plantation were analyzed in May2011. The results were:soil pH varied from3.1to3.5; entire P, entire K, available P and available K increased with the decreasing of slope locations by altitude, but entire N and hydrolysable N did not; there were significant differences for both entire P and K between U and L and for available K between M and L (P<0.05). This survey found that the soil in this research region was lack of P and soil acidity was very high. Therefore, for improving soil fertility and forest productivity, measures such as applying lime into soil, protecting the litter, and increasing soil P content by applying the organic and inorganic P fertilizer should be taken.(6) According to the results based on both the methods of per unit mass and per unit leaf area, it was found that K resorption ability of E. grandis decreased with the increasing of soil K content (resorption ability is a comprehensive index of resorption efficiency and resorption proficiency, i.e. higher resorption efficiency and lower resorption proficiency represent more resorption ability, vice versa), but both of N and P resorption ability did not have this phenomenon. P resorption ability, not only judging by the mean value of three slope locations, but also in situations of each slope location, was much higher than that of N and K. Both of which partly indicated that there is a negative correlation between E. grandis’s nutrient resorption ability and soil fertility. The phenomenon without the negative correlation between N, P resorption ability of E. grandis and soil N, P content respectively, probably was resulted for lacking of significant variation among slope locations.(7) The mean values of N, P and K resorption efficiency calculated by per unit mass were3%higer than that calculated by per unit area, respectively. There were differences in the results of which one was higher between the upper and the middle slope location of N resorption efficiency and P resorption proficiency calculated by different methods, and in monthly dynamics of N, K resorption proficiency between two calculation methods, respectively. |
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