| Chinese fir is the characteristic fast-growing tree. It is also one of the most important timber forest afforestation species in southern China, with the increasing plantation cultivation area and successive planting of Chinese fir. Because of the lack of effective phosphorus in south China seriously restricted to maintain long-term productivity for Chinese fir plantation. Due to different plants or different genotypes plants had a significant difference on the adaptability to nutrient stress. In recent years, some researches had shown that there were obvious differences between P absorption and utilization efficiency of different Chinese fir clones. High phosphorus (P) utilization efficiency Chinese fir clones could change physiological indexes through enhancing photosynthetic efficiency, improving acid phosphatase activity in leaves and root, increasing the type and number of organic acids, and adjust morphological indexes such as root phenotype, root configuration to response to low P stress.However, the hyperplasia of plant roots will increase the consumption of limited P nutrition in the body under low P environment. According to Lynch’s "cost-benefit" theory, which concerned on the behavior of root finding nutrient, when P resources in plant were insufficient to meet the nutrient requirements of the scope of root expansion, root growth were blocked obviously, it meant the opportunity of nutrients capture from the soil was greatly reduced in plants. How plants balanced the absorption and consumption of limited phosphorus nutrient in the low phosphorus environment to maintain the normal growth? Some scholars found that the low phosphorus stress could induce some plant root cortex cells dissolved and formed cavity, the cavity was quickly occupied by the air to be aerenchyma, on the one hand, reduced the respiration consumption of old tissue in the stress, eased competition of photosynthate by different organization, had a role to ensure normal growth of young tissue; on the other hand, phosphorus compounds nutrition dissolved from cortex will be shipped to other parts of the plant to meet the needs of phosphorus and other compounds for plants, the nutrient cycle utilization was conducive to the growth and development of plants. In view of the experience of above forefathers’ research, this study thought that different Chinese fir clones were regulated by series of physiological index to low phosphorus environment, some clones improved the opportunities for finding phosphorus to adapt to low phosphorus environments through the hyperplasia of root, but some of the clones were not obvious, which could still maintain a high productivity by accelerating the phosphorus circulation in body. Those may be related to the degree of root cortex tissue dissolving and the release of P content were different.To verify this hypothesis, this paper selected 13 half-sib families Chinese fie seedlings as research subjects, which based on our previous selection of obvious different root architecture under low phosphorus stress. By simulation of phosphorus stress environment in laboratory, observed the changes of cortical tissue dissolved of primary root tips, root apex under the condition of different phosphorus treatments, analyzed the height, diameter, root growth of Chinese fir, compared the accumulation and allocation biomass of Chinese fir under different phosphorus treatment, researched the variation of phosphorus content, cumulative amount of phosphorus and the whole plant phosphorus use efficiency of root, stem and leaf under low phosphorus stress environment, analyzed the correlation between solubility of root cortex tissue and changes of the above index, clarified the relationship between phosphorus use efficiency and dissolved phosphorus of the root cortex tissue, for in-depth discussion of phosphorus efficient utilization genotype and provides the theory basis for internal response mechanism to low phosphorus stress of Chinese fir. Provided morphological, anatomical and physiological theory,and practice rules for the screening of excellent production, fast-growing Chinese fir species, the main results were as follows:(1) Different phosphorus treatment had an influence on aerenchyma by root cortex dissolve for different Chinese fir family, which exists obvious difference. Histiocyte in root tip and root apex of all Chinese fir families were growth normal under the condition of normal phosphorus treatment; Under the condition of moderate phosphorus stress, only cortex tissue of No.32 family root tip appeared a small amount of dissolved phenomenon, most of the seedling root apex cortex tissue were present different levels of dissolved phenomenon except for No.20, No.25, No.40, No.41; Under the condition of serious phosphorus stress, No.15, No.20, No.25, No.38, No.41 had no aerenchyma in root tip, the percentage of dissolution area from big to small was No.28, No.30,No.27,No.40, No.4, No.23, No.32 and No.36, the root apex cortical tissue had dissolution phenomenon except No.41, compared with the normal supply phosphorus and moderate phosphorus stress, the cortical tissue dissolving area of root apex in serious phosphorus stress was bigger, the dissolving cortical tissue from big to small was No.4, No.32, No.36, No.15,No.30, No.28, No.40, No.23, No.27, No.25, No.20 and No.38.(2) The aerenchyma of Chinese fir root cortex significantly related to seedling height, ground diameter, root growth under low phosphorus stress. Under the condition of different phosphorus, the incremental of height, average ground diameter showed:normal phosphoric> moderate phosphorus stress> serious phosphorus stress. For the root growth of Chinese fir, with the deepening of phosphorus stress, the root growth increment of No.20, No.25, No.38, No.40 and No.41 were increased, on the contrary, the root growth increment of No.4, No.32 and No.36 family gradually reduce, analyzing the correlation from the cortex solubility and height, ground diameter and root growth found that cortex tissue solubility and seedling height had a significant positive correlation as the stress aggravating but this correlation was the opposite from ground diameter and cortex solubility. Root volume, total root length, root surface area, average diameter were negatively related with root cortex tissue solubility under phosphorus stress environment, and with the deepen of stress, the negative correlation gradually significant.(3) The relationship between Chinese fir root cortex aerenchyma formation and the distribution of each organ biomass accumulation under low phosphorus stress is obvious, with the deepen of phosphorus stress, the biomass of stem and leaf of No.20, No.25, No.38, No.40, No.41 were gradually decreased, but the biomass of root and root cap ratio were increased; Each organ biomass of other family’s stem and leaf were gradually increased with the degree of phosphorus stress, but biomass of root and root cap ratio were decreased; Correlation analysis of solubility cortex and biomass showed that solubility of root cortex tissue had a negative correlation with the root-shoot ratio under the stress environment, the correlation coefficient of stem and leaf biomass and root cortex tissue solubility increased gradually. With the deepening of stress, the correlation coefficient of the root tip and root apex cortex tissue solubility with stem and leaf biomass also were increased gradually, while root biomass and solubility of root cortex tissue had a negative correlation.(4) The root cortex aerenchyma formation of Chinese Fir had obvious correlation with the phosphorus content of different organs, P accumulation and whole plant phosphorus use efficiency under low phosphorus stress. Under the condition of different phosphorus treatment, the average content of phosphorus and phosphorus accumulation of root, stem, leaf under different treatment shown as normal phosphoric> moderate phosphorus stress> serious phosphorus stress; From the correlation with root cortex tissue solubility, root cortex tissue solubility had a negative correlation with the root phosphorus content and root p accumulation under the condition of stress, with the stress degree aggravating, the correlation was not obvious between phosphorus use efficiency and root cortex tissue solubility, with the increasing cortex tissue solubility, the correlation coefficient also increased gradually.(5) In conclusion, the Chinese fir which root cortex tissue can dissolve had obvious correlation with phosphorus use efficiency under the condition of low phosphorus, such as No.4 family which was dissolved obviously, with the deepening of phosphorus stress, the increment of root system were decreased gradually, the root biomass, phosphorus content and phosphorus accumulation also had such rule, but the biomass, phosphorus content, phosphorus accumulation of the leaf and stem had increased with the degree of stress, the seedling height, ground diameter, phosphorus use efficiency also showed the same patterns; For the No.41 family, which was not dissolved obvious, despite the cortex cells did not dissolve, Its root proliferation obvious, and maintain a high phosphorus use efficiency with the stress degree aggravating, the adaptive strategy of different Chinese fir family to low phosphorus stress is difference, the purpose to maintain the normal growth of plant. |
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