| Plant population is the sum of the different age individuals. The age structure and survival process reflects the fluctuation characteristics and environmental adaptation mechanism of the population. Individual survival tyep and growth model at different age classes are closely related with resource distribution characters. In front of lots of selection pressures and constraints, plants have evolved many allometric relationships. Allometric growth relationship not only reflects the requirements of basic physics laws to biological structure, the evolutionary optimization demands of biological individual physiological efficiency, but also provides an important method of ecological scale transformation from the individual to the population and the ecosystem. Salix psammonphila is typical of windbreak and sand-fixation plant in north China region. However, the natural aging of the plations influence the stability of the structure and function of continuous. Therefore, using the age structure and dynamic, the allometric relationship between of the function traits change with the age increasing of the cluster branches, which can be better realize the life-history strategies along an age-sequential and understand the senescence mechanism of S. psammophila.This study focuses on the naturally senescence of S. psammonphila plantation, using the cluster branches, by analysis the population age structure and quantity dynamic, the benefit cost ration and the allometric scale change along the age class, that the allometric scale include the basal diameter with the branch length & length, the stem with twig and leaf et al., the twig number with number. The purpose of the study was to reveal the natural aging process and regulatory mechanism and the resource trade-off strategy of S. psammonphil. Moreover, the result could add a rich range of materials of the plant life history strategies, and provide theoretical guidance for tending management of S. psammonphila plantation.The main results and conclusion obtained in the present study run as follows:(1) The population analysis showed that the branches were characterized by the abundance of 3-year-old branches, and the age structure of branches was spindle shaped. The stationary life table of S. psammonphila branches indicated that the observed life expectancies were the highest in 1-year-old branches, while the mortality rate and disappearance rate were the highest in 5- year-old branches. The survival curve of S. psammonphila branches tended to be of Deevey-Ⅱ type. The survivability of the branches declined at young age and fluctuated at old age. The dynamic index of population size of Vpi’ was close to zero under random disturbance, indicating that the age structure of the branches tended to be stable and was very sensitive to environment disturbance. The time sequence model predicted that the number of individuals increased in the coming 2, 4, 6 and 8 age classes, but the number in young individual deceased. It was assumed that S. psammonphila population would decline from a lack of recruitment of young individuals if appropriate action is not taken to protect and foster these plants.(2) There were some close allometric relationships between the branch longitudinal growth and diameter growth, the branch height growth and branch length growth, and with the diameters at different height of the branch. The allometric scale between the basal diameter growth and longitudinal growth were 0.85(height growth) and 0.71(length growth), and the young and old branch have the isometry scale, and the middle-age branch has the allometric scale. The allometric scale between diameter at 100 cm height and the basal diameter was higher the diameter at 50 cm height and the basal, and the values were 1.24 and 1.17, it indicated that the diameter growth faster at the height than that at the basal, and the allometric relationships werre more outstanding in young branch. Meanwhile, the allometric relationship between the branch height and branch length was very closely, the allometric scale was 1.26, and the 2-year-old branches have the height scale.(3) Biomass accumulation varied with branch basal diameter(BD), branch lengths(BL) and branch age(Age) increased, and BD has a higher coefficient of determination in the form of power functions; The number of the resources allocated to stem, twigs and leaves were changed with the S. psammophila branches growing. There showed the power functions better with BD than BL which the percentages of resource allocated to stem and leaves, and the percentages of twigs biomass to total biomass was better with BL; There existed an allometric relationship between the MS(stem mass), MT(twig mass) and ML(leaf mass), with the SMA slopes were 1.56(αT-S), 1.09(αL-S) and 0.69(αL-T), respectively. The twigs have the highest values which increasing with the branches growing, and the stem has the lowest values of that. Therefore, our results indicated that the optimal partitioning theory and metabolic scaling theory complement each other, and it can explain the biomass changed and the scaling relationship for stem, twigs and leaves in S. psammophila branches.(4) The branch size and age class affect the twig number and the twig size, the number of twig was reduced and the size was increased along the branch growth, and the effects of basal diameter was higher. There is a close negative correlation relationship between the twig number and the twig size, which the twig number was the twig intensity based on basal diameter area, volume, stem & twig biomass and stem biomass. The allometric relationship between twig size and twig number based on stem & twig mass was height coefficient. There is a common slope between with the different age groups of the twig number trade-off the size. With the common slope, the regression intercept was increased with the branch aged, indicated that the old branch has the bigger twig at the constant twig number.(5) The metabolic exponent based on the leaf biomass and total biomass was 0.97 for all branches of the S. psammophila, which was significantly greater than the constant 3/4 propose by the WBE model. The branching radius exponent and branching length exponent for all branches of S. psammophila were 2.67 and 3.83, which were significantly greater than the constant values of 2.0 and 3.0, respectively. 2) The range of branching radius exponents and branching length exponents among the age classes were 2.64-3.24 and 2.86-4.30, respectively. Meanwhile, the estimated values and calculated values of metabolic exponents were 1.01-1.29 and 0.94-1.13, respectively. However, the values of all above were statistically indistinguishable among the six age classes. Furthermore, the common slopes among the six age classes for estimated values and calculated values of metabolic exponents, branching radius exponents and branching length exponents were 1.08, 1.00, 2.84 and 3.35, which were significantly greater than the constant values. 3) The changes of the intercept at the y-axis shifted negatively at the common slope of estimated metabolic exponents, and significantly elevation shifted between groups, the higher age class branches has the greater shift. And these indicated that the age classes changed the metabolic exponents nothing, and changed the metabolic constant significant with branches ages, that the older branch has the lower metabolic activation than younger branches at the same size of S. psammophila branches.(6) The stem & leaf construction cost and leaf benefit are increased with the branch age increasing, the logistic model have good fitting between the cost, benefit and age class. The benefit cost ration was descend with the age increasing, and the 4-age-old branch has the lowest values, and after it, the values were small, it can be fitted by the power function. Which the benefit cost ratio descend was caused by the photosynthetic and leafing efficiency descend, and the specific leaf weight and the stem & leaf construction increased. |
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