Plant Allometric Study Of Biomass Allocation Pattern And Biomass Production Rates

Metabolic theory of ecology is one of attractive area researchs in ecology. This theory predicts that metabolic rates of plants, B, like those of animals, should scale as the 3/4 power of body size M (i.e. B∝M^3/4). In combination with metabolic rate and other ecological variables, as well as translation of information across spatial, temporal, and organizational scales, this theory can explain growth, development, population dynamics, molecular evolution, and patterns of species diversity. The theory, though it being well known, is still controversial.With four different but related studies, this thesis aimed to address two central derivative deductions from the metabolic ecology that have important implications to a variety of important ecological and evolutionary phenomena, e.g., root biomass estimation, carbon exchange between forest ecosystems and the atmosphere, and global research. (1) Aboveground biomass, Ma, (the sum of the stem and leaf biomass) scales, on average, isometrically with respect to below-ground biomass, Mr, (root biomass) at individual level; (2) the rates of biomass production, P, are expected to scale as the 3/4 power of total mass.Firstly, I focused on the environmental influence on the biomass allocation pattern. Interspecific above- and below-ground biomass (M_A and M_R, respectively) data were collected from five sites in northwest China, which were arranged along a natural aridity gradient (aridity index ranging from 0.95 to 1.98). Model Type II regression protocols were used to compare the numerical values of M_A vs. M_R scaling exponents (i.e. slopes of log-log linear relationships) for five sites. The results indicated that the aboveground biomass scaled isomatrically with the belowground biomass and statistically indistinguishable difference was observed among the five scaling exponents (i.e. M_A∝M_R^≈1.0), which were consistent with the "canonical" biomass allocation pattern between above- and below-ground biomass. However, significant variation was observed in the y-intercepts of the five regression curves, largely because of the variation in absolute root biomass at five sites. Then, biomass allocation patternwas scaled up. The theory of metabolic ecology has suggested that aboveground biomass (M_A = stem +leaf) scales isometrically with below-ground biomass (M_R, root biomass) at individual level. I wondered if the same proportions could be holding true across diverse forest-types, regardless of vegetation composition. Two compendia for forest-level above- and below-ground dry biomass per hectare were examined to test the hypothesis that M_A vs. M_R scales isometrically and in the same manner as reported for data from individual plants. The results indicated that above-ground forest biomass scaled, on average, isometrically with respect to below-ground biomass (regardless of how the data were sorted).Thirdly, I extended the biomass allocation patterns derived from metabolic ecology, aiming to provide a new method for the estimation of the regional forest biomass. The derived model was based on the assumption that branches were proportional to stem biomass. The model predicted that any pair of stem biomass, aboveground biomass (the sum of branch, stem and leaf) and total biomass (aboveground + root) scaled isometrically with each other. The empirical results using independent data sets supported the model's predictions, and such relationships could be scaled up to the community level, regardless the environmental conditions (e.g. precipitation, temperature and stand age).Finally, relationships between annual dry mass production and total biomass were tested. Metabolic ecology predicts a 3/4 power relationship between annual dry mass production rates P and body size M regardless stand age (i.e., P∝M^3/4), which has important implications to the evaluation of carbon fluxes, ecosystem health, global carbon budgets, and a variety of other phenomena. To test this prediction, I examined a large data set from Chinese forests with stand age ranging between 20 - 200 yr (10 groups). My analyses indicated ten P vs. M scaling exponents were statistically indistinguishable and shared a common (nearly isometric) slope (i.e. P∝M^≈1.0), and their Y-intercepts systematically declined with increasing stand age. Clearly, P vs. M scaling relationships were inconsistent with the 3/4 scaling prediction. These results may be due to systematic variance in N and average tree M with increasing stand age resulting from changes in tree size frequency distributions.