A Study Of The Allometric Scaling Law On The Plant Photosynthetic And Respiratory Rates, In Relation To Plant Body Size And Nitrogen Content

According to metabolic scaling theory (MST), plant metabolic rate is nearly isometric to body size (biomass) for seedlings and samplings, and the scaling power is convergent to a constant 3/4 with the increasing of plant size. Subsequently, on the basis of MST, metabolic theory of ecology (MTE) put forward that the integration of plant size, temperature and nutritional conditions regulate individual metabolism. However, there are some academic issues about the generality of MST and MTE. This study aimed to test the metabolic scaling theory and develop the metabolic theory of ecology by analyzing the scaling relationship of metabolic rate with plant size and nitrogen content.Here, about 2000 plant individuals,152 species, including 88 herbaceous angiosperm species, 45 broadleaf angiosperm species and 19 conifer gymnosperm species, were used to explore i) the scaling relationship of whole-plant carbon assimilation rate, whole-plant dark respiration, instantaneous carbon use efficiency to whole-plant biomass and nitrogen content; ii) the scaling relationship of leaf, stem and root dark respiration to corresponding organ's biomass and nitrogen content.Through analyzing the scaling relationship between whole-plant photosynthetic rate and biomass, it was revealed that the allometric power for coniferous gymnosperm significantly differed from broadleaf and herbaceous angiosperm groups, but no significance was found between broadleaf and herbaceous angiosperm groups. It was also shown that the scaling exponent of temperature corrected whole-plant respiration to biomass for herbaceous angiosperm group significantly differed from broadleaf angiosperm and coniferous gymnosperm groups, but no significance was found between broadleaf and conifer groups. However, the scaling powers of non-temperature corrected respiration to biomass were not significantly different among these three plant groups, only the difference of intercept among them was significant. There was no identical allometric power for these three different plant groups. Through analyzing the scaling growth relationship between whole-plant photosynthetic rate and nitrogen content, it was shown that the allometric power of coniferous gymnosperm significantly differed from broadleaf and herbaceous angiosperm groups, but no significance was found between broadleaf and herbaceous angiosperm groups. The whole-plant respiration rate and nitrogen content scaling growth relationship were strongly significant among three different plant groups. Therefore, there was no constant exponent power between whole-plant carbon assimilation rate, respiration and nitrogen content.The scaling relationship of leaf respiration to biomass and nitrogen content were nearly closed to isometric relationship for these three different plant groups. The scaling relationship of stem respiration to biomass significantly differed between broadleaf and conifer groups, conversely, the scaling of stem respiration to nitrogen was not significantly different. The scaling of non-temperature corrected root respiration to biomass of coniferous gymnosperm significantly differed from broadleaf and herbaceous angiosperm groups, but no significance was found between broadleaf and herbaceous angiosperm groups. The scaling of temperature-corrected root respiration to biomass significantly differed among these three plant groups. The scaling relationship of root respiration to nitrogen content for herbaceous angiosperm group significantly differed from broadleaf angiosperm and coniferous gymnosperm groups, but no significance was found between broadleaf angiosperm and coniferous gymnosperm groups.There were not significant linear regression relationship between the instantaneous carbon use efficiency and whole-plant biomass for herbaceous and broad-leaved angiosperm groups. For coniferous gymnosperm group, however, the instantaneous carbon use efficiency significantly declined with increasing plant size.So, conclusions had been drawn as following:1) The scaling exponent of metabolic rate to body size is not varying from 1 to 3/4 or a constant 3/4 but varying from 1 to 2/3, and the covariation between exponent and the scaling constant (intercept) is strongly significant;2) The metabolic rate is varying with nitrogen content as allometric relationship instead of isometric relationship;3) The difference of slope-intercept covariation among these three plant groups is probably related to the distinction of evolutionary morphologic and physiological traits;4) Metabolism of plant is restricted by both plant body size and nutritional conditions. That is different from animal's regulation by the inner fractal-like vascular network. It is probably due to the distinctive nutrition style between them. Particularly, plant photosynthetic rate is mainly regulated by leaf nitrogen content. In general, through analyzing large numbers of datasets, this study not only provides empirical evidence for developing the metabolic theory of ecology but also has paramount implications for plant individual carbon balance, ecosystem carbon budgets, and modeling about forest production, carbon flux and patterns of biomass distribution.