Variation Of Intraspecific Interaction And Metabolism Of Energy Substances Of Different Crops In Different Density Gradients

Plant density dependence has been a central research area in ecology.The essence of plant density dependence effect is neighbor plant interaction including positive and negative factors.Previous studies indicated that positive and negative interactions change along with environmental stress gradients.However,it is still unclear whether crop intra-specific interactions change along with ontogeny and population density in good environment condition.Furthermore,based on MTE and the principles of energy metabolism,ecologists have developed a general model that describes the relationship between metabolism rate and body size for organism.While,the test for the model almost focused on a certain growth stage of plants.It is still unclear whether crops(from seedling stage to the mature period)follow the same allometric laws under different population density(different intensity of competition).And is there some intrinsic relationship between these allometric laws and intraspecific interaction?In order to explore the above questions,the experiment of 15 density gradients was conducted for three crop species(soybean,wheat and corn)respectively.Five traits(plant height,basal diameter,canopy,biomass and density)were investigated for five times during crop growth.Relative interaction intensity(RII)was calculated based on individual biomass to explore dynamic variation of population positive interaction along with crop ontogeny and density gradients.Analysis results showed that: 1)During crop seedling stage,population positive interaction is detected with medium density,which facilitate plant growth and development;2)During the mature period,interactions between neighbor individuals change from positive to negative.Meanwhile,competition intensity increase along with increasing population density.Self-thinning phenomenon may occur at strong competition intensity.3)There is no constant allometric exponent value between plant height and basal diameter.Plant height increased with growing basal diameter for corn and wheat,while soybean is the opposite.4)The allometric exponent change from 0(seedling stage)to-3/4(mature period)between average individual biomass and population density.5)The allometric exponent change from 1(seedling stage)to 3/4(mature period)between each component dry mass(except reproductive biomass)and above ground dry mass.But the allometric exponent between reproductive dry mass and above ground dry mass is 1 to 3/2 at the mature period.It is suggest that growth rate of reproductive organs is larger than other organs at the mature period.6)The allometric exponents are different between each component dry mass and above ground dry mass under different interactions(facilitation and competition)at the different growth stages respectively.But the varying patterns of three kinds of crops are consistent.The allometric exponent between stem biomass and above ground biomass under facilitative condition is greater than that under competitive condition,while leaf is the opposite.And the patterns of sheath(or petiole)and leaf are the same.This study could provide experimental foundation for further exploring the mechanism of plant positive/negative interaction variation.Furthermore,the results verified Allee effect and Stress Gradient Hypothesis,and improved MTE,and provide scientific foundation for agricultural management.