Effect Of Density, Individual And Seed Size On Distribution Of Biomass

Individual level and populations, community are the main research contents of ecology.Size as one of the basic traits of an organism, its growth and development affects the morphology, growth rate, metabolic rate and the ability to reproduce and so on, and size are modulated by their genetic variation and environmental factors, as same as population density,different population density lead to multiple intraspecific competition, affect the morphological characteristics of the species. Optimal allocation theory and allometric distribution theory of plant biomass of is a results that plant adapt to altered habitat environment; allocation of plant biomass is the most fundamental the restriction for the plant competition. The experiment is based on the above two ecology theories, consists a field trials and a greenhouse experiment. Field trials included 17 density gradient(1, 3, 5, 7, 9, 12, 16, 20,30, 60, 80, 100, 300, 400, 500, 600 and 700 plant m-2) for corn, it was conducted from June to October in 2014 at Northwest Agriculture and Forestry University to determine the morphological and agronomic traits during maize growth season. To represent genetic variation in grain crops around the world, we selected 32 genotypes from 20 major grain crop species(oil, cereal and legume crops) in greenhouse experiment, 11 of which were dicotyledons and nine were monocotyledons. Seed biomass of the 32 genotypes spanned two orders of magnitude(Fig. S1). We studied the allometric relationships of MB vs. MA during the seedling stage to test two hypotheses:(1) after long-term domestication by humans, MB does not scale in an isometric manner with respect to MA in grain crops, and(2) large-seeded genotypes allocate more biomass to roots during seedling growth. The results showed that:(1) With the change of time, average corn plant height for 3 and 9 plant m-2increased firstly until 70 days, then had no changes. The plant hight for higher densities increaseduntil55 days, then had no changes anymore. At the harvest stage, the higher the densities had smaller stem diameter. The plant height first increase then decease with the increase of density,which means moderate competition can promote the increase of plant height. Fierce competition inhibits the growth of plant height. With the increase of density, the biomass in different organs decreased significantly, the percentages of leaf, stem, sheath in aboveground biomass gradually increases, but percentage of Reproductive organ biomass is obviously decreased. Within the scope of the low density, with the increase of density, grain yield per plant and the ground biomass did not change substantially, but when beyond a certain range, with the increase of density, both of them linear decreased. The relationship between grain yield and biomass on the ground in line with the conic function, with the increase of density, grain yield and biomass per area linearly increase then decease. For annual crops of corn, the relationship between the density and yield does not meet the laws of Constant Final Yield.(2) There were significantly allometric relationship between organs, and organs versus bodymass. Biomass of organs and shoot biomass were negatively correlated with densities.With increasing density, less biomass was allocated to leaves, stems, sheath, more biomass were allocated to Reproductive organ biomass. Distribution of corn biomass was size independent.(3) The scaling exponent of MB vs. MA during 30 days of growth was 0.937 across the32 grain crop genotypes, 0.999 for the dicotyledons and 1.034 for the monocotyledons. Based on the 95% CIs of the MB vs. MA scaling exponent(αRMA) of the data sets for the 32 genotypes, eight values exceeded 1.0, nine values were less than 1.0 and the remaining 15 values were statistically indistinguishable from 1.0. Seed size was positively correlated with the scaling exponents of MB vs. MA for the 32 genotypes(P<0.05), which means large-seeded species generally had more potential for allocating biomass to roots during the seedling stage. These findings suggest that a uniform isometric relationship exists in grain crop species and that artificial selection in crop species has not changed this relationship. In addition, larger seeds are an evolutionarily-stable strategy based on high grain yield per area.