The Study Of Plant Phenotypic Plasticity And Life-history Strategies

Phenotypic plasticity of life history characters in plant size, morphologic character, and vegetative growth, reproductive growth in response to different light, nutrient, planting density and sowing dates was test to reveal plant strategies to adapting variable environment. Six main conclusions could be obtained from the field experiments conducted during the years from 2003 to 2005 and they were as follow:(1) Amaranthus retroflexus show high morphologic plasticity in response to different light, nutrient and density. Plant height, width, branch number and branch length decreased with decreasing light and nutrient, but increased with decreasing density. Allometric relationship between height and mass was not influenced by external light, nutrient and density; allometric exponents between width, branch number and mass decreased with increasing density; allometric exponents between between branch number and mass decreased with decreasing light. Allometric exponents between lateral growth (width and branch number) and vertical growth (height) decreasing with increasing planting density and decreasing light, but not influenced by nutrient. Adaptative plant form greatly depends on light environment, which is the degree of crowding by neighbours (competition for light). As competition for light increases, there should generally be an increasing premium on vertical growth through stronger apical dominance to minimize shading by neighbours. Conversely, as competition for light decreases, there should be an increasing premium on branching that is achieved through weaker apical dominance to maximize light capture.(2) Static allometric analysis among the individuals in different light or nutrient treatments show that variation in biomass allocation as a function of plant size rather than in response to limiting resources in most stages of life cycle. While dynamic allometric analysis support optimal partitioning theory that decreased nutrient supply increased allocation to roots, and decreased light supply increased allocation to leaves. Plants allocated relatively more biomass to roots than to leaves as plants grew larger. Conflation of static allometric relationships with dynamic allometric growth may be the source of great confusion within the literature on plant allometry. Static allometric relationship only can represent size-dependent allocation among individuals of different size at one point in time; it should not be taken as indication of the allometric pattern over the course of growth and development.(3) Allometric analysis between reproductive biomass and vegetative biomass across treatments showed that reproductive effort increased with size in response to different planting densities, but decreased with size in sowing dates experiment. The allometric exponent between treatments was not influenced by planting densities, but had significant variation with sowing date. Total branch length could explain most of the variation of reproductive accumulation and allocation in planting density experiments. For the plants with different sowing dates, total branch length was the main determinant of reproductive biomass, while reproductive effort mainly depended on the number of primary branches per unit stem mass. Architectural constraints with size result in size dependent reproduction. Size-dependent reproduction in A. retroflexus was influenced by available resources and environmental conditions through the mechanisms of self-regulation of architectural traits.(4) Life-history characters showed high plasticity in response to different sowing dates. Later germinating plants had relatively faster growth rate and smaller size at reproduction than earlier germinating plants. Delaying germination led to relatively earlier reproduction and a relatively greater allocation to reproduction. Much of the variation (60%) could be explained by a single axis of a PCA analysis. The attributes on this axis were similar to the C-R axis of...