The Study On Plant Seedling Growth Strategy

Life-history strategy is the significant research area of plant population ecology. The seedling stage is the most critical stage of a plant life history, not only the development of seedling plays an important effect on the plant survial and establishment, but also influenced the size of the population, persistence and impact of genetic variability, and ultimately affect the species composition of community. Therefore, research on seedling growth strategy under different environmental donditions helps to know and elucidate plant growth evolution and ecological adaptation traits. Convolvulus arvensis was used to study the effects on radicle growth of global warming simulated by altering dual temperature gradient; Malva verticillata、Abutilon theophrasti and Pharbitis purpurea were used to test the phenotypic plasticity of hypocotyl under the interaction of light and burial depth of seeds; Ricinus communis was used to comparative study the photosynthetic characteristics of cotyledon and primary leaf during early seedling development stage; Pharbitis purpurea was used to test the compensatory growth and photosynthetic responses to clipped cotyledon and second leaf, and the compensatory growth responses of seedlings of Pharbitis purpurea to tissue removal at different burial depths, and discussed the compensatory mechanism of cotyledon of dicotyledonous species; Leonurus japonica、Datura stramonium、Abutilon theophrasti and Pharbitis purpurea were used to test the effect of different seed depths and light on seedling emergence and growth; Amaranthus retroflexus、Abutilon theophrasti and Pharbitis purpurea were used to test the interaction effect of simulated nitrogen deposition and global warming simulated by alternating temperature regimes on seedling emergence and growth.The results shown of dual variable temperature gradient in the global warming that it retarded seedling morphology and biomass allocation independent with soil temperature when the air temperature was 10℃, it promoted seedling morphology and biomass allocation dependent with soil temperature increasing when the air temperature was 20℃, it inhibited the height and root length of seedling, fine root number and seedling biomass dependent with soil temperature increasing when theair temperature was 30℃. The seedling morphology and biomass accumlation were increase with air temperature increase at the same soil temperature condition, and altered the distribution of fine root.In each burial depth treatment, the length of hypocotyl aboveground was dcreased with increasing light transmission, but the weight of it was increased with increasing light transmission. The length of hypocotyl belowground was not significantly effect by light transmission, but the weight of it was increased with increasing light transmission. In each light transmission treatment, the length and weight of hypocotyl aboveground were decreased with increasing burial depths, but the length and weight of belowground were increased with increasing burial depths. And there was no interaction effect among seed size, light transmission and burial depth on length of hypocotyl. Moreover, in each light transmission treatment, with increasing burial depth, the aboveground hypocotyl-mass ratio decreased, while the belowground hypocotyl-mass ratio increased. In each burial depth, with increasing light transmission, the aboveground hypocotyl-mass ratio decreased, and while the belowground hypocotyl-mass ratio increased. And the significant effects were found for seed size, light transmission and burial depth and their interaction on aboveground or belowground hypocotyl-mass ratio.The growth of cotyledonary area accorded with exponential growth mode y = a*(1-e-bx), but the area of first true leaf accorded with logisitic growth mode y = a/[1+e-(x-x0)/b]. The net photosynthetic rate of cotyledon on 13d-age has the maximum value in the life cycle of cotyledon, and achieved the peak at 13:00 in each day. According to the results of net photosynthetic rate of cotyledon and leaf on the same day age, the PN of cotyledon is higher than that of leaf at the primary stage, and there is no significant difference at middle stage, but the PN of leaf was significant higher than that of cotyledon at end of the stage. The PN of cotyledon and leaf accorded with binomial growth mode y=-0.0855x2+2.0513x+1.284 and y=-0.0272x2+1.5423x-4.0277, respectively.The longevity, area, thickness and biomass of remnant cotyledon of clipped cotyledon treatment (CC) were significantly heigher than those of clipped second leaf treatment (CL) and control group (CG), but there was no significant difference between CL and CG. The remnant cotyledon of CC and CG exhibited over- and equal-compensatory growth, respectively. But the seedling height, root length, biomass accumlation and allocation of CC were significantly lower than those of CL and CG, but there was no significant difference between CL and CG. The seedlings of CC and CL exhibited under- and equal-compensatory growth, respectively. The diurnal changes in photosynthetic rates showed significantly different patterns which were unimodal curve (CC) and bimodal curve (CL and CG), respectively. The PN of primary leaves of CL and CG treatments showed similar photosynthetic patterns characterized by a bimodal curve, and PN of the primary leaf of CL was slightly higher than that of CG treatment.The ramnant cotyledon and leaf can exhibit compensatory growth after cotyledon and leaf tissue damaged at seedling stage, and the compensatory growth of remnant cotyledon was significantly higher than that of remnant leaf. Further experiments showed that the compensatory growth of cotyledonary traits which emerge from 2cm depth significant higher than those from 5cm depth. In contrast, the relative compensatory growth rates of cotyledon area and mass were greater at 5 cm depth. The results of this sutdy shown that cotyledon can develop an compensatory strategy to minimize the negative influence for lossing leaf tissue, and provide an useful indication for seedling growth strategy under different habitats.The seedling emergence was decreased with increasing burial depths, but the time to emergence was increased with increasing burial depth. Moreover, the emergence and the time to emergence were not significantly affected by light transmission treatment. The area and thickness of cotyledon of four species were decreased with increasing burial depth. In each burial depth, the area of cotyledon was increased with decreasing the light transmission, the thickness of cotyledon was decreased with decreasing the light transmission. The total biomass of seedling was decreased with increasing burial depth, and decreased with decreasing light transmission. And the above and below-ground biomass ratio was increased with increasing burial depth, and decreased with decreasing the light transmission. Meanwhile, it was increased with increasing seed size. The SLA of cotyledon was increased with increasing burial depth, increased with increasing light transmission, and decreased with increasing seed size. The LWR of cotyledon was decreased with increasing burial depth, increased with decreasing light transmission, and increased with increasing seed size. The LAR of cotyledon was decreased with increasing burial depth, increased with decreasing light transmission, and decreased with increasing seed size. The RMR of seedling was decreased with increasing burial depth, decreased with decreasing light transmission, and increased with increasing seed size.The emergence ratio, leaf numbers, area of cotyledon, seedling height and seedling biomass increased, and weight of cotyledon and root length increased and then decreased trend, but the below and above-ground ratio exhibited decreasing and then increasing trend under alternating temperature regimes with low temperature increasing more than high temperature in the same nitrogen concentration situation. In each alternating temperature regimes, seedling emergence, leaf numbers, cotyledonary area, weight, root length and seedling biomass increased and then decreased with increasing nitrogen concentration, but below- and above-ground ratio decreased and then increased. All of the traits increased with increasing seed size under all nitrogen concentration and alternating temperature regimes with low temperature increasing more than high temperature treatment.