Responses Of Reproductive Characteristics And Allometric Exponent Of Ephemerals Cardamine Hirsuta To Environmental Heterogeneity And The Relative Mechanisms

Plants evolved many allometric patterns in response to natural selection pressures, density and the dramatic changing global ecological environment have been the important natural selection pressures. This study analysised the seed germination, growth characteristics, biomass accumulation and allocation, flowering phenology and fruit traits of ephemerals Cardamine hirsuta through the way of simulating warming by open-top chambers, light intensity, water stress and different matrixes combined with population density, in an attempt to explore how the allometric relationship and adaptive characteristics respond to environment heterogeneity, in order to provide scientific evidence and theoretical support for rational use and protection of ephemerals resources. The main results are as follows:(1)The seed germination percentage and index of C. hirsuta showed no significant effect to simulated warming, while warming significantly promoted the growth of height and stem biomass accumulation, and significantly increased total leaf area, mean leaf area, leaf area ratio, so that their allometric exponent became larger, but had no significant influence on leaf number and branch number. The flowering onset and the peak flowering date of OTC were later than CK, but endset of flowering advanced, flower duration shortened. Besides, warming significantly increased fruit number, fruit length, seed number, reduced fruit diameter and thousand seed weight. It showed that warming facilitated plant’s metabolism and photosynthesis, thus promoted the growth of leaf, height, stem biomass accumulation and fruits, even prompted concentrative flowering so as to complete the whole life cycle successfully. Moreover, the allometric relationship changed due to warming, and density effect was obvious.(2)The seed germination percentage of C. hirsuta rose with the decrease of light intensity. Under the pressure of density and shading condition, plants were unable to produce more leaves with limited resources, so C. hirsuta increased height and leaf area to better photosynthesis, and the slope of total leaf area and density became calm in CK treatment. Shading resulted in photosynthesis weakened, photosynthate reduced, therefore branch number, fructification ability and biomass accumulation decreased, however, the ratio of stem and leaf biomass rose up, besides, the allometric exponent among each organ biomass changed with light intensity and was in accordance with the optimal allocation theory. The flowering phenology between different light intensity treatments was different, the onset time, the peak flowering date, the end of flowering of S1 was significantly earlier than CK and S2, yet S2 was significantly later than CK. C. hirsuta delayed flowering when shading seriously, to lessen the damage of adverse environment, thus the allometric relationship expressed its nice adaptivity.(3)The seed germination percentage of C. hirsuta decreased when water reduced. The increase of water stress intensity significantly reduced plant height, total leaf area, mean leaf area, branch number, but leaf area ratio and leaf area index increased. The biomass accumulation significantly decreased under water deficit, photosynthate transferred to underground to promote root growth, get more water and nutrients to enhance its competitive ability. The flowering phenology was different between each density and water treatment, the duration of flowering shortened in high density, the flowering onset of W3 delayed compared with W1 and W2, thus flower duration significantly shortened, flowering number and fructification were significantly inferior to W1 and W2. Meanwhile, the reduction of allometric exponent reflected the adaption of C. hirsuta to water stress within a scope, but the growth will be restricted if water stress is serious.(4)There were no significant difference between matrixes treatments in seed germination percentage, but germination index of J2 was significantly higher than J1, J3. The height of J2 was significantly greater than J1, J3 at later stages, while total leaf area was significantly lower than J1, J3, leaf number of J3 was significantly more than that of J1, J2, leaf area ratio was J1>J3>J2, but there were no significant differences in mean leaf area, leaf area index and branch number. The total biomass of J2 exceeded J1, J3 at later stages, each organ biomass accumulation showed no significant difference. Root shoot ratio and root mass ratio of J3 were significantly lower than J1, J2, while relative growth rate was significantly higher than J1, J2, stem mass ratio of J2 was significantly higher than J1, J3, reproductive allocation ratio was significantly lower than J1, J3. The maximum allometric exponent of the relationships between height and root length, stem diameter, stem biomass and root biomass in J2 indicated its fast stem grow rate. The flowering onset and endset of J2 both advanced, but there were no significant influence on peak flowering date and flower duration. There existed differences among fruit number, fruit diameter and thousand seed weight, no difference in fruit length and seed number, and it showed that fruit number, fruit diameter of J3 was bigger. We can draw the conclusion that the allometric relationship varied with different matrixes and density, and turfy soil that rich in organic matter was more suitable for biomass accumulation, sandy soil promoted the growth of stem, loess was conducive to the growth of the root due to its water retention.