It is a universal phenomenon that most individuals in a plant population flower in a relatively short period of time as influenced by photoperiod. Puccinellia chinampoensis is a salt-tolerant tuft grass. The flowering stage of P. chinampoensis populations lasts for about 20 days in alkalized meadow in the Songnen Plains of China, while the ripping stage lasts for only a few days.
Large samples of reproductive tillers of P. chinampoensis population were randomly marked with labels every three days at the early earring stage, and the samples marked at five times were reaped together at the dough stage. The differences of the quantitative characters with time were compared among the five samples. Regressive analyses between the means of the quantitative characters and the time of prolonged reproductive growth, and correlation analyses between the growth and the production of every sample were made. The fitted equations with the highest R2 were selected from linear, power, exponential and quadratic functions as the models to describe the relationships. The early earring stage was defined as the date when spikes reached about one centimeter from top leaf. The reproductive growth stage was defined as the period from early earring to dough stage. The time of prolonged reproductive growth for each of the samples was defined as the time difference between its reproductive growth time and that of the last sample.
Results of statistical analysis showed that there were significant differences among the five samples in spike biomass and the longer the reproductive growth time, the larger the variances of the quantitative characters, reflecting large phenotypic plasticity of the reproductive tillers in P. chinampoensis population. As the time of reproductive growth prolonged by 16 days, the mean height of tillers increased by 23.16%, and the mean length of spikes by 25.70%, the mean biomass of tillers by 74.99%, the mean biomass of spikes by 1.63 times and the mean reproductive allocation by 93.25%. Prolonged time of reproductive growth had a positive effect on the growth and production of tillers, especially the increase of spike biomass and the allocation of nutrients to spikes.
Results of regressive analysis showed that tiller height, tiller biomass and spike biomass of P. chinampoensis population increased exponentially with the time of prolonged reproductive growth, and spike length and reproductive allocation increased linearly, while reproductive growth radio increased first and then decreased, namely a parabola pattern. By comparing increasing rate (coefficient) ‘b’ in the regressive equations, it was indicated that the assimilated products in the tillers were first allocated to the growth and development of spikes, and then to that of tillers. When the contributions to present population and future population were estimated by tiller biomass and spike biomass respectively, the longer the time of prolonged reproductive growth, the larger the contribution to present and future populations.
There was the same growth regulation among the reproductive tillers in P. chinampoensis population with different earring dates. Spike length increased exponentially with tiller height in an allometry way, and spike biomass increased linearly with tiller biomass in an isogony way. Regular changes of increasing rate ‘b’ in the correlation equations indicated that there were orderly processes in the growth of tiller height and spike length, and matter production and transmission. When the five samples were combined and analyzed as one single sample, the regulating process of increasing rate was not detected.