| Leymus Chinesis is a perennial, rhizomatous species of Gramineae. Reproduction is mainly by clonal propagation. The plant is highly tolerant of drought, low fertility and high pH, often forming monodominant stands. The regeneration of aboveground shoots occurs principally by tillering, through rhizomes. These, furthermore, are likely associated with several different types of buds. Each year, the process of addition of a new bud and its subsequent development into a daughter shoot, can offset programmed mortality losses of parent shoots, and can influence aboveground shoot population density. Therefore, understanding the contributions of the belowground bud bank to a plant population is of great importance for exploring clonal propagation mechanisms in plants.It was investigated that the seasonal dynamics of bud bank, the effects of high sexual reproductive allocation on bud bank and daughter shoots, the changes of bud bank under different parent shoot density, C and N compound of apical rhizome bud response to bud bank seasonal dynamics, the effect of covering treatment during different growing phase on bud bank. The main results and conclusions were as follows:(1) Each bud type has distinct earliest timings to break. B1-1 begins to generate during late May, but B1-2, B2 and B3 occur during late June. This may be due to apical dominance which is a result of hormonal suppression and/or to resource competition between apical and basal meristems. Throughout the growing season, B1 appeared at much lower densities than the other bud types. At the end of the growing season B1 emerged into DS1, which contributes only approximately 5% of the total daughter shoots. B3 maintaining much higher densities and proportions than other bud types. Thus, DS3 originating from B3 accounted for about 79% of total daughter shoots. Plants can produce intermediate numbers and proportions of DS1, which originate from B1 and make up about 16% of total daughter shoot density. During late October in two years there exist a stable proportion of type-specific buds and daughter shoots, indicating a successful mechanism for stabilizing the dominant species population. During the early season, some preformed buds adopted a bet-hedging strategy, responding to precipitation variation; subsequently the plant pursued an expanding strategy and, finally, a propagation strategy.(2)Responses of plant modules are different at different sexual reproductive allocation. High sexual reproductive allocation can result in a significantly lower density in young rhizome amount, length, B1 + DS1, and B2 +DS2, but a significantly higher C3 + DS3 density, finally a significantly lower density in total bud + total daughter shoot. Furthermore, high sexual reproductive allocation did not decrease the density in each daughter shoot type, but showing significantly more DS3. We conclude that high sexual reproductive allocation can affect not only the clonal offspring density, but also its spreading distance. L chinensis can produce a more phalanx and/or compact spatial arrangement under condition of high sexual reproductive allocation, a more guerrilla and/or loose growing form under condition of low sexual reproductive allocation. (3)Compared with lower parent shoot density patch, higher parent shoot density patch can produce higher DS1 and DS3 density, lower DS2 density, and similar young rhizome length density which peak later by about two months. Also, Compared with higher parent shoot density patch, lower parent shoot density patch can produce higher proportion of spreading shoot (B1, DS1, B2 and DS2) in which lower parent shoot density patch have lower B1, DS1 density. We conclude as follows. L. Chinesis have lower shoot density during the early stage of evolution of plant life history; it can produce lower proportion of clumping shoot to maintain and consolidate its territory, also produce higher proportion of spreading shoot to occupy new territory. These spreading shoot is composed of higher proportion of B2 and DS2, lower proportion of B1 and DS1. When it advances to the late stage of evolution of plant life history, parent shoot density rise with increasing proportion of clumping shoot (B3 and DS3), decreasing proportion of spreading shoot. With plant life evolution advancing, we can hypothesize there will exist a stable proportion of spreading shoots and clumping shoots to out-compete other species in areas colonized by parental shoots.(4)There were similar content of C and N compound between B1-1 and B1-2, indicating that the changing of Bl-1 into B1-2 may be not caused by C and N compound variation. Sucrose is a main component among soluble sugar; it has seasonal dynamics similar to soluble sugar. When flood disturbance occur, sucrose play a key role in survival of L .Chinesis. There were different seasonal variation between soluble sugar and total N. During autumn, majority of C and N compound in Bl-1 and B1-2 is used to reserve into young rhizome, minor of that for plant growth. During the early growing stage, high sexual reproduction allocation result in lower soluble sugar content; during the late growing stage, L. Chinesis allocate higher soluble sugar into B1-1 and B1-2 due to no sexual reproduction.(5)The covering treatment during from 20 May to 20 June or from 20 June to 20 July did not affect B1, DS1, B2, DS2, B3, DS3, total bud, total daughter shoot, young rhizome length density, and biomass, highness of parent shoot, proportion of spreading shoot and clumping shoot; but, covering treatment from 20 July to 20 August or from 20 August to 20 September significantly increase B1, DS1, B2, DS2, B3, DS3, total bud, total daughter shoot, young rhizome length density and highness of parent shoot, did not affect total bud+total daughter shoot density, furthermore, increase proportion of spreading shoot and decrease proportion of clumping shoot. Therefore, we hypothesize that it may be a growing strategy through which when environment condition is fitting, L. Chinesis can produce high proportion of spreading shoot to occupy new area, resulting in establishing stable and dominant populations throughout the eastern Eurasian Steppe.
|
PDF Full Text Request