| Phenotypic plasticity is defined as the property of a genotype to produce different phenotypes when exposed to different environments. Plasticity differences between species have important implications in terms of ecological and evolutional consequence. The phenotypic plasticity of an endangered plant, Mosla hangchowensis Matsuda response to soil water statuses was compared in this paper with three widely distributed plants, M. chinensis Maxim, Mosla scabra (Thunb.) C. Y. Wu et H. W. Li and Mosla dianthera (Buch.-Ham.) Maxim. The growth, architectural, physioecological and reproductive plasticity across three history period of four Mosla species were studied. We present the comparative study to probe into phenotypic plasticity patterns of these four Mosla species in response to different soil water content, aiming to find out the relationship between the phenotypic plasticity and field abundance and evolutional divergence, and then to find out the endangered mechanism of M. hangchowensis. The five treatments were interpreted in terms of relative soil water content (RWC) and measured in terms of soil water holding capacity (WHC). For the 1st treatment, soil water was maintained as constant saturation (CS, simulate the wet habitat); For the 2nd treatment, plants were not watered unless the RWC dropped to 80% WHC. Similarly, distilled water was added to saturation whenever WHC dropped to 60%, 40%, and 20% in the 3rd, 4th and 5th treatment, respectively. The five treatments were defined as constant saturation (CS), W80, W60, W4o and W2o, respectively. And the results indicated:1. At the vigorous vegetative growth period in July, M. hangchowensis had the lowest phenotypic plasticity while M. scabra had the highest. At the early blooming period in September, M. dianthera had the highest phenotypic plasticity while M. chinensis had the lowest. Before the end of the reproductive growth in November, it was also M. dianthera which had the highest phenotypic plasticity and M. chinensis which had the lowest. Viewed from the whole history period that the phenotypic plasticity orders were: M. dianthera > M. scabra > M. hangchowensis > M. chinensis. In the growing process, the phenotypic plasticity of M. scabra and M. chinensis decreased gradually, while the phenotypic plasticity of M hangchowensis and M. dianthera increased.2. M. scabra and M. dianthera can rapidly adjust their architectural traits in response to soil water statuses, while M. hangchowensis responded more sluggishly, and M. chinensis responded most sluggishly.3. The optimum water niches (OWN) of M. hangchowensis was from 40% soil water holding capacity (WHC) to 80% WHC, but M. hangchowensis distributes in drought environment in the field, so the actual water niches (AWN) separated from OWN in M. hangchowensis. M. hangchowensisadopted K-strategy to produce less bigger seeds, that is disadvantage to maintain the population in the field because of the severely condition and less competition of the offspring. The OWN of M chinensis was also from 40% WHC to 80% WHC, and M. chinensis distributes in relatively dry environment which is the edge of its OWN, while M. chinensis allocated more mass to produce more smaller seeds adopting the r-strategy. However, M chinensis couldn't be dominant species because of the high mortality of the seedlings and the less competition for light. The OWN of M. scabra was from 40% WHC to 80% WHC too. M. scabra was competitive because of its better vegetative growth and taller growth than M. hangchowensis and M. chinensis. The OWN of M. dianthera was from 40% WHC to 100% WHC, it can distribute from dry environment to wet environment in the field. And it had very competitive superiority in the wet water condition because of the higher apical, but high endurance in dry condition with simply vegetative growth but more reproductive growth.4. The reason that M hangchowensis being endangered is that it has disadvantage phenotypic plasticity orientation; the phenotypic plasticity can't make it more competitive and endurant. Thoug...
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