Causes of variation in generative reproduction of Polygonatum odoratum (Miller) Druce in N-Poland populations
Seed production, seedling establishment and survival into the generative phase are important stages in the life cycles of clonal species. The aim of this study was to assess the variation of generative reproduction and factors affecting its size in the natural populations of Polygonatum odoratum. It was hypothesized that: (a) seed output in a population is strongly affected by biotic and abiotic environmental factors, and weakly related to population abundance, (b) seeds’ ability to germinate and seedlings’ survival depend on the seed size. The field studies were conducted in five populations of Polygonatum odoratum in 2000–2011. Sex allocation in flowers was estimated as the number of hermaphrodite flowers on shoots and ovules in ovaries. Generative shoots, flowers and fruits on them were recorded in each population. The type and size of damage to plants by large herbivores and insects were recorded. The three sowing experiments were conducted in order to estimate seedling performance and survival. The populations differed significantly in the fraction of hermaphrodite flowers and ovule number. The number of generative shoots and flowers on them as well as the seed output significantly differentiated the populations and patches. In the first year of study, the mean seed output ranged from 0.3 to 123.7 m⁻², and it markedly decreased in two populations, where there was no seed at last years of study. Generative shoots were often grazed by roe-deer, leaves were eaten by Phymatocera aterrima and flowers were infested by Contarinia polygonati larvae. Seedling emergence was significantly correlated with the mean seed mass. Seven-year-old individuals were able to reach generative phase. In conclusions, the results suggest that the generative shoots provide a long-term inflow of seeds to the population. Under experimental conditions, substantial survival enabled the plants to potentially reach generative maturity. In studied populations, the most important reason for dynamic of seed output was animal pressure (in order – grazing, flower infestation and defoliation). The effect of these biotic factors was visible in a short period – in the current year. In contrast, the impact of abiotic factors (e.g. lighting), was appeared in a longer period.
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