Mast seeding or masting refers to intermittent and synchronous production of large seed crops in a population of perennial plants. It is generally accepted to be regulated by internal resource level. However, the latest studies demonstrated that seed production relies exclusively on current-year photo-assimilate and not on stored carbohydrate. Therefore, the role of resource level in determining the floral initiation is unclear yet. Here, we monitored seasonal variations in three key flowering genes (FLOWERING LOCUS T in leaves, LEAFY and APETALA1 in winter buds), internal resources (carbohydrates and nitrogen) in leaves, current-year shoots and three-year-old twigs and soil nutrients from both fruiting and non-fruiting trees of mature Fagus creneta forests. We report how internal resource level is related to flowering gene expresses and influenced by soil nutrient supply.
Results/Conclusions
Floral gene expressions were related to flowering rate at both branch and individual levels and highly variable between branches when flowering rate in an individual tree was low. Similar nitrogen concentrations in leaves, current-year shoots and three-year-old twigs were found between trees inrespective of whether they initiated floral buds. Starch concentration in 3-year twigs sampled in October correlatied with FLOWERING LOCUS T in leaves, suggesting that resource started to accumulate after floral initiation. Available nitrogen in soil fluctuated significantly seasonally and yearly and influenced by soil temperature. Together with our previous finding that nitrogen storage decreases in the year following masting, resource storage may not be the trigger of floral initiation but the limiting factors for masting in F. crenata.