Research Interests

Previous studies (2, 3) suggested trees and herbs showed different flowering patterns but their conclusions were inconsistent. This discrepancy arose due to the lack of variables to qualitatively evaluate phenology. Therefore, I suggested phenological variables for quantitative comparison of flowering phenology and compared the flowering phenology of trees and herbs using flowering data of 48 plant species obtained from the Biodiversity Conservation Area, Kyushu University, Japan. As a result, though there was no significant difference in the mean flowering length of individuals between trees and herbs, the total flowering length of species was shorter in trees than in herbs due to the strong synchronization of flowering between tree individuals. Furthermore, it is suggested that the shorter flowering of tree species is due to evolution in the direction of increasing synchrony between individuals.

Nagahama, A., T. Yahara. 2019. Quantitative comparison of flowering phenology traits among trees, perennial herbs, and annuals in a temperate plant community. American Journal of Botany, 106(12): 1–13. [PDF]

2. Yumoto 1987, Ecological Research. 3. Cortés-Flores et al. 2017, American Journal of Botany.

Recent studies (4) developed models that integrate temperature and photoperiod signals into the network of floral regulatory genes, and predicted the shortening of flowering duration under warming. Nevertheless, empirical testing of the model prediction is still lacking. We performed temperature manipulation experiments and common garden experiments to test the model predictions using plants from two distant populations of Arabidopsis halleri. We also quantified expression levels of two major flowering-time genes and compared the observed and predicted gene expression patterns. Our experiments in the laboratory and the field demonstrated that flowering duration of A. halleri was significantly shortened under warming conditions. The observed gene expression dynamics in the warming condition were predicted well by the gene regulatory model.

Nagahama, A., Y. Kubota, A. Satake. 2018. Climate warming shortens flowering duration: a comprehensive assessment of plant phenological responses based on gene expression analyses and mathematical modeling. Ecological Research, 33(5): 1059–1068. [PDF]

4. Satake et al. 2013, Nature Communications.

In East and Southeast Asia, specific phenological patterns have been observed in each forest (1, 2). However, there has been insufficient ecological comparison of the phenological pattern lacking seasonality of tropical rainforests and phenological pattern showing annual seasonality of tropical seasonal and temperate forests. To comprehensively understand the phenology in East and Southeast Asia, I focused on tropical montane forests, where the ancestral taxa of angiosperms were distributed (5). The presence/absence of leafing, flowering, and fruiting were recorded every three months in the dominant 91 species (500 individuals) in survey plots in a tropical montane forest in southern Vietnam. As a result, all 91 species showed new leaves in the beginning of the rainy season, but only 70 species bloomed during the observation period. These results indicated that the tropical montane forest of Vietnam is the mixture of species that bloom annually, such as species in temperate forest, and bloom every few years, such as general flowering species in tropical rain forest. (preparing)

1. Rathcke & Lacey 1985, Annual review of ecology and systematics. 2. Yumoto 1987, Ecological Research. 5. Axelrod 1966, Evolution.