Comparative ecology of Monochoria korsakowii and M. vaginalis

Abstract

Two native annual species, Monochoria korsakowiiRegel et Maack and M. vaginalis (Burm. fil.) Kunth, occur in Japan. Although they show similar habitat preferences, these plants are now in contrasting situations in Japan; while M. vaginalis is a noxious weed, M. korsakowii, a once common weed of rice fields, has diminished its distributional range and is now listed as a vulnerable species. For the purpose of conservation and management of M. korsakowii, the life history traits of these species were investigated with particular emphasis on the seasonal growth cycles, patterns of dry matter distribution and photosynthetic and transpiration rates. We found significant differences in phenology and seasonal growth between M. korsakowii and M. vaginalis. M. korsakowii germinated about a month earlier and flowered one and a half months later than M. vaginalis. While shoot to root dry weight ratio in M. korsakowii was larger than 1.0, that in M. vaginalis was smaller than 1.0 during growth. Differences were also found in leaf life span, numbers of leaves and flowers per individual plant and transpiration rate. These findings support the belief that the decline of M. korsakowii relates, to some extent, to the recent changes in agricultural practices in Japan.