Rg. Wetzel et Mj. Howe, High production in a herbaceous perennial plant achieved by continuous growth and synchronized population dynamics, AQUATIC BOT, 64(2), 1999, pp. 111-129
Continuous changes in the population dynamics, above- and belowground bioma
ss, growth rates, and production of the emergent rush Juncus effusus were e
valuated over an annual period in a sub-temperate riparian wetland. Extant
and emerging individual photosynthetic culms (shoots) were labeled individu
ally and their growth dynamics quantified in replicated plots. Lengths of l
iving (chlorophyllous) portions and basal diameters of several thousand ind
ividual culms were determined at weekly intervals and converted to biomass
by regression of surface areas to mass. Shoots emerged continuously at all
times of the year; the number of ramets increased four times from summer to
winter (12,000 - >30,000 culms m(-2)). Individual culms in November-Decemb
er, however, were generally smaller (41-52%) than in summer. Maximum growth
of individual new culms ranged from a maximum of 6.4 mg per day in June (4
0-50 days to maximum biomass) to 1.1 mg per day in November (70-110 days to
reach maximum biomass in winter). Due to continuous recruitment and gradua
l culm senescence, numerous multiple cohorts occurred on an annual basis. R
oot production was also evaluated from changes in seasonal biomass and from
experimental studies of changes in aboveground biomass in relation to thos
e of rooting tissues. Annual root production was approximately 42% of shoot
production. Average annual production estimates of combined above- and bel
owground components was 9832 g AFDM m(-2) per year. The extremely high prod
uction rates of this Juncus species result from the continuous growth while
simultaneously shoot densities changed as the inverse of biomass seasonall
y. These processes maximized photosynthetic carbon fixation under mild clim
atic conditions of the winter and spring seasons. This dynamic growth strat
egy is likely to be common among herbaceous perennial emergent aquatic plan
ts in mild climatic regions. (C) 1999 Elsevier Science B.V. All rights rese
rved.