Growth performance of Phragmites australis in Japan: influence of geographic gradient

Most of the research on Phragmites australis is restricted to sites on the European continent even though P. australis occurs abundantly in many regions in the Asian and other continents under different climatic and habitat conditions. The effect of latitude on the growth and phenological characteristics of P. australis is of importance when translating results from one geographic site to another to effectively manage and conserve reed stands. Therefore, the effects of seasonal variations of above- and below-ground biomass, stand morphology and production, and radiation conditions on growth performance of a P. australis stand in Akigase Park in Saitama Prefecture, Japan, were investigated to examine the hypotheses that: (a) the overall light extinction coefficient of P. australis at a given growth stage may be modified by the sun elevation; and (b) phenological and growth/production traits of P. australis may be correlated with the latitude, by comparing the present study with published field studies from Europe and Australia. The P. australis stand was moderately productive, having a net aerial and below-ground production of 1980 and 1240 g m(-2), respectively, and a maximum shoot density of 120+/-9 shoots per m2. We found that the overall light extinction coefficient, kappa, at the different growth stages of P. australis depends on sun elevation, theta, displaying a quadratic distribution (kappa = -7.58+0.28theta-0.002theta2). Therefore, in detailed production studies, kappa should always be presented with its respective theta values to estimate light attenuation characteristics. The comparison of the growth performance of P. australis across the geographic gradient revealed differences in phenological and growth/production traits. Shoot growth and panicle formation started earlier in northern latitudes (on the European continent) and later in southern latitudes (on the Australian continent) than in Japan (on the Asian continent). Strong correlations were observed between the degrees C-day-based growth parameters and the latitudes illustrating the dependence of the phenological and growth/production traits on temperature in the different geographic regions. These results are discussed with respect to possible effects on adaptation of P. australis to colder climates.