Seasonal dynamics of resource translocation between the aboveground organs and age-specific rhizome segments of Phragmites australis

This study aims to test the hypothesis that resource translocation patterns between rhizomes and the aboveground organs depend not only on the season but also on rhizome age. Changes in rhizome biomass and storage reserves of Phragmites australis were therefore investigated to explore the age specificity of rhizomes in resource translocation patterns. Above and belowground biomass were harvested six times between April and December from an undisturbed monospecific stand, and analyzed to give rhizome age-specific dry mass and total non-structural carbohydrate (TNC) contents. Seven rhizome age-classes were recognized, from <1 to 6-year-old. Changes in dry weight and in TNC per unit area of each rhizome age-class were used to describe seasonal patterns in growth and mortality, translocation and movement of assimilates on an areal basis. TNC budgets were prepared based on these data and estimates of losses due to tissue mortality and respiration for each age-class. The seven age-classes had similar growth patterns but differed when translocation occurred, with older rhizomes translocating a substantial amount in spring to the aboveground organs to establish new shoots. Before summer, the photosynthates were evenly allocated to each age-class, while the recovery of TNC in segments was earlier with younger ones. The allocation in autumn was mainly to young rhizome segments. Older segments became severely depleted during winter, with high mortality; however, the youngest rhizome segments survived, which can be interpreted as an internal re-distribution of resources. This study clearly showed that there is a clear variation between rhizome age-classes in belowground resource translocation patterns depending on the season.