Age-specific seasonal storage dynamics of Phragmites australis rhizomes: a preliminary study

Author: Karunaratne Shiromi  

Publisher: Springer Publishing Company

ISSN: 0923-4861

Source: Wetlands Ecology and Management, Vol.12, Iss.5, 2004-10, pp. : 343-351

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Abstract

Age-specific seasonal rhizome storage dynamics of a wetland stand of Phragmites australis (Cav.) Trin. ex Steud. in Japan, were investigated from April to October 2000. For each sampling date, above- and below-ground biomass and age-specific rhizome bulk density, ?rhiz were measured. Seven rhizome age classes were recognized, from <1 year="" to="" six="" years="" old,="" based="" on="" their="" position="" within="" the="" branching="" hierarchy="" as="" main="" criteria="" and="" rhizome="" color,="" condition="" of="" nodal="" sheaths="" and="" condition="" of="" the="" shoots="" attached="" to="" vertical="" rhizomes="" as="" secondary="" criteria.="">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 mean shoot height of 2.33 ± 0.12 m. In spring, shoot growth started at the expense of rhizome reserves, decreasing the rhizome biomass as well as ?rhiz. Both parameters reached the seasonal minimum in May followed by a subsequent increase, indicating a translocation of reserves to rhizomes from shoots after they become self supporting. For each sampling date, ?rhiz increased with rhizome age. Given that the quantity of reserves remobilized by the rhizomes for spring shoot growth, as assessed by the drop in bulk density from April to May, were positively correlated (r = 0.97, P 0.05) with rhizome age, it is proposed that for spring shoot formation older rhizomes remobilize stored reserves more actively than younger ones. Given that the accumulation of rhizome reserves (rise in bulk density) from May to August, May to September or May to November was negatively correlated (r = 0.97, 0.92 and 0.87, respectively, P < 0.05)="" with="" rhizome="" age,="" it="" seemed="" possible="" that="" younger="" rhizomes="" were="" ‘recharged’="" at="" a="" higher="" rate="" than="" older="" ones.="" these="" resource="" allocation="" mechanisms="" pertaining="" seasonal="" rhizome="" storage="" dynamics="" are="" of="" paramount="" importance="" in="" formulating="" management="" and="" conservation="" strategies="" of="" wetlands="" and="" aquatic="" habitats.="" our="" results="" indicate="" that="" a="" harvest="" of="" above-ground="" biomass="" from="" may="" to="" june="" would="" be="" more="" effective="" in="" reducing="" the="" growth="" than="" a="" harvest="" in="" july="" to="" august="" or="" later,="" when="" rhizome="" reserves="" have="" already="" been="" replenished.="" however,="" the="" latter="" may="" remove="" a="" larger="" shoot="" bound="" nutrient="" stock,="" still="" preserving="" a="" healthy="" stand="" for="" the="" subsequent="" years.="">