MEPS 130:169-178 (1996)  -  doi:10.3354/meps130169

The proportional allocation of photosynthetically fixed carbon to the root and shoot system of salt marsh plants is an important element in the carbon cycle of tidal salt marshes. The commonly applied field methods giving insight on this point are based on successive harvesting of biomass. These methods, however, lack accuracy and do not yield reliable data over short time intervals. In the present study, the stable carbon isotope ¹³C was used as a tracer of carbon flow in Spartina anglica. Shoot clusters of this halophyte were incubated with ¹³CO₂ (ca 1 h) in a salt marsh in the SW Netherlands. Four days after the incubations, shoots and roots/rhizomes were sampled to determine enrichment with the heavy isotope. Although S. anglica is a clonal plant, only a minor part of the excess ¹³C incorporated in plant tissues due to the incubation procedure was found outside the incubation plots. The data revealed the dynamic nature of carbon allocation in S. anglica, leading to seasonal changes in the ratio of carbon allocated to above-ground versus below-ground tissues. The ratio was highest in August (6.19) and lowest in September (1.60), but more carbon was always invested in above-ground plant parts than in below-ground plant parts. These findings strongly suggest that, on an annual basis, above-ground biomass production outweighs below-ground biomass production in this S. anglica population. Root/rhizome production over short-term periods (10 to 12 d) was calculated by combining the data on the ratios of ¹³C allocation with measurements of above-ground biomass increments over these periods. On an annual basis, above-ground and below-ground biomass production was estimated to be 1130 and 556 g dry wt m^-2, respectively. A survey of the literature shows that the ratio of shoot to root/rhizome production of Spartina spp. vegetation is highly variable, ranging from a clear dominance of shoot production (as is suggested by our data) to the completely opposite situation with root/rhizome production amply exceeding shoot production. This may imply considerable differences in the functioning of Spartina-dominated marsh systems, e.g. with respect to the dominance of aerobic or anaerobic mineralization processes and to mineralization-linked cycling of sulphur and nitrogen.

Spartina anglica . Salt marshes . Carbon allocation . Production . Stable carbon isotopes