Macrophyte root and rhizome decay: the impact of nutrient enrichment and the use of live versus dead tissue in decomposition studies

The decomposition of roots and rhizomes of two macrophytes, Eleocharis cellulosa and Typha domingensis, was studied in oligotrophic phosphorus (P) limited marshes of northern Belize. The experiment was conducted in long-term control and P enriched plots in five limestone-based inland marshes. Decomposition of naturally senescent root and rhizome litter was studied over 9 months using litterbags. Belowground litter was acquired by growing plants in unenriched (control) or P enriched marsh soils for 5 months. Plants were then allowed to naturally senesce using a split root design, which promoted nutrient retranslocation. The resulting senescent litter had 30 % higher C:P and 40 % lower P content than living roots and rhizomes. There were no differences in C:N among treatments or senescent versus live litter. Litterbags, filled with control or enriched root and rhizome litter, were buried in the upper 10–14 cm soil in the corresponding plot of each marsh. Differences in the rate of decay between species were greatest for rhizome tissue, with Typha decaying more than twice as fast as Eleocharis. For both species, however, tissue P enrichment had no effect on coarse root and rhizome decay. Enhanced root production from P enrichment, coupled with no change in decay, should lead to enhanced accretion over time. Additional tests, using litterbags filled with living roots and rhizomes, yielded dramatically different results between treatments compared to senescent tissue. Results from senescent belowground tissue also differed from shoot decomposition. Caution should be exercised when inferring belowground decomposition from live tissue and aboveground rates of decay.