Root decomposition in coastal wetlands of Southeast Queensland, Australia

Root decomposition is a key coastal wetland ecological process. Despite this, there are limited empirical studies on root decomposition. In this study, we investigated the effect of species, root size and burial habitat on root decomposition of supratidal tree species (Casuarina glauca, Melaleuca quinquenervia), and intertidal mangrove (Avicennia marina) and saltmarsh species (Sarcocornia quinqueflora, Sporobolus virginicus) in Southeast Queensland, Australia. Decomposition curves for all tested factors indicated a plateau in remaining root mass by the end of the experiment; the plateau was therefore inferred to indicate the “expected liable fraction”. Root decomposition rates and fractions of expected labile root biomass of supratidal and intertidal species were not significantly different. The percentage mass remaining of fine roots (<2 mm) of woody species varied by species, but that of coarse roots (2–20 mm) did not vary among species. Decomposition rates and expected labile fractions of roots of intertidal species were not significantly different between burial in the same habitat (“at home”) versus in habitats dominated by other species (“away”). Overall, we found lowest variation in percentage mass remaining, followed by expected labile fractions and root decomposition rates across species and habitats after 14 months. The mean root decomposition rate using two-pool asymptotic models was 0.0169 ± 0.0019 day⁻¹; the mean expected labile fraction was 28.3 ± 1.0 %. These experimental root decomposition results across the intertidal to supratidal zone provide insights to the drivers of decomposition rates in coastal wetlands that can be used in ecological models.