Decomposition of mangrove roots: Effects of location, nutrients, species identity and mix in a Kenyan forest

Abstract

Mangrove trees may allocate >50% of their biomass to roots. Dead roots often form peat, which can make mangroves significant carbon sinks and allow them to raise the soil surface and thus survive rising sea levels. Understanding mangrove root production and decomposition is hence of theoretical and applied importance. The current work explored the effects of species, site, and root size and root nutrients on decomposition. Decomposition of fine (3 mm diameter) and coarse (>3 mm diameter, up to a maximum of w9 mm) roots from three mangrove species, Avicennia marina, Bruguiera gymnorrhiza and Ceriops tagal was measured over 12 months at 6 sites along a tidal gradient in Gazi Bay, Kenya. C:N and P: N ratios in fresh and decomposed roots were measured, and the effects on decomposition of root size and age, of mixing roots from A. marina and C. tagal, of enriching B. gymnorrhiza roots with N and P and of artefacts caused by bagging roots were recorded. There were significant differences between species, with 76, 47 and 44 % mean dry weight lost after one year for A. marina, B. gymnorrhiza and C. tagal respectively, and between sites, with generally slower decomposition at dryer, high tidal areas. N enriched B. gymnorrhiza roots decomposed significantly faster than un-enriched controls; there was no effect of P enrichment. Mixing A. marina and C. tagal roots caused significantly enhanced decomposition in C. tagal. These results suggest that N availability was an important determinant of decomposition, since differences between species reflected the initial C: N ratios. The relatively slow decomposition rates recorded concur with other studies, and may overestimate natural rates, since larger (10e20 mm diameter), more mature and un-bagged roots all showed significantly slower rates.

Distribution of dissolved organic carbon and KMnO4-oxidizable carbon along the low-to-high intertidal gradient in a mangrove forest

“…This would render these organic materials less available to most microorganisms and leave them less susceptible to microbial degradation along the low-to-high intertidal gradient. In addition, an increase in the C/N ratios of both soils and leaves occurred with the low-to-high intertidal gradient of the study area (Tables 1 and 2) which would also result in a decrease of the decomposition rate of organic carbon (Huxham et al 2010). This decrease of the decomposition rate may be suitable for the accumulation of the SOC fractions.…”

Root decomposition of Artemisia halodendron and its effect on soil nitrogen and soil organic carbon in the Horqin Sandy Land, northeastern China

“…Root diameter is an important factor that controls root decomposition (Scheu and Schauermann 1994;Jackson and Schulze 1997;Graaff et al 2013). Researchers have shown that thinner roots decay more rapidly than thicker roots, especially during the later stages of decomposition (Huxham et al 2010). For example, in Eucalyptus urophylla, Xu et al (2013) found initially similar decay rates for three root diameter classes (<1, 1-2, and 2-3 mm) for 180 days, but significantly different rates during later phases (the <1 mm roots decomposed more rapidly than the others).…”

“…Moreover, it has been well established that environmental factors play a key role in the decomposition of plant roots. In a Kenyan forest, the decomposition rate of mangrove roots was affected by root size, but varied between different regions, with higher rates for small roots and in tidal areas (Huxham et al 2010). Previous research in subtropical humid forests has shown that the mean daily loss of fine root mass was positively correlated with precipitation, air temperature, soil moisture, and soil pH (Arunachalam et al 1996).…”

“…For example, in the Sanjiang Plain of northeastern China, root decomposition rates of wetland plants were affected by the site's hydrology, temperature, and pH (Guo et al 2008). In a Kenyan forest, the decomposition rate of mangrove roots was affected by root size, but varied between different regions, with higher rates for small roots and in tidal areas (Huxham et al 2010).…”

Description of the soil and root biomass of two subtropical mangroves in Antonina and Guaratuba Bay, Paraná State, Brazil

“…The textural composition of the soil in this area has a greater proportion of sand, which facilitates the deeper development of roots and, consequently, an increase in volume (Fitter 1987). The volume of roots in mangrove soils is an important characteristic because it contributes organic matter annually (McKee 2011), but this addition is dependent on the decomposition rate of these roots (Huxham et al 2010). Some studies demonstrated that root decomposition could vary among species due to intrinsic features of each species and their chemical composition (Huxham et al 2011).…”