Nutrient dynamics and leaf litter decomposition in a subtropical mangrove forest at Oura Bay, Okinawa, Japan

Abstract

Dynamics of nutrients (carbon, nitrogen and phosphorus) in decomposing leaves was studied using litterbags in a subtropical mangrove dominated by Bruguiera gymnorrhiza (L.) Lamk and Kandelia candel (L.) Druce (Okinawa, Japan). In addition to fresh yellow leaves, degradation of treated leaves (dried at 50°C and 80°C) was also investigated. Comparison was made between species, locations (lower and upper mangroves) and among treatments. Results showed that K. candel leaves with higher initial N concentrations (low C:N ratio) decayed faster than B. gymnorrhiza leaves; decay constants were 0.062 and 0.022 per day. This finding implies that degradation rate is species specific and depends on the initial chemical composition of leaves, particularly the C:N ratio. Furthermore, B. gymnorrhiza leaves, with lower initial N levels, gained more N from external sources (i.e. bacteria) than K. candel leaves which exhibit a high initial N content. Leaves in the upper mangroves decayed much more slowly than in lower mangroves; decay constants were 0.019 and 0.022 per day. The overall decay rates of dried leaves were lower than those of fresh leaves, decreasing in the order: fresh leaves 0.022, 50°C 0.019 and 80°C 0.018. The t 0.5 values were 32, 36 and 38 days respectively. Drying of mangrove leaves prior to incubation in the field significantly altered the pattern of mass loss, nutrient loss and delayed microbial recolonization. A single exponential equation described losses of ash-free dry weight, C, and P for the two species, sites and treatments. Only N in K. candel leaves was described by the single exponential equation.

Litter degradation and CN dynamics in reforested mangrove plantations at Gazi Bay, Kenya

“…Most studies on mangrove litter degradation and concomitant nutrient dynamics have hitherto concentrated on differences among: tidal elevations (Twilley et al, 1986(Twilley et al, , 1997Mfilinge et al, 2002), species and seasons (Tam et al, 1990;Twilley et al, 1997;Woitchik et al, 1997;Mfilinge et al, 2002) and litter components (Steinke et al, 1983;Van der Valk and Attiwill, 1984;McKee and Faulkner, 2000). Specific stand management regimes, i.e., regulated exploitation versus excessive extractive pressure which leads to deforestation, and subsequent reforestation in areas where natural regeneration is impeded, do influence nutrient recycling (Ashton et al, 1999), Reforestation has been found to alter site physico-chemical conditions (McKee and Faulkner, 2000;Bosire et al, 2003) and is thus assumed to ultimately restore the functional importance of nutrient fluxes through it among other ecosystem functions.…”

The decomposition characteristics of the seagrass <i>Thalassia hemprichii</i> in Okinawa, Japan

“…Thus, an increase in the TOC concentration may be due to the rising con centrations of structural carbonates per plant and as a result of the loss of other constituents (sugars and starches) in the detritus. The remaining, insoluble plant components are then left to decay (Mfilinge et al 2002;Blum et al 1988). …”

“…The initial decreasing trend in the TOC concentration over time in seagrass leaves of Posidonia oceanica lasted for seven days (Mateo 1997), while that of mangrove leaves (Bruguiera gymnorrhiza and Kandelia candel) lasted for 17-31 days (Mfilinge et al 2002).Moreover, studies have also shown that, the degradation of plant materials and the concentration of plant microbes were greater in seagrass leaves than in mangrove leaves (Blum et al 1988, Boer 2000, Holmer and Olsen 2002. Therefore, in this study, the initial decreasing trend in the changes at leaf litter TOC concentration over time was due to a rising propor-tion of structural carbonate per dry matter as a result of the loss of other plant components to detritus.…”

“…In autumn 2007, the estimated net loss of TOC and TN in seagrass during decomposition at each site was calculated as follows (Mfilinge 2002 Table 1). …”

Changes in Organic, Inorganic contents, Carbon Nitrogen ratio in decomposingAvicennia marinaand Rhizophora mucronataleaves on tidal mudflats in Hajambro creek, Indus delta, Pakistan

“…There are various factors controlling rate of decomposition and energy release, such as, the degree and frequency of tidal inundation, soil temperature [17] and moisture [18], and the presence or absence of the litter-consuming fauna within mangrove forest [19][20][21]. Litter decomposition also increases soil fertility [23].…”