Litter mixing effect on decomposition rate and nutrient release to water: low quality leaves of coastal species

Non-additive effect on litter decomposition often occurs in mixed terrestrial communities but little investigated on coastal ecosystems. We selected three common mangrove species and one alien saltmarsh species from a coastal wetland stand to test whether non-additive effect occurs when the litters of these coastal species mixed together. To avoid the heterogeneity of soil conditions and to detect nutrient release into water, we conducted an in vitro litter-bag experiment in a glasshouse. Among three litter mixtures, the non-additive effect was observed in the litter mixture composed of mangrove species Aegiceras corniculatum vs. Kandelia obovata (antagonistic) and A. corniculatum vs. Avicennia marina (synergistic), but not in the litter mixture of A. corniculatum vs. Spartina alterniflora (the alien saltmarsh species). The strength of non-additive effect was unrelated to litter initial trait dissimilarity. Instead, litter decomposition rate and mass remaining of litter mixtures were strongly related to the community-weighted mean of leaf carbon. The nutrients and carbon released into water were more likely controlled by litter decomposition rate rather than by litter initial nutrient concentrations. These findings would lead to the expectations on ecosystem scale that the mangrove stand mixed with A. corniculatum and K. obovata accumulates more organic carbon in the sediment and releases less nutrients into water column than the stand composed of A. corniculatum and A. marina . It is also implying that the alien species S. alterniflora invasion may not reduce soil carbon stock of mangrove forests. These hypotheses need to be further tested and which will be suggestive for the protection or reconstruction of coastal wetlands.

Additive Effects of Sediment and Nutrient on Leaf Litter Decomposition and Macroinvertebrates in Hyporheic Zone

Despite the fact that leaf decomposition constitutes an important function in rivers, how multiple environmental stressors simultaneously affect it remains largely unknown. This study investigated the interactive effects of fine sediments (particle size: <2 mm; experimentally manipulated) and a specific nutrient (i.e., nitrate) on subsurface (hyporheic) leaf litter decomposition rate and macroinvertebrates in a gravel-bed river and its tributary in eastern Hokkaido, Japan. The experiment was conducted by measuring leaf litter decomposition of dried Alnus japonica leaves (3 ± 0.05 g) in benthic and hyporheic zones with and without sediment treatments at four sites that had a gradient of nitrate concentration. The decomposition rate was comparable between the two zones but was slowed down by sediment addition in the hyporheic zone. The functional responses were highly predictable for the individual stressors. Detritivore invertebrates were the main driving component of decomposition in the decreased leaf litter decomposition rate under a higher fine sediment condition, whereas higher nitrate accelerated the leaf litter decomposition rate by stimulated microbe-driven decomposition as well as detritivore feeding. Overall, the negative effect of fine sediment could be offset in the presence of nitrate while considering gross functional responses. We demonstrated the additive effects of fine sediment and nitrate on leaf litter decomposition in the hyporheic zone.

Estimation of biomass, carbon stocks and leaf litter decomposition rate in teak Tectona grandis Linn plantations in city forest of Hasanuddin University, Makassar

Teak Tectona grandis Linn is still used as the main product in the form of wood, while other products, especially environmental services have not received much attention. This study analyzed biomass, carbon stocks and decomposition rate of leaf litter in teak plantations in city forest of Hasanuudin University, Makassar. The individual biomass of teak plants is calculated using the allometric equation, Y=0.11x ρ x D2.62. Carbon stocks were analyzed using a formulation, C=0.47xB. The leaf litter decomposition rate is expressed as the ratio of the remaining litter dry weight, with the formulation, X= (A-B)/A. The number of teak plants in 5 sample plots were 239 trees with an average stem diameter of 20.6cm and an average height of 9.02m. Total biomass in 5 sample plots was 51,712.61g. Carbon stock in 5 sample plots was 24,304.92g. Decomposition rate average of leaf litter of 24.4g during 60 days incubation. The existence of teak plantations is able to reduce CO2 in the atmosphere by as much as 89,199.06gCO2 and resulting in a decomposition rate of teak leaf litter 0.4g per day