Plant species- and stage-specific differences in microbial decay of mangrove leaf litter: the older the better?

Abstract

Leaf litter and its breakdown products represent an important input of organic matter and nutrients to mangrove sediments and adjacent coastal ecosystems. It is commonly assumed that old-grown stands with mature trees contribute more to the permanent sediment organic matter pool than younger stands. However, neither are interspecific differences in leaf decay rates taken into account in this assumption nor is our understanding of the underlying mechanisms or drivers of differences in leaf chemistry sufficient. This study examines the influence of different plant species and ontogenetic stage on the microbial decay of mangrove leaf litter. A litterbag experiment was conducted in the Matang Mangrove Forest Reserve, Malaysia, to monitor leaf litter mass loss, and changes in leaf litter chemistry and microbial enzyme activity. Four mangrove species of different morphologies were selected, namely the trees Rhizophora apiculata and Bruguiera parviflora, the fern Acrostichum aureum and the shrub Acanthus ilicifolius. Decay rates of mangrove leaf litter decreased from A. ilicifolius to R. apiculata to B. parviflora to A. aureum. Leaf litter mass, total phenolic content, protein precipitation capacity and phenol oxidase activity were found to decline rapidly during the early stage of decay. Leaf litter from immature plants differed from that of mature plants in total phenolic content, phenolic signature, protein precipitating capacity and protease activity. For R. apiculata, but not of the other species, leaf litter from immature plants decayed faster than the litter of mature plants. The findings of this study advance our understanding of the organic matter dynamics in mangrove stands of different compositions and ages and will, thus, prove useful in mangrove forest management.

Crab‐driven processing does not explain leaf litter‐deposition in mangrove crab burrows

“…This difference persisted over the experiment, irrespective of whether they had been buried or kept on the surface, although contents decreased over the course of the experiment (by 96% for B. gymnorhiza (p < .0001); by 94% inside burrows vs. 96% on the surface for C. tagal [p < .0001]). Such a drastic reduction in the phenolic content of mangrove litter over the first weeks of decay has recently been described by Pradisty et al (2021). Like for toughness, there were no significant differences between treatments (B. gymnorhiza: p = .445; C. tagal: p = .142).…”

“…Such feeding preferences of detritivores are likely due to changes in the content of water-soluble secondary compounds, such as phenolics, and toughness during early decay (Zimmer, 2019). For instance, tannin contents of leaf litter decreased by 68% over 8 weeks through leaching in B. gymnorhiza (Steinke et al, 1993), and even more in B. parviflora (Pradisty et al, 2021). Accordingly, N. smithi assimilated little of 2-week-old litter, but assimilation efficiencies increased to 30%-60% when fed with 4-to 8-week-old litter (Giddins et al, 1986).…”

“…While this is often used as a first proxy for food quality, many leaf compounds, such as phenolics, can vary in their content within a given C:N ratio value. Thus, the quality of litter as substrate for decay and decomposition cannot adequately be described by only the C:N ratio (c.f., Pradisty et al, 2021), and other parameters have been used as proxies for the quality of leaf litter as food for detritivores, for example, phenolic content (Micheli, 1993;Bärlocher & Graça, 2020, and references therein;Pradisty et al, 2021) and physical toughness (Graça & Zimmer, 2020, and references therein). The ultimate test for changes in litter characteristics that affect the feeding and nutrition of consumers, however, is quantifying the actual uptake and utilization of the respective food sources (see, e.g., Nordhaus & Wolff, 2007).…”

Co-benefits of protecting mangroves for biodiversity conservation and carbon storage

“…Maximum canopy height, an indicator of light interception 27 that reflects the relative resourceuse capacity of a species in a community, determines community scale biomass allocation and carbon storage 3,4,[28][29][30] . Plant traits such as leaf carbon, nitrogen and their ratio, leaf dry matter content or contents of phenolic compounds, as indicators of litter quality for decay and decomposition, could influence nutrient cycling and productivity [31][32][33][34] . For instance, higher litter nitrogen content or phenolic content could enhance microbial litter decay and drive sediment carbon content and productivity in mangroves [34][35][36] .…”

“…Plant traits such as leaf carbon, nitrogen and their ratio, leaf dry matter content or contents of phenolic compounds, as indicators of litter quality for decay and decomposition, could influence nutrient cycling and productivity [31][32][33][34] . For instance, higher litter nitrogen content or phenolic content could enhance microbial litter decay and drive sediment carbon content and productivity in mangroves [34][35][36] .…”