Species and site differences in the decomposition of litters and roots from wet heathlands

The decomposition of litter and roots from a site dominated by Erica tetralix and a site dominated by Molinia caerulea was measured using mesh bags. Leaf litter and roots of each species were incubated on both sites. The experiments lasted up to 3 years. The weighted decomposition constant was 0.23 per year for Molinia litter, and 0.10 per year for Erica litter; the decomposition constants for roots were 0.29 per year for Molinia but only 0.03 per year for Erica. The decomposition rates of leaf litters and roots were similar on both sites, and the chemical composition of the materials determined the decomposition rate. Litters and roots with high lignin concentrations decomposed slowly. During the experiments, most materials showed a net retention of N and P. Large net N releases were measured only for Molinia roots and basal internodes, and a large net P release was measured only for Molinia roots. It was concluded that the rate of accumulation of soil organic matter per gram of plant debris is slower on the site dominated by Molinia than on the site dominated by Erica. In the long term, N and P are probably released faster from Molinia than from Erica plant debris. Key words: decomposition, heathlands, Molinia, Erica.

Decomposition of Bauhinia purpurea leaf litter in a polluted and unpolluted Hong Kong waterway

Decomposition of Bauhinia purpurea L. leaves in litter bags submerged in the Tai Po Kau Forest Stream (TPKFS) and the Lam Tsuen River (LTR) was investigated during the winter of 1988 and the summer of 1989. At every collection, temperature, pH, turbidity, dissolved oxygen, and biological oxygen demand (BOD5) were measured. In winter, the organically enriched LTR was categorized as polluted based on BOD5, turbidity, and heterotrophic bacteria counts, whereas the TPKFS was always relatively clean. Weight loss of leaf litter at both sites was very rapid when compared with published values and exhibited a distinct seasonal pattern. The decomposition rate of leaf litter (using the single exponential decay model) varied linearly with mean water temperature. Carbon content of the leaf litter decreased during decomposition and was, as expected, negatively correlated with the percent ash content. Except in the first 2 weeks, the nitrogen content of decomposing leaf litter decreased with time at a rate correlated with the abundance of heterotrophic bacteria in winter leaf litter (insufficient data were available in summer). Based on the results of the winter study only, the decomposition of leaf litter seems to be suppressed in the polluted river. Key words: decomposition, carbon, nitrogen, water pollution, heterotrophic bacteria.

Litter decomposition under snow cover in a balsam fir forest

In a subalpine balsam fir forest in Quebec, Canada, mass losses, respiration rates, and nitrogen and sulphur dynamics were measured on fir needles, birch leaves, lichens (mixed species), and small twigs decomposing under deep (> 1.5 m) winter snow for 6 months. Mass losses ranged from <6% (twigs) to 70% (lichens) and relative decomposition rates of needles and leaves were reversed from those expected at higher temperatures. Isolation of fir needles from direct contact with the snow did not affect decay rate, nor was decay accelerated by spring snowmelt. In situ respiration rates increased from about 1 mg CO2/(g∙day)) in February to 3–5 mg CO2/(g∙day)) in May, mostly because of rising temperatures. Summer respiration rates were much higher (> 6 mg CO2/(g∙day)). Nitrogen and suphur concentrations increased in all nonwoody litter over winter, but only birch leaves and some fir needles appeared to assimilate nutrients from the environment. Melting snow could easily have provided all of the nitrogen and sulphur taken up by decomposing litter. Decomposing lichens released 40 and 60%, respectively, of their initial nitrogen and sulphur contents. A literature review indicates mass losses from leaf litter decomposing under deep snow vary according to the proportion of labile material in the litter and usually constitute 40–60% of total first-year mass losses. Key words: decomposition, winter, balsam fir, snow.

A STANDARD CURVE FOR INTER-SITE COMPARISON OF CELLULOSE DEGRADATION USING THE COTTON STRIP METHOD

Cotton cloth was buried in contrasting soils for various lengths of time until close to physical disintegration. Cellulose degradation was assessed by comparing the tensile strength of cloth after recovery with that before burial. A curve was derived for loss of tensile strength of cloth, when rotting under constant conditions. The curve was linearized by a mathematical technique analogous to taking logarithms when there is exponential decay. By means of the linearization, rates of degradation were compared between widely differing sites, using both our own data and reworked data from the literature. The time to 50% loss of tensile strength ranged from 3.2 days in an incubator at 29 °C to 1.2 yr in an arctic tundra. A mathematical model of the decay process suggests that the rate of degradation depends mainly on the physico-chemical environment of the cotton in the soil, and is insensitive to the size of microbial inoculum. Key words: Decomposition, cotton strips, site comparison, cellulose degradation, soil burial test

Gliricidia leaves decomposition: The effect of particle size on microbial respiration

Legume leaves used as green manure are a potential alternative to commercial fertilizers for non-legume crop production. Therefore, many researches have been conducted to understand the pattern of legume leaf decomposition and its release of nutrients. A study on Gliricidia leaves decomposition was conducted under laboratory conditions to elucidate the effect of grinding size of Gliricidia leaves (S1 = ≤ 0.5 mm, S2 = 4 mm, and S3 = 9 mm) on microbial respiration and N mineralization after incorporation in to the soil. The early stages of the incubation were found to be significantly influenced by the particle size of the Gliricidia leaves. Particle size S2 (4 mm) was reported to exhibit the highest C and NH4+-N mineralization. However, in the case of NO3+-N mineralization, no treatment was found to be significant. It could thus be hypothesized that physical protection of finely ground (< 0.5 mm) Gliricidia leaves was responsible for the relatively low rates of decomposition. Key Words: Decomposition, mineralization, Gliricidia leaves. DOI: 10.3329/bjar.v34i3.3957 Bangladesh J. Agril. Res. 34(3) : 343-350, September 2009