Decomposition and nutrient release of four potential mulching materials for poplar plantations on upland sites

The application of organic residues and the release dynamics of nutrients during decomposition may be crucial to improving poplar growth in upland areas. Field experiments were conducted in Guizhou Province, southwestern China, to determine differences in biomass decomposition of four potential mulching materials in one-year-old poplar plantations. Results showed the initial total content of N, P, K, Ca and Mg in the mulches ranged from 30.0 to 35.0 g/kg and was significantly greater in Quercus fabri, Imperata cylindrica var. major and Pteridium aquilinum var. latiuscukum than in Coriaria nepalensis. The weight loss pattern of these four species during decomposition could be best described by a double exponential decay model, and monthly decay rate coefficients (k) were in the order Q. fabri > C. nepalensis > I. cylindrica > P. aquilinum over a one-year period. Total nutrient (N, P and K) release of the four mulching materials ranged from 74.2 to 90.8% of the initial content after one year of decomposition, while nutrients were released in the order K > P>N. Nutrient release was fastest in C. nepalensis followed by Q. fabri, I. cylindrica, and slowest in P. aquilinum. Thus, taking into account initial nutrient content, nutrient additions and decay rates, the sprouts of woody species (Q. fabri and C. nepalensis) with massive foliage proved to be more important as nitrogen sources than the grass or fern.     

Wetland macrophyte decomposition under different nutrient conditions: Relationships between decomposition rate, enzyme activities and microbial biomass

We used oligotrophic, P-limited herbaceous wetlands of northern Belize as a model system, on which to document and explain how changes in nutrient content along a salinity gradient affect activities of extracellular enzymes involved in macrophyte decomposition. To determine what is more important for decomposition, the initial litter quality, or site differences, we used reciprocal litter placement in a combined “site quality” and “litter quality” experiment running from August 2003 to April 2004. The experiment was set up in long-term control and nutrient addition plots (P, N, and NP) established in 2001 in 15 limestone-based inland marshes with a wide range of water conductivities (200-6000 μS) and a uniform pH (7.0-7.7) dominated by emergent macrophytes, Eleocharis spp. There were no differences among the plots in total sediment N and water NH₄-N, but total and KCl-extractable sediment P and water PO₄-P were significantly higher in P and NP plots throughout the duration of the experiment. The initial litter N content was slightly but significantly different between control and N plots versus P and NP plots (5.7 and 7.1 mg g⁻¹, respectively). The difference was much bigger for litter P content, 0.1 and 0.7 mg g⁻¹, respectively. Enzyme activities of alkaline phosphatase, leucine-aminopeptidase, arylsulfatase, and β-glucosidase were measured fluorometrically in Eleocharis litter in both the litterbag experiment and the naturally decomposing material. Total phospholipid fatty acid (PLFA) content in litter samples was used as a measure of microbial biomass present. Phosphatase always exhibited the highest activity of the enzymes studied, followed by leucine-aminopeptidase, arylsulfatase and β-glucosidase. There were no significant differences between enzyme activities from litterbags and the unconfined litter. Phosphatase activity was significantly suppressed in P-addition plots under all salinity levels while the activities of the remaining enzymes were significantly higher in P-enriched plots. There was a strong correlation between decomposition coefficient k-values and most of the enzymes as well as between the amount of PLFA and enzyme activities. PLFA, arylsulfatase, and litter C/P were the best predictors of k-values.