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Leaf litter mixtures and the amount of litter biomass in the litter standing stocks can affect the decomposition rates by modifying physical properties and resource heterogeneity in the litter layers. However, the potential interactive effects of litter mixtures and the amount of litter biomass on decomposition have been overlooked in the literature, even though both aspects of litter layer may be highly variable in space and time, within and across ecosystems. In a field experiment conducted in a seasonally dry tropical forest (also known as restinga forest), we investigated the individual and interactive effects of litter mixing and litter biomass on the decomposition of leaf litter from four species of trees, at both species- and assemblage-level. We hypothesized that the mixing of litter and higher litter biomass would both promote litter decomposition, and that litter mixture effects on decomposition at assemblage- and species specific-level would be stronger under higher litter biomass. Mixing of litter and the amount of litter in the standing stocks had no significant individual effects on decomposition, neither at the assemblage- or species specific-level. However, we observed an interactive effect between both experimental factors for the decomposition of a single species, where, contrary to our predictions, the decomposition of Andira legalis at low litter biomass was slightly reduced in the litter mixture. Our results indicate that litter decomposition in the restinga ecosystem should be highly predictable with knowledge of species composition and species-specific decomposition rates, and suggest that, at least for seasonally dry tropical ecosystems, the mixing of litter may have only a small effect on the decomposition process. [ABSTRACT FROM AUTHOR]

Abstract: Several ongoing projects are harvesting maritime biomass from the Baltic Sea for eutrophication mitigation and utilisation of the recovered biomass. Some of this biomass comprises common reed (Phragmites australis), one of the most widespread vascular plants on Earth. Reed utilisation from eutrophied coastal areas needs to be evaluated. Therefore, a system analysis was performed of reed harvesting for biofuel and biofertiliser production. The specific objectives of the analysis were to: investigate the methane yield associated with anaerobic co-digestion of reed; make a primary energy assessment of the system; quantify Greenhouse Gas (GHG) savings when a fossil reference system is replaced; and estimate the nutrient recycling potential of the system. The results from energy and GHG calculations are highly dependent on conditions such as system boundaries, system design, allocation methods and selected indicators. Therefore a pilot project taking place in Kalmar County, Sweden, was used as a case study system. Laboratory experiments using continuously stirred tank reactor digesters indicated an increased methane yield of about 220 m3 CH4/t volatile solids from co-digestion of reed. The energy balance for the case study system was positive, with energy requirements amounting to about 40% of the energy content in the biomethane produced and with the non-renewable energy input comprising about 50% of the total energy requirements of the system. The net energy value proved to be equivalent to about 40 L of petrol/t reed wet weight. The potential to save GHG emissions compared with a fossil reference system was considerable (about 80%). Furthermore an estimated 60% of the nitrogen and almost all the phosphorus in the biomass could be re-circulated to arable land as biofertiliser. Considering the combined benefits from all factors investigated in this study, harvesting of common reed from coastal zones has the potential to be beneficial, assuming an appropriate system design, and is worthy of further investigations regarding other sustainability aspects. [Copyright &y& Elsevier]

Abstract: A model of competition between plasmid-bearing and plasmid-free organisms in the chemostat with periodic input of nutrient and two distributed delays is investigated. The delays model the fact that the nutrient is partially recycled after the death of the biomass by bacterial decomposition. It is assumed that there is inter-specific competition between the plasmid-bearing and plasmid-free organisms as well as intra-specific competition within each population. Analysis of the extinction of the organisms, including plasmid-bearing and plasmid-free organisms, and the permanence of the system are carried out. Furthermore, sufficient conditions ensuring the existence and global stability of the positive periodic solution are established. Numerical simulations illustrate the theoretical results. Finally, we present a procedure by which one can control the parameters of the model to keep the plasmid-bearing organism stay eventually in a desired set. [Copyright &y& Elsevier]

Abstract: The asymptotic behavior of solutions of a chemostat-type model in which two species compete for a limiting nutrient supplied at a constant rate is considered. The model incorporates a general nutrient uptake function and two distributed delays. The first delay models the fact that the nutrient is partially recycled after the death of the biomass by bacterial decomposition and the second indicates that the growth of the species depends on the past concentration of the nutrient. Furthermore, it is assumed that there is interspecific competition between the two species as well as intraspecific competition within each species. Conditions for boundedness of solutions and existence of nonnegative equilibria are given. By constructing appropriate Liapunov-like functionals, some sufficient conditions for global attractivity of the positive equilibrium is obtained. The combined effects of the two different delays are studied. The main results of Freedman and Xu [H.I. Freedman, Y. Xu, Models of competition in the chemostat with instantaneous and delayed nutrient recycling, J. Math. Biol. 31 (1993) 513–527] and Ruan and He [S. Ruan, X.-Z. He, Global stability in chemostat-type competition models with nutrient recycling, SIAM J. Appl. Math. 58 (1) (1998) 170–192] are improved and extended. [Copyright &y& Elsevier]

Abstract: In an effort to generate more information on the use of biosolids in the turf industry, a study was conducted to compare the effectiveness of biosolids with recommended organic sources in enhancing soil microbial populations and N availability in putting green sand rootzones. The treatments included four types of rootzones as follows: sand (control), sand mixed with Dakota reed-sedge peat (10%, v/v), sand mixed with yard-waste compost (10%, v/v), and sand mixed with biosolids (10%, v/v), which were established at the North Shore Country Club golf course, Glenview, IL, USA in 1997. All plots received the same fertilizers mainly in organic forms at 100kgNha−1 year−1. Creeping bentgrass (Agrostis palustris) turf was established, and was managed as a practice putting green. Soil microbial biomass in the rootzone (0–30cm) was higher either under compost (fall 2004 and summer 2005) or biosolids (summer 2003) than other treatments. Rootzone ammonium oxidizer populations were higher with biosolids (5400g−1 soil) than peat (1200g−1 soil) and compost (500g−1 soil) amendment and in control (400g−1 soil) in summer 2003. The nitrite oxidizer populations were higher with biosolids (24000g−1 soil) than compost (8300g−1 soil) and peat (4700g−1 soil) amendment and in control (3700g−1 soil) in summer 2005. Soil potentially mineralizable N, also being lowest in control, was higher in the biosolids-amended than compost- and peat-amended rootzones. In most seasons, the nitrate concentrations in biosolids rootzone (3.16–19.3mgkg−1) were higher than in compost (2.79–17.7mgkg−1), peat (1.83–14.4mgkg−1), and control rootzone (0.81–15.2mgkg−1). The study indicates that while compost could restore soil microbial biomass better than peat, biosolids could maintain greater N supply than peat and compost. [Copyright &y& Elsevier]