No abstract

Shredded straw of Miscanthus was composted in 800-L boxes with different amounts of pig slurry added as nitrogen source. The impact of the different initial C/N ratios (11, 35, 47, 50, and 54) on the composting process and the end product was evaluated by examining chemical and microbiological parameters during 12 months of composting. Low initial C/N ratios caused a fast degradation of fibers during the first three months of composting (hemicellulose: 50-80%, cellulose: 40-60%), while high initial C/N ratios resulted in 10-20% degradation of both hemicellulose and cellulose. These differences were reflected in the microbial biomass and respiration, which initially were higher in low C/N treatments than in high C/N treatments. After 12 months of composting, this situation was reversed. Composts with high initial C/N ratios had high microbial biomass (15-20 mg ATP g-1 OM) and respiration rates (200 mg CO2 h-1 g-1 OM) compared to treatments with low initial C/N ratios (less than 10 mg ATP g-1 OM and 25 mg CO2 h-1 g-1 OM). This could be explained by the microorganisms being nitrogen limited in the high C/N ratio treatments. In the low C/N ratio treatments, without nitrogen limitation, the high activity in the beginning decreased with time because of exhaustion of easily available carbon. Different nitrogen availability was also seen in the nitrification patterns, since nitrate was only measured in significant amounts in the treatments with initial C/N ratios of 11 and 35. The microbial community structure (measured as phospholipid fatty acid, PLFA, profile) was also affected by the initial C/N ratios, with lower fungal/bacterial ratios in the low compared to the high C/N treatments after 12 months of composting. However, in the low C/N treatments higher levels of PLFAs indicative of thermophilic gram-positive bacteria were found compared to the high C/N treatments. This was caused by the initial heating phase being longer in the low than in the high C/N treatments. The different fungal/bacterial ratios could also be explained by the initial heating phase, since a significant correlation between this ratio and heat generated during the initial composting phase was found.

Microbial biomass and community structure were investigated in two composts using the phospholipid fatty acid technique. The composts consisted of shredded straw of Miscanthus with the addition of pig slurry to give an initial C:N ratio of about 25. Samples were taken following changes in the compost temperature (at 5°C intervals) during the first month of composting and additionally after 2 and 3 months. The total microbial biomass, measured as total amount of phospholipid fatty acid, peaked after 1 day with about six times the initial values. The temperature also peaked after 1 day, being above 60°C, and then slowly declined to around 25°C over 3 months. Microbial biomass was approximately halved during this time. When the total amount of phospholipid fatty acid was separated into indicator phospholipid fatty acids for different groups of microorganisms, these groups showed different patterns during the composting process. Gram‐positive bacteria increased rapidly with increasing temperature and decreased with decreasing temperature. Gram‐negative bacteria and fungi increased initially up to a temperature around 50°C, but decreased during the extreme heating phase. When the temperature declined to about 50°C, the amounts of phospholipid fatty acids indicative of these two groups increased again. The phospholipid fatty acid indicative of actinomycetes, 10Me18:0, was at a low level during the whole experiment, but increased slightly during the last month of composting. The development of the microbial community in the two composting systems was similar during the initial thermophilic phase of the composting process, but the communities after 3 months differed.

Sixteen open-top chambers (diameter, 3.66 m) were established in a scrub oak habitat in central Florida where vegetation was removed in a planned burn prior to chamber installation. Eight control chambers have been continuously exposed to ambient air and eight have been continuously exposed to elevated CO 2 at twice-ambient concentration (ϳ700 ppm) for 5 years. Soil cores were collected from each chamber to examine the influence of elevated atmospheric CO 2 on the fungal community in different soil fractions. Each soil sample was physically fractionated into bulk soil, rhizosphere soil, and roots for separate analyses. Changes in relative fungal biomass were estimated by the ergosterol technique. In the bulk soil and root fractions, a significantly increased level of ergosterol was detected in the elevated CO 2 treatments relative to ambient controls. Fungal community composition was determined by terminal-restriction fragment length polymorphism (T-RFLP) analysis of the internal transcribed spacer (ITS) region. The specificities of different ITS primer sets were evaluated against plant and fungal species isolated from the experimental site. Changes in community composition were assessed by principal component analyses of T-RFLP profiles resolved by capillary electrophoresis. Fungal species richness, defined by the total number of terminal restriction fragments, was not significantly affected by either CO 2 treatment or soil fraction.

No abstract