Carbon Quality of Four-Year-Old Woodchips in a Denitrification Bed Treating Agricultural Drainage Water

A denitrification bed is a system that can reduce the nitrate concentration in subsurface drainage water. There is a need to investigate the carbon quality of old woodchips to gain a better understanding of the effect of age on woodchip properties. The objectives of this study were to characterize the carbon quality and carbon to nitrogen (C/N) ratio of aged woodchips and to examine the suitability of a denitrification bed for a replicated experiment. To achieve these goals, we excavated four-year-old woodchips along the length of a 106.4 m long denitrification bed near Willmar, Minnesota, and analyzed them for particle size, C/N ratio, and carbon quality. Particle size analysis showed similarities from 12.5 to 106.4 m along the bed. We found a mean C/N ratio ranging from 58.4 ±3.17 to 153.4 ±9.57 (smallest at the inlet). The mean lignocellulose index (LCI, a measure of carbon quality) of the four-year-old woodchips ranged from 0.47 to 0.57 (highest at the inlet). The woodchip particle sizes, C/N ratios, and LCI from 25.9 to 106.4 m along the bed length were similar. In conclusion, the C/N ratio and LCI of the four-year-old woodchips showed effects of decomposition and increased woodchip carbon recalcitrance over time, respectively. Keywords: Denitrifying bioreactor, Tile drainage, Water quality, Woodchip bioreactor.

Microfungus communities of Japanese beech logs at different stages of decay in a cool temperate deciduous forest

Fallen logs of Japanese beech ( Fagus crenata Blume) at various stages of decomposition were sampled from a cool temperate deciduous forest in Japan and studied for differences in the associated microfungus communities. Wood samples were directly plated onto each of two different media for the identification of fungal species. Approximately 1500 isolations were made, which represent 96 species of filamentous microfungi, consisting of 16 zygomycetes and 80 anamorphic ascomycetes. The number of species per log (α-diversity) increased with log decomposition, while dissimilarity of species composition among logs (β-diversity) showed a unimodal response with the optimum at the intermediate decay stage. The water content and nitrogen concentration of the wood were positively correlated, while the lignocellulose index and relative density were negatively correlated with α-diversity. Stepwise regression models suggested that lignocellulose index was the single most important determinant of variation in α-diversity and explained 31% of variation. Eighteen fungal species frequently isolated from the logs were classified into four groups based on their occurrence patterns. These groups occurred successively during log decomposition, and the succession in early stage of log decomposition was related with relative density, while the succession in late stage was related with water content and nitrogen concentration of wood.

Leaf litter chemistry controls on decomposition of Pacific Northwest trees and woody shrubs

The effects of initial leaf litter chemistry on first-year decomposition rates were studied for 16 common Pacific Northwest conifers, hardwoods, and shrubs at the H.J. Andrews Experimental Forest in western Oregon. Leaf litters were analyzed for C, N, P, K, Ca, Mg, proximate organic fractions (nonpolar, polar, acid-hydrolyzable extractives, acid-hydrolyzable lignin, and acid-unhydrolyzable residue, previously termed "Klason lignin"), and biochemical components (total phenolics, reactive polyphenols, water-soluble carbohydrates, water-soluble proanthocyanidins, and water- and acid-unhydrolyzable proanthocyanidins). By including measurements of reactive and residual phenolic fractions and acid-hydrolyzable lignin, these analytical methods improve upon traditional proximate leaf litter analyses. Significant differences in litter chemistries and decomposition rates were found between species. For all species combined, the 1-year decay rate (k) values had highly significant correlations (P < 0.001) with 30 out of the 36 initial chemistry variables tested in this study. The three highest correlations were with acid-unhydrolyzable proanthocyanidins, lignocellulose index, and acid-unhydrolyzable residue (r = 0.83, –0.81, –0.80, respectively, with P < 0.0001 and n = 339). We found that no single litter chemistry variable was a universal predictor of the 1-year k value for each of the individual 16 species studied, though phenolic components were more frequent significant (P < 0.001) predictors of decomposition rate.