Print PageAtmospheric nitrogen deposition has the potential to impact forest productivity, microbial associations, nutrient cycling and stand dynamics. However, among the least studied aspects of these processes are the production and decomposition of dead woody biomass, or coarse woody debris (CWD). This study analyzes the influence of chronic simulated N deposition on the decomposition of CWD along a latitudinal gradient in Michigan. Excessive N availability may generate conditions in which decomposition slows or is inhibited. Under such conditions, there could be an accumulation of CWD biomass in N-amended plots. Inhibiting lignin decomposition could potentially blur the qualitative delineations of decay class labels. Previous findings found a slight increase in mortality in the N-amended plots. Determining the diameter distribution of this mortality will reveal possible impacts of N deposition on stand dynamics. Methodology included comparing tree mortality and CWD biomass for both ambient and simulated N deposition treatments, classifying downed dead wood as well as snags by their respective visual qualitative decay classes, and calculating densities by decay class.
Results/Conclusions
Since N deposition treatments began in 1994, 304 trees have died in the N-amended plots which represent 17% more than ambient plots. Increased mortality in the N-amended plots is found mostly in the smaller to intermediate diameter classes (6 to 18 cm). Density of CWD from the visual decay classes 3 and 4 were greater in the N deposition treatments than decay classes 3 and 4 in the ambient plots. These results are perhaps attributed to the response of lignin degrading basidiomycete fungi to N-deposition. Although qualitative classification indicated little response to simulated N deposition, our quantitative analysis indicates N deposition has the potential to alter rates of wood decomposition and dead woody C accrual.
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