Charcoal and Nitrogen Cycling in Forest Ecosystems.

Charcoal is a natural byproduct of wildland and thus is a ubiquitous component of temperate coniferous forest soils. Until recently, however, there has been a dearth of information available regarding the biochemical importance of charcoal in the soil ecosystem. A series of field and laboratory studies have been conducted to determine the extent to which charcoal influences nutrient cycling in forest ecosystems and to explore possible mechanisms for these effects. The longevity of charcoal in soil result in its accumulation over time in fire maintained ecosystems, however, the potency of charcoal as a driver of microbial nutrient transformations may decline with time since fire. Nitrification rates in ponderosa pine forest soils were greatly increased in the presence of charcoal; whereas, ammonium additions to these soils had no effect on nitrification rates suggesting that nitrification in these forests are not substrate limited, but rather limited by rapid immobilization or inhibitory compounds that can be adsorbed by charcoal. Polyphenols and terpenes are readily adsorbed by charcoal which may either reflect sorption of inhibitory compounds or sorption of available C, both of which could increase net nitrification. The temperature of charcoal formation influences charcoal quality with higher temperature charcoal exhibiting greater sorption capacity and porosity. Charcoal addition to soils exhibiting naturally high rates of nitrifier activity did not stimulate an increase in net nitrification. Charcoal deposited during fire events plays a major role as a mediator of nutrient dynamics and represents a significant portion of the soil carbon pool in fire maintained temperate ecosystems. Further studies, however, are warranted to more clearly elucidate mechanisms by which charcoal alters ecosystem processes.