The Influence of Tree Species, Nitrogen Fertilization, and Soil C to N ratio on Gross Soil Nitrogen Transformations

Abstract

To investigate controls on gross N transformations in forest soils, a 15N pool dilution technique was used on soils of single‐species plots of five major tree species (red oak [Quercus rubra L.], sugar maple[Acer saccharum Marsh.], hemlock [Tsuga canadensis (L.) Carr], beech [Fagus grandifolia Ehrh.] and yellow birch [Betula alleghaniensis Britton]) in the Catskill Mountains of New York State. Catskill forest soils had high rates of gross mineralization and NH4+ consumption, indicating rapid NH4+ cycling, a pattern not captured by net N mineralization assays. Sugar maple had the highest rates of gross mineralization and NH4+ consumption. Rates of gross nitrification were similar to rates of net nitrification for all species. Sugar maple had the highest gross nitrification rates, while hemlock and red oak had the lowest rates. There were no significant species differences in NO3− consumption. Fertilization of the plots did not significantly alter N cycling rates with the exception of yellow birch, where N fertilization decreased NO3− consumption. We observed a significant negative relationship between net nitrification and soil C/N ratio in both organic and mineral horizons, but our results indicate that the mechanism underlying that relationship was different in the two horizons. In the mineral horizon, limitation of net nitrification in soils of high C/N ratio probably resulted from low gross NH4+ production. In organic horizons, low NH4+ production was not a significant factor and higher NO3− consumption explained some of the pattern. Understanding the roles individual tree species as well as excess N input play in regulation of the N cycle will improve forest management and prediction of forest responses to elevated N deposition.

In situ gross nitrogen transformations differ between temperate deciduous and coniferous forest soils

“…to NO 3 -was similar in both forest soils (*0.1 lg N g -1 day -1 ) and four to nine times lower than the gross N mineralization rate. While higher nitrification rates have been reported for temperate forest soils (Booth et al 2005;Christenson et al 2009;Verchot et al 2001), the current values exceed rates measured in the same region (Vervaet et al 2004). At Harvard Forest, mineral soils of deciduous and pine forests had similar gross nitrification rates (Venterea et al 2004).…”

“…Nitrogen cycling in forest soils can vary among the dominant tree species (Christenson et al 2009;Lovett et al 2004;Yan et al 2008;Zeller et al 2007) because tree species affect physicochemical and biological characteristics of soils (Binkley and Giardina 1998). Soil microbial biomass, activity, and community structure can thus be tree species dependent (Hackl et al 2005;Priha et al 2001).…”

“…Tree species effects on net soil N transformation rates have been reported more often (Yan et al 2008;Zhong and Makeshin 2004) than effects on gross N rates (Christenson et al 2009). However, a better understanding of N cycling in forest soils requires the quantification of gross N rates, since high gross ammonium (NH 4 ? )…”

Cross-biome assessment of gross soil nitrogen cycling in California ecosystems

“…Thus, deciduous forests with lower soil C:N ratios may have higher gross nitrification rates comparable to the other biomes in our study. Cross-site comparisons of forests that included both deciduous and coniferous trees have also documented negative relationships between soil C:N ratios and both gross nitrification (Bengtsson et al, 2003;Christenson et al, 2009) and net nitrification (Lovett et al, 2004;Venterea et al, 2003). Christenson et al (2009) found lower gross nitrification rates in forests with lower gross mineralization rates and hypothesized that NH 4 þ supply likely limited nitrification in mineral soil horizons.…”

“…Cross-site comparisons of forests that included both deciduous and coniferous trees have also documented negative relationships between soil C:N ratios and both gross nitrification (Bengtsson et al, 2003;Christenson et al, 2009) and net nitrification (Lovett et al, 2004;Venterea et al, 2003). Christenson et al (2009) found lower gross nitrification rates in forests with lower gross mineralization rates and hypothesized that NH 4 þ supply likely limited nitrification in mineral soil horizons. In support of this hypothesis, the meta-analysis by Booth et al (2005) showed that gross N mineralization was the strongest predictor of gross nitrification (with R 2 ¼ 0.32) across woody, grassland, and agricultural ecosystems.…”