Effects of experimental freezing on soil nitrogen dynamics in soils from a net nitrification gradient in a nitrogen-saturated hardwood forest ecosystem

Abstract

This study examined effects of soil freezing on N dynamics in soil along an N processing gradient within a mixed hardwood dominated watershed at Fernow Experimental Forest, West Virginia. Sites were designated as LN (low rates of N processing), ML (moderately low), MH (moderately high), and HN (high). Soils underwent three 7-day freezing treatments (0, -20, or -80 8C) in the laboratory. Responses varied between temperature treatments and along the gradient. Initial effects differed among freezing treatments for net N mineralization, but not nitrification, in soils across the gradient, generally maintained at LN < ML MH < HN for all treatments. Net N mineralization potential was higher following freezing at -20 and -80 8C than control; all were higher than at 0 8C. Net nitrification potential exhibited similar patterns. LN was an exception, with net nitrification low regardless of treatment. Freezing response of N mineralization differed greatly from that of nitrification, suggesting that soil freezing may decouple two processes of the soil N cycle that are otherwise tightly linked at our site. Results also suggest that soil freezing at temperatures commonly experienced at this site can further increase net nitrification in soils already exhibiting high nitrification from N saturation.Résumé : Nous avons étudié les effets du gel du sol sur la dynamique de N dans le sol le long d'un gradient de transformation de N dans un bassin versant dominé par des feuillus mélangés à la Forêt expérimentale de Fernow, en Virginie-Occidentale. Les stations ont été classées sur la base du taux de transformation de N: LN (faible), ML (modérément faible), MH (modérément élevé) et HN (élevé). Les sols ont subi trois périodes de gel de 7 jours (0, -20 ou -80 8C) en laboratoire. Les réactions ont varié selon la température ainsi que le long du gradient. Les effets initiaux étaient différents selon l'intensité du gel dans le cas de la minéralisation nette mais pas dans le cas de la nitrification dans les sols le long du gradient qui s'est généralement maintenu à LN < ML < MH < HN avec tous les traitements. Le potentiel de minéralisation nette de N était plus élevé à la suite d'un gel à -20 et -80 8C que chez le témoin et plus élevé qu'à 0 8C dans tous ces traitements. Le potentiel de nitrification nette suivait le même patron. La station LN faisait exception: la nitrification nette était faible peu importe le traitement. La réponse de la minéralisation de N au gel était très différente de celle de la nitrification, indiquant que le gel du sol peut découpler deux processus du cycle de N dans le sol qui sont par ailleurs étroite-ment reliés dans notre site. Les résultats indiquent aussi que le gel du sol à des températures qui surviennent couramment dans ce site peut augmenter davantage la nitrification nette dans les sols où la nitrification est déjà élevée à cause de la saturation en N.[Traduit par la Rédaction]

Increased nitrogen leaching following soil freezing is due to decreased root uptake in a northern hardwood forest

“…It is possible that increases in nitrification following soil frost may also contribute to NO 3 − leaching (Gilliam et al ., ). In our study, the low concentrations of NH 4 + and high concentrations of NO 3 − in the B horizon of the snow‐removal plots suggest that most of the excess NH 4 + in the Oa horizon was nitrified.…”

“…Increases in N export following experimental soil freezing in mixed hardwood forests at the Fernow Experimental Forest, West Virginia were attributed in part to elevated rates of nitrification (Gilliam et al ., ), but elevated N leaching could not be explained by increased rates of nitrification alone in the majority of other forests studied (Fitzhugh et al ., ; Callesen et al ., ; Christopher et al ., ; Hentschel et al ., ). Rather, most studies purport that reduced plant uptake is the primary mechanism for increased N losses (Boutin & Robitaille, ; Fitzhugh et al ., ; Groffman et al ., ; Matzner & Borken, ; Kreyling, ; Brooks et al ., ).…”

Effects ofin situfreezing on soil net nitrogen mineralization and net nitrification in fertilized grassland of northern China

“…, 2010). Gilliam et al. (2010) suggested that mild freezing may inhibit N mineralizing microbes and stimulate N immobilizing groups.…”

“…Seasonal patterns of NH 4 + and NO 3 – may be attributed to freezing, which can disrupt coupling between soil N mineralization and microbial immobilization of N (Maithani et al. , 1998; Gilliam et al. , 2010).…”

Climate Change Impacts on Plant Pathogens and Plant Diseases

“…Increased frequency and duration of soil frost has been associated with changes in microbial activity (Gilliam et al 2010), injury of fine roots (Tierney et al 2001;Cleavitt et al 2008), and increased export of carbon and nutrients, such as nitrogen during the growing season, which is associated with changes in microbial activity (Matzner and Borken 2008). Kreyling et al (2012) examined the effects of a range of freeze-thaw scenarios and their effects on root injury and fungal community composition, biomass, and root injury.…”