Temporal and spatial variation of nitrogen transformations in nitrogen-saturated soils of a central Appalachian hardwood forest

Abstract

Abstract:We studied temporal and spatial patterns of soil nitrogen (N) dynamics from 1993 to 1995 in three watersheds of Fernow Experimental Forest, W.V.: WS7 (24-year-old, untreated); WS4 (mature, untreated); and WS3 (24-year-old, treated with (NH 4 ) 2 SO 4 since 1989 at the rate of 35 kg N·ha -1 ·year -1 ). Net nitrification was 141, 114, and 115 kg N·ha -1 ·year -1 , for WS3, WS4, and WS7, respectively, essentially 100% of net N mineralization for all watersheds. Temporal (seasonal) patterns of nitrification were significantly related to soil moisture and ambient temperature in untreated watersheds only. Spatial patterns of soil water NO 3 -of WS4 suggest that microenvironmental variability limits rates of N processing in some areas of this N-saturated watershed, in part by ericaceous species in the herbaceous layer. Spatial patterns of soil water NO 3 -in treated WS3 suggest that later stages of N saturation may result in higher concentrations with less spatial variability. Spatial variability in soil N variables was lower in treated WS3 versus untreated watersheds. Nitrogen additions have altered the response of N-processing microbes to environmental factors, becoming less sensitive to seasonal changes in soil moisture and temperature. Biotic processes responsible for regulating N dynamics may be compromised in N-saturated forest ecosystems.Résumé : Nous avons étudié les patrons temporels et spatiaux de la dynamique de l'azote (N) du sol, de 1993 à 1995, dans trois bassins versants de la forêt expérimentale de Fernow : WS7 (âgé de 24 ans et non traité); WS4 (mature et non traité); WS3 (âgé de 24 ans et traité avec (NH 4 ) 2 SO 4 depuis 1989 au taux de 35 kg N·ha -1 ·an -1 ). La nitrification nette était respectivement de 141, 114 et 115 kg N·ha -1 ·an -1 pour WS3, WS4 et WS7, soit essentiellement 100% de la minéralisation nette pour tous les bassins versants. Les patrons temporels (saisonniers) de nitrification étaient significativement reliés à l'humidité du sol et à la température ambiante seulement dans les bassins versants non traités. Les patrons spatiaux de NO 3 -de la solution de sol du WS4 indiquent que la variabilité micro-environnementale limite le taux de recyclage de N dans certaines aires de ce bassin versant saturé en N, en partie à cause des espèces d'éricacées pré-sentes dans la strate herbacée. Les patrons spatiaux de NO 3 -de la solution du sol dans le WS3 traité indiquent que des stades plus avancés de saturation de N peuvent se traduire par de plus fortes concentrations avec moins de variabilité spatiale. La variabilité spatiale des variables de N du sol était plus faible dans le WS3 comparativement aux bassins versants non traités. Les ajouts de N ont altéré la réponse des microorganismes associés au cycle de N vis-à-vis les facteurs environnementaux en les rendant moins sensibles aux changements saisonniers d'humidité et de température du sol. Les processus biotiques responsables de la régulation de la dynamique de N peuvent être compromis dans les éco-systèmes forestiers saturés en N...

Vegetation and Acidification

“…5-18). Thus, the seasonal pattern of change in herb cover that is consistent with seasonal patterns of change in net nitrification on WS4 and WS7 appears to be absent on WS3, likely related to decoupling of N cycle from biotic controls due to acidification treatments, as noted by Gilliam et al (2001). However, N:P ratio was among the longer (i.e.…”

Acidification and Nutrient Cycling

“…However, there were no significant differences in nitrification rates between WS3 and WS7 (Venterea et al 2004), similar to the results of Gilliam et al (2001b). Therefore, Venterea et al (2004) speculated that a slight decrease in the pH of the upper soil horizon on WS3 (this was also noted in Chapter 3, a decrease of 4.34 to 4.20 in the 0-10 cm horizon during 1994-2002) may have caused increased protonation of nitrification-derived NO 3 , and the subsequent abiotic formation of NO, which contributed to the differences in NO emissions between WS3 and WS7.…”

“…Net nitrification on WS3, WS4, and WS7 was 141, 114, and 115 kg N ha -1 yr -1 , respectively (Gilliam et al 2001b, Christ et al 2002, and essentially equal to 100% of net mineralization for these watersheds. These rates do not differ significantly among watersheds.…”

“…Studies of N dynamics in the soils of the Fernow watersheds have shown that rates of net mineralization and net nitrification are high on both WS3 and WS4, compared with other forested ecosystems (Gilliam et al 2001b). Net nitrification on WS3, WS4, and WS7 was 141, 114, and 115 kg N ha -1 yr -1 , respectively (Gilliam et al 2001b, Christ et al 2002, and essentially equal to 100% of net mineralization for these watersheds.…”

Vegetation and Acidification

“…There is a suggestion that P may be limiting to black cherry on both watersheds. Other supporting data (Gilliam et al 2001, W.T. Peterjohn, unpublished data) also provide evidence of a P limitation.…”