Temperature increase accelerates nitrate release from high-elevation red spruce soils

Abstract

One possible consequence of predicted increases in global temperature is an increase in soil organic matter decomposition rates and (or) nitrification rates. In nitrogen-saturated ecosystems, such a change could lead to an increase in nitrate production, since much of the ammonium released from decomposition of organic matter would be converted to nitrate rather than taken up by plants or microorganisms. In a high-elevation red spruce (Picearubens Sarg.) stand, soil at 15 cm below the surface of the sunny and shaded sides of a recent clearing were found to exhibit a significant temperature differential (Δ = 1.2 °C, p < 0.01). Soil solutions collected at 15 cm from the warmer, sunny side over an 18-month period had higher (p < 0.01) mean concentrations of nitrate (71% greater), Mg (58% greater), and Al (24% greater) than those from the shaded side. Fluxes of nitrate and Mg were 30–33% higher on the sunny side of the clearing (p = 0.10, p < 0.01, respectively). If global climate changes result in accelerated releases of nitrate that are widespread in high-elevation spruce–fir forests, elevated Al levels and (or) base cation leaching losses may result, with possible negative consequences for forest health.

Nitrogen leaching from natural ecosystems under global change: a modelling study

“…Studies that report leaching fluxes support the LPJ-GUESS results in that N-rich sites usually show a clear increase in N leaching (Joslin and Wolfe, 1993;Lükewille and Wright, 1997;Schmidt et al, 2004), while N-poor sites have a less strong response (Schmidt et al, 2004). It should be noted, however, that soil warming experiments may not be fully compatible with our results since they only account for the effect of increased N availability on vegetation productivity but not direct effects of increased temperature on plants.…”

A meta-analysis of the response of soil respiration, net nitrogen mineralization, and aboveground plant growth to experimental ecosystem warming

“…However, in N-sufficient or N-rich environments, particularly those in the northern hemisphere which are already impacted by elevated atmospheric N deposition, a warming-induced increase in internal N production could lead to or further exacerbate conditions of "N saturation", where the input of N equals or exceeds the ability of an ecosystem to assimilate the added N (Aber et al 1989. Joslin and Wolfe (1993) and Lukewille and Wright (1997), for example, have demonstrated warming-induced increases in soil leachate and run-off N. Symptoms of N saturation may include plant tissue nutrient imbalances, forest decline (and consequently declines in net ecosystem C sequestration), increased gaseous loss of N (with consequent feedback to global warming as NO and N 2 O are "greenhouse" gases), and increased N leaching from soils with consequent declines in associated surface water quality (Vitousek et al 1997;Fenn et al 1998).…”

“…These experiments have shown that rates of soil respiration generally increase with warmer temperatures (Peterjohn et al 1993(Peterjohn et al , 1994McHale et al 1998;Rustad and Fernandez 1998a), but the response to warming of other ecosystem processes has been more variable, and general response patterns have been difficult to identify. For example, litter decomposition, CH 4 production and oxidation, N cycling rates and losses, net C flux, and plant productivity have all been shown to increase, decrease, or remain unchanged by warming (Van Cleve et al 1990;Joslin and Wolfe 1993;Peterjohn et al 1993Peterjohn et al , 1994Hantschel et al 1995;Robinson et al 1995;Hobbie 1996;Lukewille and Wright 1997;Ineson et al 1998;Jamieson et al 1998;Jones et al 1998;McHale et al 1998;Rustad and Fernandez 1998b;Olszyk et al 1998;Shaver et al 1998;Arft et al 1999;Hartley et al 1999;Verburg et al 1999;Welker et al 1999;Johnson et al 2000;Rustad et al 2000; Thompson et al 2000;Welker et al 2000).…”

Soil Carbon Dynamics Along an Elevation Gradient in the Southern Appalachian Mountains

“…Predictions from prior research indicate a potential loss of forest soil C stocks in the southern Appalachians with regional warming due to accelerated decomposition of soil organic matter (Garten et al, 1999). Furthermore, warming could negatively impact high elevation forests more than those at low elevations by contributing to disruption of the N cycle (Joslin and Wolfe, 1993;Joslin and Johnson, 1998;Melillo et al, 2002). *Details about the hypothesized effect of N availability on litter decomposition are explained by Berg and Matzner (1997) and Berg et al (2001) Townsend et al (1995; Trumbore et al (1996); Chambers (1998); Conant et al (1998);Garten et al (1999);Wang et al (2000); Kane et al (2003) Lindberg et al (1988Lovett and Kinsman (1990);Miller et al (1993);Garten and Van Miegroet (1994); Lawrence et al (2000); Bohlen et al (2001) Knoepp and Swank (1998) Conant et al (1998);Conant et al (2000); Wang et al (2000) reduced decomposition rates and longer turnover times increase soil C stocks greater soil N availability contributes to higher soil C stocks through effects on decomposition* poor substrate quality limits N mineralization decomposition rates increase from xeric to mesic sites (up to a limit where saturation inhibits decomposition) On the other hand, hypotheses about changing litter C:N ratios and higher limit values to litter decomposition (Berg et al, 1996;Berg, 2000) suggest a negative feedback on global warming as a consequence of greater humus formation (Berg and Matzner, 1997;Berg et al, 2001) and reduced decomposition losses of forest soil C in a N-rich environment.…”