Soil δ¹⁵N patterns in old-growth forests of southern Chile as integrator for N-cycling

Abstract

Old-growth forests of southern Chile represent an important reserve of temperate (rain) forests in the world. Wetter and colder forest ecosystems appear to be more efficient in conserving and recycling N such that mostly non-plant available N species are lost, which could be indicated by more depleted delta15N values of the soil and plants. Hydrological N loss from the old-growth forests in southern Chile occurs mainly via dissolved organic nitrogen and not via dissolved inorganic N. Forest disturbances (e.g. fire, clear-cutting or enhanced N deposition) cause (abrupt) changes in ecosystem N-cycling processes. In this study, we hypothesized that delta15N signatures of soil profiles under old-growth forests could be used as an integrator for ecosystem N-cycling, and changes of these delta15N profiles could be valuable to assess ecosystem resilience towards disturbances. Six old-growth forests were selected in the phytogeographical region of the Valdivian rain forest in southern Chile. One of the sites has been partly burned in February 2002. First, we observed that ecosystems with higher mean annual precipitation and lower mean annual temperature were relatively more depleted in 15N. Secondly, we found that a forest fire caused a 100-fold increase of the nitrate export and induced an enrichment of the soil delta15N signal in the upper 20 cm.

Increasing abundance of soil fungi is a driver for 15N enrichment in soil profiles along a chronosequence undergoing isostatic rebound in northern Sweden

“…EVects of Wres on nitrogen isotopic signatures are however complex, since the eVect appears negligible below a temperature of 200°C and above a temperature of 600°C (Saito et al 2007). Enhanced nitriWcation rates after wildWres may potentially result in 15 N enrichment, especially in the upper soil layers (Boeckx et al 2005). In boreal forests, wildWres can lead to pulses of NO 3 losses, and increased NO 3 concentrations in the humus layer can remain for longer time periods (DeLuca et al 2002).…”

Thermal alteration of soil organic matter properties: a systematic study to infer response of Sierra Nevada climosequence soils to forest fires

“…In a wood charring experiment (non-oxygen atmosphere) at 150, 340, and 480 • C, Czimczik et al (2002) observed an enrichment of δ 13 C at 150 • C where there was no C concentration change but a depletion of δ 13 C at 340 and 480 • C, with charring where the C concentration increased over 50 % due to charring. Fires tend to lead to enrichment of 15 N. This is particularly observed in soils immediately in the aftermath of fires (Boeckx et al, 2005;Grogan et al, 2000;Herman and Rundel, 1989;Huber et al, 2013), but there is limited information available on the exact temperature ranges that cause specific levels of 15 N enrichment. In this study, we observed enrichment of 15 N up to 350 • C and depletion after 350 • C for all soils (Fig.…”

Nitrogen-15 signals of leaf-litter-soil continuum as a possible indicator of ecosystem nitrogen saturation by forest succession and N loads

“…The species diversity, biogeochemical cycles, productivity and carbon (C) sequestration of forest ecosystems are largely regulated by nitrogen (N) dynamics via plant uptake, soil N transformation and loss (Perakis and Hedin 2002;Frey et al 2004;Boeckx et al 2005;Luyssaert et al 2008). Chronic atmospheric N deposition can obviously alter N transformation and loss processes, such as mineralization Chen and Högberg 2006), nitrification (Fenn et al 1998;Venterea et al 2004), ammonia volatilization (Huygens et al 2007) and N 2 O emission (Venterea et al 2003;Zhang et al 2008a), as well as organic and inorganic N losses (McDowell et al 2004;Fang et al 2009a, b), and their responses depend on ecosystem N saturation status .…”