Substrate age and tree islands influence carbon and nitrogen dynamics across a retrogressive semiarid chronosequence

Abstract

The long‐term dynamics of carbon (C) and nitrogen (N) in semiarid ecosystems remain poorly understood. We measured pools and fluxes of surface soil C and N, as well as other soil properties, under tree canopies and in intercanopy spaces at four sites that form a volcanic substrate age gradient in semiarid piñon‐juniper woodlands of northern Arizona, United States. Clay content and soil water‐holding capacity increased consistently with substrate age, but both soil organic C and N increased only up to the 750,000 year site and then declined at the oldest (3,000,000 year) site. Measures of soil C and N flux displayed a similar pattern to total C and N pools. Pools and fluxes of C and N among the three canopy types became more homogeneous with substrate age up to the 750,000 year site, but disparity between tree and intercanopy microsites widened again at the oldest site. The δ15N of both tree leaves and surface soils became progressively more enriched across the substrate age gradient, consistent with a N cycle increasingly dominated by isotope fractionating losses. Our results point to consistencies in patterns of ecosystem development between semiarid and more humid ecosystems and suggest that pedogenic development may be an important factor controlling the spatial distribution of soil resources in semiarid ecosystems. These data should help both unify and broaden current theory of terrestrial ecosystem development.

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

“…Moreover, foliar d 15 N increased from the pine to the mixed forest and finally to the broadleaf forest when not considering tree species. These results indicate that foliar d 15 N increases with the increase of forest successional stage or forest stand age, which is consistent with those reported by other researchers (Chadwick et al 1999;Selmants and Hart 2008). Therefore, both tree species and forest succession determine the pattern of foliar d 15 N.…”

Understanding ecosystem retrogression

“…(Northup et al 1995), and for the Swedish lake island sequence (Wardle et al 1997). This is also supported by 15 N stable isotope analyses of plant and soil material from both the Swedish island chronosequence (Hyodo and Wardle 2009) and the northern Arizona sequence (Selmants and Hart 2008), which points to more conservative N cycling during retrogression. These shifts to recalcitrant forms of N during retrogression can be independent of or secondary to P limitation.…”

“…As such, they contribute to the development of general principles about the extrinsic factors that regulate community and ecosystem properties and processes, both above and below ground. In particular, these include the roles of soil nutrient limitation, species adaptations and historic disturbance regime (Walker and Syers 1976, Wardle et al 1997, Vitousek 2004, Selmants and Hart 2008. These drivers operate on a range of temporal scales, but it is the cumulative effects of these processes and their influence on very long-term processes such as pedogenesis that distinguishes retrogression from shorter-term successional pathways.…”

Variation in woody plant mortality and dieback from severe drought among soils, plant groups, and species within a northern Arizona ecotone

“…Because soil structure and texture influence infiltration, evaporation, and water-holding capacity (Noy-Meir 1973;Brady 1974;Hillel 2004), soil parent material can influence tree survival (Ogle et al 2000;Moore et al 2004;Gitlin et al 2006;Fensham and Fairfax 2007). Previous reports indicate that the southwestern U.S. woodland soils derived from volcanic cinders have rockier, drier, and more nutrient-poor surface horizons than finer textured sedimentary-derived soils (Mopper et al 1991;Gehring and Whitham 1995;Cobb et al 1997;Swaty et al 1998;Selmants and Hart 2008). Yet, studies of tree growth rate suggest surprisingly high resource availability at sites with cinder-derived soil.…”