15N natural abundances and N use by tundra plants

Abstract

Plant species collected from tundra ecosystems located along a north-south transect from central Alaska to the north coast of Alaska showed large and consistent differences in N natural abundances. Foliar δN values varied by about 10% among species within each of two moist tussock tundra sites. Differences in N contents among species or plant groups were consistent across moist tussock tundra at several other sites and across five other tundra types at a single site. Ericaceous species had the lowest δN values, ranging between about -8 to -6‰. Foliar N contents increased progressively in birch, willows and sedges to maximum δN values of about +2‰ in sedges. Soil N contents in tundra ecosystems at our two most intensively studied sites increased with depth and δN values were usually higher for soils than for plants. Isotopic fractionations during soil N transformations and possibly during plant N uptake could lead to observed differences in N contents among plant species and between plants and soils. Patterns of variation inN content among species indicate that tundra plants acquire nitrogen in extremely nutrient-poor environments by competitive partitioning of the overall N pool. Differences in plant N sources, rooting depth, mycorrhizal associations, forms of N taken up, and other factors controlling plant N uptake are possible causes of variations in δN values of tundra plant species.

Ice-age megafauna in Arctic Alaska: extinction, invasion, survival

“…The spread of organic soils was accompanied by the replacement of grass-and forb-dominated vegetation by moisture-loving sedges, mosses, lichens, and shrubs, all of which have lower d 15 N values (Nadelhoffer et al, 1996;Fox-Dobbs et al, 2008). A decline in d 15 N is also consistent with the spread of colder, more stable soils with shallower rooting depths (Nadelhoffer et al, 1996), all of which are features of a paludified landscape. Additional evidence for the effects of regional paludification may come from the d 15 N record in horse bones, the taxon with the most dated bones (Fig.…”

“…The isotopic values of a plant are controlled by complex interactions between its physiology, soil moisture, temperature, soil fertility, and atmospheric CO 2 levels (Heaton, 1999;Stevens and Hedges, 2004;Koch et al, 2009). Although trophic fractionation means that plant and bone isotope values do not match exactly, measurements of modern plants from northern Alaska indicate that graminoids tend to be enriched in 15 N and depleted in 13 C compared to forbs, lichens, and shrubs (Nadelhoffer et al, 1996;Ben-David et al, 2001;Wooller et al, 2007;Fox-Dobbs et al, 2008). When considered together, the isotopic values of modern plants and the bone-isotope values are consistent with the interpretation that on the ice-age landscape muskoxen and caribou were eating plant taxa that today are associated with moist acidic tundra.…”

“…Paludification would have closed the open nitrogen cycle that formerly operated in warmer, better drained mineral soils and intensified the recycling of N from organic compounds and therefore its fractionation (Stevens and Hedges, 2004). The spread of organic soils was accompanied by the replacement of grass-and forb-dominated vegetation by moisture-loving sedges, mosses, lichens, and shrubs, all of which have lower d 15 N values (Nadelhoffer et al, 1996;Fox-Dobbs et al, 2008). A decline in d 15 N is also consistent with the spread of colder, more stable soils with shallower rooting depths (Nadelhoffer et al, 1996), all of which are features of a paludified landscape.…”

Stable nitrogen isotope patterns of trees and soils altered by long-term nitrogen and phosphorus addition to a lowland tropical rainforest

“…In particular, d 15 N values from tropical trees growing on soils relatively high in P may be less isotopically sensitive to N deposition than trees growing on relatively P poor soils. Similarly, 2 years of P addition to an arctic ecosystem increased foliar d 15 N values significantly in two common plant species, but not in two rare species; a pattern attributed to increased N mineralization following P addition (Giblin et al 1991, Nadelhoffer et al 1996.…”

Abiotic, Biotic, and Evolutionary Control of the Distribution of C and N Isotopes in Food Webs

“…This permits us to (1) outline the impact of abiotic and biotic forces on plant nutrient pools and, hence, nutrient sources for higher trophic levels; (2) assess whether patterns generated at different evolutionary timescales (intra-and interspecific) bear similarities with respect to their environmental determinants; and (3) test the hypothesis that groups at the base of the trophic chain display greater evolutionary dependence on their isotopic ratios than their consumers. The isotopic composition of producers is in fact expected to be strongly dependent on species physiology (influenced by phylogenetic origin), abiotic control, and the impact of consumers (Nadelhoffer et al 1996;Frank et al 2000), while that of consumers should largely match or magnify changes in their resources (the stoi- …”