Variation in nitrogen-15 natural abundance and nitrogen uptake traits among co-occurring alpine species: do species partition by nitrogen form?

Abstract

In the N-limited alpine tundra, plants may utilize a diversity of N sources (organic and inorganic N) in order to meet their nutritional requirements. To characterize species-level differences in traits related to N acquisition, we analyzed foliar δN, nitrate reductase activity (NRA) and mycorrhizal infection in co-occurring alpine species during the first half of the growing season and compared these traits to patterns of N uptake using a N (N-NH, N-NO) or C,N ([1]-C-N-glycine) tracer addition in the greenhouse. C enrichment in belowground tissue indicated that all species were capable of taking up labeled glycine, although only one species showed uptake of glycine potentially exceeding that of inorganic N. Species showing the most depleted foliar δN and elevated NRA in the field also tended to show relatively high rates of NO uptake in the greenhouse. Likewise, species showing the most enriched foliar δN also showed high rates of NH uptake. The ratio of NO:NH uptake rates and growth rate explained 64% and 72% of the variance in foliar δN, respectively, suggesting that species differ in the ability to take up NO and NH in the field and that such differences may enable species to partition soil N on the basis of N form.

Foliar and soil 15N natural abundances provide field evidence on nitrogen dynamics in temperate and boreal forest ecosystems

“…(Fig. 3a, b) (Miller and Bowman 2002;Falkengren-Grerup et al 2004;Kahmen et al 2008). The observed pattern of foliar δ 15 N in our study can be explained by the increasing NO 3 − : NH 4 + uptake ratio (Table 3 and Fig.…”

Stable Nitrogen Isotopic Changes in Winter Wheat (<i>Triticum aestivum</i> L.) Induced by its Growth Temperature

“…15 N values of leaves and roots were lower than soil δ 15 N, which is testified in other studies (Evans and Ehleringer, 1993;Garten, 1993;Högberg and Johannisson, 1993;Michelsen et al, 1998;Miller and Bowman, 2002;Koba et al, 2003).…”

Nitrogen uptake strategies of edaphically specialized Bornean tree species

“…We used 15 N recovery in shoots to examine species' capacities for NH þ 4 and NO À 3 uptake, as in previous studies (e.g., McKane et al 2002;Miller and Bowman 2002). Only leaves harvested at 48 h (e.g., Andersen and Turner 2013) were used in our analysis due to the low 15 N recovery in leaves harvested at 24 h. Although microbial transformation of the added N forms could have occurred within the 48 h incubation period, we interpret our 15 N uptake results as an estimate of the capacity of plants to take up N from NH þ 4 to NO À 3 sources, and not as an indication of preference for those forms, per se.…”

“…In alpine tundra, some plant species have been found to absorb all N forms supplied, but alter uptake of them depending on the intensity of competition for N and the identity of neighboring plants (Miller and Bowman 2002;Miller et al 2007). Similarly, based on 15 N natural abundance in vegetation and soils, tree species in Hawaiian tropical forests along a rainfall gradient did not appear to specialize on different soil N pools, but rather responded to changes in the availability of soil N to exploit the most abundant N-form (Houlton et al 2007).…”