The δ¹⁵N of lettuce and barley are affected by AM status and external concentration of N

Abstract

Mean δ"&N † of whole-plants of lettuce and barley varied by 3 = when given a chemically and isotopically uniform N source. This variation was related to the presence, absence and species of arbuscular mycorrhizal (AM) fungi and to external N concentration. A highly AM-susceptible plant (lettuce) responded to treatments differently than a less susceptible one (barley). The largest change in whole plant δ"&N was related to the experimental combination most likely to be found in field conditions : species of fungus interacting with varying external concentrations of N.The mechanisms underlying observed variations of plant δ"&N are not understood, nor can they be approached directly using δ"&N. However, descriptive data, such as presented here, are important to the development of a mechanistic model, because they suggest relationships for future research, using inter alia "&N-enriched tracers. They also confirm that plant N sources, cannot be identified using plant δ"&N, even when the type of mycorrhizal association (endo vs. ecto) is known.Key words : 15-N natural abundance, arbuscular mycorrhiza, Hordeum, Lactuca. Various authors have reported that arbuscular mycorrhizal (AM) infection increases the number of chemical forms of soil N which are available to the host plant (e.g. Azco! n, El-Atrch & Barea, 1988 ; Azco! n, Go! mez & Tobar, 1992 ;Tobar, Azco! n & Barea, 1994 ;Ibijbijen et al., 1996). A change in the chemical type of N source (i.e. NO $ − -N, NH % + -N, or various forms of organic N) could entail a change of δ"&N for the whole plant if these sources have different δ"&N values and could also incur different internal plant-partitionings of δ"&N (Yoneyama, 1995 ; Handley & Scrimgeour, 1997 and references therein). There are also data (Handley et al., 1993) showing that given only one, inorganic N source, plant δ"&N (whole and internal partitioning) can * To whom correspondence should be addressed. E-mail : lhandl!scri.sari.ac.uk † The naturally occurring ratio of heavy-to-light isotopes of N compared with a universally agreed standard.

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

“…All but two of the species in our study were AM infected, and fractionation associated with mycorrhizal uptake and/or transfer of isotopically depleted N may have contributed to depleted foliar δ 15 N values (Handley et al 1993;Azcón-G-Aguilar et al 1998;Hobbie et al 1999). When ratios of N uptake :N supplied are high, however, fractionation may be minimal (Handley et al 1993;Högberg et al 1999).…”

Community scale 15N isoscapes: tracing the spatial impact of an exotic N2‐fixing invader

“…δ 15 N of bulk leaf material of non‐fixing native plant species can provide such a tracer, integrating the N‐enrichment of the system from an external N‐source after disturbance by an invasive N 2 ‐fixing species. In contrast, soil δ 15 N provides a less appropriate tracer in sandy soils with very low soil nitrogen content, which makes it typically difficult to follow the flow of N from N 2 ‐fixing species through the soil to other plant species (Azcón‐Aguilar et al. 1998; Handley et al.…”

“…d 15 N of bulk leaf material of non-fixing native plant species can provide such a tracer, integrating the N-enrichment of the system from an external N-source after disturbance by an invasive N 2 -fixing species. In contrast, soil d 15 N provides a less appropriate tracer in sandy soils with very low soil nitrogen content, which makes it typically difficult to follow the flow of N from N 2 -fixing species through the soil to other plant species (Azcón-Aguilar et al 1998;Handley et al 1999). In our case, soil N content outside the acacia canopy and in uninvaded areas was always below the detection limit, preventing the use of soil d 15 N. Further, the d 15 N signatures of total soil N are not necessarily representative of the d 15 N of N-compounds available to plants (Högberg 1997;Pardo et al 2007).…”

Biochar increases arbuscular mycorrhizal plant growth enhancement and ameliorates salinity stress

“…capitata). Lettuce, being an important crop, is known to be moderately salt sensitive (Shannon and Grieve, 1998;Kohler et al, 2009) and is a known AM host (Azcón-Aguilar et al, 1998). Approximately 15 days old seedlings from commercial culture were planted in the mesocosms after washing the roots to remove the substrate.…”