Effects of the ecto‐ and VA‐mycorrhizal fungi Hydnagium carneum and Glomus clarum on the δ¹⁵N and δ¹³C values of Eucalyptus globulus and Ricinus communis

Abstract

Glasshouse experiments with Ricinus communis showed that the presence/absence of a VA mycorrhizal fungus (Glomus clarum) changed the δ15N value of the host by as much as 2‰ when the plants were given urea (released as NH4+) as their only N‐source. This small change in Δ15N would create a large error in calculating sources of plant N. In particular, these results throw into doubt any models of N‐cycling which assume that soil N can be treated as a single source. The correct N‐source value for VAM‐infected NH4− ‐using plants may be the δ15N of soil NH4++ 2‰. Treatment effects were also found in the distribution of δ15N and % N among plant organs. Plants with VAM had a lower N:P atom ratio and were larger in total biomass. Carbon discrimination (δ13C) was greater in the VA‐infected plants. The measured effects of VAM infection suggest that for some plants the fungus may be the primary site of N assimilation. A parallel experiment with Eucalyptus globulus and the ectomycorrhizal fungus Hydnangium carneum resulted in no significant differences in any of the variables measured for this host‐fungus pair when the sole N‐sources were inorganic (NO3− and NH4+ released from urea). Ectomycorrhizal fungi are diverse in their physiological behaviour, and these data should not be taken as being representative of the whole group. More work is required with other types of mycorrhiza and more complex sources of N. Future work will include a water balance to partition the effects of water use and nutrient supply in determining δ13C. An on‐line combustion‐ANCA‐MS method is described for fully automated measurement of natural abundance levels of 15/14N and 13/12C for plant materials. This method achieves the required precision while dramatically increasing sample throughout.

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

“…on three soil types; unpublished data) is more appropriate than the extra-tropical 2.0 % value used elsewhere (Houlton et al 2007;Handley et al 1993). This fractionation value accounts for the combined effects of internal plant N allocation and the minor fractionation associated with the transfer of N by arbuscular mycorrhizal fungi (Shearer and Kohl 1986;Handley et al 1993). In seven of the 61 solvable models (11 % of total) species 9 plot solutions included nitrate proportions that exceeded the 100 % upper fractional limit of N use.…”

Correlating molecular markers with physiological expression in Hordeum, a developing approach using stable isotopes

“…Whole shoots only (harvested, oven-dried and milled) were analysed for d^^C and (^^^N using a Europa Scientific 20-20 continuous-fiow isotope ratio mass spectrometer (Handley et aL, 1993). Machine precision for repeated samples is routinely 0-3 %o for 8^^N and • I / tor o \ WnPrP n X = I _X -X I /…”

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

“…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.…”

“…For Ricinus communis, Handley et al, (1993) found a change in the δ"&N value of the whole plant (0n7 =) and in the distribution of δ"&N values between root and shoot when fungal-inoculated and uninoculated plants were compared. In that experiment, the plants were given only one source of inorganic N, and all observed effects should have been attributable to the presence or absence of AM infection.…”