EFFECTS OF THE ECTO-MYCORRHIZAL AND VA-MYCORRHIZAL FUNGI HYDNAGIUM-CARNEUM AND GLOMUS-CLARUM ON THE DELTA-N-15 AND DELTA-C-13 VALUES OF EUCALYPTUS-GLOBULUS AND RICINUS-COMMUNIS
Ll. Handley et al., EFFECTS OF THE ECTO-MYCORRHIZAL AND VA-MYCORRHIZAL FUNGI HYDNAGIUM-CARNEUM AND GLOMUS-CLARUM ON THE DELTA-N-15 AND DELTA-C-13 VALUES OF EUCALYPTUS-GLOBULUS AND RICINUS-COMMUNIS, Plant, cell and environment, 16(4), 1993, pp. 375-382
Glasshouse experiments with Ricinus communis showed that the presence/
absence of a VA mycorrhizal fungus (Glomus clarum) changed the deltaN-
15 value of the host by as much as 2 parts per thousand when the plant
s were given urea (released as NH4+) as their only N-source. This smal
l change in deltaN-15 would create a large error in calculating source
s 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 sour
ce. The correct N-source value for VAM-infected NH4- using plants may
be the deltaN-15 of soil NH4+ + 2 parts per thousand. Treatment effect
s were also found in the distribution of deltaN-15 and % N among plant
organs. Plants with VAM had a lower N:P atom ratio and were larger in
total biomass. Carbon discrimination (deltaC-13) Was greater in the V
A-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 a
ny of the variables measured for this host-fungus pair when the sole N
-sources were inorganic (NO3- and NH4+ released from urea). Ectomycorr
hizal fungi are diverse in their physiological behaviour, and these da
ta should not be taken as being representative of the whole group. Mor
e work is required with other types of mycorrhiza and more complex sou
rces of N. Future work will include a water balance to partition the e
ffects of water use and nutrient supply in determining deltaC-13. An o
n-line combustion-ANCA-MS method is described for fully automated meas
urement of natural abundance levels of N-15/14 and C-13/12 for plant m
aterials. This method achieves the required precision while dramatical
ly increasing sample throughout.