Plantago lanceolata L. was grown for 104 d with (M) or
without
(NM) arbuscular mycorrhizal colonization under
conditions of ambient (CAMB=350 μl l−1)
and elevated (CELEV=540 μl l−1)
CO2. Sequential harvests (H) were taken at 41 (H1),
76 (H2) and 104 d (H3) to determine the
time-course of mycorrhizal influence on the response
of the plant to CO2 enrichment. Total yields of M plants
were greater than those of NM from H2 onwards. Plants
in the MELEV treatment were significantly larger than those
in
the MAMB at 104 d. There were significant but much
smaller differences in yield between NMELEV and NMAMB.
The differences in total yield arose through impact of
CELEV on both shoots and roots. Total root length was
greater in MELEV than in MAMB only at H3,
but total length
of mycorrhizal root was greater at H2 and H3.
The percentages of root length colonized and that occupied by
arbuscules and vesicles were greater in MELEV than in
MAMB at the last two harvests, indicating increased
sequestration of carbon in internal fungal structures. Though extraradical
hyphal lengths were greater in MELEV
than in MAMB at H2 and H3, the differences
were not significant. Phosphorus inflow and P content of M plants were
higher than those of NM plants at H2 and H3, and
were higher in MELEV than in MAMB at H3.
anova revealed no
significant interactions between CO2 and mycorrhizal treatment.
The results are discussed in relation to carbon sequestration in mycorrhizal
systems and likely impacts of CO2
enrichment on P. lanceolata grown under field conditions. The
importance of sequential harvesting for realistic
determination of responses to CO2 is stressed.