Aruscular mycorhizal fungi alter plant allometry and biomass - density relationships

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† Background and Aims Plant biomass–density relationships during self-thinning are determined mainly by allometry.
Both allometry and biomass–density relationship have been shown to vary with abiotic conditions, but the
effects of biotic interactions have not been investigated. Arbuscular mycorrhizal fungi (AMF) can promote plant
growth and affect plant form. Here experiments were carried out to test whether AMF affect plant allometry and
the self-thinning trajectory.
† Methods Two experiments were conducted on Medicago sativa L., a leguminous species known to be highly
dependent on mycorrhiza. Two mycorrhizal levels were obtained by applying benomyl (low AMF) or not (high
AMF). Experiment 1 investigated the effects of AMF on plant growth in the absence of competition. Experiment
2 was a factorial design with two mycorrhizal levels and two plant densities (6000 and 17 500 seeds m22). Shoot
biomass, root biomass and canopy radius were measured 30, 60, 90 and 120 d after sowing. The allometric
relationships among these aspects of size were estimated by standardized major axis regression on log-transformed
data.
† Key Results Shoot biomass in the absence of competition was lower under low AMF treatment. In self-thinning
populations, the slope of the log (mean shoot biomass) vs. log density relationship was significantly steeper for
the high AMF treatment (slope ¼ –1.480) than for the low AMF treatment (–1.133). The canopy radius–
biomass allometric exponents were not significantly affected by AMF level, but the root–shoot allometric exponent
was higher in the low AMF treatment. With a high level of AMF, the biomass–density exponent can be
predicted from the above-ground allometric model of self-thinning, while this was not the case when AMF
were reduced by fungicide.
†Conclusions AMF affected the importance of below-ground relative to above-ground interactions and changed
root vs. shoot allocation. This changed allometric allocation of biomass and altered the self-thinning trajectory.
OriginalsprogEngelsk
TidsskriftAnnals of Botany
Vol/bind107
Udgave nummer3
Sider (fra-til)407-413
Antal sider7
ISSN0305-7364
DOI
StatusUdgivet - 2011

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