Abstract
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 m(-2)). 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 = -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.
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Claims 8
Claim · model-written summary
Low AMF reduced shoot biomass without competition.
- Taxon
- Medicago sativa L.
Medicago sativae0e1t0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Shoot biomass in the absence of competition was lower under low AMF treatment”
t0“Medicago sativa L.”
e1“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 = -1·480) than for the low AMF treatment (-1·133)”
Claim · model-written summary
The self-thinning biomass-density slope was steeper with high AMF than low AMF.
- Taxon
- Medicago sativa L.Medicago sativae0t0
- Treatment
- high AMF treatmente0
- Interactor
- AMFe0symbiont
- Outcome
- slope of the log (mean shoot biomass) vs. log density relationshipe0
- Direction
- steepere0
- Value
- -1·480e0
- Qualifier
- -1·133e0
- Comparator
- low AMF treatmente0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“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 = -1·480) than for the low AMF treatment (-1·133)”
t0“Medicago sativa L.”
Claim · model-written summary
AMF level did not significantly affect canopy radius-biomass exponents.
- Taxon
- Medicago sativa L.Medicago sativae0e1t0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The canopy radius-biomass allometric exponents were not significantly affected by AMF level”
t0“Medicago sativa L.”
e1“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 = -1·480) than for the low AMF treatment (-1·133)”
Claim · model-written summary
The root-shoot allometric exponent was higher under low AMF.
- Taxon
- Medicago sativa L.Medicago sativae0e1t0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the root-shoot allometric exponent was higher in the low AMF treatment”
t0“Medicago sativa L.”
e1“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 = -1·480) than for the low AMF treatment (-1·133)”
Claim · model-written summary
The above-ground allometric model predicted the biomass-density exponent under high AMF.
- Taxon
- Medicago sativa L.Medicago sativae0e1t0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“With a high level of AMF, the biomass-density exponent can be predicted from the above-ground allometric model of self-thinning”
t0“Medicago sativa L.”
e1“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 = -1·480) than for the low AMF treatment (-1·133)”
Claim · model-written summary
The above-ground allometric model did not predict the biomass-density exponent when fungicide reduced AMF.
- Taxon
- Medicago sativa L.Medicago sativae0e1t0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“while this was not the case when AMF were reduced by fungicide”
t0“Medicago sativa L.”
e1“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 = -1·480) than for the low AMF treatment (-1·133)”
Claim · model-written summary
The authors concluded that AMF changed below-ground relative to above-ground interactions and root-shoot allocation.
- Taxon
- Medicago sativa L.Medicago sativae0e1t0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“AMF affected the importance of below-ground relative to above-ground interactions and changed root vs. shoot allocation”
t0“Medicago sativa L.”
e1“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 = -1·480) than for the low AMF treatment (-1·133)”
Claim · model-written summary
Changed biomass allocation altered the self-thinning trajectory.
- Taxon
- Medicago sativa L.Medicago sativae0e1t0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“This changed allometric allocation of biomass and altered the self-thinning trajectory”
t0“Medicago sativa L.”
e1“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 = -1·480) than for the low AMF treatment (-1·133)”
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