Different soil moisture conditions change the outcome of the ectomycorrhizal symbiosis between Rhizopogon species and Pinus muricata

Abstract

The outcome of species interactions often depends on the environmental conditions under which they occur. In this study, we tested how different soil moisture conditions affected the outcome of the ectomycorrhizal symbiosis between three Rhizopogon species and Pinus muricata in a factorial growth chamber experiment. We found that when grown in 7% soil moisture conditions, ectomycorrhizal plants had similar biomass, photosynthesis, conductance, and total leaf nitrogen as non-mycorrhizal plants. However, when grown at 13% soil moisture, ectomycorrhizal plants had significantly greater shoot biomass, higher photosynthetic and conductance rates, and higher total leaf nitrogen than non-mycorrhizal plants. The differences in plant response by mycorrhizal status in the two soil moisture treatments corresponded with evidence of water limitation experienced by the fungi, which had much lower colonization at 7% compared to 13% soil moisture. Our results suggest that the outcome of the ectomycorrhizal symbiosis can be context-dependent and that fluctuating environmental conditions may strongly affect the way plants and fungi interact.

Abiotic conditions affect floral antagonists and mutualists of Impatiens capensis (Balsaminaceae)

“…In addition, varying abiotic conditions may alter the outcome of interactions. For example, mycorrhizal associations with plant roots can be benefi cial, neutral, or antagonistic depending on nitrogen availability and soil moisture ( Heath and Tiffi n, 2007 ;Kennedy and Peay, 2007 ). Because the abiotic environment can alter conditionality in interactions ( Bronstein, 1994 ;Gomulkiewicz et al, 2003 ;Kersch and Fonseca, 2005 ), integrating the effects of abiotic conditions on biotic interactions may provide a mechanistic underpinning to observations of variation in selective pressures across local, regional, and landscape scales.…”

Testing the ecological stability of ectomycorrhizal symbiosis: effects of heat, ash and mycorrhizal colonization on Pinus muricata seedling performance

“…The ability of symbionts to choose partners and set the amount of trade is thought to be one of the main stabilizing mechanisms in cooperative interactions (Herre et al 1999;Sachs et al 2004). Kennedy and Peay (2007) drew a similar conclusion on regulation of mutualistic exchange from the observation that mycorrhizal benefits decreased under simulated drought conditions, but fungal colonization never resulted in reduced host-fitness. In the reported instances of mycorrhizal parasitism in agricultural settings it appears that certain arbuscular mycorrhizal fungi are able to override their partner's ability to regulate mutualistic exchange (Johnson 1993;Johnson et al 1997).…”

“…Percent root weight colonization was calculated as (weight of EM roots) / (weight of EM roots + non-EM roots) × 100. While this colonization metric is calculated differently than the % root tip or % root length metrics used in many studies, expressing colonization in terms of root weight is biologically meaningful, repeatable, and may be less sensitive to differences in root tip morphology between species of EM fungi (Kennedy et al 2006;Kennedy and Peay 2007;Kennedy et al 2009). …”

“…Multiple studies have documented changes in the symbiosis between environments, fungal species, and even genotypes of the same species (Beckford et al 1985;Burgess et al 1994;Kennedy and Peay 2007;Nara 2006;Piculell et al 2008;Zhou and Sharik 1997). However, true exploitation, i.e.…”

“…Past work in this system (e.g. Kennedy and Peay 2007) has indicated some degree of plant control over ectomycorrhizal colonization levels. For this reason we hypothesized that ectomycorrhizal symbiosis would remain mutualistic via the plants' ability to control fungal colonization levels to optimize growth based on changes in resource acquisition costs.…”