Sympatric pairings of dryland grass populations, mycorrhizal fungi and associated soil biota enhance mutualism and ameliorate drought stress

Abstract

1. There is evidence that the distribution of ecotypes of plants and their symbiotic arbuscular mycorrhizal (AM) fungi and other associated soil biota may be structured by the availability of essential soil nutrients; and that locally adapted partnerships most successfully acquire limiting nutrients. This study tests the hypotheses that plant genotypes are adapted to the water availability of their local environment, and this adaptation involves associations with local soil biota, including AM fungi. 2. We grew semi-arid Bouteloua gracilis ecotypes from relatively wet and dry sites, with either sympatric or allopatric soil inoculum under moderate and extreme soil drying treatments to examine (a) how varying degrees of water limitation influence grass responses to soil biota and (b) the relationship between AM fungal structures and the responses. 3. Under extreme soil drying, the dry site ecotype tended to perform better than the wet site ecotype. Both ecotypes performed best in either drying treatment when inoculated with their sympatric soil biota. Sympatric pairings produced more AM fungal hyphae, arbuscules and dark septate fungi. Extreme soil drying tended to accentuate these apparent benefits of sympatry to both plants and fungal symbionts, relative to the moderate drying treatment. 4. Our findings support the hypothesis that AM symbioses help Bouteloua gracilis ecotypes adapt to local water availability. This conclusion is based on the observations that as water became increasingly limited, sympatric partnerships produced more AM fungal hyphae and arbuscules and fewer vesicles. The abundances of hyphae and arbuscules were positively correlated with plant growth, suggesting that in sympatric pairs of plants and AM fungi, allocation to fungal structures is optimized to maximize benefits and minimize the costs of the symbioses. This provides strong evidence that co-adaptation among plants and their associated AM fungi can ameliorate drought stress. 5. Synthesis. Our study documents the role of locally adapted soil borne plant symbionts in ameliorating water stress. We found a relationship between AM fungal structures in roots and plant performance. Generally, plants and fungi from the same site resulted in more positive effects on plant growth.

Functional diversity and identity of plant genotypes regulate rhizodeposition and soil microbial activity

“…Though the underlying mechanisms are still poorly understood, the weakening or reversal of trait relationships, including the relationship between specific leaf area and resource acquisition strategy, has been reported when examining intraspecific as opposed to interspecific variation (Grady et al ., 2013; Anderegg et al ., 2018). The observed pattern may also relate to the observation that plants occupying harsh environments, and usually characterised by low specific leaf area (Pierce et al ., 2013), form strong mutualisms with soil microorganisms (Rodriguez et al ., 2008; Johnson et al ., 2010; Hempel et al ., 2013; Remke et al ., 2021). This is particularly evident for endophytic symbioses, but our findings suggest that genotypes with more conservative growth strategies may also invest relatively more carbon in stimulating free‐living microorganisms via root exudation.…”

Disentangling nematode and arbuscular mycorrhizal fungal community effect on the growth of range-expanding Centaurea stoebe in original and new range soil

“…Water availability has shown to influence the functioning of soil communities (Hawkes et al 2017) and the composition of fungal and bacterial communities in soil with soil communities adapted to contemporary water availability being more beneficial for plant growth (Lau and Lennon 2012;Remke et al 2020). Thus enhanced growth of range expanding C. stoebe with soil communities from the original range during drought suggests that these soil communities are better adapted to drought conditions than soil communities in the new range.…”

The joint effect of host plant genetic diversity and arbuscular mycorrhizal fungal communities on restoration success

“…Plant tissue phosphorus content was positively correlated with AM fungal extra‐radical hyphal density and proportion of root length colonized by arbuscules, suggesting the importance of AM fungi driving such local adaptation (Johnson, Wilson, et al., 2010). Similarly, a recent study has demonstrated that partnerships between Bouteloua gracilis and AM fungi that shared adaptation to water availability resulted in the highest growth of host plants (Remke et al., 2020). The importance of local adaptation is further confirmed by a meta‐analysis, demonstrating that plants had greatest increase in biomass in response to AM fungi when both of the symbiotic partners, as well as the soil, originated from the same location (Rúa et al., 2016).…”