Effects of Inoculum Additions in the Presence of a Preestablished Arbuscular Mycorrhizal Fungal Community

Abstract

cCommunities of arbuscular mycorrhizal fungi (AMF) are crucial for promoting plant productivity in most terrestrial systems, including anthropogenically managed ecosystems. Application of AMF inocula has therefore become a widespread practice. It is, however, pertinent to understand the mechanisms that govern AMF community composition and their performance in order to design successful manipulations. Here we assess whether the composition and plant growth-promotional effects of a synthetic AMF community can be altered by inoculum additions of the isolates forming the community. This was determined by following the effects of three AMF isolates, each inoculated in two propagule densities into a preestablished AMF community. Fungal abundance in roots and plant growth were evaluated in three sequential harvests. We found a transient positive response in AMF abundance to the intraspecific inoculation only in the competitively weakest isolate. The other two isolates responded negatively to intra-and interspecific inoculations, and in some cases plant growth was also reduced. Our results suggest that increasing the AMF density may lead to increased competition among fungi and a trade-off with their ability to promote plant productivity. This is a key ecological aspect to consider when introducing AMF into soils. It is an ongoing objective in ecology to understand the mechanisms that shape the community structure and productivity of ecosystems, in order to ultimately maintain the services ecosystems provide. Thereby, soil communities belowground are known to be a key element in maintaining the productivity and diversity of communities aboveground (1, 2). Arbuscular mycorrhizal fungi (AMF) are a guild of soil organisms that are dependent upon plant hosts to acquire carbon and that provide in exchange many services for the plants, such as improving their nutrient acquisition, productivity, coexistence, and pathogen protection (3). Considering the large potential of these symbiotic fungi to contribute to the ecological sustainability of managed ecosystems, efforts are being made to improve the resource use efficiency of arable and degraded soils by introducing AMF inocula. However, there are many questions remaining regarding the conditions under which introduction of AMF into soils is successful at improving the plant growth-promotional effects of AMF communities (4). The current challenge for improving soil productivity by AMF community manipulations is in understanding the ecological constraints, such as competitive and complementary interactions with AMF genotypes present in the soil (5).AMF differ in their life traits and nutrient-foraging strategies (6, 7). These differences can be the basis for the complementary effect of greater AMF richness (8) or may favor the more-beneficial partners under the given conditions (9, 10). On the other hand, AMF colonizing a root system compete for space and the plant-derived carbohydrates (11), with potential trade-offs with the beneficial effects of the symbiosis with the host pl...

Arbuscular mycorrhiza differentially affects synthesis of essential oils in coriander and dill

“…It can be speculated that possible competition for root space and host resources between the presumed multiple native AMF could result in less promotional effects on the synthesis of some compounds. Decreased benefits of the symbiosis due to competition between AMF have been previously documented (Bennet and Bever 2009;Janoušková et al 2013). The present results clearly show that aromatic plant species differ in their response to a same AMF treatment and that this response further differs depending on the abundance and variety of AMF colonizing the roots.…”

Inoculation of drought-stressed strawberry with a mixed inoculum of two arbuscular mycorrhizal fungi: effects on population dynamics of fungal species in roots and consequential plant tolerance to water deficiency

“…disease tolerance). When introducing AMF into field-grown strawberry production, it will be necessary to further understand how an introduced new species or isolate affects native populations (Janoušková et al 2013), although with the significant trend of strawberry production moving to soil-less substrates (Takeda 1999), the use of AMF inoculation may give greater benefits.…”

Contrasting effects of cover crops on ‘hot spot’ arbuscular mycorrhizal fungal communities in organic tomato

“…This may have great ecological consequences, leading to introduction of invasive strains that are deleterious to native AMF biodiversity (Janoušková et al 2013;Schwartz et al 2006). Knowledge of how native AMF communities in organic systems are affected by common agronomic practices including cover crop and crop management is a crucial step towards effective utilization of AMF in sustainable crop production.…”