Effects of arbuscular-mycorrhizal fungal colonization on management of saline lands

Abstract

The overall aim of the research presented in this thesis was to evaluate the importance of arbuscular-mycorrhizal ( AM ) colonization of plants in management of saline lands. Some aspects of application of AM fungi in revegetation of saline lands are also reported. Effects of AM pre-inoculation on mycorrhiza-responsive and non-responsive plant growth and establishment were evaluated under glasshouse conditions. The advantages of mycorrhizal fungal inoculation in increasing plant salinity tolerance and establishment in saline conditions were related to the responses of host species to AM fungi. Pre-inoculation with Glomus intraradices increased plant growth, nutrient uptake and establishment of mycorrhiza responsive Trifolium subterraneum in saline conditions, but non-mycorrhiza responsive Festuca arundinacea did not get growth benefits from AM in saline conditions. The main mechanism underlying increased plant growth and establishment in saline conditions in mycorrhiza responsive plants was increased plant nutrient uptake, particularly phosphorus ( P ) , at an early growth stage. The improvement could be explained by higher soil volume exploration by hyphae and / or roots, faster nutrient uptake and microbial changes in the soil rhizosphere. AM inoculation and P application effects on salinity tolerance were compared in Trifolium subterraneum. Application of P increased plant growth and salinity tolerance in saline conditions, but AM inoculation increased nutrient uptake and plant salinity tolerance more efficiently than P application. Effects of salinity on AM colonization of chenopods were investigated under glasshouse conditions. Salinity had no effects on AM colonization of Atriplex nummularia, but AM inoculation increased plant growth and nutrient uptake. The growth improvement was attributed to benefits from low AM colonization, and changes in bacterial community composition in the rhizosphere. Roles of AM fungi in influencing P leaching from soil were investigated in experiments with repacked cores under both non-saline and saline conditions. Increased plant size via AM inoculation significantly decreased P leaching in the soil profile under both non-saline and saline conditions in low P soils. Increased root volume and extension external hyphal network were the main effects of AM fungi in increasing plant size under saline and non-saline conditions, which led to scavenging more P and depleting more soil available P, thereby decreasing P losses via leaching. Application of P increased plant size and decreased P leaching, but on the other hand increased soil available P and decreased AM colonization.