Barley Responses to Drought and Arbuscular Mycorrhizal Colonisation

Drought is a major agricultural challenge threatening production of crops. Barley is the fourth
most important crop globally in terms of production quantity and yield is expected to suffer
drought-related reductions of 17% by 2050 (FAO STAT 2020, Li et al. 2009). Arbuscular
mycorrhizal (AM) fungi have been shown to alleviate drought-stress symptoms in many crop
species but few studies have focussed on barley, particularly with regards to
mycorrhiza-mediated drought alleviation (Jayne & Quigley 2014, Zhang et al. 2019).
This thesis characterises the effects of AM colonisation on the physiological and
metabolomic responses of spring barley (Hordeum vulgare cv. Concerto) to drought under
controlled glasshouse conditions.
In an initial experiment conducted in uncolonised plants, the imposed drought treatment
reduced biomass, leaf relative water content and photosystem II efficiency of barley.
Stomatal conductance (gs) was reduced in droughted plants by the 5th day of drought, and
photosynthetic rate (A) had declined by the 11th day of drought treatment. Metabolomic
fingerprints of polar leaf extracts acquired by DI-ESI-MS showed clear distinction in
response to drought at both the 11th and 18th day of drought, with flavonoids, flavonoid
glycosides and cinnamate derivatives putatively identified as influential in the drought stress
response of this cultivar.
In a separate fully factorial experiment, the only differences attributed to AM colonisation
were a reduced root biomass in AM well-watered plants and a one day delay in the
drought-induced decline of photosystem II efficiency. Metabolomic fingerprints of polar leaf
extracts acquired by LC-ESI-MS suggested that phenylpropanoids and alkaloids were
differentially expressed at tillering and stem elongation stages of development. Despite little
AM-mediated drought alleviation in this cultivar, subtle metabolomic differences between AM
and NM drought response suggested effects of the symbiosis on stress signalling
(jasmonate biosynthesis) and protecting photosynthetic machinery (tetrapyrrole biosynthesis,
electron transport).