Effects of deficit irrigation frequency on plant growth, water use and physiology of Pelargonium x hortorum and tomato (Solanum lycopersicum L. cv. Ailsa Craig)

Boyle, Richard and Dodd, Ian and McAinsh, Martin (2015) Effects of deficit irrigation frequency on plant growth, water use and physiology of Pelargonium x hortorum and tomato (Solanum lycopersicum L. cv. Ailsa Craig). PhD thesis, Lancaster University.

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In horticultural sectors where water is a threatened resource, altering irrigation frequency may present a viable approach to reduce water use, without any negative effect on crop yield and/or quality. However, our understanding of the physiological impact of this approach in containers in a peat based substrate is limited. Pelargonium x hortorum Bullseye plants were grown in glasshouse conditions under well-watered (WW; daily replacement of 100% of evapotranspiration (ET)), frequent (FDI), or infrequent (IDI) deficit irrigation regimes (50% of ET supplied daily or cumulatively every 4 days, respectively) for four weeks. Both FDI and IDI resulted in short-term increases in water use efficiency, and longer term increases in plant quality (canopy compactness) compared to WW plants. From a physiological perspective, stomatal conductance (gs) decreased similarly under both FDI and IDI, but there were treatment differences in leaf water potential (Ψleaf). FDI resulted in a more positive Ψleaf compared to WW plants, whilst Ψleaf under IDI was typically the lowest. Given the lack of a consistent response for Ψleaf, this suggested another mechanism was regulating stomata in P.hortorum. Under a single drying cycle, different components of the xylem sap were measured. Xylem sap pH, Ca2+ and NO3 - did not change, but the plant hormone abscisic acid (ABA) increased in the xylem sap ([X-ABA]leaf) under both irrigation treatments as soil moisture decreased, and showed a strong relationship with gs both in vivo and in a detached leaf transpiration bioassay. However, when plants were irrigated daily at a percentage of daily ET (adapted from FDI), plants showed an attenuated ABA response compared to when irrigation was withheld (adapted from IDI). It was hypothesised that this may have been a root-derived response due to spatial variation in soil moisture distribution, which was investigated in tomato (Solanum lycopersicum). Similar results were found where gs decreased as [X-ABA]leaf increased, but again the ABA response was attenuated. Furthermore, stomata showed similar sensitivity to ABA under both irrigation treatments. However, similar results were found for root tissue ([ABA]root) and xylem ([X-ABA]root) ABA, and modelling revealed that both localised root water uptake and soil moisture content are important for explaining the variation in [X-ABA]root between irrigation treatments. This research furthers the fundamental understanding of ABA signalling and suggests that irrigation frequency can be altered for a short period of the growing cycle to deliver specific grower objectives.

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Thesis (PhD)
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25 Nov 2015 09:08
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15 Mar 2024 00:02