Barley responses to combined waterlogging and salinity stress: separating effects of oxygen deprivation and elemental toxicity

Abstract

Salinity and waterlogging are two major factors affecting crop production around the world and often occur together (e.g., salt brought to the surface by rising water tables). While the physiological and molecular mechanisms of plant responses to each of these environmental constraints are studied in detail, the mechanisms underlying plant tolerance to their combined stress are much less understood. In this study, whole-plant physiological responses to individual/combined salinity and waterlogging stresses were studied using two barley varieties grown in either vermiculite (semi-hydroponics) or sandy loam. Two weeks of combined salinity and waterlogging treatment significantly decreased plant biomass, chlorophyll content, maximal quantum efficiency of PSII and water content (WC) in both varieties, while the percentage of chlorotic and necrotic leaves and leaf sap osmolality increased. The adverse effects of the combined stresses were much stronger in the waterlogging-sensitive variety Naso Nijo. Compared with salinity stress alone, the combined stress resulted in a 2-fold increase in leaf Na+, but a 40% decrease in leaf K+ content. Importantly, the effects of the combined stress were more pronounced in sandy loam compared with vermiculite and correlated with changes in the soil redox potential and accumulation of Mn and Fe in the waterlogged soils. It is concluded that hypoxia alone is not a major factor determining differential plant growth under adverse stress conditions, and that elemental toxicities resulting from changes in soil redox potential have a major impact on genotypic differences in plant physiological and agronomical responses. These results are further discussed in the context of plant breeding for waterlogging stress tolerance.

QTL for chlorophyll fluorescence of barley plants grown at low oxygen concentration in hydroponics to simulate waterlogging

“…A possible explanation could be that these QTL affect other genes responsible for changes in the metabolic processes causing toxicity (Zeng et al 2013), ethylene production initiating aerenchyma formation or some of the other processes not directly related to energy production (Agarwal and Grover 2006;Colmer and Voesenek 2009;Ahmed et al 2013). However, the meta-analysis did confirm the presence of QTLs on 4H and 7H.…”

Some physiological responses of wheat and bean to soil salinity at low matric suctions

“…The decline in root extension is a consequence of a decrease in the uptake and balance of nutrients. Zeng et al (2015) showed that, compared to salinity stress, the combined stress of aeration and salinity doubles the Na + concentration and decreases K + c in barley leaves by 40%. These effects are influenced by soil redox potential and accumulation of Mn and Fe under waterlogged conditions.…”

Physiological responses of selected African sorghum landraces to progressive water stress and re-watering

“…Individual leaves were placed in (5 x 8 cm) brown paper bags and oven-dried at 70 o C for 48 h. The dry weight (DW) was then recorded and LWC was calculated on a fresh weight basis using the following equation (Kirkman, 2005;Zeng et al, 2013):…”

“…During water stress at the seedling stage, the percentage leaf water content (LWC) of the third leaf was calculated (Kirkman, 2005;Zeng et al, 2013). blade was excised for quantification of percentage LWC; and (e) proline was quantified following the protocol described by Bates et al (1973).…”