4.1 Effects of waterlogging on phenology and implications for yield
Waterlogging caused transient reductions in biomass accumulation, but the final impact on grain yield depended on the capacity of the plant to recover after waterlogging and before maturity (Romina, Abeledo, Mantese, & Miralles, 2017). In this study, Franklin showed a better ability to recovery from short-term waterlogging treatment (WL1) compared with other barley genotypes. WL1 caused a 26% yield loss in Franklin compared with around 40% in the other sensitive genotypes. This is because Franklin has a longer growth duration, thus a longer period of shoot biomass recovery. It is worth mentioning that this capacity to recover decreased the later waterlogging was imposed in the phenological cycle. Previous studies have shown that the capacity of barley to recover shoot biomass after waterlogging is related to genotypic and environmental propensity to produce new tillers (de San Celedonio et al., 2016; Robertson, Zhang, Palta, Colmer, & Turner, 2009). Thus, when barley plants are waterlogged late in their lifecycle (e.g. beginning of stem elongation), they are not able to produce new tillers and compensate for the lost shoot biomass caused by waterlogging (Romina et al., 2017).
Waterlogging treatments (WL1-3) delayed maturity (Fig. 6b) across genotypes, with WL3 having the greatest effect on phenology. As well, WL3 had the greatest effect on biomass, suggesting that imposition of waterlogging later in the crop lifecycle has the greatest implications for yield. Such yield penalisation can occur either via reductions in biomass accumulation (WL3) or in yield components if waterlogging is imposed very late in the crop lifecycle (WL4).
In barley, flowering date is primarily a function of temperature, photoperiod and vernalisation (Liu et al., 2020 ). The rate of leaf emergence and final leaf number determine the duration of the period between emergence and anthesis (Alzueta, Abeledo, Mignone, & Miralles, 2012). Here, waterlogging at early growth stages (WL1-3) inhibited leaf appearance rate and reduced final leaf number, delaying maturity date. This is because oxygen deficiency predisposes to denitrification with the consequent rapid loss of nitrate in waterlogged soils. Since nitrate is essential for physiological function, plants’ growth and appearance are quickly affected. In this study, all barley genotype leaves started to become yellow 5 days after being waterlogged, and leaf yellowing area increased with waterlogging durations. The early yellowing of basal leaves during waterlogging coincides with lower photosynthetic rate (Hossain et al., 2011) and water-soluble carbohydrates, and this could be the possible reason that shoot growth was reduced in this study. The phenology of two waterlogging-tolerant genotypes, TAMF169 and Macquarie+, were the least delayed by waterlogging, indicating that the ability to avoid phenological delay may be regarded as a criterion to evaluate waterlogging tolerance. There is little information available in the literature to support this claim. As such, we call for further work on the relationships between waterlogging tolerance and the impact of waterlogging on phenology.