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.