Abstract
Waterlogging occurs frequently at the stem elongation stage of wheat in southern China, decreasing post-anthesis photosynthetic rates and constraining grain filling. This phenomenon, and the mitigating effect of nutrient application, should be investigated as it could lead to improved agronomic guidelines. We exposed pot-cultured wheat plants at the stem elongation stage to waterlogging treatment in combination with two rates of potassium (K) application. Waterlogging treatment resulted in grain yield losses, which we attributed to a reduction in the 1,000-grain weight caused by an early decline in the net photosynthetic rate (Pn) post-anthesis. These decreases were offset by increasing K application. Stomatal conductance (Gs) and the intercellular CO2 concentration (Ci) decreased in the period 7–21 days after anthesis (DAA), and these reductions were exacerbated by waterlogging. However, in the period 21–28 DAA, Gs and Ci increased, while Pn decreased continuously, suggesting that non-stomatal factors constrained photosynthesis. On DAA 21, Pn was reduced by waterlogging, but photochemical efficiency (ΦPSII) remained unchanged, indicating a reduction in the dissipation of energy captured by photosystem II (PSII) through the CO2 assimilation pathway. This reduction in energy dissipation increased the risk of photodamage, as shown by early reductions in ΦPSII in waterlogged plants on DAA 28. However, increased K application promoted root growth and nutrient status under waterlogging, thereby improving photosynthesis post-anthesis. In conclusion, the decrease in Pn caused by waterlogging was attributable to stomatal closure during early senescence; during later senescence, a reduction in CO2 assimilation accounted for the reduced Pn and elevated the risk of photodamage. However, K application mitigated waterlogging-accelerated photosynthetic reductions and reduced yield losses.
Highlights
About 15–20% of global wheat production is affected by waterlogging every year, and this proportion is rising due to frequent extreme weather events during the ongoing global warming process (Trnka et al, 2014; Herzog et al, 2016; Manik et al, 2019)
Grain yields were not significantly different among treatments C, C + K, and W + K (Table 1), indicating that yield reduction resulting from waterlogging was offset by increased K application
We found no significant difference in photosynthetic rate (Pn), stomatal conductance (Gs), quantum efficiency of PSII (PSII), or Fv/maximum chlorophyll fluorescence (Fm) among treatments (Figure 2), indicating that waterlogging has negligible effects on photosynthesis
Summary
About 15–20% of global wheat production is affected by waterlogging every year, and this proportion is rising due to frequent extreme weather events during the ongoing global warming process (Trnka et al, 2014; Herzog et al, 2016; Manik et al, 2019). Waterlogging occurs when pores in the soil fill with water due to heavy rainfall and poor soil drainage. Wheat is a dry land crop that is extremely sensitive to waterlogging stress. The rice–wheat rotation system commonly used in southern China causes soil compaction, which exacerbates waterlogging stress. The key growth periods of wheat from the stem elongation to booting stages occur in this season (Chen et al, 2018). Waterlogging during these developmental stages reduces wheat yield to a greater extent than excessive rainfall in others (Celedonio et al, 2014). Waterlogging between the stem elongation and booting stages is a crucial factor constraining wheat production
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