Abstract
Recently, several reports have suggested that the growth and grain yield of wheat are significantly influenced by high atmospheric carbon dioxide concentration (CO2) because of it photosynthesis enhancing effects. Moreover, it has been proposed that plants with large carbon sink size will benefit more from CO2 enrichment than those with small carbon sink size. However, this hypothesis is yet to be test in winter wheat plant. Therefore, the aim of this study was to examine the effect of elevated CO2 (eCO2) conditions on the quantum efficiency of photosystem II (PSII) photochemistry in large ear-type (cv. Shanhan 8675; greater ear C sink strength) and small multiple ear-type (cv. Early premium; greater vegetative C source strength) winter wheat varieties. The experiment was conducted in a free air CO2 enrichment (FACE) facility, and three de-excitation pathways of the primary reaction of PSII of flag leaf at the anthesis stage were evaluated under two CO2 concentrations (ambient [CO2], ∼415 μmol⋅mol–1, elevated [CO2], ∼550 μmol⋅mol–1) using a non-destructive technique of modulated chlorophyll fluorescence. Additionally, the grain yield of the two varieties was determined at maturity. Although elevated CO2 increased the quantum efficiency of PSII photochemistry (ΦPSII) of Shanhan 8675 (SH8675) flag leaves at the anthesis stage, the grain number per ear and 1,000-kernel weight were not significantly affected. In contrast, the ΦPSII of early premium (ZYM) flag leaves was significantly lower than that of SH8675 flag leaves at the anthesis stage, which was caused by an increase in the regulatory non-photochemical energy dissipation quantum (ΦNPQ) of PSII, suggesting that light energy absorbed by PSII in ZYM flag leaf was largely dissipated as thermal energy. The findings of our study showed that although SH8675 flag leaves exhibited higher C sink strength and quantum efficiency of PSII photochemistry at the anthesis stage, these factors alone do not ensure improved grain yield under eCO2 conditions.
Highlights
According to the IPCC (The Intergovernmental Panel on Climate Change) report, atmospheric CO2 concentration has been on an increase since the industrial revolution and is predicted to increase to 550 μmol·mol−1 in 2,050 and 1,020 μmol·mol−1 (RCP8.5) by the end of the century (Stocker et al, 2013; Dier et al, 2019)
The qN of ZYM was significantly higher (p < 0.05) than that of Shanhan 8675 (SH8675) (Figures 3B,C), indicating that elevated CO2 (eCO2) significantly increased the thermal dissipation potential of ZYM compared with that of SH8675
We examined the effect of elevated CO2 on the primary reaction of photosystem II (PSII) and carbon allocation in two winter wheat varieties with different ear C sink strengths
Summary
According to the IPCC (The Intergovernmental Panel on Climate Change) report, atmospheric CO2 concentration has been on an increase since the industrial revolution and is predicted to increase to 550 μmol·mol−1 in 2,050 and 1,020 μmol·mol−1 (RCP8.5) by the end of the century (Stocker et al, 2013; Dier et al, 2019). Atmospheric CO2 is an essential environmental factor necessary for photosynthesis, and it is commonly believed that photosynthesis is stimulated by elevated CO2 (eCO2) in C3 crops, because the ribulose-1,5-bisphosphate carboxylaseoxygenase (RuBisCO) is not substrate-saturated under the current ambient CO2 (aCO2) concentrations (Long et al, 2006; Aranjuelo et al, 2013). Several studies have examined the effects of eCO2 on wheat photosynthesis; most of the studies focus on the dark phase of photosynthesis. The effect of eCO2 on the primary reaction of photosystem II (PSII) in wheat is not fully understood. There is a need to examine the primary reaction of PSII in wheat photosynthetic organs under future eCO2 environments for sustainable wheat production
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