Genetic Variation in Photosynthetic Maintenance and Post-Chill Recovery for Early Season Maize Plantings
Earlier maize planting could extend the growing season and improve synchronization of crop nitrogen demand with biogenically available soil nitrogen in spring, but seedling photosynthesis and development are strongly constrained by chilling. Eleven genetically diverse maize inbred lines were evaluated under a spring-like controlled environment regime containing five days of chilling stress followed by a recovery period, and across four early-spring field environments. Gas exchange, chlorophyll fluorescence, chlorophyll status, immature-leaf growth, vegetative stage, biomass, and visible cold injury were quantified to characterize physiological and developmental responses during chilling and recovery. Chilling substantially reduced net CO2 assimilation and rapidly decreased {Phi}PSII, while stomatal conductance responded slower. Genotypic differences in assimilation and {Phi}PSII were compressed during prolonged chilling but reemerged during recovery. Chilling also slowed immature-leaf elongation and largely arrested vegetative developmental progression; both resumed rapidly after warming, and advanced recovery stage development was associated with a greater fraction of mature leaf biomass. Assimilation and {Phi}PSII were most tightly associated during recovery and remained positively associated across field environments, although the strength of this relationship depended strongly on environment. Field expression of genotype effects was highly environment dependent, but broad-sense heritability was moderate to high for a variety of measured photosynthetic and physiological traits. Compared with the benchmark chilling-tolerant C4 grass Miscanthus, the maize panel exhibited similar photosynthetic performance, underscoring the accession dependence of this comparative benchmark. Taken together, these results identify photosynthetic maintenance and recovery as separable components of early-season cold performance and characterize physiologically informative and heritable traits associated with chilling stress resilience.