Seed size is closely related to phosphorus use efficiency and photosynthetic phosphorus use efficiency in common bean

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Abstract
Seed size might have a significant impact on the growth and phosphorus (P) efficiency of the common bean by 1) enhancing seed reserves so the young plant has higher growth rate and hence higher biomass produced by per unit P absorbed and/or 2) increasing cell size in leaf tissue so the plant has greater leaf expansion and thereby permitting higher photosynthesis rate per unit P. To verify this hypothesis, parameters related to plant growth, photosynthesis, and P use efficiency were evaluated for common bean genotypes from different geographic origins with contrasting seed size and tolerance of P deficiency. It was found that under hydroponic conditions, shoots responded more sensitively to P deficiency than roots, and inhibition of shoot growth by P limitation was mainly reflected by reduction in leaf area. Large‐seeded Andean genotypes were better than small‐seeded Mesoamerican genotypes in leaf growth and expansion hence the former had better shoot growth and higher P efficiency Ratio (PER), which was defined as the amount of biomass produced per unit P in the tissue. There was significant genotypic variation in CO2 exchange rate (CER) and photosynthetic phosphorus use efficiency (PPUE), defined as CER per unit P in the leaf tissue. The large‐seeded Andean genotypes in general had lower CER but higher PPUE, particularly in the primary leaves. We conclude that 1) seed size is closely related to P efficiency in common bean mainly by affecting leaf growth and expansion and 2) although CO2 exchange rate is not positively correlated with seed size, large‐seeded genotypes appear to have higher photosynthetic P use efficiency at early growth stage.