Unravelingthe photosynthetic mechanisms of soybean cultivars under phosphorus deficiency

Abstract

Crop growth and development depend on photosynthesis, but the photosynthetic process largely depends on phosphorus (P). However, most soils have low P fertility, which can compromise crop yields. The use of phosphate fertilizer is an alternative that provides Pi to plants, however it is a finite and expensive resource. Therefore, understanding the mechanisms that different genotypes present under P deficiency and how the interaction of other abiotic factors influence the mechanisms of efficiency in the use of P are essential for the selection of sustainable genotypes. We carried out two different experiments, the objective of the first being to elucidate how P deficiency affects the recovery from recurrent water stress in soybean cultivars with different levels of drought tolerance and the second aimed to understand the efficiency and response mechanism in use of P used by different soybean genotypes, relating photosynthetic and growth parameters. The results of the first experiment indicated that phosphorus deficiency delayed stomatal closure, prolonging photosynthetic decline under drought stress among cultivars. Interestingly, phosphorus-deficient plants showed faster recovery in photosynthetic rates and stomatal conductance compared to those adequately supplied with phosphorus. The sensitive cultivar demonstrated greater photosynthetic recovery after going through two cycles of water deficit, attributed to the improvement in mesophyll conductance. In contrast, the tolerant cultivar showed consistent photosynthetic responses regardless of phosphorus availability. These findings highlight the adaptive plasticity of soybeans to water deficit, modulated by genetic factors and influenced by phosphorus availability, highlighting the complex interaction between nutrient status and drought tolerance on crop productivity. The results of the second experiment demonstrated that cultivars with high photosynthetic responsiveness to P are also responsive in grain production. Responsive cultivars showed an increase in the carboxylation rate, RuBP regeneration and use of P-trioses in high phosphorus. The photosynthetic performance of the efficient and non-P-responsive cultivar was supported by the increased allocation of metabolic P and decreased lipid P, in addition to the more robust photosynthetic apparatus from the initial stages of development. The biggest difference between efficient and inefficient cultivars, regardless of response capacity, is the ability to dissipate excess energy in a regulated manner. Regardless of the P use efficiency mechanism, P deficiency affected the production of different genotypes.