Phosphorus fertilization induces nectar secretion for honeybee visitation and cross-pollination of almond trees

Precise phosphorus (P) application requires a mechanistic understanding of mineral effects on crop biology and physiology. Photosynthate assimilation, metabolism, and transport require phosphorylation, and we postulated that P is critical for the bloom and fruit-set of almond trees that rely on stored carbohydrate reserves. Hence, we studied the growth, physiology and carbohydrate dynamics in 2-year-old almond trees irrigated with P concentrations between 1 mg l(-1) and 20 mg l(-1). Almond trees attained maximal photosynthesis, transpiration, and growth by 6 mg P irrigation. Nevertheless, almond trees continued to extract P in 10 mg P and 15 mg P l(-1) irrigations, which corresponded to larger yields. We attributed the augmented productivity to increased fruit-set (59% between 6 mg P l(-1) and 15 mg P l(-1)), caused by more frequent (29%) honeybee visits. High P improved pollinator visitation by enabling almond trees to utilize more of their starch reserves for nectar secretion (which increased by similar to 140% between 6 mg P l(-1) and 15 mg P l(-1)). This work elucidates the benefits of P fertilization to plant-pollinator mutualism, critical to almond productivity, and reveals novel indices for optimal P application in almond orchards.

Automated summary

This study demonstrates that irrigating 2-year-old almond trees with 6 mg P can maximize photosynthesis, transpiration, and growth. However, irrigation with 10 mg P and 15 mg P l(-1) continues to promote almond tree growth and increase yields.