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

Abstract

Precise phosphorus (P) application requires a mechanistic understanding of mineral effects on crops' biology and physiology. Photosynthates 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 two-year-old almond trees irrigated with P concentrations between 1 and 20 mg L -1. Almond trees attained maximal photosynthesis, transpiration, and growth by 6 mg P L -1 in irrigation. Nevertheless, almond trees continued to extract P in 10 and 15 mg P L -1 irrigations, which corresponded to bigger starch reserves and yields. We attributed the augmented productivity to increased fruit-set (59% between 6 and 15 mg L -1 P), caused by more frequent (29%) honeybee visits. High P improved pollinators' visitation by enabling almond trees to utilize more of their starch reserves for nectar secretion (which increased by ~140% between 6 and 15 mg P L -1). This work illuminates P fertilization's benefits to plant-pollinator mutualism, critical to almond productivity, and reveals novel indices for optimal P application in almond orchards.

Disease management during bloom affects the floral microbiome but not pollination in a mass‐flowering crop

“…Two microliters of treated nectar was applied to each flower, and after 2 days of exposure to pollinators, flowers were carefully removed along with the pedicel and placed in individual 1.5 ml microcentrifuge tubes containing 0.5 ml of water. This treatment volume approximates that of 24 h, per flower nectar production in Nonpareil (Abrol, 1995), as well as falls within the range of production volumes observed for related cultivars (Abrol, 1995; Karunakaran et al, 2021). Flowers were positioned such that the stigma did not touch the tube's surface and the pedicle was in water (Brittain et al, 2013).…”

Bumblebees sense rootstock-mediated nutrition and fertilization regime in tomato

“…The results suggest that pollinator visitation can be used as an indicator for precise P application to maximize yield and P use e ciency in a pollinatordependent species such as almonds. As a consequence, P fertilization affects sink activity and quality attributes of owers affecting fruit set as has been observed in olive (Erel et al 2016) and almond (Karunakaran et al 2021)trees, as it also seems to occurs in tomato.…”

“…4c), which could be due to the metabolic changes provoked, nonvisually observed but detected by the insects. Recently, it has been reported that P fertilization can improve almond yield by promoting pollinator (honeybees) visitation through mobilizing starch reserves and producing extra nectar (Karunakaran et al 2021). The results suggest that pollinator visitation can be used as an indicator for precise P application to maximize yield and P use e ciency in a pollinatordependent species such as almonds.…”