Leaf Phosphorus Concentration Regulates the Development of Cluster Roots and Exudation of Carboxylates in Macadamia integrifolia.

Xin Zhao,Kemo Jin,Jianbo Shen,Hans Lambers,Yang Lyu

doi:10.3389/fpls.2020.610591

Xin Zhao, Kemo Jin + Show 3 more

Open Access

https://doi.org/10.3389/fpls.2020.610591

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Abstract

Phosphorus (P) deficiency induces cluster-root formation and carboxylate exudation in most Proteaceae. However, how external P supply regulates these root traits in Macadamia integrifolia remains unclear. Macadamia plants were grown hydroponically with seven P levels to characterize biomass allocation, cluster-root development, and exudation of carboxylates and acid phosphatases. Plant biomass increased with increasing P supply, peaking at 5 μM P, was the same at 5–25 μM P, and declined at 50–100 μM P. Leaf P concentration increased with increasing P supply, but shoot biomass was positively correlated with leaf P concentration up to 0.7–0.8 mg P g–1 dry weight (DW), and declined with further increasing leaf P concentration. The number of cluster roots declined with increasing P supply, with a critical value of leaf P concentration at 0.7–0.8 mg P g–1 DW. We found a similar trend for carboxylate release, with a critical value of leaf P concentration at 0.5 mg g–1 DW, but the activity of acid phosphatases showed a gradually-decreasing trend with increasing P supply. Our results suggest that leaf P concentration regulates the development and functioning of cluster roots, with a critical P concentration of 0.5–0.8 mg g–1, above which macadamia growth is inhibited.

Highlights

Phosphorus (P) is an essential nutrient for all life on the earth (Baker et al, 2015; Cong et al, 2020)
The greatest root/shoot ratio was found at 0 μM P, with a one-third decrease in all P treatments compared with no P supply (Figure 1B)
We found that biomass of macadamia increased with increasing P supply, with no further increase from 5 to 25 μM P, and a decrease when P supply surpassed 10 μM (Figure 1A)

Summary

Introduction

Phosphorus (P) is an essential nutrient for all life on the earth (Baker et al, 2015; Cong et al, 2020). Phosphorus in soil has a very low solubility and mobility. The availability of P in soil limits plant growth in many agricultural systems (Marschner, 1995; Cong et al, 2020). Plant strategies to efficiently acquire P from soil play important roles in increasing plant growth and yield (Shen et al, 2011). One of the most important strategies for increasing P acquisition includes root morphological modifications, involving higher root/shoot

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