Nitrogen Source Influences the Effect of Plant Growth-Promoting Rhizobacteria (PGPR) on Macadamia integrifolia

Marta Gallart,Chanyarat Paungfoo-Lonhienne,Axayacatl Gonzalez,Stephen J Trueman

doi:10.3390/agronomy11061064

Abstract

The potential of plant growth-promoting rhizobacteria (PGPR) to improve plant growth and nutrient acquisition has received increased attention. This study investigated the synergistic effects of combining PGPR Paraburkholderia sp. SOS3 with the addition of inorganic N fertilizer (iN) or a combined application of inorganic N with organic manure-based fertilizer (iNoN) at low and high levels of N fertilization on Macadamia integrifolia seedling growth. We studied plant growth, mineral N in soil-leachate, and media physicochemical and microbial characteristics. Growth of seedlings fertilized with iNoN at high N level (iNoN 100) was enhanced by PGPR inoculation, with an increase of 32% in total biomass and 43% in N uptake, compared with uninoculated seedlings. No significant PGPR effect was observed on growth under low or high inorganic N treatments but PGPR significantly reduced N leaching after 3 weeks of fertilization. We found a positive relationship between media and plant δ15N and plant N uptake, and a strong increase in microbial-biomass N under the most productive fertilization treatment (iNoN 100 with PGPR), compared with the other N treatments (without or with PGPR). The results suggest that PGPR improves N acquisition by reducing mineral N loss and increasing plant N availability, but that these effects depend on the N form and N level.

Highlights

Human alteration of the global nitrogen (N) cycle is one of the most important drivers of global climate change [1]
Macadamia growth increased with the increasing application rate of combined inorganic and organic fertilizer, though only when plant growth-promoting rhizobacteria (PGPR) was added
Macadamia seedlings grown in substrate amended with the inorganic N with organic manure-based fertilizer (iNoN) 100 treatment had 32% higher total biomass (Table 2, Figure 1b), 27% higher leaf dry mass (Figure 1b,c), 26% higher stem dry mass (Figure 1b,d) and 60% higher fine-root dry mass (Figure 1e) when inoculated with PGPR than when they were uninoculated

Summary

Introduction

Human alteration of the global nitrogen (N) cycle is one of the most important drivers of global climate change [1]. This perturbation is driven predominantly by the increased production and use of inorganic fertilizers to sustain intensive agriculture and crop production [2]. A new revolution in agricultural innovation is required to ensure efficient fertilizer use without harming the environment [5]. This paradigm shift toward sustainable agriculture is essential to support the growing global population through a changing climate

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Results

Conclusion