Nickel Availability in Soil as Influenced by Liming and Its Role in Soybean Nitrogen Metabolism.

Fernando G De Macedo,José Lavres,Wilson T Lopes Da Silva,Felipe Furlan,Joe C Polacco,Elcio F Santos,Joana D Bresolin

doi:10.3389/fpls.2016.01358

Fernando G De Macedo, José Lavres + Show 5 more

Open Access

https://doi.org/10.3389/fpls.2016.01358

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Abstract

Nickel (Ni) availability in soil varies as a function of pH. Plants require Ni in small quantities for normal development, especially in legumes due its role in nitrogen (N) metabolism. This study investigated the effect of soil base saturation, and Ni amendments on Ni uptake, N accumulation in the leaves and grains, as well as to evaluate organic acids changes in soybean. In addition, two N assimilation enzymes were assayed: nitrate reductase (NR) and Ni-dependent urease. Soybean plants inoculated with Bradyrhizobium japonicum were cultivated in soil-filled pots under two base-cation saturation (BCS) ratios (50 and 70%) and five Ni rates – 0.0; 0.1; 0.5; 1.0; and 10.0 mg dm-3 Ni. At flowering (R1 developmental stage), plants for each condition were evaluated for organic acids (oxalic, malonic, succinic, malic, tartaric, fumaric, oxaloacetic, citric and lactic) levels as well as the activities of urease and NR. At the end of the growth period (R7 developmental stage – grain maturity), grain N and Ni accumulations were determined. The available soil-Ni in rhizosphere extracted by DTPA increased with Ni rates, notably in BCS50. The highest concentrations of organic acid and N occurred in BCS70 and 0.5 mg dm-3 of Ni. There were no significant differences for urease activity taken on plants grown at BSC50 for Ni rates, except for the control treatment, while plants cultivated at soil BCS70 increased the urease activity up to 0.5 mg dm-3 of Ni. In addition, the highest values for urease activities were reached from the 0.5 mg dm-3 of Ni rate for both BCS treatments. The NR activity was not affected by any treatment indicating good biological nitrogen fixation (BNF) for all plants. The reddish color of the nodules increased with Ni rates in both BCS50 and 70, also confirms the good BNF due to Ni availability. The optimal development of soybean occurs in BCS70, but requires an extra Ni supply for the production of organic acids and for increased N-shoot and grain accumulation.

Highlights

Nickel (Ni), is the 22nd most abundant element in the earth’s crust and is found in natural soils in trace concentrations (Hussain et al, 2013)
Rhizosphere soil Ni available by DTPA in treatment under BCS50 was 93% higher than BCS70 (Table 1). This difference was clearly observed in Ni dosage of 10 mg dm−3 in which, the BCS50 showed Ni available 114% higher than BCS70 in the same dosage
It was observed that at BCS70 and 0.5 mg dm−3 Ni, soybean plants exhibited a 50% increase in leaf N compared to the control treatment (BCS70 and no Ni supplementation)

Summary

Introduction

Nickel (Ni), is the 22nd most abundant element in the earth’s crust and is found in natural soils in trace concentrations (Hussain et al, 2013). It is an essential element for plants and for many bacteria (Brown, 2007). Until recently urease was the only known Ni-containing enzyme in higher plants (Polacco et al, 2013), but Mustafiz et al (2014) reported that plant glyoxalase-I requires Ni for maximal activity. While glyoxalase-I appears to be activated by Ni in vitro (Mustafiz et al, 2014), in the absence of other proteins, Ni activation of urease requires three accessory proteins. The assembly of the urease Ni metallocenter is not yet clearly understood (Carter et al, 2009; Witte, 2011)

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