The impact of foliar nickel fertilization on urease activity in pecan trees

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Abstract

The aim of the present work is to analyze the effect of different foliar products of nickel (Ni) onthe nutrient concentration, chlorophyll content, and enzymatic activity of urease as the possible bioindicator of the levels of Ni in the leaves of pecan [Carya illinoinensis (Wangenh.) K. Koch]. The experiment consisted of the foliar application of Ni to pecan cv. Western Schley, using two commercial products: Nickel Plus®T1 and SpeedfolTM Pecano T2 , and a control T0 received no Ni treatment. The following variables were evaluated: the total chlorophyll concentration, the concentration of macro- and micronutrients including Ni, and the activity of urease. The results demonstrated that the pecan trees treated with Ni increased in the concentration of this element and that the product Nickel Plus® T1 increased by 41.24% with respect to control. The foliar application of Ni led to significant differences in the foliar concentrations of N, P, K, Ca, Mg, Fe, Mn, Cu, Zn, and Ni. Chlorophyll showed a significant reaction to the foliar application of Ni. The enzymatic activity of urease proved to be positively related to the foliar level of Ni, and thus could be considered a good physiological bioindicator of the nutritional state of foliar Ni in the leaflets of the pecan tree.

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Urea metabolism in plants.

Claus-Peter Witte (2011)

Urea is a plant metabolite derived either from root uptake or from catabolism of arginine by arginase. In agriculture, urea is intensively used as a nitrogen fertilizer. Urea nitrogen enters the plant either directly, or in the form of ammonium or nitrate after urea degradation by soil microbes. In recent years various molecular players of plant urea metabolism have been investigated: active and passive urea transporters, the nickel metalloenzyme urease catalyzing the hydrolysis of urea, and three urease accessory proteins involved in the complex activation of urease. The degradation of ureides derived from purine breakdown has long been discussed as a possible additional metabolic source for urea, but an enzymatic route for the complete hydrolysis of ureides without a urea intermediate has recently been described for Arabidopsis thaliana. This review focuses on the proteins involved in plant urea metabolism and the metabolic sources of urea but also addresses open questions regarding plant urea metabolism in a physiological and agricultural context. The contribution of plant urea uptake and metabolism to fertilizer urea usage in crop production is still not investigated although globally more than half of all nitrogen fertilizer is applied to crops in the form of urea. Nitrogen use efficiency in crop production is generally well below 50% resulting in economical losses and creating ecological problems like groundwater pollution and emission of nitric oxides that can damage the ozone layer and function as greenhouse gasses. Biotechnological approaches to improve fertilizer urea usage bear the potential to increase crop nitrogen use efficiency. Copyright Â© 2010 Elsevier Ireland Ltd. All rights reserved.