Growth, Mineral Nutrients, Photosynthesis and Related Physiological Parameters of Citrus in Response to Nitrogen Deficiency

Wei-Tao Huang,Xu-Feng Chen,Yi-Zhi Xie,Xin Ye,Lin-Tong Yang,Li-Song Chen,Jiuxin Guo,Jiang Zhang,Huan-Huan Chen

doi:10.3390/agronomy11091859

Abstract

Limited data are available on the physiological responses of Citrus to nitrogen (N) deficiency. ‘Xuegan’ (Citrus sinensis (L.) Osbeck) and ‘Shantian pummelo’ (Citrus grandis (L.) Osbeck) seedlings were fertilized with nutrient solution at a N concentration of 0, 5, 10, 15 or 20 mM for 10 weeks. N deficiency decreased N uptake and N concentration in leaves, stems and roots and disturbed nutrient balance and homeostasis in plants, thus inhibiting plant growth, as well as reducing photosynthetic pigment levels and impairing thylakoid structure and photosynthetic electron transport chain (PETC) in leaves, hence lowering CO2 assimilation. The imbalance of nutrients intensified N deficiency’s adverse impacts on biomass, PETC, CO2 assimilation and biosynthesis of photosynthetic pigments. Citrus displayed adaptive responses to N deficiency, including (a) elevating the distributions of N and other elements in roots, as well as root dry weight (DW)/shoot DW ratio and root-surface-per-unit volume and (b) improving photosynthetic N use efficiency (PNUE). In general, N deficiency had less impact on biomass and photosynthetic pigment levels in C. grandis than in C. sinensis seedlings, demonstrating that the tolerance of C. grandis seedlings to N deficiency was slightly higher than that of C. sinensis seedlings, which might be related to the higher PNUE of the former.

Highlights

After carbon, nitrogen (N) is an essential element required in larger amounts by plants than any other elements
74% in C. grandis and C. sinensis seedlings, respectively, relative to 20 mM N treatment, while other N treatments had no significant effect on these ten parameters, with only a few exceptions
The root dry weight (DW)/shoot DW ratio was higher in C. sinensis seedlings than in C

Summary

Introduction

Nitrogen (N) is an essential element required in larger amounts by plants than any other elements. N, as a component of chlorophyll (Chl), nucleic acids, amino acids, proteins, plant hormones, coenzymes and secondary metabolites, accounts for 1–5%. N plays a key role in various metabolic processes of plants such as Chl biosynthesis and photosynthesis [1,2]. The common N deficiency symptoms of crops include arrested vegetative growth, leaf yellowing, narrow leaves and reduced yields [2,4,5]. To meet the required high crop yields, N fertilizers have been widely applied [3,6]. The amounts of N fertilizers applied in the world from 11.4 Tg fertilizer

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