Chapter 8 – Quantifying Crop Responses to Nitrogen Deficiency and Avenues to Improve Nitrogen Use Efficiency

Publisher Summary This chapter develops a general theoretical framework of the regulation of N uptake and distribution at two levels of organization: the individual plant and the plant population (i.e., the crop). Its aim is to identify the buffering effect on some physiological traits when scaling up from organ to whole plant and to crop. From this theoretical framework, it derives a functional tool for the determination of N status of plant and crop, and then to quantify the degree of N deficiency. Using this diagnostic tool it analyzes quantitatively the response of important physiological processes to N deficiency. Further it examines the concept of nitrogen use efficiency (NUE) in light of the theory developed; avenues for improving NUE through plant breeding and agronomic strategies are identified. The nitrogen metabolism of plants is controlled by physiological process such as nitrate or ammonium transport through cell membranes in root, nitrate reduction in root and leaf, N2 fixation within nodules in legumes, and ammonium assimilation. Each of these metabolic processes is regulated at molecular levels with some degree of genetic variability. But when all these processes are integrated by scaling up to whole plant and plant population or community level the overall integrated regulation of N uptake and N use efficiency can be resumed by very general rules with very low interspecific variability.