## 2 Yielding as an Effect of Reduced N Fertilization  
N is essential for plant growth as it is a key component of proteins, chlorophyll, and nucleic acids, driving processes like photosynthesis and protein synthesis [7,17]. Consequently, N directly influences the growth rate of plants, their productivity, and the quality of the yields obtained [18]. Plants that receive adequate N doses exhibit vigorous vegetative growth, characterized by lush green leaves and a strong root system, which enhances their ability to absorb water and nutrients from the soil [19]. Roots develop in response to N availability because N affects both the depth and spread of the roots [19]. When N is abundant, plants tend to develop a denser root system, which increases nutrient and water absorption [19]. This structural adaptation enables the plant to support faster growth and withstand periods of low moisture. In the soil, N typically occurs as NO3\({}^{-}\) and ammonium ions [NH4\({}^{+}\)], which are absorbed by roots through specialized transporters [7,19]. The transport of nitrate within the plant is facilitated by specialized NO3\({}^{-}\) transporters located in root cell membranes [7]. These transporters enable the uptake and movement of NO3\({}^{-}\) from the soil into root cells and, from there, throughout the plant. The two primary transport types, NRT1 and NRT2, vary in their affinity for NO3\({}^{-}\) and are activated depending on the concentration of nitrate in the soil [7,19]. Figure 1 presents the process of N absorption by the plant and its use in creating chlorophyll and the synthesis of amino acids and proteins, ultimately contributing to plant growth and photosynthesis. N is absorbed by plants from the soil predominantly in two forms: NO\({}_{3}\)\({}^{-}\) and NH\({}_{4}\)\({}^{+}\). These forms become available through the processes of organic matter [OM] mineralization and soil microbial transformations, such as nitrification and denitrification [19]. Once taken up by plants, NO\({}_{3}\)\({}^{-}\) undergoes reduction to NH\({}_{4}\)\({}^{+}\), a necessary step for its incorporation into organic compounds [19]. The resulting NH\({}_{4}\)\({}^{+}\) is utilized in amino acid synthesis through key biochemical pathways, most notably the glutamine cycle [7; 19]. Amino acids like Gln and Glu derived from NH\({}_{4}\)\({}^{+}\) are essential building blocks for proteins and other nitrogenous compounds crucial for plant structure and function [19]. N is also fundamental for chlorophyll synthesis [20]. Chlorophyll, the green pigment vital for capturing light energy in photosynthesis, contains N in its porphyrin ring structure: Mg(N\({}_{4}\)), where N atoms coordinate a central magnesium [Mg] ion [20]. This structure enables chlorophyll to absorb light and initiate the light-dependent reactions of photosynthesis [7; 19; 20]. Although N does not directly participate in the photochemical reactions of photosynthesis, it supports the process by facilitating chlorophyll production and enabling the synthesis of proteins and enzymes involved in photosynthetic metabolism [19; 20]. One of the most significant effects of N fertilization is the enhancement of photosynthetic efficiency, which translates into greater biomass production and higher yields [17]. The close relationship between chlorophyll content and N content in plants is fundamental to understanding how plants capture and use light energy for growth and development. Chlorophyll, the green pigment critical for light absorption in photosynthesis, has N in its molecular structure [7; 17]. This connection is especially strong because approximately 70% of a plant's leaf N is localized in chloroplasts, the structures responsible for photosynthesis and the production of chlorophyll pigments [17]. Within chloroplasts, the thylakoid membranes house the protein complexes that conduct the light-dependent reactions of photosynthesis, including photosystems [7; 17]. These complexes are N-rich as they contain various proteins that require nitrogen to function.