Natural Variations and Dynamic Changes of Nitrogen Indices throughout Growing Seasons for Twenty Tea Plant (Camellia sinensis) Varieties

Tea (Camellia sinensis (L.) O. Kuntze) leaves are harvested multiple times annually accompanied by a large amount of nitrogen (N) removed. Therefore, tea plantations are characterized by high requirements of N. This study aimed to assess the variations of N-level, apparent N remobilization efficiency (ANRE), and N utilization efficiency (NUtE) and their dynamic changes during growing seasons for twenty tea varieties. The N-level was highest in the one bud with two leaves as the youngest category, followed by mature leaves attached to green-red stems, and then by aging leaves attached to grey stems. The dynamic N-level presented different profiles of “S”-, “U”-, and “S-like”-shape in the three categories of leaves during the growing seasons. Here, specifically defined ANRE indicated N fluxes in a specific category of leaves, showing that sources and sinks alternate during the period of two consecutive rounds of growth. The dynamic of averaged NUtE followed an “S”-shape. The results revealed annual rhythms and physiological characters related with N indices, which were variety dependent and closely related with the amount of N requirements at proper time. An optimized NUtE is a complex character determined by the combination of tea plantation management and breeding practices to achieve sustainable development with economic benefit.