About the formation of Саmellia sinensis (L.) O. Kuntze resistance under insufficient water supply at the root fertilization with calcium clay

In the conditions of Russian Black Sea coast and in many other regions of the world (China, India) tea plant is faced with seasonal water shortages leading to a significant loss of productivity - according to different authors, up to 40-50 % (M. Mukhopadhyay et al., 2014; L.S. Malyukova, 2014). In this regard, physiological and biochemical mechanisms of tea plant resistance to water shortages as well as the effectiveness of various exogenous inducers are being researched; more drought-resistant cultivars are being searched for the breeding. Considerable interest in research is related to the study of application of exogenous calcium, which is a mediator in signaling within the cell when there is a synthesis of stress proteins, which, in turn, provide the resistance to adverse environmental factors, as well as the subsequent exit from this state (X.Y. Gao et al., 1999; M.Y. Shu et al, 2000). The papers showed calcium effect on reducing oxidative damage in various plants (including tea plant) at drought by inducing antioxidant system (X.Y. Gao et al., 1999; M. Lee et al, 2004; S.S. Medvedev, 2005; H. Upadhyaya et al., 2012; E.G. Rikhvanov et al., 2014). In Russia, it is the first time when in a field experiment we studied an effect of root fertilization with calcium on the functional state of tea plants and the mode of their nutrition at low water supply. Calcium was introduced into the soil in the form of a natural fertilizer (clay and lime matter containing 40 % of CaO) at 100 kg CaO per ha along with macronutrients (N240P70K90) against solely N240P70K90 in control. During summer periods of high moisture deficit (late July to August) we studied the dynamics of catalase activity in mature leaves and 3-leaf fleshes, pH of the cell sap, water supply and water loss, as well as chemical composition of plants and soil. It was found that under the influence of calcium in the stressful period there were an increase in catalase activity in mature leaves (by 10-19 ml of O2/g within 3 min at different periods), a reduction of water loss (on average by 20 %), a lesser alkalescency of the cell sap (by 0.05-0.07 units), and a significant (by 27-33 %) increase in plant productivity, which indicates more stable functional state both during water stress and rehydration. Catalase activity in shoots (to a lesser extent in mature leaves) correlated with the pH of the cell sap ( r = 0.93 and r = 0.53, respectively), which determined its important role in the formation of tea plant oxidative state. More adapted restructuring of the plants to extreme conditions and their subsequent effective recovery was due to the effect of calcium fertilizers on the cation-exchange capacity of soil absorbing complex, i.e. 1.5-3-fold enhancing the calcium exchange, while maintaining the potassium status and subsequent coordinated absorption of major biogenic nutrient elements, which provides preferential flow of potassium and calcium in plants as compared to nitrogen and phosphorus.