Juglans mandshurica Maxim. в условиях Среднего Поволжья (эколого-физиологические особенности)

Abstract

The walnut species Juglans mandshurica Max. demonstrates acclimation to the temperate-continental climate of the Middle Volga region: the naturalized species discovered in forests is characterized by high productivity of the generative individuals, good germination of seeds, a high abundance of pregenerative individuals. The article outlines results of the complex study of Juglans mandshurica Max. inhabiting the forests of the Volga-Kama Reserve. The analysis is based on the data of the 2016 growing season. Features under investigation: phenophase; seasonal variations of the xylem sap flow, chlorophyll content (SPAD) and leaf area index (LAI). The date when all the leaves became fully expanded is in mid-May. The daily dynamics of sap flow has one peak. The maximum rates of sap flow which characterizes the phenophase of fully expanded leaves were observed from 11 am to 2 pm. The time of reaching the maximum rates of sap flow for phenophase of unfolding and not fully expanded leaves shifts to more late hours comparing with the previous ones. Sap flow of the walnut naturally depends on weather conditions: positively correlated with air temperature and solar radiation, negatively correlated with humidity. Range of sap flow walues: from 0,02 kgh-1cm-1 (the leafless phase in the beginning and in the end of the growing season, cloudy and rainy weather), to 0,23 kgh-1cm-1 (the end of July – the beginning of August). The highest rate of sap flow corresponds to the following conditions: maximum values of solar radiation (700 Wm-2), +28 °С air temperature, 40 % air humidity. The peak of the walnut leaves chlorophyll content (SPAD) was observed on August 14th and coincides with the peak of the leaf area index (LAI).