METABOLIC CHANGES IN LEAVES OF NATURAL FOREST TREES UNDER ALTITUDE-ASSOCIATED GRADIENT OF MICROCLIMATE AND LIGHT

Abstract

  The present work has explored the influence of immediate microclimate conditions associated with different slope altitude on metabolic processes in leaves of woody species. In the recent years, climate change tending to aridity features enhancement, have made more pressing the forests survival and the trees adaptive capabilities studying. The problem of natural forests conservation and restoration is relevant inUkraine as well, especially in the Steppe zone, because of the forest ecosystems developing under the unfavorable conditions of geographic mismatch; therefore forests are very sensitive to any environmental changes.

The study was carried out on the territory of Bellegarde’ Prisamarsky International Biosphere Reserve (48°45'01.56"N 35°28'31.09"E) in the natural old-growth (more than 85 years old) mixed deciduous forest. Studied areas have been located on the southern slope of the river Samara right steep bank in the lower (52 ma.s.l.), middle (74 ma.s.l.) and upper (96 ma.s.l.) altitude of the slope.

Autochthonous arboreal flora of natural forest was represented by the edificatory species Quercus robus L. and Fraxinus excelsior L., and some co-dominant species including Tilia cordata Mill., Acer platanoides L., Acer campestre L., and Ulmus laevis Pall. The objects of study were chosen in the upper tier (F. excelsior, an ash) and lower tier (T. cordata, linden) of natural forest.

The gradient character of increasing temperature and light levels dependent on slope altitude together with reducing relative humidity level under the canopy of trees was established. This direction of the local changes in the environmental factors was defined as conventional increase in aridity traits at moving upwards on slope. Trees leaves metabolic responses to these local changes have been identified. The leaves of F. excelsior and T. cordata were selected from 5-7 trees in each parts of the slope in May 2016. Leaves chlorophyll (total level, Chl a, and Chl b) content and antioxidant enzyme catalase activity were measured.

Decreasing amount of chlorophyll in leaves of both tree species at the middle and upper parts of the slope compared with index on lower part were found, respectively at 15% and 20% for linden, and at 23% and 33% for ash. Correlation coefficients of total chlorophyll content with light intensity, temperature and relative humidity were similar in linden leaves (respectively, r = - 0.83, r = - 0.98, and r = 0.96) and ash leaves (respectively, r = - 0.84, r = - 0.99, and r = 0.97).

In contrast, catalase activity in leaves of T. cordata and F. excelsior had opposite directions of change along the slope altitude.  Catalase activity in linden leaves decreased by 1.4 and 2.0 times at the middle and upper level relative to the bottom part of the slope, while enzyme activity in ash leaves increased 1.1 and 1.5 times respectively. Correlation coefficients of catalase activity in T. cordata leaves with light, temperature, and humidity were high, respectively r = - 0.93, r = - 1.00, and r = 1.00. At the same time, dependence of F. excelsior leaves catalase activity has been expressed by such coefficients: r = 1.00, r = 0.89 and r = - 0.93, respectively for light, temperature, and humidity.

Thus, a very high sensitivity of arboreal trees leaves photosynthetic and antioxidant processes even to slight changes in environmental features at different slope altitude was established. T. cordata and Fraxinus excelsior showed various adaptive strategies to altitude-associated changes of microclimate conditions including temperature and light intensity increase together with relative humidity decrease. In linden leaves, the positive dependences were established between both metabolic processes and humidity together with negative influence of temperature and light. In leaves of ash, chlorophyll content also increased due to humidity level, while catalase activity increasing was associated with light and temperature growth. Study results can be used to assess the adaptive potential of tree species to enhancing aridity traits, as well as for design of planted forests resistant to climate change.