The effect of in climatic changes of the central black earth region of Russia on apple-trees

Introduction

From our point of view, the most important factors determining agricultural losses nowadays are the increase of instability and stresses of weather conditions [11, 12, 13]. Long-term analysis of the reaction of fruit plants sorts has shown that the simultaneous combination of different stressor types is the most dangerous for them. The low genotypic resistance of a sort, the plantation's location, the low level of agrotechnical care increase the stress exposure. The physiological condition of the perennial plants is constituted of the balance between positive and negative impacts throughout their whole life. Each period has its own effect on the physiological processes in plants. The reaction to stress exposure may show up not only immediately, but as consequences one or few years later [4, 6, 11].

Materials and Methods

The analysis of manifestation of limiting temperature conditions for the growth of apple-trees was carried out on the basis of the data about the borderline temperature values that were developed by the expert way.

The metaarchive of MARS project (MARS, IESJRC) over the last 20 years was using as the actual meteorological data for the area of the study. The initial data for this archive is the information of the global atmospheric circulation model of the European Centre for Medium-Range Weather Forecasting (ECMWF) in Reading (UK). The 10-year sum of effective air temperatures and the 10-year sum of atmospheric precipitation was taken as meteorological evaluation parameters.

The apple-trees of autumn and winter sorts that grow in Michurinsk District of Tambov Region were used as model research objects.

Photosynthesis activity has been determined by using a-chlorophyll fluorescence registration through IFSR-2 appliance by the method Genty at all [10]. We used the (Fv/Fm) indicator that characterizes the work activity of photosynthetic appliance combined with Fv/Fm dispersion within a single plant [2, 7].

The timing of the entry to the dormancy and the end of this period for plants have been determined by the method Y.S. Nesterov [5].

The statistical data processing has been performed using the dispersive analysis [3].

Results and Discussion

Nowadays one of the main limiting factors for fruit plants is daily fluctuations of air temperatures. Approximation of the average annual temperatures curve showed that average annual air temperatures vary slightly, some increases thereof was detected, especially since 1997, but that process seems to be very stretched in time and ranges in the scope exceeding one century. At the same time, variation (expressed through dispersion of average annual rates) of average annual air temperatures per decades (1931-2014) shows that, starting from the 1970s, the instability of average annual temperatures has significantly increased: the difference between maximum and minimum average annual temperatures was 2.2°С in 1960-1969, 5.4 °С in 1990-1999 and 8.1°С – in 2000-2014, i.e. this is a doubtless trend toward increasing the amplitude of air temperature fluctuations.

10-year analysis of the average minimum and maximum temperatures allowed to reveal noticeable changes of thermal regime in the crucial periods for apple- and pear-trees: in October-November (preparation and transition of plants to the physiological dormancy), in January-February (the physiological dormancy, coming out of the dormancy), in the end of April — the beginning of May (blooming, fruit-setting). The considerable growth in dispersion of daily temperatures was determined in October-November (1.1 rel.units in 1960-1970 and 9.8 rel.units in 2000-2014) and in March-April (3.5 rel.units in 1960-1970 and 14.7 rel.units in 2000-2014).

Significant changes in the water regime was detected in connection with distribution of precipitation over months. Thus, in 1960-1970 the greatest number of precipitation (up to 70% within the same year) was in October-March, whereas in 2000-2014 the dampest months were September, February and June.

The growth of instability of the water and thermal regime influenced the number of thaw days during January-February. The average number of thaw days in January grew from 2.9 (1960-1969) to 9.5 in 2000-2014 at the simultaneous growth of average maximum thaw temperatures from 0,8 to 3.5 °С; in February from 5 (1960-1969) to 9 (2000-2014), at the thaw temperature from 0.5 to 3.1°С. The fluctuation range of air temperature during the winter thaws increased considerably. Thus, while in the 1960s the average maximum temperature range during January thaws was 8.8 °С, in the last decade it was up to 21.9 °С and in February these values were 9.4 °С and 22.9°С respectively.

The analysis of plants in orchards of Tambov, Lipetsk, Belgorod Regions in the annual cycle allowed us to find out the most energy-consuming, i.e. the most vulnerable periods of the apple-tree development. The periods are the beginning of vegetation (when energy reserves spent in winter yet cannot be replenished at the expense of the photosynthetic activity of the leaves, but the need of the plants for energy is very high), blooming and fruit-settings (because, in addition to the consumption for formation of full fruits, the process of buds differentiation and laying of the future year's yield starts at this time) [6, 7, 9].

One of the main limiting factors for fruit plants nowadays is the range of daily air temperature fluctuation. We determined that, in comparison with the most stable decade (1960-1970), the daily temperature dispersion grew in 3 times, at that, the peaks of the temperature dispersion maximums were noted from the 3rd ten days of April to the 1st ten days of June, i.e. in the most energy-consuming period of fruit plants vegetation [1, 6, 9].

In view of increasing destabilization of weather conditions, the genotype of the fruit plants doesn't always response adequately to these changes [2]. In the 1950th-1980ths the researchers pointed that the dormant period for apple-tree plants began in August-September and ended in the mid-January [5].

During our research holding in 2002-2013 we noticed that the dormant period began for the apple-trees in October-November, but ended in the beginning of January.

In certain years the deep dormant period had already ended in the end of December. An early finish of the dormant period was noticed, the period itself was reduced. For this reason, the risks of plants damage by the negative factors of winter season get aggravated.

Conclusions

Based on the above-mentioned facts, it can be fairly stated that in the mid zone of horticulture, the water and temperature regime has undergone certain changes, causing the increase of its stressfulness for the perennial fruit plants. It has led to the decline in ecological sustainability of fruit crop plantations and to the need for developing and applying the system of protective measures that are not effective without taking into account the degree of destruction of a plant metabolic systems and forecast of the plants reaction to the stressors exposure.

The long-term year-round monitoring of the state of fruit plants according to the enzymic and photosynthetic activity indices has allowed to determine certain regularities that help to predict the response of the plant body to the stressors exposure of water and thermal regime:

➢ the likelihood and the degree of winter damages of the plants depends on their physiological condition in the period of preparation and entry into the dormant condition. It is predetermined by the combination of weather conditions in the vegetation period, activity and direction of physiological processes in September-October and the attenuation period of the enzymic and photosynthetic activity;

➢ The intensity of reaction to the spring period stressors depends on the level of weather conditions stressfulness in autumn and winter, the scale and safety of the energetic pool that can be indirectly evaluated by the level of enzymic activity and intensity of photosynthetic processes in chlorophyll-containing tissues of buds as well as the cambial layer in autumn and winter period. So, the high activity of catalase enzyme in December-January, during the thaw period proves the intensification of metabolic processes and increases the risk of both winter and spring damages;

➢ The plant body reaction to summer stressors is predetermined by the functional condition of the plants and its stressfulness rate in the spring period, as well as by the weather conditions of the vegetation period.

Thus, the new components have been developed and the criterial indicators have been defined that allow to correctly evaluate the degree of stressfulness of the negative weather conditions, to diagnose the level and direction of functional system reaction of the plant body, and to create an efficient model of protective measures for fruit crops plantations in the conditions of the Central Black Earth Region.