2. The main abiotic stress factors limiting crop cultivation and production in Bulgaria. Climate changes, drought, water deficit and heat stress

The plants as all living systems can exist only in particular parameters of the outer environment, thus they are part of the open dynamic systems with automatic regulations. This adjustability of the plants is a result of their long evolutionary pathway and mainly by the joint action of instability, heredity (or the genetic traits) and the natural selection. During the phylogenies, each species has acquired its adaptability to certain environmental conditions of the medium by a different mechanism. At the same time, today plants are frequently exposed to environmental stresses due to climate changes.
Drought is becoming a serious problem for humanity on a global and regional scale, including in Bulgaria.
Drought and extremely high temperatures are the most common stressors for agricultural crops in Bulgaria. The negative influence on agricultural crops and crop production is complex and its effect on all plant physiological processes. As a result of this impact, there is a decrease in the quantity and quality of agricultural production.

Keywords: stress factors, drought stress, water deficit, heat stress, climate changes