Stress disorders of woody plants as a consequence of damage from high temperatures and fires

Abstract

Plants are sessile organisms that are under the constant influence of the environmental conditions in which they grow. Any change in "inanimate" factors that have a significant impact on plant growth and development is collectively referred to as "abiotic stress". Extreme temperatures, especially in changed climatic conditions, are one of the most harmful abiotic factors, which cause heat stress in plants. The effects of high temperatures can be manifested through various morphological, physiological and genetic changes in the plant organism. Generally speaking, plants can be divided into three groups according to temperature requirements: psychrophilic plants, mesophilic plants and thermophilic plants. Most woody species belong to the group of mesophilic plants, which require temperatures between 10 and 30 °C for successful growth and development. As the temperature changes on a daily and seasonal basis in relation to the optimal range, certain changes occur in the plant organism that are necessary to maintain cell growth and homeostasis. Regardless of their ability to adapt to temperature oscillations, plants that have been exposed to temperatures above the optimal level for a long time can show symptoms of irreversible damage, which manifest as heat stress. Generally speaking, this type of stress is considered to occur when the temperature is 10- 15 °C higher than usual at some time of the year, and lasts long enough to cause irreversible damage or disturbances in plant growth and development. As the intensity, duration and degree of temperature change change, so do the various effects of heat stress on plants. In order to survive, plants must adapt to changes in environmental conditions through a specific response that depends on the physiology and morphology of a species. According to their level of tolerance to high temperatures, plants can be divided into three categories: heat-sensitive, relatively heat-sensitive, and heattolerant. The shape and strength of tolerance to high temperatures mostly depend on the plant species, tissue type and cells that are exposed to negative influences. The increase in ambient temperature can also jeopardize the productivity of agricultural crops and forest trees, which has been visible in recent decades in light of climate change and projections regarding the security of supply of the growing population on Earth. Injuries resulting from high temperatures during a fire can initiate a cascade of complex mechanisms that affect the physiology of trees after a fire. The discovery of exact physiological mechanisms and corresponding specific injuries that occur on individual trees, as well as in forest ecosystems, are the focus of intensive modern research. Recent studies have made critical strides in understanding the physiological processes in trees that manifest after fire injuries, and these injuries can affect the tree in combination with some other stressful conditions, such as drought and insect and pathogen attacks. The paper presents a conceptual framework that combines all these processes, their mutual interactions and possible responses, and puts these plant responses in the context of existing hypotheses about the impacts of specific disturbances on plants and ecosystems. By focusing on carbon and water as the main factors in the functioning of the plant organism, this paper presents cambium/phloem necrosis and xylem damage as the main effects of fire injuries. The resulting lack of carbon and hydraulic dysfunction of plants are associated with drought and insect attack. Assessing the precise relationships of the processes presented will be crucial to fully understanding how fires can affect tree functionality and will help improve fire risk assessment and predict tree mortality models. Knowledge of the physiological responses of trees is important for a better assessment of ecosystem dynamics after a fire and their interaction with climate disturbances, and especially taking into account the predicted increase in the frequency and intensity of fires.