**2. Main abiotic plant stresses in central Europe**

Abiotic stress is a main cause of reduced yield in the case of healthy plants. In this context, many scientific research projects have dealt with the impact of weather and climate change on agricultural crops. They were primarily focused on the impact of stress evaluation – especially drought and air and soil temperature extremes. The main current problems are lack of soil water or soil drought as well as high air temperatures. It has also been proved that there has been a prolongation of the growing season – 15 to 25 days – in central Europe in the last 20 years. This is accompanied also by an increasing probability of risk of vegetation frost. Concrete adaptation measures that would eliminate the impacts of climate change are still not a reality.

Monitoring of meteorological elements is crucial for the precise description of microclimatic conditions and their influence on plant physiological processes. The outcomes of microclimate monitoring provide valuable data for growth, plant protection, yield, and irrigation models as well as a wide range of other applications. Monitoring of air temperature and humidity as well as temperature and soil moisture and solar radiation should be an integral part of all growing trials – pot or field based. It is difficult to find any kind of cultivation experiment where the soil moisture and air temperature do not play important roles.

Globally, agriculture accounts for 80–90% of the freshwater used by humans. In many crop production systems such a water use is unsustainable. An interdisciplinary approach involv‐ ing agronomical opportunities and plant breeding in order to deliver "more crop per drop" is needed [2]. In the field, the upper limit of water productivity for well-managed, disease-free, water-limited cereal crops is typically 20 kg ha-1 mm-1 (grain yield per water used). Climate development in Europe since 1990 has been unfavorable for cereal yields because of heat stress during grain filling and drought during stem elongation. Drought during the generative phase decreases the number of based spikelets and grains. Another critical period is also flowering, when water shortage impact is worse than during other stages of development. During the stage of seed filling water stress disrupts the process of synthesis and storage of starch and storage proteins. It has been confirmed [3] that early drought reduces the number of offshoots and number of grains per ear. Late drought at the time of the development of leaves and grain filling causes leaves to age and their photosynthetically active surface decreases faster than in irrigated plants. Late drought negatively affects grain size.

Spring cereal yields decreased by 45–75 kg ha-1 due to decreased precipitation of 10 mm [4]. The highest values of water requirement in plants were observed in the stages from shooting to heading, during an intensive increase of biomass. During this period, the plants utilized up to 5 mm of water per day. Seasonal deficits of precipitation during the growing season in central Poland were -145 and -169 mm for barley and wheat, respectively. In the growing season they utilized from 293 to 314 mm of the soil water [5].

Moisture certainty analyses in the Czech Republic (central Europe) proved there was an increase in the driest areas and that drought event probability increased in during the 1961– 2010 period [6]. An increase in air temperature above normal months and the loss of normal precipitation months were identified. An increase in temperature and precipitation extremes in the future, across climatic conditions and types of landscapes in the Czech Republic, was found [7]. The occurrence of meteorological drought, as well as the occurrence of hydrological, agronomic, physiological, socio-economic, and other kinds of drought is an important feature of the Czech climate. Lack of soil moisture is expected in the main growing season (approxi‐ mately 200 days) when the rainfall does not exceed 340 mm. In connection with the stress effects on yield and quality the most important indication for growers is the presence of agronomic drought. This is defined as a state where the amount of moisture in the soil is less than that required by a particular plant. Literature often defines agronomic drought as a decline in soil moisture below the permanent wilting point (i.e., approximately -1.5 MPa) which stops water uptake and, subsequently, plants growing. It has been claimed [8] that the proportion of usable water – not reducing yields – varies according to crop type and stage of development between 45% and 75% of the available water holding capacity (AWHC). [9] use soil moisture in the root zone at 65% AWHC as a limiting value for barley before transpiration is reduced.

**2. Main abiotic plant stresses in central Europe**

666 Abiotic and Biotic Stress in Plants - Recent Advances and Future Perspectives

Abiotic stress is a main cause of reduced yield in the case of healthy plants. In this context, many scientific research projects have dealt with the impact of weather and climate change on agricultural crops. They were primarily focused on the impact of stress evaluation – especially drought and air and soil temperature extremes. The main current problems are lack of soil water or soil drought as well as high air temperatures. It has also been proved that there has been a prolongation of the growing season – 15 to 25 days – in central Europe in the last 20 years. This is accompanied also by an increasing probability of risk of vegetation frost. Concrete adaptation measures that would eliminate the impacts of climate change are still not a reality.

Monitoring of meteorological elements is crucial for the precise description of microclimatic conditions and their influence on plant physiological processes. The outcomes of microclimate monitoring provide valuable data for growth, plant protection, yield, and irrigation models as well as a wide range of other applications. Monitoring of air temperature and humidity as well as temperature and soil moisture and solar radiation should be an integral part of all growing trials – pot or field based. It is difficult to find any kind of cultivation experiment

Globally, agriculture accounts for 80–90% of the freshwater used by humans. In many crop production systems such a water use is unsustainable. An interdisciplinary approach involv‐ ing agronomical opportunities and plant breeding in order to deliver "more crop per drop" is needed [2]. In the field, the upper limit of water productivity for well-managed, disease-free, water-limited cereal crops is typically 20 kg ha-1 mm-1 (grain yield per water used). Climate development in Europe since 1990 has been unfavorable for cereal yields because of heat stress during grain filling and drought during stem elongation. Drought during the generative phase decreases the number of based spikelets and grains. Another critical period is also flowering, when water shortage impact is worse than during other stages of development. During the stage of seed filling water stress disrupts the process of synthesis and storage of starch and storage proteins. It has been confirmed [3] that early drought reduces the number of offshoots and number of grains per ear. Late drought at the time of the development of leaves and grain filling causes leaves to age and their photosynthetically active surface decreases faster than in

Spring cereal yields decreased by 45–75 kg ha-1 due to decreased precipitation of 10 mm [4]. The highest values of water requirement in plants were observed in the stages from shooting to heading, during an intensive increase of biomass. During this period, the plants utilized up to 5 mm of water per day. Seasonal deficits of precipitation during the growing season in central Poland were -145 and -169 mm for barley and wheat, respectively. In the growing

Moisture certainty analyses in the Czech Republic (central Europe) proved there was an increase in the driest areas and that drought event probability increased in during the 1961– 2010 period [6]. An increase in air temperature above normal months and the loss of normal precipitation months were identified. An increase in temperature and precipitation extremes

where the soil moisture and air temperature do not play important roles.

irrigated plants. Late drought negatively affects grain size.

season they utilized from 293 to 314 mm of the soil water [5].

The availability of soil water, together with global radiation belong to the main agrometeoro‐ logical elements which determine the transpiration performance of plants. Global radiation has a primary effect on the transpiration of plants, however, in the case of drought stress occurrence, one may expect a major influence to be played by soil moisture on the course of transpiration. A crop's reaction to a decrease in soil water capacity is different for different crop species. The high evapotranspiration requirements of the environment may cause a loss of soil water through excessive transpiration in non-sensitive plants.

Water shortage–induced stress often goes hand in hand with temperature stress. Transpiration is the main mechanism a plant has to protect itself against overheating. Leaf temperature increases with increase in air temperature. Effective use of water implies maximal soil moisture capture for transpiration, which also involves reduced non-stomatal transpiration and minimal water loss by soil evapotranspiration.

The dependence of maize transpiration on air temperature, air humidity, solar radiation, soil moisture, wind speed, and leaf temperature were quantified [10]. Significant relationships between transpiration, global radiation, and air temperature were found. Conclusive depend‐ ence of transpiration on leaf surface temperature and wind speed was found (Fig. 3–6). Transpiration in maize plants was significantly influenced by soil moisture under moderate and severe drought stress. The dependence of transpiration on meteorological elements decreased with increasing deficiency of water. A correlation between transpiration and plant dry matter weight, plant height, and weight of corn cob was found. These results will be utilized in an effort to make the calculations of evapotranspiration in computing models more accurate.

Breeding for maximal soil moisture capture for transpiration is therefore the most important target for yield improvement under drought stress. Conclusions have been made [11] that differences in the effective use of water expressed as different yields under the same conditions can be partly attributed to different root system sizes (RSS) (probably due to deeper rooting) and can be improved by breeding. A value of 55% AWHC [12] has been suggested as a qualitative and not stressful value for all growth phases except at the beginning of flowering (45%) and plant maturation.

 Fig. 3 Course of sap flow (red line; kg h-1) and its dependence on air temperature change **Figure 3.** Course of sap flow (red line; kg h-1) and its dependence on air temperature change (black line; °C).

(black line; °C).

(black line; W m-2).

0

1 .

Wind speed (m.s-1)

Fig. 5.Course of sap flow (red line; kg h-1) its dependence on global solar radiation intensity

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.01

0.02

0.03

0.04

Sap flow (kg.h-1)

0.05

0.06

Fig. 6 Course of sap flow (red line; kg h-1) and its dependence on wind speed (black line; m s-

Breeding for maximal soil moisture capture for transpiration is therefore the most important

target for yield improvement under drought stress. Conclusions have been made **[11]** that

differences in the effective use of water expressed as different yields under the same

conditions can be partly attributed to different root system sizes (RSS) (probably due to

deeper rooting) and can be improved by breeding. a value of 55% AWHC [12] has been

suggested as a qualitative and not stressful value for all growth phases except at the beginning

The amount of usable soil water was calculated using the agrometeorological model AVISO

at 21 experimental sites for the period 1975–2007 (% AWHC) **[13]**. A decrease in usable soil

water (% AWHC decrease up to 24%) in a growing season was observed at 20 localities in the

Fig. 4 Course of sap flow (red line; kg.h-1) and its dependence on leaf surface temperature

0.01

0.02

0.03

0.04

Sap flow (kg.h-1)

0.05

0.06

(black line; °C).

Air temperature (°C)

changes (black line; °C).

0 15 30 45 60 75 90 105 120 135 150 165 Ordinal number

0 15 30 45 60 75 90 105 120 135 150 165 Ordinal number

(black line; W m-2).

0

100

200

300

Global radiation R1 (w.m-2)

400

500

600

of flowering (45%) and plant maturation.

1 .

 Fig. 3 Course of sap flow (red line; kg h-1) and its dependence on air temperature change **Figure 4.** Course of sap flow (red line; kg h-1) and its dependence on leaf surface temperature changes (black line; °C).

0 15 30 45 60 75 90 105 120 135 150 165 Ordinal number

of flowering (45%) and plant maturation.

0 15 30 45 60 75 90 105 120 135 150 165 Ordinal number

Fig. 5.Course of sap flow (red line; kg h-1) its dependence on global solar radiation intensity

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.01

Sap flow (kg.h-1)

Wind speed (m.s-1)

Sap flow (kg.h-1)

Leaf temperature (°C)

0 15 30 45 60 75 90 105 120 135 150 165 Ordinal number

0 15 30 45 60 75 90 105 120 135 150 165 Ordinal number

0.01

0.01

0.02

0.03

0.04

Sap flow (kg.h-1)

0.05

0.06

0.02

0.03

0.04

Sap flow (kg.h-1)

0.05

0.06

Fig. 6 Course of sap flow (red line; kg h-1) and its dependence on wind speed (black line; m s-

Breeding for maximal soil moisture capture for transpiration is therefore the most important

target for yield improvement under drought stress. Conclusions have been made **[11]** that

differences in the effective use of water expressed as different yields under the same

conditions can be partly attributed to different root system sizes (RSS) (probably due to

deeper rooting) and can be improved by breeding. a value of 55% AWHC [12] has been

0.01

0.02

0.03

0.04

Sap flow (kg.h-1)

0.05

0.06

suggested as a qualitative and not stressful value for all growth phases except at the beginning

The amount of usable soil water was calculated using the agrometeorological model AVISO

at 21 experimental sites for the period 1975–2007 (% AWHC) **[13]**. A decrease in usable soil

water (% AWHC decrease up to 24%) in a growing season was observed at 20 localities in the

0.01

0.06

0.02

0.03

0.04

Sap flow (kg.h-1)

Leaf temperature (°C)

0.05

0.06

Fig. 4 Course of sap flow (red line; kg.h-1) and its dependence on leaf surface temperature

0 15 30 45 60 75 90 105 120 135 150 165 Ordinal number

0 15 30 45 60 75 90 105 120 135 150 165 Ordinal number

0.01

0.01

0.02

0.03

0.04

Sap flow (kg.h-1)

0.05

0.06

0.02

0.03

0.04

Sap flow (kg.h-1)

0.05

0.06

Fig. 5.Course of sap flow (red line; kg h-1) its dependence on global solar radiation intensity

0.0

0.1

0.2

0.3

0.4

Wind speed (m.s-1)

0.5

0.6

0.7

Fig. 6 Course of sap flow (red line; kg h-1) and its dependence on wind speed (black line; m s-

water (% AWHC decrease up to 24%) in a growing season was observed at 20 localities in the

0 15 30 45 60 75 90 105 120 135 150 165 Ordinal number

changes (black line; °C).

34

Air temperature (°C)

qualitative and not stressful value for all growth phases except at the beginning of flowering

0 15 30 45 60 75 90 105 120 135 150 165 Ordinal number

**Figure 3.** Course of sap flow (red line; kg h-1) and its dependence on air temperature change (black line; °C).

0 15 30 45 60 75 90 105 120 135 150 165 Ordinal number

0 15 30 45 60 75 90 105 120 135 150 165 Ordinal number

**Figure 4.** Course of sap flow (red line; kg h-1) and its dependence on leaf surface temperature changes (black line; °C).

Fig. 3 Course of sap flow (red line; kg h-1) and its dependence on air temperature change

(black line; °C).

changes (black line; °C).

0 15 30 45 60 75 90 105 120 135 150 165

0 15 30 45 60 75 90 105 120 135 150 165 Ordinal number

0 15 30 45 60 75 90 105 120 135 150 165 Ordinal number

> 0 15 30 45 60 75 90 105 120 135 150 165 Ordinal number

0.01

0.02

0.03

0.04

Sap flow (kg.h-1)

Leaf temperature (°C)

0.05

Air temperature (°C)

0.06

Fig. 5.Course of sap flow (red line; kg h-1) its dependence on global solar radiation intensity

0.0

(black line; W m-2).

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.01

0.02

0.03

0

0.01

0.02

0.03

0.04

Global radiation R1 (w.m-2)

0.05

0.06

0.04

100

Sap flow (kg.h-1)

Wind speed (m.s-1)

0.05

300

200

Sap flow (kg.h-1)

0.06

400

500

600

Fig. 6 Course of sap flow (red line; kg h-1) and its dependence on wind speed (black line; m s-

Breeding for maximal soil moisture capture for transpiration is therefore the most important

target for yield improvement under drought stress. Conclusions have been made **[11]** that

differences in the effective use of water expressed as different yields under the same

conditions can be partly attributed to different root system sizes (RSS) (probably due to

of flowering (45%) and plant maturation.

deeper rooting) and can be improved by breeding. a value of 55% AWHC [12] has been

0.01

0.02

0.03

0.04

Sap flow (kg.h-1)

0.05

0.06

1 .

suggested as a qualitative and not stressful value for all growth phases except at the beginning

The amount of usable soil water was calculated using the agrometeorological model AVISO

at 21 experimental sites for the period 1975–2007 (% AWHC) **[13]**. A decrease in usable soil

water (% AWHC decrease up to 24%) in a growing season was observed at 20 localities in the

(45%) and plant maturation.

668 Abiotic and Biotic Stress in Plants - Recent Advances and Future Perspectives

(black line; °C).

Air temperature (°C)

changes (black line; °C).

(black line; W m-2).

0

100

200

300

Global radiation R1 (w.m-2)

Leaf temperature (°C)

Fig. 3 Course of sap flow (red line; kg h-1) and its dependence on air temperature change

0.01

0.02

0.03

0.04

Sap flow (kg.h-1)

0.05

0.06

Fig. 4 Course of sap flow (red line; kg.h-1) and its dependence on leaf surface temperature

(black line; °C).

Air temperature (°C)

changes (black line; °C).

0 15 30 45 60 75 90 105 120 135 150 165 Ordinal number

0 15 30 45 60 75 90 105 120 135 150 165 Ordinal number

(black line; W m-2).

0

100

200

300

Global radiation R1 (w.m-2)

400

500

600

of flowering (45%) and plant maturation.

1 . 400

500

600

of flowering (45%) and plant maturation.

0 15 30 45 60 75 90 105 120 135 150 165 Ordinal number

1 .

Wind speed (m.s-1)

Fig. 5.Course of sap flow (red line; kg h-1) its dependence on global solar radiation intensity

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.01

0.02

0.03

0.04

Sap flow (kg.h-1)

0.05

0.06

Fig. 6 Course of sap flow (red line; kg h-1) and its dependence on wind speed (black line; m s-

Breeding for maximal soil moisture capture for transpiration is therefore the most important

target for yield improvement under drought stress. Conclusions have been made **[11]** that

differences in the effective use of water expressed as different yields under the same

conditions can be partly attributed to different root system sizes (RSS) (probably due to

deeper rooting) and can be improved by breeding. a value of 55% AWHC [12] has been

suggested as a qualitative and not stressful value for all growth phases except at the beginning

The amount of usable soil water was calculated using the agrometeorological model AVISO

at 21 experimental sites for the period 1975–2007 (% AWHC) **[13]**. A decrease in usable soil

water (% AWHC decrease up to 24%) in a growing season was observed at 20 localities in the

Ordinal number (black line; W m-2). **Figure 5.** Course of sap flow (red line; kg h-1) its dependence on global solar radiation intensity (black line; W m-2). Fig. 4 Course of sap flow (red line; kg.h-1) and its dependence on leaf surface temperature

0.01

1

0.01

0.02

0.03

0.04

Sap flow (kg.h-1)

0.05

0.06

0.01

Fig. 6 Course of sap flow (red line; kg h-1) and its dependence on wind speed (black line; m s-

0.01

0.02

0.03

0.04

Sap flow (kg.h-1)

0.05

0.06

Breeding for maximal soil moisture capture for transpiration is therefore the most important

target for yield improvement under drought stress. Conclusions have been made **[11]** that

differences in the effective use of water expressed as different yields under the same

conditions can be partly attributed to different root system sizes (RSS) (probably due to

deeper rooting) and can be improved by breeding. a value of 55% AWHC [12] has been

suggested as a qualitative and not stressful value for all growth phases except at the beginning

The amount of usable soil water was calculated using the agrometeorological model AVISO

at 21 experimental sites for the period 1975–2007 (% AWHC) **[13]**. A decrease in usable soil

water (% AWHC decrease up to 24%) in a growing season was observed at 20 localities in the

0.02

at 21 experimental sites for the period 1975–2007 (% AWHC) **[13]**. A decrease in usable soil Fig. 5.Course of sap flow (red line; kg h-1) its dependence on global solar radiation intensity **Figure 6.** Course of sap flow (red line; kg h-1) and its dependence on wind speed (black line; m s-1).

The amount of usable soil water was calculated using the agrometeorological model AVISO at 21 experimental sites for the period 1975–2007 (% AWHC) [13]. A decrease in usable soil water (% AWHC decrease up to 24%) in a growing season was observed at 20 localities in the long-term trend. Statistically significant relationships were found between grain yield of spring barley and level of AWHC (% AWHC). The optimum range for the amount of usable soil water for the production of spring barley (65%–75% AWHC) was defined by long-term calculations of soil water in combination with a series of yield trials (Fig. 7).

**Figure 7.** Relationship between the soil water supply (% AWHC) and yield of spring barley grain.

Decreasing winter precipitation, increasing winter air temperatures, and increasing levels of CO2 in atmosphere were forecast as global climate changes for central Europe. The negative effects of water stress were partially compensated for by elevated CO2 concentration. Warmer winters could lead to northward expansion of the areas suitable for cropping. However, for crops with a determinate growth habit (e.g. cereals) acceleration of development under warmer conditions could reduce the time available for growth before maturity thereby tending to reduce grain yield. Combining these effects with the fertilizing effect of increasing atmos‐ pheric CO2 concentration, yield of wheat could be 30%–55% higher if there is enough water [14]. For non-determinate crops (e.g. root crops) the warmer climate would extend the growing season. However, there is the possibility that the more frequent, damagingly high summer temperature events could reduce yields of both cereal and root crops. Water can be limiting not only due to global warming but also due to higher yields caused by new varieties and by higher levels of agronomic inputs. Breeding for greater RSS could be therefore one of the strategies for avoiding the impact of water stress. For example, the grain yield of winter wheat varieties in dry years is generally positively correlated with RSS. In a dry year, the varieties that showed the greatest difference in RSS were found to exhibit a yield difference of 860 kg ha-1, approximately translating to an additional use of 15 mm of subsoil water [11].
