Crop Adaptation to Climate Change

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Contents

  1. Climate changes require better adaptation to drought -- ScienceDaily
  2. Diversity is the best climate insurance
  3. Biotechnology for crop adaptation
  4. Crop adaptation to climate change

Nevertheless, at elevated CO 2 , stomatal conductance is often reduced, so the canopy and tissue temperature increase, resulting in a thermal influence on phenological development. Elevated CO 2 , together with other global change factors, affects crop architecture and flowering time in a variety of ways. Tillering of wheat increased in response to elevated CO 2 , with an old, tall cultivar being significantly more responsive than a young, semidwarf one Ziska, The result was that the yield superiority of the modern cultivar disappeared at high CO 2 Ziska, Climate change will lead to the intensification of agriculture in northern Europe and other boreal and nemoral zones.

Thus these regions are predicted to gain many benefits from climate change, as the areas suitable for crop production will expand and new crops can be introduced to production. Some of the greatest temperature increases are expected in the Nordic region. While this will reduce some incidences of chilling, it will increase the occurrence of heat stress episodes, to which current cultivars are not adequately tolerant. The increases inCO 2 concentration are expected to be beneficial to the crops with C3 metabolism that provide the basis for high-latitude agriculture, as long as temperatures remain in the moderate range that is predicted.

The impacts on autumn-sown crops are more geographically variable. Yield is expected to strongly decrease in most southern areas, and increase in northern or cooler areas e. The more uneven distribution of rainfall predicted by the models Section 1 , with longer droughts in the spring, heavier and less frequent downpours in summer, and more rain inautumn and winter with less snow cover, will decrease potential crop productivity, and more attention will need to be paid towards these factors and crop responses to them. The changes in temperature and rainfall patterns will bring an increased risk of pest attacks limiting or destroying the crop production.

Plants can, however, adapt to the environment. The responses of plants to the environment influence the development of new cultivars, new cropping systems and crop management practices.


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The phenology, or timing of growth, of the crop determines how much light it can intercept and thus the potential biomass accumulation. The phenology of modern crops is fitted to their growing environment; that is, different developmental stages occur at appropriate times, so oilseed crops or small grain cereals flower in midsummer rather than too soon or too late.

The rates of developmental processes and growth are determined by temperature, and in some cases daylength. Therefore, concepts such as growing degree days have been found useful for describing, modelling, and predicting crop growth. Crop growth is affected by genotype, environment and management practices, and the environmental factors include temperature, daylength, radiation, nutrient and water availability, and CO 2 concentration. Late spring and early autumn frosts limit boreal crop production, and climate change is not expected to alter this situation markedly, so there is limited scope for increasing crop yields in the future by extending the growing period.

The drawback for winter crops in boreal conditions has been poor overwintering, the main reason for which is not inadequate frost resistance but damage caused by pathogenic fungi Microdochium spp. Sometimes the plant stand is almost completely lost Jamalainen, Moreover, ice encasement, frost-drought and frost-heaving as well as waterlogging can destroy overwintering plant stands.

When snow cover lasts for several months without soil freezing, winter cereals in particular can die from starvation, as plants respire throughout the winter under the snow cover, utilizing carbohydrate reserves Jamalainen, Since the duration of permanent snow cover has been forecast to shorten, the importance of snow mould should decrease, even though the rainy autumn and winter days that promote the disease are forecast to increase.

Good management practises, such as timely sowing, appropriate fungicide applications, and avoidance of too dense canopies in the autumn will further decrease the incidence of snow mould. Phenological change as a response to climate warming has been documented in crop plants and natural communities across the northern hemisphere Walther et al. The advancesin timing of spring events, including earlier flowering, maturity, leaf unfolding, budburst, shooting, closure of the stands, and ear formation, correspond to patterns of human-induced climate change Rosenzweig et al.

The mean temperature of the month preceding onset was shown to have the most predictive value for timing, with effects also from the second preceding month and the month of onset Menzel et al. Changes in timing of farm activities, including drilling, tilling, harvesting, were also strongly correlated with changes in temperature Menzel et al.

Temperature, together with photoperiod, is a seasonal cue and a major determinant of the rate of plant development, and warmer temperatures that shorten developmental stages of determinate crops will lead to reduction of the yield. Crop physiological responses to temperature largely determine their adaptation to different climatic zones and seasons; the level of photosynthetically active radiation and the length of growing season determine the upper limit of productivity, and the phenological stage of a crop is influenced by temperature and by light quality.

Daylength has a further impact on development and as it increases in spring it can determine the transition from the vegetative to the reproductive phase. At the start of the high-latitude growing season, daylength is already longer than the critical value for many cultivars developed at lower latitudes. In cereals, this vegetative-reproductive transition limits biomass production, since there is no further vegetative development, whereas in pasture crops and other species with indeterminate habit, vegetative growth continues. Winter damage in rye. Snow mould kills the overwintering plants under snow cover and sometimes hardly any plants survive.

Antti Tuulos. Autumn sowing in the boreal zone is currently restricted by the onset of autumn rains that make agricultural practices difficult. Autumn-sown crop establishment occurs during a period of cooling soil and air temperatures and shortening day length. Wetter, warmer autumn conditions are therefore likely to continue to restrict sowing, but to allow crops to develop further than they do now before the onset of winter, and thus to be at greater risk of winter damage. The effect of increased autumn temperatures on vernalization has not been studied, but clearly hardening will be delayed.

Changes in timing of the emergence and establishment of autumn-sown crops which are related to harvesting and subsequent drilling are little related to temperature Menzel et al. The genetic and environmental moderation of the timing of flowering, by determining the season length, and hence the availability of radiation, water and nutrient resources for growth, and by affecting the exposure of the crop to climate extremes, is therefore central to the success of the crop.

The intensity and daily duration of solar radiation varies depending on elevation and latitude. At high latitudes, solar radiation has a high red content, on account of the lower angle of the sun in the sky, even in midsummer. Cloud further decreases the amount of available radiation. Intercepted solar radiation is linearly related to dry matter accumulation. An earlier developing and later maturing crop thus has the potential to capture and utilize the radiation for a longer period, within the limits set by the risks of cold temperatures in the spring and autumn. Extreme temperatures, even though not yet harmful, increase the respiration of the crops and thus limit biomass accumulation.

Primary production is determined by a function of available incident solar radiation across the season, the efficiency of light interception by the crop and the efficiency of conversion of absorbed energy into biomass Sun et al. This last step,the RUE, is affected by crop developmental stage, leaf tissue structure, and location level of solar radiation and diffuse radiation , and through photosynthesis temperature as well as N and water availability. Leaves with a high N content have high photosynthetic activity and RUE, which is saturated at certain leaf N levels depending on species.

RUE varies among species and developmental stages since there are differences in biochemical components of the plant products and in photosynthesis. During early stages of crop establishment when the photosynthetic capacity of the leaves is still limited, RUE is usually lower than at later stages. In potato producing starch-containing tubers forming early in the season, the conversion of photosynthate to starch can be higher than 0. Species with C4 photosynthesis have generally higher RUE than C3 species, while legumes that use some energy for symbiotic nitrogen fixation have lower RUE than other crops.

Careful analysis of RUE could reveal the growth- and yield-limiting factors that could be improved by management practises and breeding in an attempt to maximize biomass for partitioning into yield. Increased rooting depth can be an advantageous trait under rising temperatures when crop demand for water is increased. Increased SLA is advantageous only in cases when the grain yield is restricted by too short a period of pre-anthesis growth, as found in boreal areas. On the other hand, increase in early vigour results in rapid use of water reserves in rainfed areas early in the growing season.

Flowering, which is essential for the partitioning of biomass into grain yield, is initiated in response to both environmental cues temperature, daylength and the autonomous pathway that is related to the developmental stage of plant. Flowering is a major developmental pathway that is regulated by ambient temperature. Epigenetic regulation also affects vernalization, another temperature-dependent pathway of flowering.

In addition to flowering, epigenetic regulation has important roles in other developmental processes and responses to environmental cues, including abiotic and biotic stress Jarillo et al. Warmer developmental conditions and maternal drought stress can decrease seed dormancy, allowing germination in non-optimal conditions Qaderi et al. Hence, high temperature can also have an impact on seed lot homogeneity and stability. Berger et al. The first is a signal from the environment, the second is a responding signal in the cell that specifies the affected chromosomal location, and the third is a sustaining signal that perpetuates the chromatin change in subsequent generations.

The heritability of environmentally induced traits has special relevance in the context of climate change, as it can have a role in long-term environmental adaptation. Histone variants and post-translational modifications to histones are able to alter physical properties of nucleosomes and serve as a mechanism for regulating DNA exposure. Histone variant H2A. The chromatin status at the FT locus responds to temperature and is altered in the absence of H2A. Understanding the molecular basis of the temperature sensing mechanism is essential in order to predict the responses of plants to further increases in temperature and to use this information in breeding crops to cope with climate change.

In general, the phenological stages determining yield of autumn-sown crops occur earlier than in spring-sown crops, thereby avoiding heat stress, but also being slower and allowing a longer period for tiller and spikelet formation. An early beginning of the growing season and low spring temperatures increase tiller formation, whereas increasing temperatures between stem elongation and anthesis decrease the number of tillers. Tiller survival is, however, very sensitive to water deficit, which can have a marked role in some years. The crop canopy is leafy in early spring before the spring crops are sown and thus, the canopy can make better use of incoming radiation Figure 5.

Many of the same principles apply to autumn-sown broadleaf crops with an indeterminate growth habit, such as faba bean Link et al. Warmer soil temperature increased the green leaf area index, above-ground biomass, and nitrogen content during early developmental stages of winter wheat, without significantly affecting the generative stages and yield of the crop Patil et al. Thus the crop had an opportunity to utilize the incoming radiation for accumulating biomass and nitrogen, which could at later stage be converted into grain yield.

Modelling of sorghum Sorghum bicolor L. Utilization of carbohydrate reserves stored in the stem allows continuation of grain filling in drought- or heat-stressed cereal plants Blum, Reduced plant size and leaf area mainly account for increased water use efficiency in crops, but they usually result in lower yield potential. Component traits included large leaf area with selective killing of older leaves under stress, and osmotic adjustment that allows fast recovery after stress relief Blum, , Temporary storage of carbohydrate reserves, as found in many cereal stems, allows a crop to adjust to fluctuation of assimilate supply by maintaining a viable sink, preventing sink-limitation and feedback inhibition of the enhanced potential photosynthesis following elevated CO 2 levels.

Pathways affecting flowering and stress responses as influenced by climate change in the boreal region. Vernalization and CBF act in a coordinated fashion to regulate FLC that, in turn, regulates further downstream genes to induce flowering. In the future, increased episodes of abiotic stresses can lead to even more severe losses in yield.

The production of crops with improved responses to wide-ranging environmental conditions is needed, for boreal agriculture as much as for that at lower latitudes. Breeding methodology should, as always, be effective. Increasing yield stability under different stress conditions is a challenge to breeders as it is difficult to synchronize the crop cycle with the most favourable environmental conditions. In boreal climates, crop plants have to be adapted to both the long photoperiod and low temperature, andthecombination of timing, duration, intensity, and frequency of heat, drought, frost, flooding, disease and pest stresses cannot be predicted.

Winter crops already cover the soil surface and efficiently utilize available resources, such as solar energy, when spring crops have just formed their first true leaves. A, spring turnip rape, B, winter turnip rape, C, spring lentil, D, winter lentil, E, spring cereal and F, winter cereal.

All photographs were taken on 30 May Antti Tuulos. Biotechnological manipulations can assist the development of sustainable crops for the boreal zone. In contrast, the effects of elevated CO 2 on C4 photosynthesis are small, and generally significant only in drought conditions Leakey et al. Crops under elevated CO 2 required more N than those under current ambient levels in order to produce optimum yield Sun et al. Integration of agronomy, physiology, genetics and omics is necessary to identify novel ways to improve NUE of cereals and oilseeds in order that yield is maintained at lower N input levels or higher C:N ratios.

Manipulation of glutamine synthase genes in maize had significant impacts on grain yield, whereas the genes underlying variation in root length, branching and soil volume exploration remain harder to identify and hence manipulate Hirel et al. Strategies to improve the N economy of wheat, and applicable to other non-N-fixing crops, include maximizing N capture through effective root morphology, optimizing N uptake and assimilation by activity of glutamine synthetase and other enzymes, and optimizing N partitioning to grain by remobilizing stem N while maintaining leaf photosynthetic activity and N content with stay-green mutations Foulkes et al.

The enhanced availability of photosynthate resulting from high atmospheric CO 2 concentration has been shown to increase N fixation in several legume species, so grain quality and protein content are generally maintained Rogers et al. Doubled CO 2 concentration ppm instead of ppm resulted in higher photosynthetic water use efficiency in faba bean Vicia faba L. Nevertheless, at elevated CO 2 , stomatal conductance is often reduced, so the canopy and tissue temperature increase, resulting in a thermal influence on phenological development. Elevated CO 2 , together with other global change factors, affects crop architecture and flowering time in a variety of ways.

Tillering of wheat increased in response to elevated CO 2 , with an old, tall cultivar being significantly more responsive than a young, semidwarf one Ziska, The result was that the yield superiority of the modern cultivar disappeared at high CO 2 Ziska, Climate change will lead to the intensification of agriculture in northern Europe and other boreal and nemoral zones. Thus these regions are predicted to gain many benefits from climate change, as the areas suitable for crop production will expand and new crops can be introduced to production.

Some of the greatest temperature increases are expected in the Nordic region. While this will reduce some incidences of chilling, it will increase the occurrence of heat stress episodes, to which current cultivars are not adequately tolerant. The increases inCO 2 concentration are expected to be beneficial to the crops with C3 metabolism that provide the basis for high-latitude agriculture, as long as temperatures remain in the moderate range that is predicted.

The impacts on autumn-sown crops are more geographically variable. Yield is expected to strongly decrease in most southern areas, and increase in northern or cooler areas e. The more uneven distribution of rainfall predicted by the models Section 1 , with longer droughts in the spring, heavier and less frequent downpours in summer, and more rain inautumn and winter with less snow cover, will decrease potential crop productivity, and more attention will need to be paid towards these factors and crop responses to them.

Climate changes require better adaptation to drought -- ScienceDaily

The changes in temperature and rainfall patterns will bring an increased risk of pest attacks limiting or destroying the crop production. Plants can, however, adapt to the environment. The responses of plants to the environment influence the development of new cultivars, new cropping systems and crop management practices. The phenology, or timing of growth, of the crop determines how much light it can intercept and thus the potential biomass accumulation. The phenology of modern crops is fitted to their growing environment; that is, different developmental stages occur at appropriate times, so oilseed crops or small grain cereals flower in midsummer rather than too soon or too late.

The rates of developmental processes and growth are determined by temperature, and in some cases daylength. Therefore, concepts such as growing degree days have been found useful for describing, modelling, and predicting crop growth. Crop growth is affected by genotype, environment and management practices, and the environmental factors include temperature, daylength, radiation, nutrient and water availability, and CO 2 concentration. Late spring and early autumn frosts limit boreal crop production, and climate change is not expected to alter this situation markedly, so there is limited scope for increasing crop yields in the future by extending the growing period.

The drawback for winter crops in boreal conditions has been poor overwintering, the main reason for which is not inadequate frost resistance but damage caused by pathogenic fungi Microdochium spp.

Diversity is the best climate insurance

Sometimes the plant stand is almost completely lost Jamalainen, Moreover, ice encasement, frost-drought and frost-heaving as well as waterlogging can destroy overwintering plant stands. When snow cover lasts for several months without soil freezing, winter cereals in particular can die from starvation, as plants respire throughout the winter under the snow cover, utilizing carbohydrate reserves Jamalainen, Since the duration of permanent snow cover has been forecast to shorten, the importance of snow mould should decrease, even though the rainy autumn and winter days that promote the disease are forecast to increase.

Good management practises, such as timely sowing, appropriate fungicide applications, and avoidance of too dense canopies in the autumn will further decrease the incidence of snow mould. Phenological change as a response to climate warming has been documented in crop plants and natural communities across the northern hemisphere Walther et al. The advancesin timing of spring events, including earlier flowering, maturity, leaf unfolding, budburst, shooting, closure of the stands, and ear formation, correspond to patterns of human-induced climate change Rosenzweig et al.

The mean temperature of the month preceding onset was shown to have the most predictive value for timing, with effects also from the second preceding month and the month of onset Menzel et al. Changes in timing of farm activities, including drilling, tilling, harvesting, were also strongly correlated with changes in temperature Menzel et al. Temperature, together with photoperiod, is a seasonal cue and a major determinant of the rate of plant development, and warmer temperatures that shorten developmental stages of determinate crops will lead to reduction of the yield.

Crop physiological responses to temperature largely determine their adaptation to different climatic zones and seasons; the level of photosynthetically active radiation and the length of growing season determine the upper limit of productivity, and the phenological stage of a crop is influenced by temperature and by light quality. Daylength has a further impact on development and as it increases in spring it can determine the transition from the vegetative to the reproductive phase.

At the start of the high-latitude growing season, daylength is already longer than the critical value for many cultivars developed at lower latitudes. In cereals, this vegetative-reproductive transition limits biomass production, since there is no further vegetative development, whereas in pasture crops and other species with indeterminate habit, vegetative growth continues. Winter damage in rye. Snow mould kills the overwintering plants under snow cover and sometimes hardly any plants survive. Antti Tuulos. Autumn sowing in the boreal zone is currently restricted by the onset of autumn rains that make agricultural practices difficult.

Autumn-sown crop establishment occurs during a period of cooling soil and air temperatures and shortening day length. Wetter, warmer autumn conditions are therefore likely to continue to restrict sowing, but to allow crops to develop further than they do now before the onset of winter, and thus to be at greater risk of winter damage.

Biotechnology for crop adaptation

The effect of increased autumn temperatures on vernalization has not been studied, but clearly hardening will be delayed. Changes in timing of the emergence and establishment of autumn-sown crops which are related to harvesting and subsequent drilling are little related to temperature Menzel et al. The genetic and environmental moderation of the timing of flowering, by determining the season length, and hence the availability of radiation, water and nutrient resources for growth, and by affecting the exposure of the crop to climate extremes, is therefore central to the success of the crop.

The intensity and daily duration of solar radiation varies depending on elevation and latitude. At high latitudes, solar radiation has a high red content, on account of the lower angle of the sun in the sky, even in midsummer. Cloud further decreases the amount of available radiation. Intercepted solar radiation is linearly related to dry matter accumulation. An earlier developing and later maturing crop thus has the potential to capture and utilize the radiation for a longer period, within the limits set by the risks of cold temperatures in the spring and autumn.

Extreme temperatures, even though not yet harmful, increase the respiration of the crops and thus limit biomass accumulation. Primary production is determined by a function of available incident solar radiation across the season, the efficiency of light interception by the crop and the efficiency of conversion of absorbed energy into biomass Sun et al. This last step,the RUE, is affected by crop developmental stage, leaf tissue structure, and location level of solar radiation and diffuse radiation , and through photosynthesis temperature as well as N and water availability. Leaves with a high N content have high photosynthetic activity and RUE, which is saturated at certain leaf N levels depending on species.

RUE varies among species and developmental stages since there are differences in biochemical components of the plant products and in photosynthesis. During early stages of crop establishment when the photosynthetic capacity of the leaves is still limited, RUE is usually lower than at later stages. In potato producing starch-containing tubers forming early in the season, the conversion of photosynthate to starch can be higher than 0.

Species with C4 photosynthesis have generally higher RUE than C3 species, while legumes that use some energy for symbiotic nitrogen fixation have lower RUE than other crops. Careful analysis of RUE could reveal the growth- and yield-limiting factors that could be improved by management practises and breeding in an attempt to maximize biomass for partitioning into yield.

Increased rooting depth can be an advantageous trait under rising temperatures when crop demand for water is increased. Increased SLA is advantageous only in cases when the grain yield is restricted by too short a period of pre-anthesis growth, as found in boreal areas. On the other hand, increase in early vigour results in rapid use of water reserves in rainfed areas early in the growing season. Flowering, which is essential for the partitioning of biomass into grain yield, is initiated in response to both environmental cues temperature, daylength and the autonomous pathway that is related to the developmental stage of plant.

Flowering is a major developmental pathway that is regulated by ambient temperature. Epigenetic regulation also affects vernalization, another temperature-dependent pathway of flowering. In addition to flowering, epigenetic regulation has important roles in other developmental processes and responses to environmental cues, including abiotic and biotic stress Jarillo et al. Warmer developmental conditions and maternal drought stress can decrease seed dormancy, allowing germination in non-optimal conditions Qaderi et al.


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Hence, high temperature can also have an impact on seed lot homogeneity and stability. Berger et al. The first is a signal from the environment, the second is a responding signal in the cell that specifies the affected chromosomal location, and the third is a sustaining signal that perpetuates the chromatin change in subsequent generations.

The heritability of environmentally induced traits has special relevance in the context of climate change, as it can have a role in long-term environmental adaptation. Histone variants and post-translational modifications to histones are able to alter physical properties of nucleosomes and serve as a mechanism for regulating DNA exposure. Histone variant H2A. The chromatin status at the FT locus responds to temperature and is altered in the absence of H2A. Understanding the molecular basis of the temperature sensing mechanism is essential in order to predict the responses of plants to further increases in temperature and to use this information in breeding crops to cope with climate change.

In general, the phenological stages determining yield of autumn-sown crops occur earlier than in spring-sown crops, thereby avoiding heat stress, but also being slower and allowing a longer period for tiller and spikelet formation. An early beginning of the growing season and low spring temperatures increase tiller formation, whereas increasing temperatures between stem elongation and anthesis decrease the number of tillers. Tiller survival is, however, very sensitive to water deficit, which can have a marked role in some years. The crop canopy is leafy in early spring before the spring crops are sown and thus, the canopy can make better use of incoming radiation Figure 5.

Many of the same principles apply to autumn-sown broadleaf crops with an indeterminate growth habit, such as faba bean Link et al. Warmer soil temperature increased the green leaf area index, above-ground biomass, and nitrogen content during early developmental stages of winter wheat, without significantly affecting the generative stages and yield of the crop Patil et al. Thus the crop had an opportunity to utilize the incoming radiation for accumulating biomass and nitrogen, which could at later stage be converted into grain yield.

Modelling of sorghum Sorghum bicolor L. Utilization of carbohydrate reserves stored in the stem allows continuation of grain filling in drought- or heat-stressed cereal plants Blum, Reduced plant size and leaf area mainly account for increased water use efficiency in crops, but they usually result in lower yield potential. Component traits included large leaf area with selective killing of older leaves under stress, and osmotic adjustment that allows fast recovery after stress relief Blum, , Temporary storage of carbohydrate reserves, as found in many cereal stems, allows a crop to adjust to fluctuation of assimilate supply by maintaining a viable sink, preventing sink-limitation and feedback inhibition of the enhanced potential photosynthesis following elevated CO 2 levels.

Pathways affecting flowering and stress responses as influenced by climate change in the boreal region. Vernalization and CBF act in a coordinated fashion to regulate FLC that, in turn, regulates further downstream genes to induce flowering. In the future, increased episodes of abiotic stresses can lead to even more severe losses in yield. The production of crops with improved responses to wide-ranging environmental conditions is needed, for boreal agriculture as much as for that at lower latitudes.

Temperature alterations can take many forms: changes in average temperature; changes in daytime high and nighttime low temperatures; and changes in the timing, intensity and duration of extremely hot or cold weather. However, plant responses to each type of temperature alteration is species-specific and mediated through both photosynthetic activity for biomass accumulation, which is responsible for plant growth, and the phenological and morphological changes, which occur during plant development.

The effect will depend on how sensitive each species is at their stage of development when the temperature alteration occurs. Adapting to these effects will require different types of responses. To predict the responses of species to new temperature alterations, it is necessary although not sufficient to know how the same species have responded in the past to similar changes.

Crop adaptation to climate change

Below are some of the findings from the few phenological studies of sufficient length on annual crops. Changes in precipitation regimes include changes in seasonal mean, the timing and intensity of individual rainfall events, and the frequency and length of droughts. Each of these factors is critical to crop productivity. The impact of changes in precipitation will be particularly marked when they are combined with temperature alterations that affect the crop's evaporative demands.

This may lead to different forms of moisture stress depending on the phenological stage the crop has reached. The specific impacts of changes in precipitation regimes on crops vary significantly because around 80 percent of the cropped area is rainfed and produces 60 percent of world's food Tubiello et al. The general prediction is that, with climate change, areas that already receive high levels of rainfall will receive more, and those that are dry will become drier Liu and Allan, The reduction in seasonal mean precipitation will have a greater impact on areas with degraded soils.

Soils with lower levels of organic carbon retain less water at low moisture potentials. Furthermore, crops grown in nutrient-poor soils, especially those lacking potassium, recover less quickly from drought stress once water is again available Lipiec et al.

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To help their crops use water more efficiently, farmers must pay attention to improving and maintaining soil fertility see module B7 on sustainable soil and land management for climate-smart agriculture, Chapter B on sustainable soil management for increased crop productivity and Box B1. As rainfall becomes more variable, farmers may no longer be able to rely on their knowledge of the seasonality of climatic variables. Shifting planting seasons and weather patterns will make it harder for farmers to plan and manage production. For example, a later start of the rainy season or an earlier end, or both, reduces the time that crops have to complete their growth cycle and, ultimately, causes yield losses Linderholm, For photosensitive species, a change in the duration of the rainy season may cause a mismatch between their reproductive cycle, which is determined by day length, and the availability of sufficient soil moisture to produce good yields.

Another expected impact of climate change is an increased occurrence of extreme weather events. Even where mean values for precipitation are not projected to change, there are likely to be more significant extreme weather events that will reduce crop yields. Heavy rain, hail storms and flooding can physically damage crops. Extremely wet conditions in the field can delay planting or harvesting. Prolonged droughts can cause complete crop failure Tubiello and van der Velde, Plants weakened by the direct effects of weather stresses are generally more vulnerable to indirect stresses.

For example, plants suffering from waterlogging are less resilient to viruses, and plants affected by drought are less able to outcompete weeds for soil moisture and nutrients Simpson, In addition, if pests shift into regions outside the distribution of their natural enemies, the effectiveness of biocontrol will decrease unless a new community of enemies will provide some level of control. The distribution of insect pests is influenced by temperatures. With global warming, insects, whose body temperature varies with the temperature of the surrounding environment poikilothermic x are most likely to move polewards and to higher elevations Bebber et al.

Pest distribution will also respond to changes in cropping patterns to cope with climate change. Major insect pests of cereals, pulses, vegetables, and fruit crops, which may move to temperate regions, include cereal stem borers Chilo , Sesamia , and Scirpophaga spp. The extent of crop losses will depend on geographical distribution of insect pests; the dynamics of the insect population; insect biotypes; the alterations in the diversity and abundance of arthropods; changes in herbivore-plant interactions; the activities and abundance of natural enemies; species extinctions; and the efficacy of crop protection technologies.

Weeds will also be affected by climate change. For invasive plants with tolerances for higher temperatures, which are currently restricted by low temperatures, such as Vallisneria spp. The species with higher mobility would be favoured.