**8. Nutrient deficiency stress**

In the other types of stress reviewed, high irradiance, extremes of temperature, water deficit, and salinity, it was explained how the proper management and care of the soil constitutes a critical component for its mitigation. In the case of the deficit of mineral nutrients, this part is especially relevant since the soil or substrate is the primary source of nutrients. Environmental conditions that induce mineral deficiency are manifold, as well as the ability of plant species and their microbiome to absorb, transport, assimilate and store nutrients. The different combinations of irradiance, temperature, relative humidity, physicochemical and biotic characteristics of the soil impose different needs both in quantity and in the molar balance of the elements used by the plants for their metabolism. It is known about C/N, N/P, K/Ca, Ca/Mg, among other ratios, but it is a complex challenge to have the necessary information to appropriately manage the nutrition (time, quantity, chemical form and balance with other elements) of crops during their growth, especially in extensive crops and those developed in the soil.

Different agronomic approaches, such as the 4R and Integrated Nutrient Management (INM), are currently being used to increase the ratio between the amount of fertilizer absorbed by the plants and the amount of fertilizer applied to the soil, or nutrient use efficiency (NUE). The aim is to reduce the ecological and economic costs of agricultural practices, achieving a higher return concerning food production without contravening the sustainability of the edaphic system [103, 121, 122]. The main characteristic of the 4R and INM approaches is that they are integrated processes, not directed to a single practice or a single component of the ecosystem (**Figure 3**).

Almost all of the above practices focus to a greater or lesser extent on soil quality care, quality being defined as soil capacity to provide the environmental services associated with the water cycle and mineral elements, soil support vegetation, animal life and edaphic microbiome, storage of C and other minerals, among others. Soil quality can be monitored in a variety of ways, but a very sensitive indicator is the amount of organic matter in the soil, which, when it decreases, signals a degradation process [103]. The quality of the soil is closely related to the quantity and frequency of tillage applied; the greater the amount of heavy machinery working in the field the greater is the soil degradation.

Another indicator of soil quality is the ability to maintain the necessary mineral elements in a bio-available form for plants. The plants take up through the roots the dissolved elements in the solution of the soil, in turn, this edaphic component is in a homeostatic process of exchange of elements with the mineral and organic components of the soil [124]. The edaphic microbiome plays a key role in this dynamic equilibrium by solubilizing, precipitating and synthesizing new minerals from the available elements. For all the processes before mentioned certain conditions of pH, EC, and redox potential are necessary to facilitate the interchange of elements between the different phases of the system, the organic matter of the soil fulfilling a crucial role in the maintenance of such conditions. Again, as in the stresses described in earlier parts of this manuscript, the importance of conserving and managing organic matter in agricultural soils arises.

For most of the mineral elements, high and low-affinity transporters responsible for their absorption, transport to the radical cortex and vascular bundles have been described for their distribution and assimilation in all organs of the plant [125]. The functionality of these transporters depends on the bioavailability of the element in the rhizosphere (the volume of soil modified directly by the root surface). This bioavailability depends on physicochemical factors, which are significantly buffered by the presence of organic matter [122], and biotic factors that encompass the root microbiome and the root activity that modifies the rhizo-

**Figure 3.** An integrated approach to agronomic practices to mitigate P and Zn deficits in crops. It is an example of the integral agronomic management described in the text, aimed at reducing the deficit of two very relevant nutrients from a perspective of sustainable agricultural production and from the point of view of human food, for which there are

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that solubilize

sphere through excretion of organic acids, metabolites, and enzymes, and H+

restrictions as far as the availability and effectiveness of available fertilizer sources [123].

minerals [126].

**8. Nutrient deficiency stress**

168 Plant, Abiotic Stress and Responses to Climate Change

oped in the soil.

ecosystem (**Figure 3**).

ing in the field the greater is the soil degradation.

organic matter in agricultural soils arises.

In the other types of stress reviewed, high irradiance, extremes of temperature, water deficit, and salinity, it was explained how the proper management and care of the soil constitutes a critical component for its mitigation. In the case of the deficit of mineral nutrients, this part is especially relevant since the soil or substrate is the primary source of nutrients. Environmental conditions that induce mineral deficiency are manifold, as well as the ability of plant species and their microbiome to absorb, transport, assimilate and store nutrients. The different combinations of irradiance, temperature, relative humidity, physicochemical and biotic characteristics of the soil impose different needs both in quantity and in the molar balance of the elements used by the plants for their metabolism. It is known about C/N, N/P, K/Ca, Ca/Mg, among other ratios, but it is a complex challenge to have the necessary information to appropriately manage the nutrition (time, quantity, chemical form and balance with other elements) of crops during their growth, especially in extensive crops and those devel-

Different agronomic approaches, such as the 4R and Integrated Nutrient Management (INM), are currently being used to increase the ratio between the amount of fertilizer absorbed by the plants and the amount of fertilizer applied to the soil, or nutrient use efficiency (NUE). The aim is to reduce the ecological and economic costs of agricultural practices, achieving a higher return concerning food production without contravening the sustainability of the edaphic system [103, 121, 122]. The main characteristic of the 4R and INM approaches is that they are integrated processes, not directed to a single practice or a single component of the

Almost all of the above practices focus to a greater or lesser extent on soil quality care, quality being defined as soil capacity to provide the environmental services associated with the water cycle and mineral elements, soil support vegetation, animal life and edaphic microbiome, storage of C and other minerals, among others. Soil quality can be monitored in a variety of ways, but a very sensitive indicator is the amount of organic matter in the soil, which, when it decreases, signals a degradation process [103]. The quality of the soil is closely related to the quantity and frequency of tillage applied; the greater the amount of heavy machinery work-

Another indicator of soil quality is the ability to maintain the necessary mineral elements in a bio-available form for plants. The plants take up through the roots the dissolved elements in the solution of the soil, in turn, this edaphic component is in a homeostatic process of exchange of elements with the mineral and organic components of the soil [124]. The edaphic microbiome plays a key role in this dynamic equilibrium by solubilizing, precipitating and synthesizing new minerals from the available elements. For all the processes before mentioned certain conditions of pH, EC, and redox potential are necessary to facilitate the interchange of elements between the different phases of the system, the organic matter of the soil fulfilling a crucial role in the maintenance of such conditions. Again, as in the stresses described in earlier parts of this manuscript, the importance of conserving and managing

**Figure 3.** An integrated approach to agronomic practices to mitigate P and Zn deficits in crops. It is an example of the integral agronomic management described in the text, aimed at reducing the deficit of two very relevant nutrients from a perspective of sustainable agricultural production and from the point of view of human food, for which there are restrictions as far as the availability and effectiveness of available fertilizer sources [123].

For most of the mineral elements, high and low-affinity transporters responsible for their absorption, transport to the radical cortex and vascular bundles have been described for their distribution and assimilation in all organs of the plant [125]. The functionality of these transporters depends on the bioavailability of the element in the rhizosphere (the volume of soil modified directly by the root surface). This bioavailability depends on physicochemical factors, which are significantly buffered by the presence of organic matter [122], and biotic factors that encompass the root microbiome and the root activity that modifies the rhizosphere through excretion of organic acids, metabolites, and enzymes, and H+ that solubilize minerals [126].

use of rock dust, materials obtained as an industrial by-product, and in the form of nanomaterials, which raises the possibility that the biotic processes and abiotic systems of the soil system transform these materials into nutrients in available forms. Similarly, the application of so-called biological fertilizers or biofertilizers, such as *Rhizobiaceae*, *Azotobacter*, *Azospirillum*, vesicular-arbuscular mycorrhizae (VAM), phosphate solubilizing bacteria (PSB), and plant growth-promoting rhizobacteria can be used in combination with organic and inorganic fer-

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The option of using biofertilizers should be emphasized. Some advantages mean that the alternative of using biofertilizers can be considered as useful to make food production more efficient and sustainable: they are a natural and non-polluting source of fertilizing elements for crops; beneficial microorganisms can be isolated and produced locally, with techniques and technology available in many parts of the world, which also has a multiplier effect of local bio-industries; microorganisms that benefit the plant with a greater bioavailability of mineral elements also increase their productivity and tolerance to abiotic stress through the production of growth regulators and metabolites that restrict the growth of

Also, the development of nanofertilizers with a greater efficiency in its absorption and impact in the plant is an open subject, but that undoubtedly will contribute of relevant form to the improvement of the nutrition of the plants. It has been proven experimentally that all essential elements for plants are absorbed and used by plants in their nanometric form. However, the more diversified and larger application of this technology still requires that the safety

The combination of technologies in an integral way (**Figure 4**) can offer many advantages against a non-benign climate scenario. The greater or lesser bioavailability of mineral elements can be modified through soil improvement practices such as the use of organic matter and the application of inorganic fertilizers and biofertilizers. Soil management and nutrition in combination with the use of crop varieties with greater efficiency in nutrient absorption is also advisable. To do this, from the use of traditional selection techniques to the use of genetically modified varieties or genome-editing are a determining factor in an integrated approach

A comprehensive approach to the management of abiotic stress based on soil management techniques, the use of currently available technologies for irrigation and plant care, the use of materials, nanomaterials, biofertilizers, and growth regulators that can be applied at different stages of plant growth. The application of the mentioned techniques in combination with the use of improved or genetically modified varieties may allow the addition and synergy of different effects in various levels of description of agricultural systems. This synergy is expected

issues of the use of nanomaterials in crops destined to food production be solved [46].

to the management of nutrient deficiencies in agriculture. [129, 130].

to lead to more resilient systems in the face of climate change.

tilizers [127].

pathogens [128].

**9. Conclusions**

**Figure 4.** Integral application of different technologies for the management of abiotic stress as a tool to improve food production in a climate change scenario.

The use of cover crops, the incorporation of organic matter in the form of compost, biochar, and biosolids is recommended to increase the bioavailability of mineral elements. In the same way the controlled use of organic and inorganic forms of the applied elements, including the use of rock dust, materials obtained as an industrial by-product, and in the form of nanomaterials, which raises the possibility that the biotic processes and abiotic systems of the soil system transform these materials into nutrients in available forms. Similarly, the application of so-called biological fertilizers or biofertilizers, such as *Rhizobiaceae*, *Azotobacter*, *Azospirillum*, vesicular-arbuscular mycorrhizae (VAM), phosphate solubilizing bacteria (PSB), and plant growth-promoting rhizobacteria can be used in combination with organic and inorganic fertilizers [127].

The option of using biofertilizers should be emphasized. Some advantages mean that the alternative of using biofertilizers can be considered as useful to make food production more efficient and sustainable: they are a natural and non-polluting source of fertilizing elements for crops; beneficial microorganisms can be isolated and produced locally, with techniques and technology available in many parts of the world, which also has a multiplier effect of local bio-industries; microorganisms that benefit the plant with a greater bioavailability of mineral elements also increase their productivity and tolerance to abiotic stress through the production of growth regulators and metabolites that restrict the growth of pathogens [128].

Also, the development of nanofertilizers with a greater efficiency in its absorption and impact in the plant is an open subject, but that undoubtedly will contribute of relevant form to the improvement of the nutrition of the plants. It has been proven experimentally that all essential elements for plants are absorbed and used by plants in their nanometric form. However, the more diversified and larger application of this technology still requires that the safety issues of the use of nanomaterials in crops destined to food production be solved [46].

The combination of technologies in an integral way (**Figure 4**) can offer many advantages against a non-benign climate scenario. The greater or lesser bioavailability of mineral elements can be modified through soil improvement practices such as the use of organic matter and the application of inorganic fertilizers and biofertilizers. Soil management and nutrition in combination with the use of crop varieties with greater efficiency in nutrient absorption is also advisable. To do this, from the use of traditional selection techniques to the use of genetically modified varieties or genome-editing are a determining factor in an integrated approach to the management of nutrient deficiencies in agriculture. [129, 130].
