Agricultural Sustainability under Climatic Extremes

Agricultural Sustainability under Climatic Extremes: Comparison

Please note this is a comparison between Version 1 by Marcelo Carvalho Minhoto Teixeira Filho and Version 2 by Dean Liu.

The challenging alterations in climate in the last decades have had direct and indirect influences on biotic and abiotic stresses that have led to devastating implications on agricultural crop production and food security. Extreme environmental conditions, such as abiotic stresses, offer great opportunities to study the influence of different microorganisms in plant development and agricultural productivity.

PGPBs
abiotic stresses
growth-promoting fungi

1. Introduction

The severe impacts of transmutation with intense episodes of extreme weather can have significant consequences on agricultural outputs that should cause widespread food insecurity and affect survival of populations ^[1][2][1,2]. The severity, frequency, magnitude, and duration of extreme climatic events will become more highlighted and noticeable in the future [3]. The alterations in climate extremes have a direct or indirect influence on biotic and abiotic stresses with devastating impacts on agricultural crop production and food security [4]. Biotic stresses comprising phytopathogens and pests [5], as well as abiotic stresses including drought [6], soil salinity ^[6][7][6,7], heavy metals ^[8][9][8,9], flooding [10], high irradiance [11], low temperature [12] and high temperature [13], can cause intensified impacts on plant growth, physiology, metabolism, nutrient acquisition, and ecological desertification. The diverse effects of abiotic stresses on different mechanisms of plants are summarized in Figure 1.

Figure 1. An overview of the effects of abiotic stresses on the different mechanisms of plants.

In changing climate scenarios, intervention with microbes is considered a new sustainable strategy in agricultural production and mitigation of the resilient impacts of stresses [14]. The beneficial microbes and endophytes exhibit real-time amplifications to alleviate the devastating climatic impacts on plant health, physiology and biochemical aspects ^[14][15][14,15]. These microbial communities have several adaptations to abiotic stresses under different ecological processes, including facilitation of organic matter decomposition and nutrient acquisition in the rhizosphere of several plants [16]. Beneficial microbes, including plant growth-promoting rhizobacteria (PGPR), may have a controversial influence or no influence at all on plant growth and fitness under stressful environments, whereas other strains of PGPR have beneficial effects under climate-induced stressful extremes [17]. The PGPR engineered for agricultural practices boost plant growth, pathogen control, and microbial ecosystems by alleviating abiotic resiliencies ^[18][19][18,19].

Plant growth-promoting rhizobacteria tackle abiotic stresses by boosting several physiological and biochemical processes (nutrient uptake, photosynthesis, and source–sink relationships), metabolism and the regulation of homeostasis, osmotic potential, protein function, phytohormone production (indole-3-acetic acid and 1-aminocyclopropane-1-carboxylic acid deaminase), enzymatic activity, and nutrient solubilization ^[20][21][22][20,21,22]. To combat the punitive impact of abiotic stresses, numerous PGPR strains (including Bradyrhizobium sp. SUTNa-2 [23], Pantoea dispersa IAC-BECa-132, Pseudomonas sp., Enterobacter sp. [24], Bacillus amyloliquefaciens EPP90, Bacillus subtilis, Bacillus pumilus [25], Curtobacterium sp. SAK 1 [26], Burkholderia phytofirmans PsJNT [27], Pseudomonas putida KT2440 [28], Enterobacter sp. [29], Serratia marcescens, Microbacterium arborescens, Enterobacter sp. [30], Bacillus cereus PK6-15, Bacillus subtilis PK5-26 and Bacillus circulans PK3-109 [31], Azospirillum lipoferum FK1 [32], and Azospirillum brasilense Sp7 and Azospirillum brasilense Sp245 [33] have been used to facilitate the management mechanisms of different cereal and legume crops under stressful environments. Plant growth-promoting rhizobacteria employ various strategies to endure harsh weather conditions.

In addition, root-associated microbes such as fungi can potentially influence different ecological processes to optimize plant health and growth, resulting in a great impact on plant physiology, nutrition, and survival ability that improves plant tolerance against environment-induced stresses ^[34][83]. These endophytic fungi confer abiotic stresses through the synthesis of various plant beneficial substances (ACC-deaminase, auxins, gibberellins, abscisic acid, siderophores) and solubilize nutrients for healthy plant growth ^[35][36][84,85]. The fugal endophytes form a mutualistic association with plants to promote photosystem activity, protein accumulation, primary metabolism that leads to higher growth, and tolerance under abiotic stresses ^[37][38][65,86]. Plants develop mutualistic relationships with several plant growth-promoting endophytic fungi, including Piriformospora indica ^[38][86], arbuscular Mycorrhizal fungi ^[37][65], Trichoderma albolutescens, Trichoderma asperelloides, Trichoderma orientale, Trichoderma spirale, and Trichoderma tomentosum ^[39][87], Penicillium aurantiogriseum 581PDA3, Alternaria alternate 581PDA5, Trichoderma harzianum 582PDA7 ^[40][88], and Porostereum spadiceum AGH786 ^[41][89], which can increase tolerance against abiotic stresses by improving the biochemical and physiological processes of different plants, as summarized in Figure 2.

Figure 2. Mechanisms against abiotic stresses adapted from microorganisms.

2. Drought Stress

Disruption in the water cycle has become a serious challenge to overcome that is an alarming worry to farmers, horticulturists, and the world’s population as it threatens the food needs of humans and animals. In this context, farmers have increased the amount of irrigation to improve the quantity and quality of agricultural crops; however, this strategy could increase the cost of production ^[42][90]. Drought can be described as an unfavourable environmental condition with an insufficient level of moisture that can affect normal development and growth cycle of plants ^[43][91]. It has been highlighted that drought can reduce yield and cultivation potential (ideal yield) of soybean by up to 70% ^[44][92].

3. Salt Stress

Salinity is one of the major global and environmental concerns that limits agricultural productivity and is attributed to extreme episodes of climatic changes ^[45][116]. Water quality and irrigation management irrespective of source, such as dams, ponds, rivers, artesian wells, or high-depth aquifers, contains salt complexes ^[46][117]. These salt complexes include some of the important cationic species, such as calcium (Ca²⁺), magnesium (Mg²⁺), sodium (Na²⁺), and potassium (K⁺), and among the anionic complexes are chloride (Cl⁻), carbonate (CO₃²⁻), bicarbonate (HCO₃⁻), sulfate (SO₄²⁻), and boron (B) that all can have deleterious effects on agriculture ecosystems and plant productivity. Thus, the increased accumulation of these salts in low-quality irrigation water on arable land converts the land into non-usable and non-productive soil ^[47][118]. Soils irrigated with saturated water extract with an EC of 4.0 dS m⁻¹ (40 mmol L⁻¹ of NaCl) are considered to be saline and can cause osmotic pressure of 0.2 MPa that leads to a reduction in vegetable yields ^[48][119].

4. Heavy Metals

Heavy metals (HMs) are a serious threat to agriculture that can significantly harm different environmental, ecological, and nutritional factors of plants. The rising population has led to increased fertilizer use for higher food production, which can consequently lead to contamination of the environment and food chains ^[49][142]. The anthropogenic activities of humans, including mining, various industries, metallurgy, the use of chemical fertilizers containing HMs, and transportation, have led to a dramatic increase in HM accumulation in the ecosystem ^[50][51][143,144]. Heavy metals released into the air, environment, and soil can be absorbed by plants through roots and leaves, which can disrupt plant metabolism and cause several health risks to humans ^[50][52][143,145]. Edible plants are the major source of food in the human diet, and their contamination with toxic metals may result in catastrophic health hazards ^[50][143].

5. High Temperature

High temperature is one the major abiotic stress in extreme climates that has deleterious impacts on crop yield, global production, human health, and socio-economic damage and wildfires ^[53][54][173,174]. The exposure of plants to unsuitable temperatures during crop cycles results in reduced growth and biochemical aspects. Prolonged heat stress has severe implications on different metabolic processes, including water relations, heat shock proteins, carbohydrate metabolism, and physiological disruptions that lead to cell death ^[43][55][91,175]. High temperature stress crucially affects the grain filling stage ^[56][176], grain quality ^[57][177], grain protein content ^[58][178], biomass, phenology, leaf senescence, grain yield ^[59][179], and the plant canopy in wheat ^[60][180]. High temperature stress also has drastic influences on several crops, including rice ^[61][181], sorghum ^[62][182], pearl millet ^[63][183], maize ^[64][184], and wheat ^[65][185].

6. Low Temperature

Low temperature is also one of the most devastating environmental factors that affects plant growth and productivity. Occasional drops in the temperature of agricultural soils can affect the activity of terrestrial biota and plant growth. Low temperature corresponds to chilling (0–15 °C) that usually occurs in temperate regions and decreases plant productivity. These conditions stimulate the growth of saprophytic fungi that may disrupt soil nutrient cycling and compromise plant health ^[66][215]. Low temperatures disturb cellular homeostasis and some ROS, including hydrogen peroxide (H₂O₂), singlet oxygen (O₂⁻), and HO^., and also disrupt some cellular functions related to proteins, lipids, carbohydrates, and DNA that may cause cell death in plants ^[67][68][217,227].

7. Flood Stress and Oxygen Deficit

Global agriculture is severely affected by climate change. Flooding is one of the most drastic conditions of climate extremes and has detrimental impacts on soil fertility and nutrients, causing disruption to the crucial processes of plants ^[69][237]. The intensity and frequency of flooding is increasing due to climate extremes that could be a serious threat to the stability and productivity of ecosystems ^[70][238]. Plants frequently experience stresses that are typically caused by insufficient water or a lack of oxygen in flooding conditions. Flooding leads to localized depletion of oxygen due to stagnant water and sediment deposition on the soil surface ^[71][239]. The inhibition of cellular respiration and the submersion of non-photosynthetic plant tissues or roots under flooding are some of the most serious plant stresses ^[72][240].

8. Light Stress

Sunlight is one the major factors of photosynthesis that provides the necessary energy for plant growth and development. Despite this, intense light, especially its ultraviolet (UV) part, causes serious damage to DNA, proteins, and other cellular components of plants ^[73][251]. Sunlight damages photosynthetic machinery, primarily photosystem II (PSII), increases ROS production, and causes photo-inhibition that can hinder plant photosynthetic activity, growth, and productivity ^[74][252]. Excess light accelerates ROS production in PSI and PSII of chloroplasts, which may balance photo-inhibition and the repair of plant cells ^[74][252]. Light-triggered plant responses depend on the fluency, exposure time, and acclimation of plants before light exposure ^[73][251]. Reductions in the quantity and quality of light could signal plants to activate defensive systems by enhancing adaptive alterations in stem morphology ^[74][252]. The signaling pathways of light can balance the constructive and destructive impact of light on plant defense and growth mechanisms.