Desert Microbes for Boosting Sustainable Agriculture in Extreme Environments

Abstract

A large portion of the earth's surface consists of arid, semi-arid and hyper-arid lands. Life in these regions is profoundly challenged by harsh environmental conditions of water limitation, high levels of solar radiation and temperature fluctuations, along with soil salinity and nutrient deficiency, which have serious consequences on plant growth and survival. In recent years, plants that grow in such extreme environments and their naturally associated beneficial microbes have attracted increased interest. The rhizosphere, rhizosheath, endosphere, and phyllosphere of desert plants display a perfect niche for isolating novel microbes. They are well adapted to extreme environments and offer an unexploited reservoir for bio-fertilizers and bio-control agents against a wide range of abiotic and biotic stresses that endanger diverse agricultural ecosystems. Their properties can be used to improve soil fertility, increase plant tolerance to various environmental stresses and crop productivity as well as benefit human health and provide enough food for a growing human population in an environment-friendly manner. Several initiatives were launched to discover the possibility of using beneficial microbes. In this review, we will be describing the efforts to explore the bacterial diversity associated with desert plants in the arid, semi-arid, and hyper-arid regions, highlighting the latest discoveries and applications of plant growth promoting bacteria from the most studied deserts around the world.

Keywords: DARWIN21; PGPR; desert agriculture; desert microbes; plant microbiota; world hunger.

FIGURE 1

A global distribution of the desert areas according to their Aridity index. Deserts distribution throughout the land surface, making up 33% of the total land area. The map indicates the most famous deserts in each continent, the Mojave, Sonoran, and Chihuahua Desert in North America and the Atacama Desert in South America. The largest desert are in the world the Sahara Desert in North Africa, along with the Kalahari and Namibia deserts in the southern parts of Africa. In the Middle East, the Negev and the Arabian Peninsula Deserts. In East Asia, the Thar Desert in North India and parts of Pakistan and in west Asia the Lut Desert, while the Gobi and Taklamakan Deserts cover North China and a large part of Mongolia. In Australia, Great Sandy and Gibson Deserts are shown. The map classifies the deserts based on the global Aridity index (AI), which is defined as the numerical indicator of the degree of climatic dryness in a specific location. The map shows the hyper-arid zones in bright yellow, semi-arid zones in orange, and arid zones in brown. Source: Adapted from World Atlas of Desertification (Cherlet et al., 2018).

FIGURE 2

The life in the desert. The illustration highlights the abiotic factors affecting the life in the deserts, such as the low precipitation and high temperate fluctuations, high solar radiation which results in high water evaporation that result in salt ions accumulation in the soil causing soil salinity and affecting the soil composition. Plants in the deserts live in close association with the microorganisms that are inhabiting the plant aerial parts (phyllosphere microbiota), inside the plant root and in the zone around the root (root microbiota) where the root exudates are secreted to attract the bulk soil microbes. A number of factors including soil properties and composition, the water availability, the soil electrical conductivity and pH are responsible to shape the plant microbial communities and filter the selected microbes to improve fitness of plant and microbes. A second factor is the location and the associated climatic conditions, and finally, the host plant for the selection of the most beneficial associations, through means of plant defense mechanisms and immunity, root exudate secretions (this includes different quorum sensing mimicking compounds) and the host plant genotype.