The role of microorganisms and small plants in combating desertification

Introduction

Arid and semi-arid regions occupy an estimated area of about 66.7 million km^2 of the planet and are home to about 2 billion people, and are expected to increase in size as a result of the current scenarios in climate change. Desertification is the process of land degradation in arid, semi-arid, and dry sub-humid regions, resulting from various factors such as climate change, human activities, and loss of biodiversity. Desertification affects the livelihoods of millions of people who depend on the land for food, water, and income. It also contributes to global warming, as degraded soils release more carbon dioxide into the atmosphere. Poor soil structure and low organic matter reduce the water-holding capacity of the soil, which is also linked with loss of fertility and increased emission of greenhouse gases. Loosely aggregated coarse soil speeds up the rate of soil degradation processes, which include a reduction in organic carbon, acceleration of soil erosion, loss of soil fertility and loss of biodiversity.

One of the ways to combat desertification is to restore the ecological functions and productivity of the land, by enhancing the soil quality, water retention, and vegetation cover. Microorganisms and small plants play a vital role in this process, as they interact with each other and with the soil to form complex and resilient ecosystems. Microorganisms, such as bacteria, fungi, and algae, can help to improve the soil fertility, structure, and moisture, by fixing nitrogen, decomposing organic matter, and forming symbiotic associations with plant roots. Small plants, such as grasses, herbs, and shrubs, can help to prevent soil erosion, reduce evaporation, and provide organic matter and nutrients for the soil and other plants. Together, microorganisms and small plants can create a positive feedback loop that enhances the land restoration and reduces the vulnerability to desertification.

Diversity and Functions of Microorganisms and Small Plants in Arid and Semi-arid Ecosystems

Microorganisms and small plants in arid and semi-arid ecosystems are very diverse and perform various functions that help to maintain the ecological balance and productivity of these harsh environments. Microorganisms, such as bacteria, fungi, and algae, can be found in the soil, on the plant surfaces, or inside the plant tissues. They can help to improve the soil fertility, structure, and moisture, by fixing nitrogen, decomposing organic matter, and forming symbiotic associations with plant roots. For example, rhizobia are bacteria that can form nodules on the roots of leguminous plants and convert atmospheric nitrogen into a form that plants can use. Mycorrhizal fungi are fungi that can colonize the roots of most plants and enhance their uptake of water and nutrients. Cyanobacteria are algae that can form crusts on the soil surface and prevent erosion, increase water infiltration, and fix carbon and nitrogen.

Small plants, such as grasses, herbs, and shrubs, can be found in different types of arid and semi-arid ecosystems, such as deserts, steppes, savannas, and dry forests. They can help to prevent soil erosion, reduce evaporation, and provide organic matter and nutrients for the soil and other plants. For example, cacti are succulent plants that can store water in their stems and survive in extremely dry conditions. Aloe are herbs that can produce gel-like substances that have medicinal and cosmetic properties.

Together, microorganisms and small plants can create a positive feedback loop that enhances the land restoration and reduces the vulnerability to desertification. They can also interact with each other and with other organisms, such as insects, animals, and humans, in complex and dynamic ways. For example, some plants can attract pollinators or seed dispersers by producing flowers, fruits, or nectar. Some microorganisms can protect plants from pathogens or herbivores by producing antibiotics or toxins. Some plants and microorganisms can also form mutualistic or antagonistic relationships with each other, depending on the environmental conditions and the availability of resources.

Benefits and Challenges

Using microorganisms and small plants for land restoration has many benefits, such as improving soil quality, water retention, and vegetation cover, enhancing biodiversity and ecosystem services, reducing carbon emissions and greenhouse effect, and supporting food security and livelihoods. However, there are also some challenges, such as selecting the appropriate species and sources of microorganisms and small plants, ensuring their survival and adaptation in harsh conditions, monitoring their effects and interactions with other organisms, and scaling up their application and dissemination. Some examples of successful projects and practices include using soil transplant, inoculating plants with beneficial microorganisms, and reintroducing native microbiome and mycorrhizal fungi. Some examples of unsuccessful projects and practices include using non-native or invasive species, applying excessive or inappropriate amounts of microorganisms and small plants, and neglecting the socio-economic and cultural aspects of land restoration.

Soil Stabilizing Microorganisms

Soil is a complex and dynamic system that hosts a large number of microorganisms, such as bacteria, fungi, and algae. These microorganisms are involved in various biogeochemical cycles, such as carbon, nitrogen, phosphorus, and sulfur cycles, that regulate the availability and transformation of nutrients and organic matter in the soil. The activity and diversity of microorganisms in desert soil are influenced by several abiotic factors, such as moisture, temperature, and organic carbon content. Moisture is one of the most limiting factors for microbial activity, as it affects the diffusion of oxygen, nutrients, and metabolites, as well as the enzyme activity and cell growth. The aerobic bacterial population ranges from <10 (Atacama) to 1.6 × 107 g^−1 (Nevada) of desert soil, while the sand dunes of Thar have about 1.5 × 102–5 × 104 g^−1 soil. Spore-forming Gram-positive bacteria are predominant among bacteria, as they can survive desiccation and high temperatures by forming dormant structures. Actinomycetes account for approximately 50% of the total microbial biomass of desert soil. The dominant genera of actinomycetes in desert soil are coryneforms, i.e., Cystobacter, Archangium, Polyan-gium, Myxococcus, Stigmatella, and Sorangium, followed by Bacillus, Acinetobacter, Proteus, Micrococcus, and Pseudonym. Cyanobacteria also play a significant role in the desert soil ecosystem, especially in terms of nitrogen fixation and primary production. The biological soil crust is a characteristic feature of desert lands, composed of several types of microorganisms, such as cyanobacteria, green algae, lichens, mosses, and fungi. The dominant cyanobacteria of the Thar Desert are Oscillatoria pseudogeminata, Chroococcus minu-tus, Phormidium tenue, and Nostoc species. Additionally, the fungal population varies from nil to 6.3 × 103 in the desert of Uzboi Taky, with dominant genera that include Curvularia, Aspergillus, Mucor, Fusarium, Pénicillium, Paecilomyces, Stemphyli, and Phoma. Xerophilic mushrooms have also been observed in desert soil, such as Coprinus, Fomes, Terfezia, and Terman. Microorganisms contribute to the formation and stabilization of soil structure through the secretion of extracellular polymeric substances (EPS), bioenzymes, and various organic acids. Fungal hyphae promote the aggregation of soil particles and increase the stability of macroaggregates by producing EPS and glomalin (a recalcitrant glycoprotein) that act as binding agents. Mycorrhizal fungi form symbiotic associations with plant roots and enhance their water and nutrient uptake by extending their hyphal network in the soil. EPS also protect the bacterial cells from desiccation and predation by forming a capsule around them. The clay minerals, along with decomposed organic matter and minerals, are precipitated on the EPS layer that serves as a biological glue to form microaggregates. Microorganisms also participate in the humification process, which is the conversion of organic matter into humus, a stable and complex organic substance that improves the soil fertility and water retention. Soil aggregates increase the availability of nutrients for plant uptake, as they provide a large surface area for the adsorption of nutrients. Soil microorganisms also influence the soil fertility and productivity by regulating the nutrient cycling and availability. Therefore, soil microorganisms are an essential component of the terrestrial ecosystem, particularly in dry-lands.

Soil Stabilization Using Small Plants

Small plants are essential for soil stabilization in deserts, as they can improve the soil quality, water retention, and vegetation cover. They can also enhance the biodiversity and ecosystem services, reduce the carbon emissions and greenhouse effect, and support the food security and livelihoods of the people living in deserts. However, they are often overlooked or underestimated, and their role in combating desertification is not well known. Therefore, we need to learn more about them and how to use them to restore degraded lands.

One of the main causes of desertification is the loss of vegetation cover, which exposes the soil to wind and water erosion, reduces the water retention, and lowers the soil fertility. To restore the degraded lands, many people think that planting larger plants, such as trees and shrubs, is the best solution. However, this is not always the case, as larger plants may not survive or thrive in the harsh conditions of deserts, and may require more water and resources than the land can provide.

A better alternative is to use small plants, such as grasses, herbs, and succulents, that are well adapted to the extreme conditions of deserts. These plants can grow in low water and nutrient availability, high temperature and salinity, and variable rainfall and humidity. They can also help to improve the soil conditions in a way that can support larger plants in the future. Some of the benefits of using small plants for combating desertification are:

• They prevent soil erosion: Small plants can cover the soil surface and protect it from being blown or washed away by the wind and water. They can also slow down the water flow and increase the water infiltration, which reduces the runoff and flooding. This helps to preserve the soil structure and stability, and prevent the formation of gullies and dunes.
• They reduce evaporation: Small plants can shade the soil and lower its temperature, which reduces the evaporation of water from the soil. They can also transpire water through their leaves, which increases the humidity and cools the air. This helps to conserve the soil moisture and create a microclimate that is more favorable for plant growth.
• They provide organic matter and nutrients: Small plants can add organic matter and nutrients to the soil by shedding their leaves, roots, and stems. This improves the soil fertility, structure, and moisture retention. The organic matter and nutrients can also feed the microorganisms in the soil, which help to break down the organic matter and release more nutrients. Some plants, such as legumes, can also add nitrogen to the soil by forming symbiotic relationships with bacteria that can fix nitrogen from the air.
• They form soil aggregates: Small plants can help to bind the soil particles together and form soil aggregates, which are clumps of soil that have spaces between them. Soil aggregates improve the soil aeration, drainage, and stability. They also provide habitats for microorganisms and plant roots. Some plants, such as grasses, can secrete sticky substances that act as glue to hold the soil particles together.

Small plants are very important for the soil and the environment, especially in deserts where the land is dry and barren. In my hometown, Dehong, Bastak, which is located in the western border of Hormozgan province, Iran, there are many kinds of small plants that can grow in the harsh conditions of the desert. Some examples of these plants are:

These plants are perennial plants, which means they can live for more than two years. They have strong root systems that help them survive the hot and dry summers, and also help to stabilize the soil and improve its fertility. They also provide food and habitat for many animals and insects, and enhance the biodiversity and ecosystem services of the desert. They are very valuable and useful plants for my hometown and the desert.

Conclusion

Microorganisms and small plants are essential allies in the fight against desertification, as they can restore the ecological functions and productivity of degraded lands, and support the livelihoods of millions of people who depend on them. By using microorganisms and small plants for land restoration, we can not only improve the soil quality, water retention, and vegetation cover, but also enhance the biodiversity and ecosystem services, reduce the carbon emissions and greenhouse effect, and support the food security and livelihoods of the land users. Microorganisms and small plants have a great potential to combat desertification, as they are diverse, adaptable, and resilient, and can interact with each other and with the soil in complex and dynamic ways. However, their potential is often overlooked or underestimated, and their application is often limited or ineffective. Therefore, we need to increase our awareness, knowledge, and action on the role of microorganisms and small plants in combating desertification, and apply them in a scientific, participatory, and sustainable manner.

Desertification is a global problem that threatens the environment, the economy, and the society. It requires more research, awareness, and action from all stakeholders, such as scientists, policymakers, land users, and the general public. More research is needed to understand the causes, effects, and solutions of desertification, and to develop and test new technologies and methods for using microorganisms and small plants for land restoration. More awareness is needed to educate and inform the people about the importance and potential of microorganisms and small plants in combating desertification, and to motivate and inspire them to take action. More action is needed to implement and scale up the application of microorganisms and small plants in different regions and contexts, and to monitor and evaluate their impacts and outcomes. By doing so, we can not only combat desertification, but also contribute to the sustainable development goals and the global common good.