The term “plant microbiome” refers to the collective community of microorganisms that live on and within plants. Microbial diversity is a trait that forms part of the extended phenotype of the host, and important on the health, fitness and the evolution
Phyllosphere
- The phyllosphere is the aerial portion of the plant’s surface. It includes leaves, stems, and flowers colonized by microorganisms; it includes bacteria, fungi, viruses, and other microorganisms. there is a microorganisms carrying capacity of the leaf.
- Phyllosphere is characterized by high humidity and fluctuating temperature. some microorganisms forms mutualistic relationships with the plant. such as providing beneficial nutrients and protecting it from the pathogens.
- Bacteria are by far the most abundant inhabitants of the phyllosphere.
- Filamentous fungi are considered as transient inhabitants
The leaf surface as a microbial habitat
- The leaf surface is a hostile environment for the micro organisms. Because it has limited nutrients, changing temperature, changing nutrients, exposure to the UV radiation, competition.
- Plant cuticles have different 3D crystalline structures that can change with the leaf’s age. It limited the passive diffusion of the nutrients and water vapor from the plant interior.
- The availability of the carbon containing nutrients on the leaves are the main determinant for the epiphytic colonization.
Epiphytic-fitness of plant microbiome
Epiphytic fitness is defined as the ability of the organism to survive and reproduce in the epiphytic habitat. it very important for the evolution of the microorganisms.
Some epiphytic traits of the microorganisms
- Metabolic adaptations – utilized various carbon compounds, such as sugar, amino acids, and specific carbon sources such as methanol.
- Resistant to abiotic stress – bacteria cell produced extracellular polymeric substances (EPS), it help to maintain a hydrated layer of the bacteria which help to protection from the desiccation.
- Epiphytic bacteria produce biosurfactants, which help increase their wettability, enhancing the leaching of the substrate.
- protection against UV radiation by pigment production. Most UV-tolerant strains produced pink and orange pigments.
Phyllosphere Organisms-Significance
Some of significant contributions of phyllosphere organisms are given below:
- Contribute to nutrient cycle – decomposition of organic material and recycling nutrients, fix atmosphere nitrogen
- Pest and disease control – bacteria and fungi produced natural compound that can protect the plant from the pests and diseases.
- Pollination and seed dispersal – insects and other animals in the phyllosphere are contributed to seed dispersal and pollination
- Improve the biodiversity – phyllosphere contains diverse community including including bacteria, fungi, algae
- Climate regulation – Lichens and mosses can regulate the local climate by modifying the temperature, humidity, by adsorbing and reflecting the solar energy.
- Alter plant growth by producing plant growth hormones
- Induce disease in the plant host
- Outcompete, kill, those microorganisms that cause disease or frost injury.
Rhizosphere
Rhyzosphere is the soil environment surrounding the plants roots. it is a complex and dynamic environment between microorganisms are the plants root systems.
Some important roles of the rhizosphere microorganisms
- Plant roots secreted nutrient that favor the growth of microorganisms, these microorganisms are help to produced nutrients such as nitrogen, phosphorus, sulfur compounds.
- Pests and diseases control – microorganisms produced compound that are toxic to certain pathogens. when some plants are under pathogenic attack plants select the specific microbial community from the rhizosphere. when plants are grow in the disease-suppressive soil disease does not developed even in the susceptible plants.
- Maintain the soil structure and stability of the soil; microorganisms produced EPS; agglutinin, LPS
- Cycling of carbon, nitrogen, other useful elements with in the soil.
- contributed to overall biodiversity of the ecosystem because it is a diverse community of the microorganisms including bacteria, fungi, algae.
Rhizodeposition
The release of organic material from the root as they grow through the soil. It contains variety of compounds including exudates (amino acids, organic acids, simple sugars) actively secreted compounds like hormones, enzymes, mucilage, gases.
Major regions of rhizodeposition.
- Loss of the cap and border cells.
- Loss of insoluble mucilage
- Loss of soluble root exudates
- Loss of volatile organic carbons.
- loss to symbionts
- loss due to cell death and lysis
Rhizosphere manipulation
Rhizosphere manipulation is the process of changing the composition or activity of the microorganisms in the rhizosphere.
Some strategies that can be used for rhizosphere manipulation.
- Inoculation of the beneficial microorganisms – Biofertilizers, Biological control agents
- Introduce biostimulants – such as plant growth hormones, microbial metabolites, that promote the plant growth and change the composition of the rhizosphere bacteria
- Crop rotation – this will change the composition of the crops.
- Use cover crop – this will introduced new types of microorganisms into the soil.