Abstract

A forest is a large area of land covered with big trees of different species, approximately covering one-third of the Earth's surface. Forest ecosystems are more than what can be seen physically (aboveground); below the ground level, they are extraordinarily diverse and have unique communities of microbiomes with a large population of bacteria and fungi species. These microorganisms are essential to how plants interact with the soil environment and are necessary to access critically limiting soil resources. This book chapter focuses on the ecosystems below and above ground level of a forest microbiome, including the soil microorganisms, their importance, and the diverse interrelationships among soil microorganisms (parasitism, mutualism, commensalism). The aboveground part of a plant is known as the phyllosphere, harboring diverse microorganisms, such as viruses, bacteria, filamentous fungi, yeast, algae, and rarely protozoa and nematodes with a role in disease resistance that is critical to plant health and development. The rhizosphere is the soil region immediately adjacent to and affected by plant roots where plants, soil, microorganisms, nutrients, and water meet and interact. In this region, plants and microbes coordinate and show a symbiotic relationship by fulfilling each other's nutrient requirements, roles, and functions. The endosphere is the plant interior and is colonized by endophytes, and their functions range from mutualism to pathogenicity. Archaebacteria, anaerobic bacteria, aerobic prokaryotes, fungi, and viruses exist as forest biomes. Examples of fungi include Trichoderma harzianum and obligate parasites Puccinia striiformis and Gremmeniella abietina. Plants, fungal endophytes, mycoviruses, and the environment all participate in a four-way interactive system.