Tropical Soil Microbial Communities
Tropical soil ecosystems are diverse and complex and are different from those of temperate ecosystems. The various ecosystems found within the tropics provide the setting for diverse microbial niches and evolution. There is not a meaningful correlation be
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Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 Desert Soil Communities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86 Semiarid Soil Communities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 Mangrove Soil/Sediment Communities . . . . . . . . . . . . . . . . . . . . . 89 Rainforest Soil Communities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 Roles of Tropical Soil Bacteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
Introduction In this chapter, we focus on tropical soil ecosystems and review some of their bacterial communities. We start by describing the tropics and tropical soils and then describe bacterial community diversity and function based on case studies of those soils. We end the chapter looking at the positive role soil bacteria can play in tropical agriculture and food production. Tropical soils are those found between the Tropic of Cancer (latitude at 23½ North) and the Tropic of Capricorn (23½ South) imaginary lines around the Earth that delineate the zone where the sun’s rays will be perpendicular for at least 1 day in the year. Between these latitudes lies an area that accounts for about 40% of the Earth’s surface. If we look at a globe and focus on the area within the tropics and then remove the deserts and then the Atlantic, Pacific, and Indian oceans, what we are left with are the remnants of the World’s tropical rainforests and savannahs. Approximately 40% of the World’s population depends on those soils for a home and sustenance. Of 270 countries and island groups on the planet, 169 countries have all or a part of their territory within the tropics (IUCN 1988). Simplifying this we see that the tropics include Mexico, all Central American countries, all Caribbean countries, most South American countries, the vast majority of African countries, much of India and Southern Asia, a bit of China, all of Oceania, and a large part of Australia. To say that tropical soils are important would be an understatement, but what is a tropical soil and what determines its characteristics? Soil is the thin layer of material on the Earth’s surface made up of minerals and organic matter that serves as the natural growth media for land plants. Its formation and usefulness depend on five main factors: parent rock, climate, topography, biological interactions, and time. Human intervention also plays an increasingly important role especially in agricultural soils where fertility is managed. At the global scale, it is climate and
time that explain the soil types that we see in the tropics today. Within the tropics, climate is often described as tropical humid or dry. Tropical humid can be further divided into: tropical wet with no dry season, tropical monsoonal with a short dry season and heavy rains in other months, and tropical savannah with a dry winter season. Tropical soils are generally old (>100,000 years) and often ancient (>10 million years). This length of ti
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