101 Questions answered
The Role of Soil Texture in Supporting Microbial Life
Short answer: there is less food and water in sandy soils.
Soil texture has a major influence on both the abundance and composition of soil microbes.
As clay content increases, so does the ability to hold carbon (food for biota) and water. Carbon is the biggest driver of microbial ecology. The more carbon in a system, the more microbes it can support, and the more diverse the types of carbon, the more diverse the microbial community. For example, fungi are more effective at breaking up complex carbon compounds like cellulose and lignin, while bacteria are better at breaking down more labile carbon.
Second is water. Soil microbes are essentially aquatic. They live where the water is—in pores, in films on aggregates, and inside aggregates. As clay content increases so does the amount of water the soil can hold.
Now, when we talk about soil water we tend to talk about plant available water holding capacity i.e. what the plant can use. Clays can hold more water than a sand, but plants can’t access about 25% of the water. They can’t use the water present in tiny pores, inside aggregates, or as films coating a soil particle – but soil microbes can. They live happily in these tiny pockets or films of water.
Finally, surface area. Clay particles are microscopic and have a much larger surface area than sands, meaning more places for microbes to hang out. Because clays have smaller pores, they also offer hiding places for bacteria. You may find bacteria will be more dominant in a clayey soil than a sandy soil, while fungi are more dominant in sandy soil.
