fineroot

Fineroot is a term used to describe the smallest roots of a plant, typically less than about 2 millimeters in diameter. They comprise the absorptive portion of the root system, including root hairs and young lateral roots, and are distinguished from thicker, more structural roots.

Fineroots are widely distributed in the upper soil layers of most species, though some plants extend fineroot production deeper under certain conditions. They exhibit high branching and surface area, which enhances water and nutrient uptake. Many fineroots are colonized by mycorrhizal fungi, which extend the effective absorptive surface and influence nutrient acquisition and plant health.

The primary function of fineroots is the uptake of water and mineral nutrients, but they also participate in carbon allocation, rhizodeposition, and soil-plant interactions. Fineroot systems are highly dynamic, with production and senescence occurring on timescales of weeks to months and sometimes years, depending on species and environmental conditions such as soil moisture, temperature, and nutrient status.

Ecologically, fineroots contribute to belowground carbon cycling, soil structure, and nutrient dynamics, affecting ecosystem productivity and resilience. In forestry and agriculture, their health and turnover influence drought tolerance, nutrient-use efficiency, and soil fertility.

Measurement and terminology vary in the literature. Researchers assess fineroot biomass, length, and turnover using methods such as minirhizotrons, soil cores, or ingrowth cores. Definitions are often based on diameter thresholds or root order, with the finest absorbing roots typically categorized as first- or very low-order roots.