How does fine root influence aggregates? comparing root diameter distribution of two herbaceous plants: a pot experiment

Abstract

Purpose The main objective of this study was to investigate the impact and importance of herb fine roots in different diameter ranges on soil aggregate stability. Materials and methods A laboratory experiment was conducted to disentangle and evaluate the effect of fine roots on soil aggregates. Two herbs, alfalfa (Medicago sativa) with taproots and tall festuca (Festuca arundinacea) with fibrous roots, were selected for single and mixed planting. Root configuration and aggregate stability were measured after different growth periods (30, 60, and 120D). Results and discussion During the growth period of our study, fine roots (< 0.5mm) accounted for the vast majority in soil, while coarse roots (> 1mm) appeared only in soil containing taproots. Planting could improve the mechanical and water stability of aggregates, with enhancement effects displayed as tall festuca > alfalfa, and mixed planting > single planting. Mechanical stability has a higher demand for finer roots. The density increase of very fine roots (< 0.25mm) can improve mechanical stability continuously, but other diameter roots, especially for diameter > 1mm, will have adverse effects on stability after the density reaches a certain threshold. Roots in each diameter range can improve aggregate water stability, but the correlation between root density and water-stable indices decreased gradually with the increase of root diameter. Conclusions The higher ratio of finer roots makes fibrous roots have a better effect on aggregate stability than taproots. Fine roots improve the stability of aggregates mainly by combining 0.5-5mm aggregates to form > 5mm aggregates, and soil organic matter provides raw materials for this process by combining microaggregates (< 0.25mm). RLD is a suitable parameter for predicting changes in aggregate stability, and finer roots could explain more variation in aggregate stability.