Mucilage addition increases aggregate stability and tolerance of microbes to soil drying

Abstract

Background and Aims Polysaccharide-rich mucilage from plant roots alters soil structure and microbial microhabitats, potentially modifying microbial responses to drying and rewetting. Here we tested the hypotheses that mucilage strengthens soil aggregates, increases microbial survival during dry–rewet cycles, and alters respiration responses to drying and rewetting. Methods To distinguish effects arising from the physical and biophysical properties of mucilage from those due to added carbon, we compared soil amended with 0.1 mg g −1 mucilage with soil receiving the same amount of carbon as glucose. Half of the soils were kept well-watered, while half were dried slowly over 24 days, rewet and monitored for a further 20 days. We adopted an integrative approach linking physical properties (aggregate stability) with microbial responses (PLFA) to mechanistically scale from microbial microhabitats to survival and respiration. Results Mucilage degraded quickly; nevertheless, at minimum water content the extracellular polysaccharide content of mucilage-amended soil was more than twice as large as soils receiving glucose. Wet sieving indicated mucilage amendment and dry-rewet cycle increased aggregate stability. Respiration averaged 12% faster in mucilage-amended than glucose-amended soil. At minimum water content in the dry–rewet treatment, the PLFA pool was 50% larger in mucilage-amended soil, indicating increased microbial survival under water deficit. Conclusion We conclude that mucilage, for example from plant roots, has complex effects on soil that extend beyond that of a physical binding agent and also include significant effects on microbial survivorship and activity across dry-rewet cycles.