TY - JOUR

T1 - Importance of microbial communities at the root-soil interface for extracellular polymeric substances and soil aggregation in semiarid grasslands

AU - Bettermann, Antje

AU - Zethof, Jeroen H. T.

AU - Babin, Doreen

AU - Cammeraat, Erik L. H.

AU - Solé-Benet, Albert

AU - Lázaro, Roberto

AU - Luna, Lourdes

AU - Nesme, Joseph

AU - Sørensen, Søren J.

AU - Kalbitz, Karsten

AU - Smalla, Kornelia

AU - Vogel, Cordula

PY - 2021

Y1 - 2021

N2 - In the past years, extracellular polymeric substances (EPS) produced by soil microorganisms received an increasing interest, as they not only protect microbes against environmental stresses, but seem to play a pivotal role in soil structure formation as well. Within soils, root deposits provide an important source of easily accessible energy and nutrients, stimulating microbial growth to produce EPS. Especially under semiarid climates, where a full vegetation cover cannot be sustained, large gradients in living conditions for microbes can be found between the root-soil interface and barren intercanopy spaces.In this study, we aimed to elucidate the plant-specific effects on microbes, EPS production and soil aggregation. At two sites in southern Spain, differing in carbonate and graphite content, legume shrubs of Anthyllis cytisoides and grass tussocks of Macrochloa tenacissima were selected. Soil samples were taken in the adjacent bare interspace, under the canopy and of the rhizosphere. From these samples the microbial community (here bacteria and archaea), EPS(-saccharide) content and soil aggregation (The rhizoplane microbial communities differed strongly between plant species and sites, whereby site was the most important factor shaping the communities. The plant species effect on microbial communities diminished strongly with distance to the root surface. At the carbonate-poor Rambla Honda site (site 1), plant species-specific effects were observed in the rhizoplane and rhizosphere, whereas in the carbonate-rich Alboloduy site (site 2) almost no plant species-specific effects were found at the genus level. The larger heterogeneity in microbial communities at site 1 was reflected in EPS-saccharide contents and subsequent soil aggregation, while no difference in soil aggregation was found at site 2. Both parameters increased strongest in the Anthyllis cytisoides rhizosphere at site 1.Despite the lack of a strong gradient with distance from the root at the carbonate-rich site 2, microbial taxa were found by network analysis that positively correlated to EPS-saccharide contents and/or soil aggregation. The relationship between the identified taxa and EPS and/or aggregation relationships were clearest at the root-soil interface, while several other taxa were found to be widely occurring in the other soil compartments too.In conclusion, we found in all compartments potential EPS producers, which could have influenced soil aggregation. Nevertheless, microbes with higher relative abundance in the rhizoplane were linked to higher EPS contents, especially in conjunction with legume shrubs, and subsequently related to soil aggregation. The spatial extent of the root effect was only governed by carbonate contents, as higher carbonate content diminished the observed root effects on the microbial community and subsequent soil aggregation.

AB - In the past years, extracellular polymeric substances (EPS) produced by soil microorganisms received an increasing interest, as they not only protect microbes against environmental stresses, but seem to play a pivotal role in soil structure formation as well. Within soils, root deposits provide an important source of easily accessible energy and nutrients, stimulating microbial growth to produce EPS. Especially under semiarid climates, where a full vegetation cover cannot be sustained, large gradients in living conditions for microbes can be found between the root-soil interface and barren intercanopy spaces.In this study, we aimed to elucidate the plant-specific effects on microbes, EPS production and soil aggregation. At two sites in southern Spain, differing in carbonate and graphite content, legume shrubs of Anthyllis cytisoides and grass tussocks of Macrochloa tenacissima were selected. Soil samples were taken in the adjacent bare interspace, under the canopy and of the rhizosphere. From these samples the microbial community (here bacteria and archaea), EPS(-saccharide) content and soil aggregation (The rhizoplane microbial communities differed strongly between plant species and sites, whereby site was the most important factor shaping the communities. The plant species effect on microbial communities diminished strongly with distance to the root surface. At the carbonate-poor Rambla Honda site (site 1), plant species-specific effects were observed in the rhizoplane and rhizosphere, whereas in the carbonate-rich Alboloduy site (site 2) almost no plant species-specific effects were found at the genus level. The larger heterogeneity in microbial communities at site 1 was reflected in EPS-saccharide contents and subsequent soil aggregation, while no difference in soil aggregation was found at site 2. Both parameters increased strongest in the Anthyllis cytisoides rhizosphere at site 1.Despite the lack of a strong gradient with distance from the root at the carbonate-rich site 2, microbial taxa were found by network analysis that positively correlated to EPS-saccharide contents and/or soil aggregation. The relationship between the identified taxa and EPS and/or aggregation relationships were clearest at the root-soil interface, while several other taxa were found to be widely occurring in the other soil compartments too.In conclusion, we found in all compartments potential EPS producers, which could have influenced soil aggregation. Nevertheless, microbes with higher relative abundance in the rhizoplane were linked to higher EPS contents, especially in conjunction with legume shrubs, and subsequently related to soil aggregation. The spatial extent of the root effect was only governed by carbonate contents, as higher carbonate content diminished the observed root effects on the microbial community and subsequent soil aggregation.

KW - High-throughput amplicon sequencing

KW - Carbonate

KW - Rhizosphere

KW - Rhizoplane

KW - ORGANIC-MATTER

KW - PLANT

KW - DIVERSITY

KW - BACTERIAL

KW - MICROORGANISMS

KW - STABILITY

KW - INVOLVEMENT

KW - GRADIENT

KW - SEQUENCE

KW - PATTERNS

U2 - 10.1016/j.soilbio.2021.108301

DO - 10.1016/j.soilbio.2021.108301

M3 - Journal article

VL - 159

JO - Soil Biology & Biochemistry

JF - Soil Biology & Biochemistry

SN - 0038-0717

M1 - 108301

ER -