Microbial metabolic activity in Amazon floodplain forest and agricultural soils

Abstract

Microorganisms play an essential role in ecosystem functions. An increasingly used method for conducting functional analyses of a soil microbial community is based on the physiological profile at the community level. This method allows the metabolic capacity of microorganisms to be assessed based on patterns of carbon consumption and derived indices. In the present study, the functional diversity of microbial communities was assessed in soils from seasonally flooded-forest (FOR) and -traditional farming systems (TFS) in Amazonian floodplains flooded with black, clear, and white water. The soils of the Amazon floodplains showed differences in the metabolic activity of their microbial communities, with a general trend in activity level of clear water floodplain > black water floodplain > white water floodplain. The redundancy analysis (RDA) indicated that soil moisture (flood pulse) was the most important environmental parameter in determining the metabolic activity of the soil microbial communities in the black, clear, and white floodplains. In addition, the variance partitioning analysis (VPA) indicated that the microbial metabolic activity of the soil was more influenced by water type (41.72%) than by seasonality (19.55%) and land use type (15.28%). The soil microbiota of the white water floodplain was different from that of the clear water and black water floodplains in terms of metabolic richness, as the white water floodplain was mainly influenced by the low substrate use during the non-flooded period. Taken together, the results show the importance of considering soils under the influence of flood pulses, water types, and land use as environmental factors when recognizing functional diversity and ecosystem functioning in Amazonian floodplains.

Keywords: Biolog ECO plates®; drought and flooding; environmental factor; functional diversity; substrate type.

Figure 1

Sampling sites in the Brazilian Amazon, land use and flood line in the three study areas seasonally flooded with “black water (A), white water (B), and clear water (C). Adapted from “Active methane processing microbes and the disproportionate role of NC10 phylum in methane mitigation in Amazonian floodplains”, by Bento et al., (2021).

Figure 2

Average well color development (AWDC) and richness of substrate use by the microbial community in floodplain Amazonian soils flooded with black water (BWF), clear water (CWF), and white water (WWF) under different land uses (FOR, forest and TFS, traditional farming system) and sampled in two seasonal periods (NF, not flooded and F, flooded) based on the use of carbon sources 168 h after incubation in BIOLOG™ EcoPlate. The bars accompanied by values indicate the value of p obtained by Mann–Whitney test.

Figure 3

AWDC and richness of substrate utilization based on the use of carbon substrates in 168 h by the microbial community in soils from Amazonian black, clear and white water floodplains. Water types are abbreviated as follows: BWF, black water floodplain, CWF, clear water floodplain, WWF, white water floodplain. Bars accompanied by values indicate the value of p obtained by the Tukey test.

Figure 4

Heatmap showing carbon utilization response for the different substrate guilds—amino acids, amines, carboxylic acids, carbohydrates, phenolic compounds, and polymers and with dendrogram of the utilization of the 31 carbon sources by the soil microbial community in different floodplain Amazonian soils. Water types are abbreviated as follows: BWF, black water floodplain, CWF, clear water floodplain, WWF, white water floodplain. The different land uses (FOR, forest and TFS, traditional farming system) and sampled in two seasonal periods (NF, non-flooded and F, flooded) based on the use of carbon sources 168 h after incubation in BIOLOG™ EcoPlate.

Figure 5

Restricted ordination diagram for the first two axes of redundancy analysis (RDA) based on soil physicochemical factors and their relationship with the utilization of carbon sources at 168 h by the microbial community at three sampling points (P1, P2, and P3) of forest sites and traditional farm systems of Amazonian floodplain river black water (in blue), clear water (in yellow) and white water (in grey) at two seasonal periods (non-flooded and flooded). The four geometric shapes represent the non-flooded forest site (inverted triangle), traditional non-flooded farming system (square), flooded forest site (circle) and traditional flooded farming system (rhombus).

Figure 6

Variance partitioning analysis (VPA) of the contribution of seasonality, land use and water type to the variation in the consumption of substrate guilds (amino acids, amines, carboxylic acids, carbohydrates, phenolic compounds, and polymers) by the microbial community in floodplain soils from different Amazonian waters.