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MicrobiologyMicroorganisms
Peer-reviewed journal article

Impact of soil moisture on microbial diversity and their enzyme activity on agricultural soil

Kalisa Amarsingh BogatiiD, Piotr SewerniakiD, Maciej WalczakiD

Abstract

In this study, the impact of a two-month of drought stress on the microbial abundance, their enzymes and functional diversity in four agricultural soil (Gniewkowo (G), Lulkowo (L), Nieszawa (N), and Suchatowka (S) sites from Poland) was investigated during summer season. The physicochemical parameters (pH, organic carbon (C), calcium carbonate (CaCO3), total nitrogen (N), nitrate (NO3-), ammonium (NH4+), total phosphorus (P), available phosphate (P2O5)), and specific biological parameters (microbial abundance, CLPP, and soil enzymes (phosphatases (acid; ACP and alkaline; AKP), dehydrogenase (DH), and urease (UR)) were conducted on the soil samples in this study. The physicochemical and biological data were compared between zero-week (T0) and 8th week (T8) time intervals. The microbial enumeration showed higher bacterial populations (496.63 x 104 CFU g-1 dry soil) compared to actinomycetes (13.43 x 104 CFU g-1 dry soil), and lowest were the fungal population (67.68 x 102 CFU g-1 dry soil) at T8. The functional diversity showed strong positive significance in the G, N and S sites at T8. On the contrary, most of the L sites showed negative significance with the utilization of amines only, by the end of the experiment. Overall, the microbial population, their enzymes and functional diversity showed positive correlation with soil moisture content in all four investigated sites. The findings of our study indicate that soil biological activities in agricultural regions can be modified by a mere two months of drought.

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In-depth summary

✦ Multi-agent verified full-text synthesis

Claude Opus 5.5 · xhigh effort · 8 Nov 2026 · from the full text of version 1 (7 Oct 2024) · CC BY 4.0

Two months of induced summer drought in four Polish agricultural soils lowered bacterial counts, dehydrogenase activity and BIOLOG carbon-substrate use, each tracking declining soil moisture.

Drought threatens agricultural output, yet its effects on soil ecosystem resilience are rarely studied, and it is still unclear whether microbial survival depends on a particular soil water content. Extending previously published spring and autumn drought work, this summer experiment tests culturable microbial counts, enzyme activities and carbon-substrate profiles as drought indicators in four contrasting agricultural soils.

Key results

  1. ShownCulturable bacteria far outnumbered actinomycetes and fungi. Bacterial counts peaked at week 1, when moisture was highest, then fell by week 8 at every site, most sharply in the sandy Suchatówka soil. Fungi trended downward, and actinomycetes stayed broadly stable.

    Overall counts (Table 4): bacteria 496.63 x 10^4, actinomycetes 13.43 x 10^4, fungi 67.68 x 10^2 CFU g^-1 dry soil. Bacteria were highest at G (648.67 x 10^4) and about 356 x 10^4 at S and L. The bacterial decline by T8 was significant (p<0.05) at all sites. The fungal decline from T0 to T8 was significant only at G (p<0.05). · Abstract; 3.2.1 Microbial concentration

  2. ShownOf the enzymes measured, dehydrogenase activity was most affected by drying: it fell significantly from week 0 to week 8 at every site except Lulkowo. Urease instead tended to be higher at week 8, and alkaline phosphatase made up most of the phosphatase activity.

    DH decreased from T0 to T8 (p<0.05) at G, N and S, but not L. UR was lower at T0 than T8 (p<0.05 at G only) and fluctuated over weeks 1 to 4. Acid vs alkaline phosphatase shares: 6.25% vs 93.49%. Moisture fell by 88.74 - 96.91% by the end. Moisture vs enzyme Pearson r 0.02-0.99 (except UR at N8). · 3.2.2. Enzyme activities; 4.3. Impact of soil moisture on enzyme…

  3. ShownCarbon-substrate use on BIOLOG EcoPlates declined over the drought, and few substrates were still used by week 8. Gniewkowo kept the highest metabolic activity, while Lulkowo and Suchatówka showed the weakest use of particular substrate groups.

    AWCD declined from T1 to T8, at rates that differed significantly between soils. L was lowest for carboxylic/acetic acids, amino acids and amines; S was lowest for carbohydrates and polymers. Moisture vs the five substrate groups: r 0.11-0.98. Average moisture content: 4.69% (G), 5.90% (L), 8.71% (N), 5.11% (S). · 3.2.3. Analysis of soil microbial communities…; 4.4. Carbon Substrate Utilization…

  4. ShownDrying changed soil chemistry differently at each site. Phosphorus pools and nitrate shifted everywhere, carbon and nitrogen fell in the clay-richest Nieszawa fluvisol, and ammonium moved in opposite directions at Gniewkowo and Suchatówka.

    Moisture peaked at week 1 and fell most in the sandy S soil. P, P2O5 and NO3 differed between T0 and T8 at all sites (p<0.05). NH4+ fell at G and rose at S (p<0.05). Moisture vs physicochemistry: r 0.179-0.994. In the PCA, five components captured 97.5% of the variance and the first two 59.1%. · 3.1 Chemical properties of soil samples; 4.1. Soil parameters

  5. SuggestedAcross sites, culturable abundance, enzyme activities and substrate use correlated positively with soil moisture, and abundance correlated positively with enzyme activity, consistent with moisture driving biological activity. Lulkowo diverged in the enzyme and substrate PCA.

    Moisture vs microbial abundance: r 0.15-0.99. Abundance vs enzyme correlations were positive at T0 and T8. In the biological-variable PCA, five components captured 87.7% of the variance and the first two 61.7%. L samples showed no association with enzymes and a negative association with amines only. · 3.2.1 Microbial concentration; 3.2.2. Enzyme activities; 3.2.3. Analysis of soil microbial communities…; 5. Conclusions

Methods, data and reproducibility

Soil taken at 20 cm depth from four sites was kept in 20 roofed outdoor barrels through an 8-week drought in summer 2022. Physicochemistry was measured at weeks 0 and 8. Dilution-plate counts, four enzyme activities and BIOLOG EcoPlate profiles were measured at weeks 0, 1, 2, 4 and 8. Data were analyzed with two-way ANOVA, Tukey tests, Pearson correlation and PCA.

  • Gniewkowo (G) arable soil, gleyic luvisol Phaeozem, 52.901355°N, 18.432330°E, near Toruń, Poland; sampled 18th July 2022 into drought barrels · soil microbial community (bacteria, actinomycetes, fungi) · n = five barrels (weeks 0, 1, 2, 4, 8); triplicate assays
  • Lulkowo (L) arable soil, stagnic luvisol, 53.090471°N, 18.581886°E, near Toruń, Poland; sandy, low organic carbon · soil microbial community (bacteria, actinomycetes, fungi) · n = five barrels (weeks 0, 1, 2, 4, 8); triplicate assays
  • Wielka Nieszawa (N) arable soil, fluvisol, 53.006132°N, 18.466123°E, near Toruń, Poland; highest clay content · soil microbial community (bacteria, actinomycetes, fungi) · n = five barrels (weeks 0, 1, 2, 4, 8); triplicate assays
  • Suchatówka (S) arable soil, haplic luvisol, 52.907913°N, 18.468645°E, near Toruń, Poland; sandiest and most calcareous site · soil microbial community (bacteria, actinomycetes, fungi) · n = five barrels (weeks 0, 1, 2, 4, 8); triplicate assays
  • Historic Toruń humidity records (July to September 2022) from timeanddate.com, used to interpret nitrogen and moisture fluctuations
Methods & tools
Biolog EcoPlates (31 carbon sources) read on a Multiskan FC microplate reader at 590 nm, Ten-fold dilution plating on plate count, rose bengal and actinomycete isolation agars, Dehydrogenase assay (TTC reduced to triphenylformazan; Thalmann 1968), Acid/alkaline phosphatase assay with p-nitrophenyl phosphate (Tabatabai 1982), Urease assay (Kandeler and Gerber 1988), Vario Macro Cube elemental analyzer (total C and N), Olsen method (available P); Bleck method modified by Gebhardt (total P), Scheibler apparatus (CaCO3), Bouyoucos areometric method (soil texture), Merck Spectroquant Prove 100 (nitrate, ammonium), R 4.3.2 with ggplot2, Two-way ANOVA, Tukey test, Pearson correlation, PCA
Data & accessions
https://www.timeanddate.com/weather/poland/torun/historic?month=7&year=2022
Reagents & environment
R software V.4.3.2 with the ggplot2 package for statistics and visualization.
Reproducibility gaps
Study data are only available on request, and no code or data repository is given. The only URL is a third-party weather record.
Limitations (4)
  • The authors say the imposed drought may have been too short, or caused too little water loss, to shift functional diversity meaningfully. Some EcoPlate substrates (4-hydroxy benzoic acid, α-ketobutyric acid, L-phenylalanine, α-cyclodextrin) were not affected at all. · stated by the authors
  • The authors note that large information gaps remain and suggest meta-analysis or advanced molecular techniques, plus finer study of microbial dynamics across aggregate sizes and preferential flow paths, to better resolve drought responses. · stated by the authors
  • No well-watered control barrels are described, so drought effects are confounded with elapsed time and summer conditions. Moisture-biology links rest on Pearson correlations reported as ranges (down to r= 0.02), with no per-test p-values or multiple-testing correction. · noted in this summary
  • The text contradicts itself: the results report a significant bacterial decline at all sites, but the discussion says bacteria were unaltered. The same PCA variance values (87.7%, 61.7%) are given for three variable sets, and the figure legends cite one-way ANOVA where the methods say two-way. · noted in this summary

Who should read:Read this if you study how drought reshapes agricultural soil microbiology and want culture-based counts, enzyme assays and BIOLOG profiles from a summer barrel-drying experiment on four Polish soils.

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