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California Grassland Precipitation Legacy Soil Community

Community ID CommunityMech:000215
Ecological State PERTURBED
Environment California Mediterranean-climate grassland soil — ontology label: grassland soil
ENVO:00005750 · HabitatMech ↗

A semiarid California Mediterranean-climate grassland soil microbial community studied under two field-imposed precipitation regimes (100 percent versus 50 percent of mean annual precipitation) and assayed during the first autumn rewet. Quantitative H2-18O stable-isotope-probing, 16S rRNA amplicon sequencing, metagenomics, and metatranscriptomics revealed that reduced winter precipitation imposed a lasting legacy on community turnover: microbial growth declined by about one order of magnitude and mortality by about two orders of magnitude relative to ambient plots, lowering community growth efficiency (new biomass growth divided by respiration). Soil organic carbon shifted from microbial-necromass-derived lipid-, amino-sugar-, and protein-like compounds toward more oxidized lignin- and tannin-like plant detritus compounds. Meta-omics linked high-CGE communities to N-rich necromass consumption with elevated amino acid and peptidoglycan biosynthesis and aromatic compound degradation, while low-CGE communities had elevated carbohydrate metabolism and lipid turnover consistent with plant-detritus processing and membrane maintenance.

Taxonomy

Taxon Ontology ID Functional Roles Abundance
grassland soil bacteria — ontology label: Bacteria NCBITaxon:2 · TaxonMech · TraitMech
PRIMARY_DEGRADER SECONDARY_FERMENTER
DOMINANT
  • PMID:41964077 - SUPPORT (IN_VIVO)
    "measured microbial growth and mortality via quantitative 18O stable isotope probing and 16S rRNA gene amplicon sequencing"

Ecological Interactions

The graph shows only explicitly linked interaction participants. Community members without an asserted participant link are omitted; membership alone does not imply an interaction.

Ecological interaction network for California Grassland Precipitation Legacy Soil Community Bipartite graph where circles represent taxa and non-circular symbols represent interactions. Rare or untyped interactions share the Other symbol; exact curated types remain in the interaction details.
Taxon
Other

Necromass Recycling at High Community Growth Efficiency

HYPOTHESIZED - higher source-defined community growth efficiency was associated with amino-acid/peptidoglycan biosynthesis and aromatic-degradation transcripts, interpreted as greater necromass recycling. Formula-class and transcript patterns do not identify transferred molecules or measure those pathway fluxes.

Metabolites: amino acid (CHEBI:33709 · MediaIngredientMech · CMMMech), peptidoglycan (CHEBI:8005 · MediaIngredientMech · CMMMech)

Biological Processes:

Evidence

  • PMID:41964077 - PARTIAL (IN_VITRO)
    "microbes appeared to consume more energetically favorable N-rich necromass"
  • PMID:41964077 - PARTIAL (IN_VITRO)
    "increased amino acids and peptidoglycan biosynthesis and greater aromatic compound degradation"

Plant Detritus Degradation at Low Community Growth Efficiency

HYPOTHESIZED - carbohydrate/lipid-associated transcription at lower relative community growth efficiency was interpreted as allocation toward plant detritus use and maintenance. These associations are not measured substrate-specific degradation or membrane-repair fluxes.

Biological Processes:

Evidence

  • PMID:41964077 - PARTIAL (IN_VITRO)
    "communities had elevated carbohydrate metabolism and lipid turnover"
  • PMID:41964077 - PARTIAL (IN_VITRO)
    "increased investment in plant detritus degradation and membrane repair and maintenance rather than growth"

Precipitation-Legacy Turnover Suppression

After one winter rainfall-treatment season, laboratory-rewetted soil showed lower bacterial/archaeal qSIP growth and mortality estimates under reduced-precipitation history. CO2 differences were nonsignificant, not equivalent. CGE is cumulative new biomass divided by cumulative CO2 and scaled to the observed maximum, not absolute carbon-use efficiency or measured long-term soil-carbon loss.

Metabolites: water (CHEBI:15377 · MediaIngredientMech · CMMMech)

Downstream Effects:
→ Necromass Recycling at High Community Growth Efficiency

HYPOTHESIZED - lower mortality could reduce necromass supply and recycling after rewetting. This source interpretation is not traced transfer or experimentally isolated mediation.

→ Plant Detritus Degradation at Low Community Growth Efficiency

HYPOTHESIZED - reduced turnover and associated transcription could shift resource allocation toward detritus use and maintenance. Shared treatment responses do not establish this pathway as the cause.

Evidence

  • PMID:41964077 - SUPPORT (IN_VITRO)
    "microbial growth declined by ~1 order of magnitude, yielding decreased community growth efficiency"
  • PMID:41964077 - SUPPORT (IN_VITRO)
    "microbial mortality declined by ~2 orders of magnitude"

Knowledge gaps & discussions (1)

KNOWLEDGE_GAP OPEN Do direct substrate tracing and resolved turnover measurements validate the proposed recycling and allocation mechanisms?

PMID:41964077 uses interval-average 16S qSIP estimates and relative CGE after laboratory wet-up. Fungal turnover, identified metabolites, equivalence of CO2 output and multiyear carbon-stock change are not established. Preserve both source-proposed arrows as hypotheses; non-graph protocol wording remains outside this draft.

Attaches to: ecological_interactions#Necromass Recycling at High Community Growth Efficiency, ecological_interactions#Plant Detritus Degradation at Low Community Growth Efficiency, ecological_interactions#Precipitation-Legacy Turnover Suppression

External Resources

Name Repository Resource ID
Primary publication for the California grassland precipitation legacy community
PubMed record for the Hernandez et al. 2026 Microbiome paper on precipitation-legacy effects on grassland soil microbial community growth efficiency. 		OTHER PMID:41964077
  • PMID:41964077 - SUPPORT (IN_VIVO)
    "reduced winter rainfall decreases microbial turnover following rewetting without a concurrent reduction in CO2 emissions"
DOI landing page
DOI link to the Microbiome paper. 		OTHER doi:10.1186/s40168-026-02395-9

Environmental Factors

Factor Value Unit
Imposed precipitation regime 100 percent vs 50 percent mean annual precipitation N/A
  • PMID:41964077 - SUPPORT (IN_VIVO)
    "two precipitation regimes (100% vs. 50% mean annual precipitation)"
Autumn rewetting with H2-18O laboratory rewet with isotopically labeled water N/A
  • PMID:41964077 - SUPPORT (IN_VIVO)
    "soils were rewetted in the laboratory with H218O and sampled at 0 h, 3 h, 24 h, 48 h, 72 h, and 168 h post rewet"
Soil organic carbon composition shift necromass-like to plant-detritus-like compounds N/A
  • PMID:41964077 - SUPPORT (IN_VIVO)
    "shifted from lipid-like, amino-sugar-like, and protein-like compounds (indicative of microbial necromass) to more oxidized lignin-like and tannin-like compounds (indicative of decomposing plant-derived compounds)"

Growth Media

rewetted Hopland grassland topsoil, labelled with 98-atom% H2-18O (or natural-abundance water as control)

Preparation notes: Roots removed and soil sieved to 2 mm before use. The wet-up is the experiment: 1 mL of 98-atom% H2-18O (or natural-abundance water for controls) was pipetted evenly onto 5 g of soil and mixed, taking it from 3% to an average 22% gravimetric moisture. 88 microcosms in total. The soil is substrate and inoculum together, so there is no formulated medium. Held at ROOM TEMPERATURE, which the source does not quantify, so `temperature` is left unset rather than assigned a conventional 20-25 C. No pH or atmosphere is reported: the jars were sealed with air headspace for CO2 accumulation, which is not a defined gas mix, so `atmosphere` and `headspace_gas` are also unset.

Evidence

PMID:41964077

"This field site is at the Hopland Research and Extension Center (HREC) located in Northern California (39° 00′ 14.6″ N, 123° 05′ 09.1″ W) on territory originally occupied by the indigenous Pomo Nation."

PMID:41964077

"In August 2018, at the end of the summer dry-down when the gravimetric soil moisture was 3%, topsoil samples (0–15 cm, approximately 4700 cm3) were collected from eight plots (n = 4 each for 50 and 100% MAP; total of 48 samples) with cleaned shovels"

PMID:41964077

"immediately placed into jumbo-sized Ziplock bags, and transferred to Lawrence Livermore National Laboratory where roots were removed and soils were homogenized by sieving (2 mm) to remove rocks and large plant debris in a greenhouse with a dry and hot atmosphere."

PMID:41964077

"Briefly, 5 g of sieved soil from each of the 8 plots was transferred each to 11 Nalgene flat bottom vials (15 mL) for a total of 88 microcosms."

PMID:41964077

"One milliliter of isotopically enriched water (98-atom H218O) or natural abundance water (control) was slowly and evenly pipetted onto the soil and gently mixed with the pipette tip, resulting in a final average gravimetric soil moisture of 22%."

PMID:41964077

"Two vials each were then immediately sealed inside a 500-mL mason jar with lids fitted with septa (to facilitate headspace sampling) and incubated at room temperature in the dark."

Cross-Mech Suite Links

Explore related entities across the CultureBotAI X-Mech knowledge bases:

HabitatMech: California Mediterranean-climate grassland soil ↗ TaxonMech: grassland soil bacteria ↗ TraitMech: grassland soil bacteria ↗ CultureMech Growth Media ↗ PathwayMech Pathways ↗