Core conclusion from supplied evidence: Cross-study comparison is feasible but inference quality hinges on three harmonization steps: (1) unit conversion to a common basis (bulk nmol H2 h⁻¹ g⁻¹ soil, per-cell, and per-microcosm rates are reported inconsistently); (2) explicit water-potential context, since H2 uptake persists to Ψ ≈ -70 to -100 MPa with peak uptake at 15–35% saturation across temperate and arid soils ; and (3) separating gene-presence (DNA) from activity (RNA/rates), since hhyL expression explained only R² = 0.45 of oxidation-rate variation .
Recommended pipeline (Snakemake, Python3/R): (a) Ingest rate tables from each study; normalize to nmol h⁻¹ g⁻¹ dry soil; flag missing SDs/replicates. (b) Meta-regression with `statsmodels`/`metafor`-style random-effects models, moderators = water potential, SOC, temperature, aridity index. (c) Cross-validate activity inference: compare in situ field rates vs ex situ microcosms (Antarctic in situ H2 mean 0.30–0.383 nmol h⁻¹ g⁻¹ ). (d) Warming-response divergence: long-term warming increases CO/H2 sinks via higher cell numbers but reduces per-cell activity (RNA:DNA ≈ 0.22 vs 0.39 for NiFe hydrogenases) — a key blindspot if tools infer activity from MAG abundance alone. (e) Global desert context: 75 desert soils with 911 desert MAGs show widespread lithoautotrophy and trace-gas capacity (H2 consumption at 19/25 native sites) .
Inference-quality flags to encode: unit ambiguity (per-microcosm vs per-gram, e.g. warming study rates 0.72/0.076 nmol h⁻¹ per microcosm); diffusion-model assumptions (constant tortuosity); primer bias in amplicon-only studies (Namib work is 16S-based without metagenomic confirmation); and the known underrepresentation of HA-HOB in reference databases, which biases MAG-based rate inference. Confidence in pooling: moderate — high-quality single studies, but heterogeneous units, small n, and one-season temporal coverage limit a single pooled effect estimate.
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