= D. M. Linn
{c}
<D. M. Linn> is the first author credited in the 1984 soil study with <J. W. Doran> that related <water-filled pore space> to microbial activity. The researchers examined <carbon dioxide> production, oxygen uptake and <nitrous oxide> production in samples from different tillage settings.<Effect of Water-Filled Pore Space on Carbon Dioxide and Nitrous Oxide Production in Tilled and Nontilled Soils by D. M. Linn and J. W. Doran>[Original byline; Abstract, measured responses]{ref}
The motivating idea was to relate activity to the fraction of pore volume occupied by <water>, rather than to water amount alone. This connects a biological rate to the <soil>'s available pore space. The reported aerobic maximum near sixty percent <water-filled pore space> describes the study's conditions and should not be converted into a universal optimum for every soil or microbial process.<Effect of Water-Filled Pore Space on Carbon Dioxide and Nitrous Oxide Production in Tilled and Nontilled Soils by D. M. Linn and J. W. Doran>[Abstract, laboratory response and tillage comparison]{ref}
A constructed example illustrates rate normalization. Suppose a sample containing $50\,\mathrm g$ dry soil produces $20\,\mu\mathrm{mol}$ <carbon dioxide> in eight hours. Its average production rate per dry mass is
$$
\frac{20\,\mu\mathrm{mol}}{50\,\mathrm g\times8\,\mathrm h}=0.05\,\mu\mathrm{mol\,g^{-1}\,h^{-1}}.
$$
A second sample producing $40\,\mu\mathrm{mol}$ from $100\,\mathrm g$ over the same interval has the same normalized rate. Twice as much collected gas does not establish twice the activity per unit mass.
Linn and Doran's contribution shows why both environmental state and measurement normalization matter. <Water-filled pore space>, dry soil mass and elapsed time are different parts of the experimental description; none can replace the others. Establishing which comparison is meaningful is part of explaining the biology, rather than merely formatting its numerical results.
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