Which finding, if true, would most directly support the researchers' …

|Question 13Verbal

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Soil thawing in Alaska has been accelerating in response to climate warming, potentially enabling increased carbon dioxide (

C O_{2}

) absorption through greater productivity of Port Clarence Indian paintbrush (Castilleja caudata) plants and other vegetation, but also potentially enabling increased

C O_{2}

output through greater heterotrophic respiration (

C O_{2}

generated by the activity of soil microorganisms). Hydrologist Yonghong Yi and her colleagues developed a model incorporating numerous inputs—years of soil moisture and snow cover data among them—to evaluate the effects of warming on the

C O_{2}

balance in Alaska, concluding that net

C O_{2}

is likely to increase if warming hastens spring snow melt.

Which finding, if true, would most directly support the researchers' conclusion?

Early snow melt slows the growth of plant species such as C. caudata by reducing soil insulation, and it suppresses heterotrophic respiration.

Early snow melt amplifies the effect of soil moisture on the growth of plant species such as C. caudata and on the rate of heterotrophic respiration.

Early snow melt reduces the amount of soil moisture available for the growth of plant species such as C. caudata, and it raises the rate of heterotrophic respiration.

Early snow melt extends the period in which plant species such as C. caudata can absorb

C O_{2}

but has no effect on the rate of heterotrophic respiration.