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

|Question 12Verbal

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Growing seasons in Alaska have been extending further into the year as a result of climate changes, potentially enabling increased carbon dioxide (

C O_{2}

) absorption through greater productivity of marsh cinquefoil (Comarum palustre) 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 solar radiation and snow cover data among them-to evaluate the effects of climate changes on the

C O_{2}

balance in Alaska, concluding that net

C O_{2}

is likely to increase if seasonal snow cover arrives earlier relative to the onset of soil surface freezing.

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

The effect of solar radiation on the growth of vegetation and on the rate of heterotrophic respiration is stronger during the period of seasonal snow cover than during the period without snow cover.

Relatively early snow cover reduces the amount of soil moisture available for the growth of plant species such as C. palustre and lowers the rate of heterotrophic respiration.

Seasonal snow cover tends to persist longer in areas of relatively low vegetation growth and high heterotrophic respiration than in areas of relatively high vegetation growth and low heterotrophic respiration.

The soil insulation provided by snow cover enables heterotrophic respiration to continue during a period in which plant species such as C. palustre are typically not growing.