What percentage of the total global carbon is contained in the atmosphere (in $, \%$)?

$A$: Agriculture and aquaculture are man-maintained ecosystems.
$R$: All biotic and abiotic factors are managed by humans in these ecosystems.

Which one of the following statements is correct for secondary succession?

Out of the total cost of various ecosystem services, the soil formation accounts for $P$, while contributions of other services like recreation and nutrient cycling are less than $Q$ each. The value of climate regulation and habitat for wildlife is about $R$ each. Identify $P, Q,$ and $R$.

Outline the salient features of carbon cycling in an ecosystem.

Which of the following ecosystems would be most stable?