Which of the following elements has a much lower atmospheric input compared to carbon?

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

$A$ farmer harvests his crop and expresses his harvest in three different ways.
$(a)$ $I$ have harvested $10$ quintals of wheat.
$(b)$ $I$ have harvested $10$ quintals of wheat today in one acre of land.
$(c)$ $I$ have harvested $10$ quintals of wheat in one acre of land,$6$ months after sowing.
Do the above statements mean one and the same thing? If your answer is yes,give reasons. If your answer is 'no',explain the meaning of each expression.

Plant succession occurring in a sandy area is known as:

Which of the following is an abiotic component of an ecosystem?

Identify the pioneer species that colonize bare rock.