Productivity is the rate at which biomass is generated in an ecosystem. Because it is a rate, the unit must include both an area (or volume) term and a time term.

Standard expressions are $\text{g}{\text{m}}^{-2}{\text{yr}}^{-1}$ or $(\text{KCal}{\text{m}}^{-2}){\text{yr}}^{-1}$, which allow direct comparison of productivity across ecosystems.

$\therefore$ Option (1) is correct.