The mean biomass per unit area and the net primary productivity for four ecosystems $P, Q, R$ and $S$ are tabulated below.



The four ecosystems most likely could be:

• A

  $\begin{array}{|l|l|} \hline \text{P: Tropical rainforest} & \text{Q: Temperate grassland} \\ \text{R: Desert} & \text{S: Algal bed} \\ \hline \end{array}$
• B

  $\begin{array}{|l|l|} \hline \text{P: Desert} & \text{Q: Tropical rainforest} \\ \text{R: Temperate grassland} & \text{S: Algal bed} \\ \hline \end{array}$
• C

  $\begin{array}{|l|l|} \hline \text{P: Algal bed} & \text{Q: Temperate grassland} \\ \text{R: Tropical rainforest} & \text{S: Desert} \\ \hline \end{array}$
• Correct answer
  D

  $\begin{array}{|l|l|} \hline \text{P: Temperate grassland} & \text{Q: Algal bed} \\ \text{R: Tropical rainforest} & \text{S: Desert} \\ \hline \end{array}$

Hence, the correct answer is option: 'D'.