Question

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

Ecosystem	Mean biomass per unit area (kg $m^{-2}$)	Net primary productivity (g $m^{-2}y{r}^{-1}$)
P	$1.6$	$500$
Q	$2.0$	$2000$
R	$44$	$2000$
S	$0.67$	$71$

The four ecosystems most likely could be.

• A. P: Tropical rainforest, Q: Temperate grassland, R: Desert, S: Algal bed
• B. P: Desert, Q: Tropical rainforest, R: Temperate grassland, S: Algal bed
• C. P: Algal bed, Q: Temperate grassland, R: Tropical rainforest, S: Desert
• D. P: Temperate grassland, Q: Algal bed, R: Tropical rainforest, S: Desert

Answer 1

The correct option is D P: Temperate grassland, Q: Algal bed, R: Tropical rainforest, S: Desert

Net primary productivity is the amount of carbon used after respiration from gross primary productivity. Based on net primary productivity, ecosystems may be grouped into following types:
1. High productive ecosystems: Net productivity is about 2000-4000 g m⁻² yr⁻¹. For example, tropical rainforests, coral reefs, estuaries etc.
2. Average productive ecosystems: Net productivity is about 1000-2000 g m⁻² yr⁻¹ with a daily output of 3-5 g m⁻². For example, temperate forests.
3. Less productive ecosystems: Net productivity is about 200-1000 g m⁻² yr⁻¹ with a daily output of about 0.5-3.0 g m⁻². For example, grassland ecosystems and savanna.
4. Low productive ecosystems: Net productivity is less than 200 g m⁻² yr⁻¹ . For example, desserts.
Based on this data, P should be temperate grassland , Q should be algal bed, R should be tropical rainforest and S should be desert.
NPP for both Q and R is same i.e., 2000 g m⁻² yr⁻¹ since the mean biomass is more for R, it indicates that R is tropical rainforests as these are the most productive ecosystems.
So, the correct answer is D.