Question 12: What will be the P/R ratio of a climax community and a pioneer community. What explanation could you offer for the changes seen in P/R ratio of a pioneer community and the climax community.
Answer:
Productivity is defined as the rate of formation of biomass in an ecosystem which is usually expressed in the unit of mass per unit area per unit time. Productivity is different from biomass as productivity is the rate at which organic matter is created by the producers whereas biomass is the amount of organic matter present at any given time which is generally expressed in wet and dry terms. In the P/R ratio P is the productivity and R is the respiration. In this the total rate of photosynthesis, including the biomass that used in respiration process during the measurement is known as Gross Primary Productivity (GPP). And, the rate of storage of biomass in the plants which exceeds the respiratory use by them is known as Net primary Productivity (NPP). This can be described as following equation:
NPP (Net primary Productivity) = GPP (Gross Primary Productivity) - R (Respiration by autotrophs)
So, according to the community energetics attribute the P/ R ratio (shows the relationship between gross production and community respiration) in the early successional species or pioneer stage or species will be greater or less than 1 and in late successional or at the climax stage, this ratio will approaches 1.
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