Ecosystem — Part 2: Productivity and decomposition: visual lesson, CBSE Class 12 Biology

Lesson

Productivity and decomposition

Part 2 — how much organic matter an ecosystem makes, and how dead matter is broken down.

In this lesson you will

Define primary and secondary productivity, GPP and NPP
Calculate NPP from GPP and respiration
Describe the steps of decomposition and the factors that affect it

Concept

Primary production and productivity

Primary production is the amount of biomass or organic matter produced per unit area over a time period by plants during photosynthesis, expressed as weight (g per square metre) or energy (kcal per square metre). The rate of biomass production is productivity.

\text{Productivity units: } \mathrm{g\,m^{-2}\,yr^{-1}} \ \text{or} \ \mathrm{kcal\,m^{-2}\,yr^{-1}}

Table of productivity terms and meanings
Term	Meaning
Gross primary productivity (GPP)	Rate of production of organic matter during photosynthesis
Respiration (R)	Part of GPP used by plants themselves
Net primary productivity (NPP)	GPP − R: biomass available to consumers
Secondary productivity	Rate of formation of new organic matter by consumers

Worked example

Worked example 1: from GPP to NPP

A crop field has a GPP of 2400 kcal per square metre per year, and the plants use 900 kcal per square metre per year in respiration. Find the NPP and the percentage of GPP used in respiration.

$\text{NPP} = \text{GPP} - R = 2400 - 900 = 1500\ \mathrm{kcal\,m^{-2}\,yr^{-1}}$ .
Respiration share $= \dfrac{900}{2400} \times 100 = 37.5$ percent.
NPP is what herbivores and decomposers can use.

Worked table: NPP equals 1500
Quantity	kcal per square metre per year
GPP	2400
Respiration	900
NPP	1500

Cookies