Difference Between Net Primary And Gross Primary Productivity

In ecology, Primary Productivity is the rate at which biomass is produced by organisms which converts inorganic substrates into complex organic substances. Biomass is simply the amount of matter that’s stored in the bodies of a group of organisms. Productivity can be defined for any trophic level or other group, and it may take units of either energy or biomass.

Primary production typically occurs through photosynthesis; when greenplants convert solar energy, carbon dioxide, and water to glucose, and eventually to plant tissue. It also refers to the rate at which some organisms like. Bacteria that thrive in deep sea convert chemical Energy to biomass through chemosynthesis. There are two basic types of productivity:

• Gross Primary Productivity
• Net Primary Productivity

A high primary productivity rate in the ecosystems is obtained when the physical factors (for instance: water, nutrients and climate) are favourable. The presence of some forms of secondary energy can also help to increase the primary productivity rate.

What Is Gross Primary Productivity (GPP)?

Gross primary productivity is the amount of carbon fixed during photosynthesis by all producers in the ecosystem. GPP can also be described as the rate of production of organic matter during photosynthesis. 

In other words, Gross primary productivity, or GPP, is the rate at which solar energy is captured in sugar molecules during photosynthesis (energy captured per unit area per unit time). Producers such as plants use some of this energy for metabolism/cellular respiration and some for growth (building tissues).

Every autotroph in the environment which is considered for the measurement and calculation are the producers of GPP (Gross Primary Production/Productivity) and are the part of the ecosystem. The calculations of GPP include the energy which is used in other activities, including respiration energy too.

How is GPP Calculated?

Given that GPP (Gross primary production) is the total biological productivity of an ecosystem. The formula for calculating GPP will be:

GPP=NPP +RR

Where,
NPP= Net primary productivity
GPP= Gross primary productivity
RR= Respiratory Rate

If the GPP (Gross Primary Production/Productivity) is decreased because of any reasons, The NPP (Net Primary Product) will also be decreased in the same manner. GPP (Gross Primary Production/productivity is dependent on the producers.

What you need to know about GPP

• GPP refers to the amount of organic substance synthesized by the producers in unit time per unit area.
• It describes how much glucose is produced during photosynthesis.
• The value of GPP is always comparatively higher.
• GPP (Gross Primary Production) is completely dependent on chlorophyll.
• GPP (Gross Primary Production) is directly linked to the producers.
• When it comes to GPP (Gross Primary Production), NPP (Net Primary Product) does not affect it at all.
• The calculations of GPP includes the energy which is used in other activities, including respiration energy.

Also Read: Difference Between Primary And secondary succession

What Is Net Primary Productivity (NPP)?

Net primary productivity is s the difference of the energy that’s fixed by the autotrophs and their own respiration losses. It is the rate at which an ecosystem accumulates energy or biomass excluding the energy it uses for the process of respiration. In other words, it’s the rate at which energy is stored as biomass by plants or other primary producers and made available to the consumers in the ecosystem. This typically corresponds to the rate of photosynthesis, minus respiration by the photosynthesizers.

Net primary productivity varies among ecosystems and depends on many factors. These include solar energy input, temperature and moisture levels, carbon dioxide levels, nutrient availability, and community interactions (e.g., grazing by herbivores). These factors affect how many photosynthesizers are present to capture light energy and how efficiently they can perform their role.

How is NPP calculated?

From the definition of NPP, it typically corresponds to gross primary productivity minus the rate of energy loss to metabolism and maintenance. 

NPP= GPP- RR

Where,
NPP= Net primary productivity
GPP= Gross primary productivity
RR= Respiratory Rate

• This formula is important as it diligently associates GPP to NPP and also makes the metabolic losses and respiratory losses of autotrophs/producers count.
• Generally, NPP is calculated and measured at the level/scale of “ecosystem” and over relatively longer frames/intervals of time(such as a year/s).

What you need to know about NPP

• NPP refers to the amount of organic substance stored by autotrophs or producers in unit time per unit area.
• It describes how much glucose is produced excluding the amount of energy utilized for respiratory processes.
• The value of NPP is always comparatively lower.
• NPP (Net Primary Product) does not depend on or affected by Chlorophyll content.
• NPP (Net Primary Product) is directly linked to the consumers.
• NPP (Net Primary Product) is calculated from the GPP (Gross Primary Production), therefore GPP (Gross Primary Production) affects the NPP (Net Primary Product).
• Net Primary Production (NPP) = the Gross Primary Production (GPP) minus Respiration (R).

Also Read: Difference Between Autotrophs And Heterotrophs

NPP vs GPP In Tabular Form

References

• Diaz S. (2013). Ecosystem Function Measurement, Terrestrial Communities. Encyclopedia of Biodiversity (Second Edition), 72-89.
• DellaSala D.A. (2021). Imperiled Terrestrial Ecosystems: Nature in Retreat. Reference Module in Earth Systems and Environmental Sciences. https://doi.org/10.1016/B978-0-12-821139-7.00089-1
• lark, D.A.; Brown, S.; Kicklighter, D.W.; Chambers, J.Q.; Thomlinson, J.R.; Ni, J. (2001). “Measuring net primary production in forests: Concepts and field methods”. Ecological Applications. 11 (2): 356–370. doi:10.1890/1051-0761(2001)011[0356:MNPPIF]2.0.CO;2. ISSN 1051-0761
• Sigman, D.M.; Hain, M.P. (2012). “The Biological Productivity of the Ocean” (PDF). Nature Education Knowledge. 3 (6): 1–16.
• Wright R.T., Boorse D.F. Environmental Science: Toward a Sustainable Future (11th Edition) 11th Edition. ISBN-13: 978-0321598707