Question1-EE2

Three Components of Plant Respiration

Growth Respiration, Maintenance Respiration, and Ion Uptake Respiration

Growth Respiration

• Purpose: Energy required to synthesize new tissues.

• Occurs when: Plants build leaves, stems, roots, reproductive structures.

• Cost driver: Chemical construction cost of molecules (e.g., lignin vs. sugars).

Proportional to: Amount of biomass produced.

Maintenance Respiration

• Purpose: Keeps existing tissues alive.

• Includes: Ion transport, protein turnover, membrane repair, phloem loading.

• Influenced by: Temperature, tissue nitrogen content, tissue age.

• Occurs continuously, even without growth.

Ion Uptake Respiration

• Purpose: Active transport of nutrients into roots.

• High when: Nutrients are scarce or soils are cold (slower diffusion).

• Energetically expensive because it requires ATP to move ions against gradients.

Sugars and starch construction costs

Low

because simple chains, high in fast growing plants

proteins and lipids construction costs

High

because energy dense, reduced nitrogen and carbon

Lignin and cellulose

Highest, very high

because complex, many bonds

Plants with ___ lignin or ____ carbon have higher growth respiration costs because these molecules are expensive to build.

high, structural

High SLA plants

Thin, soft leaves; fast-growing species, more stomata, more photosynthetic rate

Low SLA plants

Thick, tough leaves; slow-growing species.

High SLA also have

• High nitrogen content → high respiration rate.

• Low construction cost (less lignin).

• High whole-plant respiration because they also have:

  • High root uptake respiration

  • High photosynthesis

Low SLA also have

• Low nitrogen → lower respiration.

• High construction cost (more lignin).

• Lower whole-plant respiration because tissues last longer and roots are less metabolically active.