0.00327
g/cm²/day
32.72
g/m²/day
0.00327
g/cm²/day
32.72
g/m²/day
The Net Assimilation Rate (NAR) Calculator computes the rate of dry mass increase per unit leaf area per unit time. NAR is a key component of classical growth analysis that measures the net photosynthetic productivity of leaves, accounting for both carbon gain and respiratory losses. It bridges whole-plant growth and leaf-level physiology, providing insight into how efficiently a plant's leaves convert light energy into new biomass.
Enter the initial and final dry masses, initial and final leaf areas, and the time interval. The calculator returns NAR in both g/cm²/day and g/m²/day, the standard units used in growth analysis literature.
The calculator uses the classical NAR formula from plant growth analysis:
NAR = ((W₂ - W₁) x (ln LA₂ - ln LA₁)) / ((LA₂ - LA₁) x (t₂ - t₁))
Where W is whole-plant dry mass, LA is total leaf area, and t is time. This formula assumes that leaf area changes exponentially over the measurement interval. The logarithmic correction accounts for the fact that average leaf area over time is better represented by the logarithmic mean than the arithmetic mean when leaf area is increasing.
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Results
A plant growing from 10 to 25 g with leaf area expanding from 200 to 500 cm² over 14 days has an NAR of about 32.7 g/m²/day.
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Results
A shade plant growing modestly over 21 days shows a lower NAR of about 7.8 g/m²/day.
In classical growth analysis, RGR can be decomposed as RGR = NAR x LAR, where LAR is the Leaf Area Ratio (leaf area per unit plant mass). NAR represents the efficiency of carbon gain per unit leaf area, while LAR represents how much leaf area the plant deploys per unit of its own mass. Plants can achieve the same RGR through different combinations of NAR and LAR.
NAR values typically range from 2-10 g/m²/day for shade-tolerant species to 10-25 g/m²/day for crop plants and fast-growing herbaceous species under favorable conditions. C4 plants (like maize and sugarcane) often have higher NAR than C3 plants due to their more efficient photosynthetic pathway. NAR tends to decrease as plants grow and mutual shading of leaves increases.
When leaf area is changing exponentially, the simple arithmetic mean underestimates the average leaf area over the interval. The logarithmic formula ((LA₂ - LA₁) / (ln LA₂ - ln LA₁)) gives the correct mean leaf area under exponential growth assumptions. This correction becomes more important when the difference between LA₁ and LA₂ is large relative to their values.
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