Question

Leaf relative growth rate (LRGR) can be calculated using which of the following expressions?

• A. \( LRGR = \dfrac{\log LW_2 - \log LW_1}{t_2 - t_1} \)
• B. \( LRGR = \dfrac{LW_2 - LW_1}{t_2 - t_1} \)
• C. \( LRGR = \dfrac{\log LW_2 + \log LW_1}{t_2 - t_1} \)
• D. \( LRGR = \dfrac{LW_2 + LW_1}{t_2 - t_1} \)

Hint:

Remember growth analysis formulas use log-transformed weights, not raw weights.

Answer 1

The Correct Option is A

This question checks whether you know the exact shape of the relative growth rate formula when it is applied to leaf weight. Let's check each option using logic instead of just recalling the formula.

1. Option 1, LRGR = (log LW2 - log LW1)/(t2-t1): a relative rate always compares change to the starting size, and growth analysts do this by taking the log of each weight first, then finding the difference over time. This removes the effect of the leaf's actual size, which is exactly what relative growth rate means.
2. Option 2, LRGR = (LW2 - LW1)/(t2-t1): a plain weight difference over time gives the Absolute Growth Rate, which depends on leaf size and is not relative at all.
3. Option 3, LRGR = (log LW2 + log LW1)/(t2-t1): adding two logs together does not represent any change, it just gives a combined magnitude with no meaning as a rate.
4. Option 4, LRGR = (LW2 + LW1)/(t2-t1): adding raw weights and dividing by time gives a meaningless quantity, since growth is about change, not a sum.

Only option 1 uses logs to remove the effect of starting size and a difference, not a sum, to capture change over time.

Let's summarize:

• Relative growth rate uses log-transformed weights because plant growth is close to exponential.
• The rate is a difference of logs over a time difference, never a sum.

So the correct formula for LRGR is option 1.