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

Step 1: Understanding the Concept.
Relative growth rate (RGR) is a basic idea in plant growth analysis. It tells us how fast a plant part is gaining dry weight compared to the weight it already has. When we look only at the leaf, this same idea is called the Leaf Relative Growth Rate (LRGR).

Step 2: Key Formula or Approach.
Plant growth is close to an exponential process, much like money growing with compound interest. So growth analysis formulas use natural logs of the weight readings, not the plain weight values. The general rule is \[ RGR = \frac{\log_e W_2 - \log_e W_1}{t_2 - t_1} \] where \(W_1\) and \(W_2\) are dry weights recorded at times \(t_1\) and \(t_2\).

Step 3: Detailed Explanation.
Applying the same rule to leaf weight (LW) gives \[ LRGR = \frac{\log LW_2 - \log LW_1}{t_2 - t_1} \] which matches option 1 exactly. Option 2 uses the plain difference \(LW_2 - LW_1\) with no log, so it actually gives the Absolute Growth Rate, not a relative rate. Option 3 adds the two log values instead of subtracting them, which has no real growth meaning. Option 4 adds the plain weights instead of subtracting logs, again describing something other than a relative rate.

Step 4: Final Answer.
The correct expression uses the difference of the logs of leaf weight over the time interval. \[ \boxed{LRGR = \frac{\log LW_2 - \log LW_1}{t_2 - t_1}} \]