A research team is studying the effects of three different fertilizers (X, Y, and Z) on the growth of a specific plant species. They have four experimental plots with different fertilizer combinations:

• Plot 1: Fertilizer X only
• Plot 2: Fertilizer Y only
• Plot 3: Fertilizer X and Fertilizer Z only
• Plot 4: Fertilizer Y and Fertilizer Z only

After a period of observation, they note the following:

• Plants in plots with Fertilizer X showed significantly increased height compared to a control group (no fertilizer).
• Plants in plots with Fertilizer Y showed a slightly increased leaf area compared to the control group.
• Plants in Plot 3 (X and Z) showed no significant difference in height compared to the control group.
• Plants in Plot 4 (Y and Z) showed significantly increased height compared to the control group.

Based on these observations, which of the following conclusions is best supported?