Height-related changes in stomatal conductance, chlorophyll Content index and diameter of rubber tree (Hevea brasiliensis) saplings

This study aimed at investigating the influences of tree height on the physiology of rubber tree (Hevea brasiliensis) saplings specifically its relationships with stomatal conductance, chlorophyll content index and diameter. A total of 50 rubber tree saplings were sampled in five growth stages (i.e, 45, 90, 135, 180 and 225 days). The means of rubber tree saplings height were 19cm, 46cm, 81cm, 135cm and 194cm, respectively. Measurements for stomatal conductance and chlorophyll content index were taken from 07:30 to 13:00 hours with the recorded air temperature range from 25°C to 35°C. The stomatal conductance and chlorophyll content index were measured using leaf porometer and chlorophyll meter (SPAD 502 plus), respectively. Stem diameter was measured using a digital caliper while height was measured using a measuring tape. Correlation analysis indicated that there was a significant inverse relationship between the height and stomatal conductance (r=−0.47, p≤0.0001). In contrast, the chlorophyll content index showed a significant positive relationship with height (r=0.55, p≤0.0001) which suggests that the increase in chlorophyll content index contributes to the increment of height of tree saplings. Meanwhile, there was a strong positive relationship between height and diameter (r=0.903, p≤0.0001) which indicates the presence of development in apical and lateral growth in rubber plants. Future work will involve an evaluation of the three variables measured above as predictor variables for the development of carbon sequestration model.