The effects of watering on cambial activity in the stems of evergreen hardwood ( Samanea saman ) during the pre-monsoon season in subtropical Bangladesh

Water stress has a significant impact on tree growth. However, the effects of watering on cambial activity and its influence on tree growth in subtropical climates is poorly understood. The present study analyzed the cambial activity on the stem of evergreen hardwood Samanea saman in response to either high frequency or low frequency watering during the pre-monsoon season in subtropical Bangladesh. We used two groups of seedlings: one group of seedlings was watered daily (high frequency watering), while the second group of seedlings was watered at 4–5-day intervals (low frequency watering). Samples for sequential observations of cambial activity by microscopy were collected from the main stems of seedlings of both groups. At the start of the experiment on March 25, 2015, during the pre-monsoon season, the cambium was inactive with no evidence of cell division. After 10 days of high frequency watering, cambial cell division and xylem differentiation were initiated. New cell plates were formed in the phloem side of the cambium. However, the cambium was inactive when low frequency watering was supplied. Supplying water in high frequency reactivated the cambium with forming small to large vessels. In contrast, the cambium remained inactive when low frequency watering was supplied throughout the experiment. These results suggest that continuous supply of water to the soil is one of the most important factors for cambial reactivation during pre-monsoon season in subtropical trees. Furthermore, our findings of artificial watering treatments might help to better understand the response of cambium to changes in precipitation patterns under natural conditions, allowing us to learn more about how cambium of subtropical trees responds to climate change.