The Effects of Fruits Load on Frond Elongation of Date Palms.

Date palms serve as an important cash crop with highly nutritive fruits and are widely cultivated in the Mediterranean region. Palm fronds synthesize carbohydrates by water and CO₂ assimilation to promote growth and bearing fruits. Daily frond elongation is affected by both fruits load and water availability. Due to high elongation rate and easy measurement of frond, a thorough comprehension of fruits load effects on frond elongation might be helpful in irrigation scheduling.

Twelve date palms, six with fruits removed (“without fruit”) and six non-thinned (“with fruits”), were irrigated with equal amounts of water at levels sufficient for maintaining optimal soil water conditions. During the measurement, rotary encoder, a cheap and easy-using electro-mechanical device, was initially utilized to measure transient frond elongation with resolution of 0.5 mm in wireless sensor network. The results showed that palms with fruits had significantly lower frond elongation rate (24 mm d^-1) than those without fruit (36 mm d^‑1). Frond elongation were minimized during daytime and mainly occurred at night. Additionally, Palms with fruits had significantly higher photosynthesis, stomata conductance and transpiration rate as compared to those without fruit, which indicated that palms with fruits synthesized more carbohydrates and consumed more water. Specifically, the temporal soil water content pattern indicated higher root water uptake under non-thinned fruits load regime. Similarly, the relative frond water potential in palms with fruits was significantly lower than those without fruit, providing facilitated water uptake due to higher water potential gradient between roots and fronds.

This study revealed behaviors of frond and soil-plant water relations under different fruits load regimes. Explicit effects of fruits load on frond elongation are beneficial to optimize irrigation management in order to improve water productivity.