Weather variables and soil moisture regime influences on stomatal conductance and leaf water potential of oil palm

Although oil palm (OP) is an important crop that occupies 10.7 million hectares in the South East-Asia, equivalent to 42.8% of the global OP coverage, information regarding weather relationship with OP gaseous exchange and photosynthetic characteristics remains scanty. This study investigated the empirical relationship between meteorological elements and stomatal conductance (STC) and leaf water potential (LWP) water stress indices in mature OP trees. The STC, LWP, meteorological elements and soil moisture content (SMC) were measured on-field and concurrently for 120 days. The best STC performance was when the relative humidity (RH) was between 98.3% to 82.6%. The STC became highest between 24.5°C to 27.6°C and lowest at 30.1°C – 32.7°C. For vapor pressure deficit (VPD), 0.06 to 1.09 kPa caused a positive response of STC, while 1.5 to 2.73 kPa limited it by 50.1%. Increased LWP was observed at 35.2°C-37.0°C, VPD of 2.6 kPa, and RH below 58.3%. The OP on clay at 91.1% SMC was lower in STC than that under sandy clay at 86.2% SMC by 16.4%. Under the highest soil wetness (91.1%-clay and 86.2%-sandy clay), the LWP of the OP was still higher in palms under clay. The SMR curve showed the clay soil to have a higher SMC across all the potentials than the sandy clay. Correlation output indicated that STC positively correlated with RH (r=0.66) and negatively with VPD. The finding disentangled key actors involved in OP gaseous exchange and inferred that OP under clay has a higher proneness to water stress.

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