Detecting potassium mediated drought response in oil palm (Elaeis guineensis): An isotopic study on frond bases

Abstract
Oil palm is currently the most important vegetable oil crop though increasingly suffering from
droughts as a result of anthropogenic global warming ( 1
). The mechanisms behind the witnessed
yield losses upon these droughts remain poorly understood. Stomatal closure is a known primary
drought response in plants, however, it has not previously been closely investigated in oil palm.
In dicotyldons, carbon isotope analysis is commonly used for retro-spective analysis of stomatal
conductance during a specific moment in the past however having difficulties with sub-annual
resolution. In this pilot study, the drought response of the tropical commodity crop oil palm was
investigated by an carbon isotope analysis. A novel approach was proposed to overcome the current
lack of sub-annual resolution and indistinctive annual rings by using physiological traits of the crop.
The usability of frond bases for carbon isotopes analysis as an analogue for annual tree rings was
tested by matching the time series with climate data. Herein, the isotopic signature of a severe
drought was sought and analysed in respect to the involvement of K+. The results of this study did
not follow the expected isotope pattern where a peak in isotopes was anticipated during the drought
period. Suggestions were made that this was due to utilization of non-structural carbohydrates,
alternative whole-wood components, timing of the hardening of the frond bases, exhausts of a close
by mill or local decomposition and respiration rates. The isotope analysis did reveal a response to
hydrological conditions, where higher soil water content coincided with increased discrimination
against the heavier carbon isotope. This study found 6% lower yields in the drier areas due to an El
Nino event, though general yields were comparable between the hydrological conditions. The earlier
found precipitation threshold of oil palms of 100 mm month−1 was supported by the yield numbers
in this study. Potassium revealed its importance during the drought response, though its role was
found detrimental to the palms here which could not be explained. Higher levels of K+ in the drier
areas were suggested to be due to higher levels of reactive oxygen species production in response to
the drought which in turn might have stimulated more uptake of K+.