Photosynthetic characteristics and nutrient status of oil palm under different fertilizer management regimes

Better management of soil nitrogen fertilizer is important for not only improving oil palm productivity but also for minimizing the environmental impacts through reduced soil nutrient losses (Pardon et al. 2016). Incorporating this trade-off in land surface models (LSMs) that consider management impacts on ecosystem carbon and water fluxes would be invaluable; however, LSMs require parameter estimates of leaf photosynthesis and transpiration for diagnostic and modeling purposes. Therefore, a 3-week field study is planned to be conducted to investigate the effect of different nitrogen fertilizer management regimes (reduced herbicide and fertilizer application) on the photosynthetic characteristics and nutrient status of oil palm. In addition to the standard photosynthetic measurements, temperature response curves of leaves of oil palm will be measured. This additional measurement will enable us to examine the optimal temperature for leaf photosynthesis and assess how it compares with managed and unmanaged plots. The measurements will be performed in the oil palm management experiment ( in Jambi, Indonesia. Current results indicate that reduced intensity of fertilizer and herbicide application does not have much impact on the yield of oil palm. Thus, we hypothesize that the leaf nutrient contents and photosynthetic capacity of oil palm are not much affected by management. In this study, a master’s student will perform leaf gas exchange measurements in the managed and unmanaged oil palm plots.
• The student will measure leaf gas exchanges on five different leaves from the top of the canopy. Before gas exchange measurements, branches will be cut, gently lowered to the ground with ropes and recut under water within 15 min (Albert et al. 2018) to avoid water stress. The measurements for carbon dioxide (A/Ci) and temperature (A/T) response curves will then be carried out. After the measurements, leaf-lets will be punched to obtain disks, which will be used for determining nitrogen, phosphorus and carbon contents of leaves. Every leaf-let will be packed together with its corresponding disk and brought to the University of Goettingen for further analysis.
• The student will carry out analysis and interpretation of the A/Ci and A/T response curves using the R statistical software. The effect of the Ci value at which the A/Ci curve switches between the Rubisco (Vcmax) and electron transport-limited portions (Jmax) of the curve will also be examined.
• The student will have the opportunity to contribute to a scientific publication.
The ideal candidate will have interests and motivation in forest ecology and plant ecophysiology, and eager to learn measurements using a portable photosynthetic system (LiCOR 6800). Interest/knowledge of programming skills (e.g. R) is an advantage.

Albert LP, Wu J, Prohaska N, Camargo PB de, Huxman TE, Tribuzy ES, Ivanov VY, Oliveira RS, Garcia S, Smith MN, Junior RCO, Restrepo‐Coupe N, Silva R da, Stark SC, Martins GA, Penha DV, Saleska SR (2018) Age-dependent leaf physiology and consequences for crown-scale carbon uptake during the dry season in an Amazon evergreen forest. New Phytologist 219:870–884.

Pardon L, Bessou C, Nelson PN, Dubos B, Ollivier J, Marichal R, Caliman J-P, Gabrielle B (2016) Key unknowns in nitrogen budget for oil palm plantations. A review. Agronomy for Sustainable Development 36:20.

Supervisors: Ashehad Ali, Christian Stiegler and Alexander Knohl