Spatial characterization of photosynthetic parameters and nutrient status of oil palm, rubber, shrubs and tree species in a lowland tropical setting

Master’s thesis project announcement:
The Knohl lab in the Department of Bioclimatology (http://www.uni-goettingen.de/de/67076.html) is seeking two Masters’ students to investigate spatial characterization of photosynthetic parameters and nutrient status of oil palm, rubber, shrubs and tree species in a lowland tropical setting.


Land surface models (LSMs) often assume that the parameters related to photosynthetic capacity and foliar nutrient contents are constant for a given plant functional type and this concept is unchanged when LSMs are run at spatial scales including tropical regions. The reason can be attributed to lack of spatial data and the fact that we know little about the effects of soil texture and age of the plantation on photosynthetic capacity and foliar nutrient contents of tropical woody tree and crop species. Determining this relationship requires intensive data collection, which includes performing leaf gas exchange measurements on oil palm, rubber, shrub and forest land-use types, differing in species composition, soil fertility and plantation age. Additionally, it requires deriving photosynthetic parameters from analysis of assimilation rate vs internal CO2 concentration curves (A/Ci), and developing relationships with foliar nitrogen and phosphorus contents. Therefore, a 6-weeks field study is planned to be conducted in Jambi, Indonesia to examine how photosynthetic parameters and foliar nutrient concentrations varies under soil fertility and plantation age differences. We hypothesize that (1) oil palms have a higher leaf photosynthetic capacity than forest and rubber trees due to a higher leaf nutrient status caused by fertilizer application, (2) within forest species, (a) leaf photosynthetic capacity increases with tree diameter at breast height, (b) variation in leaf photosynthetic capacity can be better explained by the joint influences of leaf nitrogen and phosphorus than by leaf nitrogen uniquely.

In this study, we seek 2 Masters’ students, who will perform leaf gas exchange measurements in different time period (period 1: July to August, period 2: September to October).
- The student will measure leaf gas exchanges on six 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 A/Ci 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 response curves using the R statistical software. The effect of the Ci value at which the A/Ci curve switches between the Rubisco and electron transport-limited portions 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. For more information or questions about the position, please contact Ashehad Ali (ashehad.ali@uni-goettingen.de).

Supervisors:
Ashehad Ali, Christian Stiegler and Alexander Knohl

References:
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.