PARENT SESSION
Oral Session # 72: GIS and Remote Sensing I.
Presiding: J Drake
Thursday, August 7. 8:00 AM to 11:30 AM, SITCC Meeting Room 203.

Hyperspectral imaging serves as a powerful tool to monitor the spatio-temporal dynamics of photosynthesis within a drought-stressed tropical canopy.

Rascher, Uwe¹, ¹ Biosphere 2 Center, Oracle, AZ, USA

ABSTRACT- Thus far, the spatio-temporal dynamics of photosynthetic light use efficiency of complex canopies cannot be quantified non-destructively by passive, remote sensing techniques. However, hyperspectral imaging techniques and indices derived thereof have the potential for large scale ecosystem monitoring and can be closely linked to photosynthetic electron transport. The tropical rainforest within the Biosphere 2 Laboratory provides an ideal testbed for hyper-spectral instrumentation and can deliver data from complex canopy structures. A new field portable hyperspectral imaging device proofs a detectable change in the reflectance signature from a complex tropical canopy, which was subjected to a mild, prolonged drought. Ecosystem carbon balance responded to drought. The effects occurred within days and the changes were reversible within weeks. Reduced gross photosynthetic production (GPP) was off-set by reduced soil respiration, leaving the 24 hour net ecosystem exchange almost unaffected. The reduction of GPP reflects two underlying mechanisms: (i) an increased leaf-fall during the first days of the drought, which resulted in decreased foliage coverage of the canopy and (ii) reduced maximum photosynthetic electron transport rate, which was recorded on 50 different leaves using chlorophyll fluorescence techniques. Both effects, were also detected within the hyperspectral reflectance images of the canopy. Moreover, the canopy was not affected uniformly. Patches of the canopy responded more strongly than others, which can be deducted from the hyperspectral images and also from simultaneously performed leaf level measurements. Indices, such as the photosynthetic reflectance index (PRI), were used to quantify those spatio-temporal effects.

Key words: chlorophyll fluorescence, hyperspectral reflectance imaging, spatio-temporal dynamics, tropical canopy