Introduction Materials and methods Conclusions • On well-drained clays, 60% of a Central Amazon forest’s upper canopy crowns exhibited massive leaf flush; • Within these 60% , most turned over their leaves in the five driest months, possibly a strategy to protect young vulnerable leaves from pathogens and herbivores; • This behavior causes a strong seasonal fluctuation in the abundance of healthy efficient leaves, 3-8 months of age, coincident with seasonal fluctuation of landscape-scale photosynthesis and photosynthetic capacity. Bruce W Nelson 1 , Julia V Tavares 1 , Jin Wu 2 , Dalton M Valeriano 3 , Aline P Lopes 1 , Suelen F Marostica 1 , Giordane Martins 1 , Neill Prohaska 2 , Loren Albert 2 , Alessandro C De Araujo 4 , Antonio O Manzi 1 , Scott R Saleska 2 and Alfredo R Huete 5 (1)National Institute for Amazon Research (INPA)<bnelsonbr@gmail.com>, Manaus, AM, Brazil, (2)University of Arizona, Tucson, AZ, United States, (3)National Space Research Institute (INPE), São José dos Campos, SP, Brazil, (4)Brazilian Agricultural Research Corporation (EMBRAPA), Belem, PA, Brazil, (5)University of Technology Sydney, Plant Functional Biology and Climate Change, Ultimo, Australia References Albert, L. et al. (2014). Leaf demography and physiology of the Tapajós National Forest: could phenology cause a forest-level increase in gross primary productivity during the dry season? AGU Fall 2014 abstract B11G-0108. (https://agu.confex.com/agu/fm14/meetingapp.cgi#Paper/26480) Coley, P. D., & Barone, J. A. (1996). Herbivory and plant defenses in tropical forests. Annual Review of Ecology and Systematics, 305-335. Lieberei, R. (2007). South American leaf blight of the rubber tree (Hevea spp.): new steps in plant domestication using physiological features and molecular markers. Annals of Botany, 100(6), 1125-1142. Restrepo-Coupe, N., da Rocha, H. R., Hutyra, L. R., da Araujo, A. C., Borma, L. S., Christoffersen, B., ... & Saleska, S. R. (2013). What drives the seasonality of photosynthesis across the Amazon basin? A cross-site analysis of eddy flux tower measurements from the Brasil flux network. Agricultural and Forest Meteorology, 182, 128-144. Wu, J. et al. (2014) Partitioning the climatic and biological controls on photosynthetic fluxes in Amazonian tropical evergreen forests. AGU Fall 2014 Abstract B11G-106. (https://agu.confex.com/agu/fm14/meetingapp.cgi#Paper/29946). Seasonality of central Amazon forest leaf flush using tower-mounted RGB camera (Abstract B11G-107) 0 5 10 15 20 25 30 35 40 45 50 Dec 2011 - Apr 2012 (five wettest mo.) Jun 2012 - Oct 2012 (five driest mo.) Dec 2012 - Apr 2013 (five wettest mo.) Jun 2013 - Oct 2013 (five driest mo.) Percent of all live crowns Flushing crowns (%) WET DRY WET DRY 0 200 400 600 800 1000 1200 0 10 20 30 40 50 60 Nov-11 May-12 Dec-12 Jun-13 Jan-14 TRMM Precip. (mm/mo) Percent of all upper canopy crowns Precip. (mm/mo) leaf age 0-2 mo leaf age 3-8 mo • 60% of live crowns flushed a massive amount of new leaves each year. • Flushing was concentrated in the five driest months, when 44% of all live crowns massively flushed. • In the five wettest months only 11% of live crowns mass- flushed new leaves. • Dry season flushing causes leaves in the age bracket of 3-8 months to reach peak abundance in late dry to early wet season; • Leaf photosynthesis is most efficient at this age (Albert et al. 2014, Wu et al. 2014); • Leaf demography may therefore drive early wet season peaks in landscape scale Gross Ecosystem Productivity and Photosynthetic Capacity, measured at this same site (Restrepo-Coupe et al. 2013); • A similar seasonal pattern of dry season leaf flush is seen at two other Central Amazon flux tower sites on well-drained clay soils (Restrepo-Coupe et al. 2013, Lopes et al. in prep.) Sept 18 Sep 24 Sep 30 Oct 06 Oct 12 Oct 18 Oct 24 Oct 30 Nov 06 Nov 12 Nov 18 Nov 24 Nov 30 We deployed a Stardot Netcam XL RGB camera with a 1024 x 768 resolution CMOS sensor, 66 o HFOV lens, fixed oblique south view, fixed iris, fixed white balance and auto-exposure. Images were logged every 15 seconds to a passively cooled FitPC2i with heat-tolerant SSD drive. Camera and PC automatically rebooted after power outages. We report results for two full years, from 1 Dec 2011 through 30 Nov 2013. Images in six day intervals were selected near local noon for homogeneous diffuse lighting under cloudy sky and for a standard reflected radiance (± 10%). Crowns showing two easily recognized phenophases were tallied: (1) massive flushing of new light-green leaves and (2) complete or nearly complete leaf loss. RESULTS I. Flushing Seasonality Few crowns flush new leaves in five wettest months (blue arrows) Many crowns flush in five driest months (orange arrows) 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 Arbitrary crown number Date Duration of leafless crown states, year 1 Five wettest months Five driest months 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Arbitrary crown number Date Duration of leafless crown states, year 2 Five wettest months Five driest months • 40-50% of flushing crowns dropped all their leaves prior to adding new leaves; • The deciduous stage lasted 36 +/- 25 days and occurred mostly in dry months; • Leaf-off phase is brief, followed by dry season leaf flush, so is not likely to be a consequence of water limitation! • Pre-flush leaf drop may be driven by non- physical factors, e.g., to reduce sources of infection of vulnerable new leaves by pathogens and epiphylls present on old leaves; • Similarly, avoiding leaf flush in wet season protects young leaves from herbivores and pathogens -- most active in humid months (Coley & Barrone 1996, Lieberei 2007). II. Preflush Leafless Phase Camera with enclosure top removed Tower-mounted RGB cameras can contribute data to the debate on seasonality of photosynthesis in Amazon upland forests and to improved modelling of forest response to climate change. In late 2010 we began monitoring upper crown surfaces of ~65 living trees or vines from a 54 m tall eddy-flux tower on a well-drained clay-soil plateau. This Central Amazon site (60.2091 W, 2.6092 S) is in a large forest reserve 60 km north of Manaus. • Ten week filmstrip shows one corner of monitored area. Two large crowns drop all their leaves, then each massively flushes a new leaf cohort. • Entire monitored area covers ~65 upper canopy crowns (see next). III. Leaf Demography View publication stats View publication stats