Above- and Below-Ground Net Primary Productivity Across Ten Amazonian Forests on Contrasting Soils

ORE Open Research Exeter TITLE Above- and below-ground net primary productivity across ten Amazonian forests on contrasting soils AUTHORS Malhi, Y; Metcalfe, DB; Silva-Espejo, JE; et al. JOURNAL Biogeosciences DEPOSITED IN ORE 19 June 2013 This version available at http://hdl.handle.net/10871/11001 COPYRIGHT AND REUSE Open Research Exeter makes this work available in accordance with publisher policies. A NOTE ON VERSIONS The version presented here may differ from the published version. If citing, you are advised to consult the published version for pagination, volume/issue and date of publication Biogeosciences Discuss., 6, 2441–2488, 2009 Biogeosciences www.biogeosciences-discuss.net/6/2441/2009/ Discussions © Author(s) 2009. This work is distributed under the Creative Commons Attribution 3.0 License. Biogeosciences Discussions is the access reviewed discussion forum of Biogeosciences Above- and below-ground net primary productivity across ten Amazonian forests on contrasting soils L. E. O. C. Aragao˜ 1, Y. Malhi1, D. B. Metcalfe1,11, J. E. Silva-Espejo2, E. Jimenez´ 3, D. Navarrete3,4, S. Almeida5, A. C. L. Costa6, N. Salinas1,2, O. L. Phillips8, L. O. Anderson1, T. R. Baker8, P. H. Goncalvez6,7, J. Huaman-Ovalle´ 2, M. Mamani-Solorzano´ 2, P. Meir11, A. Monteagudo12, M. C. Penuela˜ 3, A. Prieto13, C. A. Quesada8,9,10, A. Rozas-Davila´ 2, A. Rudas14, J. A. Silva Junior6, and R. Vasquez´ 12 1Environmental Change Institute, School of Geography and the Environment, University of Oxford, South Parks Road, OX1 3QY, Oxford, UK 2Universiadad Nacional San Antonio Abad, Cusco, Peru 3Grupo de Estudio de Ecosistemas Terrestres Tropicales, Universidad Nacional de Colombia, Leticia, Colombia 4Fundacion´ Puerto Rastrojo, Bogota,´ Colombia 5Museu Paraense Emilio Goeldi, 66077-530 Belem,´ Brazil 6Universidade Federal do Para,´ Belem,´ Para, Brazil 7Universidade Federal de Viçosa, Vicosa, Minas Gerais, Brazil 2441 8 Earth and Biosphere Institute, School of Geography, University of Leeds, LS2 9JT, UK 9 Institito National de Pesquisas Amazonicas,ˆ Manaus, Brazil 10 Departamento de Ecologia, Universidade de Bras´ılia, Brazil 11 School of Geography, University of Edinburgh, Edinburgh, UK 12 Jardin Botanico de Missouri, Oxapampa, Pasco, Peru 13 Instituto Alexander von Humboldt, Claustro de San Agust´ın, Villa de Lleva, Boyaca, Colombia 14 Universidad Nacional de Colombia, Instituto de Ciencias Naturales, Apartado 7495, Bogota,´ Colombia Received: 18 December 2008 – Accepted: 26 January 2009 – Published: 25 February 2009 Correspondence to: L. E. O. C. Aragao˜ ([email protected]) Published by Copernicus Publications on behalf of the European Geosciences Union. 2442 Abstract The net primary productivity (NPP) of tropical forests is one of the most important and least quantified components of the global carbon cycle. Most relevant studies have focused particularly on the quantification of the above-ground coarse wood productiv- 5 ity, and little is known about the carbon fluxes involved in other elements of the NPP, the partitioning of total NPP between its above- and below-ground components and the main environmental drivers of these patterns. In this study we quantify the above- and below-ground NPP of ten Amazonian forests to address two questions: (1) How do Amazonian forests allocate productivity among its above- and below-ground com- 10 ponents? (2) How do soil and leaf nutrient status and soil texture affect the productivity of Amazonian forests? Using a standardized methodology to measure the major elements of productivity, we show that NPP varies between 9.3±1.3 Mg C ha−1 yr−1 (mean±standard error), at a white sand plot, and 17.0±1.4 Mg C ha−1 yr−1 at a very fertile Terra Preta site, with an overall average of 12.8±0.9 Mg C ha−1 yr−1. The studied 15 forests allocate on average 64±3% and 36±3% of the total NPP to the above- and below-ground components, respectively. The ratio of above-ground and below-ground NPP is almost invariant with total NPP. Litterfall and fine root production both increase with total NPP, while stem production shows no overall trend. Total NPP tends to increase with soil phosphorus and leaf nitrogen status. However, allocation of NPP to 20 below-ground shows no relationship to soil fertility, but appears to decrease with the increase of soil clay content. 1 Introduction Plants are able to capture and accumulate atmospheric carbon via photosynthesis or gross primary productivity (GPP), and synthesis of organic compounds. The amount 25 of organic carbon retained in plant biomass over time, which results from the difference between GPP and autotrophic respiration (Ra), is known as net primary productiv- 2443 ity (NPP). Globally, it has been estimated that the terrestrial biosphere fixes annually between 46 Pg C (Del Grosso et al., 2008) and 63 Pg C (Grace, 2004) through NPP, approximately the same amount that is fixed by oceans (Field et al., 1998). Despite covering only around 13% of the total land cover area (Bartholome´ and Belward, 2005; 5 Del Grosso et al., 2008), tropical forests alone have a major impact on global carbon cycling, accounting for about a third of overall terrestrial NPP (Field et al., 1998; Malhi and Grace, 2000; Grace, 2004; Del Grosso et al., 2008). Detailed understanding of the total NPP of tropical forests, including both above- and below-ground productivity (NPPAG and NPPBG, respectively), is limited by challenging 10 logistics and elevated research costs. Hitherto, most of the on-site measurements of NPP for tropical forests have been based on few sites and do not present adequate data on below-ground NPP (Clark et al., 2001a). Amazonia, home to over half of the world’s tropical forest area, is no exception. Most studies that attempted to measure NPP in this ecosystem focused exclusively on above-ground wood productivity (e.g. Chambers 15 et al., 2001; Malhi et al., 2004; Quesada et al., 2009a). Malhi et al. (2009) compiled a synthesis of carbon production for three Amazonian forests (key sites of the Large Scale Biosphere-Atmosphere Experiment in Amazonia – LBA) based on detailed measurements of the individual above and below-ground C cycling components. In order to improve our understanding of the biogeochemical function of Amazonian 20 forests, and model their vulnerability to climate change and human-induced impacts, there is a need to expand our knowledge on the primary productivity of these ecosys- tems, taking into account their spatial heterogeneity. The understanding of how these processes vary across the region and across soil types would therefore assist in plan- ning the development of the Amazon region within the global climate change mitigation 25 and adaptation framework. Based on the analysis of 104 forest plots across Amazonia from the RAINFOR network (Amazon Forest Inventory Network; Malhi et al., 2002), Malhi et al. (2004) demon- strated that wood production varies by up to a factor of three across Amazonian forests. The lowest wood productivities are found on heavily weathered oxisols (United States 2444 Department of Agriculture soil classification – USDA), or ferralsols (World Reference Base soil classification – WRB) in lowland eastern Amazonia; the highest on fertile allu- vial soils and inceptsols (USDA classification system) or fluvisols and cambisols (WRB classification system) in western Amazonia (Ecuador and Peru). More fertile sites in 5 western Amazonia tend to favour fast growing, low wood density species (Baker et al., 2004), which are likely to allocate relatively more to wood and leaf production and less to structural and chemical defences and their associated construction and maintenance metabolic costs. However, beyond the stand-level wood production pattern across the region, almost nothing is known about the amount of carbon being allocated by other 10 components of the NPP, the partitioning of total NPP (NPPtotal) between its above- and below-ground components, NPPAG and NPPBG respectively, and the main environmental drivers of any site-to-site variation. Therefore, in this paper we provide the first inter-site quantification of the major components of NPPtotal for Amazonian forest stands on contrasting soils using standardized on-site measurements of the major 15 above- and below-ground components of forest NPP. A companion paper in this issue (Chave et al., 2009) examines patterns of canopy NPP across Amazonia in greater detail. Another (Quesada et al., 2009a) relates Amazon above-ground productivity to its potential edaphic and climate drivers. The total NPP of a tropical forest stand can be broken down as: 20 NPPtotal = NPPAG + NPPBG (1) Each of the components of NPPtotal can be described as the sum of its subcomponents (Clark et al., 2001a; Malhi et al., 2009). Thus, NPPAG can be expressed as: NPPAG = NPPfinelitter + NPPbranch + NPPstem + NPPVOC (2) where NPPfinelitter is the canopy production (leaves, twigs <2 cm diameter, flowers and 25 fruits), NPPbranch is the production of branches >2 cm diameter, NPPstem is the production of coarse woody biomass, calculated as the change in the stem biomass of trees >10 cm diameter plus the biomass recruited during the measurement interval. NPPVOC 2445 is the emission of volatile organic carbon compounds (see Malhi et al., 2009 for greater discussion of these terms). The canopy production, NPPfinelitter is estimated to be equal to the rate of litterfall; this assumes the forest is in near-steady state and that there is little loss of this production through insect herbivory or decomposition before the litter

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