and below-ground net primary productivity across ten Amazonian forests on contrasting soils

20 Pages·2009·0.49 MB·English

Biogeosciences,6,2759–2778,2009
Biogeosciences
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©Author(s)2009. Thisworkisdistributedunder
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Above- and below-ground net primary productivity across ten
Amazonian forests on contrasting soils
L.E.O.C.Araga˜o1,2,Y.Malhi1,D.B.Metcalfe1,2,J.E.Silva-Espejo3,E.Jime´nez4,D.Navarrete4,5,S.Almeida6,
A.C.L.Costa7,N. Salinas1,3,O.L.Phillips9,L.O.Anderson1,E.Alvarez4,T.R.Baker9,P.H.Goncalvez7,8,
J.Huama´n-Ovalle3,M.Mamani-Solo´rzano3,P.Meir12,A.Monteagudo13,S.Patin˜o4,M.C.Pen˜uela4,A.Prieto14,
C.A.Quesada9,10,11,A.Rozas-Da´vila3,A.Rudas15,J.A.SilvaJr.7,andR.Va´squez13
1EnvironmentalChangeInstitute,SchoolofGeographyandtheEnvironment,UniversityofOxford,SouthParksRoad,
OX13QY,Oxford,UK
2ClimateChangeandSustainabilityGroup,SchoolofGeography,UniversityofExeter,AmoryBuilding,RennesDrive,
Exeter,Devon,EX44RJ,UK
3UniversiadadNacionalSanAntonioAbad,Cusco,Peru
4GrupodeEstudiodeEcosistemasTerrestresTropicales,UniversidadNacionaldeColombia,Leticia,Colombia
5Fundacio´nPuertoRastrojo,Bogota´,Colombia
6MuseuParaenseEmilioGoeldi,66077-530Belem,Brazil
7UniversidadeFederaldoPara,Belem,Para,Brazil
8UniversidadeFederaldeVicosa,Vicosa,MinasGerais,Brazil
9EarthandBiosphereInstitute,SchoolofGeography,UniversityofLeeds,LS29JT,UK
10InstititoNationaldePesquisasAmazoˆnicas,Manaus,Brazil
11DepartamentodeEcologia,UniversidadedeBras´ılia,Brazil
12SchoolofGeography,UniversityofEdinburgh,Edinburgh,UK
13JardinBotanicodeMissouri,Oxapampa,Pasco,Peru
14InstitutoAlexandervonHumboldt,ClaustrodeSanAgust´ın,VilladeLleva,Boyaca,Colombia
15UniversidadNacionaldeColombia,InstitutodeCienciasNaturales,Apartado7495,Bogota,Colombia
Received: 18December2008–PublishedinBiogeosciencesDiscuss.: 25February2009
Revised: 11November2009–Accepted: 11November2009–Published: 1December2009
Abstract. The net primary productivity (NPP) of tropi- sure the major elements of productivity, we show that NPP
cal forests is one of the most important and least quan- variesbetween9.3±1.3MgCha−1yr−1(mean±standarder-
tified components of the global carbon cycle. Most rel- ror), at a white sand plot, and 17.0±1.4MgCha−1yr−1 at
evant studies have focused particularly on the quantifica- a very fertile Terra Preta site, with an overall average of
tion of the above-ground coarse wood productivity, and lit- 12.8±0.9MgCha−1yr−1. The studied forests allocate on
tle is known about the carbon fluxes involved in other el- average 64±3% and 36±3% of the total NPP to the above-
ements of the NPP, the partitioning of total NPP between and below-ground components, respectively. The ratio of
its above- and below-ground components and the main en- above-ground and below-ground NPP is almost invariant
vironmental drivers of these patterns. In this study we with total NPP. Litterfall and fine root production both in-
quantify the above- and below-ground NPP of ten Amazo- creasewithtotalNPP,whilestemproductionshowsnoover-
nian forests to address two questions: (1) How do Ama- all trend. Total NPP tends to increase with soil phospho-
zonian forests allocate productivity among its above- and rus and leaf nitrogen status. However, allocation of NPP to
below-ground components? (2) How do soil and leaf nu- below-ground shows no relationship to soil fertility, but ap-
trientstatusandsoiltextureaffecttheproductivityofAma- pearstodecreasewiththeincreaseofsoilclaycontent.
zonian forests? Using a standardized methodology to mea-
Correspondenceto: L.E.O.C.Araga˜o
([email protected])
PublishedbyCopernicusPublicationsonbehalfoftheEuropeanGeosciencesUnion.
2760 L.E.O.C.Araga˜oetal.: NetprimaryproductivityinAmazonianforests
1 Introduction stratedthatwoodproductionvariesbyuptoafactorofthree
across Amazonian forests. The lowest wood productivities
Plants are able to capture and accumulate atmospheric car- are found on heavily weathered oxisols (United States De-
bonviaphotosynthesisorgrossprimaryproductivity(GPP), partment of Agriculture soil classification – USDA), or fer-
andsynthesisoforganiccompounds. Theamountoforganic ralsols (World Reference Base soil classification – WRB)
carbon retained in plant biomass over time, which results in lowland eastern Amazonia; the highest on fertile alluvial
fromthedifferencebetweenGPPandautotrophicrespiration soils and inceptsols (USDA classification system) or fluvi-
(Ra),isknownasnetprimaryproductivity(NPP).Globally, sols and cambisols (WRB classification system) in western
ithasbeenestimatedthattheterrestrialbiospherefixesannu- Amazonia (Ecuador and Peru). More fertile sites in west-
allybetween46PgC(DelGrossoetal., 2008)and63PgC ern Amazonia tend to favour fast growing, low wood den-
(Grace,2004)throughNPP,approximatelythesameamount sity species (Baker et al., 2004), which are likely to allo-
thatisfixedbyoceans(Fieldetal.,1998). Despitecovering caterelativelymoretowoodandleafproductionandlessto
only around 13% of the total land cover area (Bartholome´ structural and chemical defences and their associated con-
andBelward,2005;DelGrossoetal.,2008),tropicalforests struction and maintenance metabolic costs. A companion
alonehaveamajorimpactonglobalcarboncycling,account- paperinthisissue(Chaveetal.,2009)examinespatternsof
ing for about a third of overall terrestrial NPP (Field et al., canopy NPP across Amazonia in greater detail. This study
1998; Malhi and Grace, 2000; Grace, 2004; Del Grosso et suggests that soil type is not a major determinat of litterfall
al.,2008). patternsacrossAmazonia,however,infertilewhitesandsoils
Detailed understanding of the total NPP of tropical (5.42±1.91Mgha−1yr−1) have significantly lower litterfall
forests, including both above- and below-ground productiv- productionthanothersoiltypesandseemstoprioritizecar-
ity(NPPAGandNPPBG,respectively),islimitedbychalleng- bon allocation to photosynthetic organs over that to repro-
ing logistics and elevated research costs. Hitherto, most of duction.
the on-site measurements of NPP for tropical forests have Another (Quesada et al., 2009a) relates Amazon above-
beenbasedonfewsitesanddonotpresentadequatedataon ground productivity to its potential edaphic and climate
below-groundNPP(Clarketal.,2001a).Amazonia,hometo drivers. This analysis revealed that forest structure and dy-
overhalfoftheworld’stropicalforestarea,isnoexception. namicsarestronglyrelatedtophysicalandchemicaledaphic
Most studies that attempted to measure NPP in this ecosys- conditions. On one hand tree turnover rates were mostly
temfocusedexclusivelyonabove-groundwoodproductivity influenced by soil physical properties, on the other hand,
(e.g. Chambers et al., 2001; Malhi et al., 2004; Quesada et forest growth rates were mainly related to available soil
al.,2009a). Malhietal.(2009)compiledasynthesisofcar- phosphorus,suggestingthatsoilsmaybeadeterminantfac-
bonproductionforthreeAmazonianforests(keysitesofthe tor on forest functioning and composition at a Basin wide
Large Scale Biosphere-Atmosphere Experiment in Amazo- scale. However, beyond the stand-level wood and leaf pro-
nia – LBA) based on detailed measurements of the individ- duction pattern across the region, almost nothing is known
ual above and below-ground C cycling components. GPP abouttheamountofcarbonbeingallocatedbyothercompo-
estimatefromthecomponentstudieswasinagreementwith nentsoftheNPP,thepartitioningoftotalNPP(NPP )be-
total
estimates derived from ecosystem flux measurements, giv- tweenitsabove-andbelow-groundcomponents,NPP and
AG
ing increased confidence in both approaches to estimating NPP respectively, and the main environmental drivers of
BG
tropicalforest’sGPP.Moreover,thisstudyindicatedthatold- anysite-to-sitevariation. Therefore,inthispaperweprovide
growthorinfertiletropicalforestsmayhavelowcarbonuse thefirstinter-sitequantificationofthemajorcomponentsof
∼
efficiency(CUE=0.3)incomparisontorecentlydisturbedor NPP forAmazonianforeststandsoncontrastingsoilsus-
total
∼
fertile tropical forests (CUE=0.5), highlighting the hetero- ing standardized on-site measurements of the major above-
geneityofforestprocessesintheAmazon. andbelow-groundcomponentsofforestNPP.
Inordertoimproveourunderstandingofthebiogeochem- The total NPP of a tropical forest stand can be broken
ical function of Amazonian forests, and model simulations downas:
of their vulnerability to climate change and human-induced
NPP =NPP +NPP (1)
impacts,thereisaneedtoexpandourknowledgeonthepri- total AG BG
mary productivity of these ecosystems, taking into account EachofthecomponentsofNPP canbedescribedasthe
total
their spatial heterogeneity. The understanding of how these sumofitssubcomponents(Clarketal., 2001a; Malhietal.,
processesvaryacrosstheregionandacrosssoiltypeswould 2009). Thus,NPP canbeexpressedas:
AG
thereforeassistinplanningthedevelopmentoftheAmazon
NPP =NPP +NPP +NPP +NPP (2)
regionwithintheglobalclimatechangemitigationandadap- AG canopy branch stem VOC
tationframework. where NPP is the canopy production (leaves, twigs
canopy
Based on the analysis of 104 forest plots across Amazo- <2cm diameter, flowers and fruits), NPP is the pro-
branch
niafromtheRAINFORnetwork(AmazonForestInventory ductionofbranches>2cmdiameter,NPP istheproduc-
stem
Network; Malhi et al., 2002), Malhi et al. (2004) demon- tion of coarse woody biomass, calculated as the change in
Biogeosciences,6,2759–2778,2009 www.biogeosciences.net/6/2759/2009/
L.E.O.C.Araga˜oetal.: NetprimaryproductivityinAmazonianforests 2761
thestembiomassoftrees>10cmdiameterplusthebiomass
recruited during the measurement interval. NPP is the
VOC
emissionofvolatileorganiccarboncompounds(seeMalhiet
al.,2009,forgreaterdiscussionoftheseterms). Thecanopy
production,NPP isestimatedtobeequaltotherateof
canopy
litterfall; this assumes the forest is in near-steady state and
thatthereislittlelossofthisproductionthroughinsecther-
bivoryordecompositionbeforethelitterhitstheground.
NPP can be divided into three major subcomponents
BG
(Eq.3):
NPP =NPP +NPP +NPP (3)
BG fineroot coarseroot exudates
Where NPP is the fine root (<2mmdiameter) pro-
fineroot
duction, NPP is the production of coarse roots
coarseroot
(>2mmdiameter)andNPP isthecarbonlossthrough
exudates
exudatesandmycorrhizae, which ischallengingtomeasure
andisnotconsideredhere. Fig. 1. Location of the study area within South America (lower-
In this study we quantify the above- and below-ground rightpanel)andlocationofthestudiedplotswithinthestudiedarea.
NPPoftenAmazonianforeststoaddresstwogeneralques- Plotlocationsareapproximatedinordertodisplayallplots.
tions: (1) how do Amazonian forests allocate productivity
among its above- and below-ground components? (2) How
dosoilandleafnutrientstatusandsoiltextureaffectthepro- 2 Studysites
ductivityofAmazonianforests?
Based on the concepts above, these two questions can be We analysed the NPPtotal and its above- and below-ground
decomposedintofivespecificquestions,whichwetacklein subcomponentsfortenforestplotsacrossAmazonia(Fig.1).
thispaper: WedirectlyquantifiedNPPemployingaconsistentmethod-
ology in eight plots: three plots at Caxiuana˜, Brazil (CAX-
1. How do NPP and NPP and their subcomponents
AG BG 03, CAX-06 and CAX-08), two at Tambopata, Peru (TAM-
varywithNPP ?
total 05 and TAM-06), two at Amacayacu, Colombia (AGP-01
2. IsthepartitioningbetweenNPP andNPP invariant and AGP-02) and one at Zafire, Colombia (ZAR-01). In
AG BG
withchangesinNPP ? addition, we used published data compiled from two other
total
Brazilian sites in Manaus (MAN-05) and Tapajo´s (TAP-04)
3. IsthepartitioningbetweenNPPstemandNPPcanopycon- (Malhietal.,2009)tosupportouranalysis.
stant?
Thesesitesarepartoftheintensivesurveyedplotswithin
the RAINFOR network where measurements of all the ma-
4. HowdoesNPPvarywithsoilandleafnutrientsstatus?
jorcomponentsoftheCcyclearebeingmeasuredsincethe
5. How does the partitioning of NPP vary with soil and endof2004orbeginningof2005(seemethodssection),and
leafproperties? wherestemproductivityhasbeenmeasuredsinceasearlyas
the 1980s. All directly studied plots were one-hectare (ha)
WethereforeaimtoinvestigateinthisstudyhowNPP and
total
inarea;theresultsfromManausandTapajo´swereasynthe-
its subcomponents vary across a wide range of Amazonian
sisfromseveralstudyplots(Malhietal.,2009). Asummary
forests on different soil types. Specifically, our objectives
ofplotsname, locationandbasicclimatedata(Malhietal.,
areto:
2004)isgiveninTable1.
1. Quantify and describe the patterns of NPPtotal across a Allforestssurveyedinthisstudyare“primary”old-growth
gradientofsoilconditions. rainforests with the exception of CAX-08, which is a well
preserved late successional forest growing on a very fer-
2. Quantify the partitioning of NPP among its major
total
tileIndianDarkEarth(orTerraPretadoIndio)soil(Hortic
aboveandbelow-groundcomponents.
Archeo-Anthrosol,Kampfetal.,2003).Thissoilwasformed
3. Investigate if the partitioning between NPPcanopy and byhumanactivitiesfromancientinhabitantsthathaveoccu-
NPPstemisconstant. piedthisareabetween720–300yearsBP(RuivoandCunha,
2003; Lehmann et al., 2003). This was selected as one of
4. Determinehowsoilfertilityandtexture,basedonavail-
thefewTerraPretasitesintheregioncoveredbyforestthat
able soil phosphorus, nitrogen and clay content data
has remained largely undisturbed for at least 40 years since
(Quesadaetal.,2009a,b)influenceNPPinAmazonian
the creation of Caxiuana˜ National Forest reserve. More de-
forests.
tailsabouteachsitesurveyedaregivenbelow. Foreachsite
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2762 L.E.O.C.Araga˜oetal.: NetprimaryproductivityinAmazonianforests
Table1. Sitecodes,locationsandclimaticcharacteristicsofthetenAmazoniansitesevaluatedinthisstudy. Theclimatedatapresentedin
thistablearemeanvaluesfrom1960–1998derivedfromtheUniversityofEastAngliaObservationalClimatology(Newetal.,1999)and
publishedinMalhietal.(2004). Cumulativeannualrainfallisgiveninmmyr−1,dryseasonlength(DSL)inmonths,correspondstothe
sumofconsecutivemonthswithrainfall<100mmmonth−1,andtemperatureisthemeanannualtemperature(MAT)inCelsiusdegrees.
Studysites Climate
RAINFORsitescode Name Country Location Rainfall DSL MAT
Lat Long mmyr−1 months Celsiusdegrees
AGP-01 AguaPudreplotE Colombia −3.72 −70.3 2723 0.0 25.5
AGP-02 AguaPudreplotU Colombia −3.73 −70.4 2723 0.0 25.5
CAX-03 Caxiuana˜droughtexperimentcontrolplot Brazil −1.72 −51.5 2314 4.0 26.9
CAX-06 Caxiuana˜fluxtowersite Brazil −1.72 −51.5 2314 4.0 26.9
CAX-08 Caxiuana˜TerraPretasite Brazil −1.72 −51.5 2314 4.0 26.9
MAN-05 Manaus Brazil −2.5 −60.0 2272 3.0 27.1
TAM-05 TambopataRAINFORplot3 Peru −12.8 −69.7 2417 3.5 25.2
TAM-06 TamboapataRAINFORplot4 Peru −12.9 −69.8 2417 3.5 25.2
TAP-04 Tapajo´sfluxtowersite Brazil −2.5 −55.0 1968 4.5 26.1
ZAR-01 Zafire,Varillal Colombia −4.0 −69.9 2723 0.0 25.5
wealsocompileddataonleafnitrogenandphosphoruscon- forest, with a 25m height canopy, on relatively fertile clay
centrations(N andP ,respectively;Fyllasetal.,2009), plinthosols(aquicentisolsinUSDAsoiltaxonomy).
leaf leaf
soiltypes,followingtheWRBsoiltaxonomytobeconsistent AtZafire,Colombiaourfocuswasona1-haplotlocated
withQuesadaetal.(2009b), soiltexture(claycontent), and onawhitesandsite,ZAR-01(Jime´nezetal.,2009). Thisis
soilnitrogenandphosphorusconcentrations(N andP , part of the Rio Caldero´n Forest Reserve, around 50km east
soil soil
respectively; Quesada et al., 2009a). These data are shown oftheAmacayacusite. Theplotwassetupinanareaofpri-
inTable2. maryforestonwhitesandpodzol(spodosolintheUSDAsoil
At Caxiuana˜, Brazil, we surveyed three 1-ha plots taxonomy), locally known as Varillal. This forest is shorter
(100m×100m). All plots are located at the Caxiuana˜ Na- thantheforestatAmacayacu,withanaverageheightof20m.
tional Forest in Para´ State. The plot CAX-06, is a tall pri- ThisforesttypeisscarceinwesternAmazoniabutmorefre-
mary forest (35m height canopy) situated on a clay ferral- quent in the Guyana Shield and is similar to the formations
sol (oxisol in USDA soil taxonomy) near a flux tower site alongtheRioNegro.Thesoilinourplothasanimpermeable
(Malhi et al., 2009). The CAX-03 plot is a sandier site lo- hardpanlayerat∼100cmdepth(Jime´nezetal.,2009).
cated2kmtofurthersouth,whichwasthecontrolplotfora AtTapajo´s,Brazil,wefocusonthesitesreportedbyMalhi
droughtexperiment(Metcalfeetal.,2007a).TheTerraPreta et al. (2009). The main site is the km 67 flux tower (TAP-
site (CAX-08) is a late successional forest on an Archaeo- 04, Hutyra et al., 2007; Saleska et al., 2003) and its vicin-
Anthrosol (this classification was modified from the WRB ity. ThissiteislocatedwithintheboundariesoftheTapajo´s
soiltaxonomybyKampfetal.(2003)toencompassthevari- National Forest in Para´ State. The plots are established in
abilityofTerraPretasoilsinAmazonia). TheCAX-08site old-growthforestwithcanopyheightaround35m. Thesoils
islocatedabout15kmtothesouthoftheprimarystudyarea, are very clay-rich Belterra clay ferralsols, interspersed with
bytheedgeofalargeriverbay. sandiersoilpatches. Thekeyplotsarefour1-hatransectses-
At Tambopata, Peru, we surveyed two pre-existing long- tablishedin1999immediatelytotheeastofthetower(Rice
term1-haplots(100m×100m)locatedattheTambopataBi- etal.,2004;Pyleetal.,2008).
ologicalReserve,inMadredeDiosRegion. TheplotTAM- AtManaus, Brazil, thestudysiteswerealsofocusonthe
05 was set up on relatively infertile Pleistocene cambisols sites reported in Malhi et al. (2009). The main sites are the
(inceptsolsinUSDAsoiltaxonomy),withanaveragecanopy K34 flux tower site (Arau´jo et al., 2002), and the various
heightof30m. TheplotTAM-06wasonalisols(ultisolsin studies that have been conducted in its vicinity. The plots
USDAsoiltaxonomy)onafertileHolocenealluvialterrace. arestablishedinold-growthTerraFirmeforestsonclay-rich
ThecanopyinthisplothasthesameaverageheightasTAM- ferrasols,extensivelydissectedbyrivervalleyshostinglower
05,butagreaterdensityofpalms. biomassforestonfrequentlywaterloggedpodzols. Thekey
At Amacayacu, Colombia, our focus was on two 1-ha forestplotsintheareaarethethree1-ha“Bionte”plotsonthe
terrafirmeforestplotsAGP-01andAGP-02(Jime´nezetal., plateaux, providing annual census data since 1989, and the
2009). Both are located at the Amacayacu National Nat- two5-ha(20×2500m)“Jacaranda”transectplotsthatdrape
ural Park, near the border between Colombia, Brazil and acrosstheplateau-valleylandscape.
Peru. Theplotsweresetupinanareaofprimaryold-growth
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L.E.O.C.Araga˜oetal.: NetprimaryproductivityinAmazonianforests 2763
Table2. Leafnutrientconcentration(mgg−1)andsoilavailablephosphorusconcentration(mgkg−1),nitrogenconcentration(%)andclay
content(%)forthetenAmazoniansitesevaluatedinthisstudy.LeafdataarederivedfromFyllasetal.(2009)andsoildatafromQuesadaet
al.(2009b).NotethatthesoiltypeisinaccordancewiththeWorldReferenceBasesoilclassificationsystem(WRB).
Leafnutrient Soil
RAINFORcode
Nitrogen Phosphorus Type Clay Nitrogen Phosphorus
AGP-01 20.87 1.06 EndostagnicPlinthosol(Alumic,Hyperdystric) 42.12 0.16 25.36
AGP-02 19.17 0.96 EndostagnicPlinthosol(Alumic,Hyperdystric) 43.10 0.16 25.43
CAX04 20.63 0.55 VeticAcrisol(Alumic,Hyperdystric) 16.30 0.07b 12.31b
CAX-06 19.13 0.53 GericAcricFerralsol(Alumic,Hyperdystric,Clayic) 47.53 0.13 12.31b
CAX-08 HorticArchaeo-Anthrosol(Ebonic,Clayic,Mesothropic,Mesic,Ferralic) 41.41 0.17 80.00
MAN-05 19.89a 0.54a GericFerralsol(Alumic,Hyperdystric,Clayic) 66.21a 0.16a 7.28a
TAM-05 23.99 1.05 HaplicCambisol(Alumic,Hyperdystric,Clayic) 7.41 0.16 32.34
TAM-06 24.80 1.88 HaplicAlisol(Hyperdystric,Siltic) 9.66 0.17 33.06
TAP-04 22.58 0.75 GericFerralsol(Alimic,Hyperdystric,Clayic,Xanthic) 89.25 0.14 15.45
ZAR-01 OrtseincPodzol(Oxyaquic) 0.64 0.11 14.36
aValuesarefromMAN-05plot.
bValuesareaveragesfromnearbyplotsCAX-01andCAX-02.
Foramoredetailedviewofthelandscapeattributes,such structures(flowers,fruitandseeds)andunidentifiedmaterial,
as vegetation type and structure, topography and plot loca- andweighed.
tions,ofmanyoftheseplotsseeAndersonetal.(2009). At Tapajo´s, litterfall values compiled by Malhi et
al.(2009)werefrom: (1)Riceetal.(2004),whocalculated
fine litterfall from 30 circular mesh traps (0.43m diameter,
3 Materialsandmethods 0.15m2), randomly located throughout the 19.75-ha survey
area;(2)Silveretal.(2000),whoestimatedfinelitterfallrates
3.1 AbovegroundNPP in six to ten 4m×12m plots, using six 0.9m2 baskets per
plot;and(3)Nepstadetal.(2002),whoused0.5m2 trapsat
3.1.1 Litterfall 100 points arrangedas a regular grid within two 1-ha plots.
At all sites litter was collected at biweekly intervals. For
At Caxiuana˜ and Tambopata, one litter trap with an area of Manaus, following Malhi et al. (2009), we used the mean
0.25m2 (0.5m×0.5m) was installed in the centre of each valuesfromLuiza˜oetal.(2004).
of the twenty-five 20 by 20m subplots in the plots CAX-
06andCAX-08inAugust2004. InJanuary2005thesame 3.1.2 Branchproduction
design was installed at Tambopata (TAM-05 and TAM-06).
Litterfallinthesefourplotswascollectedeveryfifteendays The production of large branches was not measured in this
from September 2004 to December 2006 in Caxiuana˜ and experiment. ForcompletenessofourNPPestimateweused
from February 2005 to December 2006 in Tambopata. Lit- a branchfall average rate for all plots of 1MgCha−1yr−1
terfall in the third 1-ha plot in Caxiuana˜ (CAX-03) was based upon data from two studies carried out in Amazonia:
recorded monthly from November 2001 to December 2006 one in Manaus that reported a rate of 0.4MgCha−1yr−1
usingtwentycirculartraps(area=1m2)randomlyplacedin (Chambersetal.,2001)andasecondoneintheTapajo´sthat
November2001. estimatedabranchfallrateof1.6±0.8MgCha−1yr−1(Nep-
At Amacayacu and Zafire one litter trap with an area of stadetal., 2002). Fortheanalysisoferrorpropagation(see
0.50m2 (0.5m×1.0m) was installed in 2005 in the centre below)weusedaconservativeuncertainty±100%(Malhiet
of each of the twenty-five 20 by 20m subplots in the plots al., 2009). It is possible that sites with higher NPPstem and
AGP-01, AGP-02 and ZAR-01. In all three sites litterfall alsohigherstembreakageinwesternAmazoniawouldhave
was collected biweekly for two years at AGP-01 and AGP- higherNPPbranchrates.
02,andfor1.5yearsatZAR-01.
3.1.3 Coarsewoodybiomassproduction
For all of these sites sites, traps were made with a PVC
frameanda1mmnylonmeshandwereplacedat1mabove
Woodproductivity(NPP )wasestimatedbyrepeatedcen-
stem
the ground surface. Litter retrieved from the traps was im-
suses of tree diameters and stems newly recruiting into the
mediatelysundriedandsubsequentlydriedinthelaboratory
10cmdiametersize-class,takingintoaccounttaxon-specific
oven at 60◦C until constantweight. Each dried samplewas
variationinwooddensity.
separated into leaves, twigs (<2cm diameter), reproductive
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2764 L.E.O.C.Araga˜oetal.: NetprimaryproductivityinAmazonianforests
At Caxiuana˜, the censuses at CAX-06 and CAX-08 were 3.2 BelowgroundNPP
carriedoutfrom2004–2006withanaveragecensusinterval
of 0.78±0.11 years (CAX-06) and 1.16±0.23 years (CAX- 3.2.1 Coarserootproductivity
08). AtCAX-03recensusestookplaceannuallyfrom2001–
2006(Metcalfeetal.,2009). Productionofcoarserootsisaverydifficulttermtoquantify.
At Tambopata, a much longer time interval was avail- Forthisstudyweassumedthattheproductivityperunitmass
able for both plots (TAM-05 and TAM-06). The censuses ofallrootsthatarenotincludedinthefinerootproductivity
at TAM-05 were carried out from 1985 to 2005 with an (i.e. roots >2mm diameter) is the same as the productivity
average census interval of 2.79±0.50 years, and at TAM- of the above ground biomass and that belowground coarse
06 from 1987 to 2005 with average census interval of root biomass is 21±3% of above-ground biomass (Malhi
3.19±0.87years. et al., 2009). Hence, NPPcoarseroot=0.21 (±0.03)×NPPstem.
At Amacayacu and Zafire, plots AGP-01, AGP-02 and This may underestimate NPPcoarseroot as the productivity of
ZAR-01censuseswerecarriedoutannuallybetween2004– smaller roots is likely to be greater than the productivity of
2006(Jime´nezetal.,2009). themassivestructuralroots.
AtTapajo´sandManausweusedvaluespublishedinMalhi
et al. (2009). For Tapajo´s, NPP is an average of two 3.2.2 Finerootproductivity
stem
surveys at km 67 reported by Pyle et al. (2008) (20ha in
total), and for Manaus values are an average of the Bionte, This term was directly quantified in CAX-06, CAX-08,
JacarandaandBDFplots(usingtherecentvaluesfromPyle CAX-03,TAM-05,TAM-06,AGP-01,AGP-02andZAR-01
etal.,2008,forthelatter). using the ingrowth cores technique (Vogt et al., 1998; Ste-
Forallplotsthesamemethodologywasappliedtoderive ingrobeetal., 2000; Hendricksetal., 2006; Metcalfeetal.,
biomassandstemgrowth. Initially,foreachplottheabove- 2008). Fine-roots considered here are defined as <2mm in
groundbiomass(AGB,kgdryweightha−1)ofalltreeswith diameter.
diameter at breast height (DBH) ≥10cm, including palms, At Caxiuana˜ and Tambopata, sixteen root-free ingrowth
wascalculatedusingtheequationproposedbyChamberset cores with an area of 154cm2 and depth of 30cm were in-
al. (2001) for central Amazonian forests, and modified by stalled in each plot (CAX-06, CAX-08, CAX-03, TAM-05,
Baker et al. (2004) to allow for variation in wood density TAM-06)ina20mby20mregulargrid,20mfromtheedge
(Eq.4). of the plot. Ingrowth cores were installed at the beginning
ofNovember2004intheCaxiuana˜plots(CAX-06,CAX-08,
AGB=Xn σi (4) CAX-03)andatthebeginningofJune2005intheTambopata
0.67 plots (TAM-05 and TAM-06). At each sampling point, one
1
( ) soil core were extracted, keeping the soil layers separated
h i
× exp 0.33(lnD )+0.933(lnD )2−0.122(lnD )3−0.37 to avoid the transference of soil with high nutrient content
i i i
fromthetoptothebottomlayers. Rootsweremanuallyre-
moved and the remaining soil was reinserted into the hole
where D and σ are, respectively, the diameter (cm) and
i i
wood density (gcm−3) of tree i, n is the number of stems surroundedbya1cmplasticmeshbag. Thisprocedurewas
repeatedeverythreemonthsinallplotsfromNovember2004
per plot. To be consistent with other studies we considered
toNovember2005inCaxiuana˜ andfromJune2005toApril
thecarbonfractioninthedrybiomasstobe0.5.
2007 in Tambopata. At each three-month interval ingrowth
FollowingMalhietal.(2004)weestimatedthewoodypro-
cores were removed from the soil and all fine roots manu-
ductivity for each plot at each census interval by subtract-
ally extracted following the method described by Metcalfe
ing the AGB of the surviving trees at second census (t ) by
1
et al. (2007c) which corrects for underestimates in, partic-
the first census (t ) and added to this total the AGB that
0
ularly fine, root mass. Afterwards, the root free soil cores
of new recruits. However, variation in census intervals af-
were reinserted into the same holes. Roots were then dried
fects estimates of wood productivity, as trees that grew but
at 60◦C until constant weight, subsequently cleaned for re-
diedbeforethesecondcensusaremissed. Specifically,esti-
moval of soil particles and weighed to determine dry root
matesofwoodproductivitydecreaseapproximatelylinearly
massproducedduringeachthree-monthinterval.
withincreasingcensusintervallength.Wethereforeusedthe
AtAmacayacu,thirteeningrowthcoresandatZafirefour-
plot-specificcensus-intervalcorrectionproposedbyMalhiet
teen ingrowth cores with an area of 23.6cm2 and depth of
al. (2004), adjusted for AGB values instead of basal area
20cmwereinstalledintheplotsAGP-01,AGP-02andZAR-
(Phillips et al., 2009). The correction varies approximately
01 (Jime´nez et al., 2009). The ingrowth cores at AGP-01
asthesquareofthegrowthrate.
andAGP-02wereinstalledatthreedifferentdates: February
2004 (Experiment 1), using cores surrounded by a 4mm2
mesh bag, and September 2004 (Experiment 2) and Febru-
ary 2006 (Experiment 3), using cores with no mesh. At
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L.E.O.C.Araga˜oetal.: NetprimaryproductivityinAmazonianforests 2765
plotZAR-01installationtookplaceinSeptember2004(Ex- Soilsampleswereair-driedandhadroots, detritus, small
periment 2) and February 2006 (Experiment 3) using no rocksandparticlesover2mmremoved. Sampleswerethen
meshcores. Thecollection,extractionandprocessingofthe analysed for: (1) complete phosphorus fractionation (mod-
roots were fairly similar to the one presented for Caxiuana˜. ified from Hedley et al. 1982), (2) nitrogen (Pella, 1990;
Detailed description of the methods is given in Jime´nez et Nelson and Sommers, 1996), and (3) particle size analysis
al. (2009), so here we give a summary of the methods. Ex- usingtheBoyoucosmethod(GeeandBauder,1986).
periment1wascarriedoutfromFebruary2004toJuly2006, In this study we used the readily available P, which is
Experiment 2 from September 2004 to July 2006 and Ex- defined as sum of the P immediately accessible in solution
periment3fromFebruary2006toDecember2006. Thefirst (measured as the resin P), plus that organic and inorganic
collectionwascarriedout5–7monthsafterinstallationofthe phosphorusthatcanbeextractedbybicarbonate. Itappears
ingrowthcoresforthethreeexperiments.Subsequentcollec- a good measure of the phosphorus that plant roots are able
tionswerecarriedout2–4monthsafterthere-installationof toextractatlittlecost,andhenceagoodmeasureofplantP
theroot-freeingrowthcores. Forthepresentstudyweused availability(Quesadaetal.,2009a).
an average value of all experiments to better represent inter The leaf phosphorus and nitrogen concentrations used in
andintra-annualvariabilityoffine-rootproduction. thisstudywereobtainedfromFyllasetal.(2009). Leafsam-
AtTapajo´s,weusedthevaluesoffinerootproductionre- plingandanalysisprotocolsaredescribedindetailinLloyd
portedinMalhietal.(2009). Finerootproductionatthissite etal.(2009). Inbrief, 12to40treesper1haplotwereran-
was calculated by Silver et al. (2000) using the sequential domlyselectedandleafsamplesforeachtreewerecollected
coring method at TAP-04, sampling 0–10cm depth with a fromfullsuncanopypositionswiththehelpofatreeclimber.
6cmdiametercorereverytwomonthsfortwoyears. Subse- Leaveswerecleanedanddried,milledandstoredforlabora-
quently,rootproductionwasestimatedusingacompartment toryanalysis.
flowmodel (Sanantonio andGrace, 1987), with decayrates Samples from Peruvian and Colombian sites were anal-
calculated directly from a trenching experiment. The study ysed at the Central Analytical and Stable Isotopes Facili-
wasconductedinsixplotsapproximately4m×12minsize. ties at the Max-Planck Institute for Biogeochemistry (MPI-
All data from Caxiuana˜, Tambopata, Amacayacu, Zafire BGC)inJena,Germany. SamplesfromBraziliansiteswere
and Tapajo´s were adjusted following Malhi et al. (2009) to analysed for phosphorus at Instituto Nacional de Pesquisas
accountforrootproductiontoone-meterdepth. Noexisting daAmazoˆnia(INPA)andfornitrogenatEmpresaBrasileira
dataonfine-rootproductionwerefoundforManaus. There- de Pesquisas Agropecua´rias (EMBRAPA), both in Manaus,
fore,anaveragevalueofplotsonsimilarsoiltypes(acrisols Brazil. Leafnitrogenconcentrationsweredeterminedinthe
andferrasols)atCAX-06,CAX-03,TAP-04wasusedtoes- BrazilianandGermanlaboratoriesusingfinelygroundplant
timatefine-rootproductioninthissite. material in an elemental analyser (Elementar Analysensys-
In addition, we compiled fine root stand biomass data, teme, Hanau, Germany). At INPA, phosphorus concentra-
adjusted to one meter depth, in order to estimate fine root tionsweredeterminedafteraciddigestionoftheleafmaterial
turnover (stand biomass/productivity) as a complementary inaUVvisiblespectrophotometer(Model1240,Shimadzu,
measure of fine root dynamics across the fertility gradient. Kyoto,Japan). AttheMPI-BGCsampleextractswereanal-
For Caxiuana˜, values of fine root stand biomass for all the ysedbyanICP-OES(ModelOptima3300DV,PerkinElmer,
three plots are reported in Metcalfe et al. (2008). For the Norwalk, CT, USA). For all chemical analyses the equip-
twoplotsatAmacayacuandtheoneatZafire,valuesoffine mentswereinter-calibrateforconsistencyoftheresults.
root biomass are from Jime´nez et al. (2009). For Tapajo´s
weusedthevaluesoffinerootturnoverreportedbySilveret 3.4 Propagationofuncertaintiesanddataanalyses
al. (2005). Fine root stand biomass for Tambopata was di-
rectly estimated in this study (TAM-05=7.7MgCha−1 and Alluncertaintyestimatesthroughoutthetextarereportedas
TAM-06=5.0MgCha−1). standarderrorsassumingnormaldistributions. Uncertainties
arepropagatedbyquadratureofabsoluteerrors(Malhietal.,
3.3 Soilandleafdata 2009). Therefore, if y is the sum of a number of variables
x ...x ...x ,eachwithassociateduncertainty1x ,thenthe
1 i n i
The soil available phosphorus and nitrogen concentrations absoluteuncertaintiesarepropagatedinquadrature(Eq.5):
(0–30cm depth) and texture used in this study were ob-
n
X
tained from Quesada et al. (2009c), and methods are only (1y)2= (1x )2 (5)
i
briefly summarized here. For each 1-ha plot, five to twelve i=1
soil cores were collected using an undisturbed soil sam-
Thisassumesthatuncertaintiescanbeconsideredtobeinde-
pler (Eijkelkamp Agrisearch Equipment BV, Giesbeek, The
pendentandnormallydistributed. Itisimportanttonotethat
Netherlands). All sampling was done following a standard
uncertainty values represent uniquely the precision of mea-
protocol (see http://www.geog.leeds.ac.uk/projects/rainfor/
surements and that biases related to methodological issues
projdocs.html).
were not accounted for in the error analysis due to the lack
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2766 L.E.O.C.Araga˜oetal.: NetprimaryproductivityinAmazonianforests
Table3. NetprimaryproductivityofeachsubcomponentofthetotalNPP(NPPtotal)foreachoneofthestudiedsites. TheNPPvalues
aregiveninMgCha−1yr−1 withitsassociatedstandarderror(S.E.). NotethatforManausanaveragevalueofplotsonsimilarsoiltypes
(acrisolsandferrasols)atCAX-06,CAX-03,TAP-04wasusedtoestimatefine-rootproductioninthissite.
Site CAX-06 CAX-03 CAX-08 TAP-04 MAN-05 TAM-05 TAM-06 AGP-01 AGP-02 ZAR-01
NPP S.E. NPP S.E. NPP S.E. NPP S.E. NPP S.E. NPP S.E. NPP S.E. NPP S.E. NPP S.E. NPP S.E.
NPPcanopy 3.8 0.10 3.5 0.10 5.4 0.20 6.5 0.70 3.6 0.70 5.6 0.30 4.6 0.24 3.9 0.20 3.7 0.20 2.7 0.10
NPPbranch 1.0 1.00 1.0 1.00 1.0 1.00 1.0 1.00 1.0 1.00 1.0 1.00 1.0 1.00 1.0 1.00 1.0 1.00 1.0 1.00
NPPstem 1.7 0.21 2.6 0.20 2.5 0.26 3.8 0.07 2.6 0.06 2.8 0.24 2.6 0.42 3.4 0.30 3.8 0.30 1.3 0.30
NPPcoarseroot 0.4 0.04 0.4 0.03 0.5 0.05 1.0 0.30 0.8 0.20 0.6 0.10 0.6 0.09 0.7 0.06 0.8 0.06 0.3 0.06
NPPfineroot 3.9 0.40 4.0 0.90 7.6 0.93 2.0 0.30 3.3 0.34 6.8 1.00 4.8 0.57 2.2 0.40 2.2 0.40 3.9 0.68
NPPvoc 0.1 0.13 0.1 0.13 0.1 0.13 0.1 0.13 0.1 0.13 0.1 0.13 0.1 0.10 0.1 0.10 0.1 0.10 0.1 0.10
NPPAG 6.7 1.04 7.2 1.03 9.0 1.06 11.4 1.20 7.3 1.23 9.5 1.08 8.4 1.11 8.4 1.07 8.6 1.07 5.1 1.05
NPPBG 4.2 0.40 4.4 0.90 8.1 0.93 3.0 0.40 4.1 0.40 7.4 1.00 5.4 0.58 3.0 0.41 3.0 0.40 4.2 0.68
NPPtotal 10.9 1.11 11.6 1.37 17.0 1.41 14.4 1.30 11.4 1.29 16.9 1.47 13.8 1.26 11.3 1.14 11.7 1.14 9.3 1.26
of available information. Probable sources of unaccounted variedbetween3.0±0.4MgCha−1yr−1atTAP-04,AGP-01
errors are discussed throughout the text and their potential andAGP-02and8.1±0.9MgCha−1yr−1atCAX-08.
magnitudeisquantifiedinClarketal.(2001a). To investigate if NPP in our analysis presents the same
All the results of the estimated fluxes reported in this trend as proposed by Malhi et al. (2004), where plots on
study are in MgCha−1yr−1. 1MgCha−1yr−1 is equal to morefertilesoilsinwesternAmazoniahavegreaterNPP ,
stem
100gCm−2yr−1,or0.264µmolCm−2s−1. we ordered the data presented in Table 3 by increasing soil
The partitioning of NPP into its subcomponents, the availablephosphorus(Fig.2). Asexpected,themorefertile
total
relationship between NPP and NPP and the effect sites sit to the west, with exception of the “artificially” fer-
canopy stem
of soil and leaf nutrient status and soil texture on patterns tileTerraPretasite,CAX-08intheeast(themostfertileof
ofabove-andbelow-groundNPPacrossthetenAmazonian all our sites), and the anomalous white sand ZAR-01 in the
sites was assessed using linear regression analysis. In ad- west. ThetrendofincreasedNPPstem towardsthemorefer-
dition, we ran a set of correlation analyses, including the tilesites,assuggestedbyMalhietal.(2004)isnotobviousin
Pearson product-moment, Spearman rank and Kendall tau, oursmallerdataset. However,thereisatendencyofgreater
between NPPtotal, NPPAG, and NPPBG and climate and en- NPPAG, NPPBG and NPPtotal towards the more fertile sites,
vironmental variables. We opted for presenting the results whichwillbefurtherexploredinthefollowingsections.
of both parametric and non-parametric tests because of our NPP varied between 2.7±1.1MgCha−1yr−1 at the
canopy
small sample size (n between 7 and 9). A z-test was ap- white sand plot (ZAR-01) and 6.5±0.7MgCha−1yr−1
plied, when necessary, to compare mean values and regres- at Tapajo´s (TAP-04) (Fig. 3). NPP varied between
stem
sion slopes. For the regression analyses, plots AGP-01 and 1.3±0.3MgCha−1yr−1 at the white sand plot (ZAR-01)
AGP-02 were merged into a single plot average to avoid and 3.8±0.1MgCha−1yr−1 at Tapajo´s (TAP-04), while
spatial autocorrelation issues. Moreover, for the analyses NPP variedbetween2.0±0.3MgCha−1yr−1 atTAP-
fineroot
wherebelow-groundproductivityisexplicitlytakenintoac- 04and7.6±0.9MgCha−1yr−1attheanthrosolCAX-08.
count,plotMAN-05wasremovedasplotlevelestimatesof WiththenotableexceptionoftheTAP-04site,NPP
canopy
NPPfinerootisinexistent. was greater in the more fertile sites. NPPstem, on the other
hand,ismaximalintheplotsTAP-04,AGP-01andAGP-02,
which are in the middle of our soil fertility gradient. Con-
4 Results versely, these same plots have the lowest NPPfineroot among
all plots. Overall, sites on the most fertile soils tended to
4.1 Patternsofnetprimaryproductivityacrossthesites have higher NPPfineroot, with values being similarly high in
theveryfertileanthrosolCAX-08andinthemoderatelyfer-
The estimated NPP for the ten plots analysed ranged tilecambisolsandalisolsatTambopata(TAM-05andTAM-
total
between 9.3±1.3MgCha−1yr−1 at the white sand 06)(Fig.3).
plot, ZAR-01, and 17.0±1.4MgCha−1yr−1 at the The TAP-04 site has distinct patterns of extremely high
Terra Preta site, CAX-08 (Table 3). Similarly, the NPP and low NPP in comparison to other plots with
AG BG
above-ground NPP (NPP ) has its lowest value at similarsoilandclimatecharacteristics. TheforestatTapajo´s
AG
ZAR-01 (5.1±1.1MgCha−1yr−1), however, the high- isallocatingadisproportionalamountofCtoabove-ground
est NPP was estimated for the Tapajo´s site, TAP-04 biomass gain, which may be a consequence of large-scale
AG
(11.4±1.2MgCha−1yr−1). Below-ground NPP (NPP ) recentnaturaldisturbanceorchronicon-goingmortality(see
BG
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L.E.O.C.Araga˜oetal.: NetprimaryproductivityinAmazonianforests 2767
Fig.2. Thenetprimaryproductivityofthetenstudiedsites. Bars
correspondtotheNPPtotalofeachsite.Eachbargivestheabsolute
contributionofeachsubcomponenttotheNPPtotal.Negativevalues
wereusedtorepresentthebelow-groundproductivity,andtoobtain
thecorrectpositivevaluesbelow-groundcomponentsmustbemul-
tipliedby−1. Sitesareorderedinanincreasedorderofsoilavail-
ablephosphorus(Table2)andallvaluesareinMgCha−1yr−1.
discussion section). For subsequent analyses we therefore
presentsomeoftheresultsbothwithandwithouttheTapajo´s
site.
4.2 PartitioningofNPP intoitssubcomponents
total
Theregressionanalysisshowedthatthereisasignificantin- Fig.3. Thenetprimaryproductivityofthemajorsubcomponents
crease of both NPPAG (R2=0.58, p=0.02, n=9) and NPPBG of the NPPtotal in the ten studied sites: (a) fine litter production;
(R2=0.55, p=0.03, n=8) with increasing NPP (Fig. 4a). (b) stem production; and (c) fine root production. All values are
total
Thisrelationshipbecomesmuchmoresignificantwithoutthe in MgCha−1yr−1with their respective standard errors. Sites are
plot TAP-04 forboth NPP (R2=0.76, p=0.005, n=8) and rankedbyincreasingsoilavailablephosphorus(Table2).
AG
NPP (R2=0.83, p=0.004, n=7) (Fig. 4a). This indicates
BG
that the partitioning pattern may differ between old-growth
systemsin“quasi-equilibrium”andrecentlydisturbedforests However, Fig. 4b shows that the proportion of NPPtotal al-
(Malhietal.,2009). located below-ground is inversely correlated with the total
There is no significant difference (z-test) in the slopes of amount of C allocated to stem growth (R2=0.58, p=0.03,
therelationofNPP andNPP withNPP whetheror n=8). However,thisresultcouldbesomewhatbiasedbythe
AG BG total
not TAP-04 is included. This is indicative of fairly invari- factthatourestimationofNPPcoarseroot accountedinthees-
antallocationbetweenNPPAG andNPPBG acrossthebroad timationofNPPBG iscalculatedasaproportionofNPPstem.
NPP gradient. Evenusingonlytheproportionallocatedtofinerootinstead
total
By dividing the NPP of each component by NPP we ofthetotalbelow-groundallocation,whichisanindependent
total
quantified the relative proportion of NPP allocated to measurement, the relationship is strong (R2=0.61, p=0.02,
total
each component. Our results show that the ten Amazo- n=8).
nian forests studied allocate between 53% (CAX-08) and NPP is very strongly correlated with NPP
total canopy
79% (TAP-04) of the NPPtotal into NPPAG and between (R2=0.73, p=0.003, n=9), especially when TAP-04 is ex-
21% (TAP-04) and 37% (CAX-08) into NPPBG. We found cluded (R2=0.98, p<0.001, n=8). As NPPcanopy is a ma-
that NPPcanopy, NPPstem and NPPfineroot are on average jor component of NPPtotal the result of the previous anal-
33.5±1.5%,21.3±2.2%,31.4±3.5%oftheNPPtotal,respec- ysis may be redundant. To check the validity of this test
tively. we regressed NPP against the result of the difference
canopy
TherelativeproportionofNPPallocatedtobelow-ground between NPP and NPP . The correlation between
total canopy
(NPP /NPP ) was not significantly related to NPP these two completely independent variables was significant
BG total total
assuggestedabovebytheanalysisoftheregressionslopes. when excluding TAP-04 (R2=0.38, n=9, p=0.08; R2=0.90,
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2768 L.E.O.C.Araga˜oetal.: NetprimaryproductivityinAmazonianforests
with and without the Tapajo´s site respectively) (Fig. 5a, c).
Interestingly, stem production did not vary much along the
NPP gradient (Fig. 5b). NPP hence seems to be a
canopy
strong predictor of NPP in old-growth, low disturbance
total
Amazonianforestswiththeinvertedlinearregressionbeing
NPP =2.81(±0.25)×NPP −1.22(±1.06).
total canopy
In summary, the sites with higher NPP tend to have
total
higher NPP (mainly higher NPP ) and also higher
AG canopy
NPP (mainly NPP ). The fractional allocation of
BG fineroot
NPP tobelow-groundisinvariantacrosstheNPP gra-
total total
dientbutvariesinverselywithNPP ,decreasingfrom47%
stem
whenNPP =2.5MgCha−1yr−1 (CAX-08)to21%when
stem
NPP =3.8MgCha−1yr−1(TAP-04).
stem
4.3 RelationshipbetweenNPP andNPP
canopy stem
Malhi et al. (2004) reported a strong proportionality be-
tween NPP and NPP . They combined data on lit-
canopy stem
terfall and stem production from sites investigated in their
study and published by Clark et al. (2001a) and found
that: NPP =1.73 (±0.09)×NPP . Despite the lin-
stem canopy
ear trend, we did not find a significant relationship using
only our dataset (NPP =1.63 (±0.14)×NPP , n=9,
stem canopy
p=0.2). The weak relationship observed in our data alone
is mainly caused by Colombian site (AGP) with high stem
production and relatively low litterfall production. Without
this plot, the relationship is similar to the one presented by
Malhi et al. (2004), with no significant difference between
theslopes(z-test)(NPP =1.78(±0.11)×NPP , n=8,
canopy stem
R2=0.64, p<0.02). A significant relationship is also re-
Fig. 4. (a) The relationship between the above-ground NPP tained (NPP =1.67 (±0.07)×NPP , n=29, R2=0.67,
canopy stem
and the total NPP (dark grey squares), with the regression lines
p<0.001) when we merge all data together, including this
for all data (black) and without the Tapajo´s site (black dashed).
studyandMalhietal.(2004)(Fig.6).
The linear regression equations are (all data – NPPAG=0.51
(±0.16)×NPPtotal+1.55 (± 2.17), n=9, R2=0.58, p=0.02; with-
4.4 Effectofsoilandleafphosphorusandnitrogenand
outTapajo´s–NPPAG=0.43(±0.10)×NPPtotal+2.15(±1.32),n=8,
R2=0.76, p=0.005) and the relationship between below-ground soiltextureonpatternsofabove-andbelow-ground
NPP and the total NPP (light grey triangles), with the regression NPPinAmazonia
linesforallsite(grey)andwithouttheTapajo´ssite(greydashed).
The linear regression equations are (all data – NPPAG=0.49 Theobservedresponsesinourstudyareconsistentwiththe
(±0.18)×NPPtotal−1.55(±2.43),n=8,R2=0.55,p=0.03;without predictionsofthehypothesisofsoilphosphoruslimitationof
Tapajo´s – NPPBG=0.55 (±0.11)×NPPtotal−2.05 (± 1.49), n=7, NPPinAmazoniantropicalforests(seealsoQuesadaetal.,
R2=0.83, p=0.004). (b) The relationship between the propor- 2009a). We demonstrated that NPP is significantly cor-
total
tion of NPPtotal allocated below-ground (NPPBG/NPPtotal) and relatedtosoilavailablephosphorus(R2=0.54,n=9,p=0.03)
the NPPAG (dark grey squares), NPPcanopy (black triangles) and (Fig. 7a). The correlation between these two variables was
NPPstem (light grey diamonds). The regression line in black also significant according to the Spearman rank correlation
indicates a significant relationship between (NPPBG/NPPtotal)
(R=0.73, n=9, p=0.03)andtheKendalltau(tau=0.54, n=9,
and NPPstem ((NPPBG/NPPtotal)=−0.08 (±0.03)×NPPstem+0.59
(±0.08),n=8,R2=0.58,p=0.03). p=0.05)(Table4). Ontheotherhand,wedidnotfindaclear
relationship between NPP and soil nitrogen (R2=0.29,
total
p=0.13)(Fig.7b). Wealsodidnotfindsignificantrelation-
ships between NPP and any other soil and climate vari-
total
n=8, p<0.001, with and without considering the Tapajo´s able,excepttotalextractableP(seeQuesadaetal.,2009c,for
siterespectively),reinforcingthesignificanceofthecorrela- method) according to both Spearman (p=0.01) and Kendall
tionbetweenNPP andNPP . Moreover, NPP is tau (p=0.02) (Table 4). These results indicate that soil
total canopy total
alsosignificantlycorrelatedwithNPP whenexcluding phosphorus is likely to be more important than nitrogen in
fineroot
thesiteTAP-04(R2=0.44,p=0.07andR2=0.77,p<0.009, thedeterminationofNPP acrossAmazonia. Theslopeof
total
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