Soils&and&nutrient&cycling&in&tropical&forests&

Carlos&A.&Sierra&Max&Planck&Ins;tute&for&

Biogeochemistry&

Outline&

•  Nutrient&plant&demands&•  The&biogeochemical&heterogeneity&of&the&tropical&biome&

•  Humans&and&the&cycling&of&nutrients&

Essen;al&elements&for&life&

Essen%al(Nutrients(of(Plants(

& ( ( (Chemical ( (Atomic(Ionic(forms ( ( ( ( (Approximate(dry((((((((Element (((( ( (symbol( (weight(Absorbed(by(plants (____ (concentra%on_____((((Macronutrients&&&&Nitrogen & & & &N & & &14.01& & &NO3

I,&&NH4+ & & & & & & &4.0&%&Phosphorus & & &P & & &30.98& & &PO4

3I,&HPO42I,&H2PO4

I & & &&&&&&&0.5&%&Potassium& & &&& &K & & &39.10& & &K+ & & & & & & & &4.0&%&Magnesium & & &Mg & &24.32& & &Mg2+ & & & & & & &0.5&%&Sulfur & & & & &S & & &32.07& & &SO4

2I & & & & & & &0.5&%&Calcium & & & &Ca& &&&&&&40.08 & &&&&&&Ca2+ & & & & & & &1.0&%&

Micronutrients,Iron & & & & &Fe& & &55.85& & &Fe2+,&Fe3+ & & & & & &&200&ppm&Manganese & & &Mn & &54.94& & &Mn2+ & & & & & &&200&ppm&Zinc & & & & &Zn& & &65.38& & &Zn2+ & & & & & &&&&30&ppm&Copper & & & &Cu& &&&&&&63.54 & & &Cu2+ & & & & & &&&&10&ppm&Boron & & & & &B & & &10.82& & &BO3

2I,&B4O72I& & & & &&&&&&&&&&60&ppm&&

Molybdenum & & &Mo & &95.95& & &MoO42I & & & & & &&&&&&2&ppm&

Chlorine & & & &Cl & & &35.46& & &ClI && & & & & &&&&&3000&ppm&

Essen.al,Carbon & & & &C & & &12.01& & &CO2 & & & & & &&40&%&Hydrogen & & & &H & & &&&1.01 & & &H2O & & & & & &&&&6&%&Oxygen & & & &O & & &16.00& & &O2,&H2O & & & & & &&40&%&________________________________________________________________&

&Plant&;ssues&also&contain&other&elements&(Na,&Se,&Co,&Si,&Rb,&Sr,&F,&I)&which&are&not&needed&for&the&normal&growth&and&development.&

Primary&func;ons&of&elements&Func%on( Elements( Chemical(form( Examples(

Structural& H,&O,&C,&N,&P,&S,&Si,&B,&F,&Ca&

Organic&compounds&

Biological&molecules,&cell&walls,&;ssue,&skeletons,&etc.&

Electrochemical& H,&Na,&K,&Cl,&HPO4

I2&Free&ions& Message&

transmission,&cellular&signaling,&energy&metabolisms&

Cataly;c&(acid&base)&

Zn,&Ni,&Fe,&Mn& Complexed&with&enzymes&

Diges;on,&hydrolisis,&PO4&removal&in&acid&media&

Cataly;c&(redox)& Fe,&Cu,&Mn,&Mo,&Se&

Complexed&with&enzymes&

Reac;ons&with&O2,&N&fixa;on,&reduc;on&of&nucleo;des&

Sterner&&&Elser,&2002.&

Chapin&et&al.,&2011&

Nutrient&supply&constraints&the&produc;vity&of&terrestrial&ecosystems&

Chapin&et&al.&2002.&

N,&P,&and&K&are&the&most&important&nutrients&that&contribute&to&plant&growth&in&agroIecosystems&

Source:&FAO&2005&

Justus&von&Liebig's&Law(of(the(Minimum&

“Plant&growth&is&controlled&not&by&the&total&amount&of&resources,&but&by&the&scarcest&resource”&

y = min{fN (N), fP (P ), fK(K), . . . , fL(L)}

Nutrient&supply&constraints&the&produc;vity&of&ecosystems&

The&supply&of,&and&demand&for,&N&and&P&are&usually&in&close&balance&

Davidson&&&Howarth&2007.&&

N&and&P&are&the&most&important&nutrients&for&

biological∾vity&

Sterner&&&Elser&2002&

Different&biological&molecules&have&fixed&stoichiometric&propor;ons&

Sterner&&&Elser&2002&

C,&N,&and&P&can&be&found&in&constant&propor;ons&in&the&oceans&

N:P&ra;os&might&be&indicators&of&nutrient&limita;on&in&terrestrial&ecosystems&

N:P&<&14&

N:P&>&16&

N:P&ra;os&appear&to&indicate&P&limita;on&in&tropical&ecosystems&

Hedin&2004&

Soil&nutrients&change&with&soil&development&

Lambers&et&al.&2008&

Soil&pH&and&nutrient&concentra;ons&

Phosphorus&in&soils&decreases&with&;me&

Walker&&&Syers&1976&

Test&of&the&Walker&&&Syers’&model&in&a&longIterm&chronosequence&in&Hawaii&

Crews&et&al.&1995&

Test&of&the&Walker&&&Syers’&model&in&a&longIterm&chronosequence&

in&Hawaii&

Crews&et&al.&1995&

Changes&in&nutrient&limita;on&with&soil&development&

Vitousek&&&Farrington&1997&

Take&home&messages&

•  Nitrogen&and&phosphorus&are&the&main&nutrients&that&control&plant&growth&

•  N&and&P&limits&plant&produc;on&in&a&synergis;c&fashion.&Addi;ons&of&N&must&be&balanced&by&more&P&and&vice&versa.&

•  P&limita;on&is&related&to&soil&development.&As&a&consequence&tropical&forests&are&believe&to&be&P&limited.&&

The&biogeochemical&heterogeneity&of&the&tropical&biome&

Soils&of&Africa&

Source:&hmp://www.swac.umn.edu/classes/soil4505/doc/unit10af.htm&

USDA&soil&orders&and&soil&development&

Soils&of&the&Amazon&basin&

Quesada&et&al.&2011&

Soil&development&in&the&Amazon&

Oxisols&(USDA)&or&Ferralsols&(WRB)&

• Highly&weathered&• High&clay&content&but&of&low&ac;vity&(1:1Itype)&• Deep&soils&>&20m&• Good&drainage&• Low&natural&fer;lity&• High&concentra;ons&of&Fe&and&Al&oxides&• Moderately&acid&

Ul;sols&(overlaps&with&Plinthosols)&

• Highly&weathered&• Clay&weathering&and&transloca;on&• Acid&B&horizon&with&<&35%&CEC&• No&calcareous&material&• &<&10%&weatherable&minerals&in&topsoil&

Spodosolos&(Podzols)&

• Intensive&acid&leaching&• Subsurface&horizon&with&illuvia;on&of&organic&mamer&• WhiteIsand&horizon&of&eluvia;on&• Some&of&the&most&nutrient&poor&forest&in&the&tropics&

do&Nascimento&et&al.&(2004)&

But&tropical&forests&are&supposed&to&be&the&most&produc;ve&ecosystems&on&Earth!&

Beer&et&al.&2010&

Tropical&forest&paradox&

„The%tropical%rainforest%thus%has%a%rela2vely%rich%nutrient%economy%perched%on%a%nutrient7poor%substrate“%

Whimaker&1975&

Primary&produc;vity&is&controlled&by&the&availability&and&the&efficiency&of&resources&

NPP = min{L · LUE,N ·NUE,W ·WUE}

L = Light

N = Nutrients

W = Water

Agren&&&Andersson&2012&

Strategies&to&increase&NUE&in&tropical&forests&

•  Retransloca;on&•  NIfixa;on&and&symbio;c&associa;ons&

•  Root&mats&

Limi;ng&nutrients&are&retranslocated&before&leaf&abscission&&

Fife&et&al.&2003&

Roots&do&not&appear&to&retranslocate&nutrients&

Gordon&&&Jackson&2000&

N&fixa;on&in&tropical&forests&

Hedin&et&al.&2009&

NIfixing&organisms&

FreeIliving&N&fixers&in&a&tropical&forest&

Reed&et&al.&2008&

Legumes&are&important&NIfixers,&but&not&always,&not&everywhere&

Barron&et&al.&2010&

Roots&release&organic&substances&&(chelates&and&phosphatases)&to&

mineralize&P&

RootImats&

Jordan&&&Escalante&1980&

Strategies&to&increase&NUE&in&tropical&forests&

•  Retransloca;on&•  NIfixa;on&and&symbio;c&associa;ons&

•  Root&mats&

•  LongIlived&;ssue&(leaves)&•  Defense&compounds&against&herbivory&

•  Adjust&shoot&to&root&ra;os&

The&biogeochemical&heterogeneity&of&the&tropical&biome&

Wood&produc;vity&seems&related&to&soil&age&in&the&Amazon&basin&

Malhi&et&al.&2004&

Soil&P&may&explain&differences&in&aboveground&wood&produc;on&

But&aboveground&NPP&may&not&tell&us&the&whole&story&

Clay soils Sandy soils

Aboveground NPP

Prod

uctiv

ity (M

g C

ha−

1 yr−1

)

02

46

810

Clay soils Sandy soils

Belowground NPP

Prod

uctiv

ity (M

g C

ha−

1 yr−1

)

02

46

810

Clay soils Sandy soils

Total NPP

Prod

uctiv

ity (M

g C

ha−

1 yr−1

)

02

46

810

Clay soils Sandy soils

LAI index

LAI i

ndex

(m−2

m−2

)

02

46

810

Jimenez&et&al.&2014&

TakeIhome&message&

•  The&tropical&biome&is&highly&diverse&in&its&biogeochemistry,&but&most&regions&have&highly&weathered&soils&

•  Highly&weathered&soils&suggest&P&limita;on&in&these&forests,&however&they&are&s;ll&highly&produc;ve&

•  This&paradox&can&be&resolved&in&terms&of&the&efficiency&of&nutrient&use&

Humans&and&the&cycling&of&nutrients&

Shiuing&cul;va;on&

Shiuing&cul;va;on&

Ecosystem&recovery&auer&slashIandIburn&

Uhl&&&Jordan&1984&

Ecosystem&recovery&auer&slashIandIburn&

Uhl&&&Jordan&1984&

Recovery&cycle&and&soil&proper;es&

Chazdon&2014&

Biomass&recovery&in&tropical&America&

Poorter&et&al.&2016&Nature&530:&211I214&

Biomass&recovery&in&tropical&America&

Poorter&et&al.&2016&Nature&530:&211I214&

What&are&the&effects&of&large&scale&deforesta;on&on&nutrient&cycling?&

Effects&on&aqua;c&ecosystems&

Important&amounts&of&N&are&removed&by&deforesta;on,&but&it&can&recover&in&secondary&forests&

Markewitz&et&al.&2004&

P&is&also&removed&but&an&important&por;on&is&retained&by&minerals&in&the&soil&

Markewitz&et&al.&2004&

N&recovers&auer&agricultural&abandonment&

Davidson&et&al.&2007&

A&new&paradigm&

Davidson&et&al.&2007&

N&fixa;on&seems&to&be&key&for&phosphatase&produc;on&

Houlton&et&al.&2008&

C&stocks&can&recover&auer&decades&of&landIuse&

0 20 40 60 80 100

050

100

150

200

Successional age (years)

TAG

B (M

g C

ha!1 )

050

100

150

200

0 20 40 60 80 100

010

2030

4050

60

Successional age (years)

TBB

(Mg

C ha!1 )

010

2030

4050

60

0 20 40 60 80 100

02

46

810

Successional age (years)

TDM

(Mg

C ha!1 )

02

46

810

0 20 40 60 80 100

050

100

150

200

Successional age (years)

SO

C (M

g C

ha!1 )

050

100

150

200

0 20 40 60 80 100

0100

200

300

400

Successional age (years)

TCS

(Mg

C ha!1 )

0100

200

300

400

0 50 100 150

0.0

0.2

0.4

0.6

0.8

1.0

Successional age (years)

Proportion

TAGB/TCSTAGB/TM

Sierra&et&al.&2012&

Con;nuous&cul;va;on&and&fer;liza;on&

Stocking&2003&

However,&con;nuous&cul;va;on&is&not&sustainable&

2002 2004 2006 2008 2010 2012

0200

400

600

800

1000

Year

Ferti

lier u

se (k

g ha

-1 a

rabl

e la

nd)

ColombiaChinaGermanyUSAWorld

Phosphorous&peak&

Phosphorus&use&efficiency&

TakeIhome&messages&

•  SlashIandIburn&of&tropical&forests&make&nutrients&available&for&crops,&but&produc;vity&decline&over&;me&

•  Regrowing&forest&can&recover&nutrient&stocks&over&;me&

•  N&is&a&key&nutrient&for&forest&recovery&•  Current&fer;lizer&use&is&not&sustainable&

Topics&for&discussion&

•  Environmental&consequences&of&largeIscale&conversion&of&tropical&forests&(oil&palm,&soy).&

•  Sustainability&of&crop&produc;on&in&tropical&regions.&

•  Possible&solu;ons&to&balance&food&produc;on&and&nutrient&loss.&