Source: INPE and IBGE

What did we know about the biogeochemsitry of tropical forests in 1982?What did we know about the biogeochemsitry of tropical forests in 1982? Paradox - luxurious vegetation under poor tropical soils Paradox - luxurious vegetation under poor tropical soils Hardy (1936), Milne (1937): “The trees depend for their maintenance on a nearly Hardy (1936), Milne (1937): “The trees depend for their maintenance on a nearly self-contained circulation of plant nutrients elements”self-contained circulation of plant nutrients elements” Larger nutrient stocks in the biomass not in the soil Larger nutrient stocks in the biomass not in the soil Nutrient conserving mechanism: Nutrient conserving mechanism: superficial roots superficial roots mycorrhizae mycorrhizae rapid turnover of small roots rapid turnover of small roots sclerophyllous leaves sclerophyllous leaves compounds against herbivory compounds against herbivory epiphylls Medina Jordan epiphylls Medina Jordan What did we know about the biogeochemsitry of tropical forests in 1982?What did we know about the biogeochemsitry of tropical forests in 1982? Paradox - luxurious vegetation under poor tropical soils Paradox - luxurious vegetation under poor tropical soils Hardy (1936), Milne (1937): “The trees depend for their maintenance on a nearly Hardy (1936), Milne (1937): “The trees depend for their maintenance on a nearly self-contained circulation of plant nutrients elements”self-contained circulation of plant nutrients elements” Larger nutrient stocks in the biomass not in the soil Larger nutrient stocks in the biomass not in the soil Nutrient conserving mechanism: Nutrient conserving mechanism: superficial roots superficial roots mycorrhizae mycorrhizae rapid turnover of small roots rapid turnover of small roots sclerophyllous leaves sclerophyllous leaves compounds against herbivory compounds against herbivory epiphylls Medina Jordan epiphylls Medina Jordan

What did we know about the biogeochemsitry of tropical forests in 1982? Several investigators published in Plant and Soil 67 (1982) studies showing…. Stocks of N in tropical soil larger than stocks of N in the biomass Stocks of N in tropical soil larger than stocks of N in the biomass (opposite of Ca, Mg, Na, K) High input of N via biological fixation High input of N via biological fixation Suggesting open N cycle: high input and losses Suggesting open N cycle: high input and losses N “equilibrium”: fragile and complex balance – land use would disrupt N “equilibrium”: fragile and complex balance – land use would disrupt such balance Tropical forest richer in N than temperate forests Tropical forest richer in N than temperate forests What did we know about the biogeochemsitry of tropical forests in 1982? Several investigators published in Plant and Soil 67 (1982) studies showing…. Stocks of N in tropical soil larger than stocks of N in the biomass Stocks of N in tropical soil larger than stocks of N in the biomass (opposite of Ca, Mg, Na, K) High input of N via biological fixation High input of N via biological fixation Suggesting open N cycle: high input and losses Suggesting open N cycle: high input and losses N “equilibrium”: fragile and complex balance – land use would disrupt N “equilibrium”: fragile and complex balance – land use would disrupt such balance Tropical forest richer in N than temperate forests Tropical forest richer in N than temperate forests

What do we know about the N biogeochemsitry of terra-firme forests today? What do we know about the N biogeochemsitry of terra-firme forests today?

Manaus – Cuieiras Reserva – INPA – LBA site Source: Luizão et al. (2004); Nardoto et al. (2008) Source: Luizão et al. (2006); Nardoto et al. (2008)

Santarém FLONA – Tapajós IBAMA LBA site Source: Silver et al. (2000)

Santarém FLONA – Tapajós IBAMA LBA site Source: Silver et al. (2000)

Caxiuanã National Forest – Museu Goeldi – LBA site Source: Sotta et al. (2008)

NH 4 + NO 3 - N2N2N2N2 OM Mineralization Nitrification N 2 O + N 2 + NO Denitrification Biological fixation NH 3 Volatilization 0‰ 15 to 35‰ 0 to 33‰ 29‰ -2 to +2‰ Isotopic Fractionation in the Nitrogen Cycle Source: Högberg, N

Terra-Firme (sand soils) 15 N 14 N 15 N-depletion 15 N-depletion δ 15 N 14 N 15 N Gaseous N losses (NO + N 2 O) 15 N 14 N 15 N-enrichment δ 15 N 15 N Leaching 14 N 15 N Gaseous N losses (NO + N 2 O) Leaching Terra-Firme (clay soils) 15 N 14 N Source: Michela Figueira

Source: Nardoto et al. (2008); Silver et al. (2000); Sotta et al. (2008) Terra-firme LBA site: Manaus, Santarém and Caixuanã

Maburu Hill Forest Reserve – Guyana (there is good science outside LBA…) Source: Pons et al. (2007)

Santarém SGC Manaus Rebio Samuel Caxiuanã Sotta et al. (2008) Source: Nardoto et al. (2008) See: Perez et al. (2006 See: Perez et al. (2006) Mabura - Guyana Pons et al. (2007) Terra-firme sites under clay soils

Terra-firme forest under the same precipitation regime (local scale)

Terra-firme forest under the same soil type (texture) but with distinct annual rainfall but with distinct annual rainfall

W. Schroeder

Forest x Pasture (disturbance of the equilibrium) Source: Mellilo, Neill, Cerri and others…..several references

Source: “handsome” Davidson et al. (2008)

What do we know about the N biogeochemsitry of tropical forests today? Terra-firme forests are indeed N-rich systems with an “intense” N cycling via soil- plant-atmoshpere. They are richer than temperate forests, white-sand vegetation types, like caatingas and campinaras, and also richer than savannas, like cerrados Terra-firme forests are indeed N-rich systems with an “intense” N cycling via soil- plant-atmoshpere. They are richer than temperate forests, white-sand vegetation types, like caatingas and campinaras, and also richer than savannas, like cerrados Considering local scales this richness and “intensity” depends on the soil texture Considering local scales this richness and “intensity” depends on the soil texture Considering a regional scale, besides soil texture, annual precipitation is another important driver in the N richness and “intensity “ of terra-firme forests Considering a regional scale, besides soil texture, annual precipitation is another important driver in the N richness and “intensity “ of terra-firme forests The replacement of terra-firme forests by pasture tend to impoverish the N cycle The replacement of terra-firme forests by pasture tend to impoverish the N cycle and reduces its “intensity” As terra-firme forests recover from disturbances the richness and intensity of the As terra-firme forests recover from disturbances the richness and intensity of the N cycle tends to be restored. The degree of recovery is still unknown What do we know about the N biogeochemsitry of tropical forests today? Terra-firme forests are indeed N-rich systems with an “intense” N cycling via soil- plant-atmoshpere. They are richer than temperate forests, white-sand vegetation types, like caatingas and campinaras, and also richer than savannas, like cerrados Terra-firme forests are indeed N-rich systems with an “intense” N cycling via soil- plant-atmoshpere. They are richer than temperate forests, white-sand vegetation types, like caatingas and campinaras, and also richer than savannas, like cerrados Considering local scales this richness and “intensity” depends on the soil texture Considering local scales this richness and “intensity” depends on the soil texture Considering a regional scale, besides soil texture, annual precipitation is another important driver in the N richness and “intensity “ of terra-firme forests Considering a regional scale, besides soil texture, annual precipitation is another important driver in the N richness and “intensity “ of terra-firme forests The replacement of terra-firme forests by pasture tend to impoverish the N cycle The replacement of terra-firme forests by pasture tend to impoverish the N cycle and reduces its “intensity” As terra-firme forests recover from disturbances the richness and intensity of the As terra-firme forests recover from disturbances the richness and intensity of the N cycle tends to be restored. The degree of recovery is still unknown

The big “gap” The major “fuel” of the nitrogen cycle of terra-firme forests is biological The major “fuel” of the nitrogen cycle of terra-firme forests is biological nitrogen fixation. This is recognized since 1936, however, it appears that legumes only fix nitrogen under special conditions. We do not understand why. We need a better understanding of N inputs to the forest via BNF. The big “gap” The major “fuel” of the nitrogen cycle of terra-firme forests is biological The major “fuel” of the nitrogen cycle of terra-firme forests is biological nitrogen fixation. This is recognized since 1936, however, it appears that legumes only fix nitrogen under special conditions. We do not understand why. We need a better understanding of N inputs to the forest via BNF. N 2 + 3H 2 + energy 2NH 3

Future needs Modelling efforts – Rainfor data - 82 sites (Jon Lloyd and colleagues) Modelling efforts – Rainfor data - 82 sites (Jon Lloyd and colleagues) Future needs Modelling efforts – Rainfor data - 82 sites (Jon Lloyd and colleagues) Modelling efforts – Rainfor data - 82 sites (Jon Lloyd and colleagues) MAP (mm) Clay (0-5cm) Foliar  15 N Source: Nardoto et al. (in prep.) N richness & intensity