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Net nitrogen mineralization and net nitrification rates in soils following deforestation for pasture across the southwestern Brazilian Amazon Basin landscape (1997)

Neill, Christopher ; Piccolo, Marisa C. ; Cerri, Carlos C. ; [et al.]

Springer

Oecologia 110 (1997), S. 243-252

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ISSN: 1432-1939

Keywords: Key words Brazilian Amazon ; Tropical forest ; Tropical pasture ; Nitrification ; Nitrogen mineralization

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Previous studies of the effect of tropical forest conversion to cattle pasture on soil N dynamics showed that rates of net N mineralization and net nitrification were lower in pastures compared with the original forest. In this study, we sought to determine the generality of these patterns by examining soil inorganic N concentrations, net mineralization and nitrification rates in 6 forests and 11 pastures 3 years old or older on ultisols and oxisols that encompassed a wide variety of soil textures and spanned a 700-km geographical range in the southwestern Brazilian Amazon Basin state of Rondônia. We sampled each site during October-November and April-May. Forest soils had higher extractable NO3 −-N and total inorganic N concentrations than pasture soils, but substantial NO3 −-N occurred in both forest and pasture soils. Rates of net N mineralization and net nitrification were higher in forest soils. Greater concentrations of soil organic matter in finer textured soils were associated with greater rates of net N mineralization and net nitrification, but this relationship was true only under native forest vegetation; rates were uniformly low in pastures, regardless of soil type or texture. Net N mineralization and net nitrification rates per unit of total soil organic matter showed no pattern across the different forest sites, suggesting that controls of net N mineralization may be broadly similar across a wide range of soil types. Similar reductions in rates of net N transformations in pastures 3 years old or older across a range of textures on these soils suggest that changes to soil N cycling caused by deforestation for pasture may be Basin-wide in extent. Lower net N mineralization and net nitrification rates in established pastures suggest that annual N losses from largely deforested landscapes may be lower than losses from the original forest. Total ecosystem N losses since deforestation are likely to depend on the balance between lower N loss rates from established pastures and the magnitude and duration of N losses that occur in the years immediately following forest clearing.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s004420050157

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2

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Natural abundance of 15N in soils along forest-to-pasture chronosequences in the western Brazilian Amazon Basin (1994)

Piccolo, Marisa C. ; Neill, Christopher ; Cerri, Carlos C.

Springer

Oecologia 99 (1994), S. 112-117

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ISSN: 1432-1939

Keywords: Stable isotopes ; Nitrogen ; Fixation Forest ; Rondônia

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract We examined the natural abundance of 15N in soil profiles along two chronosequences in the western Brazilian Amazon Basin state of Rondônia, to investigate possible mechanisms for changes to soil nitrogen sources and transformations that occur as a result of land use. One chronosequence consisted of forest and 3-, 5- and 20-year-old pasture, the other of forest and 8- and 20-year-old pasture. The δ15N values of surface soil and soil to 1 m depth in the native forest ranged from 9.8 to 13.6‰ and were higher than reported for temperate forest soils. Fractionation associated with nitrification and denitrification and selective losses of 15N-depleted nitrate, could potentially result in a strong enrichment of nitrogen in soil organic matter over the time scale of soil development in highly weathered tropical soils. Pasture surface soils were 1–3‰, depleted in 15N compared with forest soils. Lower δ15N values in 20-year-old pastures is consistent with greater cumulative inputs of 15N-depleted atmospheric-derived nitrogen, fixed by free-living bacteria associated with planted pasture grasses in older pastures, or differential plant utilization of soil inorganic N pools with different δ15N values. The pattern of δ15N values following conversion of forest to agricultural use differs from the pattern in the temperate zone, where pasture or cultivated soils are typically more enriched in 15N than the forest soils from which they were derived.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00317090

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Net nitrogen mineralization and net nitrification along a tropical forest-to-pasture chronosequence (1994)

Piccolo, Marisa C. ; Neill, Christopher ; Cerri, Carlos C.

Springer

Plant and soil 162 (1994), S. 61-70

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ISSN: 1573-5036

Keywords: Amazonia ; Brazil ; nitrification ; nitrogen mineralization ; tropical forest ; tropical pasture ; ultisol

Source: Springer Online Journal Archives 1860-2000

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Abstract Soil inorganic nitrogen pools, net mineralization and net nitrification rates were compared during the dry season along a chronosequence of upland (terra firme) forest, 3-, 9- and 20-year-old pastures in the western Brazilian Amazon Basin state of Rondônia to investigate the influence of forest conversion to pasture on soil nitrogen cycles. Surface soil (0 to 10 cm) from forest had larger extractable inorganic nitrogen pools than pasture soils. In the forest, NO 3 − pools equaled or exceeded NH 4 + pools, while pasture inorganic N pools consisted almost exclusively of NH 4 + . Rates of net N mineralization and net nitrification in seven -day laboratory incubations were higher in the seven - day forest than in the pastures. Net N mineralization rates did not differ significantly among different-aged pastures, but net nitrification rates were significantly lower in the 20-year-old pasture. Higher net N mineralization and net nitrification rates were measured in laboratory and in situ incubations of sieved soil, compared with in situ incubations of intact soil cores. Rates calculated in seven-day incubations were higher than determined by longer incubations. Sieving may increase N mineralization and/or decrease N immobilization compared with intact cores. We concluded that 7-day laboratory incubation of sieved soil was the most useful index for comparing N availability across the chronosequence of forest and pasture sites. High net nitrification rates in forest soils suggest a potential for NO 3 − losses either through leaching or gaseous emissions.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF01416090

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4

Electronic Resource

15N natural abundance in forest and pasture soils of the Brazilian Amazon Basin (1996)

Piccolo, Marisa C. ; Neill, Christopher ; Melillo, Jerry M. ; [et al.]

Springer

Plant and soil 182 (1996), S. 249-258

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ISSN: 1573-5036

Keywords: nitrogen ; nitrogen fixation ; stable isotopes ; tropical forest ; tropical pasture

Source: Springer Online Journal Archives 1860-2000

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Abstract The natural abundance of 15N was examined in soil profiles from forests and pastures of the Brazilian Amazon Basin to compare tropical forests on a variety of soil types and to investigate changes in the sources of nitrogen to soils following deforestation for cattle ranching. Six sites in the state of Rondônia, two sites in Pará and one in Amazonas were studied. All sites except one were chronosequences and contained native forest and one or more pastures ranging from 2 to 27 years old. Forest soil δ15N values to a depth of 1 m ranged from 8‰ to 23‰ and were higher than values typically found in temperate forests. A general pattern of increasing δ15N values with depth near the soil surface was broadly similar to patterns in other forests but a decrease in δ15N values in many forest profiles between 20 and 40 cm suggests that illuviation of 15N-depleted nitrate may influence total soil δ15N values in deeper soil where total N concentrations are low. In four chronosequences in Rondônia, the δ15N values of surface soil from pastures were lower than in the original forest and δ15N values were increasingly depleted in older pastures. Inputs of atmospheric N by dinitrogen fixation could be an important N source in these pastures. Other pastures in Amazonas and Pará and Rondônia showed no consistent change from forest values. The extent of fractionation that leads to 15N enrichment in soils was broadly similar over a wide range of soil textures and indicated that similar processes control N fractionation and loss under tropical forest over a broad geographic region. Forest δ15N profiles were consistent with conceptual models that explain enrichment of soil δ15N values by selective loss of 14N during nitrification and denitrification.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00029056

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Nitrous oxide nitrification and denitrification 15N enrichment factors from Amazon forest soils (2011)

Perez, Tibisay ; Garcia-Montiel, Diana ; Trumbore, Susan E. ; [et al.]

Ecological Society of America

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Publication Date: 2022-05-25

Description: Author Posting. © Ecological Society of America, 2006. This article is posted here by permission of Ecological Society of America for personal use, not for redistribution. The definitive version was published in Ecological Applications 16 (2006): 2153–2167, doi:10.1890/1051-0761(2006)016[2153:NONADN]2.0.CO;2.

Description: The isotopic signatures of 15N and 18O in N2O emitted from tropical soils vary both spatially and temporally, leading to large uncertainty in the overall tropical source signature and thereby limiting the utility of isotopes in constraining the global N2O budget. Determining the reasons for spatial and temporal variations in isotope signatures requires that we know the isotope enrichment factors for nitrification and denitrification, the two processes that produce N2O in soils. We have devised a method for measuring these enrichment factors using soil incubation experiments and report results from this method for three rain forest soils collected in the Brazilian Amazon: soil with differing sand and clay content from the Tapajos National Forest (TNF) near Santarém, Pará, and Nova Vida Farm, Rondônia. The 15N enrichment factors for nitrification and denitrification differ with soil texture and site: −111‰ ± 12‰ and −31‰ ± 11‰ for a clay-rich Oxisol (TNF), −102‰ ± 5‰ and −45‰ ± 5‰ for a sandier Ultisol (TNF), and −10.4‰ ± 3.5‰ (enrichment factor for denitrification) for another Ultisol (Nova Vida) soil, respectively. We also show that the isotopomer site preference (δ15Nα − δ15Nβ, where α indicates the central nitrogen atom and β the terminal nitrogen atom in N2O) may allow differentiation between processes of production and consumption of N2O and can potentially be used to determine the contributions of nitrification and denitrification. The site preferences for nitrification and denitrification from the TNF-Ultisol incubated soils are: 4.2‰ ± 8.4‰ and 31.6‰ ± 8.1‰, respectively. Thus, nitrifying and denitrifying bacteria populations under the conditions of our study exhibit significantly different 15N site preference fingerprints. Our data set strongly suggests that N2O isotopomers can be used in concert with traditional N2O stable isotope measurements as constraints to differentiate microbial N2O processes in soil and will contribute to interpretations of the isotopic site preference N2O values found in the free troposphere.

Description: This work was funded by the National Science Foundation (SET, award #ATM-9905784; SCT, award #EAR- 0312004). We also received support from a National Science Foundation Major Research Instrumentation award (SCT, #ATM-9871077) and an instrumentation award to the University of California–Irvine from the W. M. Keck Foundation.

Keywords: Amazon forest soils ; Denitrification ; Isotopic enrichment factors ; Isotopomers ; Nitrification ; Nitrous oxide ; Site preference

Repository Name: Woods Hole Open Access Server

Type: Article

Format: application/pdf

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Runoff sources and land cover change in the Amazon : an end-member mixing analysis from small watersheds (2011)

Neill, Christopher ; Chaves, Joaquin E. ; Biggs, Trent ; [et al.]

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Publication Date: 2022-05-26

Description: Author Posting. © The Author(s), 2011. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Biogeochemistry 105 (2011): 7-18, doi:10.1007/s10533-011-9597-8.

Description: The flowpaths by which water moves from watersheds to streams has important consequences for the runoff dynamics and biogeochemistry of surface waters in the Amazon Basin. The clearing of Amazon forest to cattle pasture has the potential to change runoff sources to streams by shifting runoff to more surficial flow pathways. We applied end member mixing analysis (EMMA) to ten small watersheds throughout the Amazon in which solute composition of streamwater and groundwater, overland flow, soil solution, throughfall and rainwater were measured, largely as part of the Large-Scale Biosphere-Atmosphere Experiment in Amazonia. We found a range in the extent to which streamwater samples fell within the mixing space determined by potential flowpath end members, suggesting that some water sources to streams were not sampled. The contribution of overland flow as a source of stream flow was greater in pasture watersheds than in forest watersheds of comparable size. Increases in overland flow contribution to pasture streams ranged in some cases from 0% in forest to 27 to 28% in pasture and were broadly consistent with results from hydrometric sampling of Amazon forest and pasture watersheds that indicate 17- to 18-fold increase in the overland flow contribution to stream flow in pastures. In forest, overland flow was an important contribution to stream flow (45 to 57%) in ephemeral streams where flows were dominated by stormflow. Overland flow contribution to stream flow decreased in importance with increasing watershed area, from 21 to 57% in forest and 60 to 89% in pasture watersheds 〈10 ha to 0% in forest and 27 to 28% in pastures in watersheds 〉100 ha. Soil solution contributions to stream flow were similar across watershed area and groundwater inputs generally increased in proportion to decreases in overland flow. Application of EMMA across multiple watersheds indicated patterns across gradients of stream size and land cover that were consistent with patterns determined by detailed hydrometric sampling.

Description: This work was supported by National Science Foundation (DEB-0315656, DEB-0640661), the NASA LBA Program (NCC5-686, NCC5-69, NCC5-705, NNG066E88A) and by grants from Brazilian agencies FAPESP (03/13172-2) and CNPq (20199/2005-5).

Keywords: Cattle pasture ; Deforestation ; Flowpaths ; Principal components analysis ; Overland flow ; Soil solution

Repository Name: Woods Hole Open Access Server

Type: Preprint

Format: application/pdf

Format: image/jpeg

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