Nitrification Rates in Two Undisturbed Tropical Rain Forests and Three Slash-and-Burn Sites of the Venezuelan Amazon

Montagnini, Florencia; Buschbacher, R.

doi:10.2307/2388435

Cited by 62 publications

(43 citation statements)

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“…Mean rates of N net mineralization as obtained from 8-d in situ-incubations were close to values reported from other tropical forests on moderately fertile soils (1-3 μgN g −1 d −1 ), while lower mineralization rates were observed in forests on oxisols, ultisols or other less fertile substrates, and also in some montane Lamb 1980;Robertson 1984;Chandler 1985;Vitousek and Denslow 1986;Vitousek and Sanford 1986;Matson et al 1987;Marss et al 1988;Montagnini and Buschbauer 1989). That the mineralization rates in East Ecuador were relatively high at montane elevation may be explained by the rather low C/N ratios along this transect.…”

Section: Elevational Change In N Availabilitysupporting

confidence: 83%

Variability of indices of macronutrient availability in soils at different spatial scales along an elevation transect in tropical moist forests (NE Ecuador)

2010

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The availability of key plant nutrients may change with elevation in tropical mountains due to altitudinal gradients in temperature and moisture which affect pedogenesis and nutrient cycling. In a transect from upper lowland to montane forests in NE Ecuador, we tested the hypotheses that (1) the availability of P is low in low-elevation forests but increases upslope, while the availability of N is relatively high at low elevations but decreases with elevation, and (2) increasing amounts of calcium, magnesium and potassium are stored on top of the soil with progressive humus accumulation toward higher elevations, likely to improve nutrient availability. In each 20 plots in undisturbed natural forest at 500, 1000, 1500 and 2000 ma.s.l., we measured in situ N net mineralization and nitrification rate (N NM and N NI , buried bag method), plant-available phosphorus (P a , resin-bag method), and salt-exchangeable calcium, potassium and magnesium concentrations (Ca ex , K ex , Mg ex ) in the organic and mineral topsoils. N NM and N NI , and the Ca ex , K ex and Mg ex concentrations were much more variable at the plot level than across the four elevations, while P a varied equally at small and large spatial scales. P a increased more than 10fold from 500 to 2000 m. The net release of nitrate dominated over ammonium at all elevations. While mass-related N NM and N NI rates and also organic matter C/N ratio in the topsoil remained invariant along the slope, N NM and N NI rates per ground area decreased by about 40% from 500 to 2000 m. Thus, the N NM /P a ratio decreased markedly with elevation proving our first hypothesis. In support of the second hypothesis, the pools of Ca ex , Mg ex and K ex in the organic layers increased with elevation, demonstrating the key role that organic topsoil horizons are playing for forest nutrition at high elevations. We suggest that the large difference in N versus P availability of tropical (upper) lowland and montane forests is likely to be a key factor influencing the species composition and productivity along tropical mountain slopes.

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Section: Elevational Change In N Availabilitysupporting

confidence: 83%

Variability of indices of macronutrient availability in soils at different spatial scales along an elevation transect in tropical moist forests (NE Ecuador)

2010

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“…Robertson (1984) also reported 100% of net N mineralized was nitrified in a Costa Rican forest. Net nitrification rate exceeded net N mineralization 'rate during the wet season in Amazon Basin forests on both ultisols and oxisols near San Carlos, Venezuela (Montagnini and Buschbacher, 1989).…”

Section: Net N Mineralization and Net Nitrification In Tropical Foresmentioning

confidence: 89%

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

1994

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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 Rond6nia 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 + pools, while pasture inorganic N pools consisted almost exclusively of NH +. 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.

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“…In the Amazon, this pattern occurs over a wide area on Oxisols and Ultisols (Neill et al, 1997). Second, although rates of net N mineralization and net nitri®cation are lower in established pastures, inorganic N pools, net mineralization rates and net nitri®-cation rates may be elevated in the immediate postclearing period (Matson et al, 1987;Montagnini and Buschbacher, 1989). We currently interpret these patterns to indicate that after a brief period of elevated N turnover following the disturbance of clearing, N turnover gradually declines as pastures age.…”

Section: Introductionmentioning

confidence: 94%

Nitrogen dynamics in Amazon forest and pasture soils measured by 15N pool dilution

Neill

Píccolo²,

Melillo

et al. 1999

Soil Biology and Biochemistry

119

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Clearing tropical forests of the Amazon Basin for pasture alters rates of soil nitrogen cycling. Previous studies have shown that rates of soil net N mineralization and net nitri®cation are lower in established pastures than in forests. We compared soil inorganic N concentrations, rates of net and gross mineralization and net and gross nitri®cation in a chronosequence and an experimental slash-and-burn plot in RondoÃ nia. Soils of pastures 4, 10 and 21-yr-old contained more NH 4 + and less NO 3 À than soils of forest. Soil NH 4 + and NO 3 À concentrations were elevated for 2 months after burning but were similar to pools in the forest after 8.5 months. Rates of net N mineralization and net nitri®cation decreased from forest to 21-yr-old pasture. Rates of gross N mineralization were similar in forest, 4-and 10-yr-old pasture then declined in 21-yr-old pasture. These ®ndings indicate that when forests are converted to pasture, soil N turnover is maintained for a period of a decade or longer, but N turnover eventually slows in old pastures. As older pastures come to dominate deforested regions of the Amazon, the total N cycled in soils of the region is likely to decrease, but not as quickly as studies based on net mineralization and net nitri®cation alone would indicate. #

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Nitrification Rates in Two Undisturbed Tropical Rain Forests and Three Slash-and-Burn Sites of the Venezuelan Amazon

Cited by 62 publications

References 0 publications

Variability of indices of macronutrient availability in soils at different spatial scales along an elevation transect in tropical moist forests (NE Ecuador)

Variability of indices of macronutrient availability in soils at different spatial scales along an elevation transect in tropical moist forests (NE Ecuador)

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

Nitrogen dynamics in Amazon forest and pasture soils measured by 15N pool dilution

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