Chemical composition and nutrient loading by precipitation in the Trachypogon savannas of the Orinoco llanos, Venezuela

Montes, R.; Jose, Juan

doi:10.1007/bf00004219

Cited by 16 publications

(4 citation statements)

References 23 publications

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“…Our estimates of wet atmospheric deposition of N and P based on literature data from East Africa and our own measurements were in line with values reported for other savanna ecosystems (1.3-6.4 kg N and 0.3-0.5 kg P ha -1 y -1 ) (Montes and San Jose 1989;Chacon and others 1991;Sanhueza and Crutzen 1998;Laclau and others 2005;Bustamante and others 2006). Dry deposition is likely to be minimal in our study area because the prevailing winds come from the Indian Ocean; this was also found for a coastal savanna in Congo (Laclau and others 2005).…”

Section: Nutrient Input and Output Fluxes And Balancessupporting

confidence: 90%

N and P Cycling in Tanzanian Humid Savanna: Influence of Herbivores, Fire, and N2-Fixation

2010

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Availabilities of nitrogen (N) and phosphorus (P) have a strong influence on plant growth and the species composition of savannas, but it is not clear how these availabilities depend on factors such as fire, N 2-fixation, and activities of wild herbivores and cattle. We quantified soil N and P availabilities in various ways (extractable pools, mineralization, resin adsorption) along vegetation gradients within a recently abandoned cattle ranch and a former game reserve in Tanzania (both areas now part of the Saadani National Park). We also assessed annual N and P balances to evaluate how long-term availabilities of N and P are affected by large herbivores, symbiotic N 2-fixation, and fire. The results show that cattle ranching led to a spatial redistribution of nutrients, with the local accumulation of P being stronger and more persistent than that of N. In the former game reserve, intensively grazed patches of short grass tended to have elevated soil N and P availabilities; however, because quantities of nutrients removed through grazing exceeded returns in dung and urine, the nutrient balances of these patches were negative. In dense Acacia stands, N 2-fixation increased N availability and caused a net annual N input. Fire was the major cause for nutrient losses from tallgrass savanna, and estimated N inputs from the atmosphere and symbiotic N 2-fixation were insufficient to compensate for these losses. Our results call into question the common assumption that N budgets in annually burned savanna are balanced; rather, these ecosystems are a mosaic of patches with both N enrichment and impoverishment, which vary according to the vegetation type.

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Section: Nutrient Input and Output Fluxes And Balancessupporting

confidence: 90%

N and P Cycling in Tanzanian Humid Savanna: Influence of Herbivores, Fire, and N2-Fixation

2010

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“…A similar value of 2.2 kg ha )1 yr )1 was reported for the input of inorganic N from bulk precipitation and dry deposition in a Trachypogon savanna in Venezuelan Llanos (Montes and San Jose 1989). The input of NH 4 -N was 2.0 kg ha )1 yr )1 , but organic nitrogen input was not measured.…”

Section: Atmospheric Depositionsupporting

confidence: 70%

“…The reported inputs of inorganic N in the South American savannas are lower than the values found in an African savanna ($5 kg ha )1 yr )1 ) (Villecourt and Roose 1978 cited by Abbadie et al 1992). Comparing atmospheric deposition inputs and the amount of N in above-and belowground plant biomass in a Trachypogon savanna, Montes and San Jose (1989) suggested that 19.5% of the N required for maximum biomass of 482 g m )2 during growth season was supplied by atmospheric deposition. They pointed out that the distribution of rains seemed to determine essential differences in the nutrient inputs, as the ratio of the nutrient input during the rainy and the dry season ranged from 2.3 to 7.8.…”

Section: Atmospheric Depositionmentioning

confidence: 99%

Nitrogen cycling in tropical and temperate savannas

et al. 2006

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Savannas are the most common vegetation type in the tropics and subtropics, ranging in physiognomy from grasslands with scattered woody plants to woodlands with heterogeneous grass cover. Productivity and organic matter turnover in savannas are controlled by interactions between water and nutrient availability, and this basic environmental structure is modified by fire frequency and land management practices. We compared temperate and tropical savannas in order to understand the strength of nitrogen (N) limitation of productivity. American tropical and temperate savannas are N limited systems, and the N cycle differs according to the woody plant density, fire frequency, land use change, N deposition and N fixation. Grazing and conversion to pasture have been the predominant land-use changes in most savannas. In the Cerrado and the Llanos tropical savannas, intensified use of fire for pasture management is leading to decreased woody plant density. Oppositely, in the Chaco and North American temperate savannas, fire suppression and grazing are leading to increases in woody density. In addition, the higher soil P availability in the Gran Chaco and the higher N deposition in North American savannas may be contributing to increases of N cycling and net productivity rates. Some aspects of the N budget for savannas of the American continent are still unclear and require further analysis to determine rates of N fixation, and to understand how spatial and temporal soil heterogeneity control N fluxes through soil solution and into streams.

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“…Venezuelan and Colombian flooded savannas are characterised by acidic soils and also by redox conditions which may induce Zn and Cu solubilisation; losses by leaching and external run-off (erosion) might reach limiting levels unless they are compensated for by the inputs due to precipitation or by weathering of Zn and Cu accessory minerals. Precipitation water in neotropical savanna ecosystems is in general slightly or definitely acid [4,5], therefore, macro and micronutrient levels in such water are not expected to be particularly high. Moreover, savanna ecosystems, and within them, alluvial overflow plains in Venezuela are distant from the ocean and with a non-significant anthropogenic activity; consequently the composition of rain water should be minimally affected by marine aerosols.…”

Section: Introductionmentioning

confidence: 98%

Biogeochemistry and cycling of zinc and copper in a dyked seasonally flooded savanna

López‐Hernández

2008

Chemistry and Ecology

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There is very little information on the cycling of heavy metals in natural savannas. Venezuelan flooded savannas are characterised by acid soils with redox conditions which might induce Zn and Cu solubilisation. In those flooded savannas a network of small dykes has been constructed to control floods. The biomass accretion after dyking and the abundance of clay particles in the vertisols, dominant in the overflow plains, might be responsible for an increase in nutrient uptake and immobilisation. Due to the redox and pH conditions prevailing during flooding, some questions arise on the fate of the heavy metals. Are they significantly lost as soluble and particulate forms, which in turn, can induce a potential risk of microelement deficiency? Or, on the contrary, are heavy metal inputs in precipitation waters retained somewhere in the terrestrial pools of the watershed allowing for an adequate micronutrient economy? By using inputoutput budgets, which consider the total atmospheric input and total output in stream runoff (soluble and particulate) for zinc and copper we concluded that in Mantecal flooded savannas, a net accumulation of micronutrient in soils is actually occurring through organic and inorganic complexes, a process that is counterbalanced by the losses of particulates through erosion.

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Chemical composition and nutrient loading by precipitation in the Trachypogon savannas of the Orinoco llanos, Venezuela

Cited by 16 publications

References 23 publications

N and P Cycling in Tanzanian Humid Savanna: Influence of Herbivores, Fire, and N2-Fixation

N and P Cycling in Tanzanian Humid Savanna: Influence of Herbivores, Fire, and N2-Fixation

Nitrogen cycling in tropical and temperate savannas

Biogeochemistry and cycling of zinc and copper in a dyked seasonally flooded savanna

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