| 1. |
- Boyero, Luz, et al.
(författare)
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Riparian plant litter quality increases with latitude
- 2017
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Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- Plant litter represents a major basal resource in streams, where its decomposition is partly regulated by litter traits. Litter-trait variation may determine the latitudinal gradient in decomposition in streams, which is mainly microbial in the tropics and detritivore-mediated at high latitudes. However, this hypothesis remains untested, as we lack information on large-scale trait variation for riparian litter. Variation cannot easily be inferred from existing leaf-trait databases, since nutrient resorption can cause traits of litter and green leaves to diverge. Here we present the first global-scale assessment of riparian litter quality by determining latitudinal variation (spanning 107 degrees) in litter traits (nutrient concentrations; physical and chemical defences) of 151 species from 24 regions and their relationships with environmental factors and phylogeny. We hypothesized that litter quality would increase with latitude (despite variation within regions) and traits would be correlated to produce 'syndromes' resulting from phylogeny and environmental variation. We found lower litter quality and higher nitrogen: phosphorus ratios in the tropics. Traits were linked but showed no phylogenetic signal, suggesting that syndromes were environmentally determined. Poorer litter quality and greater phosphorus limitation towards the equator may restrict detritivore-mediated decomposition, contributing to the predominance of microbial decomposers in tropical streams.
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| 2. |
- Solomon, Christopher T., et al.
(författare)
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Sediment size and nutrients regulate denitrification in a tropical stream
- 2009
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Ingår i: Journal of The North American Benthological Society. - : University of Chicago Press. - 0887-3593 .- 1937-237X. ; 28:2, s. 480-490
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Tidskriftsartikel (refereegranskat)abstract
- Landuse changes might alter N cycling in tropical aquatic ecosystems, but understanding of N cycling in tropical streams is limited. We measured actual and potential denitrification rates during the dry season in Rio Las Marias, a 4(th)-order Andean piedmont stream in Venezuela. Our objectives were to describe spatial and temporal variation in denitrification, quantify the effects of nutrient availability and substratum particle size on denitrification, and explore potential effects of anthropogenic sedimentation on denitrification. In 4 experiments, actual and potential denitrification rates ranged from 0 to 160 and from 0 to 740 mu g N(2)O-N m(-2) h(-1), respectively. Rates were distributed approximately log-normally because of spatial variation. During a 1-mo period, actual denitrification rates decreased exponentially from 37 +/- 39 to 5 +/- 7 mu g N(2)O-N m(-2) h(-1) (mean +/- SD), probably because of a decline in water-column NO(3)-N concentration from 41 +/- 14 to 12 +/- 3 mu g NO(3)-N/L. The texture (particle size) of stream substrata markedly affected denitrification rates. Actual rates were low in cobble, gravel, and fine sediments (< 5 mm), but in fine sediments, rates increased in response to addition of excess NO(3)-N and organic C. In a 3-km stream reach, actual (but not potential) denitrification rates increased with the proportion of fine sediments (< 2 mm) in mixed substrata. This increase was nonlinear, and the threshold value occurred at 37% fine particles, above which actual denitrification rates were almost always high. An experiment simulating the effects of anthropogenic sedimentation showed that topsoil inputs resulted in denitrification rates similar to 8x higher than rates in trials where excess NO(3)-N and organic C were supplied. Denitrification is a small but potentially significant sink for available N in this N-limited system. Anthropogenic sedimentation associated with landuse change might significantly increase denitrification rates in streams.
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