Nutrient Limitation and the Stoichiometry of Nutrient Uptake in a Tropical Rain Forest Stream

Abstract

Nutrient limitation assessment is important to understand stream ecosystem functioning.Aquatic primary producers are often limited by nitrogen, phosphorus, or both, as assessed by nutrient diffusing substrata (NDS), a common method for assessing nutrient limitation in streams. But little is known regarding how this method relates to patterns of nutrient uptake at the whole-stream scale. We combined two techniques to examine nutrient limitation in a tropical stream. First, we conducted two NDS experiments using ammonium, nitrate, and phosphate alone and combined, to determine nutrient limitation at substrata scale over several weeks. Second, we conducted whole-stream nutrient addition experiments over the course of a year, using nutrients alone and in combination, to test theoretical predictions about uptake characteristics of limiting and nonlimiting nutrients. NDS results consistently indicated N limitation. Ambient uptake length (S W-amb ) suggested either P limitation (shorter S W-amb for P than N) or colimitation (similar S W-amb for both nutrients). The relationship between N uptake and concentration when added alone or with P suggested P limitation, colimitation, or neither, depending on the date. We speculate that the different conclusions arise from differences in the spatial and temporal scale assessed by these techniques and the microbial processes involved, and the potential for physical processes influencing whole-stream uptake estimates. We conclude that nutrient limitation is not as categorical as NDS results often imply, rather habitat, resource, and biotic diversity result in nutrient uptake rates that do not necessarily conform to predictions drawn from fine scale, process-specific bioassays such as chlorophyll-a accrual on NDS.

Conversion of tropical forests to agriculture alters the accrual, stoichiometry, nutrient limitation, and taxonomic composition of stream periphyton

“…Considering the threshold of 32 for the N:P molar ratio to indicate phosphorus limitation (Kahlert, 1998), the disturbed sites at Santa Maria stream would be considered N-limited by this criterion, as their N:P ratio was 24.9 ± 0.14 1SE. This result supports other nutrient limitation studies carried out with NDS in Atlantic Forest streams (Lourenço-Amorim et al, 2014;Tromboni et al, 2018).…”

Agriculture influences ammonium and soluble reactive phosphorus retention in South American headwater streams

“…Ambient uptake metrics suggested that nutrient retention was lower in our agricultural sites than in low‐intensity agricultural sites, with statistically significant differences for Sw amb for NH 4 + and SRP (Figure a) and V famb for SRP (Figure c). In our study, the uptake metrics (longer Sw amb for NH 4 + and SRP and lower V famb for SRP) generally suggested low nutrient retention when compared with metrics reported for more pristine sites in the Brazilian Coastal Atlantic Forest (Tromboni et al, ; Tromboni et al, ) or even for chronically nutrient‐rich Pampean streams in Argentina (García et al, ). In general, lower nutrient uptake capacity in agricultural streams than in less impacted/pristine streams can be attributed to (a) saturation of the biological community (Bernot et al, ); (b) reduced hydrological complexity of the channel (Argerich, Martí, Sabater, Haggerty, & Ribot, ; Sheibley et al, ); (c) loss of riparian vegetation (Weigelhofer, ); (d) restricted hyporheic water exchange with the sediments (Macrae, English, Schiff, & Stone, ); and (e) reduced adsorption capacities of the sediments (Stutter & Lumsdon, ).…”

“…We speculate this could be related with the relatively high and stable temperatures and insolation throughout the year (see Boulton et al, ) in comparison with the streams reported by Hall et al (), which are mostly from the Northern Hemisphere. This would lead to more stable biological communities, as well as to possible differences in stoichiometry and nutrient limitation (e.g., Tromboni et al, ).…”

“…Hemisphere. This would lead to more stable biological communities, as well as to possible differences in stoichiometry and nutrient limitation (e.g., Tromboni et al, 2018).…”

Nitrogen and Phosphorus Uptake Dynamics in Tropical Cerrado Woodland Streams

“…Variability in N and P retention rates and efficiency has been associated with primary production [9][10][11], hydrology and stream geomorphology [12,13], carbon availability [14][15][16], and nutrient limitation and availability [11,[17][18][19]. Several studies have assessed how environmental concentration influences the uptake of a particular nutrient [20][21][22][23].…”