Effects of nutrient enrichment on the colonization and decomposition of plant detritus by the microbiota of an arctic lake

The effects of nitrogen and phosphorus enrichment on the colonization and decomposition of plant litter (Carex) by the microbiota of Toolik Lake, Alaska, were studied in microcosms. Added phosphorus resulted in a fourfold (p ≤ 0.01) increase in the levels of ATP associated with the microbiota on fresh litter, while nitrogen-plus-phosphorus enrichments resulted in a twofold increase in the ATP associated with the microbiota of fresh (p ≤ 0.01) or partially degraded (p ≤ 0.05) litter compared with controls. Neither nitrogen nor phosphorus enrichments, alone or together, significantly altered the observed weight loss of either fresh or partially degraded litter, although additional phosphorus was immobilized by the litter microbiota when available. Subsequent experiments demonstrated that the increase in ATP resulting from nutrient enrichment occurred when the microcosms were incubated in daylight but not in the dark, suggesting that nutrient enrichment primarily stimulated the photosynthetic component of the detrital community.

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Effects of nitrogen and phosphorus on the abundance and cell size of planktonic nanoflagellate communities

Acta Limnologica Brasiliensia ◽

10.1590/s2179-975x2013005000009 ◽

2013 ◽

Vol 24 (4) ◽

pp. 427-437

Author(s):

Danielle Goeldner Pereira ◽

Fábio Amodêo Lansac-Tôha ◽

Gustavo Mayer Pauleto ◽

Luis Mauricio Bini ◽

Luiz Felipe Machado Velho

Keyword(s):

Cell Size ◽

Nutrient Enrichment ◽

Nitrogen Addition ◽

Nutrient Addition ◽

Heterotrophic Nanoflagellates ◽

Nitrogen And Phosphorus ◽

Tropical Reservoir ◽

Pigmented Nanoflagellates ◽

Density And Biomass ◽

Nitrogen And Phosphorus Enrichment

AIM: We experimentally investigated the effects of nutrients (Nitrogen and Phosphorus) enrichment on the density, biomass, and cell size of pigmented and heterotrophic plankton nanoflagellates communities. METHODS: The experiment was done in mesocosms in a tropical reservoir during a 19-day period. Four different treatments were carried out: Control (non-nutrient addition - C), phosphorus additions (P), nitrogen addition (N) and phosphorus + nitrogen addition (N + P). Each treatment was performed in triplicate, sorted randomly, thus giving a total of 12 experimental carboys, which were placed transversely in the middle of the reservoir. RESULTS: In general, pigmented and heterotrophic nanoflagellates fractions responded to nutrient addition, increasing densities and biomass values at the fertilized treatments. Opposed to expected, enriched treatments resulted in a slight decrease in mean cell size of the pigmented fraction. Moreover, in nutrient-rich treatments, pigmented nanoflagellates had higher relative abundance than in the control. CONCLUSIONS: Our results indicate that: i) the density and biomass of nanoflagellates responded to the nutrient enrichment, mainly when N and P were added together; ii) the pigmented and heterotrophic fractions showed distinct time responses to fertilization; iii) the growth of nanoflagellate community seems to be co-limited by N and P; iv) the nutrient enrichment led to a greater pigmented than heterotrophic fraction contribution; and v) among the analyzed variables, nanoflagellate densities seem to be more sensitive to changes in nutrient availability than biomass or mean cell size.

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