Phosphorus sources for phytoplankton and bacteria in Lake Michigan

Despite the fact that microbial uptake represents an important transformation of nutrients in aquatic ecosystems, few comprehensive studies have identified key parameters and evaluated their relative importance in explaining variation in uptake rates. Therefore, we performed an assessment of peer-reviewed literature that reported aquatic microbial phosphorus (P) uptake rates. The search yielded 36 different papers which presented results of 102 uptake estimates. We then constructed a meta-analysis to examine the effects of key parameters on uptake. Microbial group (benthic, planktonic), source (culture, wild), and sample time (long, short) were significant parameters in explaining observed variation in published P uptake rates. Planktonic microbes had higher P uptake rates (65 µg P µg chl a), compared with benthic (9 µg P µg chl a). Lower affinity for P by benthic microbes could be attributed to adnate growth forms, which can create boundary layers separating cells from ambient P and promoting internal P cycling. Cultured microbes exhibited higher P uptake rates compared with wild samples, although this trend was not significant (F = 2.63, p = 0.108), suggesting that cultured microbes in these studies represented reasonable analogues. Shorter sampling times yielded over 3-fold higher P uptake rates (58 µg P µg chl a) and appear to represent more accurate estimates of gross uptake. Microbes subject to longer time regimes may be physiologically altered by experimental conditions; estimates might therefore not reflect instantaneous uptake. Our results highlight the influence of ecological variation on P assimilation and provide criteria for developing a general model to predict observed variation in microbial P uptake rates.KEY WORDS: Meta-analysis · Benthic · Planktonic · Phosphorus · Ecosystem · Uptake · Mixed model Resale or republication not permitted without written consent of the publisher

Section: Discussionsupporting

confidence: 91%

Section: Introductionmentioning

confidence: 99%

Meta-analytical approach to explain variation in microbial phosphorus uptake rates in aquatic ecosystems

Price

Carrick²

2011

“…Our observations are consistent with previous detected increments in lake chl a of about 100% following rain episodes carrying Sahara dust ), or with the 5-fold increase in autotrophic versus heterotrophic biomass after a nutrient input in a Mediterranean coastal community (Duarte et al 2000). Furthermore, these results are in agreement with the prevailing idea of the higher capacity of algae to take advantage of high substrate concentrations (Tarapchak & Moll 1990), in an ecologically advantageous mechanism that allows algae to rely on intermittent pulses of P associated with allochthonous loads (Cotner & Wetzel 1992). Conversely, addition of P to P-sufficient phytoplankton in October (N:P p = 8.8) accelerated PER release.…”

supporting

confidence: 93%

Microbial plankton response to contrasting climatic conditions: insights from community structure, productivity and fraction stoichiometry

Villar‐Argaiz

Medina‐Sánchez²,

Carrillo³

2002

Climatic events are among the most important forces governing natural processes in ecosystems. Over a 3 yr period, we monitored changes in the hydrological, chemical and biological regimes of a high mountain lake severely affected by a drought that peaked in 1995. During the drought, the decrease in lake volume enhanced the contribution of the sediment to the lake nutrient budget. The community became more complex, with the appearance of ciliates and heterotrophic nanoflagellates, organisms rarely found prior to the drought. The impaired post-drought recovery of the zooplankton, which did not reach normal densities for this lake until 1997, resulted in a microbialdominated food web in 1996 and a classical grazing food web in 1997. Besides the species composition or abundance and the autotrophic to heterotrophic ratio, food web changes associated with the drought and atmospheric nutrient inputs were reflected in the stoichiometry and contribution of both bacteria and phytoplankton fractions to the planktonic particulate matter. Specific productivity measurements showed that cellular N:P ratios could be used to evaluate the growth conditions of phytoplankton but not of bacteria, indicating that an element other than P may limit bacteria growth. Assessments of phytoplankton and bacteria productivity and of the photosynthetic carbon release relative to bacteria demand in microcosms revealed that after a phosphorus pulse, the phytoplankton N:P ratio determines the nature of the interaction between phytoplankton and bacteria as either commensalistic or competitive for inorganic P. If phytoplankton N:P is initially high (P-deficient algae), a P pulse can reduce photosynthetic extracellular release (PER) and bacteria can experience C limitation, whereas if phytoplankton N:P is initially low (P-sufficient algae) and bacteria N:P is high, increased PER is observed and competition for inorganic P may occur. KEY WORDS: Drought · Atmospheric depositions · Food web · Phytoplankton vs bacteria interaction · Productivity · Stoichiometry Resale or republication not permitted without written consent of the publisherAquat Microb Ecol 29: [253][254][255][256][257][258][259][260][261][262][263][264][265][266] 2002 outlets, where most of the water is exchanged as a result of meteorological processes. Droughts represent extreme conditions of rainfall and temperature that have drastic effects on ecosystems. The fact that climatic models for Europe predict more frequent and intense droughts at lower latitudes (Houghton et al. 1996) means that further experimental research is urgently required on the effects of climate on plankton production and dynamics in aquatic ecosystems.The biological structure of ecosystems serves as an appropriate marker of the strength of the controls operating in planktonic food webs. Thus, it is commonly accepted that phytoplankton dominate the food base in the more productive eutrophic lakes, whereas heterotrophic biomass dominates in less productive lakes (del Giorgio & Gasol 1995, Biddanda et a...

“…Furthermore, relatively few tracer studies have been conducted in marine environments compared to work on the P cycle in freshwater ecosystems (Schindler 1977, Berman 1988, Tarapchak & Moll 1990. There are some studies that have investigated uptake and regeneration of inorganic P (P i ) in oceanic waters (Perry & Eppley 1981, Cuhel et al 1983, Sorokin 1985, Harrison & Harris 1986, Cotner et al 1997, and others focused on the utilization of the dissolved organic P (DOP) pool (Kuentzler 1970, Orrett & Karl 1987, Björkman & Karl 1994.…”

Section: Introductionmentioning

confidence: 99%

Phosphorus dynamics in the North Pacific subtropical gyre

Björkman¹,

Thomson-Bulldis²,

Karl³

2000

118

Phosphorus (P) dynamics were studied during several research cruises to Stn ALOHA and in the 'Climax region' of the North Pacific subtropical gyre (NPSG) in 1996(NPSG) in -1997. The aim of this study was to: (1) investigate the coupled uptake and regeneration of inorganic phosphate (P i ) and the production of dissolved organic phosphorus (DOP), (2) quantify the size of the biologically available P (BAP) pool, and (3) estimate the relative bioavailability of select organic P compounds to the natural microbial assemblages. At all stations, the microbial community was dominated by prokaryotes (> 99.5% of total cell numbers); Prochlorococcus spp. was the dominant pigmented group (> 97% by numbers), comprising 20 to 30% of the total prokaryotic population. Phosphate uptake rates were 3.0 to 8.2 nM d -1 (median = 3.5 nM d-1) and P pool turnover times ranged from 2 to 40 d (median = 9 d). The BAP pool generally exceeded the P i pool, suggesting rapid turnover of at least a portion of the much larger DOP pool. The net production of DOP was approximately 10 to 40% of the net P uptake. Both the dissolved and the particulate organic matter pools were enriched in carbon (C) and nitrogen (N) relative to P, compared to the Redfield molar stoichiometry of 106C:16N:1P. The half-saturation constant, K m , values for P i uptake were higher than the ambient P i pool concentrations, and uptake rates were positively correlated with exogenous P i additions over the range tested (P i = 25 to 250 nM). The bioavailabilities of exogenous adenine and guanine nucleotides were generally higher than other organic P compounds we tested. The net P i regeneration rate from nucleotides was up to 50 times higher than the net P i uptake rates, indicating a large potential for the regeneration of P i from specific organic compounds. These P pool dynamics observed in the NPSG are consistent with a microbial community currently under P control. KEY WORDS: Phosphate uptake rates · Turnover rates · Bioavailable phosphorus · Bacteria · North PacificResale or republication not permitted without written consent of the publisher Aquat Microb Ecol 22: 185-198, 2000 The term 'new production' has most often been used to describe the portion of the net production fuelled by the influx of allochthonous nutrients as opposed to the portion that is supported by local nutrient regeneration (the new versus regenerated production paradigm; Dugdale & Goering 1967). By current experimental application in field-based oceanographic studies, new N is generally equated to nitrate and regenerated N to the sum of ammonium and urea (Harrison 1990). However, atmospheric deposition of fixed N and gas exchange at the air-sea interface may significantly contribute to the supply of new N and other nutrients in the upper ocean (Buat-Ménard 1986, Duce 1986, in contrast to P, which has negligible atmospheric exchange (Paerl 1993). The contribution from atmospheric sources of P to the total dissolved phosphorus (TDP) pool in the upper ocean has been estimated to less th...