All of those that show corals taking up inorganic phosphate at levels below 0.02 ppm DIP, assuming that is what Sorokin claims won't take place.
This paper, for example, shows four different species take up DIP at concentrations less than 0.1 uM (less than 0.01 ppm).
During the 20th century, seawater temperatures have significantly increased, leading to profound alterations in biogeochemical cycles and ecosystem processes. Elevated temperatures have also caused massive bleaching (symbiont/pigment loss) of autotrophic symbioses, such as in...
www.nature.com
"Concentrations remained below 0.5 μM for total DIN and below 0.1 μM for DIP."
Data in Figure 2C
"(
a) Uptake rates of ammonium (μmol NH4 h−1 (mg prot)−1) (
b) nitrate (μmol NO3 h−1 (mg prot)−1) and (
c) phosphorus (μmol PO4 h−1 (mg prot)−1) for the different species at 25 °C (white color) and 30 °C (black color). Data are expressed by means ± standard deviations. Significant effects of the temperature factor were highlighted by an asterisk (*)."
https://www.nature.com/articles/srep31768/figures/2
I don't think that results must necessarily be wrong. Always there may be differences between species, origins, adaptations and kind of experiments.
I already knew this article but found it a bit difficult to understand. Nevertheless I want to point to the method described:
"Inorganic nutrient uptake was assessed, at the same time for the control and experimental tanks, at T0 and
T1, by the depletion technique63. In short, for each nutrient and incubation time, four nubbins per species (one nubbin per colony) were placed in individual 200-mL beakers maintained in a water bath at the respective experimental temperatures (25 °C or 30 °C) and light intensity (150 μ mol photons m−2 s−1). Three control beakers, without coral nubbin, were used to monitor for potential changes in water chemistry due to adsorption onto beaker surface, consumption by microbial activity, or to air contamination. After a 30 min acclimation period for corals, seawater was enriched with a stock solution of either 10 mM ammonium chloride (NH4Cl), Sodium nitrate (NaNO3), or sodium dihydrogen phosphate (NaH2PO4), in order to reach a final concentration of 3 μ M for all nutrients. Stirring bars were added to ensure a proper homogenization of the nutrient mixture in the beakers. Water samples (10 mL) were collected from each beaker and filtered through a 45 micron syringe filter immediately after the enrichment and then subsequently after 15 min, 30 min, 45 min, 60 min and 90 min. Ammonium concentrations were determined immediately after sampling, according to the spectrofluorimetric method of Holmes et al.64. Samples for nitrate and phosphate were frozen, prior to measurements using an autoanalyzer (Alliance Instrument, AMS, France).
Uptake rates of each inorganic nutrient were calculated as the difference in concentration between the 0 and
90 minutes time points, after data correction for the diminution of the beakers’ volume and verification of the
linearity in the depletion during the experiment."
If I understand this right, the initial DIP concentration was < 0.1 µM but for the uptake measurments the water was enriched to get concentrations and uptake that could be detected.
The cited literature [63] can be found
here (
psu.edu link). Here it is clear that they use enriched conditions to measure uptake. The lowest concentration they used to measure uptake was 0.5 µM P. The curve could be steeper in the low range an just as well could meet the abscissa at 0.1 or 0.2 µM P. This is the difficulty at these low concentrations.
Nevertheless the latter article is especially interesting for this thread since it clearly shows the nitrate and phosphate uptake kinetics are in the same order of magnitude and the uptake of ammonium is more efficient than the uptake of nitrate. Finally this is what this theme wants to clarify. I mean, who cares about 0.1 or 0.2 ppm nitrate? I think these are not the concentrations we are discussing here. The authors conclude corals have "high phosphate uptake requirements".
For sure it is not an easy theme.
