Forms and Lability of Phosphorus in Algae and Aquatic Macrophytes Characterized by Solution 31P NMR Coupled with Enzymatic Hydrolysis

Abstract

Solution Phosphorus-31 nuclear magnetic resonance (31P NMR) spectroscopy coupled with enzymatic hydrolysis (EH) with commercially available phosphatases was used to characterize phosphorus (P) compounds in extracts of the dominant aquatic macrophytes and algae in a eutrophic lake. Total extractable organic P (Po) concentrations ranged from 504 to 1643 mg kg−1 and 2318 to 8395 mg kg−1 for aquatic macrophytes and algae, respectively. Using 31P NMR spectroscopy, 11 Po species were detected in the mono- and diester region. Additionally, orthophosphate, pyrophosphate and phosphonates were also detected. Using EH, phytate-like P was identified as the prevalent class of enzyme-labile Po, followed by labile monoester- and diester-P. Comparison of the NMR and EH data indicated that the distribution pattern of major P forms in the samples determined by the two methods was similar (r = 0.712, p < 0.05). Additional 31P NMR spectroscopic analysis of extracts following EH showed significant decreases in the monoester and pyrophosphate regions, with a corresponding increase in the orthophosphate signal, as compared to unhydrolyzed extracts. Based on these quantity and hydrolysis data, we proposed that recycling of Po in vegetative biomass residues is an important mechanism for long-term self-regulation of available P for algal blooming in eutrophic lakes.

Characterization of phosphorus in algae from a eutrophic lake by solution 31P nuclear magnetic resonance spectroscopy

“…The mean ratio of P o /TP of the six algal samples was 69.2% in Chao Lake (Table 1). This value was greater than that of algae from Tai Lake (mean ratio of P o /TP 57.8%) (Feng et al 2016b). The previous studies reported that P o could be converted to bioavailable P (e.g., HPO 4 2− ) for algae blooming through a series of redox-driven solubilization reactions and phosphatase-mediated hydrolytic processes (Wang and Pant 2010;Zhu et al 2015).…”

“…Samples of algae were extracted by use of optimized NaOH-EDTA extracting agent (mixtures of 0.5 mol l −1 NaOH and 25 mmol l −1 EDTA) with a ratio of 150:1 (ml g −1 ), and the mixtures were shaken for 18 h at room temperature (Cade-Menun and Preston 1996;Feng et al 2016b). The extracting solutions were centrifuged (8000 × g) for 30 min, and filtered through 0.45-μm glassfiber filters (Whatman GF/C).…”

“…The supernatant solution was centrifuged (8000 × g) for 30 min and transferred to a 5-mm NMR tube. Solution 31 P NMR spectra were acquired at 24 °C on a Bruker AVANCE 400 MHz spectrometer at a 31 P frequency of 161.98 MHz, using a 90° pulse, a 5 s relaxation delay and a 0.21 s acquisition time, similar to the parameters used in Feng et al (2016b). The scan time for each sample was more than 15 h. Peak areas were calculated by integration and completed using MestrelabMNova v.10.…”

“…Algae are not usually collected by humans because they are not valuable, so that the debris is allowed to decompose in situ. The decomposition of algal residues affects the bio-cycling and release of P, increasing the risk of resurgence of algal blooms (Feng et al 2016b;Lehman et al 2017). Decaying algal debris releases both inorganic P (P i ) and P o .…”

“…Decaying algal debris releases both inorganic P (P i ) and P o . The P o constituents need to be hydrolyzed to bioavailable P o by various enzymes (Feng et al 2016b). Therefore, the forms and concentrations of P in algae shall be evaluated while algae debris is decomposing.…”