Populus × euramericana cv. 'Neva' is an important tree species in northern China. In the study, we used its potted oneyear-old seedlings as experimental material and established three treatments (CK, 0.5X, and 1.0X) according to the concentrations of phenolic acids in order to examine the effects of different concentrations on the photosynthetic characteristics and growth of poplar. With increasing concentrations of phenolic acids, the net photosynthetic rate, stomatal limitation, transpiration rate, apparent quantum yield, photochemical quenching coefficient, electron transport rate, chlorophyll content, and total biomass decreased significantly. The intercellular CO 2 concentration, light-compensation point, nonphotochemical quenching, malondialdehyde content, and root/shoot ratio increased significantly. Peroxidase and superoxide dismutase activities initially decreased and then increased. We concluded that phenolic acids significantly inhibited poplar's photosynthesis and the higher phenolic acid concentration, the greater inhibition of photosynthesis occurred. This inhibition effect was mainly caused by nonstomatal factors. Phenolic acids induced noticeable photoinhibition, resulted in the irreversible damage of membrane structure, and then changed intracellular metabolic processes. To cope with phenolic acid stress, poplar seedlings increased dissipation of excess light energy and distributed relatively more biomass to underground parts within carbon allocation.
The objective of this study was to
investigate the effects of the
cultivation time, temperature, and pH value on the yield and composition
of extracellular polymeric substances (EPS) from
Enterobacter
sp. FM-1 (FM-1) and to analyze the Pb
2+
adsorption behavior
of soluble EPS (S-EPS), loosely bound EPS (LB-EPS), and tightly bound
EPS (TB-EPS). Maximum EPS production was obtained when the cultivation
time, temperature, and pH value were 24 h, 30 °C, and 8.0, respectively.
The main components of EPS were proteins, polysaccharides, and nucleic
acids, but the different EPS types contained different proportions
and specific components. The Pb
2+
adsorption capacity of
LB-EPS was 2.23 and 1.50 times higher than that of S-EPS and TB-EPS,
respectively. After Pb
2+
adsorption by LB-EPS, the pH value
of the reaction system decreased to the lowest of 5.23, which indicated
that LB-EPS contained more functional groups that could release H
+
, which will help to better adsorb Pb
2+
through
ion exchange. The three-dimensional excitation–emission matrix
fluorescence spectroscopy (3D-EEM) analysis showed that the fluorescence
intensity of tryptophan-containing substances decreased by 85.5% after
Pb
2+
adsorption by LB-EPS, which indicated the complexation
of tryptophan-containing substances with Pb
2+
. Fourier
transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy
(XPS) O spectra indicated that the C=O peak from protein amide
I of tryptophan-containing substances in LB-EPS was mainly responsible
for the complexation of Pb
2+
. After the adsorption of Pb
2+
, the proportion of the C=O peak in LB-EPS increased
by 33.89%, indicating that the complexation of LB-EPS with Pb
2+
was mainly attributed to the O atom in the C=O terminus
of protein amide I.
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