| The mangrove forest that has the very high litter production is the only primary producer of woody plant in coastal and estuarine aquatic ecosystems. In biological activity of plants, phenolic acid is a vital secondary metabolites and an allelochemical interacts in plant-plant. Plant residues or litter decomposition is one of the important entries for phenolic acids into the environment. Researches showed that most of the phenolic acids have allelopathy.This research focused on a Mangrove Plant, Kandelia obovata,in the estuary of Jiulong River and used high performance liquid chromatography (HPLC) method to study the dynamic change of phenolic acids content in the process of leaf litter decomposition. By assessing the impact of phenolic acids on physiological and biochemical and the density of Nitzschia closterium-a preponderant algae in Jiulong River estuary, this paper discussed the allelopathic effect of leaf litter on algae and provided a new theoretical basis for preventing and controlling the algae blooms safely and effectively. The following conclusions were drawn from this study:1. Water-extract of undecomposed Kandelia obovata leaf litter had allelopathy on Nitzschia closterium, which appeared concentration effect. When the water-extract was in a low concentration, the allelopathic effect was not obvious. With the increase of concentration, the inhibition effect enhanced and showed as the density and relative growth rate of algae in treatment group was significantly lower than that of control group. The algae in treatment group entered the decline phase prematurely under400mg-L-1processing. In comparison, water-extract of half-decomposed Kandelia obovata leaf litter (half decomposition period, tso=48days) showed no significant effect on the growth of Nitzschia closterium.2. Under high temperature processing, the inhibition effect of water-extract of Kandelia obovata leaf litter on Nitzschia closterium was reduced or unobvious, which indicated that algal inhibition allelochemical in Kandelia obovata leaf was instable in high-temperature condition. 3. Used HPLC method to analyse the phenolic acid allelochemical in undecomposed and half-composed Kandelia obovata leaf litter, the results stated that PHBA, vanillic acid, syringic acid, chlorogenic acid and caffeic acid were detected from Kandelia obovata leaf litter, and chlorogenic acid had the highest content; In addition, the content of phenolic acid reduced following the decomposition of leaf. It considered that only vanillic acid and syringic acid had been detected in half-decomposed Kandelia obovata leaf litter, with a ratio of1.223μg·g-1and0.508μg·g-1, respectively.4. Under the treatment of five phenolic acids, the density and relative growth rate of Nitzschia closterium in treatment group was lower than that of CK. Moreover, along with phenolic acid concentration rising, the inhibiting effect is also enhanced. All groups entered the decline phase prematurely except for vanillic acid treatment group, and syringic acid showed a remarkable inhibiting effect. The sequence of inhibition strengthen is: syringic acid>chlorogenic acid>caffeic acid>benzoic acid>vanillic acid. Different concentration of mixed acids had different inhibiting effects, there was insignificant difference in inhibiting effects when in low concentration (diluted5to10times).5. Different concentration of phenolic acid influenced the content of chlorophyll a, soluble sugar and protein in Nitzschia closterium. As phenolic acid concentration improved, chlorophyll a content decreased. With hydroxybenzoate acid, eugenol acid and caffeic acid concentration rose, soluble sugar showed a trend of firstly decreased then increased and finally decreased. Under chlorogenic acid treating the soluble sugar showed opposite trend, firstly increased then decreased and finally increased. Protein presented various change tendencies in different phenolic acids, under vanillic acid and mixed acid treatment, with the increase of acid concentration, the protein content went up in the first place, after that it went down; Under hydroxybenzoate acid and caffeic acid treating, the protein content was reduced first and increased later; Under chlorogenic acid treatment, the protein content had no significant change.In conclusion, in the wake of the decomposition of Kandelia obovata leaf litter, its phenolic acid content gradually weakened and its allelopathic effect on Nitzschia closterium was also weakened. Different concentration of phenolic acid and mixed acids all have allelopathic effect on Nitzschia closterium, and along with the increase of acid concentration, the inhibiting effect enhanced. |
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