Based On BIOLOG-ECO Technology, The Effects Of Leaf Litter On The Microbial Diversity Of Mangrove Plants Were Studied

The decomposition of mangrove litter is an important pathway to export organic compound from plants to the environment.Microorganism plays an important role in the decomposition and mineralization of organic matter.Although decomposition and nutrient cycling in litter have been extensively studied,the dynamic process of drench solution such as plant polyphenol and its effects on sediments and microbial diversity during the decomposition of mangrove leaf litter remain unknown.BIOLOG,an efficient and effective method to study the functional diversity of microbial communities,can reveal the relationship between microorganisms and environments.An indoor tidal system simulated the process of litter decomposition in the field was constructed in our laboratory to follow the temporal release of polyphenol,and BIOLOG technology was used to study the effects of leaf litter decomposition,particularly the drench solution,on soil microbial diversity.The aim of this study was to provide theoretical basis for further analysis on the important ecological functions of mangrove plant litter in the intertidal zone.Three typical mangrove plant species,namely Kandelia obovata,Avicennia marina and Sonneratia apetala,were studied.The leaf litter of each species at three different weights(0,8,100 g)was placed on the surface of 2.5 kg well-mixed soil collected from a mature mangrove forest.The artificial seawater at a salinity of 10 ‰ was used to simulate the periodic submergence conditions in the intertidal zone with a daily cycle of 8 hours high tide and 16 hours low tide.Distilled water was regularly added.After 2,4,6,7,14,21,28,42,56,77,105,133,161 days of litter decomposition,samples were collected to investigate the dynamic changes of plant polyphenols and nitrogen content in seawater and soil physicochemical properties.The microbial diversity in mangrove soil was analyzed by the BIOLOG-ECO technique.The results are as follows:1.Soluble polyphenols released from the broken tissues and cells in leaf and leached into artificial seawater in the early stage of decomposition.This led to increases in the content of tannin but decreases in the content of ammonia nitrogen in artificial seawater.There was a significant negative correlation between the concentration of condensed tannins and the concentration of ammonia nitrogen in artificial seawater,as a large amount of condensedtannins could bind with nitrogen substance.2.The pH of three kinds of mangrove soil varied from neutral to acid.The pH value and the content of nitrate in soil decreased at first and increased afterwards during the decomposition of leaf litter,but the temporal trends of soil salinity and electrical conductivity were the opposite.The concentration of litter placed on soil surface significantly affected the soil moisture content,with significantly higher moisture in the high concentration litter group than that of the low concentration and control(without any litter).In summary,significant short-term fluctuation in the physical and chemical properties of soil was observed in the early stage of leaf litter decomposition(a month or so),but became stable towards the later stage of decomposition.3.BIOLOG-ECO results showed the slopes of their AWCD curves between 12 to 120 hours with different litter concentrations were large,then decreased gradually with incubation time.The three-way analysis of variance on AWCD values indicated that the capacity of microorganisms to metabolize carbon was higher at early than latter stages of litter decomposition.The capacity of soil microorganisms in Avicennia marina and Sonneratia apetala groups to metabolize carbon was significantly higher than that in Kandelia obovata group.The carbon metabolism capacity in high and low concentration litter groups was significantly higher than that in control.The results of cluster analysis and the changes of microbial community diversity indices(Shannon diversity index,Simpson index and McIntosh index)were similar to that of AWCD values.In the early stage of leaf litter decomposition in all three plant species,the carbon metabolism ability of microorganisms and the diversity of the microbial community in soil were increased,improving the degree of soil microorganisms to utilize carbon sources.Amino acids,lipids and sugars were the substrate used by microorganisms,while the usage of acids,amines and alcohols was relatively low.Microorganisms in Sonneratia apetala group could use more varieties of sugars as carbon sources than in Avicennia marina and Kandelia obovata groups,probably related to the hydrolyzed tannin contained in Sonneratia leaves supplying more carbon for soil microorganisms.The degree of using carbon sources by soil microorganisms in Kandelia obovata group was lower than that in Avicennia marina and Sonneratia apetala groups,possibly due to the decreasing supply of carbon sources as condensed tannin in Kandeliaobovata leaves might be bound with protein and sugar thus less available.