Influences of sample storage and grinding on the extraction of soil amino sugars

Soil amino sugars have been widely used to evaluate the potential roles of microbes in mediating soil carbon(C)cycling and various pretreatment methods were used for its extraction.However,few studies assessed their potential influences on the soil amino sugar extraction.In this study,we investigated the effects of sample storage method and grinding on amino sugar extraction across different climatic zones and land uses.Results showed that the concentrations of soil amino sugars varied greatly among sample pretreatments and their impacts were highly dependent on climatic condition and land use.Specifically,higher concentrations of amino sugars were extracted from field-moist samples than dried samples in subtropical grassland,temperate forest and arable land with no significant differences among storage methods for the samples from subtropical forest,arable land,and temperate grassland.Moreover,grinding improved the extraction efficiency of amino sugars for the dried soils.Due to the reduced extraction concentration in dried soils,field-moist samples were recommended in priority.For the dried soils used for the long-term storage,grinding can be an option to improve the extraction efficiency.Such information will be valuable for reducing the uncertainty and improving the accuracy during the determination of soil amino sugars.

Determining short chain fatty acids in sewage sludge hydrolysate: A comparison of three analytical methods and investigation of sample storage effects

In anaerobic digestion, the production of short-chain fatty acids （SCFAs） can be beneficial or harmful to the overall process, depending on the concentration of accumulated acids. Therefore, the accurate determination of the SCFA concentration in both fresh and stored sludge hydrolysates is important. To select a suitable method for monitoring SCFAs during the anaerobic digestion of sewage sludge, the accuracy of three available analytical methods, including 5 pH point acid titration （TITRA5）, gas chromatography （GC）, and spectrophotometry, were compared in the present study. The results revealed that TITRA5 and GC displayed better agreement in the achieved measurements and higher precision and accuracy than the spectrophotometric assay, as supported by the application of different statistical models. TITRA5 excelled in titrating unfiltered hydrolysate while simultaneously measuring the alkalinity, whereas the GC method provided detailed information on the contribution of different fatty acids to the total acidity. In contrast, the spectrophotometric assay suffered from many forms of interference, depending on the sample＇s matrix. SCFA production followed the pattern of enzymatic reactions and fitted the Michaelis-Menten model. In addition to promoting TITRA5 as an accurate and robust analytical tool for routine SCFA analyses, this comparative study also demonstrated the possibility of storing hydrolysate samples at different temperatures and durations without altering the SCFA measurements.

Evidence of functional and structural changes in the microbial community beneath a succulent invasive plant in coastal dunes

Coastal dunes represent priority habitats for conservation due to the provision of valuable ecosystem services such as land protection,water supply or biodiversity conservation.Soil microbial communities are of crucial importance to maintain plant diversity due to harsh environmental conditions,water limitation and nutrient scarcity.Invasive alien plants represent a major threat to ecosystem conservation.Here,we explored different impacts of Carpobrotus edulis,a succulent plant invading coastal areas worldwide,on the function and structure of bacterial communities.Sand represents a challenging substrate due to low organic matter content and limited microbial activity.We optimized bacterial extraction for functional evaluation before assessing ecosystem impacts produced by C.edulis.We compared 12 extracting procedures combining different soil storage,sample amount and extracting solutions on the functional activity of sand communities through the community-level physiological profile.We further explored the function(using Biolog Ecoplates)and structure[using polymerase chain reaction–denaturing gradient gel electrophoresis(PCR-DGGE)]of bacterial communities from dunes invaded by C.edulis.Saline solution consistently increased bacterial cells detected by cytometry(P≤0.001).Principal component analysis suggested a limited temporal framework(0–24 h)in which community function can be explored without significant alterations in C substrate consumption.Changes under C.edulis invasion exhibited a different pattern of C substrate utilization comparing native and non-native zones(interspecific),but also between native zones(intraspecific),suggesting that functional impacts are site-dependent.Complementary,results obtained from PCR-DGGE indicated that the bacterial community structure of native dunes significantly differed from dunes invaded by C.edulis.