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Research Area 4 - Microbial Community Diversity Shift as Environmental Biosensor

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A ​​recent study (Guo et al. 2010) shows that farming practices in China are acidifying the nation's soils and threatening long term productivity at a time when food concerns worldwide have never been higher. Chinese agriculture has intensified greatly since the early 1980s on a limited land area with large inputs of chemical fertilizers and other resources. The rates of nitrogen applied in some regions are extraordinarily high as compared with those of North America and Europe. These have degraded soils and environmental quality in the many areas in China. With high agricultural intensity, comes the use of pesticides which could be detrimental to soil and water quality. Soil treatments that affect soil pH may lead to changes in soil microbial communities which mediate many processes essential to the productivity and sustainability of soil. Deng and Tabatabai (1996a.b, 1997) reported that these management systems influence the soil enzymes involved in C, N, S, and P cycling. Most microorganisms proliferate in neutral soil, thus any activity that would lead to acidic soil pH is detrimental to vast population of microorganism. Understanding of microbial properties such as biomass, activity, and diversity are important in furthering knowledge of the factors contributing to soil health, and result of such analysis may also be useful to farmers in devising practical measures of soil quality (Hill et al. 2000), and increase C sequestration thus minimizing global warming.  

In 2010 the Chinese government released a national pollution survey which revealed a surprisingly high link between water pollution and agricultural and forest practices, such as overuse of fertilizer and pesticides (Guo et al. 2010). The enzymes present in soils are dependent on the functioning of soil microorganisms and their activity not only reflects soil fertility, but also reflects soil conditions and microbial populations (Chenge et al. 2002). Because microbes are at the bottom of the food chain, they will be the first to response to environmental changes.  Microbial community biomass, respiration, N mineralization rate, and fungal abundance have been reported to increase with greater plant diversity (Zak et al. 2003).  Seasonal and temporal variations in nutrients or physical conditions may affect the microbial community and diversity leading to difficulties in data interpretation and meaningful conclusions. Surveying microbial communities and diversities and studying their processes can be use as a biosensor to predict the changing environment. 

The objectives of this study are to (i) assess microbial population, (ii) investigate microbial processes, and (iii) identify and quantify enzymatic activity in selected urban, agriculture, and forest ecosystems. The study will establish (a) link between ecosystem disturbance and microbial diversity, (b) microbial processes and global warming, and (c) nutrient cycling and enzyme activities. Culturable microbial community/diversity will be evaluated using the most probable number (MPN)  method and plate count (De Leij et al.1993) whereas the unculturable community will be evaluated by analyzing soil DNA extracted using Ultraclean Soil DNA kit (Mo Bio Laboratories, CA). Microbial processes will be evaluated using chloroform fumigation method, and potential enzyme activities will be assayed based on Tabatabai (1994) and Tazisong et al. (2008). The REU students will be given hands-on training on molecular (DNA fingerprinting) and traditional (culture based) techniques used for surveying soil microbial organisms in environmental samples. The students will also be exposed on the use of state-of-the-art instrumentation in quantifying and qualifying these organisms. ​