@article{dell_carley_rufty_shi_2012, title={Heat stress and N fertilization affect soil microbial and enzyme activities in the creeping bentgrass (Agrostis Stolonifera L.) rhizosphere}, volume={56}, ISSN={0929-1393}, url={http://dx.doi.org/10.1016/j.apsoil.2012.02.002}, DOI={10.1016/j.apsoil.2012.02.002}, abstractNote={High summer temperatures often cause damage to bentgrass on putting greens in transition zone regions. One of the most damaging effects is a depression of rooting. Although heat stress effects on plant functions are considered as a main reason for the damage, heat stress also may be related to organic matter (OM) accumulation and poor gas exchange into the rhizosphere. The OM accumulation and the often-observed root dieback suggest that soil microbial processes play a role in summer bentgrass decline. In this study, the impact of high temperature on soil microbial properties and enzyme activities was examined using creeping bentgrass (Agrostis stolonifera) growing in a phytotron controlled environment chamber. The high temperature exposures (34/30 °C versus 22/18 °C for controls) lasted for four weeks and the bentgrass cultures received mineral N at two rates. Our working hypothesis was that not only did high temperatures stimulate overall soil microbial and enzyme activity but also selectively modified microbial catabolic functions. To test this hypothesis, we compared temperature sensitivities and Q10 values of microbial substrate utilization patterns using a Biolog plate approach and soil enzyme activities. The results indicated that soil enzyme activities had similar responses to assay temperatures and their Q10 values averaged ∼2 with changes of laboratory assay temperatures from 12 to 22 °C and from 22 to 34 °C. Such positive responses of microbial activity to high temperatures were supported by parallel increases in rates of microbial substrate utilization. Total substrate availability in Biolog plates also increased with laboratory assay temperatures. This enhancement could not be explained by the overall stimulation of high temperature on microbial activity, but instead by selective modification of microbial community functions. Nitrogen fertilization significantly changed soil biological activities. Phenol oxidase activity was reduced by the high rate of N fertilization, whereas β-glucosidase and β-glucosaminidase activities were increased. Interactions on soil enzyme activities between growth chamber temperatures and N fertilization rates also occurred. Soil peroxidase activity was ∼three-fold greater for bentgrass subjected to heat stress and the low rate of N fertilization. Our results indicated that summer heat stress and the associated increases in root and OM degradation in bentgrass systems are related with overall temperature stimulations on soil microbial and enzyme activities as well as with modifications in functional components of the microbial community.}, journal={Applied Soil Ecology}, publisher={Elsevier BV}, author={Dell, Emily A. and Carley, Danesha Seth and Rufty, Thomas and Shi, Wei}, year={2012}, month={May}, pages={19–26} }
 @article{liu_dell_yao_rufty_shi_2011, title={Microbial and soil properties in bentgrass putting greens: Impacts of nitrogen fertilization rates}, volume={162}, ISSN={["1872-6259"]}, DOI={10.1016/j.geoderma.2011.02.009}, abstractNote={Nitrogen fertilization is important for maintaining the quality of golf course putting greens, but causes environmental concerns and affects soil organic matter buildup. Belowground biology and processes are vital to address both environmental and organic buildup issues. We examined microbial and soil properties in sand-based bentgrass putting greens that had been unfertilized or fertilized at the rates of 195, 244, and 305 kg N ha−1 yr−1 for over one year after turf establishment. Nitrogen fertilization increased soil organic C by ~ 10% and slightly modified microbial community as revealed by denaturing gradient gel electrophoresis, but had no effects on microbial biomass or C and N mineralization. We observed that changes in soil pH and enzyme activities were the functions of fertilization rates. Soil pH was reduced by ~ 0.3 to 0.8 units as fertilization rates increased. The activities of soil enzymes (β-glucosidase, N-acetyl-β-glucosaminidase, chitinase, and cellulase) were enhanced by fertilization at 195 or 244 kg N ha−1 yr−1, but was equivalent to or even lower than those in the unfertilized control when fertilization rate reached 305 kg N ha−1 yr−1. Results indicated that the activity of soil enzymes could be used as an important metric to diagnose the impacts of fertilization rates on soil. Fertilization rate at approximately 200 kg N ha−1 yr−1 appeared to be appropriate for managing putting greens.}, number={1-2}, journal={GEODERMA}, author={Liu, Yueyan and Dell, Emily and Yao, Huaiying and Rufty, Thomas and Shi, Wei}, year={2011}, month={Apr}, pages={215–221} }
 @article{tian_dell_shi_2010, title={Chemical composition of dissolved organic matter in agroecosystems: Correlations with soil enzyme activity and carbon and nitrogen mineralization}, volume={46}, ISSN={["1873-0272"]}, DOI={10.1016/j.apsoil.2010.09.007}, abstractNote={Soil enzyme-catalyzed depolymerization of organic matter results in the production of low molecular weight and dissolved organic compounds. This fraction of soil organic matter is the immediate energy, carbon and other nutrient substrates for microbial catabolic pathways and thus likely plays an important role in soil processes. The purpose of this study was to elucidate interrelationships among dissolved organic matter, soil enzyme activity, and soil C and N mineralization from diverse agroecosystems. These systems included a conventional cropping, organic cropping, integrated crop–livestock, plantation forestry, and succession from an abandoned agricultural field. We collected surface soil samples from 0 to 10 cm depth in early spring 2009 and examined the concentrations of soil-derived dissolved organic C and N, soluble phenolics, reducing sugars, and amino acids, the activities of β-glucosidase, exoglucanase, phenol oxidase, peroxidase, and β-glucosaminidase, and the rates of soil C and N mineralization. The integrated crop–livestock system showed the highest concentrations of dissolved soil organic C (78 μg C g−1 soil) as well as phenolic compounds (1.5 μg C g−1 soil), reducing sugars (23 μg C g−1 soil), and amino acids (0.76 μg N g−1 soil), and these components were up to 3-fold greater than soils under the other systems. However, soil β-glucosidase activity in the integrated crop–livestock system was significantly lower than the other systems and appeared to reflect the inhibitory role of soluble phenolics on this enzyme; this enzymatic disparity was also revealed in our preliminary study conducted in 2008. Among the five enzyme activities examined, only peroxidase activity was correlated significantly with the chemical composition of dissolved organic matter as well as soil C and N mineralization. Soil peroxidase activity was negatively related to the relative abundance of reducing sugars (i.e., reducing sugar C as a fraction of dissolved organic C, r = −0.92, P < 0.05) and positively with soil C and N mineralization (r = 0.86, P < 0.1 for C mineralization; r = 0.85, P < 0.1 for N mineralization). Furthermore, relative abundance of reducing sugars was negatively associated with soil C mineralization (r = −0.80, P < 0.1) and so was relative abundance of amino acids with soil N mineralization (r = −0.97, P < 0.01). Our results suggested that diverse agroecosystems differed in the chemical composition of dissolved organic matter and the differences could be correlated with soil peroxidase activity and soil C and N mineralization.}, number={3}, journal={APPLIED SOIL ECOLOGY}, author={Tian, Lei and Dell, Emily and Shi, Wei}, year={2010}, month={Nov}, pages={426–435} }
 @article{dell_bowman_rufty_shi_2010, title={The community composition of soil-denitrifying bacteria from a turfgrass environment}, volume={161}, ISSN={["1769-7123"]}, DOI={10.1016/j.resmic.2010.03.010}, abstractNote={Soil-denitrifying bacteria in highly-managed turfgrass systems were examined to assess their response to land-use change and time under management. Denitrifier community composition and diversity in a turfgrass chronosequence of 1 to 95-years-old were compared with those in an adjacent pine-dominant forest via molecular investigations of nirK and nosZ gene fragments. Both denaturing gradient gel electrophoresis and sequenced clone libraries revealed that the denitrifier community became more diverse after turf establishment, and the diversity was then preserved. Furthermore, the composition of the turfgrass denitrifier community was slightly affected by time under management. Meta-analysis of sequenced nirK and nosZ gene fragments from a variety of ecosystems showed that denitrifier communities in pine and turf were more similar to those in other environments than to each other, suggesting that land-use change substantially modified the composition and increased the diversity of denitrifiers. This study provides a useful baseline of nirK- and nosZ-type soil denitrifier communities to aid in the evaluation of ecological and environmental impacts of turfgrass systems.}, number={5}, journal={RESEARCH IN MICROBIOLOGY}, author={Dell, Emily A. and Bowman, Daniel and Rufty, Thomas and Shi, Wei}, year={2010}, month={Jun}, pages={315–325} }
 @article{dell_bowman_rufty_shi_2008, title={Intensive management affects composition of betaproteobacterial ammonia oxidizers in turfgrass systems}, volume={56}, ISSN={["1432-184X"]}, DOI={10.1007/s00248-007-9335-x}, abstractNote={Turfgrass is a highly managed ecosystem subject to frequent fertilization, mowing, irrigation, and application of pesticides. Turf management practices may create a perturbed environment for ammonia oxidizers, a key microbial group responsible for nitrification. To elucidate the long-term effects of turf management on these bacteria, we assessed the composition of betaproteobacterial ammonia oxidizers in a chronosequence of turfgrass systems (i.e., 1, 6, 23, and 95 years old) and the adjacent native pines by using both 16S rRNA and amoA gene fragments specific to ammonia oxidizers. Based on the Shannon-Wiener diversity index of denaturing gradient gel electrophoresis patterns and the rarefaction curves of amoA clones, turf management did not change the relative diversity and richness of ammonia oxidizers in turf soils as compared to native pine soils. Ammonia oxidizers in turfgrass systems comprised a suite of phylogenetic clusters common to other terrestrial ecosystems. Nitrosospira clusters 0, 2, 3, and 4; Nitrosospira sp. Nsp65-like sequences; and Nitrosomonas clusters 6 and 7 were detected in the turfgrass chronosequence with Nitrosospira clusters 3 and 4 being dominant. However, both turf age and land change (pine to turf) effected minor changes in ammonia oxidizer composition. Nitrosospira cluster 0 was observed only in older turfgrass systems (i.e., 23 and 95 years old); fine-scale differences within Nitrosospira cluster 3 were seen between native pines and turf. Further investigations are needed to elucidate the ecological implications of the compositional differences.}, number={1}, journal={MICROBIAL ECOLOGY}, author={Dell, Emily A. and Bowman, Daniel and Rufty, Thomas and Shi, Wei}, year={2008}, month={Jul}, pages={178–190} }
 @article{shi_dell_bowman_iyyemperumal_2006, title={Soil enzyme activities and organic matter composition in a turfgrass chronosequence}, volume={288}, ISSN={["1573-5036"]}, DOI={10.1007/s11104-006-9116-1}, number={1-2}, journal={PLANT AND SOIL}, author={Shi, Wei and Dell, Emily and Bowman, Daniel and Iyyemperumal, Kannan}, year={2006}, month={Oct}, pages={285–296} }