@article{tian_shi_2014, title={Short-term effects of plant litter on the dynamics, amount, and stoichiometry of soil enzyme activity in agroecosystems}, volume={65}, ISSN={["1778-3615"]}, DOI={10.1016/j.ejsobi.2014.08.004}, abstractNote={Addition of plant litter can affect soil enzyme activity at three scales: dynamics, amount, and stoichiometry. In this study, we examined the dependence of soil enzyme activity at all three scales on litter quality. Soils of similar texture were collected from conventional and organic farming systems, the Center for Environmental Farming Systems, Goldsboro, North Carolina, USA. Soil samples were then amended with senescent pine needles, grass materials, and soybean residues of C:N ratio 139, 50, and 9, respectively, at 2 mg C g−1 soil, and the activities of soil β-glucosidase, exoglucanase, β-glucosaminidase, and phenol oxidase were measured over the course of 90-d incubation. Relationships between the dynamics of enzyme activity and litter quality appeared to be enzyme specific. Time patterns of soil β-glucosidase and β-glucosaminidase activity were independent of litter quality, with rapid increase in enzyme activity and reaching a peak several weeks after litter addition. In contrast, time patterns of polymer-degrading enzymes (exoglucanase and phenol oxidase) were dependent on litter quality. Exoglucanase activity showed a concave function with time following the addition of soybean residues or grass materials, but increased slightly following the addition of pine needles. Cumulative activities of soil enzymes were upregulated following litter addition and could be qualitatively assessed by litter C:N ratio. The activity of β-glucosaminidase was negatively related to litter C:N ratio, being greatest in soybean residues-amended soil. Litter of a low C:N ratio was generally better than litter of a high C:N ratio for increasing soil cellulase activity and vice versa for phenol oxidase. However, the stoichiometry of soil enzyme activity was decoupled with litter C:N ratio. Soybean residues and pine needles at opposite ends of the litter C:N range were more similar in the ratio of C- to N-acquiring enzyme activity. We also examined pH effects on the expression of added enzymes. Soil enzyme activities were enhanced as soil pH increased from 6 to 8. pH-associated changes in enzyme activity were generally smaller as compared to changes caused by other factors during the 42-d incubation. Our results suggest that litter effects on the dynamics, amount, and stoichiometry of soil enzyme activity were independent of soil pH. Litter C:N was a good indicator for the total amount, but not for the dynamics or stoichiometry of soil enzyme activity.}, journal={EUROPEAN JOURNAL OF SOIL BIOLOGY}, author={Tian, Lei and Shi, Wei}, year={2014}, pages={23–29} }
 @article{tian_shi_2014, title={Soil peroxidase regulates organic matter decomposition through improving the accessibility of reducing sugars and amino acids}, volume={50}, ISSN={["1432-0789"]}, DOI={10.1007/s00374-014-0903-1}, number={5}, journal={BIOLOGY AND FERTILITY OF SOILS}, author={Tian, Lei and Shi, Wei}, year={2014}, month={Jul}, pages={785–794} }
 @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} }