The alleviation of acid soil stress in rice by inorganic or organic ameliorants is associated with changes in soil enzyme activity and microbial community composition

The effects of calcium-magnesium phosphate, rock phosphate, lime, fly ash, and animal manure as liming agents on the microbial community composition, enzyme activities involved in C, N, P, and S cycling and rice yields of acid sulfate soils were studied in a three-year field trial. Significant increases in soil pH caused by five ameliorants, particularly lime and fly ash, were observed after 3 years. Both soil exchangeable Al3+ and H+ were significantly (P < 0.05) and negatively correlated with soil pH. Increased pH led to 61-102 % increase in rice yield after 2 and 3 years but not after 1 year. Soil phospholipid fatty acid (PLFA) profiles and enzyme activities were significantly changed after 3 years of application of the soil amendments. Enzyme activities increased along gradients of soil pH, indicating that the influences of inorganic or organic ameliorants on soil enzyme activities were mainly due to the effect on soil pH value. PLFA analysis showed that this pH effect played a more important role in shaping microbial community composition than specific effects of organic and inorganic amendments. All rice yield-associated enzymes and PLFA biomarkers (e.g., gram-negative bacteria and actinomycetes) were regulated by soil pH after 3 years. These results revealed that pH-induced changes in soil enzyme activity and microbial composition might be an important mechanism in alleviating acid stress in soil cropped to rice by various ameliorants.