[Effects of elevated CO₂ concentration, warming, and winter wheat planting on soil enzyme activities.]

Understanding the responses of soil enzyme activities to elevated CO₂ concentration and warming can provide a scientific basis for nutrient management of croplands under global climate change. We conducted a pot expe-riment with climate chamber to examine the effects of elevated CO₂ concentration and warming and winter wheat growth on soil enzyme activities. There were four climate scenarios: control (CK, 400 μmol·mol^-1 CO₂ concentration+normal ambient temperature), and CO₂ concentration elevation (ECO₂, 800 μmol·mol^-1 CO₂ concentration+normal ambient temperature), elevated temperature (ET, 400 μmol·mol^-1 + temperature increased 4 ℃), and elevated CO₂ concentration and temperature (ECO₂+T, 800 μmol·mol^-1 CO₂ concentration + temperature increased 4 ℃). We measured the activities of soil β-glucosidase (βG), β-N-acetyl glucosidase (NAG), alkaline phosphate (ALP) and polyphenol oxidase (PPO) at four growth stages (JS, jointing stage; AS, anthesis stage; FS, filling stage and MS, maturity stage), with and without winter wheat planting. Without winter wheat planting, there was no significant difference in four kinds of soil enzyme activities between ECO₂ and CK, while ET and ECO₂+T treatments had significant negative effect on soil enzyme activities. With winter wheat planting, compared with CK, ECO₂ and ECO₂+T treatments did not affect the activities of those four soil enzyme; but the ET treatment had great impact on soil ALP and PPO activities. The activities of four kinds of soil enzyme were significantly diffe-rent between the ET and ECO₂+T treatments. Compared with ET treatment, ECO₂+T treatment increased soil βG activity at the JS, decreased NAG activity at the JS, increased ALP activity at both AS and FS, decreased PPO activity in the JS and increased in the AS. The interaction of elevated CO₂ concentration and warming had significant effect on soil NAG and ALP activities with and without winter wheat planting. The interaction of warming and expe-rimental stage had significant effect on four kinds of soil enzyme activities without winter wheat planting, but the interaction of warming and crop growth stage had significant effect on ALP and PPO activities with winter wheat planting. The interaction of elevated CO₂ concentration, warming and experimental period had significant effect on soil βG, ALP and PPO activities without winter wheat growth, while with winter wheat growth, it had significant impact on NAG, ALP and PPO activities. The winter wheat growth had significantly inhibitory effect on βG, NAG and ALP activities in the two early growth periods (JS+AS), significant promoting effect in the later growth periods (FS+MS), and significantly inhibitory effect on PPO activity during whole growth period. Overall, elevated CO₂ concentration did not affect soil enzyme activities, while the elevation of CO₂ concentration and temperature on soil enzyme activities differed among the soil enzymes at different growth stages. In addition, the responses of four soil enzyme activities to the interaction of elevated CO₂ concentration and warming varied with and without winter wheat planting.