大气CO_2浓度升高对不同施氮土壤酶活性的影响

Effects of elevated atmospheric CO_2 on soil enzyme activities at different nitrogen level

利用中国唯一的无锡FACE(Free-air CO2 enrichment,开放式空气CO2浓度升高)平台,研究了大气CO2浓度升高对土壤β-葡糖苷酶、转化酶、脲酶、酸性磷酸酶、β-氨基葡糖苷酶的影响。研究发现,不同氮肥处理下大气CO2浓度升高对某些土壤酶活性的影响不同。在低氮施肥处理中,大气CO2浓度升高显著降低β-葡糖苷酶活性,但是在高氮施肥处理下,大气CO2浓度升高显著增加β-葡糖苷酶活性。在低氮和常氮施肥处理中大气CO2浓度升高显著增加了土壤脲酶活性,但在高氮水平下影响不显著。在低氮、常氮施肥处理中,大气CO2浓度升高对土壤酸性磷酸酶活性没有影响,而在高氮施肥处理中显著增强了土壤中磷酸酶活性。大气CO2浓度升高对土壤转化酶活性和β-氨基葡糖苷酶的活性有增加趋势,但影响不显著。研究还发现,在不同的CO2浓度下,土壤酶活性对不同氮肥处理的响应也不同。在正常CO2浓度下,土壤中β-葡糖苷酶活性随着氮肥施用量的增加而降低,而在大气CO2浓度升高条件下,却随着氮肥施用量的增加而增加。在大气CO2浓度升高条件下,高氮施肥显著增加了转化酶和酸性磷酸酶活性,而在正常CO2浓度下,影响不显著。在大气CO2浓度升高条件下,氮肥处理对脲酶活性的影响不大,但在正常CO2浓度下,脲酶活性随着氮肥施用量的增加而增加。氮肥对β-氨基葡糖苷酶活性的影响不明显。

It has been predicted that elevated atmospheric CO2 will increase enzyme activity as a result of CO2-induced carbon entering the soil. The objective of this study was to investigate the effects of elevated atmospheric CO2 on soil enzyme activities under a rice/wheat rotation. This experiment was conducted in Wuxi, Jiangsu, China under China FACE （Free Air Carbon dioxide Enrichment） Project system. Two atmospheric CO2 concentrations （（ 580 ± 60） and （380 ± 40） μmol· mol^-1） ） and three N application treatments （low nitrogen, LN 150 kg· hm^-2, normal nitrogen, NN 250 kg· hm^-2 and high nitrogen, HN 350kg· hm^-2） were included. Soil samples （0 - 10 cm） were collected for analysis of β-glucosidase, invertase, urease, acid phosphates and β-glucosaminidase activities. Results revealed that with elevated atmospheric CO2 β-glucosidase activity significantly decreased（p 〈 0.05） at low N application rates; had no significant effect with a normal N application rate; and significantly increased （p 〈 0.05） with a high N application rate. For urease activity, at low and normal N application rates （but not high N application rate）, elevated atmospheric CO2 significantly increased （p 〈 0.05） it. With acid phosphatase elevated atmospheric CO2 only had significant higher effects （p 〈 0.05） at high N application rates. Under different CO2 concentration, effects of N fertilization are also different. Soil β-glucosidase activity at ambient CO2 concentration decreased with N fertilization, while it increased at elevated CO2 concentration. In addition, invertase and acid phosphatase activities at elevated CO2 concentrations, significantly increased （p 〈 0.05） with N treatments, but there was no effect with the ambient CO2 concentration. For urease activity, at ambient CO2 concentrations, N fertilization increased it significantly （p 〈 0.05）, whereas at elevated CO2 concentrations were not significant. Additionally, with β-glucosaminidase activity, there were no significant effects from N application. In general, then, elevated atmospheric CO2 increased soil enzyme activity, which may be attributed to the following two factors： （1） elevated atmospheric CO2 leading to more plant biomass in the soil, which in turn stimulated soil microbial biomass and activity; and （2） elevated atmospheric CO2 that increased plant photosynthesis, thereby increasing plant-derived soil enzymes.