Dynamics of soil specific enzyme activities and temperature sensitivities during grassland succession after farmland abandonment

Abstract

The influence of plant secondary succession on soil enzyme activities has been increasingly recognized recently. However, the characteristics of specific enzyme activities and temperature sensitivity (Q10) in the rhizosphere remain elusive. We collected rhizosphere and bulk soil samples from a secondary successional series (0, 7, 12, 17, 22, and 32 years after farmland abandonment, and a natural grassland reference) in a typical semi-arid ecosystems on the Loess Plateau of China. The potential activity of soil enzymes, including β-1,4-glucosidase (BG), β-1,4-N-acetylglucosaminidase (NAG), leucine aminopeptidase (LAP), and alkaline phosphatase (AP), was assayed at 37, 20 and 4 °C and expressed as activity per unit of soil organic carbon (specific enzyme activity). Q10 values were calculated at 20–37 °C and 4–20 °C, respectively. The specific enzyme activities of BG, NAG, LAP and AP in bulk soil increased to a maximum at the 17-year site and then significantly decreased in older grasslands. In the rhizosphere, specific enzyme activities increased and then decreased along the successional gradient with significantly higher value at the 7-year site and the 17-year site. The Q10 values of BG activity in bulk soil and the four enzyme’s activities in rhizosphere soil were changed significantly along the successional gradients. In general, the Q10 values at the two temperature ranges differed in bulk soil, but not in the rhizosphere soil. Along the plant successional gradient, the rhizosphere effects of specific enzyme activities gradually changed to negative values in the oldest sites. Our results indicate that plant secondary succession had different impacts on the enzyme activity and characteristics in the rhizosphere and bulk soil, and highlights the importance of temperature sensitivity and rhizosphere effects of enzyme activity along plant secondary successional gradients.