Articles | Volume 14, issue 23
Biogeosciences, 14, 5393–5402, 2017
Biogeosciences, 14, 5393–5402, 2017

Research article 01 Dec 2017

Research article | 01 Dec 2017

Modeling the effects of tree species and incubation temperature on soil's extracellular enzyme activity in 78-year-old tree plantations

Xiaoqi Zhou1,2,*, Shen S. J. Wang3,*, and Chengrong Chen2 Xiaoqi Zhou et al.
  • 1Tiantong National Station for Forest Ecosystem Research, Center for Global Change and Ecological Forecasting, Shanghai Key Lab for Urban Ecological Processes and Eco-restoration, School of Ecological and Environmental Sciences, East China Normal University, Shanghai 200241, China
  • 2Australian Rivers Institute and Griffith School of Environment, Griffith University, Nathan, Brisbane 4111, Queensland, Australia
  • 3Machine Learning Systems, Computing and Information Systems, The University of Melbourne, Melbourne 3010, Australia
  • *These authors contributed equally to this work.

Abstract. Forest plantations have been widely used as an effective measure for increasing soil carbon (C), and nitrogen (N) stocks and soil enzyme activities play a key role in soil C and N losses during decomposition of soil organic matter. However, few studies have been carried out to elucidate the mechanisms behind the differences in soil C and N cycling by different tree species in response to climate warming. Here, we measured the responses of soil's extracellular enzyme activity (EEA) to a gradient of temperatures using incubation methods in 78-year-old forest plantations with different tree species. Based on a soil enzyme kinetics model, we established a new statistical model to investigate the effects of temperature and tree species on soil EEA. In addition, we established a tree species–enzyme–C∕N model to investigate how temperature and tree species influence soil C∕N contents over time without considering plant C inputs. These extracellular enzymes included C acquisition enzymes (β-glucosidase, BG), N acquisition enzymes (N-acetylglucosaminidase, NAG; leucine aminopeptidase, LAP) and phosphorus acquisition enzymes (acid phosphatases). The results showed that incubation temperature and tree species significantly influenced all soil EEA and Eucalyptus had 1.01–2.86 times higher soil EEA than coniferous tree species. Modeling showed that Eucalyptus had larger soil C losses but had 0.99–2.38 times longer soil C residence time than the coniferous tree species over time. The differences in the residual soil C and N contents between Eucalyptus and coniferous tree species, as well as between slash pine (Pinus elliottii Engelm. var. elliottii) and hoop pine (Araucaria cunninghamii Ait.), increase with time. On the other hand, the modeling results help explain why exotic slash pine can grow faster, as it has 1.22–1.38 times longer residual soil N residence time for LAP, which mediate soil N cycling in the long term, than native coniferous tree species like hoop pine and kauri pine (Agathis robusta C. Moore). Our results will be helpful for understanding the mechanisms of soil C and N cycling by different tree species, which will have implications for forest management.

Short summary
Here, we measured soil EEA using a gradient of incubation temperatures in 78-year-old tree plantations. We established a new tree species–enzyme–C/N model to explain why exotic slash pine can grow faster, as it has longer residual soil N residence time than native pine specie. To our knowledge this is the first study to clearly show that when soils with different C contents are subject to warming, high C soil has more C losses but differences in residual C between them become larger and larger.
Final-revised paper