Tree growth rate regulate the influence of elevated CO2 on soil biochemical responses under tropical condition

Abstract

Tree growth rate can complicate our understandings of plant belowground responses to elevated CO2 (eCO2) in tropical ecosystems. We studied the effects of eCO2 on plant growth parameters, and rhizospheric soil properties including soil organic carbon (SOC), glomalin related soil protein (GRSP), microbial biomass C (Cmic), CO2 efflux (Cefflux), and microbial extracellular enzyme activities under two tropical tree saplings of fast-growing Tectona grandis (Teak) and slow-growing Butea monosperma (Butea). We exposed these saplings to eCO2 (∼550 ppm) and ambient CO2 (aCO2; ∼395 ppm) in the Indo-Gangetic plain region, and further (after 10 and 46 months) measured the changes in their rhizospheric soil properties. With respect to aCO2 treatment, eCO2 significantly increased plant height, stem and shoot weight, and total plant biomass of Teak. However, these plant traits did not considerably differed between eCO2 and aCO2 treatments of Butea. The eCO2 induced greater extent of increase in rhizospheric soil properties including SOC fractions (particulate OC, non-particulate OC and total OC), GRSP fractions (easily extractable- GRSP, difficulty extractable- GRSP and total- GRSP), Cmic, Cefflux and extracellular enzyme activities (phosphatase, dehydrogenase, β-glucosidase and fluorescein diacetate) were observed under Teak compared with Butea. Compared with aCO2 treatment, eCO2 slightly reduced soil available N and P under the Teak, but no changes were apparent between eCO2 and aCO2 treatments of the Butea. The greater extent of responses from soil variables observed after longer period (46 months) of CO2 exposure. The multivariate analysis confirmed that eCO2 treatment with Teak is more responsive compared with other treatments of Teak and Butea. This contrasting rhizospheric soil feedback to eCO2 between two tropical trees, suggesting fast-growing species will be more responsive to future climate. Such species will have a competitive advantage over coexisting less responsive species (e.g. Butea) under future eCO2 climate.