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 (C_mic), CO₂ efflux (C_efflux), 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), C_mic, C_efflux 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.

Keywords: Glomalin related soil protein; Microbial biomass carbon; Plant functional trait; Soil biochemical response; Soil enzyme; Soil organic carbon.