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

Tree growth rate can complicate our understandings of plant belowground responses to elevated CO (eCO) in tropical ecosystems. We studied the effects of eCO on plant growth parameters, and rhizospheric soil properties including soil organic carbon (SOC), glomalin related soil protein (GRSP), microbial biomass C (C), CO efflux (C), 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 eCO (∼550 ppm) and ambient CO (aCO; ∼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 aCO treatment, eCO significantly increased plant height, stem and shoot weight, and total plant biomass of Teak. However, these plant traits did not considerably differed between eCO and aCO treatments of Butea. The eCO 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, C and extracellular enzyme activities (phosphatase, dehydrogenase, β-glucosidase and fluorescein diacetate) were observed under Teak compared with Butea. Compared with aCO treatment, eCO slightly reduced soil available N and P under the Teak, but no changes were apparent between eCO and aCO treatments of the Butea. The greater extent of responses from soil variables observed after longer period (46 months) of CO exposure. The multivariate analysis confirmed that eCO treatment with Teak is more responsive compared with other treatments of Teak and Butea. This contrasting rhizospheric soil feedback to eCO 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 eCO climate.