A simple chamber technique for the in situ labelling of pasture sward with carbon (¹⁴C)

Abstract

Information on carbon (C) flows and transformations in the rhizosphere provides a basis for understanding the functioning of the system. However, the sophisticated growth cabinet facilities required for collecting quantitative data, with ¹⁴C labelling, generally limit their application under field conditions. We determined the feasibility of ‘pulse‐labelling’ pasture swards with ¹⁴C [exposing the plants to a single large ¹⁴C‐carbon dioxide (CO₂) pulse] to monitor C transformations under field conditions using a simple chamber modified to form a sealed hemisphere over an area of pasture. The ¹⁴C‐CO₂ was introduced into the hemisphere to ¹⁴C label the plant material. Assimilation of ¹⁴C‐CO₂ was checked by taking samples of the chamber atmosphere. Any leakage of ¹⁴C‐CO₂ from the chamber was also checked by taking air samples from around and outside the chamber during the assimilation period. The chamber was subsequently removed, and the pasture was opened to natural conditions. Cores were taken periodically from the treated area. Herbage, roots and soils were separated and analyzed for ¹⁴C. Incorporation of ¹⁴C‐CO₂ into the pasture sward was rapid and the variability was non‐limiting. Up to 78% of the calculated ¹⁴C‐CO₂ produced in the syringe and injected into the chamber could be accounted for in the plant/soil system four hours after labelling. The fate of the ¹⁴C label was monitored after an allocation period of 4 hour to 35 days in the plant/soil system using well established methods of analysis. This simple chamber technique appears to be useful for studying C transfers through the pasture plant/soil system and for understanding C dynamics in the field.

Notes

Present address: SpectraChem Analytical, P. O. Box 38–680, Wellington Mail Centre, New Zealand.