Bacterioplankton production in freshwater Antarctic lakes

• Published in: Freshwater Biology
• Main Authors: Laybourn-Parry, Johanna, Henshaw, Tracey, Jones, Davey J., Quayle, Wendy
• Format: Article in Journal/Newspaper
• Language: English
• Published: Blackwell Science Ltd 2004
• Subjects: Antarctica; bacterioplankton; freshwater; lakes; production; Antarctic; Antarc*
• Online Access: https://doi.org/10.1111/j.1365-2427.2004.01221.x; https://researchportal.murdoch.edu.au/esploro/outputs/journalArticle/Bacterioplankton-production-in-freshwater-Antarctic-lakes/991005560336807891

Rising atmospheric CO2 concentrations have highlighted the importance of being able to understand and predict C fluxes in plant-soil systems. We investigated the responses of the two fluxes contributing to below-ground efflux of plant root-dependent CO2, root respiration and rhizomicrobial respiration of root exudates. Wheat (Triticum aestivum L., var. Consort) plants were grown in hydroponics at 20°C, pulse-labelled with 14 CO2 and subjected to two regimes of temperature and light (12 h photoperiod or darkness at either 15°C or 25°C), to alter plant C supply and demand. Root respiration was increased by temperature with a Q10 of 1.6. Root exudation was, in itself, unaltered by temperature, however, it was reduced when C supply to the roots was reduced and demand for C for respiration was increased by elevated temperature. The rate of exudation responded much more rapidly to the restriction of C input than did respiration and was approximately four times more sensitive to the decline in C supply than respiration. Although temporal responses of exudation and respiration were treatment dependent, at the end of the experimental period (2 days) the relative proportion of C lost by the two processes was conserved despite differences in the magnitude of total root C loss. Approximately 77% of total C and 67% of 14 C lost from roots was accounted for by root respiration. The ratio of exudate specific activity to CO2 specific activity converged to a common value for all treatments of 2, suggesting that exudates and respired CO2were not composed of C of the same age. The results suggest that the contributions of root and rhizomicrobial respiration to root- dependent below-ground respiration are conserved and highlight the dangers in estimating short-term respiration and exudation only from measurements of labelled C. The differences in responses over time and in the age of C lost may ultimately prove useful in improving estimates of root and rhizomicrobial respiration.