Abstract
Using a 14C pulse-labelling technique, we studied the seasonal changes in assimilation and partitioning of photoassimilated C in the plant–root–soil components of a temperate pasture. Pasture and soil samples were taken after 4-h, and 35-day chase periods, to examine these seasonal 14C fluxes. Total C and 14C were determined in the shoot, root and soil system. The amounts of C translocated annually to roots and soil were also estimated from the seasonal 14C distribution and pasture growth. The in situ field decomposition of newly formed roots during different seasons, also using 14C-labelling, was studied for one year in undisturbed rhizosphere soil. The 14C-labelled roots were sampled five times and decomposition rates were calculated assuming first-order decomposition.
Annual pasture production at the site was 16 020 kg DM ha−1, and pasture growth varied with season being highest (75–79 kg ha−1 d−1) in spring and lowest (18–20 kg ha−1 d−1) in winter. The above- and below-ground partitioning of 14C also varied with the season. The respiratory 14C–CO2 losses, calculated as the difference between the total amounts of 14C recovered in the soil-plant system at 4 h and 35 days, were high (66–70%) during the summer, autumn and winter season, and low (37–39%) during the spring and late-spring season. Pasture plants partitioned more C below-ground during spring compared with summer, autumn and winter seasons. Overall, at this high fertility dairy pasture site, 18 220 kg C/ha was respired, 6490 kg remained above-ground in the shoot, and 6820 kg was translocated to roots and 1320 kg to soil. Root decomposition rate constant (k) differed widely with the season and were the highest for the autumn roots. The half-life was highest (111 days) for autumn roots and lowest (64 days) for spring roots. About one-third of the root label measured in the spring season disappeared in the first 5 weeks after the initial 35 Day of allocation period. The late spring, summer, late summer and winter roots had intermediate half-lives (88–94 days). These results indicate that seasonal changes in root growth and decomposition should be accounted for to give a better quantification of root turnover.
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Saggar, S., Hedley, C. Estimating seasonal and annual carbon inputs, and root decomposition rates in a temperate pasture following field 14C pulse-labelling. Plant and Soil 236, 91–103 (2001). https://doi.org/10.1023/A:1011942619252
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DOI: https://doi.org/10.1023/A:1011942619252