Net exchange of greenhouse gases from soils in an unimproved pasture and regenerating indigenous Kunzea ericoides shrubland in New Zealand

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From: Australian Journal of Soil Research(Vol. 48, Issue 5)
Publisher: CSIRO Publishing
Document Type: Report
Length: 8,515 words

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Abstract :

Monthly measurements of carbon dioxide (C[O.sub.2]), methane (C[H.sub.4]), and nitrous oxide ([N.sub.2]O) fluxes were made at 3 sites along a sequence of naturally regenerating Kunzea ericoides shrubland in New Zealand, consisting of unimproved pasture (UP), young (8-12 years) Kunzea trees (YK), and old (80 years) Kunzea trees (OK). The C[O.sub.2] flux at a base temperature of 10[degrees]C was highest at the OK site (0.51 g C[O.sub.2]/[m.sup.2].h) and lowest at the UP site (0.26 g C[O.sub.2]/[m.sup.2].h). Values of C[O.sub.2] flux were regulated by soil temperature ([T.sub.s]) throughout the year, and water availability modified the response to [T.sub.s] when root-zone water content, ([theta]), fell below 0.27-0.29 [m.sup.3]/[m.sup.3] in spring and summer. The soils were mostly C[H.sub.4] sinks, although there were net C[H.sub.4] emissions during wet periods at the YK site. The maximum C[H.sub.4] flux at the YK site was -49.7 [micro]g C[H.sub.4]/[m.sup.2].h compared with -33.4 [micro]g C[H.sub.4]/[m.sup.2].h for the UP (and -90.4 [micro]g C[H.sub.4]/[m.sup.2].h for OK), indicating the potential for rapid recovery of methanotrophic populations in the YK shrubland over 8-12 years. However, on an annual basis our data suggest that C[H.sub.4] oxidation rates decrease as land reverts from unimproved pasture to shrubland. Methane oxidation rates were strongly dependent on [theta] and only weakly dependent on [T.sub.s]. Measurements of [N.sub.2]O fluxes were below the minimum detectable limit throughout the year at the UP and YK sites, and low but dependent on both [T.sub.s] and [theta] at the OK site. Annual estimates of soil C[O.sub.2] flux were 39.9, 23.3, and 21.9 x [10.sup.3] kg C[O.sub.2]/ha.year at the OK, YK, and UP sites, respectively. All 3 sites were a net sink for C[H.sub.4], with the highest oxidation rate of -5.1 kg C[H.sub.4]/ha.year at the OK site compared with -1.52 kg C[H.sub.4]/ha.year at the UP site. On a C[O.sub.2]- equivalent basis, the OK site was a greater C[H.sub.4] sink (-127.3 kg C[O.sub.2]-e/ha.year) than a [N.sub.2]O source (77.5 kg C[O.sub.2]- e/ha.year), demonstrating the potential for soils to oxidise C[H.sub.4] with forest succession as a possible mitigation strategy for land managers to reduce net emissions. Additional keywords: carbon dioxide, methane, methane oxidation, respiration, nitrous oxide, land use change.

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Gale Document Number: GALE|A237453367