ISSN:
1365-2486
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Biology
,
Energy, Environment Protection, Nuclear Power Engineering
,
Geography
Notes:
Rainfall and its seasonal distribution can alter carbon dioxide (CO2) exchange and the sustainability of grassland ecosystems. Using eddy covariance, CO2 exchange between the atmosphere and a sparse grassland was measured for 2 years at Twizel, New Zealand. The years had contrasting distributions of rain and falls (446 mm followed by 933 mm; long-term mean=646 mm). The vegetation was sparse with total above-ground biomass of only 1410 g m−2. During the dry year, leaf area index peaked in spring (November) at 0.7, but it was 〈0.2 by early summer.The maximum daily net CO2 uptake rate was only 1.5 g C m−2 day−1, and it occurred before mid-summer in both years. On an annual basis, for the dry year, 9 g C m−2 was lost to the atmosphere. During the wet year, 41 g C m−2 was sequestered from the atmosphere. The net exchange rates were determined mostly by the timing and intensity of spring rainfall.The components of ecosystem respiration were measured using chambers. Combining scaled-up measurements with the eddy CO2 effluxes, it was estimated that 85% of ecosystem respiration emanated from the soil surface. Under well-watered conditions, 26% of the soil surface CO2 efflux came from soil microbial activity. Rates of soil microbial CO2 production and net mineral-N production were low and indicative of substrate limitation. Soil respiration declined by a factor of four as the soil water content declined from field capacity (0.21 m3 m−3) to the driest value obtained (0.04 m3 m−3). Rainfall after periods of drought resulted in large, but short-lived, respiration pulses that were curvilinearly related to the increase in root-zone water content. Coupled with the low leaf area and high root : shoot ratio, this sparse grassland had a limited capacity to sequester and store carbon. Assuming a proportionality between carbon gain and rainfall during the summer, rainfall distribution statistics suggest that the ecosystem is sustainable in the long term.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1365-2486.2004.00842.x
Permalink
