HR: 16:00h
AN: B32D-01 INVITED     [PDF]
TI: Investigating Ecosystem Functional Development Along a Temperate Rainforest Chronosequence Using Stable Isotope Techniques
AU: * Barbour, M M
EM: barbourm@landcareresearch.co.nz
AF: Landcare Research, PO Box 69 Gerald St, Lincoln, 8152 New Zealand
AU: Hunt, J E
EM: huntj@landcareresearch.co.nz
AF: Landcare Research, PO Box 69 Gerald St, Lincoln, 8152 New Zealand
AU: Richardson, S J
EM: richardsons@landcareresearch.co.nz
AF: Landcare Research, PO Box 69 Gerald St, Lincoln, 8152 New Zealand
AU: Peltzer, D A
EM: peltzerd@landcareresearch.co.nz
AF: Landcare Research, PO Box 69 Gerald St, Lincoln, 8152 New Zealand
AU: Whitehead, D
EM: whiteheadd@landcareresearch.co.nz
AF: Landcare Research, PO Box 69 Gerald St, Lincoln, 8152 New Zealand
AB: Soil chronosequences are valuable systems for investigating ecosystem development by natural substitution of space for time. The Franz Josef chronosequence in New Zealand comprises temperate mixed conifer/hardwood rainforests formed on glacial surfaces of varying age. It is particularly useful as it includes both early build-up and decline phases over a relatively short time period (ca. 120 k years). Along the sequence, soil phosphorus decreases 8-fold, from 778 to 8 mg kg$^{-1}$ soluble P. In contrast, nitrogen availability increases to peak at about 500 years, due to early successional N$_{2}$-fixing shrubs, after which it slowly declines. Ecosystem development along the sequence is characterised by marked changes in both plant species richness and tree height, with progression up to 5 k years and retrogression at older sites (ie $>$ 14 k years). The carbon isotope ratio ($\delta$$^{13}$C$_{L}$) of sunlit canopy leaves from three dominant species sampled from within each of six sites, representing the full length of the sequence, decreased from -26.2 to -31.0 per mil with increasing ecosystem age. Independent measurements of photosynthetic capacity confirmed that the decrease was due to declining maximum photosynthetic rate: N$_{2}$-fixers $>$ early successional angiosperms $>$ late successional angiosperms $>$ late successional conifers. Stable oxygen and nitrogen isotope ratios of canopy leaves are interpreted in terms of stomatal regulation of water loss and changing nitrogen source, respectively. Carbon isotope analysis of CO$_{2}$ sampled at night at different heights within the canopy allowed estimation of ecosystem discrimination ($\delta$$^{13}$C$_{R}$) using Keeling plots. Similarly to $\delta$$^{13}$C$_{L}$, $\delta$$^{13}$C$_{R}$ decreased with increasing soil age, suggesting that in high rainfall environments $\delta$$^{13}$C$_{R}$ is a good integrator of ecosystem photosynthetic capacity.
DE: 0315 Biosphere/atmosphere interactions
DE: 0400 Biogeosciences
DE: 1615 Biogeochemical processes (4805)
DE: 4805 Biogeochemical cycles (1615)
SC: Biogeosciences [B]
MN: 2003 Fall Meeting