Drainage affects tree growth and C and N dynamics in a minerotrophic peatland

作者：Choi Woo Jung^*; Chang Scott X; Bhatti Jagtar S

来源：Ecology, 2007, 88(2): 443-453.

DOI：10.1890/0012-9658(2007)88[443:DATGAC]2.0.CO;2

• black spruce
• C-13
• Larix laricina
• N-15
• N loss
• peatland drainage
• photosynthetic capacity
• Picea mariana
• stomatal conductance
• tamarack
• tree ring

The lowering of the water table resulting from peatland drainage may dramatically alter C and N cycling in peatland ecosystems, which contain one-third of the total terrestrial C. In this study, tree annual ring width and C (delta C-13) and N (delta N-15) isotope ratios in soil and plant tissues ( tree foliage, growth rings, and understory foliage) in a black spruce-tamarack ( Picea mariana-Larix laricina) mixed-wood forest were examined to study the effects of drainage on tree growth and C and N dynamics in a minerotrophic peatland in west-central Alberta, Canada. Drainage increased the delta N-15 of soil NH4+ from a range of +0.6 parts per thousand to +2.9 parts per thousand to a range of +4.6 parts per thousand to +7.0 parts per thousand most likely through increased nitrification following enhanced mineralization. Plant uptake of N-15-enriched NH4+ in the drained treatment resulted in higher plant delta N-15 (+0.8 parts per thousand to +1.8 parts per thousand in the drained plots and -3.9 parts per thousand to -5.4 parts per thousand in the undrained plots), and deposition of litterfall N enriched with N-15 increased the delta N-15 of total soil N in the surface layer in the drained (+2.9 parts per thousand) as compared with that in the undrained plots ( +0.6 parts per thousand). The effect of drainage on foliar delta C-13 was species-specicfic, i.e., only tamarack showed a considerably less negative foliar delta C-13 in the drained (-28.1 parts per thousand) than in the undrained plots (-29.1 parts per thousand), indicating improved water use efficiency (WUE) by drainage. Tree ring area increments were significantly increased following drainage, and delta C-13 and delta N-15 in tree growth rings of both species showed responses to drainage retrospectively. Tree-ring delta C-13 data suggested that drainage improved WUE of both species, with a greater and more prolonged response in tamarack than in black spruce. Our results indicate that drainage caused the studied minerotrophic peatland to become a more open ecosystem in terms of C and N cycling and loss. The effects of forested peatland drainage or drying on C and N balances deserve further research in order to better understand their roles in future global change.

• 出版日期2007-2