How litter quality affects mass loss and N loss from decomposing Sphagnum
Limpens, J. ; Berendse, F. - \ 2003
Oikos 103 (2003)3. - ISSN 0030-1299 - p. 537 - 547.
increased nitrogen deposition - elevated atmospheric co2 - swedish raised bog - vascular plants - heathland ecosystems - northern peatlands - potential decay - central alberta - carbon-dioxide - growth
Nitrogen (N) deposition may affect litter decomposition and may thus have an impact on the rate of carbon (C) sequestration in Sphagnum peatlands. We present results from four separate experiments aimed at delineating the effects of litter N-enrichment, Sphagnum species, stem part of Sphagnum, and place of incubation on decomposition rate and N release. We measured mass loss and N loss from litterbags incubated at 10-15 cm in the field for one year. Mass loss was positively related to the N/C quotient of the litter, but depended strongly on the range in N/C quotients observed; only a distinct difference in N/C quotients affected mass loss. Although hummock species decayed at a slower rate than hollow species, the differences between the species became less pronounced for old stem parts and for N-enriched litter. Old stem parts decayed at a slower rate than young stem parts, except for S. papillosum. Neither position of incubation (low hummock or hollow), nor the inorganic N concentration of the incubation environment affected mass loss. N loss was mainly determined by, and positively related to, the N/C quotient of the litter; species and stem part had minor effects. Above a N/C quotient of about 0.015, net N loss was observed for all species. We conclude that decomposition of Sphagnum is stimulated by N deposition. As the latter also affects litter N concentration and thus N release, we think that positive feedbacks through changing litter quality should be taken into account when modelling the effects of N deposition on Sphagnum peatlands and C sequestration in these systems.
Free-air CO2 enrichment (FACE) enhances biomass production in a short-rotation poplar plantation
Calfapietra, C. ; Gielen, B. ; Galema, A.N.J. ; Lukac, M. ; Angelis, P. de; Moscatelli, M.C. ; Ceulemans, R. ; Scarascia-Mugnozza, G. - \ 2003
Tree Physiology 23 (2003). - ISSN 0829-318X - p. 805 - 814.
elevated atmospheric co2 - carbon-dioxide enrichment - net primary production - light-use efficiency - soil n-availability - hybrid poplar - populus-grandidentata - crown architecture - pinus-sylvestris - fine roots
This paper investigates the possible contribution of Short Rotation Cultures (SRC) to carbon sequestration in both current and elevated atmospheric CO2 concentrations ([CO2]). A dense poplar plantation (1 x 1 m) was exposed to a [CO2] of 550 ppm in Central Italy using the free-air CO2 enrichment (FACE) technique. Three species of Populus were examined, namely P. alba L., P. nigra L. and P. x euramericana Dode (Guinier). Aboveground woody biomass of trees exposed to elevated [CO2] for three growing seasons increased by 15 to 27%, depending on species. As a result, light-use efficiency increased. Aboveground biomass allocation was unaffected, and belowground biomass also increased under elevated [CO2] conditions, by 22 to 38%. Populus nigra, with total biomass equal to 62.02 and 72.03 Mg ha(-1) in ambient and elevated [CO2], respectively, was the most productive species, although its productivity was stimulated least by atmospheric CO2 enrichment. There was greater depletion of inorganic nitrogen from the soil after three growing seasons in elevated [CO2], but no effect of [CO2] on stem wood density, which differed significantly only among species.