Effects of elevated [CO₂] on forest growth and carbon storage: a modelling analysis of the consequences of changes in litter quality/quantity and root exudation

• Published in: Plant and soil Vol. 224; no. 1; pp. 135 - 152
• Main Authors: McMurtrie, Ross E., Dewar, Roderick C., Medlyn, Belinda E., Jeffreys, Mark P.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Dordrecht Kluwer Academic Publishers 01.01.2000; Springer; Springer Nature B.V
• Subjects: Agronomy. Soil science and plant productions; biogeochemical cycles; Biological and medical sciences; biomass production; carbon; Carbon dioxide; carbon nitrogen ratio; Carbon sequestration; Chemical, physicochemical, biochemical and biological properties; Ecosystem models; Exudation; Forest ecosystems; forest litter; Forestry; forests; Fundamental and applied biological sciences. Psychology; General forest ecology; Generalities. Production, biomass. Quality of wood and forest products. General forest ecology; Leaves; Litter; Nitrogen; nitrogen content; nitrogen fixation; nutrient availability; Organic matter; Organic soils; Physics, chemistry, biochemistry and biology of agricultural and forest soils; Pine trees; Plant growth; Plant litter; Plant roots; Plants; Ratios; root exudates; simulation models; Soil organic matter; Soil science; Soils; Sweden; Sweden; Forests; Exudate; Litter; Root; Growth; Carbon dioxide; Biogeochemical cycle; Bioavailability; Nitrogen; Modeling; Carbon cycle; Medium enrichment; Nitrogen cycle; Storage; Quality; Mathematical model
• ISSN: 0032-079X; 1573-5036
• DOI: 10.1023/A:1004711707787

Many researchers have proposed that the stimulus of plant growth under elevated [CO₂] observed in short-term experiments will be moderated in the longer term by a reduction in soil nitrogen (N) availability linked to decreased litter quality and/or increased litter production. However, these negative feedbacks may be offset to some extent by a stimulus in N fixation linked to increased root exudation. The aim of this modelling study is to examine how changes in litter quality/quantity and root exudation — if they occur — will affect the CO₂ responses of net primary productivity and ecosystem carbon (C) storage on different timescales. We apply a model of C and N cycling in forest ecosystems (G'DAY) to stands of Norway spruce (Picea abies, L. Cast) growing at a N-limited experimental site at Flakaliden, Sweden, and draw the following conclusions: (1) in the absence of changes in litter quality and root exudation, the short-term CO₂ stimulus of litter quantity leads to only a minimal CO₂ stimulus of productivity or C storage in the medium term (≈ 20 years) and long term (≈ 200 years), because of constraints on soil N availability; (2) increasing plant nitrogen use efficiency (via a decrease in the N:C ratio of new litter) makes little impact on these results; (3) a significant CO₂ response in the medium term requires a substantial decrease in the N:C ratio of older litter, when it is approaching stabilisation as soil organic matter, although the long-term CO₂ response remains small; and (4) an increase in N fixation leads to a small effect on productivity in the short term, but a very large effect on both productivity and C storage in the long term. These results suggest that soil N constraints on the long-term CO₂-fertilisation effect can be overcome to a significant extent only by increases in N acquisition, although only modest increases may be required.