Epsilon Open Archive

Abstract

Theories and mathematical models were derived to analyse and predict plant and forest response to soil nitrogen (N) availability and atmospheric CO2 concentration. Soil carbon accumulation in response to long-term fertilisation was studied using measured soil C and 14C of the organic layer in a pine forest in Northern Sweden. Fertilisation increased forest growth and drastically reduced long-term litter decomposition through effects on the decomposers. In 100 years, twice as much carbon would be accumulated in the forest soil where N addition is high as where no N addition occurs. Root:shoot allocation of small plants was modelled using maximisation of relative growth rate, with and without explicit inclusion of N based maintenance respiration. The results agreed qualitatively with experimental data from birch and tomato plants and the agreement was considerably improved by the inclusion of maintenance respiration. Senescence and resorption as mechanisms of maximising photosynthetic production were used to predict LAI and resorption efficiency in relation to canopy N. This theory explained the observed LAI for four investigated plant species: red amaranth (Amaranthus cruentus), soybean (Glycine max), rice (Oryza sativa), and sorghum (Sorghum bicolor). Analytical expressions for forest photosynthesis, NPP, growth, LAI, root:leaf allocation and leaf N concentration were derived using a principle of maximal growth and optimisation of canopy N. Whole forest responses to N availability and atmospheric CO2 were predicted from basic physiological parameters. The results agreed well with results of elevated CO2 FACE experiments for sweetgum and loblolly pine trees. Finally, the findings of reduced decomposition and increased growth in response to fertilisation and elevated CO2 were evaluated in the context of the global carbon balance. A simple model of the responses of global carbon fluxes and pool turnover rates combined with a future scenario of CO2 emissions was subjected to a strong fertilisation effect on the boreal forest components. The results indicate that massive fertilisation could temporarily halt the rising of the atmospheric CO2.