Effect of elevated CO2 on carbon and nitrogen distribution within a tree (Castanea sativa Mill.) — soil system

Abstract

Two-year-old sweet chestnut trees were grown outside in normal or double CO2 atmospheric concentration. In spring and in autumn of two growing seasons, a six day labelling pulse of lac labelled CO2 was used to follow the carbon assimilation and distribution in the plant-soil system. Doubling atmospheric CO2 had a significant effect on the tree net carbon uptake. A large proportion of the additional C uptake was 'lost' through the root system. This suggests that increased C uptake under elevated CO2 conditions increases C cycling without necessarily increasing C storage in the plant. Total root derived material represented a significant amount of the 'extra-assimilated' carbon due to the CO2 treatment and was strongly correlated with the phenological stage of the tree. Increasing root rhizodeposition led to a stimulation of microbial activity, particularly near the end of the growing season. When plant rhizodeposition was expressed as a function of the root dry weight, the effect of increasing CO2 resulted in a higher root activity. The C to N ratios were significantly higher for trees grown under elevated CO2 except for the fine root compartment. An evaluation of the plant-soil system nitrogen dynamics showed, during the second season of CO2 treatment, a decrease of soil N mineralization rate and total N uptake for trees grown at elevated CO2 levels.

Increases in nitrogen uptake rather than nitrogen-use efficiency support higher rates of temperate forest productivity under elevated CO 2

“…Rapid plant growth under elevated CO 2 is associated with greater hyphal length and fungal activity in the soil and an increase in the degree to which fine roots are colonized by ectoand arbuscular mycorrhizal fungi (36,52,53). Moreover, enhanced NPP under elevated CO 2 increases the quantity of C entering soil (54,55) by increasing fine root production and turnover (56)(57)(58) and root exudation (59,60), processes that increase the metabolism of organic substrates by soil microbial communities (61)(62)(63)(64)(65) and soil respiration (66)(67)(68).…”

Growth and C allocation of Populus tremuloides genotypes in response to atmospheric CO2 and soil N availability

“…Horwath et al, 1994 ;Rouhier et al, 1994). In addition, there were clear differences in allocation to roots between early and late leaf-fall genotype pairs that were not related to timing of leaf senescence.…”

Priming depletes soil carbon and releases nitrogen in a scrub-oak ecosystem exposed to elevated CO2

“…mineralization of existing SOC (Rouhier et al, 1994;Cardon et al, 2001). Although it is difficult to detect priming effects in field experiments, they have been reported in grasslands (Pendall et al, 2003) and forests (Hoosbeek et al, 2004;Carney et al, 2007).…”