In this study, we investigated the impact of elevated atmospheric CO2 (ambient + 350 μmol mol–1) on fine root production and respiration in Scots pine (Pinus sylvestris L.) seedlings. After six months exposure to elevated CO2, root production measured by root in‐growth bags, showed significant increases in mean total root length and biomass, which were more than 100% greater compared to the ambient treatment. This increased root length may have lead to a more intensive soil exploration. Chemical analysis of the roots showed that the roots in the elevated treatment accumulated more starch and had a lower C/N‐ratio. Specific root respiration rates were significantly higher in the elevated treatment and this was probably attributed to increased nitrogen concentrations in the roots. Rhizospheric respiration and soil CO2 efflux were also enhanced in the elevated treatment. These results clearly indicate that under elevated atmospheric CO2 root production and development in Scots pine seedlings is altered and respiratory carbon losses through the root system are increased.

Under elevated atmospheric CO(2) concentrations, soil carbon (C) inputs are typically enhanced, suggesting larger soil C sequestration potential. However, soil C losses also increase and progressive nitrogen (N) limitation to plant growth may reduce the CO(2) effect on soil C inputs with time. We compiled a data set from 131 manipulation experiments, and used meta-analysis to test the hypotheses that: (1) elevated atmospheric CO(2) stimulates soil C inputs more than C losses, resulting in increasing soil C stocks; and (2) that these responses are modulated by N. Our results confirm that elevated CO(2) induces a C allocation shift towards below-ground biomass compartments. However, the increased soil C inputs were offset by increased heterotrophic respiration (Rh), such that soil C content was not affected by elevated CO(2). Soil N concentration strongly interacted with CO(2) fumigation: the effect of elevated CO(2) on fine root biomass and -production and on microbial activity increased with increasing soil N concentration, while the effect on soil C content decreased with increasing soil N concentration. These results suggest that both plant growth and microbial activity responses to elevated CO(2) are modulated by N availability, and that it is essential to account for soil N concentration in C cycling analyses.

This is the first report of the biosynthetic potential of a tuber storage organ investigated by expressed sequence tag sequencing. A cDNA library was generated from the mature tuber of field grown potato (Solanum tuberosum var. Kuras). Partial sequences obtained from 6077 clones were assembled into 828 clusters and 1533 singletons. The average read length was 592 bp, and 2254 clones were full length. 5717 clones showed homology to genes from other organisms. Genes involved in protein synthesis, protein destination and cell defense predominated in tuber compared to stolon, shoot and leaf organs. 1063 clones were unique to tuber. Transcripts of starch metabolizing enzymes showed similar relative levels in tuber and stolon. ß

 Root growth and respiration in elevated CO# (700 µmol mol −" ) was studied in three tree species, Fraxinus excelsior L., Quercus petraea. L. and Pinus sylvestris L. grown in open-top chambers (OTCs) during a long-term exposure (20 months), during which root systems were allowed to develop without restriction imposed by pots. Root growth, measured as root length using root in-growth bags was increased significantly in trees exposed to elevated CO # , although the magnitude of the response differed considerably between species and with time of sampling, the greatest effect observed after 6 months in ash (ratio of elevated : ambient, e : a ; 3n40) and the smallest effect observed in oak (e : a ; 1n95). This was accompanied by changes in specific root length, with a significant decrease in all species after 6 months, suggesting that root diameter or root density were increased in elevated CO # . Increases in root length might have resulted from an acceleration in root cell expansion, since epidermal cell size was significantly increased in the zone of elongation in ash root tips (P 0n05).Contrasting effects of elevated CO # were observed for root carbohydrates, with significant increases in soluble sugars for all species (P 0n05), but both increases and decreases in starch content were observed, depending on species, and producing a significant interaction between species and CO # (P 0n001). Exposure to elevated CO # increased the total root d. wt for whole trees of all three species after 8 months of exposure, although the magnitude of this effect, in contrast to the root in-growth study, was greatest in Scots pine and smallest in ash. No significant effect of elevated CO # was observed on the root : shoot ratio. Further detailed analysis of whole root systems after 20 months confirmed that species differences in root responses to elevated CO # were apparent, with increased coarse and fine root production in elevated CO # for Scots pine and ash respectively. Lateral root number was increased in elevated CO # for all species, as was mean root diameter. Root respiration rates were significantly reduced in elevated CO # for all three species. These results provide firm evidence that exposure of trees to future CO # concentrations will have large effects on root system development, growth, carbohydrate status and respiration. The magnitude and direction of such effects will differ, depending on species. The consequences of such responses for the three species studied are discussed. The atmospheric concentration of CO # has risen steadily over the past three decades, and concentrations are expected to continue to increase (IPCC, 1995), with a general consensus that global atmospheric CO # concentrations will increase from the pre-industrial mole fraction (270 µmol mol −" ) to 600 µmol mol −" by the second half of the next

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