In situ effects of elevated CO₂ on the carbon and nitrogen status of alpine plants

Abstract

Summary1. The effect of elevated CO 2 on tissue composition in an alpine grassland (Swiss Central Alps, 2500 m) under both natural and increased nutrient supply (NPK) is summarized. 2. During 3 years of CO 2 enrichment the concentration of total non-structural carbohydrates (TNC) in leaves increased by 32% in Leontodon helveticus (largely sugar) and by 56% in Trifolium alpinum (largely starch) but did not change significantly in the dominant sedge Carex curvula and in Poa alpina, currently a rare species at this site. 3. Enhanced mineral nutrient supply (unlike elevated CO 2 ) greatly stimulated growth but did not reduce the CO 2 -induced TNC accumulation. 4. Under elevated CO 2 nitrogen concentrations (per g TNC-free dry matter) of green leaves decreased in Leontodon (-21%) and in Trifolium (-24%) but not or only slightly in Carex and in Poa. NPK addition compensated this CO 2 effect on nitrogen concentration in Trifolium but not in the other species. 5. In below-ground tissue neither TNC nor nitrogen concentration responded to CO 2 fertilization. 6. The nitrogen pool per unit land area at peak season biomass remained unaffected by the CO 2 treatment. 7. Overall our results suggest that the late successional dominant sedge Carex curvula remains unaffected by elevated CO 2 , independently of mineral nutrient supply, whereas the co-dominant and sub-dominant forbs Leontodon helveticus and Trifolium alpinum show both an increase of TNC as well as N depletion under elevated CO 2 . 8. None of these changes in active plant tissue translate into compositional changes in naturally senesced litter suggesting caution with predictions of CO 2 effects on decomposition based on data from green plant material.

The effect of elevated atmospheric CO2 concentration and nutrient supply on gas exchange, carbohydrates and foliar phenolic concentration in live oak (Quercus virginiana Mill.) seedlings

“…Soluble sugars and starch concentrations in stem and roots have already been found not to increase in other experiments [4,28]. In contrast with our findings, starch and total non-structural carbohydrate accumulation in foliage (and other compartments) of plants grown at elevated [CO 2 ] is a much more common phenomenon [2,42,43], although it has been reported to be a strong species-specific response [29,50]. We sampled the plant material in the afternoon and Wullschleger et al [56] [28,31,41].…”

“…Elevated [CO 2 ] may also reduce dark respiration [56]. Total non-structural carbohydrates ( but it also appears that this is a species-specific response [29,50]. The magnitude of these responses may be affected by nutrient levels [15,17].…”

Maternal and direct effects of elevated CO 2 on seed provisioning, germination and seedling growth in Bromus erectus

“…The physiological mechanism behind this response may be similar to what is typically observed in leaves (e.g. Curtis 1996;Schäppi and Körner 1997). CO 2 -induced stimulation of photosynthesis may have caused an accumulation of carbohydrates in seeds leading to a dilution of the nitrogen reserves.…”

Effects of elevated CO2 and nitrogen on growth ofPoa pratensis (L.)

“…The absence of a significant CO2 growth response may be attributed to increased biomass allocation toward heterotrophic rather than autotrophic tissue, thereby leading to a higher R/S Ratio and lower LAR (Norby et al, 1992;Callaway et al, 1994). For instance, the accumulation of nonstructural carbohydrates in plant roots, which causes increases in either the respiration rate or the R/S under elevated CO2 (Schappi and Korner, 1997), may offset the positive effects of improved carbon assimilation on growth. In the current study, however, there was no indication that the proportion of beterotrophic tissue increased under elevated CO2.…”