Growth and C allocation of Populus tremuloides genotypes in response to atmospheric CO 2 and soil N availability

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65485/1/j.1469-8137.1998.00264.x.pd

Combined effects of atmospheric CO2 and N availability on the below ground carbon and nitrogen dynamics of aspen mesocosms

It is uncertain whether elevated atmospheric CO 2 will increase C storage in terrestrial ecosystems without concomitant increases in plant access to N. Elevated CO 2 may alter microbial activities that regulate soil N availability by changing the amount or composition of organic substrates produced by roots. Our objective was to determine the potential for elevated CO 2 to change N availability in an experimental plant-soil system by affecting the acquisition of root-derived C by soil microbes. We grew Populus tremuloides (trembling aspen) cuttings for 2 years under two levels of atmospheric CO 2 (36.7 and 71.5 Pa) and at two levels of soil N (210 and 970 µg N g –1 ). Ambient and twice-ambient CO 2 concentrations were applied using open-top chambers, and soil N availability was manipulated by mixing soils differing in organic N content. From June to October of the second growing season, we measured midday rates of soil respiration. In August, we pulse-labeled plants with 14 CO 2 and measured soil 14 CO 2 respiration and the 14 C contents of plants, soils, and microorganisms after a 6-day chase period. In conjunction with the August radio-labeling and again in October, we used 15 N pool dilution techniques to measure in situ rates of gross N mineralization, N immobilization by microbes, and plant N uptake. At both levels of soil N availability, elevated CO 2 significantly increased whole-plant and root biomass, and marginally increased whole-plant N capital. Significant increases in soil respiration were closely linked to increases in root biomass under elevated CO 2 . CO 2 enrichment had no significant effect on the allometric distribution of biomass or 14 C among plant components, total 14 C allocation belowground, or cumulative (6-day) 14 CO 2 soil respiration. Elevated CO 2 significantly increased microbial 14 C contents, indicating greater availability of microbial substrates derived from roots. The near doubling of microbial 14 C contents at elevated CO 2 was a relatively small quantitative change in the belowground C cycle of our experimental system, but represents an ecologically significant effect on the dynamics of microbial growth. Rates of plant N uptake during both 6-day periods in August and October were significantly greater at elevated CO 2 , and were closely related to fine-root biomass. Gross N mineralization was not affected by elevated CO 2 . Despite significantly greater rates of N immobilization under elevated CO 2 , standing pools of microbial N were not affected by elevated CO 2 , suggesting that N was cycling through microbes more rapidly. Our results contained elements of both positive and negative feedback hypotheses, and may be most relevant to young, aggrading ecosystems, where soil resources are not yet fully exploited by plant roots. If the turnover of microbial N increases, higher rates of N immobilization may not decrease N availability to plants under elevated CO 2 .Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42281/1/442-124-3-432_01240432.pd

Populus Tremuloides Photosynthesis and Crown Architecture in Response to Elevated Co-2 and Soil N Availability

We tested the hypothesis that elevated CO 2 would stimulate proportionally higher photosynthesis in the lower crown of Populus trees due to less N retranslocation, compared to tree crowns in ambient CO 2 . Such a response could increase belowground C allocation, particularly in trees with an indeterminate growth pattern such as Populus tremuloides . Rooted cuttings of P. tremuloides were grown in ambient and twice ambient (elevated) CO 2 and in low and high soil N availability (89 ± 7 and 333 ± 16 ng N g −1 day −1 net mineralization, respectively) for 95 days using open-top chambers and open-bottom root boxes. Elevated CO 2 resulted in significantly higher maximum leaf photosynthesis ( A max ) at both soil N levels. A max was higher at high N than at low N soil in elevated, but not ambient CO 2 . Photosynthetic N use efficiency was higher at elevated than ambient CO 2 in both soil types. Elevated CO 2 resulted in proportionally higher whole leaf A in the lower three-quarters to one-half of the crown for both soil types. At elevated CO 2 and high N availability, lower crown leaves had significantly lower ratios of carboxylation capacity to electron transport capacity ( V cmax / J max ) than at ambient CO 2 and/or low N availability. From the top to the bottom of the tree crowns, V cmax / J max increased in ambient CO 2 , but it decreased in elevated CO 2 indicating a greater relative investment of N into light harvesting for the lower crown. Only the mid-crown leaves at both N levels exhibited photosynthetic down regulation to elevated CO 2 . Stem biomass segments (consisting of three nodes and internodes) were compared to the total A leaf for each segment. This analysis indicated that increased A leaf at elevated CO 2 did not result in a proportional increase in local stem segment mass, suggesting that C allocation to sinks other than the local stem segment increased disproportionally. Since C allocated to roots in young Populus trees is primarily assimilated by leaves in the lower crown, the results of this study suggest a mechanism by which C allocation to roots in young trees may increase in elevated CO 2 .Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42278/1/442-110-3-328_71100328.pd

Deutschlands Fauna in Abbildungen nach der Natur mit Beschreibungen.

3.Abt.:3.Heft (1802

Deutschlands Fauna in Abbildungen nach der Natur mit Beschreibungen.

6. Abt.:2. Heft (1806

Deutschlands Fauna in Abbildungen nach der Natur mit Beschreibungen.

3.Abt.:4.Heft (1805

Deutschlands Fauna in Abbildungen nach der Natur mit Beschreibungen.

3.Abt.:2.Heft (1799