Estimates Of Carbon Balance Research Articles

Measurement and Modeling of Carbon Balance of Apple Trees

Apples have very high record yields (about 140 tons/ha sustained) that demand large amounts of carbon to be produced and partitioned into both fruit and vegetative structures. Even though large quantities of dry matter can be produced, profitability depends on the management of the carbon production and partitioning to produce the optimal balance of yield and fruit quality. The productivity is mostly related to moderate photosynthesis rates per leaf area, long leaf area duration, high seasonal radiation interception, relatively low respiration, and very high harvest index. Due to the perennial nature and large size, few good estimates of seasonal carbon balance are available. Models have been developed, but are not wellvalidated yet, but general seasonal trends are apparent. Daily net CO2 exchange begins negative with early spring growth, reaches zero near bloom, peaks about 6 to 10 weeks after bloom, then gradually declines until leaf fall. The demand of the fruit appears to increase exponentially during cell division, then levels off to a relatively constant demand until harvest. Experiments and modeling suggests that if fruit development is limited by carbon availability, the probability increases in heavily cropping trees, and will occur at about 2 to 4 weeks after bloom and before harvest. Best carbon balance appears to occur in relatively cool temperatures and in very long seasons.

Arctic Lakes and Streams as Gas Conduits to the Atmosphere: Implications for Tundra Carbon Budgets

Arctic tundra has large amounts of stored carbon and is thought to be a sink for atmospheric carbon dioxide (CO(2)) (0.1 to 0.3 petagram of carbon per year) (1 petagram = 10(15) grams). But this estimate of carbon balance is only for terrestrial ecosystems. Measurements of the partial pressure of CO(2) in 29 aquatic ecosystems across arctic Alaska showed that in most cases (27 of 29) CO(2) was released to the atmosphere. This CO(2) probably originates in terrestrial environments; erosion of particulate carbon plus ground-water transport of dissolved carbon from tundra contribute to the CO(2) flux from surface waters to the atmosphere. If this mechanism is typical of that of other tundra areas, then current estimates of the arctic terrestrial sink for atmospheric CO(2) may be 20 percent too high.

Respiration in relation to reserve substances in the submerged macrophyte Ceratophyllum demersum L.

Maintenance and growth respiration were determined in plants of Ceratophyllum demersum L. growing in a steady state. Growth respiration (0.255 mg C g AFDW −1 h −1) was three times that required for maintenance (0.072 mg C g AFDW −1 h −1). Respiration was linearly related to the water-soluble sugar level when total water-soluble sugar concentrations were lower than 6% of the plants' ash free dry weight. Initially, reducing and non-reducing sugars were utilized as substrates for respiration. Starch was mobilized when the raffinose content neared depletion. The respiration rates were higher in quiescent plants than in plants cultivated for 2–3 weeks at higher temperatures. The Q 10 values of respiration were similar in both growth stages (1.2 and 1.3 in quiescent and 2–3 weeks cultivated plants, respectively), indicating that the plant tissues were rich in carbohydrates. The presently measured respiration rates agreed well with relative growth rates determined on other occasions. The mass carbon balance and respiration estimates show generally low respiratory losses, possibly as a consequence of the rootlessness of the plant species.

Fate of Hydrocarbons During Oily Sludge Disposal in Soil

A 1,280-day laboratory simulation of the "landfarming" process explored the fate in soil of polynuclear aromatics (PNAs) and total extractable hydrocarbon residues originating from the disposal of an oily sludge. In addition to the measurement of CO(2) evolution, periodic analyses of PNAs and hydrocarbons monitored biodegradation activity. The estimation of carbon balance and of soil organic matter assessed the fate of residual hydrocarbons. Seven sludge applications during a 920-day active disposal period were followed by a 360-day inactive "closure" period with no further sludge applications. A burst of CO(2) evolution followed each sludge addition, but substantial amounts of undegraded hydrocarbons remained at the end of the study. Hydrocarbon accumulation did not inhibit biodegradation performance. Conversion of hydrocarbons to CO(2) predominated during active disposal; incorporation into soil organic matter predominated during the closure period. In this sludge, the predominant PNAs were degraded more completely (85%) than total hydrocarbons. Both biodegradation and abiotic losses of three- and four-ring PNAs contributed to this result. Some PNAs with five and six rings were more persistent, but these constituted only a small portion of the PNAs in the sludge. The study confirmed that the microbially mediated processes of mineralization and humification remove sludge hydrocarbons from soils of landfarms with reasonable efficiency.