Open-air System Research Articles

Combined use of open-air and indoor fumigation systems to study effects of SO 2 on leaching processes in Scots pine litter

Both an open-air fumigation system and a laboratory-based system were used to expose decomposing Scots pine ( Pinus sylvestris L.) needles to controlled concentrations of SO 2 (arithmetic mean ⩽48 nl litre −1) during a period, in total, of 301 days. The experimental design involved reciprocal litter transplants from ‘clean’ to ‘polluted’ air and vice versa, using the two fumigation systems. The objectives were (1) to observe the effects of SO 2 on leachate and litter chemistry, (2) to assess whether pollution-induced changes are reversible in clean air, and (3) to test the suitability of small-scale fumigation chambers (litter microcosms) compared with open-air systems in soil studies. Through the formation of SO 4 2− ions, dry-deposited SO 2 exhibited a marked capacity to remove ‘base’ cations (Ca 2+, Mg 2+ and K +) from decomposing pine needles, and also to acidify litter leachates (as indicated by proton fluxes from the litter). When litter was transferred from polluted air (48 nl litre −1 SO 2, in the open-air system) to either clean or polluted air in the laboratory, the effects of prior exposure to SO 2 on leachate composition were still evident even after 86 days: the role of base cation depletion within the litter, caused by SO 4 2−-induced leaching, is discussed. Data for SO 4 2− fluxes in leachates collected from the small-scale chambers indicated that dry deposition velocities for SO 2 were not anomalously high within this fumigation system. It is therefore concluded that microcosm studies can provide information complementary to the open-air fumigation approach in soils research.

Injury and physiological responses of Larrea tridentata (DC) Coville exposed in situ to sulphur dioxide.

The response of shrubs of Larrea tridentata (DEC) Coville (creosotebush) exposed to sulphur dioxide (SO(2)) was evaluated using in situ plants of the Majove Desert. Larrea was exposed to acute levels of 0.3 to 2.0 microl litre(-1) SO(2) for periods up to 13 days using field chambers or an open-air fumigation system. Plants exposed in the spring exhibited considerable leaf injury (necrosis and defoliation) when exposed to 2.0 microl litre(-1) SO(2), and in the autumn had leaf injury when exposed to >0.4microl litre(-1) SO(2). Injured plants had higher transpiration rates, less negative water pressure potentials, and/or lower photosynthetic rates than control plants. It is likely that Larrea would not be injured by the typically low SO(2) concentrations and dry environmental conditions of the Mojave Desert. However, if injury were to occur, it would be accompanied by changes in plant-water relations and photosynthesis, followed by recovery after the SO(2) stress was removed.

A field estimate of SO2 deposition velocities to rapidly growing soybeans

Field-grown soybeans were exposed to elevated SO2 levels in an open-air fumigation system which produced minimal alteration of the crop environment. The increase in S content of the fumigated plants as compared to unfumigated controls was used to estimate the deposition velocity of SO2 to the crop. Estimates ranged from 0.5 to 0.9 cm s−1, which is in the lower part of the range found by micrometeorological techniques, confirming that estimates based on short-term gradient measurements are realistic.

An Optical Absorption Cell with Vapor Cross Flow

In order to avoid wall contamination, and to simulate an open air system, a water vapor cross flow instrument has been designed. Vapor equilibrium is established within 30 min. A 6.3 μ infrared beam traverses the pressure, temperature, and humidity controlled vapor column. The effect of these thermodynamic parameters can be examined.

Experimental Catastrophic Selection and Tolerances to Low Oxygen Concentration in Native Arizona Freshwater Fishes

Open— and closed—system experimental designs were used to test comparative tolerance, survival, and potential natural selection in four species subjected to low dissolved oxygen concentration–the desert pupfish (Cyprinodon macularius), long—fin dace (Agosia chrysogaster), speckled dace (Rhinichthys osculus), and Gila sucker (Catostomus clarki). Different rankings of the species resulted for tolerance (closed—air system) and survival (open air system). Open—system experiments were designed that demonstrate mechanisms by which this environmental stressor produces catastrophic selection in nature. During interspecific competition, adaptive behavior and structure as well as physiological tolerance were decisive in survival.