Effects of Open‐Top Chambers on ‘Valencia’ Orange Trees

Abstract

Open‐top field chambers are the most widely used technology for evaluating the impacts of air pollutants on vegetation. This study was conducted to evaluate the long‐term effects of chambers on Valencia orange trees (Citrus sinensis [L.] Osbeck). The trees were exposed to ambient ozone (O3) for 51 months in large (4.3‐m diam. by 2.9‐m high) nonfiltered open‐top chambers (NF) and in ambient air without chambers (AA). During this period, the 12‐h daytime (M12) average O3 concentration was approximately 8% lower, and the cumulative O3 exposure for hourly average concentrations >0.1 µL L−1 (SUM10) was 29% lower than for NF than for AA trees. By December 1984 (after eight months in chambers), canopy volume for NF trees was 67% greater than for AA trees; and by March 1988 canopy volume for NF trees was 104% greater than for AA trees (P < 0.001). Specific leaf areas (cm2 g−1) were larger for NF than AA trees (P < 0.05). Total harvestable fruit weight combined for years 1986, 1987 and 1988 was 98% higher for NF than for AA trees (P < 0.01). The higher yield for NF trees was associated with lower immature fruit drop, especially during the growing seasons prior to the 1986 and 1987 harvests (P < 0.01). Warm season (April–October) rates of stomatal conductance and transpiration were 14 and 12% lower, respectively, for NF than AA trees; which coincided with 29% more negative leaf water potentials for NF than AA trees (P < 0.05) . In contrast, cool season net photosynthetic rates were 18% lower for NF than for AA trees, and starch concentrations were 31% higher in leaves from NF compared to AA trees in February 1988 (P < 0.05). Overall, the yield increases for NF compared to AA trees could, in part, be accounted for by decreased flux of O3 into leaves (based on decreased O3 exposure and leaf conductance). However, other factors, i.e., increased tree growth, altered leaf C allocation, and lack of wind stress occurring only in chambers, likely contributed to higher NF tree yields.

Effects of long‐term ozone exposure and drought on the photosynthetic capacity of ponderosa pine (Pinus ponderosa Laws.)

“…Extrapolation of results from chamber studies to plants in the field can be difficult because of inherent chamber effects on plant growth (Olszyk et al, 1992). We found consistently higher light-saturated photosynthetic rates in open-grown (AA) versus chambered (NF) seedlings (Table 1), even though concurrent conductance measurements were similar and foliar nitrogen concentrations were the same (unpublished data, this study).…”

Responses to ozone in 12 provenances of European beech (Fagus sylvatica): genotypic variation and chamber effects on photosynthesis and dry‐matter partitioning

“…The O $ flux to seedlings in chambers is further reduced by lower wind speed (higher boundary-layer resistance) and reduced PAR (decreasing g s ) (Heagle et al, 1988 ;Pleijel & Wallin, 1996). The temperature increase in the chambers was within the range as seen for other OTCs, but the reduction in PAR was higher than for other glass-or PVC-covered OTCs (Olszyk et al, 1992 ;Lee & Barton, 1993 ;Janous et al, 1996). This could be explained by the periodic shading from the polyethylene torus suspended at the rim of the chamber above the seedlings.…”

“…Experiments on air polluatants conducted in open-top chambers (OTCs) can be considered to be closer to natural conditions than glasshouse or laboratory experiments. However, OTCs are often found to cause alterations in the microclimate that affect physiology and\or growth of plants (Manning & Krupa, 1992 ;Olszyk et al, 1992 ;Karnosky et al, 1996). Open-top chambers typically reduce PAR and increase temperatures.…”

“…The increased height, leaf area and shoot biomass were typical chamber effects, probably caused by increased temperature (Manning & Krupa, 1992 ;Mortensen, 1993 ;Karnosky et al, 1996). Reduced PAR lowers the total biomass and number of branches in shade-tolerant species such as beech, but may increase height growth (Heagle et al 1988), leaf area (Olszyk et al, 1992), and SLA (Givnish, 1988). The increased SLA could also be caused by reduced UVB in the chambers (Runeckles & Krupa, 1994), a factor that also affects height and biomass increments in trees (Sullivan & Teramura, 1992).…”

Stomatal regulation in a changing climate: a field study using Free Air Temperature Increase (FATI) and Free Air CO2 Enrichment (FACE)

“…The focus of global change research on CO2 has led to the development of systems for free air CO2 enrichment (FACE), which eliminate bias from enclosing the vegetation (see Rogers et al 1986;Olszyk et al 1992 for error assessment). Particularly in transpiration studies, an undisturbed microclimate is critical, as this process depends strongly on external factors like temperature, wind speed and humidity.…”