Assessing the Impact of Higher Levels of CO2 and Temperature and Their Interactions on Tomato (Solanumlycopersicum L.)

Climate change has increasing effects on horticultural crops. To investigate the impact of CO2 and temperature at elevated levels on tomato production and quality of fruits an experiment was conducted by growing plants in open top chambers. The tomato plants were raised at EC550 (elevated CO2 at 550 ppm) and EC700 (elevated CO2 at 700 ppm) alone and in combination with elevated temperature (ET) + 2 °C in the open top chambers. These elevate CO2 and temperature treatment effects were compared with plants grown under ambient conditions. Outcome of the experiment indicated that growth parameters namely plant stature in terms of height (152.20 cm), leaf number (158.67), canopy spread (6127.70 cm2), leaf area (9110.68 cm2) and total dry matter (223.0 g/plant) were found to be high at EC700 compared to plants grown at ambient conditions in open field. The plants grown at EC700 also exhibited significantly higher number of flowers (273.80) and fruits (261.13), more fruit weight (90.46 g) and yield (5.09 kg plant−1) compared to plants grown at ambient conditions in open field. The percent increase in fruit yield due to EC varied from 18.37 (EC550) to 21.41 (EC700) percent respectively compared to open field and the ET by 2 °C has reduced the fruit yield by 20.01 percent. Quality traits like Total Soluble Solids (3.67 °Brix), reducing sugars (2.48%), total sugars (4.41%) and ascorbic acid (18.18 mg/100 g) were found maximum in EC700 treated tomato than other elevated conditions. Keeping quality was also improved in tomato cultivated under EC700 (25.60 days) than the open field (17.80 days). These findings reveal that CO2 at 700 ppm would be a better option to improve both quantitative as well as qualitative traits in tomato. Among the combinations, EC550 + 2 °C proved better than EC700 + 2 °C with respect to yield as well as for the quality traits. The tomato grown under ET (+2 °C) alone recorded lowest growth and yield attributes compared to open field conditions and rest of the treatments. The positive influence of EC700 is negated to an extent of 14.35 % when the EC700 combined with elevated temperature of + 2 °C. The present study clearly demonstrates that the climate change in terms of increased temperature and CO2 will have a positive effect on tomato by way of increase in production and quality of fruits. Meanwhile the increase in EC beyond 700 ppm along with ET may reduce the positive effects on yield and quality of tomato.

Assessing the Effectiveness of in-situ Active Warming Combined With Open Top Chambers to Study Plant Responses to Climate Change

Temperature manipulation experiments are an effective way for testing plant responses to future climate conditions, especially for predicting shifts in plant phenological events. While passive warming techniques are widely used to elevate temperature in low stature plant communities, active warming has been applied less frequently due to the associated resource requirements. In forest ecosystems, however, active warming is crucial to simulate projected air temperature rises of 3–5 K, especially at the warm (i.e., southern and low elevation) range edges of tree species. Moreover, the warming treatment should be applied to the complete height of the experimental plants, e.g., regenerating trees in the understory. Here, we combined open top chambers (OTCs) with active heat sources, an electric heater (OTC-EH) and warming cables (OTC-WC), and tested the effectiveness of these set-ups to maintain constant temperature differences compared to ambient temperature across 18 m2 plots. This chamber size is needed to grow tree saplings in mixture in forest gaps for 3 to 10 years. With passive warming only, an average temperature increase of approx. 0.4 K as compared to ambient conditions was achieved depending on time of the day and weather conditions. In the actively warmed chambers, average warming exceeded ambient temperatures by 2.5 to 2.8 K and was less variable over time. However, active warming also reduced air humidity by about 15%. These results underline the need to complement passive warming with active warming in order to achieve constant temperature differences appropriate for climate change simulations under all weather conditions in large OTCs. Since we observed considerable horizontal and vertical temperature variation within OTCs with temperature differences of up to 16.9 K, it is essential to measure and report within-plot temperature distribution as well as temporal temperature variation. If temperature distributions within large OTCs are well characterized, they may be incorporated in the experimental design helping to identify non-linear or threshold responses to warming.

Effects of CO2 concentration and UV-B radiation on date palm (Phoenix dactylifera) grown in open-top chambers

Date palm (Phoenix dactylifera L.) is a major plant grown under natural conditions in the Middle East and is subject to multiple environmental stresses. Increased concentration of atmospheric carbon dioxide (CO2) and ultraviolet-B (UV-B) irradiation in the growth environment can have a high impact on plant carbon accumulation, and the various factors can function in opposite directions or cause additive effects. The objective of the present investigation was to screen UAE date palm for susceptibility to elevated level of CO2, UVB and their combined effect on a date palm variety was assessed in transparent open - top chambers (OTC) conditions in the hot climate of UAE. After the screening of the cultivars, experiment was conducted in an OTC facility and the treatments were given for 120 days. After the treatment of the selected cultivar, content of chlorophyll a, b and total, carotenoids, protein, amino acids, phenol and activities including γ-glutamyl kinase, proline oxidase, a-tocopherol and peroxidases activity were determined. The results revealed that the high concentration of CO2 alone increased the growth parameters, whereas the treatment with UV-B significantly affected the growth of the plant relative to regulation. Enzyme observations have shown that an increase in antioxidant enzymes can affect a defense response to the abiotic stress-induced cellular damage. Further extension of this study with other cultivated varieties, other stress parameters and determination of yield parameters will give scope to identify new stress tolerant cultivars of date palm trees.

Photosynthetic Responses of Canola and Wheat to Elevated Levels of CO2, O3 and Water Deficit in Open-Top Chambers

The effects of elevated CO2 (700 ppm) and O3 (80 ppb) alone and in combination on the photosynthetic efficiency of canola and wheat plants were investigated in open-top chambers (OTCs). The plants were fumigated for four weeks under well-watered and water-stressed (water deficit) conditions. The fast chlorophyll a fluorescence transients were measured after 2 and 4 weeks of fumigation, as well as in control plants, and analyzed by the JIP-test, which is a non-destructive, non-invasive, informative, very fast and inexpensive technique used to evaluate the changes in photosynthetic efficiency. Biomass measurements were taken only after 4 weeks of fumigation. The performance index (PItotal), an overall parameter calculated from the JIP-test formulae, was reduced by elevated CO2 and O3 under well-watered conditions. In the absence of any other treatment, water stress caused a decrease of the PItotal, and it was partly eliminated by fumigation with elevated CO2 and CO2 + O3. This finding was also supported by the biomass results, which revealed a higher biomass under elevated CO2 and CO2 + O3. The decrease in biomass induced by elevated O3 was likely caused by the decline of photosynthetic efficiency. Our findings suggest that elevated CO2 reduces the drought effect both in the absence and presence of O3 in canola and wheat plants. The study also indicates that elevated O3 would pose a threat in future to agricultural crops.

Microclimate variability of Antarctic terrestrial ecosystems manipulated by open top chambers: Comparison of selected austral summer seasons within a decade

Open top chambers (OTCs) were established in the northern part of the James Ross Island, Antarctic Peninsula, as a part of long-term program in January 2007. They were installed in two typical locations differing in vegetation cover. First group was set in a seashore ecosystem dominated by moss carpet supplemented with few lichen species. The other group was located on the top of a volcanic mesa (350 m a.s.l.) with irregular cover of lichens Usnea antarctica and Umbilicaria decussata. Temperature regimes inside and outside OTCs were continuously measured and related to year-round reference meteorological data. For majority of OTC installations, temperature increase caused by OTC was apparent in the period of September-March. Detailed analysis of chamber effect on the increase in air, surface, vegetation, and ground temperatures was done for late austral summer seasons of 2007 and 2008, and 10 years later, the seasons of 2017 and 2018. The OTC-induced temperature increase was more pronounced for mesa than seashore plot. For both locations, OTC-induced increase in temperature was highest for warm days with full sunshine and limited wind speed. On stormy days with overcast sky and high wind speed, the shift in temperature was smaller. Consequences of a long-term manipulation of Antarctic terrestrial ecosystems by OTCs for moss and lichen ecophysiology are discussed.