The present study aimed to examine the interactive effects of elevated atmospheric CO2 concentration and drought stress on the growth and some of the physiological processes of Galenia pubescens. Photosynthetic rate of plants increased under elevated CO2 concentration, however drought caused significant reduction in net photosynthetic rate by (45% in 400 ppm CO2) and (27% in 700 ppm CO2) after five days simulating the drought treatment when compared with well-watered plants. Plants grown under elevated CO2 level and well-watered produced a greater biomass (17.5 ± 0.5 g per plant) compared to the plants which were grown under the ambient CO2 concentration

Fernando, Nimesha

Florentine, Singarayer

Mahmood, Ako

McLaren, David

Palmer, Grant

Sillitoe, Jim

Wright, Wendy

Federation ResearchOnline

347Twentieth Australasian Weeds ConferenceSummary The present study aimed to examine the interactive effects of elevated atmospheric CO2 con-centration and drought stress on the growth and some of the physiological processes of Galenia pubescens. Photosynthetic rate of plants increased under elevated CO2 concentration, however drought caused significant reduction in net photosynthetic rate by (45% in 400 ppm CO2) and (27% in 700 ppm CO2) after five days simulating the drought treatment when compared with well-watered plants. Plants grown under elevated CO2 level and well-watered produced a greater biomass (17.5 ± 0.5 g per plant) compared to the plants which were grown under the ambient CO2 concentration.Keywords CO2 concentrations, drought, weeds.INTRODUCTIONPlant invasion can be developed or hindered as a result of numerous changes in the climate and ecological processes. Changes in climate include; change in pre-cipitation pattern, a rise in temperature and CO2 levels and deposition of nitrogenous material, and fire regime changes that can lead to changes in resource avail-ability (Miri et al. 2012, Sheppard and Stanley 2014). There has been a report that air CO2 concentrations may be increased from the present-day 380 to 550 ppm by 2050 (Franks, 2013) and afterward to surpass 700 to 1000 ppm before the end of the 21st Century (Dietz and Stern 2009, IPCC 2015) This increase in atmos-pheric CO2 concentration will affect plant growth in a variety of ways (Dukes 2011), as it can have a direct impact upon photosynthesis and metabolism (Plett et al. 2015). The future potential of characteristics of Galenia pubescens under an elevated atmospheric CO2 concen-tration and drought is unknown. Hence, the objective of this study was to assess the effects of elevated car-bon dioxide and water availability on the physiology and growth on the exotic weed G. pubescens in order to improve management methods. Investigations into the effects of elevated carbon dioxide and drought on the growth and physiology of carpet weed (Galenia pubescens Eckl. & Zeyh.)Ako H. Mahmood1, Singarayer K. Florentine1, Nimesha Fernando1, Wendy Wright1, Grant Palmer1, David McLaren2 and Jim Sillitoe31 Centre for Environmental Management, Faculty of Science and Technology, Federation University, Mount Helen, PO Box 663, Victoria 3350, Australia2 Department of Economic Development, Jobs, Transport and Resources, Victorian AgriBiosciences Centre, Bundoora, Victoria 3086, Australia3 Research Services, Federation University, Mount Helen, Victoria 3350, Australia(akomahmood4@gmail.com)MATERIALS AND METHODSSeedlings  establishment Mature G. pubescens seeds were collected from several populations of mature plants in the Werribee region (37° 49' 5.63" S, 144° 34' 58.77" E), and cleaned seeds were placed in an airtight container until use. In the glasshouse twenty plastic pots (13 cm diameter and 13 cm high) were prepared as follows: for soil moisture movement and aeration, the sterilised industrial, seed-free sand soil was placed to a depth of 1 cm lined with paper towel. One kg of well-mixed dry sterilised soil was placed into each pot. On the top of each pot ten G. pubescens seeds were sown. Pots were labelled and placed into large white trays (44 × 36 × 7 cm) to facilitate watering from below, which ensured minimal disturbance of seeds and later, germinants. One month old G. pubescens seedlings (4–6 leaf growth stage), were thinned to one per pot and transferred to CO2 chambers.Setting-up CO2 chambers and growth conditions Two identical Steriudium e2400 model chambers were used for this experiment. Each chambers was set-up with a different CO2 concentration. One of the cham-bers was set at an ambient atmospheric CO2 concentra-tion (400 ppm), simulating the present concentration of CO2 in the atmosphere. The second chamber was placed at an elevated atmospheric CO2 concentration (700 ppm), simulating the likely future concentration of atmospheric CO2 (by the end of this century) as predicted in climate change scenarios (Franks 2013).Thereafter, 10 pots (randomly chosen) were placed in one growth chamber (with a CO2 concentration of 400 ppm). Another 10 pots (randomly chosen) were placed into the other growth chamber (with a CO2 concentration of 700 ppm). All pots were watered to field capacity based on their need for water. One week prior to the taking of measurements in each CO2 chamber, half of the plants from each chamber 348Twentieth Australasian Weeds Conference(randomly chosen) were kept well-watered and the other half were allowed to dry out slowly until visible wilting occurred. Physiological parameters The net photosynthetic rate (µmol CO2 m−2 s−1), transpiration rate (mmol H2O m−2 s−1) and stomatal conductance (gs; mol H2O m−2 s−1) were measured using a portable gas exchange sys-tem (Li-6400XT, Li-Cor, Lincoln, NE, USA), follow-ing methods described by Le et al. (2016). The water use efficiency (WUE), was determined by dividing the net photosynthetic rate value by the transpiration rate value (Shabbir et al. 2014). Plant biomass After the completion of the trial, ap-proximately at the end of the vegetative stage and the beginning of flowering, the following morphological parameters were measured: The number of branches that were present on each plant was recorded. Then the plants were harvested from the soil surface and the stems and leaves were separated and kept in labelled paper bags and oven dried at 70°C for 48 hours. The roots were removed from the soil and washed thor-oughly, were put in labelled paper bags separately and oven dried at 70°C for 48 hours. The dry leaves were added to the dry branches, to determine individual dry biomass. The root/shoot ratio was measured by dividing the root dry weight to the branch dry weight. Data analysis In order to statistically account for any potential influence of CO2 concentration and drought treatments on plant responses, a randomized complete design was used with two treatments and five replications. Data were analysed using a general linear model (GLM). The GLM was set up with two atmospheric CO2 concentrations, two irrigation levels and interaction as the main factor. An analysis was then undertaken using an adjusted sum of squares approach using 95.0% confidence intervals. A two-way analysis of variance tests was run for each trait separately to detect differences caused by each factor using the Statistix 8.1 Regd package. Means were compared by Tukey’s test at a 5% level of probability.RESULTSFigure 1 shows the effects of atmospheric CO2 concentration and water availability of the net pho-tosynthesis rate of G. pubescens seedlings at 60 days after the placement of plants in CO2 chambers, and measurements were taken four times (48 hours were between each recorded date). It should be noted that the plants under elevated CO2 concentration recorded significantly (F = 9.60, P <0.05) increases in the mean net photosynthesis rates on all recorded dates (21.3 μmol mol−1) when compared to the plants in ambient atmospheric CO2 concentration (13.3 μmol mol−1) under well-watered treatment. Whereas moisture stress significantly decreased the rate of net photosynthesis, the decrease was greater in plants that were grown under elevated CO2 conditions.The G. pubescens plants were not significantly different (F = 1.68, P = 0.2132) in their production of dry biomass by changing atmospheric CO2 concentra-tions. However, the plants were significantly differ-ent between well-watered and drought treatments in producing dry biomass (data not shown). Similarly, elevated CO2 concentration did not have a significant effect on root shoot ratio; however, data showed that the ratio was slightly decreased by increasing CO2 concentration in both well-watered and drought treatments. Regarding dry root weight, data showed no significant difference (F = 2.26, P = 0.152) among plants under both CO2 levels and water availability treatment. Dry leaf and dry shoot weight were also found not significantly affected by changing CO2 levels; in contrast, water availability significantly af-fected dry leaf and dry shoot weight. The number of branches per plant was found not to be significantly affected by changing atmospheric CO2 concentration. However, the number of branches per plant was sig-nificantly different under well-watered and drought treatments.DISCUSSIONElevated CO2 is beneficial for G. pubescens growth under well-watered conditions. The photosynthesis rate and the percentage of dry biomass were increased subsequently, whereas under drought conditions, elevated CO2 markedly showed reductions in the pho-tosynthesis rate and dry biomass of the plants. Similar results were obtained by Erice et al. (2007), who reported that plant biomass increased under elevated CO2 under well-watered conditions but not under drought. CO2 concentration had no significant effects on the leaf, shoot, and root dry weight in either CO2 concentrations. These responses are in contrast with those of many herbaceous plants (Farrar and Williams 1991, Ziska 2002). It can be concluded, that this study supported the view that the growth of G. pubescens will be signifi-cantly enhanced in a future climate with an enriched atmospheric CO2 concentration, producing taller plants with a greater biomass, and presumably with a higher seed output under well-watered conditions. These changes will have important implications for management of this noxious weed in the future.349Twentieth Australasian Weeds ConferenceACKNOWLEDGMENTSSpecial thanks are extended to the Centre for En-vironmental Management, Faculty of Science and Technology at Federation University, Australia for the provision of financial support. We also thank Mel-bourne University for allowing us to use Li-6400XT, Li-Cor. We acknowledge Wendy Cloke for provid-ing laboratory equipment. We also thank Agnieszka Wujeska-Klause for technical help and Mr Allan Adair for reviewing this manuscript.REFERENCESDietz, S. and Stern, N. (2009). Note on the timing of greenhouse gas emissions reductions: a final rejoinder to the symposium on “the economics of climate change: the stern review and its crit-ics”. Review of Environmental Economics and Policy 3, 138-40.Dukes, J.S., Chiariello, N.R., Loarie, S.R. and Field, C.B. (2011). Strong response of an invasive plant species (Centaurea solstitialis L.) to global environmental changes. Ecological Applications 21, 1887-94.Figure 1. The effect of atmospheric CO2 concentrations (a) ambient CO2 (b) elevated CO2 of the net photosynthetic rate (μmol mol−2s−1) of G. pubescens plants growing under well-watered and drought conditions. Vertical bars show standard errors of the mean from five replications.350Twentieth Australasian Weeds ConferenceErice, G., Aranjuelo, I., Irigoyen, J.J. and Sánchez-Díaz, M. (2007). Effect of elevated CO2, tempera-ture and limited water supply on antioxidant status during regrowth of nodulated alfalfa. Physiologia Plantarum 130, 33-45.Farrar, J.F. and Williams, M.L. (1991). The effects of increased atmospheric carbon dioxide and temperature on carbon partitioning, source-sink relations and respiration. Plant, Cell and Environ-ment 14, 819-30.Franks, P.J., Adams, M.A., Amthor, J.S., Barbour, M.M., Berry, J.A., Ellsworth, D.S. and Norby, R.J. (2013). Sensitivity of plants to changing atmos-pheric CO2 concentration: from the geological past to the next century. New Phytologist 197, 1077-94.Intergovernmental Panel on Climate Change (IPCC). (2015). ‘Climate change 2014: mitigation of cli-mate change, Volume 3’. (Cambridge University Press). Le, Q.V., Tennakoon, K.U., Metali, F., Lim, L.B.L. and Bolin, J.F. (2016). Ecophysiological responses of mistletoe Dendrophthoe curvata (Loranthaceae) to varying environmental parameters. Journal of Tropical Forest Science 28, 59.Miri, H.R., Rastegar, A. and Bagheri, A.R. (2012). The impact of elevated CO2 on growth and competi-tiveness of C3 and C4 crops and weeds. European Journal of Experimental Biology 2, 1144-50.Morgan, J.A., Mosier, A.R., Milchunas, D.G., LeCain, D.R., Nelson, J.A., and Parton, W.J. (2004). CO2 enhances productivity, alters species composition, and reduces digestibility of shortgrass steppe vegetation. Ecological Applications 14, 208-19.Plett, J.M., Kohler, A., Khachane, A., Keniry, K., Plett, K.L., Martin, F. and Anderson, I.C. (2015). The effect of elevated carbon dioxide on the interaction between Eucalyptus grandis and diverse isolates of Pisolithus sp. is associated with a complex shift in the root transcriptome. New Phytologist 206, 1423-36.Sheppard, C.S., Burns, B.R. and Stanley, M.C. (2014). Predicting plant invasions under climate change: are species distribution models validated by field trials? Global Change Biology 20, 2800-14.Ziska, L.H. (2002). Influence of rising atmospheric CO2 since 1900 on early growth and photo-synthetic response of a noxious invasive weed, Canada thistle (Cirsium arvense). Functional Plant Biology 29, 1387-92.

Investigations into the effects of elevated carbon dioxide and drought on the growth and physiology of carpet weed (Galenia pubescens Eckl. & Zeyh.)

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Investigations into the effects of elevated carbon dioxide and drought on the growth and physiology of carpet weed (Galenia pubescens Eckl. & Zeyh.)

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