نوع مقاله : مقاله پژوهشی

نویسندگان

گروه اگرواکولوژی، پژوهشکده علوم محیطی، دانشگاه شهید بهشتی، تهران، ایران

10.29252/envs.18.4.87

چکیده

سابقه و هدف:
نگرانی از تأثیرات احتمالی تغییر اقلیم بر روی محصولات کشاورزی باعث شده است که پژوهش­های مهمی در یک دهه گذشته  در این زمینه انجام شود. غلات بیشترین اهمیت را در تامین غذای جمعیت جهان دارد و از بین غلات مختلف گندم مهمترین نقش را بر عهده دارد. در کشور ما نیز گندم مهمترین محصول زراعی کشور است و نقش بارزی در تغذیه مردم دارد. با توجه به اهمیت این گیاه در تامین امنیت غذایی این مطالعه با هدف بررسی افزایش غلظت دی اکسید کربن بر روی عملکرد گیاه گندم انجام گرفت. به این منظور از روش فراتحلیل برای مقایسه کمی اثر CO2 بر عملکرد گیاه گندم استفاده شد.
مواد و روش­ها:
هدف از فراتحلیل به دست آوردن اطلاعات بیشتر از اطلاعات موجود است. به ­منظور دستیابی به داده­های لازم برای انجام تحقیق حاضر، از روش بررسی منابع چاپ شده استفاده شد. تعداد 75 مقاله در مورد تاثیر افزایش غلظت دی اکسید کربن بر روی عملکرد گندم استخراج شد سپس مقالات تکراری و مقالاتی که فاقد داده های مورد نظر بودند، حذف شدند و از میان مقاله­های باقی­مانده اطلاعات مربوط به CO2، اندازه نمونه، میانگین و انحراف معیار استخراج شد. در گام بعدی این مقادیر در نرم­افزار Excel ثبت شد و در نهایت با استفاده از نرم­افزار Stata 16  نمودار های درختی و قیفی لازم رسم شدند و هچنین برای بررسی سوگیری انتشار در میان مطالعات با استفاده از روش اصلاح و پر کردن و رسم نمودارهای آن، این امر بررسی شد.
نتایج و بحث:
نتایج مربوط به نمودار درختی نشان داد بعد از حذف داده­های پرت، دو گروه T2 (25-15) و T3 (35_25) دارای اثر اندازه نهایی بیشتری ( حدود 1.6) هستند که بیانگر آن است که با افزایش درجه حرارت تا 35 درجه سانتی­گراد عملکرد گیاه گندم افزایش یافته است. همچنین گروه T0 که در مقالات این گروه به درجه حرارت اشاره­ای نشده است، دارای کمترین اثر اندازه (0.38) می­باشد. پس می­توان این­گونه استنباط کرد که عملکرد گیاه گندم با افزایش درجه حرارت بین 15 تا 35 درجه سانتی­گراد و با افزایش غلظت CO2 در این دامنه دمایی، افزایش خواهد یافت. بررسی نمودار قیفی نشان داد که بیشتر مطالعات در قسمت بالای نمودار تجمع پیدا کرده­اند. این مطالعات دارای خطای استاندارد کوچک­تر، اندازه نمونه بیشتر و دقت بالاتر هستند. همچنین سوگیری جانبدارانه در جهت مثبت مشاهده شد. بعد از رسم نمودار قیفی، از روش اصلاج و پر کردن با هدف تخمین مطالعات گمشده بالقوه که به دلیل  انتشارجانبدارانه در نمودار قیفی و تنظیم برآورد اثر کلی آن­ها، می­باشد، استفاده شد. بعد از انجام روش اصلاح و پر کردن ، 6 نقطه که با رنگ نارنجی مشخص شده است، اضافه شده است. این نقاط، مطالعات گمشده­ای هستند که برای ایجاد تقارن در نمودار، نیاز به جایگذاری دارند. این نشان­دهنده آن است که مطالعات قبلی، در جهت مثبت سوگیری داشته است.
نتیجه گیری:
نتایج این مطالعه نشان داد که مطالعاتی که در سال­های اخیر انجام شده، دارای نتایج قابل استناد­تر (به دلیل اندازه نمونه­های بزرگتر و دقت بیشتر در نتایج این مطالعات) می­باشد. همچنین با توجه به این که افزایش غلظت CO2 می تواند باعث افزایش دما نیز شود، پیشنهاد می شود در مطالعات بعدی، مطالعاتی که به تاثیر متقابل افزایش غلظت CO2 و افزایش دما به صورت همزمان بر روی گیاهان زراعی مهم پرداخته­اند، با استفاده از روش فراتحلیل مورد بررسی قرار گیرند.

عنوان مقاله [English]

Validation of the effect of increasing CO2 concentration on yield of wheat plant using meta-analysis method

نویسندگان [English]

  • Bita Mahdavi Amiri
  • Jafar Kambouzia

Department of Agroecology, Environmental Sciences Inestitute, Shahid Beheshti University, Tehran, Iran

چکیده [English]

Introduction:
Concerns about the potential effects of climate change on agricultural products have prompted significant research in the past decade. Cereals are the most important food in the world population and among the various cereals, wheat plays the most important role. In our country, wheat is the most important crop in the country and has a significant role in feeding people. Due to the importance of this plant in providing food security, this study was conducted to investigate the increase in the concentration of carbon dioxide on the yield of wheat. For this purpose, meta-analysis method was used to quantitatively compare the effect of CO2 on wheat crop yield.
Material and methods:
The purpose of meta-analysis is to obtain more information than available information. In order to obtain the necessary data for the present study, the printed sources review method was used. 75 articles were extracted on the effect of increasing carbon dioxide concentration on wheat yield, then duplicate articles and articles that lacked the desired data were removed and among the remaining articles CO2 information, sample size, average and standard deviation was extracted. In the next step, these values were recorded in Excel software and finally, using Stata 16 software, the necessary forest plot and funnel plot were drawn, and to investigate the publication bias among the studies using the trim and fill method and drawing its graphs, this was investigated.
Results and discussion:
The results of the forest plot showed that after deleting the outlier data, the two groups T2 (15-25) and T3 (35_25) have a greater final size effect (about 1.6), which indicates that with increasing temperature up to Wheat plant yield increased by 35 ° C. Also, group T0, which is not mentioned in the articles of this group, has the lowest size effect (0.38). So, it can be inferred that the yield of wheat plant will increase with increasing temperature between 15 to 35 ° C and with increasing CO2 concentration in this temperature range. Examination of the funnel plot showed that most studies had accumulated at the top of the diagram. These studies have smaller standard error, larger sample size and higher accuracy.  Publication bias was also observed in a positive direction. After drawing the funnel plot, the trim and fill method was used to estimate the potential missing studies due to the biased dissemination in the funnel plot and the adjustment of the estimate of their overall effect. After performing the trim and fill method, 6 dots marked in orange are added. These points are missing studies that need to be placed to create symmetry in the graph. This indicates that previous studies have been positive.
Conclusion:
The results of this study showed that the studies conducted in recent years have more reliable results (due to the larger sample size and greater accuracy in the results of these studies). Also, considering that increasing the concentration of CO2 can also cause an increase in temperature, it is suggested that in future studies, studies that have examined the interaction between increasing the concentration of CO2 and increasing the temperature simultaneously on important crops, using the meta-analysis method should be examined.

کلیدواژه‌ها [English]

  • climate change
  • Trim and fill
  • funnel plot
  • Box plot

Adams, Richard M, Cynthia Rosenzweig, Robert M Peart, Joe T Ritchie, Bruce A McCarl, J David Glyer, R Bruce Curry, James W Jones, Kenneth J Boote and L Hartwell Allen Jr 1990. Global climate change and US agriculture. Nature 345: 219.

Asseng, S, PD Jamieson, Bruce Kimball, P Pinter, K Sayre, JW Bowden and SM Howden 2004. Simulated wheat growth affected by rising temperature, increased water deficit and elevated atmospheric CO2. Field Crops Research 85: 85-102.

Batts, GR, JIL Morison, RH Ellis, P Hadley and TR Wheeler 1997. Effects of CO2 and temperature on growth and yield of crops of winter wheat over four seasons. European Journal of Agronomy 7: 43-52.

Bax L, Moons KG (2011). Beyond publication bias. J Clin Epidemiol;64:459–62.

Begg, C. B. (1994). Publication bias. The handbook of research synthesis, 25, 299-409.

Bencze, Szilvia, Otto Veisz and Zoltan Bedő 2004. Effects of high atmospheric CO 2 and heat stress on phytomass, yield and grain quality of winter wheat. Cereal Research Communications: 75-82.

Bencze, Szilvia, Z Bamberger, Tibor Janda, Krisztina Balla, Balazs Varga, Zoltan Bedő and O Veisz 2014. Physiological response of wheat varieties to elevated atmospheric CO 2 and low water supply levels. Photosynthetica 52: 71-82.

Borenstein, M., Cooper, H., Hedges, L., & Valentine, J. (2009). Effect sizes for continuous data. The handbook of research synthesis and meta-analysis, 2, 221-235.

Bourgault, Maryse, M Fernanda Dreccer, Andrew T James and Scott C Chapman 2013. Genotypic variability in the response to elevated CO2 of wheat lines differing in adaptive traits. Functional Plant Biology 40: 172-184.

Cammarano, Davide, Reimund P Rötter, Senthold Asseng, Frank Ewert, Daniel Wallach, Pierre Martre, Jerry L Hatfield, James W Jones, Cynthia Rosenzweig and Alex C Ruane 2016. Uncertainty of wheat water use: Simulated patterns and sensitivity to temperature and CO2. Field Crops Research 198: 80-92.

Challinor, Andrew J, J Watson, David B Lobell, SM Howden, DR Smith and Netra Chhetri 2014. A meta-analysis of crop yield under climate change and adaptation. Nature Climate Change 4: 287.

Cohen, J. (1988). Statistical Power Analysis Jbr the Behavioral. Sciences. Hillsdale (NJ): Lawrence Erlbaum Associates, 18-74.

Cooper, H. M. (1998). Synthesizing research: A guide for literature reviews (Vol. 2). Sage.

Cooper, H., & Hedges, L. V. (1994). Research synthesis as a scientific enterprise. The handbook of research synthesis, 3-14.

Cuculeanu, Vasile, Adriana Marica and Catalin Simota 1999. Climate change impact on agricultural crops and adaptation options in Romania. Climate Research 12: 153-160.

Dear, K. B., & Begg, C. B. (1992). An approach for assessing publication bias prior to performing a meta-analysis. Statistical Science, 237-245.

Dier, Markus, Jan Sickora, Martin Erbs, Hans-Joachim Weigel, Christian Zörb and Remy Manderscheid 2018. Decreased wheat grain yield stimulation by free air CO2 enrichment under N deficiency is strongly related to decreased radiation use efficiency enhancement. European Journal of Agronomy 101: 38-48.

Egger, M., Smith, G. D., Schneider, M., & Minder, C. (1997). Bias in meta-analysis detected by a simple, graphical test. Bmj, 315(7109), 629-634.

Erice, Gorka, Alvaro Sanz-Saez, Amadeo Urdiain, Jose L Araus, Juan Jose Irigoyen and Iker Aranjuelo 2014. Harvest index combined with impaired N availability constrains the responsiveness of durum wheat to elevated CO2 concentration and terminal water stress. Functional Plant Biology 41: 1138-1147.

Ewert, F, D Rodriguez, P Jamieson, MA Semenov, RAC Mitchell, J Goudriaan, JR Porter, BA Kimball, PJ Pinter Jr and R Manderscheid 2002. Effects of elevated CO2 and drought on wheat: testing crop simulation models for different experimental and climatic conditions. Agriculture, Ecosystems & Environment 93: 249-266.

Fitzgerald, Glenn J, Michael Tausz, Garry O'Leary, Mahabubur R Mollah, Sabine Tausz‐Posch, Saman Seneweera, Ivan Mock, Markus Löw, Debra L Partington and David McNeil 2016. Elevated atmospheric [CO2] can dramatically increase wheat yields in semi‐arid environments and buffer against heat waves. Global Change Biology 22: 2269-2284.

Frona, D., Szenderak, J., & Harangi-Rakos, M. (2019). The Challenge of Feeding the World. Sustainability, 11(20), 5816.

Fujimura, Shigeto, Peili Shi, Kazuto Iwama, Xianzhou Zhang, Jai Gopal and Yutaka Jitsuyama 2012. Effects of CO2 increase on wheat growth and yield under different atmospheric pressures and their interaction with temperature. Plant Production Science 15: 118-124.

Ghannoum, O., Caemmerer, S. V., Ziska, L. H., & Conroy, J. P. (2000). The growth response of C4 plants to rising atmospheric CO2 partial pressure: a reassessment. Plant, Cell & Environment, 23(9), 931-942.

Gifford, RM 1992. Interaction of carbon dioxide with growth-limiting environmental factors in vegetation productivity: implications for the global carbon cycle. In Advances in Bioclimatology 1, 24-58: Springer.

Givens, G. H., Smith, D. D., & Tweedie, R. L. (1997). Publication bias in meta-analysis: a Bayesian data-augmentation approach to account for issues exemplified in the passive smoking debate. Statistical Science, 221-240.

Glass, Gene V 1976. Primary, secondary, and meta-analysis of research. Educational researcher 5: 3-8.

Grashoff, Cees, Paul Dijkstra, Sanderine Nonhebel, Ad HCM Schapendonk and Siebe C Van de Geijn 1995. Effects of climate change on productivity of cereals and legumes; model evaluation of observed year‐to‐year variability of the CO2 response. Global Change Biology 1: 417-428.

Gurevitch, J., Koricheva, J., Nakagawa, S., & Stewart, G. (2018). Meta-analysis and the science of research synthesis. Nature, 555(7695), 175-182.

Hakala, Kaija 1998. Growth and yield potential of spring wheat in a simulated changed climate with increased CO2 and higher temperature. European Journal of Agronomy 9: 41-52.

Harsimran, Kaur, SK Jalota, Kanwar Ramesh and Bharat Bhushan Vashisht 2012. Climate change impacts on yield, evapotranspiration and nitrogen uptake in irrigated maize (Zea mays)-wheat (Triticum aestivum) cropping system: a simulation analysis. Indian Journal of Agricultural Sciences 82: 213-219.

Hedges, L. V., & Olkin, I. (2014). Statistical methods for meta-analysis. Academic press.

Högy, Petra, Matthias Keck, Karsten Niehaus, Jürgen Franzaring and Andreas Fangmeier 2010. Effects of atmospheric CO2 enrichment on biomass, yield and low molecular weight metabolites in wheat grain. Journal of Cereal Science 52: 215-220.

IEA, 2012. Available online at www.iea.org/reports/world-energy-outlook-2012.

Iglesias, Ana and MI Minguez 1997. Modelling crop-climate interactions in Spain: Vulnerability and adaptation of different agricultural systems to climate change. Mitigation and adaptation strategies for global change 1: 273-288.

Iyengar, S., & Greenhouse, J. B. (1988). Selection models and the file drawer problem. Statistical Science, 109-117.

Jauregui, Ivan, Ricardo Aroca, Maria Garnica, Ángel M Zamarreño, Jose M Garcia‐Mina, Maria D Serret, Martin Parry, Juan J Irigoyen and Iker Aranjuelo 2015. Nitrogen assimilation and transpiration: key processes conditioning responsiveness of wheat to elevated [CO2] and temperature. Physiologia plantarum 155: 338-354.

Karl, T. R., Melillo, J. M., Peterson, T. C., & Hassol, S. J. (Eds.). (2009). Global climate change impacts in the United States. Cambridge University Press.

Kaur, H., Jalota, S. K., Kanwar, R., & Bhushan Vashisht, B. (2012). Climate change impacts on yield, evapotranspiration and nitrogen uptake in irrigated maize (Zea mays)-wheat (Triticum aestivum) cropping system: A simulation analysis. Indian Journal of Agricultural Sciences, 82(3), 213.

Kimball, B. A., & Idso, S. B. (1983). Increasing atmospheric CO2: effects on crop yield, water use and climate. Agricultural water management, 7(1-3), 55-72.

Kimball, B. A., Kobayashi, K., & Bindi, M. (2002). Responses of agricultural crops to free-air CO2 enrichment. In Advances in agronomy (Vol. 77, pp. 293-368). Academic Press.

Lal, Murari, KK Singh, LS Rathore, G Srinivasan and SA Saseendran 1998. Vulnerability of rice and wheat yields in NW India to future changes in climate. Agricultural and forest meteorology 89: 101-114.

Li, Jiazhen, Wenxu Dong, Oene Oenema, Tuo Chen, Chunsheng Hu, Haijing Yuan and Liying Zhao 2019. Irrigation reduces the negative effect of global warming on winter wheat yield and greenhouse gas intensity. Science of the Total Environment 646: 290-299.

Ludwig, Fulco and Senthold Asseng 2006. Climate change impacts on wheat production in a Mediterranean environment in Western Australia. Agricultural Systems 90: 159-179.

Manderscheid 2018. Decreased wheat grain yield stimulation by free air CO2 enrichment under N deficiency is strongly related to decreased radiation use efficiency enhancement. European Journal of Agronomy 101: 38-48.

Manderscheid, R and HJ Weigel 1997. Photosynthetic and growth responses of old and modern spring wheat cultivars to atmospheric CO2 enrichment. Agriculture, Ecosystems & Environment 64: 65-73.

Manderscheid, Remy, Stefan Burkart, Andreas Bramm and Hans-Joachim Weigel 2003. Effect of CO2 enrichment on growth and daily radiation use efficiency of wheat in relation to temperature and growth stage. European Journal of Agronomy 19: 411-425.

Mearns, Linda O, Cynthia Rosenzweig and Richard Goldberg 1996. The effect of changes in daily and interannual climatic variability on CERES-Wheat: a sensitivity study. Climatic change 32: 257-292.

Mitchell, RAC, DW Lawlor, VJ Mitchell, CL Gibbard, EM White and JR Porter 1995. Effects of elevated CO2 concentration and increased temperature on winter wheat: test of ARCWHEAT1 simulation model. Plant, Cell & Environment 18: 736-748.

Mitchell, RAC, VJ Mitchell, SP Driscoll, J Franklin and DW Lawlor 1993. Effects of increased CO2 concentration and temperature on growth and yield of winter wheat at two levels of nitrogen application. Plant, Cell & Environment 16: 521-529.

Moher, D., Liberati, A., Tetzlaff, J., & Altman, D. G. (2009). Group TP, Oxman A, Cook D, Guyatt G, Swingler G, Volmink J, Ioannidis J, Young C, Horton R, et al. Preferred Reporting Items for Systematic Reviews and Meta-Analyses: The PRISMA Statement. PLoS Med. Public Library of Science, 6, e1000097.

Mulholland, BJ, J Craigon, CR Black, JJ Colls, J Atherton and G Landon 1997. Effects of elevated carbon dioxide and ozone on the growth and yield of spring wheat (Triticum aestivum L.). Journal of Experimental Botany 48: 113-122.

Mulholland, BJ, J Craigon, CR Black, JJ Colls, J Atherton and G Landon 1998. Effects of elevated CO2 and O3 on the rate and duration of grain growth and harvest index in spring wheat (Triticum aestivum L.). Global Change Biology 4: 627-635.

Murad, M. H., Chu, H., Lin, L., & Wang, Z. (2018). The effect of publication bias magnitude and direction on the certainty in evidence. BMJ evidence-based medicine, 23(3), 84-86.

Nissen, S. B., Magidson, T., Gross, K., & Bergstrom, C. T. (2016). Publication bias and the canonization of false facts. Elife, 5, e21451.

Olesen, Jørgen E, Tom Jensen and Jens Petersen 2000. Sensitivity of field-scale winter wheat production in Denmark to climate variability and climate change. Climate Research 15: 221-238.

Olkin, I. (1992). Meta-analysis: methods for combining independent studies. Statistical Science, 7(2), 226-236.

Pandey, Vyas, HR Patel and BI Karande 2009. Impact analysis of climate change on different crops in Gujarat, India. ISPRS Archives 38: W3.

Rogers, GS, PW Gras, IL Batey, PJ Milham, L Payne and JP Conroy 1998. The influence of atmospheric CO2 concentration on the protein, starch and mixing properties of wheat flour. Functional Plant Biology 25: 387-393.

Rudorff, Bernardo FT, Charles L Mulchi, Edward H Lee, Randy Rowland and Roman Pausch 1996. Effects of enhanced O3 and CO2 enrichment on plant characteristics in wheat and corn. Environmental Pollution 94: 53-60.

Ruiz-Ramos, Miguel, Roberto Ferrise, A Rodriguez, IJ Lorite, Marco Bindi, Timothy R Carter, S Fronzek, Taru Palosuo, N Pirttioja and Piotr Baranowski 2018. Adaptation response surfaces for managing wheat under perturbed climate and CO2 in a Mediterranean environment. Agricultural Systems 159: 260-274.

Sæbø, Arne and Leiv M Mortensen 1996. Growth, morphology and yield of wheat, barley and oats grown at elevated atmospheric CO2 concentration in a cool, maritime climate. Agriculture, Ecosystems & Environment 57: 9-15.

Schonfeld, Manette A, Richard C Johnson, Brett F Carver and Dolores W Mornhinweg 1988. Water relations in winter wheat as drought resistance indicators. Crop Science 28: 526-531.

Shi, L., & Lin, L. (2019). The trim-and-fill method for publication bias: practical guidelines and recommendations based on a large database of meta-analyses. Medicine, 98(23).

Sinclair, Thomas R and Seligman No'am G 1995. Global environment change and simulated forage quality of wheat I. Nonstressed conditions. Field Crops Research 40: 19-27.

Tausz-Posch, Sabine, Raymond W Dempsey, Saman Seneweera, Robert M Norton, Glenn Fitzgerald and Michael Tausz 2015. Does a freely tillering wheat cultivar benefit more from elevated CO2 than a restricted tillering cultivar in a water-limited environment? European Journal of Agronomy 64: 21-28.

Tausz-Posch, Sabine, Saman Seneweera, Robert M Norton, Glenn J Fitzgerald and Michael Tausz 2012. Can a wheat cultivar with high transpiration efficiency maintain its yield advantage over a near-isogenic cultivar under elevated CO2? Field Crops Research 133: 160-166.

Tharyan, P. (1998). The relevance to meta-analysis, systematic reviews and the cochrane collaboration to clinical psychiatry. Indian journal of psychiatry, 40(2), 135.

Trnka, M, M Dubrovský, D Semeradova and Z Žalud 2004. Projections of uncertainties in climate change scenarios into expected winter wheat yields. Theoretical and applied climatology 77: 229-249.

Tuba, Zoltan, Kalman Szente and Judit Koch 1994. Response of photosynthesis, stomatal conductance, water use efficiency and production to long-term elevated CO2 in winter wheat. Journal of Plant Physiology 144: 661-668.

Tubiello, FN, C Rosenzweig, RA Goldberg, S Jagtap and JW Jones 2002. Effects of climate change on US crop production: simulation results using two different GCM scenarios. Part I: wheat, potato, maize, and citrus. Climate Research 20: 259-270.

Tubiello, Francesco N, Marcello Donatelli, C Rosenzweig and Claudio O Stockle 2000. Effects of climate change and elevated CO2 on cropping systems: model predictions at two Italian locations. European Journal of Agronomy 13: 179-189.

U.S. Census Bureau, 2012. Available online at https://www.census.gov/library/publications/2011/compendia.

Van Oijen, M and F Ewert 1999. The effects of climatic variation in Europe on the yield response of spring wheat cv. Minaret to elevated CO2 and O3: an analysis of open-top chamber experiments by means of two crop growth simulation models. European Journal of Agronomy 10: 249-264.

Verrillo, Francesca, Franz-Werner Badeck, Valeria Terzi, Fulvia Rizza, Letizia Bernardo, Antimo Di Maro, Clara Fares, Alessandro Zaldei, Francesco Miglietta and Anna Moschella 2017. Elevated field atmospheric CO2 concentrations affect the characteristics of winter wheat (cv. Bologna) grains. Crop and Pasture Science 68: 713-725.

Wang, Hong, Yong He, Budong Qian, Brian McConkey, Herb Cutforth, Tom McCaig, Grant McLeod, Robert Zentner, Ron DePauw and Reynald Lemke 2012. Climate change and biofuel wheat: A case study of southern Saskatchewan. Canadian journal of plant science 92: 421-425.

Weigel, Hans-Joachim and Remy Manderscheid 2012. Crop growth responses to free air CO2 enrichment and nitrogen fertilization: Rotating barley, ryegrass, sugar beet and wheat. European Journal of Agronomy 43: 97-107.

Weigel, HJ, R Manderscheid, H-J Jäger and GJ Mejer 1994. Effects of season-long CO2 enrichment on cereals. I. Growth performance and yield. Agriculture, Ecosystems & Environment 48: 231-240.

Wheeler, TR, GR Batts, RH Ellis, P Hadley and JIL Morison 1996. Growth and yield of winter wheat (Triticum aestivum) crops in response to CO 2 and temperature. The Journal of Agricultural Science 127: 37-48.

Wolfe, David W, Roger M Gifford, David Hilbert and Yiqi Luo 1998. Integration of photosynthetic acclimation to CO2 at the whole‐plant level. Global Change Biology 4: 879-893.

Zemankovics, M Hunkar and ZS Bacsi 1995. Wheat and maize production in hungary under doubled atmospheric co2 concentration. In Studies in Environmental Science, 741-744: Elsevier.