Effects of diazotrophic endophytes on the physiology of early to late th
20 century rice varieties in elevated CO2 conditions
Norah Hummel1, Hyungmin Tony Rho2, and Soo-­‐Hyung Kim3
1Undergraduate Researcher, 2Graduate Student, 3Faculty Advisor
Climate change will drastically affect agricultural systems in the next century
(Thrall et al., 2011), as global population increases to 9.6 billion by 2050, agricultural systems will be mandated to increase productivity and efficiency (IPCC, 2014). In the 1960s, Green Revolution grain crops were released with exceptionally higher yields than previous varieties, however, these new varieties are no longer producing with the same vigor (Ziska et al., 2012b). In the past 60 years, breeding programs have bred for certain traits including uniformity and response to chemical fertilizers (Kingsbury, 2009). As breeders selected these traits over time, other traits were inevitably deselected and lost. For example, response to diazotrophic endophytes would not have been useful to plants in past breeding programs because synthetic nitrogen fertilizers were applied to fields in excess. Now these traits could be valuable as CO2 levels continue to rise and nitrogen becomes a limiting nutrient in plant physiology.
Older varieties of wheat and rice perform better than current varieties by multiple measures to elevated CO2 (Ziska et al., 2012b). The next step is to investigate how these varieties respond to elevated CO2 but inoculated with dizotrophic endophytes, which have been shown to mitigate down regulation effects by supplying nitrogen to rice plants in elevated CO2 conditions (Rho, 2014). This capstone project tested the response of old and new rice cultivars to dizotrophic endophytes in elevated CO2 conditions.
Hypothesis:
Old variety PTB10 will respond positively to inoculation of WP5 and elevated CO2, resulting in higher physiology metrics compared to new variety N-­‐22.
Figure 6 shows A/Ci curves for PTB10 and N-­‐22 in elevated CO2 conditions with (E+) and without (E-­‐) inoculation. n=4
SPAD results
Var. p< 0.001***
CO2:Var. p<0.01**
Figures 5 mean SPAD values of N-­‐22 and PTB10 without inoculation at harvest n=4 References
Elevated CO2
Figures 6 mean SPAD values of N-­‐22 and PTB10 with inoculation at harvest n=4 Kingsbury, N. (2009). Hybrid: The history and science of plant breeding. Chicago: University of C hicago Press.
IPCC, 2014: Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, R.K. Pachauri and L.A. Meyer (eds.)]. IPCC, Geneva, Switzerland, 151 pp.
Thrall P H, Oakeshott JG, Fitt G, Southerton S, Burdon JJ, Sheppard A, Russell RJ, Zalucki M, Heino M, Ford Denison R. 2011. Evolution in agriculture: the application of evolutionary approaches to the management of biotic interactions in agro-­‐ecosystems. Evolutionary Applications 4: 200–215.
Ziska LH, Bunce JA, Shimono H, Gealy DR, Baker JT, Newton P CD, Reynolds MP, Jagadish KS V, Zhu C, Howden M, et al. 2012a. Food security and climate change: on the potential to adapt global crop production by active selection to rising atmospheric carbon dioxide. Proceedings of the Royal Society B: Biological Sciences 279: 4097–4105.
WP5 CFU from root of PTB10
N-­‐22= PTB10=
Empty pot=
Inoculation=
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Elevated CO2
Ambient CO2
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Seedling germination in water agar
Var. p< 0.05*
Inoc. p< 0.1 Figures 1 mean shoot biomass of N-­‐22 and PTB10 at ambient CO2 conditions n=4 Figures 2 mean shoot biomass of N-­‐22 and PTB10 at elevated CO2 conditions n=4 Results
though gas exchange data was insignificant, all three measurements demonstrated the same trend; largest variation in elevated and inoculated treatment. Despite no significant inoculation effect, PTB10 had higher SPAD, biomass, and chlorophyll fluorescence than N-­‐22 is elevated CO2
conditions.
Acknowledgements
Ambient CO2
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Discussion
Statistics: Statistical tests were conducted in R, including the Bartlett test for homogeneity of variances, and Shapiro’s test for population normality. All data were transformed using the Box-­‐Cox function, altering lambda. An interaction and linear mixed model were applied to see if the chamber or set had a effect on the data. A three-­‐way interaction ANOVA model was applied to analyze significance. Even CO2 p< Var.: p0< .001***
0.05*
Var. p< 0.01**
Rice (Oryza sativa) cultivars, PTB10: From India 1940s (old) and N-­‐22: From India 1960s (new) were inoculated with
WP5 (Rahnella sp. CDC 2987-­‐79). Plants were grown in low nutrient soil, Sunshine mix #2 and fertilized with nitrogen free media.
Treatment Groups
Inoc. p=0.105
Var. p=0.271
Inoc. p=0.328
Inoc:CO2 p=0.282
Materials
Gas exchange
Gas exchange data was collected using a LI-­‐6400XT machine. Samples were subject to both light response and carbon assimilation measurements. Leaf temperature was 25 degrees Celsius in the chamber head. Measurements were collected between 6am-­‐11am. Chlorophyll florescence
Fv/Fm was measured on samples after 12 weeks of growth, on the uppermost fully extended leaf. Leaves were dark adapted for 20 minutes prior to measurement.
Biomass
Destructive harvest occurred at the end of the experiment after 12 weeks of growth. Samples were dried at 70 degrees Celsius.
Weekly measurements Plants were watered in a aquaponic system with 200mL of nitrogen free fertilizer. SPAD and CCM measurements were taken on leaves third from the bottom providing a proxy for nitrogen content.
Biomass results
Gas Exchange results
Figure 5 shows Aq curves for PTB10 and N-­‐
22 in elevated CO2 conditions, with (E+) and without (E-­‐) inoculation. n=4
Methods
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Introduction
Thank you to my advisor Soo-­‐Hyung Kim for all his helpful feedback and support, and to Hyungmin Tony Rho, for his help in every process. A sincere round of thanks to everyone in the Plant Ecophysiology lab. Many thanks to Howard Black and researchers at the USDA.ARS in Stuttgart, Arkansas for sending seeds for this project. +
The experiment contained 8 treatments X2 replications with 36 pots n=4
Differences in shoot biomass, suggest that at elevated CO2, PTB10 assimilated more carbon, with higher sink capacity than N-­‐22. In the elevated CO2 treatment, PTB10 had higher chlorophyll fluorescence than N-­‐22, which could mean that photosynthetic light reactions in leaves of PTB10 are functioning more efficiently. Higher SPAD values at harvest in PTB10 suggests that these samples have a higher nitrogen content in elevated and ambient conditions, and PTB10 may use nitrogen more efficiently in general. Inoculation did not have a significant effect in any response measured as the sample size was small (n=4), it is expected that results could be insignificant. In gas exchange data p-­‐values for inoculation approached conventional significance, which suggests that with a larger sample size, CO2, variety and inoculation would show significance. In future experiments, testing the WP5 nif
mutant would isolate the effects of biological nitrogen fixation and the endophytes. Using many different “old” and “new” rice varieties would allow for comparison and potentially establish a pattern in a vitall important food crop. Finally, testing other crops like corn, soybeans, and wheat would allow us to study the state of other green revolution crops and compare the C4 and C3
photosynthetic pathway.