Tag: agriculture

Elevated CO2 and Temperature Enhance the Grain Yield and Quality of Rice

Setting the stage for their study, Roy et al. (2015) write that rice is “one of the most important C3 species of cereal crops,” adding that it “generally responds favorably to elevated CO2.” However, they note that the actual response of rice crops to elevated CO2 and warming “is uncertain.” The team of five Indian scientists set out “to determine the effect of elevated CO2 and night time temperature on (1) biomass production, (2) grain yield and quality and (3) C [carbon], N [nitrogen] allocations in different parts of the rice crop in tropical dry season.”

The experiment they designed to achieve these objectives was carried out at the ICAR-Central Rice Research Institute in Cuttack, Odisha, India, using open-top-chambers in which rice (cv. Naveen) was grown in either control (ambient CO2 and ambient temperature), elevated CO2 (550 ppm, ambient temperature) or elevated CO2 and raised temperature (550 ppm and +2°C above ambient) conditions for three separate growing seasons.

In discussing their findings, Roy et al. write that the aboveground plant biomass, root biomass, grain yield, leaf area index and net C assimilation rates of the plants growing under elevated CO2 conditions all showed significant increases (32, 26, 22, 21, and 37 percent, respectively) over their ambient counter-parts. Each of these variables were also enhanced under elevated CO2 and increased temperature conditions over ambient CO2 and temperature, though to a slightly lesser degree than under elevated CO2 conditions alone. 

With respect to grain quality, the authors report there was no difference among the parameters they measured in any of treatments, with the exception of starch and amylose content, which were both significantly higher in the elevated CO2 and elevated CO2 plus elevated temperature treatments. The C and N grain yields were also both significantly increased in both of these treatments compared with control conditions.

The results of this study thus bode well for the future of rice production in India during the dry season. As the CO2 concentration of the air rises, yields will increase.  And if the temperature rises as models project, yields will still increase, though by not quite as much. These findings, coupled with the fact that the grain nutritional quality (as defined by an increase in amylose content) was enhanced by elevated CO2, suggest there is a bright future in store for rice in a carbon dioxide-enhanced atmosphere.

 

Reference

Roy, K.S., Bhattacharyya, P., Nayak, A.K., Sharma, S.G. and Uprety, D.C. 2015. Growth and nitrogen allocation of dry season tropical rice as a result of carbon dioxide fertilization and elevated night time temperature. Nutrient Cycling in Agroecosystems 103: 293-309.

Do Negative Climate Impacts on Food Production Lead to Violence?

Introducing their important work, Buhaug et al. (2015) note that earlier research suggests there is “a correlational pattern between climate anomalies and violent conflict” due to “drought-induced agricultural shocks and adverse economic spillover effects as a key causal mechanism linking the two phenomena.” But is this really so?

Seeking an answer to this question, the four Norwegian researchers compared half a century of statistics on climate variability, food production and political violence across Sub-Saharan Africa, which effort, in their words, “offers the most precise and theoretically consistent empirical assessment to date of the purported indirect relationship.” And what did they thereby find?

Buhaug et al. report that their analysis “reveals a robust link between weather patterns and food production where more rainfall generally is associated with higher yields.” However, they also report that “the second step in the causal model is not supported,” noting that “agricultural output and violent conflict are only weakly and inconsistently connected, even in the specific contexts where production shocks are believed to have particularly devastating social consequences,” which fact leads them to suggest that “the wider socioeconomic and political context is much more important than drought and crop failures in explaining violent conflict in contemporary Africa.”

“Instead,” as they continue, “social protest and rebellion during times of food price spikes may be better understood as reactions to poor and unjust government policies, corruption, repression and market failure,” citing the studies of Bush (2010), Buhaug and Urdal (2013), Sneyd et al. (2013) and Chenoweth and Ulfelder (2015). In fact, they state that even the IPCC’s Fifth Assessment Report concludes “it is likely that socioeconomic and technological trends, including changes in institutions and policies, will remain a relatively stronger driver of food security over the next few decades than climate change,” citing Porter et al. (2014).”

And so we learn that alarmist claims of future climate-change-induced reductions in agricultural production that lead to social unrest and violent conflicts simply are not supported by real-world observations.

 

References

Buhaug, H., Benjaminsen, T.A., Sjaastad, E. and Theisen, O.M. 2015. Climate variability, food production shocks, and violent conflict in Sub-Saharan Africa. Environmental Research Letters 10: 10.1088/1748-9326/10/12/125015.

Buhaug, H. and Urdal, H. 2013. An urbanization bomb? Population growth and social disorder in cities. Global Environmental Change 23: 1-10.

Bush, R. 2010. Food riots: poverty, power and protest. Journal of Agrarian Change 10: 119-129.

Chenoweth, E. and Ulfelder, J. 2015. Can structural conditions explain the onset of nonviolent uprisings? Journal of Conflict Resolution 10.1177/0022002715576574.

Porter, J.R. et al. 2014. Food security and food production systems. Climate Change 2014: Impacts, Adaptation, and Vulnerability. Part A: Global and Sectoral Aspects. Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Ed. C.B. Field et al. (Cambridge: Cambridge University Press) pp. 485-533.

Sneyd, I.Q., Legwegoh, A. and Fraser, E.D.G. 2013. Food riots: media perspectives on the causes of food protest in Africa. Food Security 5: 485-497.

Projecting the Impacts of Rising CO2 on Future Crop Yields in Germany

Noting that the influence of atmospheric CO2 on crop growth is “still a matter of debate,” and that “to date, no comprehensive approach exists that would represent all related aspects and interactions [of elevated CO2 and climate change on crop yields] within a single modeling environment,” Degener (2015) set out to accomplish just that by estimating the influence of elevated CO2 on the biomass yields of ten different crops in the area of Niedersachsen, Germany over the course of the 21st century.

To accomplish this lofty objective the German researcher combined soil and projected future climate data (temperature and precipitation) into the BIOSTAR crop model and examined the annual difference in yield outputs for each of the ten crops (winter wheat, barley, rye, triticale, three maize varieties, sunflower, sorghum and spring wheat) under a constant CO2 regime of 390 ppm and a second scenario in which atmospheric CO2 increased annually through the year 2100 according to the IPCC’s SRES A1B scenario. Degener then calculated the difference between the two model runs so as to estimate the quantitative influence of elevated CO2 on projected future crop yields. And what did that difference reveal?

As shown in the figure below, Degener reports that “rising [CO2] concentrations will play a central role in keeping future yields of all crops above or around today’s level.” Such a central, overall finding is significant considering Degener notes that future temperatures and precipitation within the model both changed in a way that was “detrimental to the growth of crops” (higher temperatures and less precipitation). Yet despite an increasingly hostile growing environment, according to the German researcher, not only was the “negative climatic effect balanced out, it [was] reversed by a rise in CO2” (emphasis added), leading to yield increases on the order of 25 to 60 percent.

Figure 1. Biomass yield difference (percent change) between model runs of constant and changing atmospheric CO2 concentration. A value of +20% indicates biomass yields are 20% higher when modeled using increasing CO2 values with time (according to the SRES A1B scenario of the IPCC) instead of a fixed 390 ppm for the entire run.

Figure 1. Biomass yield difference (percent change) between model runs of constant and changing atmospheric CO2 concentration. A value of +20% indicates biomass yields are 20% higher when modeled using increasing CO2 values with time (according to the SRES A1B scenario of the IPCC) instead of a fixed 390 ppm for the entire run.

The results of this model-based study fall in line with the previous work of Idso (2013), who calculated similar CO2-induced benefits on global crop production by mid-century based on real-world experimental data, both of which studies reveal that policy prescriptions designed to limit the upward trajectory of atmospheric CO2 concentrations can have very real, and potentially serious, repercussions for global food security.

 

References

Degener, J.F. 2015. Atmospheric CO2 fertilization effects on biomass yields of 10 crops in northern Germany. Frontiers in Environmental Science 3: 48, doi: 10.3389/fenvs.2015.00048.

Idso, C.D. 2013. The Positive Externalities of Carbon Dioxide: Estimating the Monetary Benefits of Rising Atmospheric CO2 Concentrations on Global Food Production. Center for the Study of Carbon Dioxide and Global Change, Tempe, AZ.

A Plant Pathogen that Can’t Take the Heat

Plant pathogens have long been a thorn in the side of the agricultural industry, reducing crop production between 10-16 percent annually and costing an estimated $220 billion in economic losses (Chakraborty and Newton, 2011). What is more, there are concerns that such damages may increase in the future if temperatures rise as predicted by global climate models in response to CO2-induced global warming. Noting these concerns, Sabburg et al. (2015) write that “to assess potential disease risks and improve our knowledge of pathogen strengths, flexibility, weakness and vulnerability under climate change, a better understanding of how pathogen fitness will be influenced is paramount.”

In an attempt to obtain that knowledge, the team of four Australian researchers set out to investigate the impact of rising temperatures on Fusarium pseudograminearum, the “predominant pathogen causing crown rot of wheat in Australia” that is responsible for inducing an average of AU$79 million in crop losses each year. More specifically, they examined “whether the pathogenic fitness, defined as a measure of survival and reproductive success of F. pseudograminearum causing crown rot in wheat, is influenced by temperature under experimental conditions.”

The experiment was conducted in controlled-environment glasshouses at the Queensland Crop Development Facility in Queensland, Australia, where eleven lines of wheat were grown under four day/night temperature treatments (15/15°C, 20/15°, 25/15° and 28/15°C for 14-hour days and 10-hour nights). The first three treatments were representative of “the range of average maximum temperatures of the various wheat-growing regions across Australia,” whereas the fourth (28/15°C) treatment was intended to simulate a future warming scenario. The minimum temperatures of all treatments were kept at 15°C because “night-time temperatures over the last 50 years in the large majority of wheat-growing regions across Australia have not shown an increasing temperature trend in all seasons.” With respect to the eleven wheat lines, they were selected based on known susceptibilities and resistances to crown rot. Fourteen days after sowing a portion of each line was infected with F. pseudograminearum and then grown to maturity.

So what did the researchers find?

With respect to disease severity, Sabburg et al. report it was highest under the lowest temperature treatment and declined with increasing temperature (Figure 1a), and this general reduction was noted in all of the eleven wheat lines. Similarly, pathogen biomass was also reduced as treatment temperature increased (Figure 1b). According to the researchers, “on average, warming reduced pathogen biomass in stem base (PB-S) by 52% at either 25/15°C or 28/15°C compared with the biomass at 15/15°C.” And it also decreased the amount of relative pathogen biomass from the stem base to flag leaf node. (The flag leaf is to top leaf on the plant.)

A third fitness measure of F. pseudograminearum – deoxynivalenol (also known as “vomitoxin,” for an obvious reason) content (DON) – was also reduced in the stem base and flag leaf node tissue as temperature treatment increased. And the significance of this finding was noted by the authors as “an encouraging result if we consider temperature rises in the future,” because “DON can make food sources including wheat grains unsafe for human or animal consumption.” That’s putting it mildly!

Figure 1. Effect of temperature on (Panel A) disease severity as expressed by the length of stem base browning (cm) and (Panel B) relative pathogen biomass in stem base (PB-S) and flag leaf node tissue (PB-F) as measured by Fusarium DNA relative to wheat DNA. All measurements in wheat plants were made at maturity following stem base inoculation by Fusarium pseudograminearum. Adapted from Sabburg et al. (2015).

Figure 1. Effect of temperature on (Panel A) disease severity as expressed by the length of stem base browning (cm) and (Panel B) relative pathogen biomass in stem base (PB-S) and flag leaf node tissue (PB-F) as measured by Fusarium DNA relative to wheat DNA. All measurements in wheat plants were made at maturity following stem base inoculation by Fusarium pseudograminearum. Adapted from Sabburg et al. (2015).

In light of the above results, Sabburg et al. conclude that “this study has clearly established that temperature influences the overall fitness of F. pseudograminearum,” and that “based on our findings, warmer temperatures associated with climate change may reduce overall pathogenic fitness of F. pseudograminearum.” And given the annual production and monetary damages inflicted by this pathogen on wheat, this is news worth both reporting and celebrating!

 

References

Chakraborty, S. and Newton, A.C. 2011. Climate change, plant diseases and food security: an overview. Plant Pathology 60: 2-14.

Sabburg, R., Obanor, F., Aitken, E. and Chakraborty, S. 2015. Changing fitness of a necrotrophic plant pathogen under increasing temperature. Global Change Biology 21: 3126-3137.

 

You Say Meethane, I Say Meth-ane, Let’s Agree We Don’t Know Where It’s Coming From

Global Science Report is a weekly feature from the Center for the Study of Science, where we highlight one or two important new items in the scientific literature or the popular media. For broader and more technical perspectives, consult our monthly “Current Wisdom.”

Atmospheric concentrations of methane (CH4)—a greenhouse gas many times more potent than carbon dioxide (at least over shorter time scales)—have begun rising after a hiatus from 1999-2006 that defied all expectations. No one knows for sure why—why they stood still, or why they started up again.

There is a lot of research underway looking into the causes of the observed methane behavior and at least three new studies have reported results in the scientific literature in the past couple of months.

The findings are somewhat at odds with each other.

In February, a study led by Alex Turner, from Harvard University’s School of Engineering and Applied Sciences, was published that examined methane emissions from the US over the past 10 years or so. The researchers compared observations taken from orbiting satellites to observations made from several sites on the earth’s surface. They reported over the past decade “an increase of more than 30% in US methane emissions.” And this increase was so large as to “suggest that increasing US anthropogenic methane emissions could account for up to 30-60% of [the] global increase.”

However, the methodologies employed by Turner et al. were insufficient for determining the source of the enhanced emissions. While the authors wrote that “[t]he US has seen a 20% increase in oil and gas production and a 9-fold increase in shale gas production from 2002 to 2014” they were quick to point out that “the spatial pattern of the methane increase seen by [satellite] does not clearly point to these sources” and added that “[m]ore work is needed to attribute the observed increase to specific sources.”

Perhaps most interestingly, Turner and colleagues note that “national inventory estimates from the US Environmental Protection Agency (EPA) indicate no significant trend in US anthropogenic methane emissions from 2002 to present”—a stark contrast to their findings, and a potential embarrassing problem for the EPA. But, never fear, the EPA is on it. The EPA is now actively re-examining its methane inventory and seems to be in the process of revising it upwards, perhaps even so much as to change its previous reported decline in methane emissions to an increase. Such a change would have large implications for the US’s ability to keep the pledge made at the U.S. 2015 Climate Conference in Paris.

However, the Turner et al. results have been called into question by a prominently-placed study in Science magazine just a couple of weeks later. The Science study was produced by a large team led by Hinrich Schaefer of New Zealand’s National Institute of Water and Atmospheric Research.

Schaefer and colleagues analyzed the changes in the isotopic ratios of carbon in the methane contained in samples of air within ice cores, archived air samples, and more recent measurement systems. Different sources of methane contain different mixtures of methane isotopes, related to how long ago the methane was formed. Using this information, the authors developed a model for trying to back out the methane sources from the well-mixed atmospheric samples. Although such a procedure is somewhat tunable (i.e., you can get pretty much any answer you want (kind of like climate models!)), the authors are pretty confident in their final results. 

Salt and CO2 Better for Tomatoes, Now for Lettuce, Too

Wow, will bacon be next?

Last fall we wrote about the improvement in tomato taste that results from growing them in elevated carbon dioxide and seawater (Idso and Michaels, 2015). Now it looks like the same treatment improves lettuce. 

Enhancing crop nutritional value has long been a goal of the agricultural industry. Growing plants under less than optimal conditions for a short period of time generally increases their oxidative stress. To counter such stress, plants will usually increase their antioxidant metabolism which, in turn, elevates the presence of various antioxidant compounds in their tissues, compounds that can be of great nutritional value from a human point of view, such as helping to reduce the effects of ageing.

However, stress-induced nutritional benefits often come at a price, including a reduction in plant growth and yield, making it unproductive and costly to implement these practices in the real world. But what if there was a way achieve such benefits without sacrificing crop biomass, having our cake and eating it, too? An intriguing paper recently published in the journal Scientia Horticulturae explains just how this can happen, involving lettuce, salt stress, and atmospheric CO2.

According to Pérez-López et al. (2015), the authors of this new work, “few studies have utilized salt irrigation combined with CO2-enriched atmospheres to enhance a crop’s nutraceutical value.” Thus, the team of five Spanish researchers set out to conduct just such an experiment involving two lettuce cultivars, Blonde of Paris Badavia (a green-leaf lettuce) and Oak Leaf (a red-leaf lettuce and a common garden variety). In so doing, they grew the lettuce cultivars from seed in controlled environment chambers at either ambient or enriched CO2 for a period of 35 days after which they supplied a subset of the two treatments with either 0 or 200 mM NaCl for 4 days to simulate salt stress. Thereafter they conducted a series of analyses to report growth and nutritional characteristics of the cultivars under these varying growth conditions. And what did those analyses reveal?

On the Bright Side: The Effects of Elevated CO2 on Two Coffee Cultivars

Compliments of rising atmospheric CO2, in the future you can have a larger cup of coffee and drink it too!

In the global market, coffee is one of the most heavily traded commodities, where more than 80 million people are involved in its cultivation, processing, transportation and marketing (Santos et al., 2015). Cultivated in over 70 countries, retail sales are estimated at $90 billion USD. Given such agricultural prominence, it is therefore somewhat surprising, in the words of Ghini et al. (2015) that “there is virtually no information about the effects of rising atmospheric CO2 on field-grown coffee trees.” Rather, there exists only a few modeling studies that estimate a future in which coffee plants suffer (1) severe yield losses (Gay et al., 2006), (2) a reduction in suitable growing area (Zullo et al., 2011), (3) extinction of certain wild populations (Davis et al., 2012) and (4) increased damage from herbivore, pathogen and pest attacks (Ghini et al., 2011; 2012; Jaramillo et al., 2011; Kutywayo et al., 2013), all in consequence of predicted changes in climate due to rising atmospheric CO2.

In an effort to assess such speculative model-based predictions, the ten-member scientific team of Ghini et al. set out to conduct an experiment to observationally determine the response of two coffee cultivars to elevated levels of atmospheric CO2 in the first Free-air CO2 Enrichment (FACE) facility in Latin America. Small specimens (3-4 pairs of leaves) of two coffee cultivars, Catuaí and Obatã, were sown in the field under ambient (~390 ppm) and enriched (~550 ppm) CO2 conditions in August of 2011 and allowed to grow under normal cultural growing conditions without supplemental irrigation for a period of 2 years.

No significant effect of CO2 was observed on the growth parameters during the first year. However, during the growing season of year 2, net photosynthesis increased by 40% (see Figure 1a) and plant water use efficiency by approximately 60% (Figure 1b), regardless of cultivar. During the winter, when growth was limited, daily mean net photosynthesis “averaged 56% higher in the plants treated with CO2 than in their untreated counterparts” (Figure 1c). Water use efficiency in winter was also significantly higher (62% for Catuaí and 85% for Obatã, see Figure 1d). Such beneficial impacts resulted in significant CO2-induced increases in plant height (7.4% for Catuaí and 9.7% for Obatã), stem diameter (9.5% for Catuaí and 13.4% for Obatã) and harvestable yield (14.6% for Catuaí and 12.0% for Obatã) over the course of year 2. Furthermore, Ghini et al. report that the increased crop yield “was associated with an increased number of fruits per branch, with no differences in fruit weight.”