Changes in temperature, CO2, and precipitation under the scenarios of climate change for the next 30 yr present a challenge to crop production. This review focuses on the impact of temperature, CO2, ...and ozone on agronomic crops and the implications for crop production. Understanding these implications for agricultural crops is critical for developing cropping systems resilient to stresses induced by climate change. There is variation among crops in their response to CO2, temperature, and precipitation changes and, with the regional differences in predicted climate, a situation is created in which the responses will be further complicated. For example, the temperature effects on soybean Glycine max (L.) Merr. could potentially cause yield reductions of 2.4% in the South but an increase of 1.7% in the Midwest. The frequency of years when temperatures exceed thresholds for damage during critical growth stages is likely to increase for some crops and regions. The increase in CO2 contributes significantly to enhanced plant growth and improved water use efficiency (WUE); however, there may be a downscaling of these positive impacts due to higher temperatures plants will experience during their growth cycle. A challenge is to understand the interactions of the changing climatic parameters because of the interactions among temperature, CO2, and precipitation on plant growth and development and also on the biotic stresses of weeds, insects, and diseases. Agronomists will have to consider the variations in temperature and precipitation as part of the production system if they are to ensure the food security required by an ever increasing population.
The response of plant species to future atmospheric carbon dioxide concentrations CO2 has been determined for hundreds of crop and tree species. However, no data are currently available regarding the ...response of invasive weedy species to past or future atmospheric CO2. In the current study, the growth of six species which are widely recognized as among the most invasive weeds in the continental United States, Canada thistle (Cirsium arvense (L.) Scop.), field bindweed (Convolvulus arvensis L.), leafy spurge (Euphorbia esula L.), perennial sowthistle (Sonchus arvensis L.), spotted knapweed (Centaurea maculosa Lam.), and yellow star thistle (Centaurea solstitialis L.) were grown from seed at either 284, 380 or 719 µmol mol–1 CO2 until the onset of sexual reproduction (i.e. the vegetative period). The CO2 concentrations corresponded roughly to the CO2 concentrations which existed at the beginning of the 20th century, the current CO2, and the future CO2 projected for the end of the 21st century, respectively. The average stimulation of plant biomass among invasive species from current to future CO2 averaged 46%, with the largest response (+72%) observed for Canada thistle. However, the growth response among these species to the recent CO2 increase during the 20th century was significantly higher, averaging 110%, with Canada thistle again (+180%) showing the largest response. Overall, the CO2‐induced stimulation of growth for these species during the 20th century (285–382 µmol mol–1) was about 3× greater than for any species examined previously. Although additional data are needed, the current study suggests the possibility that recent increases in atmospheric CO2 during the 20th century may have been a factor in the selection of these species.
Summary
Projected increases in atmospheric carbon dioxide concentration CO2 may lead to differential selection and competition between weeds and crops. Yet, the current level of atmospheric CO2 ...already reflects a rapid rise (~25%) from mid‐20th century levels. To assess whether this increase could have already resulted in differential selection between weeds and crops, two temporally distinct populations of Avena fatua (wild oat) from the same geographic location, one from the 1960s (WOold) and one from 2014 (WOnew), were grown with and without a cultivated oat (CO) line, Clintland 64 (Avena sativa) at current and mid‐20th century CO2 levels (ca 320 and 402 μmol mol−1 respectively). Monocultures of each WO population differed in their response to recent increases in atmospheric CO2, with WOnew showing a significantly higher response for all vegetative parameters relative to WOold. Assessment of competitive outcomes indicated that at 315 μmol mol−1 cultivated oat was at a competitive advantage relative to either A. fatua population for leaf area and total above‐ground biomass. However, at current levels of CO2, an overall increase in WOnew competitive ability was observed relative to the cultivated oat line. Overall, these differences are consistent with, but not conclusive for, improved evolutionary fitness and increased early competitive ability of A. fatua relative to cultivated oat as a function of the recent increase in atmospheric CO2. While additional empirical studies are needed, these preliminary results indicate that weeds may be adapting rapidly to rising levels of atmospheric carbon dioxide.
Cheatgrass (Bromus tectorum) is a recognized, invasive annual weed of the western United States that reduces fire return times from decades to less than 5 years. To determine the interaction between ...rising carbon dioxide concentration (CO2) and fuel load, we characterized potential changes in biomass accumulation, C : N ratio and digestibility of three cheatgrass populations from different elevations to recent and near-term projections in atmospheric CO2. The experimental CO2 values (270, 320, 370, 420 μmol mol-1) corresponded roughly to the CO2 concentrations that existed at the beginning of the 19th century, that during the 1960s, the current CO2, and the near-term CO2 projection for 2020, respectively. From 25 until 87 days after sowing (DAS), aboveground biomass for these different populations increased 1.5-2.7 g per plant for every 10 μmol mol-1 increase above the 270 μmol mol-1 preindustrial baseline. CO2 sensitivity among populations varied with elevational origin with populations from the lowest elevation showing the greatest productivity. Among all populations, the undigestible portion of aboveground plant material (acid detergent fiber ADF, mostly cellulose and lignin) increased with increasing CO2. In addition, the ratio of C : N increased with leaf age, with CO2 and was highest for the lower elevational population. These CO2-induced qualitative changes could, in turn, result in potential decreases in herbivory and decomposition with subsequent effects on the aboveground retention of cheatgrass biomass. Overall, these data suggest that increasing atmospheric CO2 above preambient levels may have contributed significantly to cheatgrass productivity and fuel load with subsequent effects on fire frequency and intensity.
Although the role of rising atmospheric carbon dioxide concentration CO
2
on plant growth and fecundity is widely acknowledged as important within the scientific community; less research is ...available regarding the impact of CO
2
on secondary plant compounds, even though such compounds can play a significant role in human health. At present,
Artemisia annua
, an annual plant species native to China, is widely recognized as the primary source of artemesinin used in artemesinin combination therapies or ACTs. ACTs, in turn, are used globally for the treatment of simple
Plasmodium falciparum
malaria, the predominant form of malaria in Africa. In this study, artemesinin concentration was quantified for multiple
A. annua
populations in China using a free-air CO
2
enrichment (FACE) system as a function of CO
2
-induced changes both in situ and as a function of the foliar ratio of carbon to nitrogen (C:N). The high correlation between artemesinin concentration and C:N allowed an historical examination of
A. annua
leaves collected at 236 locations throughout China from 1905 through 2009. Both the historical and experimental data indicate that increases in artemesinin foliar concentration are likely to continue in parallel with the ongoing increase in atmospheric CO
2
. The basis for the CO
2
-induced increase in artemesinin is unclear, but could be related to the carbon: nutrient hypothesis of Bryant et al. (
1983
). Overall, these data provide the first evidence that historic and projected increases in atmospheric CO
2
may be associated with global changes in artemesinin chemistry, potentially allowing a greater quantity of drug available for the same area of cultivation.
To examine the impact of climate change on vegetative productivity, we exposed fallow agricultural soil to an in situ temperature and CO₂ gradient between urban, suburban and rural areas in 2002. ...Along the gradient, average daytime CO₂ concentration increased by 21% and maximum (daytime) and minimum (nighttime) daily temperatures increased by 1.6 and 3.3°C, respectively in an urban relative to a rural location. Consistent location differences in soil temperature were also ascertained. No other consistent differences in meteorological variables (e.g. wind speed, humidity, PAR, tropospheric ozone) as a function of urbanization were documented. The urban-induced environmental changes that were observed were consistent with most short-term (~50 year) global change scenarios regarding CO₂ concentration and air temperature. Productivity, determined as final above-ground biomass, and maximum plant height were positively affected by daytime and soil temperatures as well as enhanced CO₂, increasing 60 and 115% for the suburban and urban sites, respectively, relative to the rural site. While long-term data are needed, these initial results suggest that urban environments may act as a reasonable surrogate for investigating future climatic change in vegetative communities.
The sensitivity of yield and quality parameters to carbon dioxide concentration CO2 was determined for individual lines of hard‐red spring wheat released in 1903, 1921, 1965 and 1996. All cultivars ...were evaluated with respect to growth and vegetative characteristics, grain yield and nutritional quality in response to CO2 increases that corresponded roughly to the CO2 concentrations at the beginning of the 20th century, the current CO2, and the future projected CO2 for the end of the 21st century, respectively. Leaf area ratio (cm2 g−1) declined and net assimilation rate (g m2 day−1) increased in response to increasing CO2 for all cultivars during early vegetative growth. By maturity, vegetative growth of all cultivars significantly increased with the increase in CO2. Seed yield increased significantly as CO2 increased, with yield sensitivity to rising CO2 inversely proportional to the year of cultivar release. Greater CO2 yield sensitivity in older cultivars was associated with whole‐plant characteristics such as increased tillering and panicle formation. Grain and flour protein, however, declined significantly with increasing CO2 and with year of release for all cultivars, although absolute values were higher for the older cultivars. Overall, these data indicate that yield response at the whole‐plant level to recent and projected increases in CO2 has declined with the release of newer cultivars, as has protein content of grain and flour. However, if agronomic practice can be adapted to maximize individual plant performance, CO2 responsive characteristics of older cultivars could, potentially, be incorporated as factors in future wheat selection.
Valerio M, Tomecek MB, Lovelli S & Ziska LH (2011). Quantifying the effect of drought on carbon dioxide‐induced changes in competition between a C3 crop (tomato) and a C4 weed (Amaranthus ...retroflexus). Weed Research51, 591–600.
Summary
Recent and projected increases in atmospheric carbon dioxide concentration (CO2) and subsequent effects on climate are likely to alter competitive outcomes of weeds and crops. Rising CO2 per se could increase the competitive ability of C3 crops relative to C4 weeds. However, such an outcome may depend on other climatic variables. In this study, tomato, a C3 crop species, was grown from emergence to anthesis using replacement series mixtures with Amaranthus retroflexus, a C4 weed species at three different CO2, 400, 600 and 800 μmol mol−1, with and without water stress. Under well‐watered conditions, leaf photosynthetic rates and plant height, leaf area and biomass all increased with elevated CO2 for tomato relative to A. retroflexus, consistent with the kinetics of C3 photosynthesis. However, if water was limiting, a significant positive effect of CO2 was noted for plant height and biomass of A. retroflexus with increased competition. This result may be related to a greater increase in leaf water potential with rising CO2 for A. retroflexus relative to tomato under water stress. Overall, these are the first data to suggest that increases in atmospheric CO2 could still exacerbate crop losses from a C4 weed, even with a C3 crop, if drought occurs.
Summary
Projected increases in atmospheric carbon dioxide concentration
CO
2
may lead to differential selection and competition between weeds and crops. Yet, the current level of atmospheric
CO
2
...already reflects a rapid rise (~25%) from mid‐20th century levels. To assess whether this increase could have already resulted in differential selection between weeds and crops, two temporally distinct populations of
Avena fatua
(wild oat) from the same geographic location, one from the 1960s (
WO
old
) and one from 2014 (
WO
new
), were grown with and without a cultivated oat (
CO
) line, Clintland 64 (
Avena sativa
) at current and mid‐20th century
CO
2
levels (ca 320 and 402 μmol mol
−1
respectively). Monocultures of each
WO
population differed in their response to recent increases in atmospheric
CO
2
, with
WO
new
showing a significantly higher response for all vegetative parameters relative to
WO
old
. Assessment of competitive outcomes indicated that at 315 μmol mol
−1
cultivated oat was at a competitive advantage relative to either
A. fatua
population for leaf area and total above‐ground biomass. However, at current levels of
CO
2
, an overall increase in
WO
new
competitive ability was observed relative to the cultivated oat line. Overall, these differences are consistent with, but not conclusive for, improved evolutionary fitness and increased early competitive ability of
A. fatua
relative to cultivated oat as a function of the recent increase in atmospheric
CO
2
. While additional empirical studies are needed, these preliminary results indicate that weeds may be adapting rapidly to rising levels of atmospheric carbon dioxide.
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