Australian wheat production expected to decrease by the late 21st century

Climate change threatens global wheat production and food security, including the wheat industry in Australia. Many studies have examined the impacts of changes in local climate on wheat yield per hectare, but there has been no assessment of changes in land area available for production due to changing climate. It is also unclear how total wheat production would change under future climate when autonomous adaptation options are adopted. We applied species distribution models to investigate future changes in areas climatically suitable for growing wheat in Australia. A crop model was used to assess wheat yield per hectare in these areas. Our results show that there is an overall tendency for a decrease in the areas suitable for growing wheat and a decline in the yield of the northeast Australian wheat belt. This results in reduced national wheat production although future climate change may benefit South Australia and Victoria. These projected outcomes infer that similar wheat‐growing regions of the globe might also experience decreases in wheat production. Some cropping adaptation measures increase wheat yield per hectare and provide significant mitigation of the negative effects of climate change on national wheat production by 2041–2060. However, any positive effects will be insufficient to prevent a likely decline in production under a high CO₂ emission scenario by 2081–2100 due to increasing losses in suitable wheat‐growing areas. Therefore, additional adaptation strategies along with investment in wheat production are needed to maintain Australian agricultural production and enhance global food security. This scenario analysis provides a foundation towards understanding changes in Australia's wheat cropping systems, which will assist in developing adaptation strategies to mitigate climate change impacts on global wheat production.     

Response of wheat restricted‐tillering and vigorous growth traits to variables of climate change

The response of wheat to the variables of climate change includes elevated CO₂, high temperature, and drought which vary according to the levels of each variable and genotype. Independently, elevated CO₂, high temperature, and terminal drought affect wheat biomass and grain yield, but the interactive effects of these three variables are not well known. The aim of this study was to determine the effects of elevated CO₂ when combined with high temperature and terminal drought on the high‐yielding traits of restricted‐tillering and vigorous growth. It was hypothesized that elevated CO₂ alone, rather than combined with high temperature, ameliorates the effects of terminal drought on wheat biomass and grain yield. It was also hypothesized that wheat genotypes with more sink capacity (e.g. high‐tillering capacity and leaf area) have more grain yield under combined elevated CO₂, high temperature, and terminal drought. Two pairs of sister lines with contrasting tillering and vigorous growth were grown in poly‐tunnels in a four‐factor completely randomized split‐plot design with elevated CO₂ (700 µL L^?1), high day time temperature (3 °C above ambient), and drought (induced from anthesis) in all combinations to test whether elevated CO₂ ameliorates the effects of high temperature and terminal drought on biomass accumulation and grain yield. For biomass and grain yield, only main effects for climate change variables were significant. Elevated CO₂ significantly increased grain yield by 24–35% in all four lines and terminal drought significantly reduced grain yield by 16–17% in all four lines, while high temperature (3 °C above the ambient) had no significant effect. A trade‐off between yield components limited grain yield in lines with greater sink capacity (free‐tillering lines). This response suggests that any positive response to predicted changes in climate will not overcome the limitations imposed by the trade‐off in yield components.     

Spatial and technological variability in the carbon footprint of durum wheat production in Iran

Purpose

The purpose of this study was to quantify the spatial and technological variability in life cycle greenhouse gas (GHG) emissions, also called the carbon footprint, of durum wheat production in Iran.

Methods

The calculations were based on information gathered from 90 farms, each with an area ranging from 1 to 150 ha (average 16 ha). The carbon footprint of durum wheat was calculated by quantifying the biogenic GHG emissions of carbon loss from soil and biomass, as well as the GHG emissions from fertilizer application and machinery use, irrigation, transportation, and production of inputs (e.g., fertilizers, seeds, and pesticides). We used Spearman’s rank correlation to quantify the relative influence of technological variability (in crop yields, fossil GHG emissions, and N₂O emissions from fertilizer application) and spatial variability (in biogenic GHG emissions) on the variation of the carbon footprint of durum wheat.

Results and discussion

The average carbon footprint of 1 kg of durum wheat produced was 1.6 kg CO₂-equivalents with a minimum of 0.8 kg and a maximum of 3.0 kg CO₂-equivalents. The correlation analysis showed that variation in crop yield and fertilizer application, representing technological variability, accounted for the majority of the variation in the carbon footprint, respectively 76 and 21%. Spatial variation in biogenic GHG emissions, mainly resulting from differences in natural soil carbon stocks, accounted for 3% of the variation in the carbon footprint. We also observed a non-linear relationship between the carbon footprint and the yield of durum wheat that featured a scaling factor of ?2/3. This indicates that the carbon footprint of durum wheat production (in kg CO₂-eq kg^?1) typically decreases by 67% with a 100% increase in yield (in kg ha^?1 year^?1).

Conclusions

Various sources of variability, including variation between locations and technologies, can influence the results of life cycle assessments. We demonstrated that technological variability exerts a relatively large influence on the carbon footprint of durum wheat produced in Iran with respect to spatial variability. To increase the durum wheat yield at farms with relatively large carbon footprints, technologies such as site-specific nutrient application, combined tillage, and mechanized irrigation techniques should be promoted.

     

Potential impact of climate change on selected agricultural crops in north-eastern Austria

The vulnerability and adaptation of major agricultural crops to various soils in north‐eastern Austria under a changing climate were investigated. The CERES crop model for winter wheat and the CROPGRO model for soybean were validated for the agrometeorological conditions in the selected region. The simulated winter wheat and soybean yields in most cases agreed with the measured data. Several incremental and transient global circulation model (GCM) climate change scenarios were created and used in the study. In these scenarios, annual temperatures in the selected region are expected to rise between 0.9 and 4.8 °C from the 2020s to the 2080s. The results show that warming will decrease the crop‐growing duration of the selected crops. For winter wheat, a gradual increase in air temperature resulted in a yield decrease. Incremental warming, especially in combination with an increase in precipitation, leads to higher soybean yield. A drier climate will reduce soybean yield, especially on soils with low water storage capacity. All transient GCM climate change scenarios for the 21st century, including the adjustment for only air temperature, precipitation and solar radiation, projected reductions of winter wheat yield. However, when the direct effect of increased levels of CO₂ concentration was assumed, all GCM climate change scenarios projected an increase in winter wheat yield in the region. The increase in simulated soybean yield for the 21st century was primarily because of the positive impact of warming and especially of the beneficial influence of the direct CO₂ effect. Changes in climate variability were found to affect winter wheat and soybean yield in various ways. Results from the adaptation assessments suggest that changes in sowing date, winter wheat and soybean cultivar selection could significantly affect crop production in the 21st century.     

Assessment of climatic indices limiting rainfed wheat yield

In this study variation of six climatic indices including accumulated precipitation (P), accumulated potential evapotranspiration (PET), accumulated actual evapotranspiration (AET), accumulated crop evapotranspiration (ETC), accumulated water stress (S) and climatic water deficit (D), was investigated. Climatic indices and their variation were calculated during seven growth stages of wheat in five locations in the northeast of Iran from 1983 to 2008. Principal component analysis (PCA) technique was applied to explore major modes of variation in the regional climatic indices during different crop growth stages. The principle component obtained for each region was correlated to the regional winter wheat yield. Finally the regional amount of water and precipitation use efficiency (WUE and PUE) were analyzed in order to assess any possible association with wheat yield. The results showed that the highest precipitation occurred during the tillering stage and spatially decreased from north (Bojnord) to south (Birjand) and from east (Mashhad) to west (Sabzevar). The difference between the highest and the lowest precipitation across all locations was 2.5 of standard value. The variation pattern of AET, compared to other indices, showed more similarity to variation of precipitation at different growth stages and the highest AET (more than 2 of standard value in all locations) occurred during the tillering stage. The PCA indicated that effective components varied in different locations. The most positive and effective components were types of evapotranspiration that are associated with crop (ETC and AET) and precipitation. However none of these effective PCs showed a significant correlation with final yield. The PUE and WUE analysis indicated that PUE provides more information to interpret the relationship between total amounts of precipitation and the final yield.     

Responsiveness of Durum Wheat to Mycorrhizal Inoculation Under Different Environmental Scenarios

A greater understanding of how climate change will affect crop photosynthetic performance has been described as a target goal to improve yield potential. Other concomitant stressors can reduce the positive effect of elevated atmospheric CO₂ on wheat yield. Arbuscular mycorrhizal fungi (AMF) are symbiotic fungi predicted to be important in defining plant responses to rising atmospheric CO₂, but their role in response to global climatic change is still poorly understood. This study aimed to assess if increased atmospheric CO₂ interacting with drought can modify the effects of mycorrhizal symbiosis on flag leaf physiology in winter wheat. The study was performed in climate-controlled greenhouses with ambient (400 ppm, ACO₂) or elevated (700 ppm, ECO₂) CO₂ concentrations in the air. Within each greenhouse half of the plants were inoculated with Rhizophagus intraradices. When ear emergence began, half of the plants from each mycorrhizal and CO₂ treatment were subjected to terminal drought. At ACO₂ AMF improved the photochemistry efficiency of PSII compared with non-mycorrhizal plants, irrespective of irrigation regime. Mycorrhizal wheat accumulated more fructan than non-mycorrhizal plants under optimal irrigation. The level of proline in the flag leaf increased only in mycorrhizal wheat after applying drought. Mycorrhizal association avoided photosynthetic acclimation under ECO₂. However, nitrogen availability to flag leaves in mycorrhizal plants was lower under ECO₂ than at ACO₂. Results suggest that the mechanisms underlying the interactions between mycorrhizal association and atmospheric CO₂ concentration can be crucial for the benefits that this symbiosis can provide to wheat plants undergoing water deficit.     

Yield stability of hybrids versus lines in wheat,barley, and triticale

Key message

We present experimental data for wheat, barley, and triticale suggesting that hybrids manifest on average higher yield stability than inbred lines.

Abstract

Yield stability is assumed to be higher for hybrids than for inbred lines, but experimental data proving this hypothesis is scarce for autogamous cereals. We used multi-location grain yield trials and compared the yield stability of hybrids versus lines for wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), and triticale (×Triticosecale Wittmack). Our study comprised three phenotypic data sets of 1,749 wheat, 96 barley, and 130 triticale genotypes, which were evaluated for grain yield in up to five contrasting locations. Yield stability of the group of hybrids was compared with that of the group of inbred lines estimating the stability variance. For all three crops we observed a significantly (P < 0.05) higher yield stability of hybrids compared to lines. The enhanced yield stability of hybrids as compared to lines represents a major step forward, facilitating coping with the increasing abiotic stress expected from the predicted climate change.     

Rising atmospheric CO2 may affect oil quality and seed yield of sunflower (Helianthus annus L.)

The impact of rising atmospheric CO₂ on crop productivity and quality is very important for global food and nutritional security under the changing climatic scenario. A study was conducted to investigate the effect of elevated CO₂ on seed oil quality and yield in a sunflower hybrid DRSH 1 and variety DRSF 113, raised inside open top chambers and exposed to elevated CO₂ (550 ± 50 µl l^?1). Elevated CO₂ exposure significantly influenced the rate of photosynthesis, seed yield and the quality traits in both hybrid and variety. Plants grown under elevated CO₂ concentration showed 61–68 % gain in biomass and 35–46 % increase in seed yield of both the genotypes, but mineral nutrient and protein concentration decreased in the seeds. The reduction in seed protein was up to 13 %, while macro and micronutrients decreased drastically (up to 43 % Na in hybrid seeds) under elevated CO₂ treatment. However, oil content increased significantly in DRSF 113 (15 %). Carbohydrate seed reserves increased with similar magnitudes in both the genotypes under elevated CO₂ treatment (13 %). Fatty acid composition in seed oil contained higher proportion of unsaturated fatty acids (oleic and linoleic acid) under elevated CO₂ treatment, which is a desirable change in oil quality for human consumption. These findings conclude that rising atmospheric CO₂ in changing future climate can enhance biomass production and seed yield in sunflower and alter their seed oil quality in terms of increased concentration of unsaturated fatty acids compared with saturated fatty acids and lower seed proteins and mineral nutrients.     

Crop residue incorporation negates the positive effect of elevated atmospheric carbon dioxide concentration on wheat productivity and fertilizer nitrogen recovery

Background and purpose

Rapid increases in atmospheric carbon dioxide concentration ([CO₂]) may increase crop residue production and carbon: nitrogen (C:N) ratio. Whether the incorporation of residues produced under elevated [CO₂] will limit soil N availability and fertilizer N recovery in the plant is unknown. This study investigated the interaction between crop residue incorporation and elevated [CO₂] on the growth, grain yield and the recovery of ¹⁵N-labeled fertilizer by wheat (Triticum aestivum L. cv. Yitpi) under controlled environmental conditions.

Methods

Residue for ambient and elevated [CO₂] treatments, obtained from wheat grown previously under ambient and elevated [CO₂], respectively, was incorporated into two soils (from a cereal-legume rotation and a cereal-fallow rotation) 1 month before the sowing of wheat. At the early vegetative stage ¹⁵N-labeled granular urea (10.22 atom%) was applied at 50 kg?N ha^?1 and the wheat grown to maturity.

Results

When residue was not incorporated into the soil, elevated [CO₂] increased wheat shoot (16 %) and root biomass (41 %), grain yield (19 %), total N uptake (4 %) and grain N removal (8 %). However, the positive [CO₂] fertilization effect on these parameters was absent in the soil amended with residue. In the absence of residue, elevated [CO₂] increased fertilizer N recovery in the plant (7 %), but when residue was incorporated elevated [CO₂] decreased fertilizer N recovery.

Conclusions

A higher fertilizer application rate will be required under future elevated [CO₂] atmospheres to replenish the extra N removed in grains from cropping systems if no residue is incorporated, or to facilitate the [CO₂] fertilization effect on grain yield by overcoming N immobilization resulting from residue amendment.     

Effects of precipitation and temperature on crop production variability in northeast Iran

Climate variability adversely impacts crop production and imposes a major constraint on farming planning, mostly under rainfed conditions, across the world. Considering the recent advances in climate science, many studies are trying to provide a reliable basis for climate, and subsequently agricultural production, forecasts. The El Niño-Southern Oscillation phenomenon (ENSO) is one of the principle sources of interannual climatic variability. In Iran, primarily in the northeast, rainfed cereal yield shows a high annual variability. This study investigated the role played by precipitation, temperature and three climate indices [Arctic Oscillation (AO), North Atlantic Oscillation (NAO) and NINO 3.4] in historically observed rainfed crop yields (1983–2005) of both barley and wheat in the northeast of Iran. The results revealed differences in the association between crop yield and climatic factors at different locations. The south of the study area is a very hot location, and the maximum temperature proved to be the limiting and determining factor for crop yields; temperature variability resulted in crop yield variability. For the north of the study area, NINO 3.4 exhibited a clear association trend with crop yields. In central locations, NAO provided a solid basis for the relationship between crop yields and climate factors.     

Hyperaccumulation of thallium is population-specific and uncorrelated with caesium accumulation in the thallium hyperaccumulator, Biscutella laevigata

Purpose

This study investigated the residual contribution of legume and fertilizer nitrogen (N) to a subsequent crop under the effect of elevated carbon dioxide concentration ([CO₂]).

Methods

Field pea (Pisum sativum L.) was labeled in situ with ¹⁵N (by absorption of a ¹⁵N-labeled urea solution through cut tendrils) under ambient and elevated (700 μmol mol^–1) [CO₂] in controlled environment glasshouse chambers. Barley (Hordeum vulgare L.) and its soil were also labeled under the same conditions by addition of ¹⁵N-enriched urea to the soil. Wheat (Triticum aestivum L.) was subsequently grown to physiological maturity on the soil containing either ¹⁵N-labeled field pea residues (including ¹⁵N-labeled rhizodeposits) or ¹⁵N-labeled barley plus fertilizer ¹⁵N residues.

Results

Elevated [CO₂] increased the total biomass of field pea (21 %) and N-fertilized barley (23 %), but did not significantly affect the biomass of unfertilized barley. Elevated [CO₂] increased the C:N ratio of residues of field pea (18 %) and N-fertilized barley (19 %), but had no significant effect on that of unfertilized barley. Elevated [CO₂] increased total biomass (11 %) and grain yield (40 %) of subsequent wheat crop regardless of rotation type in the first phase. Irrespective of [CO₂], the grain yield and total N uptake by wheat following field pea were 24 % and 11 %, respectively, higher than those of the wheat following N-fertilized barley. The residual N contribution from field pea to wheat was 20 % under ambient [CO₂], but dropped to 11 % under elevated [CO₂], while that from fertilizer did not differ significantly between ambient [CO₂] (4 %) and elevated [CO₂] (5 %).

Conclusions

The relative value of legume derived N to subsequent cereals may be reduced under elevated [CO₂]. However, compared to N fertilizer application, legume incorporation will be more beneficial to grain yield and N supply to subsequent cereals under future (elevated [CO₂]) climates.     

The shifting influence of drought and heat stress for crops in northeast Australia

Characterization of drought environment types (ETs) has proven useful for breeding crops for drought‐prone regions. Here, we consider how changes in climate and atmospheric carbon dioxide (CO₂) concentrations will affect drought ET frequencies in sorghum and wheat systems of northeast Australia. We also modify APSIM (the Agricultural Production Systems Simulator) to incorporate extreme heat effects on grain number and weight, and then evaluate changes in the occurrence of heat‐induced yield losses of more than 10%, as well as the co‐occurrence of drought and heat. More than six million simulations spanning representative locations, soil types, management systems, and 33 climate projections led to three key findings. First, the projected frequency of drought decreased slightly for most climate projections for both sorghum and wheat, but for different reasons. In sorghum, warming exacerbated drought stresses by raising the atmospheric vapor pressure deficit and reducing transpiration efficiency (TE), but an increase in TE due to elevated CO₂ more than offset these effects. In wheat, warming reduced drought stress during spring by hastening development through winter and reducing exposure to terminal drought. Elevated CO₂ increased TE but also raised radiation‐use efficiency and overall growth rates and water use, thereby offsetting much of the drought reduction from warming. Second, adding explicit effects of heat on grain number and grain size often switched projected yield impacts from positive to negative. Finally, although average yield losses associated with drought will remain generally higher than that for heat stress for the next half century, the relative importance of heat is steadily growing. This trend, as well as the likely high degree of genetic variability in heat tolerance, suggests that more emphasis on heat tolerance is warranted in breeding programs. At the same time, work on drought tolerance should continue with an emphasis on drought that co‐occurs with extreme heat.     

Water use and yield of bioenergy poplar in future climates: modelling the interactive effects of elevated atmospheric CO2 and climate on productivity and water use

Vegetation exerts large control on global biogeochemical cycles through the processes of photosynthesis and transpiration that exchange CO₂ and water between the land and the atmosphere. Increasing atmospheric CO₂ concentrations exert direct effects on vegetation through enhanced photosynthesis and reduced stomatal conductance, and indirect effects through changes in climatic variables that drive these processes. How these direct and indirect CO₂ impacts interact with each other to affect plant productivity and water use has not been explicitly analysed and remains unclear, yet is important to fully understand the response of the global carbon cycle to future climate change. Here, we use a set of factorial modelling experiments to quantify the direct and indirect impacts of atmospheric CO₂ and their interaction on yield and water use in bioenergy short rotation coppice poplar, in addition to quantifying the impact of other environmental drivers such as soil type. We use the JULES land‐surface model forced with a ten‐member ensemble of projected climate change for 2100 with atmospheric CO₂ concentrations representative of the A1B emissions scenario. We show that the simulated response of plant productivity to future climate change was nonadditive in JULES, however this nonadditivity was not apparent for plant transpiration. The responses of both growth and transpiration under all experimental scenarios were highly variable between sites, highlighting the complexity of interactions between direct physiological CO₂ effects and indirect climate effects. As a result, no general pattern explaining the response of bioenergy poplar water use and yield to future climate change could be discerned across sites. This study suggests attempts to infer future climate change impacts on the land biosphere from studies that force with either the direct or indirect CO₂ effects in isolation from each other may lead to incorrect conclusions in terms of both the direction and magnitude of plant response to future climate change.     

Modelling climate,CO2 and management impacts on soil carbon in semi-arid agroecosystems

In agroecosystems, there is likely to be a strong interaction between global change and management that will determine whether soil will be a source or sink for atmospheric C. We conducted a simulation study of changes in soil C as a function of climate and CO₂ change, for a suite of different management systems, at four locations representing a climate sequence in the central Great Plains of the US.Climate, CO₂ and management interactions were analyzed for three agroecosystems: a conventional winter wheat-summer fallow rotation, a wheat-corn-fallow rotation and continuous cropping with wheat. Model analyses included soil C responses to changes in the amount and distribution of precipitation and responses to changes in temperature, precipitation and CO₂ as projected by a general circulation model for a 2 × CO₂ scenario.Overall, differences between management systems at all the sites were greater than those induced by perturbations of climate and/or CO₂. Crop residue production was increased by CO₂ enrichment and by a changed climate. Where the frequency of summer fallowing was reduced (wheat-corn-fallow) or eliminated (continuous wheat), soil C increased under all conditions, particularly with increased (640 L L^–1) CO₂. For wheat-fallow management, the model predicted declines in soil C under both ambient conditions and with climate change alone. Increased CO₂ with wheat-fallow management yielded small gains in soil C at three of the sites and reduced losses at the fourth site.Our results illustrate the importance of considering the role of management in determining potential responses of agroecosystems to global change. Changes in climate will determine changes in management as farmers strive to maximize profitability. Therefore, changes in soil C may be a complex function of climate driving management and management driving soil C levels and not be a simple direct effect of either climate or management.     

Altered response to nitrogen supply of mixed grassland communities in a future climate: a controlled environment microcosm study

Few studies have investigated whether responses to nutrient supply of mixed plant communities change under combined elevated CO₂ and climate warming. In this study we analyzed the response of constructed temperate grassland communities to five levels of nitrogen (N) supply, ranging from 0 to 150 kg N ha^?1, under two climate scenarios. Biomass of the plant communities responded positively to N supply in the current climate, but was insensitive to N supply in the future climate. This altered response was not the result of a changing response from a single species, but all species seemed to contribute to it. The weaker response in the future climate was caused by changes in N uptake rather than by changes in nitrogen use efficiency, as community N stocks showed the same response pattern as community biomass. Climate change apparently modified the relation between fertilizer N addition and plant available N.     

Climate change impacts on life cycle greenhouse gas (GHG) emissions savings of biomethanol from corn and soybean

Purpose

The purpose of this study is to assess and calculate the potential impacts of climate change on the greenhouse gas (GHG) emissions reduction potentials of combined production of whole corn bioethanol and stover biomethanol, and whole soybean biodiesel and stalk biomethanol. Both fuels are used as substitutes to conventional fossil-based fuels. The product system includes energy crop (feedstock) production and transportation, biofuels processing, and biofuels distribution to service station.

Methods

The methodology is underpinned by life cycle thinking. Crop system model and life cycle assessment (LCA) model are linked in the analysis. The Decision Support System for Agrotechnology Transfer – crop system model (DSSAT-CSM) is used to simulate biomass and grain yield under different future climate scenarios generated using a combination of temperature, precipitation, and atmospheric CO₂. Historical weather data for Gainesville, Florida, are obtained for the baseline period (1981–1990). Daily minimum and maximum air temperatures are projected to increase by +2.0, +3.0, +4.0, and +5.0 °C, precipitation is projected to change by ±20, 10, and 5 %, and atmospheric CO₂ concentration is projected to increase by +70, +210, and +350 ppm. All projections are made throughout the growing season. GaBi 4.4 is used as primary LCA modelling software using crop yield data inputs from the DSSAT-CSM software. The models representation of the physical processes inventory (background unit processes) is constructed using the ecoinvent life cycle inventory database v2.0.

Results and discussion

Under current baseline climate condition, net greenhouse gas (GHG) emissions savings per hectare from corn-integrated biomethanol synthesis (CIBM) and soybean-integrated biomethanol synthesis (SIBM) were calculated as ?8,573.31 and ?3,441 kg CO₂-eq. ha^?1 yr^?1, respectively. However, models predictions suggest that these potential GHG emissions savings would be impacted by changing climate ranging from negative to positive depending on the crop and biofuel type, and climate scenario. Increased atmospheric level of CO₂ tends to minimise the negative impacts of increased temperature.

Conclusions

While policy measures are being put in place for the use of renewable biofuels driven by the desire to reduce GHG emissions from the use of conventional fossil fuels, climate change would also have impacts on the potential GHG emissions reductions resulting from the use of these renewable biofuels. However, the magnitude of the impact largely depends on the biofuel processing technology and the energy crop (feedstock) type.     

Leaf carbon assimilation in a water-limited world

Abstract

Over the past 150 years the amount of CO₂ in the atmosphere has been increasing, largely as a result of land-use change and anthropogenic emissions from the burning of fossil fuels. It is estimated that the atmospheric [CO₂] will reach 70 Pa by the end of the 21st Century. The most important consequence of this rise in [CO₂] is warming the surface temperature of the Earth by 0.4 – 0.6°C per decade throughout the 21st Century. Increasing [CO₂] along with associated changes in temperature will most likely alter the structure and function of agro-ecosystems, affecting their productivity and their role as stable sinks to CO₂ sequestration. Both CO₂ and temperature are key variables affecting plant growth, development and functions. Moreover, because of the future scenario of higher temperature and evaporative demand, drought occurrences will be increased in frequency, intensity, and erratic pattern. The combination of elevated temperatures and the increased incidence of environmental stress will probably constitute the greatest risk caused by climate change to the agro-ecosystems in arid or semiarid areas of the world. The purpose of this paper is to review the exchange of carbon driving the main ecophysiological processes of plants in response to climate change and environmental stresses. Drought and salinity first affect the acquisition of CO₂ by increasing stomatal and mesophyll resistances, and only after cause irreversible damages to the biochemical apparatus. Heat stress denatures thylakoid membranes, but this action may be counteracted by the synthesis of many isoprenoids in the chloroplasts from carbon freshly fixed by photosynthesis. There is rising concern about the impact of environmental stress on tree growth with this future scenario of global climate change. The combination of elevated temperatures and the increased incidence of environmental stress (particularly drought and salinity) will probably constitute the greatest risk caused by global climate change to the forest ecosystems in arid or semiarid areas of the world.     

Estimation of the carbon dioxide (CO2) fertilization effect using growth rate anomalies of CO2 and crop yields since 1961

The effect of elevated carbon dioxide (CO₂) on crop yields is one of the most uncertain and influential parameters in models used to assess climate change impacts and adaptations. A primary reason for this uncertainty is the limited availability of experimental data on CO₂ responses for crops grown under typical field conditions. However, because of historical variations in CO₂, each year farmers throughout the world perform uncontrolled yield ‘experiments’ under different levels of CO₂. In this study, measurements of atmospheric CO₂ growth rates and crop yields for individual countries since 1961 were compared to empirically determine the average effect of a 1 ppm increase of CO₂ on yields of rice, wheat, and maize. Because the gradual increase in CO₂ is highly correlated with major changes in technology, management, and other yield controlling factors, we focused on first differences of CO₂ and yield time series. Estimates of CO₂ responses obtained from this approach were highly uncertain, reflecting the relatively small importance of year‐to‐year CO₂ changes for yield variability. Combining estimates from the top 20 countries for each crop resulted in estimates with substantially less uncertainty than from any individual country. The results indicate that while current datasets cannot reliably constrain estimates beyond previous experimental studies, an empirical approach supported by large amounts of data may provide a potentially valuable and independent assessment of this critical model parameter. For example, analysis of reliable yield records from hundreds of individual, independent locations (as opposed to national scale yield records with poorly defined errors) may result in empirical estimates with useful levels of uncertainty to complement estimates from experimental studies.     

Climate-induced land health risk in farmland systems: A case study of Qarasou sub-basin in Karkheh River Basin

The present study was carried out to investigate the impact of climate change on land suitability for agricultural development in a sub-basin of Karkheh River Basin, Iran. For this, land suitability of the sub-basin was evaluated twice; once regardless of the climate change impact, and again by involving the impact of climate change. Simple Limitation Approach was used to evaluate the suitability of the sub-basin for cultivation of winter wheat. According to the results, around 22.57% (124121.16 ha) of the study area is suitable for cropping while the capability of 39.29% (216086.13 ha) of the sub-basin was evaluated to be poor/moderate for this purpose. In this research, in order to investigate the impact of climate change on farmlands, the changing trend of the four variables of maximum and minimum temperature, precipitation, and radiation were stimulated by the year 2039 using downscaled interpolation of IPCM general circulation model under three emission scenarios of A1B, A2, and B1. The stimulation was done by LARS-WG Software. The overlaying was done once more, but this time using the stimulated values. Comparing the current and stimulated land suitability maps revealed the fact that, in the most pessimistic future under A1B scenario, approximately 15.51% (85288.95 ha) of the study area will lose its capability for farming as a result of an increase of 1.3?C in temperature, and a decrease of 20.43% mm in total precipitation. The research finding emphasizes the risk of climate change on land health for farming purposes.     

Carbon for nutrient exchange between arbuscular mycorrhizal fungi and wheat varies according to cultivar and changes in atmospheric carbon dioxide concentration

Arbuscular mycorrhizal fungi (AMF) form symbioses with most crops, potentially improving their nutrient assimilation and growth. The effects of cultivar and atmospheric CO₂ concentration ([CO₂]) on wheat–AMF carbon‐for‐nutrient exchange remain critical knowledge gaps in the exploitation of AMF for future sustainable agricultural practices within the context of global climate change. We used stable and radioisotope tracers (¹⁵N, ³³P, ¹⁴C) to quantify AMF‐mediated nutrient uptake and fungal acquisition of plant carbon in three wheat (Triticum aestivum L.) cultivars. We grew plants under current ambient (440 ppm) and projected future atmospheric CO₂ concentrations (800 ppm). We found significant ¹⁵N transfer from fungus to plant in all cultivars, and cultivar‐specific differences in total N content. There was a trend for reduced N uptake under elevated atmospheric [CO₂]. Similarly, ³³P uptake via AMF was affected by cultivar and atmospheric [CO₂]. Total P uptake varied significantly among wheat cultivars and was greater at the future than current atmospheric [CO₂]. We found limited evidence of cultivar or atmospheric [CO₂] effects on plant‐fixed carbon transfer to the mycorrhizal fungi. Our results suggest that AMF will continue to provide a route for nutrient uptake by wheat in the future, despite predicted rises in atmospheric [CO₂]. Consideration should therefore be paid to cultivar‐specific AMF receptivity and function in the development of climate smart germplasm for the future.