The impact of temperature variability on wheat yields

With current annual production at over 600 million tonnes, wheat is the third largest crop in the world behind corn and rice, and an essential source of carbohydrates for millions of people. While wheat is grown over a wide range of environments, it is common in the major wheat‐producing countries for grain filling to occur when soil moisture is declining and temperature is increasing. Average global temperatures have increased over the last decades and are predicted to continue rising, along with a greater frequency of extremely hot days. Such events have already been reported for major wheat growing regions in the world. However, the direct impact of past temperature variability and changes in averages and extremes on wheat production has not been quantified. Attributing changes in observed yields over recent decades to a single factor such as temperature is not possible due to the confounding effects of other factors. By using simulation modelling, we were able to separate the impact of temperature from other factors and show that the effect of temperature on wheat production has been underestimated. Surprisingly, observed variations in average growing‐season temperatures of ±2 °C in the main wheat growing regions of Australia can cause reductions in grain production of up to 50%. Most of this can be attributed to increased leaf senescence as a result of temperatures >34 °C. Temperature conditions during grain filling in the major wheat growing regions of the world are similar to the Australian conditions during grain filling. With average temperatures and the frequency of heat events projected to increase world‐wide with global warming, yield reductions due to higher temperatures during the important grain‐filling stage alone could substantially undermine future global food security. Adaptation strategies need to be considered now to prevent substantial yield losses in wheat from increasing future heat stress.     

Elucidating the impact of temperature variability and extremes on cereal croplands through remote sensing

Remote sensing‐derived wheat crop yield‐climate models were developed to highlight the impact of temperature variation during thermo‐sensitive periods (anthesis and grain‐filling; TSP) of wheat crop development. Specific questions addressed are: can the impact of temperature variation occurring during the TSP on wheat crop yield be detected using remote sensing data and what is the impact? Do crop critical temperature thresholds during TSP exist in real world cropping landscapes? These questions are tested in one of the world's major wheat breadbaskets of Punjab and Haryana, north‐west India. Warming average minimum temperatures during the TSP had a greater negative impact on wheat crop yield than warming maximum temperatures. Warming minimum and maximum temperatures during the TSP explain a greater amount of variation in wheat crop yield than average growing season temperature. In complex real world cereal croplands there was a variable yield response to critical temperature threshold exceedance, specifically a more pronounced negative impact on wheat yield with increased warming events above 35 °C. The negative impact of warming increases with a later start‐of‐season suggesting earlier sowing can reduce wheat crop exposure harmful temperatures. However, even earlier sown wheat experienced temperature‐induced yield losses, which, when viewed in the context of projected warming up to 2100 indicates adaptive responses should focus on increasing wheat tolerance to heat. This study shows it is possible to capture the impacts of temperature variation during the TSP on wheat crop yield in real world cropping landscapes using remote sensing data; this has important implications for monitoring the impact of climate change, variation and heat extremes on wheat croplands.     

Post‐heading heat stress and yield impact in winter wheat of China

Wheat is sensitive to high temperatures, but the spatial and temporal variability of high temperature and its impact on yield are often not known. An analysis of historical climate and yield data was undertaken to characterize the spatial and temporal variability of heat stress between heading and maturity and its impact on wheat grain yield in China. Several heat stress indices were developed to quantify heat intensity, frequency, and duration between heading and maturity based on measured maximum temperature records of the last 50 years from 166 stations in the main wheat‐growing region of China. Surprisingly, heat stress between heading and maturity was more severe in the generally cooler northern wheat‐growing regions than the generally warmer southern regions of China, because of the delayed time of heading with low temperatures during the earlier growing season and the exposure of the post‐heading phase into the warmer part of the year. Heat stress between heading and maturity has increased in the last decades in most of the main winter wheat production areas of China, but the rate was higher in the south than in the north. The correlation between measured grain yields and post‐heading heat stress and average temperature were statistically significant in the entire wheat‐producing region, and explained about 29% of the observed spatial and temporal yield variability. A heat stress index considering the duration and intensity of heat between heading and maturity was required to describe the correlation of heat stress and yield variability. Because heat stress is a major cause of yield loss and the number of heat events is projected to increase in the future, quantifying the future impact of heat stress on wheat production and developing appropriate adaptation and mitigation strategies are critical for developing food security policies in China and elsewhere.     

Contrasting performance of barley and wheat in a wide range of conditions in Mediterranean Catalonia (Spain)

Despite that the idea of better yield adaptation to low‐yielding conditions of barley than wheat is widespread, there have been few efforts in directly comparing their performance in Mediterranean conditions. We compared wheat and barley regional yields in 41 counties of Catalonia for the period 1992–2004. No differences were clear, particularly at low‐yielding conditions, with a trend for a better wheat performance in relatively high‐yielding environments. We then conducted field experiments during two consecutive seasons, sowing wheat and barley with six levels of nitrogen fertilisation under rainfed conditions (2003–04, experiment I) and two levels of nitrogen fertilisation and two water regimes (rainfed and irrigated) in 2004–05 (experiment II). In experiment I, wheat outyielded barley in treatments that received no N fertiliser (4.58 and 3.60 Mg ha^?1, respectively) indicating that the higher yield potential of wheat was associated with better performance in a condition of relatively low yield. In experiment II, wheat and barley yields were found not to be significantly different across all treatments (2.86 and 2.62 Mg ha^?1, respectively) or in the lowest yielding treatments (1.40 and 1.07 Mg ha^?1, respectively). Therefore, it seems that it may not be universally accepted that under Mediterranean conditions barley would unequivocally behave better than wheat.     

High night temperatures during grain number determination reduce wheat and barley grain yield: a field study

Warm nights are a widespread predicted feature of climate change. This study investigated the impact of high night temperatures during the critical period for grain yield determination in wheat and barley crops under field conditions, assessing the effects on development, growth and partitioning crop‐level processes driving grain number per unit area (GN). Experiments combined: (i) two contrasting radiation and temperature environments: late sowing in 2011 and early sowing in 2013, (ii) two well‐adapted crops with similar phenology: bread wheat and two‐row malting barley and (iii) two temperature regimes: ambient and high night temperatures. The night temperature increase (ca. 3.9 °C in both crops and growing seasons) was achieved using purpose‐built heating chambers placed on the crop at 19:000 hours and removed at 7:00 hours every day from the third detectable stem node to 10 days post‐flowering. Across growing seasons and crops, the average minimum temperature during the critical period ranged from 11.2 to 17.2 °C. Wheat and barley grain yield were similarly reduced under warm nights (ca. 7% °C^?1), due to GN reductions (ca. 6% °C^?1) linked to a lower number of spikes per m². An accelerated development under high night temperatures led to a shorter critical period duration, reducing solar radiation capture with negative consequences for biomass production, GN and therefore, grain yield. The information generated could be used as a starting point to design management and/or breeding strategies to improve crop adaptation facing climate change.     

Variation in cardinal temperatures for germination among wheat (Triticum aestivum) genotypes

In most tropical regions where wheat is grown under irrigation, high temperatures at sowing adversely affect crop establishment and subsequent seedling survival. The objective of this study was to compare wheat (Triticum aestivum) genotypes for their ability to germinate and grow at high temperatures during the seedling stage. Twenty-five seeds each of 14 spring wheat cultivars were placed on moist filter paper at different temperatures (5°C to 40°C) in a one-way thermogradient plate to determine the cardinal temperatures for germination. Rate of germination at each temperature for each genotype was computed as the inverse of time taken for 50% of the seeds to germinate. Rate of germination for each genotype at different temperatures was modelled with temperature to determine the base (t_b), and optimum (t_opt) temperatures. Response of germination to temperature for each genotype was calculated as the slope of a linear regression of the rate of germination on temperature below t_opt. Genotypes differed in their optimum temperatures and Mexipak (= Kalyansona) had the lowest. Range in base temperature among the genotypes was between 0°C and 2°C differences but were not statistically significant though they might be biologically significant. Genotypes differed in their response to temperature with Gomam having the lowest rate, implying that it was slow to respond to increasing temperatures. Debeira and Cham 6 showed a similar response. Three lines which had performed well in spring wheat evaluation trials for moderate rainfall areas under heat stress had the highest response rate. It is concluded that combining higher optimum temperatures with faster response rates would result in better-adapted germplasm for regions where high temperatures persist at sowing.     

Sink-limitation to yield and biomass: a summary of some investigations in spring wheat

Yield potential can be expressed as a product of light interception, radiation use efficiency (RUE), and the partitioning of biomass to grain yield, or harvest index (HI). Traits related to early or late light interception have not been shown to be associated with genetic improvement of spring wheat yield in favourable environments. It is, however, well established that yield improvement is largely a result of increased HI, although the most recent studies comparing genetic progress in HI over time in spring wheat indicate that it has not made any additional progress since the mid 1980s. These observations suggest that future genetic progress in yield will most likely be achieved by focusing on constraints to RUE. Considering the possibility that RUE may be influenced indirectly by sink limitation, it is apparent that biomass may be increased by increasing grain number, for example. Experiments with high yielding spring wheat lines containing the alien translocation 7DL.7Ag showed increased grains m‐2 (15%), yield (12%), and biomass (9%) compared with controls. The translocation was also associated with a larger investment in spike mass at anthesis (15%), more grains/spike (10%), and increased flag‐leaf photosynthetic rate during grain‐filling (20%). The data suggest that increased biomass in 7DL.7Ag lines was due to significantly increased RUE post‐anthesis, as a result of a larger kernel number (sink) that increased the demand for photosynthesis during grain‐filling. The hypothesis that increased photosynthesis and RUE may respond directly to a larger number of grains/spike was tested experimentally by imposing a light treatment during boot stage. The treatment was associated with a small increase (5%) in the proportion of biomass invested in spike mass at anthesis, reflected by on average three extra grains/spike at maturity. The treatment was associated with 25% more yield and 22% more biomass than controls, while carbon assimilation rate measured on flag‐leaves during grainfilling was 10% higher than controls. The results suggest that RUE can be increased indirectly by increasing sink strength and that the current yield limiting process in spring wheat is the determination of kernel number. Experimental data are presented on how spike fertility may be increased through breeding, for example by introgression of the multi‐ovary trait to increase grain number per spikelet. In addition, results of analysis of the physiological bases of genotype × year interaction in high yield environments are presented in the context of how such information can provide a focus for genetic studies of sink limitation.     

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.     

Ozone pollution will compromise efforts to increase global wheat production

Introduction of high‐performing crop cultivars and crop/soil water management practices that increase the stomatal uptake of carbon dioxide and photosynthesis will be instrumental in realizing the United Nations Sustainable Development Goal (SDG) of achieving food security. To date, however, global assessments of how to increase crop yield have failed to consider the negative effects of tropospheric ozone, a gaseous pollutant that enters the leaf stomatal pores of plants along with carbon dioxide, and is increasing in concentration globally, particularly in rapidly developing countries. Earlier studies have simply estimated that the largest effects are in the areas with the highest ozone concentrations. Using a modelling method that accounts for the effects of soil moisture deficit and meteorological factors on the stomatal uptake of ozone, we show for the first time that ozone impacts on wheat yield are particularly large in humid rain‐fed and irrigated areas of major wheat‐producing countries (e.g. United States, France, India, China and Russia). Averaged over 2010–2012, we estimate that ozone reduces wheat yields by a mean 9.9% in the northern hemisphere and 6.2% in the southern hemisphere, corresponding to some 85 Tg (million tonnes) of lost grain. Total production losses in developing countries receiving Official Development Assistance are 50% higher than those in developed countries, potentially reducing the possibility of achieving UN SDG2. Crucially, our analysis shows that ozone could reduce the potential yield benefits of increasing irrigation usage in response to climate change because added irrigation increases the uptake and subsequent negative effects of the pollutant. We show that mitigation of air pollution in a changing climate could play a vital role in achieving the above‐mentioned UN SDG, while also contributing to other SDGs related to human health and well‐being, ecosystems and climate change.     

留茬免耕播种对河西绿洲灌区春小麦出苗和产量的影响

本研究通过田间定位试验,探讨了河西绿洲灌区单作小麦、小麦/玉米间作、小麦/大豆间作3种典型春小麦生产模式下,长期留茬免耕播种对春小麦出苗和产量的影响,为该区域春小麦高效可持续生产提供理论依据。结果表明: 与传统翻耕相比,留茬免耕播种小麦/玉米和小麦/大豆间作的小麦出苗率、出苗均匀度下降明显,降幅分别为3.3%～8.6%、9.6%～20.5%和2.9%～8.8%、10.7%～61.7%;单作小麦的出苗均匀度有所提高,其中2019年显著增加14.9%,而出苗率在2020年显著降低4.2%;3种种植方式下,春小麦麦苗整齐度均有所下降。留茬免耕播种3种种植模式下,春小麦成穗数在收获时均与传统翻耕处理持平,差异不显著。3种模式下的春小麦均可以通过提高穗粒数和千粒重来弱化出苗对产量的影响,在收获时,春小麦籽粒产量的增幅分别为10.3%～12.9%(单作小麦)、10.5%～11.9%(小麦/玉米间作)和10.3%～22.5%(小麦/大豆间作),均达到显著水平。在农田风蚀退化极其严重的河西绿洲灌区,留茬免耕播种是春小麦生产中切实可行的耕作措施。     

Chilling to zero degrees disrupts pollen formation but not meiotic microtubule arrays in Triticum aestivum L.

Throughout the wheat‐growing regions of Australia, chilling temperatures below 2 °C occur periodically on consecutive nights during the period of floral development in spring wheat (Triticum aestivum L.). In this study, wheat plants showed significant reductions in fertility when exposed to prolonged chilling temperatures in controlled environment experiments. Among the cultivars tested, the Australian cultivars Kite and Hartog had among the lowest levels of seed set due to chilling and their responses were investigated further. The developmental stage at exposure, the chilling temperature and length of exposure all influenced the level of sterility. The early period of booting, and specifically the +4 cm auricle distance class, was the most sensitive and corresponded to meiosis within the anthers. The response of microtubules to chilling during meiosis in Hartog was monitored, but there was little difference between chilled and control plants. Other abnormalities, such as plasmolysis and cytomixis increased in frequency, were associated with death of developing pollen cells, and could contribute to loss of fertility. The potential for an above‐zero chilling sensitivity in Australian spring wheat varieties could have implications for exploring the tolerance of wheat flower development to chilling and freezing conditions in the field.     

Effects of experimentally imposed climate scenarios on flowering phenology and flower production of subarctic bog species

Climate scenarios for high‐latitude areas predict not only increased summer temperatures, but also larger variation in snowfall and winter temperatures. By using open‐top chambers, we experimentally manipulated both summer temperatures and winter and spring snow accumulations and temperatures independently in a blanket bog in subarctic Sweden, yielding six climate scenarios. We studied the effects of these scenarios on flowering phenology and flower production of Andromeda polifolia (woody evergreen) and Rubus chamaemorus (perennial herb) during 2 years. The second year of our study (2002) was characterized by unusually high spring and early summer temperatures. Our winter manipulations led to consistent increases in winter snow cover. As a result, average and minimum air and soil temperatures in the high snow cover treatments were higher than in the winter ambient treatments, whereas temperature fluctuations were smaller. Spring warming resulted in higher average, minimum, and maximum soil temperatures. Summer warming led to higher air and soil temperatures in mid‐summer (June–July), but not in late summer (August–September). The unusually high temperatures in 2002 advanced the median flowering date by 2 weeks for both species in all treatments. Superimposed on this effect, we found that for both Andromeda and Rubus, all our climate treatments (except summer warming for Rubus) advanced flowering by 1–4 days. The total flower production of both species showed a more or less similar response: flower production in the warm year 2002 exceeded that in 2001 by far. However, in both species flower production was only stimulated by the spring‐warming treatments. Our results show that the reproductive ecology of both species is very responsive to climate change but this response is very dependent on specific climate events, especially those that occur in winter and spring. This suggests that high‐latitude climate change experiments should focus more on winter and spring events than has been the case so far.     

Yield and water use of wheat (Triticum aestivum) in a Mediterranean environment: Cultivar differences and sowing density effects

Yield of eight wheat cultivars was evaluated under rainfed and irrigated conditions in a Mediterranean environment. Variation in grain yield resulted from variation in both aboveground biomass production and in harvest index. Under rainfed compared to irrigated conditions, grain yield, biomass and days to heading were decreased, whereas harvest index was increased. Grain yield of the different cultivars under rainfed conditions correlated with that under irrigated conditions in one of the two years. Among cultivars, harvest index under rainfed and irrigated conditions were correlated in both years.Water was used more efficiently for biomass production, and equally efficiently for grain production, under irrigated compared to rainfed conditions. Under rainfed conditions, crop water use efficiency was higher for cultivars developed for rainfed environments than for those developed for high-rainfall or irrigated environments. Cultivars with low-rainfall target environments had the lowest evapotranspiration under rainfed conditions. Under rainfed conditions, differences between the cultivar groups in crop water use efficiency corresponded with trends in water use efficiency of individual plants and with the ratio of photosynthesis to transpiration, measured on plants grown in a growth room.Early in the season, water was used more efficiently for biomass production at high sowing densities than at low sowing densities. Through faster biomass production and ground cover a smaller proportion of the evapotranspired water was lost in soil evaporation and a larger proportion was transpired. However, the net effect was a greater water use in the early phases of growth and consequently a lower water availability later in the season, leading to similar yields regardless of sowing density.     

Relationship between Carbon Isotope Discrimination and Grain Yield in Spring Wheat Cultivated under Different Water Regimes

In C₃ plants, carbon isotope discrimination (Δ) has been proposed as an indirect selection criterion for grain yield. Reported correlations between Δ and grain yield however, differ highly according to the analyzed organ or tissue, the stage of sampling, and the environment and water regime. In a first experiment carried out in spring wheat during two consecutive seasons in the dry conditions of northwest Mexico (Ciudad Obregon, Sonora), different water treatments were applied, corresponding to the main water regimes available to spring wheat worldwide, and the relationships between Δ values of different organs and grain yield were examined. Under terminal (post‐anthesis) water stress, grain yield was positively associated with Δ in grain at maturity and in leaf at anthesis, confirming results previously obtained under Mediterranean environments. Under early (pre‐anthesis) water stress and residual moisture stress, the association between grain Δ and yield was weaker and highly depended on the quantity of water stored in the soil at sowing. No correlation was found between Δ and grain yield under optimal irrigation. The relationship between Δ and grain yield was also studied during two consecutive seasons in 20 bread wheat cultivars in the Ningxia region (Northern China), characterized by winter drought (pre‐anthesis water stress). Wheat was grown under rainfed conditions in two locations (Guyuan and Pengyang) and under irrigated conditions in another two (Yinchuan and Huinong). In Huinong, the crop was also exposed to salt stress. Highly significant positive associations were found between leaf and grain Δ and grain yields across the environments. The relationship between Δ and yield within environments highly depended on the quantity of water stored in the soil at sowing, the quantity and distribution of rainfall during the growth cycle, the presence of salt in the soil, and the occurrence of irrigation before anthesis. These two experiments confirmed the value of Δ as an indirect selection criterion for yield and a phenotyping tool under post‐anthesis water stress (including limited irrigation).     

Satellite sun‐induced chlorophyll fluorescence detects early response of winter wheat to heat stress in the Indian Indo‐Gangetic Plains

Extremely high temperatures represent one of the most severe abiotic stresses limiting crop productivity. However, understanding crop responses to heat stress is still limited considering the increases in both the frequency and severity of heat wave events under climate change. This limited understanding is partly due to the lack of studies or tools for the timely and accurate monitoring of crop responses to extreme heat over broad spatial scales. In this work, we use novel spaceborne data of sun‐induced chlorophyll fluorescence (SIF), which is a new proxy for photosynthetic activity, along with traditional vegetation indices (Normalized Difference Vegetation Index NDVI and Enhanced Vegetation Index EVI) to investigate the impacts of heat stress on winter wheat in northwestern India, one of the world's major wheat production areas. In 2010, an abrupt rise in temperature that began in March adversely affected the productivity of wheat and caused yield losses of 6% compared to previous year. The yield predicted by satellite observations of SIF decreased by approximately 13.9%, compared to the 1.2% and 0.4% changes in NDVI and EVI, respectively. During early stage of this heat wave event in early March 2010, the SIF observations showed a significant reduction and earlier response, while NDVI and EVI showed no changes and could not capture the heat stress until late March. The spatial patterns of SIF anomalies closely tracked the temporal evolution of the heat stress over the study area. Furthermore, our results show that SIF can provide large‐scale, physiology‐related wheat stress response as indicated by the larger reduction in fluorescence yield (SIF_yield) than fraction of photosynthetically active radiation during the grain‐filling phase, which may have eventually led to the reduction in wheat yield in 2010. This study implies that satellite observations of SIF have great potential to detect heat stress conditions in wheat in a timely manner and assess their impacts on wheat yields at large scales.     

Genome-wide association study for agronomic and physiological traits in spring wheat evaluated in a range of heat prone environments

Key message

We identified 27 stable loci associated with agronomic traits in spring wheat using genome-wide association analysis, some of which confirmed previously reported studies. GWAS peaks identified in regions where no QTL for grain yield per se has been mapped to date, provide new opportunities for gene discovery and creation of new cultivars with desirable alleles for improving yield and yield stability in wheat.

Abstract

We undertook large-scale genetic analysis to determine marker-trait associations (MTAs) underlying agronomic and physiological performance in spring wheat using genome-wide association studies (GWAS). Field trials were conducted at seven sites in three countries (Sudan, Egypt, and Syria) over 2–3 years in each country. Twenty-five agronomic and physiological traits were measured on 188 wheat genotypes. After correcting for population structure and relatedness, a total of 245 MTAs distributed over 66 loci were associated with agronomic traits in individual and mean performance across environments respectively; some of which confirmed previously reported loci. Of these, 27 loci were significantly associated with days to heading, thousand kernel weight, grain yield, spike length, and leaf rolling for mean performance across environments. Despite strong QTL by environment interactions, eight of the loci on chromosomes 1A, 1D, 5A, 5D, 6B, 7A, and 7B had pleiotropic effects on days to heading and yield components (TKW, SM^?2, and SNS). The winter-type alleles at the homoeologous VRN1 loci significantly increased days to heading and grain yield in optimal environments, but decreased grain yield in heat prone environments. Top 20 high-yielding genotypes, ranked by additive main effects and multiplicative interaction (AMMI), had low kinship relationship and possessed 4–5 favorable alleles for GY MTAs except two genotypes, Shadi-4 and Qafzah-11/Bashiq-1–2. This indicated different yield stability mechanisms due to potentially favorable rare alleles that are uncharacterized. Our results will enable wheat breeders to effectively introgress several desirable alleles into locally adapted germplasm in developing wheat varieties with high yield stability and enhanced heat tolerance.

     

西北干旱区不同海拔高度地区气温变化对春小麦生长的影响

基于1981—2006年西北干旱区高海拔地（民乐站）和低海拔地（张掖站）农业气象观测站的观测资料,对民乐站和张掖站的气温变化及其对春小麦生长发育和产量的影响进行了研究.结果表明：研究期间,民乐站、张掖站的气温均呈增加趋势,且高海拔地区的增温幅度大于低海拔地区;民乐站春小麦对气温变暖的响〖JP2〗应表现为生育期缩短、产量增加,张掖站春小麦对气温变暖的响应表现为生育期缩短、产量下降;春小麦生育期内日均气温每升高1 ℃,民乐站和张掖站春小麦生育期分别缩短8.3 d和3.8 d.民乐站春小麦生育期内最高气温低于30.4 ℃时,春小麦生育期和产量均小幅增加,当超过30.4 ℃时,春小麦生育期缩短、产量下降.     

Predicted responses of arctic and alpine ecosystems to altered seasonality under climate change

Global climate change is already having significant impacts on arctic and alpine ecosystems, and ongoing increases in temperature and altered precipitation patterns will affect the strong seasonal patterns that characterize these temperature‐limited systems. The length of the potential growing season in these tundra environments is increasing due to warmer temperatures and earlier spring snow melt. Here, we compare current and projected climate and ecological data from 20 Northern Hemisphere sites to identify how seasonal changes in the physical environment due to climate change will alter the seasonality of arctic and alpine ecosystems. We find that although arctic and alpine ecosystems appear similar under historical climate conditions, climate change will lead to divergent responses, particularly in the spring and fall shoulder seasons. As seasonality changes in the Arctic, plants will advance the timing of spring phenological events, which could increase plant nutrient uptake, production, and ecosystem carbon (C) gain. In alpine regions, photoperiod will constrain spring plant phenology, limiting the extent to which the growing season can lengthen, especially if decreased water availability from earlier snow melt and warmer summer temperatures lead to earlier senescence. The result could be a shorter growing season with decreased production and increased nutrient loss. These contrasting alpine and arctic ecosystem responses will have cascading effects on ecosystems, affecting community structure, biotic interactions, and biogeochemistry.     

High yields in advanced lines of Pima cotton are associated with higher stomatal conductance, reduced leaf area and lower leaf temperature

Advanced lines of Pima cotton ( Gossypium barbadense L.) bred for higher yield potential and heat resistance have higher stomata conductance and smaller leaf areas than those of obsolete lines. In controlled experiments, five commercial lines of Pima cotton having increasing lint yield and heat resistance showed a gradient of increasing stomatal conductance and decreasing leaf size. In field experiments, heat-sensitive, low yield Pima lines showed a lower stomatal conductance than high yielding, advanced lines. This indicates that selection for high yield potential and heat resistance has imposed a selection pressure for higher stomatal conductance and smaller leaf areas. The higher stomatal conductance and smaller leaf area in the advanced lines resulted in a lower leaf temperature in both controlled environments and in the field. The largest leaf temperature differences between obsolete and advanced lines were observed in the afternoon. These differences coincided with the largest differences in stomatal conductance and the highest air temperatures. Measurements of stomatal conductance and leaf temperature in field-grown progeny from a cross between the advanced line, Pima S-6. and the obsolete line, Pima 32, showed that genetically determined differences in stomatal conductance resulted in corresponding differences in leaf temperature. None of the altered physiological traits were selected for in the breeding program, indicating that selection for the desired agronomic traits imposed selection pressures on the altered physiological traits. The increases in stomatal conductance and decreases in leaf area could represent an integrated response to selection pressures on enhanced evaporative cooling, ensuing from selection for heat resistance.