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Terrestrial ecosystems are expected to experience more intense and longer drought and heat-waves in the future. How these environmental factors and their interaction influence photosynthetic activity and water use efficiency remains, however, an open question. Since the photosynthetic activity determines yield response, we investigated gas-exchange and chlorophyll fluorescence traits of flag leaves in four winter wheat cultivars, including two genotypes widely grown in Central Europe and two genotypes considered as drought tolerant. Pot-grown plants were cultivated under natural field conditions until anthesis (DC 61). Subsequently, the plants were exposed to a set of temperature regimes with daily maxima of 26–41 °C (temperature treatment) and maximum soil water holding capacity above 70% and below 30% (drought treatment) using laboratory growth chambers. Primary photochemical reactions after 7 and 14 days of acclimation, measured as maximum quantum yield of photosystem II photochemistry and total chlorophyll content, showed typical interactions of temperature and water availability resulting in an amplified response under combined influence of drought and temperatures above 35 °C. In contrast, drought and temperature treatment had only minor effects on content of epidermal flavonols. A dominant effect of drought over temperature on stomatal conductance (GSmax) was observed. Although substantial genotype-specific responses were found, reduced stomatal conductance resulted in significant decrease in light-saturated rates of CO2 assimilation (Amax) in all genotypes studied. The GSmax–Amax relationship, however, revealed limitation of CO2 uptake by other, non-stomatal processes at temperatures above 32 °C, particularly in the sensitive genotypes. Strong interaction of combined drought and temperature treatments was found on water use efficiency (WUE). Decline in WUE with increasing temperature was steeper in water-deficit than well-watered plants of all genotypes studied. Our results thus document a strong interactive effect of elevated temperature and drought on photosynthetic carbon uptake. Detected thresholds of sensitivity to combined drought and heat stress will contribute to improved modelling of wheat growth and production under expected future climate conditions.

Heat waves and drought periods are expected to become more frequent due to climate change. This may cause a critical decline in future crop yields. However, insufficient knowledge of the interactive effects of high temperature and drought stress at specific growth stages is the cause of numerous uncertainties in modeling impacts of climate change on field crop growth and yield. Hence, the aim of this study was to investigate the effects of interactions between the short-term exposure (3 and 7 days) of two winter wheat genotypes to elevated temperature and drought stress on yield formation and photosynthetic parameters. Winter wheat plants grown under ambient conditions were subjected to four temperature regimes (with maxima at 26, 32, 35 and 38 °C) and drought in growth chambers at three critical growth stages (beginning of stem elongation – DC 31, beginning of anthesis – DC 61, and medium milk ripe – DC 75). The response of yield formation parameters was obviously modulated by variety and growth stage. Grain number was more affected by drought at DC 31 and by the temperature at DC 61. Grain weight per spike was reduced by drought stress similarly at all growth stages, but the results indicated the increasing sensitivity of this parameter to a temperature at the later growth stage. Although yield parameters only changed slightly with the length of heat and drought stress, the photosynthetic parameters were strongly affected, particularly by longer drought and the interactive effect of high temperature and drought stress. Higher temperature significantly increased the negative impact of drought on CO2 assimilation rate. Photosynthetic parameters were less affected by combined high temperatures and drought stress at DC 61 as compared to other growth stages investigated. The larger effect at the later growth stage (DC 75) can be attributed to induced senescence, among other factors, particularly in the Bohemia variety. The Tobak variety appears to be more tolerant to combined high temperatures and drought stress in terms of photosynthetic parameters. Based on the relationships between heat degree-days (HDD) and grain weight per spike we demonstrated the potential of HDD to integrate length and intensity of heat stress at different growth stages, particularly for estimation effects on yield parameters. It can be summarized that although the short-term combination of high temperatures and drought causes significant reductions in photosynthetic parameters, the impact on yield formation is much lower, indicating fast recovery of photosynthetic processes and compensation in yield formation parameters.

This study focuses on the changes in the yield stability of winter wheat and spring barley over the past 140 years and changes in the weather–yield relationships. The study area is located in the Czech Republic in eastern Central Europe between 48°37′–49°30′N and 15°29′–17°55′E and includes 4900 km2 of arable land within eight districts for which yield data were collected for the years 1869–1913 and 1961–2007. The cropping systems in the region are dominated by rain-fed production of winter wheat, spring barley and winter rape. The yields for winter wheat and spring barley have increased by a factor of 2–3 since the late 19th century, whereas the temperature and precipitation patterns showed trends toward warmer and drier conditions. There was a considerable increase in the inter-annual variability of the absolute yields in the districts. When the variability was evaluated in relative terms (i.e., compared with the yield level), it showed no change or insignificant increases in the warmest and driest regions. The study also found that the sensitivity to inter-seasonal temperature increase was much more pronounced during 1961–2007 than at the end of the 19th century and that an increase of the mean temperature by 1 °C led to yield decreases of up to 11% for winter wheat and up to 10% for spring barley. In contrast, the same temperature increase during the 1869–1913 period would have caused yield decreases of up to 8% and 5%, respectively. In the 1961–2007 period, the negative relationship between the temperature and yields of barley (wheat) was highly significant in seven (eight) of eight districts compared with only four (five) with a much weaker correlation in 1869–1913. During the early period, drier conditions had very small negative or even slightly positive effects on yields, whereas at the end of the 20th century, the May and June drought became a factor that explained a considerable proportion of the yield variability. This was the case especially for spring barley, which is more vulnerable to droughts than is winter wheat. The negative effects of increasing temperature and drought on grain yield were most pronounced in the districts that are currently the warmest and driest. The increasing vulnerability of wheat and barley production to increasing temperatures and droughts over time should be addressed by plant breeders, as there are relatively few adaptation options available to farmers except switching to other crops, which cannot fully substitute for wheat and barley. This study focuses on the changes in the yield stability of winter wheat and spring barley over the past 140 years and changes in the weather–yield relationships. The study area is located in the Czech Republic in eastern Central Europe between 48°37′–49°30′N and 15°29′–17°55′E and includes 4900 km2 of arable land within eight districts for which yield data were collected for the years 1869–1913 and 1961–2007. The cropping systems in the region are dominated by rain-fed production of winter wheat, spring barley and winter rape. The yields for winter wheat and spring barley have increased by a factor of 2–3 since the late 19th century, whereas the temperature and precipitation patterns showed trends toward warmer and drier conditions. There was a considerable increase in the inter-annual variability of the absolute yields in the districts. When the variability was evaluated in relative terms (i.e., compared with the yield level), it showed no change or insignificant increases in the warmest and driest regions. The study also found that the sensitivity to inter-seasonal temperature increase was much more pronounced during 1961–2007 than at the end of the 19th century and that an increase of the mean temperature by 1 °C led to yield decreases of up to 11% for winter wheat and up to 10% for spring barley. In contrast, the same temperature increase during the 1869–1913 period would have caused yield decreases of up to 8% and 5%, respectively. In the 1961–2007 period, the negative relationship between the temperature and yields of barley (wheat) was highly significant in seven (eight) of eight districts compared with only four (five) with a much weaker correlation in 1869–1913. During the early period, drier conditions had very small negative or even slightly positive effects on yields, whereas at the end of the 20th century, the May and June drought became a factor that explained a considerable proportion of the yield variability. This was the case especially for spring barley, which is more vulnerable to droughts than is winter wheat. The negative effects of increasing temperature and drought on grain yield were most pronounced in the districts that are currently the warmest and driest. The increasing vulnerability of wheat and barley production to increasing temperatures and droughts over time should be addressed by plant breeders, as there are relatively few adaptation options available to farmers except switching to other crops, which cannot fully substitute for wheat and barley.

Effective use of water (EUW) was evaluated along with grain yield in the same environment over different years and locations. The root system sizes of sets of winter wheat varieties (20, 20, 20 and 18 varieties in 2007, 2008, 2009 and 2010, respectively) were evaluated by measuring their electric capacity. The RSS results were compared with the yield and grain quality in official variety trials at 20, 22, 23 and 23 stations in 2007, 2008, 2009 and 2010, respectively. All varieties were tested under two conditions with low and high inputs, and in some years they were also tested after late sowing and after unsuitable forecrops at a few stations. The RSS was mostly controlled by the location; the varieties differed significantly, explaining 2.6–15.6% of the variation in RSS, while 1.7–3.9% of the total variation was unexplained. In 2007, a dry year, the RSS was significantly correlated with yield in both variants ( r 2 = 0.285* and 0.284*, respectively) and with yield of starch ( r 2 = 0.248*) at all stations. In 2008, the highest-yielding year, the correlation of RSS with yield at the three stations at the lowest altitude and with the highest temperature was negative ( r = −0.459*). In 2009, the yield was highly significantly correlated at only five locations in medium altitudes, where drought occurred, only in the high input treatment ( r 2 = 0.391**). No relationship between RSS and yield was found in the wet year 2010. The third of the varieties with the greatest RSS had an RSS that was 21% greater than those of the one-third of varieties with the smallest RSS in 2007 and a grain yield 420 kg ha −1 higher. The difference responded to additional use of about 7 mm of subsoil water. The most contrasting varieties showed a yield difference of 860 kg, i.e., approximately 15 mm of subsoil water. We conclude that differences in the EUW expressed as different yields under the same conditions can be partly attributed to different RSSs (probably due to deeper rooting) and can be improved by breeding.

International audience; This study was aimed to develop, test and provide access to a snow cover model for agrometeorological use (snowMAUS) that would rely strictly on the weather data used by all crop simulation models, i.e., diurnal temperature extremes and total daily precipitation. Such snow model can easily be used to preprocess input data in order to account for the presence or absence of snow cover whenever required by the crop modeler, without necessitating the acquisition of additional data. The snow cover model was tested across 65 sites across Austria with considerable variability in elevation (155–3111 m a.s.l.). In addition 7 sites in the Czech Republic were used to evaluate snowMAUS reliability in assessing frost damage to winter wheat crop. For illustration a case study documenting the benefit of coupling snowMAUS with process based crop model (STICS) was also included in the study. The presented work complements previous snow cover modeling studies with its focus on the development of a simple snow cover model for areas under intensive agricultural use (mostly lowlands) with 65% of stations providing weather data being located at altitudes below 800 m. The presented results proved that SnowMAUS can estimate with reasonable precision snow cover presence/absence, and to a large extent snow cover depth. The model also accurately represented seasonal variations in the number of snow days or in the volume of precipitation in the form of snow. The simplicity of the model and the fact that it relies only on the daily data is a great advantage. We have demonstrated that in areas with a high probability of winter temperatures dropping below frost-tolerance thresholds and that tend to have considerable snow cover (e.g., Central Europe), the information about snow cover presence/absence is essential for estimating potential frost damage to winter crops. The snow cover model tested in this study could be easily implemented in most crop growth models and would enhance their performance in the Central European region. The up-to-date version of the model is freely available to users in the scientific community, which should allow for model testing in different climate conditions and application with various types of agrometeorological models