The factors of global climate change specifically affect crop and weed performance. Peas (Pisum sativum L.), spring barley (Hordeum vulgare L.), and wild mustard (Sinapis arvensis L.) were exposed to elevated atmospheric CO2 concentration ([CO2]) (1400 or 700 vs. 400 μmol mol−1) and air temperature (25/18 vs. 21/14°C, day/night) to study the single and combined effects on plant growth, photosynthetic performance, and carbohydrate metabolism. Significantly greater stimulation of the photosynthetic rate was determined at the corresponding growth CO2 concentration (Agrowth), and water use efficiency (WUE) and biomass production were detected for crops than for weed exposed to elevated [CO2]. The possibilities to translocate total soluble sugars (TSS) and starch into roots are considerably higher for crop species, especially N2–fixing pea plants compared with wild mustard, while the accumulation of photosynthates in leaves of wild mustard led to higher photosynthetic downregulation and considerably lower stimulation of Agrowth. Moreover, an increase in WUE was completely eliminated at 4°C above ambient air temperature ([25/400]) in wild mustard grown under elevated [CO2], while crops still maintained slightly higher WUE. These findings suggest that investigated crop species, especially pea plants, have higher advantage than weed under rising [CO2], and this benefit is detected to be even higher under elevated [CO2] and temperature.

Different species have different sensitivity to heat waves; therefore, interspecific competition may affect the crop response to heat waves. We investigated the effects of heat waves on spring barley (Hordeum vulgare L.) grown with and without wild mustard (Sinapis arvensis L.) as well as the recovery of barleys from stress. The plants were exposed to a 7‐day 35/28ºC (day/night) heat wave at ambient CO2 (400 μmol/mol) and elevated CO2 (800 μmol/mol). All seedlings were rehydrated and returned to control conditions (21/14ºC, CO2 400 μmol/mol) after the cease of heat wave and grown for a 7‐day period of recovery. Heat wave had more pronounced negative effect on the barley's aboveground biomass under competition with mustard, whereas the response of root biomass was not influenced by the presence of weeds. The heat wave induced reductions in barley's photosynthetic rate, stomatal conductance and water use efficiency under interspecific competition were higher compared to monocultured conditions. Interspecific competition impaired and delayed the recovery of barley's biomass production and leaf gas exchange parameters after heat wave. Elevated CO2 slightly mitigated negative heat wave impact on the growth and leaf gas exchange parameters but had no effect during the recovery period.

Intensity and frequency of heat waves (HW) accompanied by drought are increasing, however, still little is known about its effect on forage plants. A pot experiment was carried out in growth chambers in order to elucidate the multiple response of forage rape to combined HW and drought (HD) under current and elevated CO2 (HD + CO2). Forage rape was proved to be relatively HD‐resistant plant, with no significant and long‐term effects on shoot growth and photosynthetic performance, and effective stimulation of antioxidative system, especially in the case of HD + CO2 exposure. Activities of enzymes of ascorbate–glutathione cycle were further stimulated by elevated CO2 even after the termination of HD treatment. Nutritive value of forage rape was also positively affected, as was shown by elevated content of water‐soluble carbohydrates after exposure and starch after the period of recovery (up to 80% and 92%, respectively). Concentrations of most macro‐ and microelements were increased, and stabilized higher or equalized to control level after the period of recovery in a similar pattern for HD and HD + CO2 exposure. However, content of Ca was reduced and remained significantly lower (~20%). One of the most important negative and lagged HD effects was reduction of dry root biomass (~30%), most possibly induced by accumulation of non‐structural carbohydrates in shoot and was not mitigated by elevated CO2. To conclude, forage rape was proved to be a promising forage crop for the future climate with increased frequency of HWs; however, a special attention should be paid to the lagged effects, such as inhibition of root growth.

This work focuses on the investigation of competition interaction between C 3 crop barley (Hordeum vulgare L.) and C 4 weed barnyard grass (Echinochloa crus-galli L.) at 2 times higher than ambient [CO 2 ] and +4 0 C higher ambient temperature climate conditions. It was hypothesized that interspecific competition will change the response of the investigated plants to increased [CO 2 ] and temperature. The obtained results showed that in the current climate conditions, a higher biomass and photosynthetic rate and a lower antioxidant activity were detected for barley grown under interspecific competition effect. While in the warmed climate and under competition conditions opposite results were detected: a higher water use efficiency, a higher photosynthetic performance, a lower dissipated energy flux and a lower antioxidant enzymes activity were detected for barnyard grass plants. This study highlights that in the future climate conditions, barnyard grass will become more efficient in performance of the photosynthetic apparatus and it will suffer from lower oxidative stress caused by interspecific competition as compared to barley.

Estimated anthropogenic global warming is currently increasing at 0.2°C per decade and will likely reach 1.5°C between 2030 and 2050 (Pishva et al., 2020). As a result, the evapotranspiration rate is enhanced and therefore increases the likelihood of drought stress in plants (Yang et al., 2010). Drought frequency and intensity in drylands is projected to increase from 1% to 30% by 2100 (Dai, 2013). Globally, about one-third of the land area is affected by drought (Pishva et al., 2020). It is a major threat and the most unpredictable constraint, causing considerable adverse effects on crop production worldwide (Anjum et al., 2017;Hussain et al., 2018).These effects include a variety of plant functional and biochemical disorders, such as reduction in the rate of carbon uptake and turgor, increased oxidative damage, changes in leaf gas exchange, activity of enzymes and ion balance, resulting in impaired development, growth