Do Increasing Atmospheric CO2 Concentrations Contribute to Yield Increases of German Crops?

The global atmospheric CO₂-concentration is increasing and there has been an increase in Germany of about 30 ppm from 340 ppm to 370 ppm CO₂ during the last two decades. The hectare yield of many crops has also increased during this time period. The objective of the present study was to estimate whether the past and future change in the atmospheric composition significantly contributes to the increase in hectare yield. Different crop species (beans, Phaseolus vulgaris, cv Pfälzer Juni; spring barley, Hordeum vulgare L., cvs. Alexis and Arena; spring wheat, Triticum aestivum L., cvs. Star and Turbo; maize, Zea mays L., cvs. Bonny and Boss) were grown at ambient (372 ppm) and at slightly elevated CO₂-concentrations (459 ppm and 539 ppm) in open-top chambers and the effect of the different CCVconcentrations on the growth and yield of the plants was measured. The past and future CO₂-effect was estimated from the slope of a linear CO₂-yield curve (percentage increase in yield per ppm CO_2′ 100% at 370 ppm) fitted to the data and those from previous studies on wheat and maize. The percentage increase in yield per ppm CO₂ is insignificant for beans, of borderline significance for silage maize (0.06 % per ppm), and 0.35 % per ppm and 0.26 % per ppm for barley and wheat, respectively. The COj-elevation primarily decreases the tiller dieback of the cereals. Considering the increase in CO₂ of 30 ppm and in the hectare yield of 25 % (barley) and 28 % (wheat) from 1970 to 1990, the contribution of CO₂ to the increase in the agricultural production is estimated to be one fourth up to one half of the increase in hectare yield of spring cereals. Given a recent yearly increase of 2 ppm the future CO_:-related increase in hectare yield is estimated to be about 0.5–0.7% per year.     

CO2 exploitation and genetic diversity in winter varieties of oilseed rape (Brassica napus); varieties of tomorrow

We investigated the CO_2] exploitation and genetic diversity inthree old and three new winter varieties of oilseed rape (Brassicanapus L.). Plants were cultivated in growth chambers with 360 ppmCO₂ and 700 ppm CO₂ under conditions simulating a normalgrowth season. Exposed to elevated CO₂ the stomatal conductance(g_s) and the maximum photosynthesis capacity (A_max) werereduced and the dry biomass and the total seed-number were increased.The response in seed-yield differed among the varieties; it was increased inthree varieties and decreased in three. The analysis of variance (ANOVA)showed that there were Treatment- and Week-effects on the g_s, andthere were Variety-, Week- and Treatment-effects on the A_max. Itwas also evident that there were a Variety- and Variety-agegroup-effect onthe seed-yield, but the Variety-agegroup-effect could not explain theVariety-effect. When either or both covariates (seed-number andbiomass) were included in the model, the covariates themselves had asignificant effect and it became evident that there was a Treatment-effecton the seed-yield.From AFLP (amplified fragment length polymorphism) markers adendrogram was constructed by the UPGMA method (unweightedpair-group method using the arithmetic averages) and [G _ST wascalculated for all possible subsets of the varieties. The three old varietiescomprised the densest cluster and were also more genetically diverse thantwo of the three new varieties. Varieties with clear changes amongCO₂ levels were rather genetically diverse.Thus, the varieties represent different traits, which could be exploited infuture breeding of oilseed rape.     

Elevated [CO2] and warming increase the macronutrient use efficiency and biomass of Stylosanthes capitata Vogel under field conditions

Stylosanthes capitata Vogel is a C3 forage legume widely cultivated in tropical and subtropical pastures. However, the nutrient dynamics of this species under future climate change is unknown. Therefore, this study aimed to evaluate the nutrient content, nutrient accumulation, nutrient use efficiency and growth of S. capitata exposed to increased [CO₂] and temperature under field conditions using two levels of atmospheric [CO₂] (ambient and elevated—600 ppm) and two canopy temperature (ambient and elevated—2°C). Treatments were applied at field conditions, for 30 days, using a free-air carbon dioxide enrichment (FACE) and a free-air temperature-controlled enhancement (T-FACE) systems. Warming showed no effects on macronutrient content, but increased the accumulation of nitrogen, potassium, calcium, magnesium and sulphur, the nutrient use efficiency and root dry mass. Elevated [CO₂] alone had no effect on most of the parameters evaluated. However, the combination of elevated [CO₂] with warming improved the nutrient accumulation, nutrient use efficiency and whole-plant growth more than under isolated conditions of elevated [CO₂] or warming. Based on our short-term results, we concluded that an increment of atmospheric [CO₂] and temperature will benefit S. capitata growth, suggesting no alterations in the actual fertilizer programs for this species.     

Relationship between Frost Tolerance and Cold-Induced Resistance of Spring Barley, Meadow Fescue and Winter Oilseed Rape to Fungal Pathogens

Plants exposed to one stress factor may become more tolerant to another. Cold is the most often documented factor inducing plant resistance to pathogens. The aim of this work was to investigate whether resistance of spring barley and meadow fescue to Bipolaris sorokiniana and resistance of winter oilseed rape to Phoma lingam induced at 5 °C for 2, 4 or 6 weeks are associated with frost tolerance, water potential and soluble carbohydrate content. Cold‐acclimated plants of each species showed increased resistance to the studied pathogens. Barley, fescue and rape plants demonstrated higher frost tolerance after hardening, but only in the case of fescue a correlation between resistance to frost and resistance to B. sorokiniana was found. A significant decrease in the water potential of leaf cells was observed in cold‐acclimated barley and fescue. In these two species, water potential greatly affected resistance to B. sorokiniana. However, only in barley did accumulation of fructose, glucose and sucrose correlate as well with changes in water potential as with cold‐induced resistance to the pathogen. In the case of hardened rape, no correlation between the studied parameters was found. The results obtained indicated that the temperature of 5 °C used during cold acclimation was not favourable for hardening of this plant species.     

Effects of free‐air CO2 enrichment and drought on root growth of field grown maize and sorghum

Increasing CO₂ concentration ([CO₂]) is thought to induce climate change and thereby increase air temperatures and the risk of drought stress, the latter impairing crop growth. The objective of this study was to investigate the effects of elevated [CO₂] and drought stress on root growth of one maize genotype (Zea mays cv. Simao) and two sorghum genotypes (Sorghum bicolor cv. Bulldozer and Sorghum bicolor × Sorghum sudanense cv. Inka) under the cool moderate climate of Central Europe. It was hypothesized that root growth stimulation due to elevated [CO₂] compensates for a reduced root growth under drought stress. Therefore, we established an experiment within a f ree‐a ir c arbon dioxide e nrichment system (FACE) in 2010 and 2011. Sorghum and maize genotypes were grown under ambient [CO₂] (385 ppm CO₂) and elevated [CO₂] (600 ppm CO₂) and in combination with restricted and sufficient water supply. Elevated [CO₂] decreased root length density (RLD) in the upper soil layers for all genotypes, but increased it in deeper layers. Higher [CO₂] enhanced specific root length (SRL) of “Simao” and “Bulldozer,” however, did not affect that of “Inka.” “Simao” achieved a higher SRL than the sorghum genotypes, indicating an efficient investment in root dry matter. Although elevated [CO₂] affected the root growth, no interaction with the water treatment and, consequently, no compensatory effect of elevated [CO₂] could be identified.     

Multi-model uncertainty analysis in predicting grain N for crop rotations in Europe

Realistic estimation of grain nitrogen (N; N in grain yield) is crucial for assessing N management in crop rotations, but there is little information on the performance of commonly used crop models for simulating grain N. Therefore, the objectives of the study were to (1) test if continuous simulation (multi-year) performs better than single year simulation, (2) assess if calibration improves model performance at different calibration levels, and (3) investigate if a multi-model ensemble can substantially reduce uncertainty in reproducing grain N. For this purpose, 12 models were applied simulating different treatments (catch crops, CO₂ concentrations, irrigation, N application, residues and tillage) in four multi-year rotation experiments in Europe to assess modelling accuracy. Seven grain and seed crops in four rotation systems in Europe were included in the study, namely winter wheat, winter barley, spring barley, spring oat, winter rye, pea and winter oilseed rape. Our results indicate that the higher level of calibration significantly increased the quality of the simulation for grain N. In addition, models performed better in predicting grain N of winter wheat, winter barley and spring barley compared to spring oat, winter rye, pea and winter oilseed rape. For each crop, the use of the ensemble mean significantly reduced the mean absolute percentage error (MAPE) between simulations and observations to less than 15%, thus a multi–model ensemble can more precisely predict grain N than a random single model. Models correctly simulated the effects of enhanced N input on grain N of winter wheat and winter barley, whereas effects of tillage and irrigation were less well estimated. However, the use of continuous simulation did not improve the simulations as compared to single year simulation based on the multi-year performance, which suggests needs for further model improvements of crop rotation effects.     

Photosynthetic Acclimation and Productivity of Mungbean Cultivars under Elevated CO2 Concentration

Mungbean [Vigna radiata (L.) Wilczek] cultivars (Pusa Baisakhi, PS 16 and P 105) were grown in field at atmospheric (360 ± 10 ppm, AC) and elevated CO₂ (650 ± 50 ppm, EC) concentrations inside open top chambers for entire period of growth and development till maturity. Leaf net photosynthesis rate (P_N) of AC and EC grown plants when compared at same CO₂ concentration showed no significant down‐regulation of P_N in EC plants. In cv. P 105, even up‐regulation of P_N was observed in EC plants. Mungbean cultivars accumulated assimilates in the leaves during the day mostly in the form of starch. Nodule number and weight were also higher in EC plants. The positive effect of elevated CO₂ on P_N, dry‐matter production and seed yield was better expressed in cv. P 105 having greater podding ability.     

江苏省冬油菜生育期内低温事件的年际变化及对产量的影响

为探讨气候变化对我国油菜生产带来的可能影响,选取江苏省地区52个气象站1961—2012年日气温资料及冬油菜产量逐年数据,采用M-K趋势检验探求冬春季节8种低温指数的变化趋势,并依托一阶差分法探讨低温指数与产量的数量关系。结果表明：（1）1961-2012年间省内大部分地区冬春季节低温事件的总天数、连续低温事件的场次、强度及持续性呈现出显著的减弱趋势;（2）不同类型低温指数中,FI1（越冬期日最低气温<-5℃的总天数）与CI4（蕾薹期连续日最低气温<0℃天气的最长持续时间）对冬油菜产量的负效应最为显著;（3）各站点产量对FI1及CI4敏感性分析表明江苏省北部地区冬油菜种植对低温灾害事件更为敏感;（4）1961-2012年间江苏大部分地区FI1及CI4的减少趋势给研究区冬油菜产量带来了一定幅度的增产。     

Heterosis and epistasis in rapeseed estimated from generation means

Summary Heterosis and epistasis in spring oilseed rape (Brassica napus L.) was analysed by comparing generation means for ten agronomic traits. Parents, F₂, F₃ and F₆ generations of four crosses with Swedish and French material were investigated. The F₂ was 11% higher in yield, earlier in flowering time, and slightly later in maturation when compared with the parents. Randomly derived single seed descent lines had an 8% lower yield, were later flowering and maturing than the parents in F₆. This poorer average performance of recombinant lines is explained by the loss of favourable epistatic interactions present in the parents.     

Field experiments and simulation to evaluate rice cultivar adaptation to elevated carbon dioxide and temperature in sub-tropical India

Location specific adaptation option is required to minimize adverse impact of climate change on rice production. In the present investigation, we calibrated genotype coefficients of four cultivars in the CERES-Rice model for simulation of rice yield under elevated CO₂ environment and evaluation of the cultivar adaptation in subtropical India. The four cultivars (IR 36, Swarna, Swarn sub1, and Badshabhog) were grown in open field and in Open Top Chamber (OTC) of ambient CO₂ (≈390 ppm) and elevated CO₂ environment (25% higher than the ambient) during wet season (June–November) of the years 2011 and 2012 at Kharagpur, India. The genotype coefficients; P1 (basic vegetative phase), P2R (photoperiod sensitivity) and P5 (grain filling phase) were higher, but G1 (potential spikelet number) was lower under the elevated CO₂ environment as compared to their open field value in all the four cultivars. Use of the calibrated model of elevated CO₂ environment simulated the changes in grain yield of −13%, −17%, −4%, and +7% for the cultivars IR 36, Swarna, Swarna sub1, and Badshabhog, respectively, with increasing CO₂ level of 100 ppm and rising temperature of 1 °C as compared to the ambient CO₂ level and temperature and they were comparable with observed yield changes from the OTC experiment. Potential impacts of climate change were simulated for climate change scenarios developed from HadCM3 global climate model under the Intergovernmental Panel on Climate Change Special Report on Emission Scenarios (A2 and B2) for the years 2020, 2050, and 2080. Use of the future climate data simulated a continuous decline in rice grain yield from present years to the years 2020, 2050 and 2080 for the cultivars IR 36 and Swarna in A2 as well as B2 scenario with rising temperature of ≥0.8 °C. Whereas, the cultivar Swarna sub1 was least affected and Badshabhog was favoured under elevated CO₂ with rising temperature up to 2 °C in the sub-tropical climate of India.     

Apical Development and Growth of Barley under Different CO2 and Nitrogen Regimes

Increases in atmospheric carbon dioxide (CO₂) concentration have stimulated interest in the response of agricultural crops to elevated levels of CO₂. Several studies have addressed the response of C₃ cereals to CO₂, but the interactive effect of nutrient supply and CO₂ on apical development and spikelet set and survival has not been investigated thoroughly. Hence, an experiment was conducted in the greenhouse to evaluate the effect of high (700 μmol CO₂mol^?1 air) and low (400 μmol mol^?1) levels of atmospheric CO₂ on apical development, spikelet set and abortion, and pre- and post-anthesis growth in spring barley (Hordeum vulgare L.) grown under high N (0.3 g N pot^?1 before sowing ?1–0.11 g N pot^?1 week^?1) and low N (0.3 g N pot^?1) regimes. The plants were grown in 5 L pots. Development of spike was hastened due to CO₂ enrichment, and the C+ plants pollinated few days earlier than the C— plants. Carbon dioxide enrichment had no effect on date of ripening. Development of spike slowed following application of extra N, and plants pollinated 10 days later and matured 2 weeks later when compared with plants under low N. Carbon dioxide enrichment did not affect the number of spikelets at anthesis. Excess N decreased spikelet abortion and the increased maximum number of spikelets under both [CO₂]. Barley plants did not tiller when grown in low [CO₂] and low N. Increased endogenous IAA concentration in those plants, recorded three days before tillers appeared in other treatments, may have contributed to this. Carbon dioxide enrichment increased the C concentration of plants, but decreased the N concentration under high N regime. Both the C and N concentration of plants were increased under high N regime. Carbon dioxide enrichment increased the total dry matter of mature plants by 9 % under high N regime and by 21 % under low N regime. Under high [CO₂] increased kernel number on tiller spikes, and increased kernel weight both on main stem and on tiller spikes resulted in a 23 % increase in kernel yield under low N regime and 76 % increase in kernel yield under high N regime. The rate of N application influenced growth and yield components to a greater extent than CO₂ enrichment. At maturity, plant dry matter, kernel weight, the number of kernels per spike, and the number of spikes per plant were higher under high N regime than under low N regime. Long days (16 h), low light intensity (280 μmol m^?2s^?1), and at constant temperature of 20 °C high [CO₂] increased kernel weight and the number of kernels on tiller spikes under high and low N application rate, but did not increase the number of kernels on main stem spike, or the number of tillers or tiller spikes per plant.     

气候变化对重庆油菜生产的影响

为了研究重庆特殊的生态气候条件与油菜生产发展的关系,基于重庆1983—2013年气象资料和油菜生产状况,分析重庆近30年来气候变化特征及其对油菜生产的影响。结果表明：分析期内重庆年平均气温变化呈现显著的曲线上升趋势,日照时数呈现显著减少趋势（在0.05水平上通过显著性检验）;重庆近30年降雨量突变发生比较频繁,线性变化趋势不明显,但相邻年份间降水量差异较大,1998年降水量为1363.5 mm是分析期内降水量最多的一年,以此为突变点,此后呈下降趋势。菌核病发病指数与3月和4月平均气温相关系数为-0.682^*达显著水平,菌核病发病指数与降雨量和日照时数相关性不显著;重庆油菜面积与温度呈显著负相关(P=-0.568^*),单产与温度相关性不显著。日照时数与油菜单产呈显著负相关(P=-0.544^*),与油菜面积相关性不显著。降雨量的线性变化趋势不明显,而且相邻年份间降水量差异较大,与油菜面积和单产相关性均不显著。     

Yield,growth and grain nitrogen response to elevated CO2 in six lentil (Lens culinaris) cultivars grown under Free Air CO2 Enrichment (FACE) in a semi-arid environment

Atmospheric CO₂ concentrations ([CO₂]) are predicted to increase from current levels of about 400 ppm to reach 550 ppm by 2050. The direct benefits of elevated [CO₂] (e[CO₂]) to plant growth appear to be greater under low rainfall conditions, but there are few field (Free Air CO₂ Enrichment or FACE) experimental set-ups that directly address semi-arid conditions. The objectives of this study were to investigate the following research questions: 1) What are the effects of e[CO₂] on the growth and grain yield of lentil (Lens culinaris) grown under semi-arid conditions under FACE? 2) Does e[CO₂] decrease grain nitrogen in lentil? and 3) Is there genotypic variability in the response to e[CO₂] in lentil cultivars? Elevated [CO₂] increased yields by approximately 0.5 t ha⁻¹ (relative increase ranging from 18 to 138%) by increasing both biomass accumulation (by 32%) and the harvest index (by up to 60%). However, the relative response of grain yield to e[CO₂] was not consistently greater under dry conditions and might depend on water availability post-flowering. Grain nitrogen concentration was significantly reduced by e[CO₂] under the conditions of this experiment. No differences were found between the cultivars selected in the response to elevated [CO₂] for grain yield or any other parameters observed despite well expressed genotypic variability in many traits of interest. Biomass accumulation from flowering to maturity was considerably increased by elevated [CO₂] (a 50% increase) which suggests that the indeterminate growth habit of lentils provides vegetative sinks in addition to reproductive sinks during the grain-filling period.     

Degradation of oxalic acid by transgenic oilseed rape plants expressing oxalate oxidase

Summary Oxalic acid is thought to have a primary role in the pathogenicity of several plant pathogens, notably Sclerotinia selerotiorum. A gene coding for the enzyme oxalate oxidase was isolated from barley roots and introduced into oilseed rape as a means of degrading oxalic acid in vivo. This report describes the production of several transgenic plants of oilseed rape and the characterisation of these plants by Southern, Western and enzyme activity assays. Plants were shown to contain an active oxalate oxidase enzyme and were tolerant of exogenously supplied oxalic acid.     

Effects of CO2 Enrichment and Drought on Photosynthesis,Growth and Yield of an Old and a Modern Barley Cultivar

Susceptibility of crops to drought may change under atmospheric CO₂ enrichment. We tested the effects of CO₂ enrichment and drought on the older malting barley cultivar Golden Promise (GP) and the recent variety Bambina (BA). Hypothesizing that CO₂ enrichment mitigates the adverse effects of drought and that GP shows a stronger response to CO₂ enrichment than BA, plants of both cultivars were grown in climate chambers. Optimal and reduced watering levels and two CO₂ concentrations (380 and 550 ppm) were used to investigate photosynthetic parameters, growth and yield. In contrast to expectations, CO₂ increased total plant biomass by 34 % in the modern cultivar while the growth stimulation was not significant in GP. As a reaction to drought, BA showed reduced biomass under elevated CO₂, which was not seen in GP. Grain yield and harvest index (HI) were negatively influenced by drought and increased by CO₂ enrichment. BA formed higher grain yield and had higher water‐use efficiency of grain yield and HI compared to GP. CO₂ fertilization compensated for the negative effect of drought on grain yield and HI, especially in GP. Stomatal conductance proved to be the gas exchange parameter most sensitive to drought. Photosynthetic rate of BA showed more pronounced reaction to drought compared to GP. Overall, BA turned out to respond more intense to changes in water supply and CO₂ enrichment than the older GP.     

Elevated CO2 modulates the effects of drought and heat stress on plant water relations and grain yield in wheat

To investigate the interactive effects of drought, heat and elevated atmospheric CO₂ concentration ([CO₂]) on plant water relations and grain yield in wheat, two wheat cultivars with different drought tolerance (Gladius and Paragon) were grown under ambient and elevated [CO₂], and were exposed to post‐anthesis drought and heat stress. The stomatal conductance, plant water relation parameters, abscisic acid concentration in leaf and spike, and grain yield components were examined. Both stress treatments and elevated [CO₂] reduced the stomatal conductance, which resulted in lower leaf relative water content and leaf water potential. Drought induced a significant increase in leaf and spike abscisic acid concentrations, while elevated [CO₂] showed no effect. At maturity, post‐anthesis drought and heat stress significantly decreased the grain yield by 21.3%–65.2%, while elevated [CO₂] increased the grain yield by 20.8% in wheat, which was due to the changes of grain number per spike and thousand grain weight. This study suggested that the responses of plant water status and grain yield to extreme climatic events (heat and drought) can be influenced by the atmospheric CO₂ concentration.     

Effect of free air carbon dioxide enrichment combined with two nitrogen levels on growth,yield and yield quality of sugar beet: Evidence for a sink limitation of beet growth under elevated CO2

The increase in atmospheric CO₂ concentration [CO₂] has been demonstrated to stimulate the growth of C₃ crops. However, little information exists about the effect of elevated [CO₂] on biomass production of sugar beet, and data from field experiments are lacking. In this study, sugar beet was grown within a crop rotation over two rotation cycles (2001, 2004) at present and elevated [CO₂] (375 μl l^?1 and 550 μl l^?1) in a free air CO₂ enrichment (FACE) system and at two levels of nitrogen supply [high (N2), and 50% of high (N1)], in Braunschweig, Germany. The objective of the present study was to determine the CO₂ effect on seasonal changes of leaf growth and on final biomass and sugar yield. Shading treatment was included to test whether sugar beet growth is sink limited under elevated [CO₂]. CO₂ elevation did not affect leaf number but increased individual leaf size in early summer resulting in a faster row closure under both N levels. In late summer CO₂ enrichment increased the fraction of senescent leaves under high but not low N supply, which contributed to a negative CO₂ effect on leaf area index and canopy chlorophyll content under high N at final harvest. Petioles contained up to 40% water-soluble carbohydrates, which were hardly affected by CO₂ but increased by N supply. More N increased biomass production by 21% and 12% in 2001 and 2004, respectively, while beet and sugar yield was not influenced. Concentration of α-amino N in the beet fresh weight was increased under low N and decreased under high N by CO₂ enrichment. The CO₂ response of total biomass, beet yield and white sugar yield was unaffected by N supply. Averaged over both N levels elevated [CO₂] increased total biomass by 7% and 12% in 2001 and 2004, respectively, and white sugar yield by 12% and 13%. The shading treatment in 2004 prevented the decrease in leaf area index under elevated [CO₂] and high N in September. Moreover, the CO₂ effect on total biomass (24%) and white sugar yield (28%) was doubled as compared to the unshaded conditions. It is concluded that the growth of the storage root of sugar beet is not source but sink limited under elevated [CO₂], which minimizes the potential CO₂ effect on photosynthesis and beet yield.     

Using Hemispherical Radiation Measurements to Predict Weight-Related Growth Traits in Oilseed Rape (Brassica napus L.) and Barley (Hordeum vulgare L.) Canopies

Methods for determining growth traits in the field are mostly work‐intensive and/or often erroneous. Further development of multi‐temporal techniques of growth analyses provided by fast and non‐destructive tools for monitoring canopy properties may result in a substantial gain for practical use. Among them, the LAI‐2000 Canopy Analyzer can be used to determine the canopy area index (CAI) resulting from radiation measurements. In plant breeding, single‐date measurements were usually made across a wide number of genoptypes. In contrast, multi‐temporal information on canopy status is needed in agronomy. In our study, data of the CAI based on hemispherical radiation measurements with the LAI‐2000 were used to estimate developmental courses of weight‐related growth traits. For this purpose, seasonal courses of shoot fresh matter, shoot dry matter, shoot N and water content and CAI of winter oilseed rape (Brassica napus L.) and spring barley (Hordeum vulgare L.) were investigated simultaneously in field experiments from 2002 to 2006 in northern Germany with and without nitrogen (N) fertilization. Courses of 2003 and 2004 were used to calculate relationships between CAI and growth traits. Results show that each of the weight‐related growth trait is related to the CAI. In this mechanistic approach relationships were found gathered across 2 years, two N‐treatments and several growth stages being unaffected by N‐fertilization, cultivar and experimental year. These relationships were verified using independent data sets of the years 2005 (winter oilseed rape and spring barley) and 2006 (winter oilseed rape). The results of the current study show that the use of LAI‐2000 and its rapid and non‐destructive determination of weight‐related growth traits over the entire growth period will substantially improve the determination of weight‐related growth traits in agriculture.     

Competition Affects the Production of First Backcross Offspring on F1-hybrids, Brassica Napus × B. Rapa

Summary Interspecific F₁-hybrids may arise in fields with transplastomic oilseed rape where B. rapa occurs as a weed. Spilled seeds, including transplastomic F₁-hybrids with B. rapa, may germinate, which creates an opportunity for production of transplastomic BC₁ with B. rapa as father (BC_1r). Field trials were made with three different proportions of B. napus, B. rapa and F₁-hybrids and three different densities. Contrary to most studies on how plant competition affects introgression between oilseed rape and B. rapa, this study focused on offspring produced on F₁-hybrids, where the F₁-hybrids had oilseed rape as maternal parent. We estimated the BC_1r production in all combinations of proportion and density, and found that B. rapa sired from 0.6–7.8% of the offspring. At the proportion with the highest abundance of F₁-hybrids the entire paternity was assessed. There was a significant density effect on the production of BC_1r but the effect differed among proportions. Both the highest and lowest frequencies of BC_1r were obtained at high plant density. Neither the proportion nor density affected the number of BC_1r per square-meter significantly. Biomass components decreased significantly from low to intermediate density, whereas a further increase in density only affected the thousand-seed weight significantly. On the basis of the results from the present experiment we conclude that introgression of transgenes from transplastomic oilseed rape to B. rapa seems most likely at current field densities of B. napus, and when B. rapa is an abundant weed.     

Does interspecific competition change the barley's response and recovery from heat wave?

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.