Contrasting Water Regimes Research Articles

Response on root regrowth potential to soil moisture in Sedum species during winter in Særheim, Norway

PurposeThe impact of winter moisture on root metabolism and root integrity has potential consequences for the geographical distribution of drought-adapted succulent species and for their long-term performance on green roofs. The interacting effects of soil characteristics and precipitation frequency on root mortality under winter conditions and the potential to grow new roots in spring were evaluated for six Sedum species under controlled conditions. MethodsTo test for the impact of soil moisture during winter on root regrowth potential in six Sedum species, we used a combination of two substrates with differing water-holding capacity and four contrasting watering regimes. Specially, for the fine and coarse substrates, total pore volume was 42 and 46 %, respectively, and maximum water-holding capacity (i.e. field capacity) was 0.50 and 0.33 kg water per L, respectively. The four watering treatments involved overhead watering to runoff (approx. 10 mm): once every second week, once a week, three times per week and three times per week with 1 cm standing water in trays from January to March 2019. ResultsIt was found that winter soil moisture had no major impact on root mortality or root regrowth potential in spring. Root mortality was not affected by watering frequency and regrowth potential showed no directional response to increased watering frequency, although species-specific responses were involved. Root diameter did not differ between the substrates, but there were some differences between the species. Sedum rupestre had on average the thickest roots (0.17 mm), followed by S. acre, S. anglicum and S. sexangulare (0.15–0.16 mm), while S. album and S. hispanicum had the thinnest roots (0.12–0.13 mm). Moreover, effects of watering frequency on root mortality and regrowth potential were not influenced by soil water-holding capacity across species. We concluded that winter soil moisture had no negative effects on root performance within the range of treatments tested here. ConclusionsRoot response to transient waterlogging or moist but unsaturated soil may not be an important mechanism for determining the survival and distribution of temperate Sedum species during winter.

Trade-offs between grain number, grain weight and fruiting efficiency of different bread wheat genotypes in response to anthesis drought stress

Cereal crops in Morocco are mainly cultivated under rainfed conditions of dryland regions. Under these conditions, they are mostly exposed to drought stress that affects different yield components. We studied the effect of anthesis drought stress on the relationships among the components of grain number (GN), thousand grains weight (TGW), fruiting efficiency (FE) and yield. And we examined fruiting efficiency (FE= grains set per g of spike dry weight at anthesis) as promising trait for further increasing yield without compromising yield components. Greenhouse experiments were conducted on 2019/2020, 2020/2021 and 2021/2022 cropping seasons. Two contrasting water regimes, irrigated and stressed treatments at anthesis growth stage were assessed. Results showed that anthesis drought stress affects negatively all components studied. Substantial decrease of 10%, 16%, 9% and 34% were recorded for GN, TGW, FE, and yield, respectively, under water stress compared to irrigated treatments. Two genotypes, namely 15/42 and Achtar, were found to be the most adapted to both stressed and irrigated conditions. Under stressed conditions yield becomes less correlated with GN (r = 0.36) and FE (r = 0.37) and more correlated with TGW (r = 0.56*). GN becomes less correlated with FE (r = 0.02) and TGW (r = -0.14). While, FE becomes more correlated with TGW (r = 0.73*). To the extent of this study, FE was found as promising selection criterion under stress conditions without compromising TGW component.

Dynamic physiological response of tef to contrasting water availabilities.

Global climate change is leading to increased frequency of extreme climatic events, higher temperatures and water scarcity. Tef (Eragrostis tef (Zucc.) Trotter) is an underutilized C4 cereal crop that harbors a rich gene pool for stress resilience and nutritional quality. Despite gaining increasing attention as an "opportunity" crop, physiological responses and adaptive mechanisms of tef to drought stress have not been sufficiently investigated. This study was aimed to characterize the dynamic physiological responses of tef to drought. Six selected tef genotypes were subjected to high-throughput whole-plant functional phenotyping to assess multiple physiological responses to contrasting water regimes. Drought stress led to a substantial reduction in total, shoot and root dry weights, by 59%, 62% and 44%, respectively (averaged across genotypes), and an increase of 50% in the root-to-shoot ratio, relative to control treatment. Drought treatment induced also significant reductions in stomatal conductance, transpiration, osmotic potential and water-use efficiency, increased chlorophyll content and delayed heading. Tef genotypes exhibited diverse water-use strategies under drought: water-conserving (isohydric) or non-conserving (anisohydric), or an intermediate strategy, as well as variation in drought-recovery rate. Genotype RTC-290b exhibited outstanding multifaceted drought-adaptive performance, including high water-use efficiency coupled with high productivity under drought and control treatments, high chlorophyll and transpiration under drought, and faster drought recovery rate. This study provides a first insight into the dynamic functional physiological responses of tef to water deficiency and the variation between genotypes in drought-adaptive strategies. These results may serve as a baseline for further studies and for the development of drought-resistant tef varieties.

Root traits and biomass production of drought‐resistant and drought‐sensitive arabica coffee varieties growing under contrasting watering regimes

AbstractDrought is a major factor affecting coffee production, and different genotypes exhibit varying degrees of resistance to drought stress. We examined root traits and biomasses of drought‐resistant (74110, Angafa, Bultum, Chala, and Gawe) and drought‐sensitive (75227, Koti, Melko CH2, Menasibu, and Mokah) Coffea arabica varieties at seedling stage under contrasting watering regimes (water stressed and well watered) for 30 days followed by 15 days of recovery to identify the association between drought resistance and root traits and dry matter partitioning, and the impact of drought stress on growth performance of arabica coffee varieties. We used a split‐plot design with three blocks, where watering regime was the whole‐plot factor and variety was the subplot factor. During water‐stress and recovery periods, the interaction effect between watering regime and variety significantly affected root traits and dry matter partitioning, while the watering‐regime main effect affected biomass. We observed a higher (1) tap root diameter (0.34 cm), lateral root number (80.7), and root volume (4.7 cm−3) for 74110; (2) lateral root number (79.3), specific root length (24.8 cm g−1), and root‐mass ratio (0.41 g g−1) for Bultum; and (3) root length density (3.3–5.2 cm cm−3), root angle (42.6°–47.8°), root‐mass ratio (0.40–0.42 g g−1), and root‐shoot ratio (0.67–0.72 g g−1) for Angafa, Chala, and Gawe under water‐stressed condition. During both study periods, biomasses were much lower under water‐stressed than under well‐watered condition. The findings show the association between drought resistance and root traits and dry matter partitioning, and the impact of drought stress on growth performance of young arabica coffee.

Genomic dissection of productivity, lodging, and morpho‐physiological traits in Eragrostis tef under contrasting water availabilities

Societal Impact StatementUnderutilized species (also known as orphan crops) present opportunities to increase crop diversity and food security. Such crops lack modern genetic tools and knowledge to facilitate efficient modern breeding approaches. A wide collection of tef (Eragrostis tef (Zucc.) Trotter) genotypes was used to identify genomic regions associated with productivity, lodging, and morpho‐physiological traits under contrasting water availabilities. The obtained results are expected to enhance modern breeding and improve tef productivity under traditional and modern cropping systems, thus improving farmers' livelihood and food security.Summary Tef (E. tef (Zucc.) Trotter) is an allotetraploid (2n = 4x = 40) C4 cereal crop, endemic to Ethiopia and mainly cultivated in the Horn of Africa. Tef is characterized by high grain and feed nutritional qualities and resilience to abiotic and biotic stresses; thus, it holds great potential to sustain food and nutrition security in Africa and other parts of the world. The objective of this study was to identify genomic regions associated with responses to contrasting water regimes, as a basis for future improvement. A tef diversity panel was genotyped with 28,837 single nucleotide polymorphisms (SNPs) and phenotyped for productivity, lodging, and morpho‐physiological traits along two seasons (2020 and 2021) under well‐watered and water‐limited treatments. A genome‐wide association study was performed to identify genomic regions associated with key traits for tef breeding. A total of 107 SNPs were associated with one or more of the studied traits, resulting in 138 marker–trait associations (MTAs) detected under both water treatments. Of these, 22 SNPs were associated with more than one trait, showing either multiple trait (pleiotropic) or multiple environment associations or both. A particularly strong association was found between grain yield, lodging, and time to heading. These findings open new avenues to further research on the genetic basis and physiological mechanisms underlying major traits in tef, as well as to marker‐assisted breeding of drought‐resilient tef cultivars.

Microbial strategies for phosphorus acquisition in rice paddies under contrasting water regimes: Multiple source tracing by 32P and 33P

Microbial acquisition and utilization of organic and mineral phosphorus (P) sources in paddy soils are strongly dependent on redox environment and remain the key to understand P turnover and allocation for cell compound synthesis. Using double 32/33P labeling, we traced the P from three sources in a P-limited paddy soil: ferric iron-bound phosphate (Fe-P), wheat straw P (Straw-P), and soil P (Soil-P) in microbial biomass P (MBP) and phospholipids (Phospholipid-P) of individual microbial groups depending on water regimes: (i) continuous flooding or (ii) alternate wetting and drying.32/33P labeling combined with phospholipid fatty acid analysis allowed to trace P utilization by functional microbial groups. Microbial P nutrition was mainly covered by Soil-P, whereas microorganisms preferred to take up P from mineralized Straw-P than from Fe-P dissolution. The main Straw-P mobilizing agents were Actinobacteria under alternating wetting and drying and other Gram-positive bacteria under continuous flooding. Actinobacteria and arbuscular mycorrhiza increased P incorporation into cell membranes by 1.4–5.8 times under alternate wetting and drying compared to continuous flooding. The Fe-P contribution to MBP was 4–5 times larger in bulk than in rooted soil because (i) rice roots outcompeted microorganisms for P uptake from Fe-P and (ii) rhizodeposits stimulated microbial activity, e.g. phosphomonoesterase production and Straw-P mineralization. Higher phosphomonoesterase activities during slow soil drying compensated for the decreased reductive dissolution of Fe-P. Concluding, microbial P acquisition strategies depend on (i) Soil-P, especially organic P, availability, (ii) the activity of phosphomonoesterases produced by microorganisms and roots, and (iii) P sources – all of which depend on the redox conditions. Maximizing legacy P utilization in the soil as a function of the water regime is one potential way to reduce competition between roots and microbes for P in rice cultivation.

Carbon dynamics as a function of soil moisture following repeated wet-dry cycles in irrigated soils

Drying-rewetting cycles are ubiquitous across natural and managed ecosystems. These cycles are known to mobilize carbon (C) in soils producing dramatic pulses in microbial respiration. While many factors contribute to these pulses, the drying-rewetting history of soils affecting carbon emissions remains unclear, especially in irrigated soils where soil moisture fluctuations are more repetitive and/or frequent than natural, seasonally influenced soils. To understand the controls of repeated wet-up and dry down effects on agricultural soils, we used a systems approach to examine the cross section of a furrow irrigated orchard to delineate soil C dynamics. Specifically, we compared two contrasting water regimes, (1) soils temporarily but repeatedly inundated during water delivery (i.e., furrows) and (2) soils at the base of trees (i.e., berms) that only receive water during precipitation events in a semi-arid Mediterranean climate. Overall, our findings show that the heterogeneous landscape of a furrow irrigated field results in two separate systems within the field scale in gaseous release of C as CO2, microbial selectivity of substrates, and mechanisms for C stabilization. By monitoring soil moisture as a function of depth for over two years, our results reveal that furrow soils undergo dramatic wet-dry cycles, while moisture within the berm is relatively constant. We were able to capture the distinct heterogeneity of soil moisture changes within the furrow and berm soils by continuously monitoring CO2 flux throughout water input events in both the wet and dry season. Soil CO2 efflux is suppressed upon irrigation within furrows, while carbon oxidation in berm soils exhibits pore-connectivity limitations that result in lower fluxes when dry. Solid phase soil C speciation determined by C 1s NEXAFS demonstrated C of higher aromaticity remained in furrow soil compared to berm soils. Microbial community analysis shows significantly different communities reside within berm and furrow soils, where furrow soils support more anaerobic metabolisms and spore-formers while berm soils have relatively higher abundance of aerobic microbes capable of degrading larger, more complex C compounds. Our findings show that water regime (periodic inundation vs episodic rainfall) controlling rewetting history can greatly differentiate C respiration within managed soils.

Inconsistent phenotypic differentiation at physiological traits in Norway spruce (Picea abies Karst.) provenances under contrasting water regimes

Abstract Norway spruce is expected to suffer from drought stress and other manifestations of climate change. This study relies on a manipulative experiment with drought-stressed and well-watered (control) seedlings, comprising five provenances of Norway spruce distributed along a steep elevational transect from 550 to 1,280 m a.s.l. within the natural range. Seedlings were subjected to measurement of physiological traits (content of phytohormones and monoterpenes, slow and fast chlorophyll a fluorescence kinetics, gas exchange, hyperspectral indices), and genotyping at 8 nuclear microsatellite loci. Comparison of the coefficient of differentiation at neutral loci (FST ) vs. differentiation at phenotypic traits (PST ) was used to identify traits underlying divergent selection. In total, 18 traits exhibited a significant PST – FST difference. However, the consistency in differentiation patterns between drought-stressed and control plants was limited, only three traits exhibited signals of selection under both treatments. This outcome indicates that the identified differentiation patterns can only be interpreted in the context of environmental setup of the experiment, and highlights the importance of common gardens in adaptation research, as they allow both elimination of environment-induced phenotypic variation and studying genotype-by-environment interaction in physiological responses to environmental stresses.

Engaging Precision Phenotyping to Scrutinize Vegetative Drought Tolerance and Recovery in Chickpea Plant Genetic Resources.

Precise and high-throughput phenotyping (HTP) of vegetative drought tolerance in chickpea plant genetic resources (PGR) would enable improved screening for genotypes with low relative loss of biomass formation and reliable physiological performance. It could also provide a basis to further decipher the quantitative trait drought tolerance and recovery and gain a better understanding of the underlying mechanisms. In the context of climate change and novel nutritional trends, legumes and chickpea in particular are becoming increasingly important because of their high protein content and adaptation to low-input conditions. The PGR of legumes represent a valuable source of genetic diversity that can be used for breeding. However, the limited use of germplasm is partly due to a lack of available characterization data. The development of HTP systems offers a perspective for the analysis of dynamic plant traits such as abiotic stress tolerance and can support the identification of suitable genetic resources with a potential breeding value. Sixty chickpea accessions were evaluated on an HTP system under contrasting water regimes to precisely evaluate growth, physiological traits, and recovery under optimal conditions in comparison to drought stress at the vegetative stage. In addition to traits such as Estimated Biovolume (EB), Plant Height (PH), and several color-related traits over more than forty days, photosynthesis was examined by chlorophyll fluorescence measurements on relevant days prior to, during, and after drought stress. With high data quality, a wide phenotypic diversity for adaptation, tolerance, and recovery to drought was recorded in the chickpea PGR panel. In addition to a loss of EB between 72% and 82% after 21 days of drought, photosynthetic capacity decreased by 16-28%. Color-related traits can be used as indicators of different drought stress stages, as they show the progression of stress.

Physiological characterization of Vitis hybrid cv Merlot Khorus under two different water regimes in northeastern Italy

Fungus–resistant varieties are gathering attention all over viticultural areas owing to their contribution to sustainable management. Sustainable viticulture implies lower inputs in terms of pesticides and water. However, investigations on the physiological behavior of fungus–resistant varieties under drought stress have been seldom conducted so far. Under climate change conditions, evaluating precise water use is particularly important to set up proper irrigation. In this study, a two-year experiment was imposed to characterize the physiological behavior of the fungus–resistant variety Merlot Khorus under two contrasting water regimes (full irrigation, WW; water deficit, WD). Berry weight and grape quality in the two treatments was also compared to evaluate the feasibility of adopting deficit irrigation strategies in the region. The study was conducted in the Friuli Venezia Giulia region (Italy). The measured values of stem water potential (Ψstem) did not highlight any severe water stress (> -1.15 MPa) in WD. However, gs and AN decreased to values typical of drought–stressed vines. Concurrently, the experiment assessed that the calculated Kcb of Merlot Khorus in northeast Italy is far different from what has been suggested by standard methodologies and the literature. The grapes under deficit irrigation showed reduced berry weight, while basic maturation parameters and anthocyanins were improved. Overall, the study indicated that Merlot Khorus appears to be a genotype suitable for dry farming or deficit irrigation management in northeastern Italy. Therefore, the results may help winegrowers to improve irrigation strategies.

15N tracers and microbial analyses reveal in situ N2O sources in contrasting water regimes of a drained peatland forest

Managed peatlands are a significant source of nitrous oxide (N2O), a powerful greenhouse gas and stratospheric ozone depleter. Due to the complexity and diversity of microbial N2O processes, different methods such as tracer, isotopomer, and microbiological technologies are required to understand these processes. The combined application of different methods helps to precisely estimate these processes, which is crucial for the future management of drained peatlands, and to mitigate soil degradation and negative atmospheric impact. In this study, we investigated N2O sources by combining tracer, isotopomer, and microbial analysis in a drained peatland forest under flooded and drained treatments. On average, the nitrification genes showed higher abundances in the drained treatment, and the denitrification genes showed higher abundances in the flooded treatment. This is consistent with the underlying chemistry, as nitrification requires oxygen while denitrification is anaerobic. We observed significant differences in labelled N2O fluxes between the drained and flooded treatments. The emissions of N2O from the flooded treatment were nearly negligible, whereas the N2O evolved from the nitrogen-15 (15N)-labelled ammonium (15NH4+) in the drained treatment peaked at 147 μg 15N m-2 h-1. This initially suggested nitrification as the driving mechanism behind N2O fluxes in drained peatlands, but based on the genetic data, isotopic analysis, and N2O mass enrichment, we conclude that hybrid N2O formation involving ammonia oxidation was the main source of N2O emissions in the drained treatment. Based on the 15N-labelled nitrate (15NO3-) tracer addition and gene copy numbers, the low N2O emissions in the flooded treatment came possibly from complete denitrification producing inert dinitrogen. At atomic level, we observed selective enrichment of mass 45 of N2O molecule under 15NH4+ amendment in the drained treatment and enrichment of both masses 45 and 46 under 15NO3- amendment in the flooded treatment. The selective enrichment of mass 45 in the drained treatment indicated the presence of hybrid N2O formation, which was also supported by the high abundances of archaeal genes.

Effects of Drought and Flooding on Phytohormones and Abscisic Acid Gene Expression in Kiwifruit.

Environmental extremes, such as drought and flooding, are becoming more common with global warming, resulting in significant crop losses. Understanding the mechanisms underlying the plant water stress response, regulated by the abscisic acid (ABA) pathway, is crucial to building resilience to climate change. Potted kiwifruit plants (two cultivars) were exposed to contrasting watering regimes (water logging and no water). Root and leaf tissues were sampled during the experiments to measure phytohormone levels and expression of ABA pathway genes. ABA increased significantly under drought conditions compared with the control and waterlogged plants. ABA-related gene responses were significantly greater in roots than leaves. ABA responsive genes, DREB2 and WRKY40, showed the greatest upregulation in roots with flooding, and the ABA biosynthesis gene, NCED3, with drought. Two ABA-catabolic genes, CYP707A i and ii were able to differentiate the water stress responses, with upregulation in flooding and downregulation in drought. This study has identified molecular markers and shown that water stress extremes induced strong phytohormone/ABA gene responses in the roots, which are the key site of water stress perception, supporting the theory kiwifruit plants regulate ABA to combat water stress.

ROOT SYSTEM ARCHITECTURE AND STEM TRAITS OF BREAD WHEAT SEEDLINGS UNDER CONTRASTING WATER REGIMES

Differential response of bread wheat seedlings to contrasting water regimes can be used to determine traits related to drought tolerance. The F1 offspring from eight crosses and 11 selected parental genotypes were simultaneously grown in hydroponic cultivation-polyethylene glycol (PEG) induced drought stress vs. control conditions. Criteria for selection of maternal and paternal genotypes were desirable traits in terms of increased tolerance to drought: longer stem length, longer primary root, large number of seminal roots, large root dry mass and stem dry mass, beginning of root branching at the greatest possible distance from beginning of the root, contrasting angle of seminal roots. The traits were measured on 14 day old seedlings: primary root length (PRL), distance to the first branch on the primary root (DFBR), number of seminal roots (NSR), total seminal root length (TSRL), angle of seminal roots (ASR), stem length (SL), root dry mass (RDM), stem dry mass (SDM), and the ratio of root dry mass to stem dry mass (RDM/SDM). Drought stress led to a decrease in the mean values of all root and stem traits by 11% on average, except for RDM/SDM which was increased. The most sensitive trait to drought stress was DFBR (25% reduction), causing root systems to branch at a shallower depth. In conditions of induced drought stress, the strongest statistically significant correlation was found among RDM and RDM/SDM (r = 0.794), SL and ASR (r = 0.708), RDM and TSRL (r = 0.673). The stress tolerance index had the strongest positive correlation with the SDM, PRL, TSRL, SL, and the stress susceptibility index with the NSR. The highest heterosis mean value was observed for PRL (24.6%) and for SL (15.6%) under drought stress. The different directions of average heterosis in induced drought stress vs. control conditions were observed for DFBR, RDM, and SDM, indicating differential traits to account for when planning breeding bread wheat for drought tolerance. Selected traits as criteria for selection and favorable combinations can be incorporated into pre-breeding and breeding schemes, directly or indirectly, aiming to achieve drought tolerance. Keywords: bread wheat; drought stress; heterosis; hydroponics; root system architecture.

Analysis of durum wheat photosynthetic organs during grain filling reveals the ear as a water stress-tolerant organ and the peduncle as the largest pool of primary metabolites

Main conclusionThe pool of carbon- and nitrogen-rich metabolites is quantitatively relevant in non-foliar photosynthetic organs during grain filling, which have a better response to water limitation than flag leaves.The response of durum wheat to contrasting water regimes has been extensively studied at leaf and agronomic level in previous studies, but the water stress effects on source–sink dynamics, particularly non-foliar photosynthetic organs, is more limited. Our study aims to investigate the response of different photosynthetic organs to water stress and to quantify the pool of carbon and nitrogen metabolites available for grain filling. Five durum wheat varieties were grown in field trials in the Spanish region of Castile and León under irrigated and rainfed conditions. Water stress led to a significant decrease in yield, biomass, and carbon and nitrogen assimilation, improved water use efficiency, and modified grain quality traits in the five varieties. The pool of carbon (glucose, glucose-6-phosphate, fructose, sucrose, starch, and malate) and nitrogen (glutamate, amino acids, proteins and chlorophylls) metabolites in leaf blades and sheaths, peduncles, awns, glumes and lemmas were also analysed. The results showed that the metabolism of the blades and peduncles was the most susceptible to water stress, while ear metabolism showed higher stability, particularly at mid-grain filling. Interestingly, the total metabolite content per organ highlighted that a large source of nutrients, which may be directly involved in grain filling, are found outside the blades, with the peduncles being quantitatively the most relevant. We conclude that yield improvements in our Mediterranean agro-ecosystem are highly linked to the success of shoots in producing ears and a higher number of grains, while grain filling is highly dependent on the capacity of non-foliar organs to fix CO2 and N. The ear organs show higher stress resilience than other organs, which deserves our attention in future breeding programmes.

Quantitative Trait Loci for Genotype and Genotype by Environment Interaction Effects for Seed Yield Plasticity to Terminal Water-Deficit Conditions in Canola (Brassica napus L.)

Canola plants suffer severe crop yield and oil content reductions when exposed to water-deficit conditions, especially during the reproductive stages of plant development. There is a pressing need to develop canola cultivars that can perform better under increased water-deficit conditions with changing weather patterns. In this study, we analysed genetic determinants for the main effects of quantitative trait loci (QTL), (Q), and the interaction effects of QTL and Environment (QE) underlying seed yield and related traits utilising 223 doubled haploid (DH) lines of canola in well-watered and water-deficit conditions under a rainout shelter. Moderate water-deficit at the pre-flowering stage reduced the seed yield to 40.8%. Multi-environmental QTL analysis revealed 23 genomic regions associated with days to flower (DTF), plant height (PH) and seed yield (SY) under well-watered and water-deficit conditions. Three seed yield QTL for main effects were identified on chromosomes A09, C03, and C09, while two were related to QE interactions on A02 and C09. Two QTL regions were co-localised to similar genomic regions for flowering time and seed yield (A09) and the second for plant height and chlorophyll content. The A09 QTL was co-located with a previously mapped QTL for carbon isotope discrimination (Δ13C) that showed a positive relationship with seed yield in the same population. Opposite allelic effects for plasticity in seed yield were identified due to QE interactions in response to water stress on chromosomes A02 and C09. Our results showed that QTL's allelic effects for DTF, PH, and SY and their correlation with Δ13C are stable across environments (field conditions, previous study) and contrasting water regimes (this study). The QTL and DH lines that showed high yield under well-watered and water-deficit conditions could be used to manipulate water-use efficiency for breeding improved canola cultivars.

Variation in Yield, Berry Distribution and Chemical Attributes of Coffea arabica Beans among the Canopy Strata of Four Genotypes Cultivated under Contrasted Water Regimes

Water availability, light, management practices, and harvest time impacts on Coffea arabica L. yield and bean quality remain uncertain. It was hypothesized that the soil water and light availability could impact berry distribution, yield, and bean chemical attributes within the plant canopy. Therefore, it was aimed to study berry yield, berry distribution, and bean chemical traits along the canopy strata of four coffee genotypes (Iapar 59, Catuaí 99 and two Ethiopian wild accessions, ‘E083’ and ‘E027’), cultivated with (IRR) and without irrigation (NI) in the two initial harvest years. The maximum height of berry occurrence was lower in NI than in IRR plants in both harvest years. In the 2nd harvest year, higher leaf-to-fruit ratio was found under NI than under IRR for all genotypes, except for Catuaí 99, while the most regular berry distribution among canopy strata was obtained in IRR ‘E083’, the highest bean yield in IRR ‘E083’ and Iapar 59, and the highest percent of useful bean biomass in NI Catuaí 99. The reduced lipid content under IRR was more important in the 1st (all genotypes) than in the 2nd harvest year (Iapar 59 and ‘E027’). As a novelty, chemical bean composition was additionally impacted by light availability along the canopy strata. Proteins declined from bottom (shaded) to upper (highly light exposed) strata, regardless of genotype and harvest year. Similar stratification was observed in caffeine in the 2nd year. Although some traits were somewhat changed among strata, no substantial quality changes occurred, thus allowing that harvest might include the entire plant and not only some specific strata. Iapar 59 and ‘E083’ showed chemical composition usually associated with high bean quality, with the highest lipid, sucrose, and soluble sugar contents, and the lowest caffeine, chlorogenic acids, and phenolic components among four genotypes, but Iapar 59 plants were less affected in their yield under NI. Based on additional responses from space occupation and yield only under IRR, the wild accession ‘E083’ must be considered in future breeding programs as promising material for intensive input conditions. High bean quality and the less variated yield under lower soil water availability qualified the Iapar 59 as the most prominent among the four genotypes.

Neglecting acclimation of photosynthesis under drought can cause significant errors in predicting leaf photosynthesis in wheat.

Extreme climatic events, such as heat waves, cold snaps and drought spells, related to global climate change, have become more frequent and intense in recent years. Acclimation of plant physiological processes to changes in environmental conditions is a key component of plant adaptation to climate change. We assessed the temperature response of leaf photosynthetic parameters in wheat grown under contrasting water regimes and growth temperatures (Tgrowth ). Two independent experiments were conducted under controlled conditions. In Experiment 1, two wheat genotypes were subjected to well-watered or drought-stressed treatments; in Experiment 2, the two water regimes combined with high, medium and low Tgrowth were imposed on one genotype. Parameters of a biochemical C3 -photosynthesis model were estimated at six leaf temperatures for each factor combination. Photosynthesis acclimated more to drought than to Tgrowth . Drought affected photosynthesis by lowering its optimum temperature (Topt ) and the values at Topt of light-saturated net photosynthesis, stomatal conductance, mesophyll conductance, the maximum rate of electron transport (Jmax ) and the maximum rate of carboxylation by Rubisco (Vcmax ). Topt for Vcmax was up to 40°C under well-watered conditions but 24-34°C under drought. The decrease in photosynthesis under drought varied among Tgrowth but was similar between genotypes. The temperature response of photosynthetic quantum yield under drought was partly attributed to photorespiration but more to alternative electron transport. All these changes in biochemical parameters could not be fully explained by the changed leaf nitrogen content. Further model analysis showed that both diffusional and biochemical parameters of photosynthesis and their thermal sensitivity acclimate little to Tgrowth , but acclimate considerably to drought and the combination of drought and Tgrowth . The commonly used modelling approaches, which typically consider the response of diffusional parameters, but ignore acclimation responses of biochemical parameters to drought and Tgrowth , strongly overestimate leaf photosynthesis under variable temperature and drought.

Nutrient Accumulation in Cover Crops under Contrasting Water Regimes in the Brazilian Cerrado

Brazilian Cerrado has a dry period, and the inclusion of new species for diversification in the production system needs to be drought-tolerant. This work aimed to evaluate biomass and nutrient accumulation in species with potential as cover crops and grain crops under different water levels. Irrigation treatments were obtained through an irrigation bar with sprinklers with increasing water flows to create a continuous gradient. The experimental design randomized complete blocks in split plots with four replications. The main plots were composed of four water regimes (167 mm, 268 mm, 381 mm and 432 mm), and the subplots were formed by the following cover crops: Amaranthus cruenthus, Chenopodium quinoa and Pennisetum glaucum, the latter already used for this purpose. Amaranthus cruenthus and P. glaucum recorded the highest dry biomass (10.16 and 9.75 Mg ha−1, respectively). Dry biomass production and the cellulose contents decreased with the reduction of water availability for all species. A. cruenthus was the species that most accumulated P (37.42 kg ha−1), K (416.92 kg ha−1), Mg (30.88 kg ha−1), S (43.53 kg ha−1), Fe (2.22 kg ha−1), B (0.124 kg ha−1) and Zn (0.240 kg ha−1). Amaranthus cruenthus produced the highest yield. Under high and low water availability conditions, A. cruenthus presents potential as a cover crop and grain cash crop, in addition to accumulating more nutrients; P. glaucum has potential as a cover crop and C. quinoa only for grain production.

Differential associations between nucleotide polymorphisms and physiological traits in Norway spruce (Picea abiesKarst.) plants under contrasting water regimes

AbstractNorway spruce is an ecologically and commercially important species, which currently suffers from climate change and is expected to decline because of heat and drought stress. A manipulative experiment with drought-stressed and well-watered (control) seedlings was established, comprising five populations of Norway spruce coming from a small territory but distributed along a steep elevational transect from 550 to 1280 m.a.s.l. Plants were phenotyped at physiological traits (content of phytohormones and monoterpenes, chlorophyll a fluorescence, gas exchange and hyperspectral indices) and genotyped using ddRAD sequencing. After filtering, 34 127 polymorphisms (SNPs) were retained and used for analysis. Association tests revealed 42 SNP-variable pairs located across 29 scaffolds exhibiting significant associations, among them 20 were found for drought-stressed seedlings and 22 for control (watered) plants. However, there was no consistency between drought-stressed and control plants, no SNP-trait pair was common for both treatments. The study demonstrated that the identified genotype–phenotype associations can only be interpreted in the context of environmental setup preceding the assessment of phenotypic traits.

Drought exerts a greater influence than growth temperature on the temperature response of leaf day respiration in wheat (Triticum aestivum).

We assessed how the temperature response of leaf day respiration (R d) in wheat responded to contrasting water regimes and growth temperatures. In Experiment 1, well‐watered and drought‐stressed conditions were imposed on two genotypes; in Experiment 2, the two water regimes combined with high (HT), medium (MT) and low (LT) growth temperatures were imposed on one of the genotypes. R d was estimated from simultaneous gas exchange and chlorophyll fluorescence measurements at six leaf temperatures (T leaf) for each treatment, using the Yin method for nonphotorespiratory conditions and the nonrectangular hyperbolic fitting method for photorespiratory conditions. The two genotypes responded similarly to growth and measurement conditions. Estimates of R d for nonphotorespiratory conditions were generally higher than those for photorespiratory conditions, but their responses to T leaf were similar. Under well‐watered conditions, R d and its sensitivity to T leaf slightly acclimated to LT, but did not acclimate to HT. Temperature sensitivities of R d were considerably suppressed by drought, and the suppression varied among growth temperatures. Thus, it is necessary to quantify interactions between drought and growth temperature for reliably modelling R d under climate change. Our study also demonstrated that the Kok method, one of the currently popular methods for estimating R d, underestimated R d significantly.