Leaf Transpiration Rate Research Articles

Should we delay leaf water potential measurements after excision? Dehydration or equilibration?

BackgroundAccurate leaf water potential (Ψw) determination is crucial in studying plant responses to water deficit. After excision, water potential decreases, even under low evaporative demand conditions, which has been recently attributed to the equilibration of pre-excision Ψw gradients across the leaf. We assessed the influence of potential re-equilibration on water potential determination by monitoring leaf Ψw and relative water content decline after excision using different storage methods.ResultsEven though leaf Ψw declined during storage under low evaporative demand conditions, this was strongly reduced when covering the leaf with a hydrophobic layer (vaseline) and explained by changes in relative water content. However, residual water loss was variable between species, possibly related to morpho-physiological leaf traits. Provided water loss was minimized during storage, pre-excision leaf transpiration rate did not affect to the magnitude of leaf Ψw decline after excision, confirming that transpiration-driven Ψw gradients have no effect on leaf Ψw determination.ConclusionsDisequilibrium in water potentials across a transpiring leaf upon excision is dissipated very quickly, well within the elapsed time between excision and pressurization, therefore, not resulting in overestimation of leaf Ψw measured immediately after excision. When leaf storage is required, the effectiveness of a storage under low evaporative demand varied among species. Covering with a hydrophobic layer is an acceptable alternative.

Efficient gene editing of a model fern species through gametophyte-based transformation.

The clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated nuclease (Cas) system allows precise and easy editing of genes in many plant species. However, this system has not yet been applied to any fern species through gametophytes due to the complex characteristics of fern genomes, genetics, and physiology. Here, we established a protocol for gametophyte-based screening of single-guide RNAs (sgRNAs) with high efficiency for CRISPR/Cas9-mediated gene knockout in a model fern species, Ceratopteris richardii. We utilized the C. richardii ACTIN promoter to drive sgRNA expression and the enhanced CaMV 35S promoter to drive the expression of Streptococcus pyogenes Cas9 in this CRISPR-mediated editing system, which was employed to successfully edit a few genes, such as Nucleotidase/phosphatase 1 (CrSAL1) and Phytoene Desaturase (CrPDS), which resulted in an albino phenotype in C. richardii. Knockout of CrSAL1 resulted in significantly (P<0.05) reduced stomatal conductance (gs), leaf transpiration rate (E), guard cell length, and abscisic acid (ABA)-induced reactive oxygen species (ROS) accumulation in guard cells. Moreover, CrSAL1 overexpressing plants showed significantly increased net photosynthetic rate (A), gs, and E as well as most of the stomatal traits and ABA-induced ROS production in guard cells compared to the wild-type (WT) plants. Taken together, our optimized CRISPR/Cas9 system provides a useful tool for functional genomics in a model fern species, allowing the exploration of fern gene functions for evolutionary biology, herbal medicine discovery, and agricultural applications.

Superior osmotic stress tolerance in oilseed rape transformed with wild-type Rhizobium rhizogenes

Key messageNatural transformation with R. rhizogenes enhances osmotic stress tolerance in oilseed rape through increasing osmoregulation capacity, enhancing maintenance of hydraulic integrity and total antioxidant capacity.Transformation of plants using wild strains of agrobacteria is termed natural transformation and is not covered by GMO legislation in, e.g., European Union and Japan. In this study, offspring lines of Rhizobium rhizogenes naturally transformed oilseed rape (Brassica napus), i.e., A11 and B3 (termed root-inducing (Ri) lines), were investigated for osmotic stress resilience. Under polyethylene glycol 6000 (PEG) 10% (w/v)-induced osmotic stress, the Ri lines, particularly A11, had less severe leaf wilting, higher stomatal conductance (8.2 times more than WT), and a stable leaf transpiration rate (about 2.9 mmol m−2 s−1). Although the leaf relative water content and leaf water potential responded similarly to PEG treatment between the Ri lines and WT, a significant reduction of the turgid weight to dry weight ratio in A11 and B3 indicated a greater capacity of osmoregulation in the Ri lines. Moreover, the upregulation of plasma membrane intrinsic proteins genes (PIPs) in roots and downregulation of these genes in leaves of the Ri lines implied a better maintenance of hydraulic integrity in relation to the WT. Furthermore, the Ri lines had greater total antioxidant capacity (TAC) than the WT under PEG stress. Collectively, the enhanced tolerance of the Ri lines to PEG-induced osmotic stress could be attributed to the greater osmoregulation capacity, better maintenance of hydraulic integrity, and greater TAC than the WT. In addition, Ri-genes (particularly rolA and rolD) play roles in response to osmotic stress in Ri oilseed rape. This study reveals the potential of R. rhizogenes transformation for application in plant drought resilience.

Differential root nutrient‐acquisition strategies underlie biogeochemical niche separation between grasses and forbs across grassland biomes

Abstract Plant nutrient composition is a reliable tool to identify plant ecological strategies and niche differentiation. Here, we aimed to (i) reveal the potential physiological mechanisms governing distinct foliar nutrient compositions among coexisting grassland species and (ii) clarify the role of taxonomy and environmental conditions in these compositions. At the local (grassland) scale, we measured root morphological and physiological traits, photosynthetic parameters and foliar concentrations of six macronutrients (N, P, S, K, Ca and Mg) and four micronutrients (Fe, Mn, Zn and Cu) across 18 coexisting species. At the regional scale, foliar macro‐ and micronutrient concentrations of 76 site‐species combinations of grasses and forbs across temperate meadow, typical, desert and saline grasslands were measured in Inner Mongolia. At the national scale, we collected the data on foliar macronutrient concentrations of 513 site‐species combinations across grasslands in Xinjiang, Qinghai‐Tibet and Inner Mongolia of China. Compared with forbs, grasses had 3.9 times higher root branching intensity, but 58% and 48% lower root carboxylate exudation and leaf transpiration rate. These distinct nutrient acquisition and transport strategies led to lower foliar nutrient (N, P, Ca, Mg and Mn) concentrations in grasses than forbs at the local scale. Most foliar micronutrient concentrations did not differ between grasses and forbs at the regional scale, whereas macronutrient concentrations were higher in forbs than grasses regardless of the grassland type at both the regional and national scales. All macronutrient concentrations exhibited stronger phylogenetic conservatism and less environmental control than micronutrients. The biogeochemical niche segregation (Euclidean distance based on PCA score of foliar macronutrient concentrations) between sympatric grasses and forbs was lower in meadow grassland than in the typical, desert and saline grasslands. Our results suggest that diverse nutrient acquisition and transport strategies can underlie the distinct foliar nutrient compositions between grasses and forbs. The linkage between potential physiological mechanisms and biogeochemical niche differentiation of grasses and forbs will advance our understanding of plant species coexistence and adaptive strategy. Read the free Plain Language Summary for this article on the Journal blog.

Building a reduced order model from CFD data on leaves to evaluate optimal climate conditions

Climate control in vertical farms or greenhouses is crucial in order to have the optimal climate for the plants. This climate can be simulated using Computational Fluid Dynamics (CFD). This way, different ventilation methods can for example be compared. Previously, plants were modeled as a porous zone, in which additional source terms are added to the energy or transpiration transport equation. In this study, ten different leaves under different orientations are studied. The heat and mass balance for each leaf is solved and the boundary layer is adequately resolved. Different leaf orientations and positions to the flow are used, so that each leaf has its own distinct boundary layer. Leaf temperature and humidity are a function of the incoming flow, but also of the incoming temperature, humidity and stomatal resistance. In order to be able to quickly assess the effects of changing boundary conditions, on the temperature and humidity of the leaves, a Reduced Order Model (ROM) is made from the CFD-data. This method allows to quickly assess the effects of a stomatal resistance, the incoming radiation or a changing inlet temperature or humidity. A ROM was built using the data from one simulation. In order to see whether the ROM is able to predict other configurations, two additional cases were solved in CFD and were compared to the ROM. Leaf temperatures and humidities only differed maximally 3.14% and were quite good at predicting this. Predicted leaf transpiration rates differed slightly more, as these differed maximally 10.5%. Overall, the ROM has proven to be a valuable and numerically cost-effective tool to predict overall leaf climate and can be a good tool when later the climate of a full plant is simulated.

Role of an Aqueous Extract of Duckweed (Lemna minor L.) in Increasing Salt Tolerance in Olea europaea L.

Salt stress is one of the preeminent abiotic stressors capable of strongly impacting crop productivity and quality. Within the array of strategies garnering interest in safeguarding crops against abiotic stresses, the use of plant biostimulants is emerging as a noteworthy avenue. For the above, there is an increasing interest in finding new plant extracts showing biostimulating effects in crops. In the present study, the efficacy of an aqueous extract from an aquatic species, the duckweed (Lemna minor L.), was assessed in olive plants (cv. Arbequina) grown in hydroponics and exposed to severe saline stress (150 mM NaCl). Salt stress caused considerable diminutions in biomass production, leaf net photosynthesis (Pn), leaf transpiration rate (E), and stomatal conductance (gs). The application of the duckweed extract resulted in a notable plant functionality recovery and counteracted the detrimental effects of the NaCl stress. Indeed, the plants stressed with NaCl and treated with the extract showed enhanced physiological and biometric traits compared to samples treated with NaCl alone. In particular, the duckweed extract improved photosynthetic activity and stomatal conductance, reduced the intercellular CO2 concentration, and ameliorated other physiological and morphological parameters. All these benefits influenced the whole plant growth, allowing samples treated with the extract to maintain a similar performance to that exhibited by the Control plants.

Genome-wide analysis of the TIFY family in Lycium and the negative regulation of stomatal development by LrJAZ2 gene

Stomata are ports that facilitate gas and water vapor exchange during plant photosynthesis and transpiration. Stomatal development is strictly regulated by endogenous hormone. Jasmonate, an important signal that modulates multiple physiological processes in plants, has been found to negatively regulate stomatal development in Arabidopsis thaliana, yet the molecular mechanisms underlying stomata development signaling remain to be understood. Jasmonate ZIM-domain (JAZ) proteins are the members of TIFY family and the key component of JA signaling pathway. Its function in stomatal development is unclear to data. Here, we screened out 24 TIFY family members against the genome of Lycium, and identified a JAZ member by combination analyses of evolutionary tree, cis-elements in promoter and gene expression patterns. Overexpression of this gene (LrJAZ2) in Lycium ruthenicum and Arabidopsis thaliana indicated LrJAZ2 negatively regulates stomatal development. Microscopic observations revealed that overexpression of LrJAZ2 negatively regulated stomatal development by decreasing stomatal density and index, which may lead to lower leaf transpiration rates. Transcriptome data indicated the overexpression of LrJAZ2 up-regulated the stomatal related genes such as LrERL2, LrPYL4, and down-regulated the LrSPCH. Collectively, our study found that LrJAZ2 is a key gene in stomatal development regulation in L. ruthenicum and provided new insights into the regulation of stomatal development.

Enhancing alfalfa photosynthetic performance through arbuscular mycorrhizal fungi inoculation across varied phosphorus application levels

This study evaluated the effects of arbuscular mycorrhizal fungi inoculation on the growth and photosynthetic performance of alfalfa under different phosphorus application levels. This experiment adopts two-factors completely random design, and sets four levels of fungi application: single inoculation with Funneliformis mosseae (Fm, T1), single inoculation with Glomus etunicatum (Ge, T2) and mixed inoculation with Funneliformis mosseae × Glomus etunicatum (Fm×Ge, T3) and treatment uninfected fungus (CK, T0). Four phosphorus application levels were set under the fungi application level: P2O5 0 (P0), 50 (P1), 100 (P2) and 150 (P3) mg·kg-1. There were 16 treatments for fungus phosphorus interaction. The strain was placed 5 cm below the surface of the flowerpot soil, and the phosphate fertilizer was dissolved in water and applied at one time. The results showed that the intercellular CO2 concentration (Ci) of alfalfa decreased at first and then increased with the increase of phosphorus application, except for light use efficiency (LUE) and leaf instantaneous water use efficiency (WUE), other indicators showed the opposite trend. The effect of mixed inoculation (T3) was significantly better than that of non-inoculation (T0) (p &amp;lt; 0.05). Pearson correlation analysis showed that Ci was significantly negatively correlated with alfalfa leaf transpiration rate (Tr) and WUE (p &amp;lt; 0.05), and was extremely significantly negatively correlated with other indicators (p &amp;lt; 0.01). The other indexes were positively correlated (p &amp;lt; 0.05). This may be mainly because the factors affecting plant photosynthesis are non-stomatal factors. Through the comprehensive analysis of membership function, the indexes of alfalfa under different treatments were comprehensively ranked, and the top three were: T3P2&amp;gt;T3P1&amp;gt;T1P2. Therefore, when the phosphorus treatment was 100 mg·kg-1, the mixed inoculation of Funneliformis mosseae and Glomus etunicatum had the best effect, which was conducive to improving the photosynthetic efficiency of alfalfa, increasing the dry matter yield, and improving the economic benefits of local alfalfa in Xinjiang. In future studies, the anatomical structure and photosynthetic performance of alfalfa leaves and stems should be combined to clarify the synergistic mechanism of the anatomical structure and photosynthetic performance of alfalfa.

Effect of sowing dates on physiological characteristics, yield, and quality of Carthamus tinctorius

A field experiment was conducted to measure the physiological characteristics, yield, active ingredient content, and other indicators of Carthamus tinctorius leaves undergoing 13 sowing date treatments. The principal component analysis(PCA) and redundancy analysis were used to analyze the correlation between these indicators to explore the effect of sowing date on the yield and active ingredient content of C. tinctorius in Liupanshan of Ningxia. The results illustrated that the early sowing in autumn and spring had significant effects on leaf photosynthetic parameters, SPAD value, antioxidant enzyme activity, nitrogen metabolism enzyme activity, filament yield, grain yield, and hydroxy safflower yellow A(HYSA) of C. tinctorius. Sowing in mid-November and late March had the best effect. Leaf transpiration rate, stomatal conductance, nitrate reductase, nitrite reductase, glutamine synthetase, and glutamate synthase increased by 44.9%, 52.4%, 15.9%, 60.8%, 10.3%, and 38.3%, respectively. The activities of superoxide dismutase, peroxidase, and catalase decreased by 10.8%, 4.1%, and 20.9%, respectively. The improvement of photosynthetic physiological characteristics promoted the dry matter accumulation and reproductive growth of C. tinctorius. The yield of filaments and seeds increased by 15.5% and 11.7%, and the yield of HYSA and kaempferol increased by 17.9% and 20.0%. In short, the suitable sowing date can promote the growth and development of C. tinctorius in Liupanshan of Ningxia, and significantly improve the yield and quality, which is conducive to the high quality and efficient production of C. tinctorius.

Evaluation of Wheat Genotypes under Water Regimes Using Hyperspectral Reflectance and Agro-Physiological Parameters via Genotype by Yield*Trait Approaches in Sakha Station, Delta, Egypt

Drought is an environmental abiotic stress that diminishes wheat production worldwide. In the present study, we evaluated fifty bread wheat genotypes (arranged in alpha lattice design) under two main water regimes, water-deficit (two surface irrigations) and well-watered (four irrigations), at different sites in two consecutive cropping seasons, 2019/20 and 2020/21. To identify the drought-tolerant genotypes, utilized several selection/phenotyping criteria, including agronomic traits, e.g., grain yield (GY) and yield components (SM); physiological parameters such as canopy temperature (CT), leaf transpiration rate (TRN), intercellular CO2 concentration (INCO); spectral reflectance indices, e.g., Leaf Chlorophyll Index (LCI), curvature index (CI), and normalized difference vegetation index (NDVI); and stress tolerance indices (STI) were determined concurrently with the grain yield. The results revealed significant differences (p ≤ 0.01) among the environments, genotypes, and their interaction for grain yield (GY), days to heading (DH), days to maturity (DM), grain filling period (GFP), grain filling rate (GFR), Normalized difference vegetation index (NDVI), plant height (PH), and spikes per square meter (SM). The genotype plus genotype by environment (GGE) and genotype by yield*trait (GYT) biplot techniques indicated that Genotype 37 (Sakha 95) and Genotype 45 performed best under well-watered and water-deficit environments. Furthermore, the same genotypes were the best from the genotype by stress tolerance indices (GSTI) approach view. Genotype 37 (Sakha 95) was superior to the GYT selection method, with physiological parameters and spectral reflectance indices. Likewise, we can identify this genotype as low-water-tolerant based on GSTI, GYT, and SRI results and recommend involving it in the drought breeding program.

Spraying exogenous hormones alleviate impact of weak-light on yield by improving leaf carbon and nitrogen metabolism in fresh waxy maize.

Insufficient light during the growth periods has become one of the main factors restricting maize yield with global climate change. Exogenous hormones application is a feasible measure to alleviate abiotic stresses on crop productivity. In this study, a field trial was conducted to investigate the effects of spraying exogenous hormones on yield, dry matter (DM) and nitrogen (N) accumulation, leaf carbon and N metabolism of fresh waxy maize under weak-light stress in 2021 and 2022. Five treatments including natural light (CK), weak-light after pollination (Z), spraying water (ZP1), exogenous Phytase Q9 (ZP2) and 6-benzyladenine (ZP3) under weak-light after pollination were set up using two hybrids suyunuo5 (SYN5) and jingkenuo2000 (JKN2000). Results showed that weak-light stress significantly reduced the average fresh ear yield (49.8%), fresh grain yield (47.9%), DM (53.3%) and N accumulation (59.9%), and increased grain moisture content. The net photosynthetic rate (Pn), transpiration rate (Tr) of ear leaf after pollination decreased under Z. Furthermore, weak-light decreased the activities of RuBPCase and PEPCase, nitrate reductase (NR), glutamine synthetase (GS), glutamate synthase (GOGAT), superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) in ear leaves, and increased malondialdehyde (MDA) accumulation. And the decrease was greater on JKN2000. While ZP2 and ZP3 treatments increased the fresh ear yield (17.8%, 25.3%), fresh grain yield (17.2%, 29.5%), DM (35.8%, 44.6%) and N (42.5%, 52.4%) accumulation, and decreased grain moisture content compared with Z. The Pn, Tr increased under ZP2 and ZP3. Moreover, the ZP2 and ZP3 treatments improved the activities of RuBPCase, PEPCase; NR, GS, GOGAT; SOD, CAT, POD in ear leaves, and decreased MDA content during grain filling stage. The results also showed the mitigative effect of ZP3 was greater than ZP2, and the improvement effect was more significant on JKN2000.

Translocation of 11C-labelled photosynthates to strawberry fruits depends on leaf transpiration during twilight

Photosynthate translocation from leaves to fruits is an important determinant of crop yield and quality. In protected cultivation, environmental control based on photosynthate translocation is indicative for realising high-yield and high-quality production. There are, however, few studies on the environmental response of photosynthate translocation, especially during twilight. In greenhouses, these transition periods are characterised by a drastic change in relative humidity (RH). In this study, we focused on light intensity as a key environmental factor to steer translocation under high RH prevailing under twilight conditions. We fed 11CO2 to a leaf of strawberry plants (Fragaria × ananassa Duch.) and analysed real-time dynamics of 11C-labeled photosynthate translocation to individual fruits on an inflorescence of intact plants by using positron emission tomography (PET) under different light intensities (i.e., 50, 200 and 400 μmol m−2 s−1). No clear relationship was obtained between 11C-photosynthate translocation and light intensity since the results revealed that translocation rates into the fruits were highest under the light intensity of 200 μmol m−2 s−1 followed by those of 400 and 50 μmol m−2 s−1. However, there was a strong negative correlation between transpiration rate of the 11C-fed leaf and 11C-photosynthate translocation rate. These novel findings indicate that transpiration, which controls leaf moisture status, is one of the drivers for photosynthate translocation towards fruits during twilight conditions.

Differential roles of abscisic acid in maize roots in the adaptation to soil drought

AbstractMaize yield reduction occurs frequently due to soil drought. Abscisic acid (ABA) is an important hormonal signal indicating drought. However, it remains unclear about the specific roles of root ABA in the adaptation to soil drought in maize. This study applied five different soil water potentials (SWP), referring to maintaining SWP at −15, −30, −45, −60, and −75 kPa, respectively, and investigated the ABA content in roots and the activities and gene expression levels of key enzymes involved in the ABA biosynthesis, the leaf photosynthetic properties, root traits, and kernel yield. The results showed that maize root ABA content, the activities and gene expressions of key enzymes involved in the ABA biosynthesis were increased with the decrease of SWP. The leaf transpiration rate, and root dry weight, length, volume, surface area, and activity, and kernel yield of maize were increased first and then decreased with the severity of soil drying. The leaf photosynthetic rate was not significantly reduced with ABA accumulation at a low ABA content in roots. Root ABA content was significantly positively correlated with leaf transpiration efficiency and root activity when ABA content was relatively low (9.03–22.02 nmol g−1 DW), whereas root ABA content was negatively correlated with leaf photosynthetic rate, leaf transpiration efficiency, root volume, and root activity when ABA content was high (28.32–39.23 nmol g−1 DW). The results indicate that maize root ABA exhibit differential roles in the adaptation to soil drought, and can positively regulate the drought‐resistance of maize at an appropriate level.

Leaf vein density correlates with crassulacean acid metabolism, but not hydraulic capacitance, in the genus Clusia.

Many succulent species are characterized by the presence of Crassulacean acid metabolism (CAM) and/or elevated bulk hydraulic capacitance (CFT). Both CAM and elevated CFT substantially reduce the rate at which water moves through transpiring leaves. However, little is known about how these physiological adaptations are coordinated with leaf vascular architecture. The genus Clusia contains species spanning the entire C3-CAM continuum, and also is known to have >5-fold interspecific variation in CFT. We used this highly diverse genus to explore how interspecific variation in leaf vein density is coordinated with CAM and CFT. We found that constitutive CAM phenotypes were associated with lower vein length per leaf area (VLA) and vein termini density (VTD), compared to C3 or facultative CAM species. However, when vein densities were standardized by leaf thickness, this value was higher in CAM than C3 species, which is probably an adaptation to overcome apoplastic hydraulic resistance in deep chlorenchyma tissue. In contrast, CFT did not correlate with any xylem anatomical trait measured, suggesting CAM has a greater impact on leaf transpiration rates than CFT. Our findings strongly suggest that CAM photosynthesis is coordinated with leaf vein densities. The link between CAM and vascular anatomy will be important to consider when attempting to bioengineer CAM into C3 crops.

Effect of Rain Cover on Tree Physiology and Fruit Condition and Quality of ‘Rainier’, ‘Bing’ and ‘Sweetheart’ Sweet Cherry Trees

A study was conducted in a commercial sweet cherry orchard in central Chile. The objective was to evaluate the rain cover effect on changes in the microclimate, vegetative growth, plant physiology and fruit quality of ‘Rainier’, ‘Bing’ and ‘Sweetheart’ sweet cherry trees. The data were compared to a control without a rain cover. The results showed that, under the rain cover, there was a 50–60% reduction in total solar radiation, as well as an increase in air temperature (+0.6 °C) and a decrease in relative humidity (−4.7 percentage points) in the upper canopy zone. Regarding the trees under rain cover, a greater shoot length (28–58%) and leaf area (24–54%) were observed among cultivars compared to the control; the trunk cross-sectional area was only significant in ‘Rainier’, it being 1.2 times greater under rain cover. CO2 assimilation showed no differences, but an increase in the leaf transpiration rate was observed. The fruit firmness and sugar content in fruits were negatively affected by the rain cover, those characteristics being of major relevance for the cherry growers. Additionally, the contents of anthocyanins and carotenoids and the antioxidant capacity were significantly lower only in ‘Rainier’ under rain cover, while the total phenol content decreased in all three cultivars. The rain cover did not negatively affect the tree physiology, but it can be detrimental in bicolor cultivars with a yellow flesh due to a lower color and phenolic compounds development.

Effect of Mulching and Drip Irrigation on Water Use Efficiency and Vegetative Growth of Mango under Small Tree System

Mango orchards in Pakistan are mostly irrigated using the basin flood method. A considerable quantity of water is lost from basins and channels through evaporation and seepage. During 2020-21, a study was conducted at Mango Small tree system located in MNS University of Agriculture Multan to examine the effect of drip irrigation systems flow rate and mulching in a split-plot design with two treatments and four replications. Main plot treatments consisted of four drip irrigation systems: Loop, single line drippers, bubbler and double line drippers. Moreover, subplots comprised two levels of mulching: no mulch and organic mulch (hay grass). The plants were irrigated by Drip irrigation on daily basis through Loop drippers of two liters per hour liter per hour (lph), single online line drippers of four lph, bubbler of two hundred lph and double online drippers of four lph discharge capacity from November to March. The drip system at a flow rate of four lph and treated with organic mulch recorded the maximum water use efficiency (6.46 kgha-1mm-1), stomatal conductance (140, 25 mmol-1m-2s-1), sub stomatal conductance (65 mmol-1m-2s-1), leaf photosynthetic rate (6.11 mmol-1m-2s-1) and leaf transpiration rate (1.84 mgm-2s-1). The plant height and scion girth did not show significant differences with changes in water flow rate and organic mulches. The maximum soil temperature (38○ C) was recorded in the non-mulched plot. The application of organic mulches not only enhanced the water use efficiency (WUE) and transpiration rate but also improved chlorophyll contents and the number of flushes.

Late topdressing can sustain wheat grain yield under straw mulching in the Loess Plateau of China

AbstractStraw mulching has been widely used to conserve soil water and enhance soil fertility in dryland cropping systems. However, the lack of soil nutrient availability due to the immobilization with straw mulch decomposition would result in a decrease in crop yield and harvest index. Based on a 9‐yr straw mulching field experiment, we evaluated the effect of late topdressing in 2 yr on crop yield under a winter wheat (Triticum aestivum L.) monoculture system in the Loess Plateau of China. Three treatments were included as straw mulching at rates of 9,000 (HSM) and 4,500 kg ha–1 (LSM) during growing season and control without mulching (CK) from 2008 to 2019. Topdressing as urea was added to each plot at wheat tillering from 2017 to 2019. Across 2 yr, straw mulching significantly increased soil water storage at most growing stages. Compared with CK, straw mulching promoted wheat growth (tiller density and plant density) but decreased grain yield and harvest index significantly. Soil mineral N contents in later wheat‐growing stages and net photosynthetic rate, transpiration rate of wheat flag leaf and leaf water use efficiency during filling stage decreased with HSM and LSM when compared with CK. However, late topdressing significantly increased wheat grain yield in both years. Generally, additional application of N fertilizer in the late growing stage could alleviate the yield decrease by straw mulching and should be considered for sustainable crop production in the Loess Plateau of China.

Growth regulation by air stream-based mechanical stimulation in tomato (Solanum lycopersicum L.) – Part II: Phenotypic and physiological responses

Plant responses to mechanical stimulation have a great potential for growth control of ornamentals plants and vegetable seedlings and is a major requirement to ensure plant compactness and stability. 21 days old tomato (Solanum lycopersicum cv. ‘Romello’) plants were exposed to regularly applied mechanical stimuli for 14 days by applying of a defined air stream through a custom-built air stream applicator. Air stream application gradually reduced total plant leaf area by 14% and promoted radial growth relative to internode length compared to the untreated control, resulting in a more compact and stable plant phenotype, which was also related to an increased stem dry matter content of the air stream-treated plants. The reduction in total plant leaf area was compensated for the translocation of proportionally more assimilates to light-harvesting tissues and to stems at the expense of dry mass accumulation in petioles. Total stem, leaf and root dry mass of air stream-treated plants were unaffected. The specific leaf area of the air stream treated plants was reduced compared to the control, resulting in an increased relative leaf greenness and consequently in an 8% higher net carbon assimilation rates on average compared to the control. Thereby, air stream-treated plants were able to maintain overall biomass accumulation at the same level as the control. Leaf transpiration rate of air stream treated plants was not markedly affected in the long-term. The technique presented should be easily transferable to other plants, such as ornamentals where the application of chemical plant growth regulators is still the most common technique for plant growth control.

The CO2 fertilization effect on leaf photosynthesis of maize (Zea mays L.) depends on growth temperatures with changes in leaf anatomy and soluble sugars

Understanding the potential mechanisms and processes of leaf photosynthesis in response to elevated CO2 concentration ([CO2]) and temperature is critical for estimating the impacts of climatic change on the growth and yield in crops such as maize (Zea mays L.), which is a widely cultivated C4 crop all over the world. We examined the combined effect of elevated [CO2] and temperature on plant growth, leaf photosynthesis, stomatal traits, and biochemical compositions of maize with six environmental growth chambers controlling two CO2 levels (400 and 800 μmol mol−1) and three temperature regimes (25/19°C, 31/25°C, and 37/31°C). We found that leaf photosynthesis was significantly enhanced by increasing growth temperature from 25/19°C to 31/25°C independent of [CO2]. However, leaf photosynthesis drastically declined when the growth temperature was continually increased to 37/31°C at both ambient CO2 concentration (400 μmol mol−1, a[CO2]) and elevated CO2 concentration (800 μmol mol−1, e[CO2]). Meanwhile, we also found strong CO2 fertilization effect on maize plants grown at the highest temperature (37/31°C), as evidenced by the higher leaf photosynthesis at e[CO2] than that at a[CO2], although leaf photosynthesis was similar between a[CO2] and e[CO2] under the other two temperature regimes of 25/19°C and 31/25°C. Furthermore, we also found that e[CO2] resulted in an increase in leaf soluble sugar, which was positively related with leaf photosynthesis under the high temperature regime of 37/31°C (R2 = 0.77). In addition, our results showed that e[CO2] substantially decreased leaf transpiration rates of maize plants, which might be partially attributed to the reduced stomatal openness as demonstrated by the declined stomatal width and stomatal area. These results suggest that the CO2 fertilization effect on plant growth and leaf photosynthesis of maize depends on growth temperatures through changing stomatal traits, leaf anatomy, and soluble sugar contents.

Water Stress Impacts on Grapevines (Vitis vinifera L.) in Hot Environments: Physiological and Spectral Responses

The projected increase in temperature and water scarcity represents a challenge for winegrowers due to changing climatic conditions. Although heat and drought often occur concurrently in nature, there is still little known about the effects of water stress (WS) on grapevines in hot environments. This study aimed to assess whether the grapevine’s physiological and spectral responses to WS in hot environments differ from those expected under lower temperatures. Therefore, we propose an integrated approach to assess the physiological, thermal, and spectral response of two grapevine varieties (Vitis vinifera L.), Grenache and Shiraz, to WS in a hot environment. In a controlled environment room (CER), we imposed high-temperature conditions (TMIN 30 °C–TMAX 40 °C) and compared the performance of well-watered (WW) and WS-ed potted own-rooted Shiraz and Grenache grapevines (SH_WW, SH_WS, GR_WW, and GR_WS, respectively). We monitored the vines’ physiological, spectral, and thermal trends from the stress imposition to the recovery after re-watering. Then, we performed a correlation analysis between the physiological parameters and the spectral and thermal vegetation indices (VIs). Finally, we looked for the best-fitting models to predict the physiological parameters based on the spectral VIs. The results showed that GR_WS was more negatively impacted than SH_WS in terms of net photosynthesis (Pn, GR-WS = 1.14 μmol·CO2 m−2·s−1; SH-WS = 3.64 μmol·CO2 m−2·s−1), leaf transpiration rate (E, GR-WS = 1.02 mmol·H2O m−2·s−1; SH-WS = 1.75 mmol·H2O m−2·s−1), and stomatal conductance (gs, GR-WS = 0.04 mol·H2O m−2·s−1; SH-WS = 0.11 mol·H2O m−2·s−1). The intrinsic water-use efficiency (WUEi = Pn/gs) of GR_WS (26.04 μmol·CO2 mol−1 H2O) was lower than SH_WS (34.23 μmol·CO2 mol−1 H2O) and comparable to that of SH_WW (26.31 μmol·CO2 mol−1 H2O). SH_WS was not unaffected by water stress except for E. After stress, Pn, gs, and E of GR_WS did not recover, as they were significantly lower than the other treatments. The correlation analysis showed that the anthocyanin Gitelson (AntGitelson) and the green normalised difference vegetation index (GNDVI) had significant negative correlations with stem water potential (Ψstem), Pn, gs, and E and positive correlation with WUEi. In contrast, the photochemical reflectance index (PRI), the water index (WI), and the normalised difference infrared index (NDII) showed an opposite trend. Finally, the crop water stress (CWSI) had significant negative correlations with the Ψstem in both varieties. Our findings help unravel the behaviour of vines under WS in hot environments and suggest instrumental approaches to help the winegrowers managing abiotic stress.