High light aggravates functional limitations of cucumber canopy photosynthesis under salinity

Cucumber grafting on indigenous cucurbit landraces confers salt tolerance and improves fruit yield by enhancing morpho-physio-biochemical and ionic attributes

Pakistan is the 8th most climate-affected country in the globe along with a semi-arid to arid climate, thereby the crops require higher irrigation from underground water. Moreover,  ~ 70% of pumped groundwater in irrigated agriculture is brackish and a major cause of secondary salinization. Cucumber (Cucumis sativus L.) is an important vegetable crop with an annual growth rate of about 3.3% in Pakistan. However, it is a relatively salt-sensitive crop. Therefore, a dire need for an alternate environment-friendly technology like grafting for managing salinity stress in cucumber by utilizing the indigenous cucurbit landraces. In this regard, a non-perforated pot-based study was carried out in a lath house to explore indigenous cucurbit landraces; bottle gourd (Lagenaria siceraria) (cv. Faisalabad Round), pumpkin (Cucurbit pepo. L) (cv. Local Desi Special), sponge gourd (Luffa aegyptiaca) (cv. Local) and ridge gourd (Luffa acutangula) (cv. Desi Special) as rootstocks for inducing salinity tolerance in cucumber (cv. Yahla F1). Four different salts (NaCl) treatments; T0 Control (2.4 dSm-1), T1 (4 dSm-1), T2 (6 dSm-1) and T3 (8 dSm-1) were applied. The grafted cucumber plants were transplanted into the already-induced salinity pots (12-inch). Different morpho-physio-biochemical, antioxidants, ionic, and yield attributes were recorded. The results illustrate that increasing salinity negatively affected the growing cucumber plants. However, grafted cucumber plants showed higher salt tolerance relative to non-grafted ones. Indigenous bottle gourd landrace (cv. Faisalabad Round) exhibited higher salt tolerance compared to non-grafted cucumber plants due to higher up-regulation of morpho-physio-biochemical, ionic, and yield attributes that was also confirmed by principal component analysis (PCA). Shoot and root biomass, chlorophylls contents (a and b), activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POX) enzymes, antioxidants scavenging activity (ASA), ionic (↑ K and Ca, ↓ Na), and yield-related attributes were found maximum in cucumber plants grafted onto indigenous bottle gourd landrace. Hence, the indigenous bottle gourd landrace 'cv. Faisalabad round' may be utilized as a rootstock for cucumber under a mild pot-based saline environment. However, indigenous bottle gourd landrace 'cv. Faisalabad round' may further be evaluated as rootstocks in moderate saline field conditions for possible developing hybrid rootstock and, subsequently, sustainable cucumber production.

Research Progress in Improving Photosynthetic Efficiency

Photosynthesis is the largest mass- and energy-conversion process on Earth, and it is the material basis for almost all biological activities. The efficiency of converting absorbed light energy into energy substances during photosynthesis is very low compared to theoretical values. Based on the importance of photosynthesis, this article summarizes the latest progress in improving photosynthesis efficiency from various perspectives. The main way to improve photosynthetic efficiency is to optimize the light reactions, including increasing light absorption and conversion, accelerating the recovery of non-photochemical quenching, modifying enzymes in the Calvin cycle, introducing carbon concentration mechanisms into C₃ plants, rebuilding the photorespiration pathway, de novo synthesis, and changing stomatal conductance. These developments indicate that there is significant room for improvement in photosynthesis, providing support for improving crop yields and mitigating changes in climate conditions.

Stomata conductance as a goalkeeper for increased photosynthetic efficiency

100-120 words. References should not be included. Abbreviations should be avoided as far as possible. Low stomatal conductance (g_s) poses a major constraint for improving photosynthetic efficiency for greater yield. Options at the molecular, leaf, canopy, and even the whole plant scales can be developed to enhance g_s for greater light and water use efficiencies. Among these, many genes regulating stomatal development and stomatal movement have been discovered and manipulated to increase light and water use efficiencies under well-watered, drought, or facility agriculture conditions with the manual-controlled growth environmental. Optimization of canopy conductance to increase whole plant photosynthesis with full consideration of the heterogeneities in g_s, microclimates and leaf ontology inside the canopy represents a largely uncharted area to improve crop efficiency.

Compost from willow biomass (Salix viminalis L.) as a horticultural substrate alternative to peat in the production of vegetable transplants

Willow (Salix viminalis L.) is a species well adapted to the environment conditions of central Europe. It is mainly cultivated for energy purposes as solid fuel. In this study, an evaluation of its suitability for other purposes was made using a 4-year old short rotation coppice (SRC) willow regrowth to produce chipped biomass which was composted. Four composting methods were used: without additives (WC), with the addition of nitrogen to narrow the C:N ratio (WN), with the addition of mycelium (WPG) and with the addition of mycelium and nitrogen (WPGN). A mixture of WC and WPGN composts was also prepared at 75:25% and 50:50% by volume. Composts, different proportion (25, 50 and 75%) of peat (SM) were evaluated for suitability as a substrate for tomato and cucumber transplant production. Tomato transplants produced in the medium were prepared from mixtures of willow composts (WPGN + WC(1) and WPGN + WC(2) and these mixtures with peat (WPGN + WC(1):SM and WPGN + WC(2):SM) were characterised as having the best parameters: plant height, lateral leaf span and number of leaves. Similarly, for cucumber transplants, better growth conditions than in peat substrate were obtained in the variant WPGN + WC(1) and WPGN + WC(1):SM. The addition of nitrogen to the composted biomass positively influenced the composting process. N concentration in the substrate was too high and toxic for the growth of tomato and cucumber transplants. At the end of the tomato and cucumber experiment, the nitrate content was 1510 and 2260 mg dm^-3, respectively, in the WN substrate. Similarly, the high N-NO₃^- content in the composted willow substrate with the addition of nitrogen and mycelium did not promote the growth of tomato and cucumber. Based on this research at least 25% of the mass of the peat can be replaced by different willow composts without having an adverse impact on seedling growth and with some of the willow compost mixtures this could be as high as 50%.

Exogenous ethanol treatment alleviates oxidative damage of Arabidopsis thaliana under conditions of high-light stress

Abiotic stresses, such as high light and salinity, are major factors that limit crop productivity and sustainability worldwide. Chemical priming is a promising strategy for improving the abiotic stress tolerance of plants. Recently, we discovered that ethanol enhances high-salinity stress tolerance in Arabidopsis thaliana and rice by detoxifying reactive oxygen species (ROS). However, the effect of ethanol on other abiotic stress responses is unclear. Therefore, we investigated the effect of ethanol on the high-light stress response. Measurement of chlorophyll fluorescence showed that ethanol mitigates photoinhibition under high-light stress. Staining with 3,3'-diaminobenzidine (DAB) showed that the accumulation of hydrogen peroxide (H₂O₂) was inhibited by ethanol under high-light stress conditions in A. thaliana. We found that ethanol increased the gene expressions and enzymatic activities of antioxidative enzymes, including ASCORBATE PEROXIDASE1 (AtAPX1), Catalase (AtCAT1 and AtCAT2). Moreover, the expression of flavonoid biosynthetic genes and anthocyanin contents were upregulated by ethanol treatment during exposure to high-light stress. These results imply that ethanol alleviates oxidative damage from high-light stress in A. thaliana by suppressing ROS accumulation. Our findings support the hypothesis that ethanol improves tolerance to multiple stresses in field-grown crops.

Thermal Analysis of Stomatal Response under Salinity and High Light

A non-destructive thermal imaging method was used to study the stomatal response of salt-treated Arabidopsis thaliana plants to excessive light. The plants were exposed to different levels of salt concentrations (0, 75, 150, and 220 mM NaCl). Time-dependent thermograms showed the changes in the temperature distribution over the lamina and provided new insights into the acute light-induced temporary response of Arabidopsis under short-term salinity. The initial response of plants, which was associated with stomatal aperture, revealed an exponential growth in temperature kinetics. Using a single-exponential function, we estimated the time constants of thermal courses of plants exposed to acute high light. The saline-induced impairment in stomatal movement caused the reduced stomatal conductance and transpiration rate. Limited transpiration of NaCl-treated plants resulted in an increased rosette temperature and decreased thermal time constants as compared to the controls. The net CO₂ assimilation rate decreased for plants exposed to 220 mM NaCl; in the case of 75 mM NaCl treatment, an increase was observed. A significant decline in the maximal quantum yield of photosystem II under excessive light was noticeable for the control and NaCl-treated plants. This study provides evidence that thermal imaging as a highly sensitive technique may be useful for analyzing the stomatal aperture and movement under dynamic environmental conditions.

Vertical distribution of gas exchanges and their integration throughout the entire canopy in a maize field

Fluxes of carbon and water along a vertical profile within a canopy, particularly the associations between canopy and ecosystem levels, are not well studied. In this study, gas exchange along the vertical profile in a maize canopy was examined. The relationships between leaf- and ecosystem-level carbon and water fluxes were compared. The results from research conducted over two growing seasons showed that during vegetative growth, the top and middle leaf layers in the canopy contribute most to the carbon and water fluxes of the entire canopy. During the grain-filling stage, gas exchange processes were performed mostly in the middle leaves with and near the ears. Significant relationships were observed between the net ecosystem CO₂ exchange rate (NEE) plus soil respiration and the assumed canopy levels (A_canopy) and between evapotranspiration rates at the ecosystem (ET) and assumed canopy levels (E_canopy). This highlights the close associations between these parameters by integrating the leaf gas exchange rates measured in a conventional leaf cuvette and those at the ecosystem level via the eddy covariance technique. These results improve our understanding of how carbon assimilation varies vertically within a canopy, highlighting the critical role of ear leaves.

Parameter estimation for functional-structural plant models when data are scarce: using multiple patterns for rejecting unsuitable parameter sets

BACKGROUND AND AIMS

Functional-structural plant (FSP) models provide insights into the complex interactions between plant architecture and underlying developmental mechanisms. However, parameter estimation of FSP models remains challenging. We therefore used pattern-oriented modelling (POM) to test whether parameterization of FSP models can be made more efficient, systematic and powerful. With POM, a set of weak patterns is used to determine uncertain parameter values, instead of measuring them in experiments or observations, which often is infeasible.

METHODS

We used an existing FSP model of avocado (Persea americana 'Hass') and tested whether POM parameterization would converge to an existing manual parameterization. The model was run for 10 000 parameter sets and model outputs were compared with verification patterns. Each verification pattern served as a filter for rejecting unrealistic parameter sets. The model was then validated by running it with the surviving parameter sets that passed all filters and then comparing their pooled model outputs with additional validation patterns that were not used for parameterization.

KEY RESULTS

POM calibration led to 22 surviving parameter sets. Within these sets, most individual parameters varied over a large range. One of the resulting sets was similar to the manually parameterized set. Using the entire suite of surviving parameter sets, the model successfully predicted all validation patterns. However, two of the surviving parameter sets could not make the model predict all validation patterns.

CONCLUSIONS

Our findings suggest strong interactions among model parameters and their corresponding processes, respectively. Using all surviving parameter sets takes these interactions into account fully, thereby improving model performance regarding validation and model output uncertainty. We conclude that POM calibration allows FSP models to be developed in a timely manner without having to rely on field or laboratory experiments, or on cumbersome manual parameterization. POM also increases the predictive power of FSP models.

Salt stress and fluctuating light have separate effects on photosynthetic acclimation, but interactively affect biomass

In nature, soil salinity and fluctuating light (FL) often occur concomitantly. However, it is unknown whether salt stress interacts with FL on leaf photosynthesis, architecture, biochemistry, pigmentation, mineral concentrations, as well as whole-plant biomass. To elucidate this, tomato (Solanum lycopersicum) seedlings were grown under constant light (C, 200 μmol m^-2 s^-1 ) or FL (5-650 μmol m^-2 s^-1 ), in combination with no (0 mM NaCl) or moderate (80 mM NaCl) salinity, for 14 days, at identical photoperiods and daily light integrals. FL and salt stress had separate effects on leaf anatomy, biochemistry and photosynthetic capacity: FL reduced leaf thickness as well as nitrogen, chlorophyll and carotenoid contents per unit leaf area, but rarely affected steady-state and dynamic photosynthetic properties along with abundance of key proteins in the electron transport chain. Salt stress, meanwhile, mainly disorganized chloroplast grana stacking, reduced stomatal density, size and aperture as well as photosynthetic capacity. Plant biomass was affected interactively by light regime and salt stress: FL reduced biomass in salt stressed plants by 17%, but it did not affect biomass of non-stressed plants. Our results stress the importance of considering FL when inferring effects of salt-stress on photosynthesis and productivity under fluctuating light intensities.

Determining Ion Toxicity in Cucumber under Salinity Stress

Cucumber (Cucumis sativus L.), an important vegetable crop, is sensitive to NaCl. Its salinity tolerance can be improved by grafting onto pumpkin rootstocks, which restricts the uptake of Na+, but not of Cl−. Although Na+ seems to be more toxic than Cl− in cucumber, tissue tolerance to Na+ and Cl− is still unclear. In this study, a mixed-salt experiment, designed for equal osmolarity and equimolar concentrations of ions between treatments, was conducted using cucumber genotypes “Aramon” and “Line-759,” which are different in Na+ and Cl− exclusion. This combination of treatments generated various patterns of ion concentrations in leaves for deriving the response curves of photosynthesis and stomatal conductance to ion concentrations. In both cultivars, photosynthesis and stomatal conductance were sensitive to leaf Na+ concentration but insensitive to Cl− concentration. In these genotypes, tissue tolerance to Na+ varied independently of Na+ exclusion. Grafting “Aramon” onto pumpkin rootstock modified the Na+/Cl− ratio in leaves, reduced Na+ uptake, enhanced K+ transport towards the young leaves, and induced Cl− recirculation to the old leaves. These results suggest that (1) cucumber cannot restrict the Na+ accumulation in leaves but is able to avoid overaccumulation of Cl−, and (2) pumpkin rootstock regulates the recirculation of K+ and Cl−, but not Na+.

CO2 uptake and chlorophyll a fluorescence of Suaeda fruticosa grown under diurnal rhythm and after transfer to continuous dark

Although only 2-4% of absorbed light is emitted as chlorophyll (Chl) a fluorescence, its measurement provides valuable information on photosynthesis of the plant, particularly of Photosystem II (PSII) and Photosystem I (PSI). In this paper, we have examined photosynthetic parameters of Suaeda fruticosa L. (family: Amaranthaceae), surviving under extreme xerohalophytic conditions, as influenced by diurnal rhythm or continuous dark condition. We report here CO₂ gas exchange and the kinetics of Chl a fluorescence of S. fruticosa, made every 3 hours (hrs) for 3 days, using a portable infra-red gas analyzer and a Handy PEA fluorimeter. Our measurements on CO₂ gas exchange show the maximum rate of photosynthesis to be at 08:00 hrs under diurnal condition and at 05:00 hrs under continuous dark. From the OJIP phase of Chl a fluorescence transient, we have inferred that the maximum quantum yield of PSII photochemistry must have increased during the night under diurnal rhythm, and between 11:00 and 17:00 hrs under constant dark. Overall, our study has revealed novel insights into how photosynthetic reactions are affected by the photoperiodic cycles in S. fruticosa under high salinity. This study has further revealed a unique strategy operating in this xero-halophyte where the repair mechanism for damaged PSII operates during the dark, which, we suggest, contributes to its ecological adaptation and ability to survive and reproduce under extreme saline, high light, and drought conditions. We expect these investigations to help in identifying key genes and pathways for raising crops for saline and dry areas.

Changes in the vertical distribution of leaf area enhanced light interception efficiency in maize over generations of selection

Breeders select for yield, thereby indirectly selecting for traits that contribute to it. We tested if breeding has affected a range of traits involved in plant architecture and light interception, via the analysis of a panel of 60 maize hybrids released from 1950 to 2015. This was based on novel traits calculated from reconstructions derived from a phenotyping platform. The contribution of these traits to light interception was assessed in virtual field canopies composed of 3D plant reconstructions, with a model tested in a real field. Two categories of traits had different contributions to genetic progress. (a) The vertical distribution of leaf area had a high heritability and showed a marked trend over generations of selection. Leaf area tended to be located at lower positions in the canopy, thereby improving light penetration and distribution in the canopy. This potentially increased the carbon availability to ears, via the amount of light absorbed by the intermediate canopy layer. (b) Neither the horizontal distribution of leaves in the relation to plant rows nor the response of light interception to plant density showed appreciable trends with generations. Hence, among many architectural traits, the vertical distribution of leaf area was the main indirect target of selection.

Environmental triggers for photosynthetic protein turnover determine the optimal nitrogen distribution and partitioning in the canopy

Plants continually adjust the photosynthetic functions in their leaves to fluctuating light, thereby optimizing the use of photosynthetic nitrogen (Nph) at the canopy level. To investigate the complex interplay between external signals during the acclimation processes, a mechanistic model based on the concept of protein turnover (synthesis and degradation) was proposed and parameterized using cucumber grown under nine combinations of nitrogen and light in growth chambers. Integrating this dynamic model into a multi-layer canopy model provided accurate predictions of photosynthetic acclimation of greenhouse cucumber canopies grown under high and low nitrogen supply in combination with day-to-day fluctuations in light at two different levels. This allowed us to quantify the degree of optimality in canopy nitrogen use for maximizing canopy carbon assimilation, which was influenced by Nph distribution along canopy depth or Nph partitioning between functional pools. Our analyses suggest that Nph distribution is close to optimum and Nph reallocation is more important under low nitrogen. Nph partitioning is only optimal under a light level similar to the average light intensity during acclimation, meaning that day-to-day light fluctuations inevitably result in suboptimal Nph partitioning. Our results provide insights into photoacclimation and can be applied to crop model improvement.

Managing Traditional Solar Greenhouse With CPSS: A Just-for-Fit Philosophy

The profit of greenhouse production is influenced by management activities (e.g., environmental control and plantation scheduling) as well as social conditions (e.g., price fluctuation). In China, the prevailing horticultural facility is the traditional solar greenhouse. The key existing problem is the lack of knowledge of growers, which in turn leads to inefficient management, low production, or unsalable products. To secure effective greenhouse management, the production planning system must account for the crop growing environment, grower's activities, and the market. This paper presents an agricultural cyber-physical-social system (CPSS) serving agricultural production management, with a case study on the solar greenhouse. The system inputs are derived from social and physical sensors, with the former collecting the price of agricultural products in a wholesale market, and the latter collecting the necessary environmental data in the solar greenhouse. Decision support for the cropping plan is provided by the artificial system, computational experiment, and parallel execution-based method, with description intelligence for estimating the crop development and harvest time, prediction intelligence for optimizing the planting time and area according to the expected targets (stable production or maximum gross profit), and prescription intelligence for online system training. The presented system fits the current technical and economic situation of horticulture in China. The application of agricultural CPSS could decrease waste in labor or fertilizer and support sustainable agricultural production.

Computational botany: advancing plant science through functional–structural plant modelling

The need to integrate the ever-expanding body of knowledge in the plant sciences has led to the development of sophisticated modelling approaches. This special issue focuses on functional–structural plant (FSP) models, which are the result of cross-fertilization between the domains of plant science, computer science and mathematics. FSP models simulate growth and morphology of individual plants that interact with their environment, from which complex plant community properties emerge. FSP models can be used for a broad range of research questions across disciplines related to plant science. This special issue presents the latest developments in FSP modelling, including the novel incorporation of plant ecophysiological concepts and the application of FSP models to address new scientific questions. Additionally, it illustrates the breadth of model evaluation approaches that are performed. FSP modelling is a very active domain of plant research which brings together a wide range of scientific disciplines. It offers the opportunity to address questions in complex plant systems that cannot be addressed by empirical approaches alone, including questions on fundamental concepts related to plant development such as regulation of morphogenesis, as well as on applied concepts such as the relationship between crop performance and plant competition for resources.