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Adding far-red (FR, 700–800 nm) light to photosynthetic active radiation (400–700 nm) proved to be a possible approach to increasing plant biomass accumulation for lettuce production in indoor vertical farms with artificial lighting as a sole-source lighting. However, how FR light addition influences plant growth, development, and metabolic processes and the optimal value of FR photon flux density for greenhouse-grown lettuce under sunlight are still unclear. This work aims to quantify the value of supplementary FR light with different intensities on lettuce morphological and physiological characteristics in a greenhouse. Lettuce 'Dasusheng' (Lactuca sativa L.) was grown in a greenhouse under seven light treatments, including white plus red LEDs with FR photon flux density at 0, 10, 30, 50, 70, and 90 µmol m−2 s−1 (WR, WR + FR10, WR + FR30, WR + FR50, WR + FR70, and WR + FR90, respectively), and lettuce grown with sunlight only was marked as natural light (NL). FR light addition improved the electron transport flux per cross section and performance index (PIabs, PItotal) and decreased the changes in relative variable fluorescence of lettuce leaves compared to plants under NL. Specifically, the PIabs of lettuce leaves were 41%, 41%, 38%, 33%, 26%, and 25% lower under control than in plants under treatments WR + FR90, WR + FR70, WR + FR50, WR + FR30, WR + FR10, and WR, respectively. Leaf number, leaf area, and biomass accumulation of lettuce followed a quadratic function with increasing FR light intensity and were the highest under treatment WR + FR50. The shoot fresh weight and dry weight of lettuce were increased by 111% and 275%, respectively, under treatment WR + FR50 compared to NL. The contents of vitamin C, reducing sugar, total soluble sugar, and starch in lettuce showed a similar trend with biomass accumulation. In conclusion, with commonly used photosynthetic photon flux density (PPFD, 400–700 nm) around 200 μmol m−2 s−1, supplementary FR light intensity of 30~50 μmol m−2 s−1 was suggested to enhance the photochemistry efficiency, biomass accumulation, and carbohydrates' contents in greenhouse-grown lettuce. [ABSTRACT FROM AUTHOR]

Adding far-red (FR, 700–800 nm) light to photosynthetic active radiation (400–700 nm) proved to be a possible approach to increasing plant biomass accumulation for lettuce production in indoor vertical farms with artificial lighting as a sole-source lighting. However, how FR light addition influences plant growth, development, and metabolic processes and the optimal value of FR photon flux density for greenhouse-grown lettuce under sunlight are still unclear. This work aims to quantify the value of supplementary FR light with different intensities on lettuce morphological and physiological characteristics in a greenhouse. Lettuce ‘Dasusheng’ (Lactuca sativa L.) was grown in a greenhouse under seven light treatments, including white plus red LEDs with FR photon flux density at 0, 10, 30, 50, 70, and 90 µmol m−2 s−1 (WR, WR + FR10, WR + FR30, WR + FR50, WR + FR70, and WR + FR90, respectively), and lettuce grown with sunlight only was marked as natural light (NL). FR light addition improved the electron transport flux per cross section and performance index (PIabs, PItotal) and decreased the changes in relative variable fluorescence of lettuce leaves compared to plants under NL. Specifically, the PIabs of lettuce leaves were 41%, 41%, 38%, 33%, 26%, and 25% lower under control than in plants under treatments WR + FR90, WR + FR70, WR + FR50, WR + FR30, WR + FR10, and WR, respectively. Leaf number, leaf area, and biomass accumulation of lettuce followed a quadratic function with increasing FR light intensity and were the highest under treatment WR + FR50. The shoot fresh weight and dry weight of lettuce were increased by 111% and 275%, respectively, under treatment WR + FR50 compared to NL. The contents of vitamin C, reducing sugar, total soluble sugar, and starch in lettuce showed a similar trend with biomass accumulation. In conclusion, with commonly used photosynthetic photon flux density (PPFD, 400–700 nm) around 200 μmol m−2 s−1, supplementary FR light intensity of 30~50 μmol m−2 s−1 was suggested to enhance the photochemistry efficiency, biomass accumulation, and carbohydrates’ contents in greenhouse-grown lettuce.

This study assessed the nitrogen nutrition index, morphogenic characteristics and tiller structure of Alexandergrass (Urochloa plantaginea (LINK) Hitch) pasture submitted to different nitrogen (N) levels (zero, 150 or 300 kg ha-1 of N). The experimental design was entirely randomized with repeated measures arrangement. The experimental animals were Angus heifers under rotational stocking grazing method. The number of animals was variable to keep 30±5 cm post-grazing sward height. Nitrogen nutrition index increased linearly according N levels (Ŷ = 59.8 + 0.1216N; P < 0.0001; r²=0.53). The leaf appearance rate adjusted to a positive linear regression model according the thermal sum (TS) with zero of N (Ŷ0N = 0.0077 + 0.0000087TS; P = 0.0308; r² = 0.72) and 150 kg ha-1 of N (Ŷ150N = 0.0020 + 0.000021 TS; P = 0.0022; r² = 0.92). The use of 300 kg ha-1 of N did not alter the leaf appearance rate (0.0124 leaf degree-days-1). The use of up to 300 kg ha-1 of N increases the Alexandergrass nitrogen content. The leaf appearance rate in Alexandergrass is modified using N while the morphogenic characteristics leaf expansion, stem expansion, phyllochron, leaf lifespan, leaf elongation duration and tiller structure are not altered by N utilization. [ABSTRACT FROM AUTHOR]

Plants exhibit morphological plasticity in response to changes in the proportion of far-red radiation (FR). However, little is known about the response to a sudden increase of FR component. Cucumber seedlings were acclimatized to radiation without FR (FR-) for 1 - 5 d after germination, and then transferred to radiation containing FR (FR+) at levels similar to those in natural sunlight. Other seedlings were acclimatized to FR- or FR+, which was maintained continuously. The sudden increase in FR damaged the cotyledons and the first true leaf, especially when radiation was changed from FR- to FR+ at days 3 or 4 after germination. Necrosis of the damaged leaves may have resulted from inhibition of water flow in leaf xylem, because wilting and decreased stomatal conductance were observed simultaneously with leaf necrosis. Plants in the treatment groups that showed the most frequent damage showed two peaks in cotyledon elongation. This suggests that the leaves that had been acclimatized to FR- were easily damaged by the sudden promotion of leaf expansion caused by FR+.

Plants compete for sunlight and have evolved to perceive shade through both relative increases in the flux of far-red photons (FR; 700 to 750 nm) and decreases in the flux of all photons (intensity). These two signals interact to control stem elongation and leaf expansion. Although the interacting effects on stem elongation are well quantified, responses for leaf expansion are poorly characterized. Here we report a significant interaction between far-red fraction and total photon flux. Extended photosynthetic photon flux density (ePPFD; 400 to 750 nm) was maintained at three levels (50/100, 200 and 500 µmol m-2 s-1), each with a range of 2 to 33% FR. Increasing FR increased leaf expansion in three cultivars of lettuce at the highest ePPFD but decreased expansion at the lowest ePPFD. This interaction was attributed to differences in biomass partitioning between leaves and stems. Increased FR favored stem elongation and biomass partitioning to stems at low ePPFD and favored leaf expansion at high ePPFD. In cucumber, leaf expansion was increased with increasing percent FR under all ePPFD levels showing minimal interaction. The interactions (and lack thereof) have important implications for horticulture and warrant further study for plant ecology. [ABSTRACT FROM AUTHOR]

Plants compete for sunlight and have evolved to perceive shade through both relative increases in the flux of far-red photons (FR; 700 to 750 nm) and decreases in the flux of all photons (intensity). These two signals interact to control stem elongation and leaf expansion. Although the interacting effects on stem elongation are well quantified, responses for leaf expansion are poorly characterized. Here we report a significant interaction between far-red fraction and total photon flux. Extended photosynthetic photon flux density (ePPFD; 400 to 750 nm) was maintained at three levels (50/100, 200 and 500 µmol m-2 s-1), each with a range of 2 to 33% FR. Increasing FR increased leaf expansion in three cultivars of lettuce at the highest ePPFD but decreased expansion at the lowest ePPFD. This interaction was attributed to differences in biomass partitioning between leaves and stems. Increased FR favored stem elongation and biomass partitioning to stems at low ePPFD and favored leaf expansion at high ePPFD. In cucumber, leaf expansion was increased with increasing percent FR under all ePPFD levels showing minimal interaction. The interactions (and lack thereof) have important implications for horticulture and warrant further study for plant ecology.

ABSTRACT: This study assessed the nitrogen nutrition index, morphogenic characteristics and tiller structure of Alexandergrass (Urochloaplantaginea (LINK) Hitch) pasture submitted to different nitrogen (N) levels (zero, 150 or 300 kg ha-1 of N). The experimental design was entirely randomized with repeated measures arrangement. The experimental animals were Angus heifers under rotational stocking grazing method. The number of animals was variable to keep 30±5 cm post-grazing sward height. Nitrogen nutrition index increased linearly according N levels (Ŷ = 59.8 + 0.1216N; P < 0.0001; r²=0.53). The leaf appearance rate adjusted to a positive linear regression model according the thermal sum (TS) with zero of N (Ŷ0N = 0.0077 + 0.0000087TS; P = 0.0308; r² = 0.72) and 150 kg ha-1 of N (Ŷ150N = 0.0020 + 0.000021 TS; P = 0.0022; r² = 0.92). The use of 300 kg ha-1 of N did not alter the leaf appearance rate (0.0124 leaf degree-days-1). The use of up to 300 kg ha-1 of N increases the Alexandergrass nitrogen content. The leaf appearance rate in Alexandergrass is modified using N while the morphogenic characteristics leaf expansion, stem expansion, phyllochron, leaf lifespan, leaf elongation duration and tiller structure are not altered by N utilization.

The photon costs of photoreduction/assimilation of nitrate (NO3−) into organic nitrogen in shoots and respiratory driven NO3− and NH4+ assimilation in roots are compared for terrestrial vascular plants, considering associated pH regulation, osmotic and ontogenetic effects. Different mechanisms of neutralisation of the hydroxyl (OH−) ion necessarily generated in shoot NO3− assimilation are considered. Photoreduction/assimilation of NO3− in shoots with malic acid synthesis and either accumulation of malate in leaf vacuoles or transport of malate to roots and catabolism there have a similar cost which is around 35% less than that for root NO3− assimilation and around 20% less than that for photoreduction/assimilation of NO3−, oxalate production and storage of Ca oxalate in leaf vacuoles. The photon cost of root NH4+ assimilation with H+ efflux to the root medium is around 70% less than that of root NO3− assimilation. These differences in photon cost must be considered in the context of the use of a combination of locations of NO3− assimilation and mechanisms of acid–base regulation, and a maximum of 4.9–9.1% of total photon absorption needed for growth and maintenance that is devoted to NO3− assimilation and acid–base regulation. [ABSTRACT FROM AUTHOR]

Plants exhibit morphological plasticity in response to changes in the proportion of far-red radiation (FR). However, little is known about the response to a sudden increase of FR component. Cucumber seedlings were acclimatized to radiation without FR (FR-) for 1 - 5 d after germination, and then transferred to radiation containing FR (FR+) at levels similar to those in natural sunlight. Other seedlings were acclimatized to FR-or FR+, which was maintained continuously. The sudden increase in FR damaged the cotyledons and the first true leaf, especially when radiation was changed from FRto FR+ at days 3 or 4 after germination. Necrosis of the damaged leaves may have resulted from inhibition of water flow in leaf xylem, because wilting and decreased stomatal conductance were observed simultaneously with leaf necrosis. Plants in the treatment groups that showed the most frequent damage showed two peaks in cotyledon elongation. This suggests that the leaves that had been acclimatized to FR-were easily damaged by the sudden promotion of leaf expansion caused by FR+. [ABSTRACT FROM AUTHOR]

In serpentine soils, the low level of calcium relative to magnesium (Ca:Mg) is detrimental to the growth of most plant species. Ecotypic variation in Erythranthe guttata allows for some populations to maintain high photosynthetic rates and biomass despite low Ca:Mg. In this study, the mechanism of tolerance was investigated by treating hydroponically grown plants with either high (1.0) or low (0.02) Ca:Mg growth solutions and assaying excised leaf discs for rates of photosynthesis and disc expansion, and for starch, Ca2+ and Mg2+ ion concentrations. Low Ca:Mg in the assay solutions reduced both photosynthesis and leaf disc expansion after one week of treatment. However, serpentine tissues show stable photosynthetic rates after one week and a recovery in leaf tissue expansion after two weeks exposure to low Ca:Mg conditions. Values for non-serpentine tissues continued to decline. Increased growth of low Ca:Mg treated discs supplied with exogenous sucrose suggests that growth in serpentine-exposed tissues is limited by availability of carbon products from photosynthesis. Serpentine leaves had higher vacuole Mg concentrations than non-serpentine leaves after three weeks of treatment with low Ca:Mg. The combination of elevated starch concentrations, reduced growth and lower vacuolar Mg concentrations in leaves of non-serpentine plants grown in low Ca:Mg indicate an inefficient use of carbon resources and starch degradation as an observed response to Mg toxicity. Together, these results suggest that serpentine E. guttata exhibits an inducible tolerance to low Ca:Mg through gradual compartmentalization of magnesium to maintain the production and metabolism of photosynthates necessary for growth. [ABSTRACT FROM AUTHOR]

Auxin is the major hormone involved in the shade-avoidance response in plants. Auxin-induced elongation of the stem is accompanied by the restraint of leaf blade expansion. The auxin transportation inhibitor, 1-N-naphthylphthalamic acid (NPA), is widely used in auxin functional studies, while the effects of NPA on soybean leaf expansion under shade conditions is still not known. This study assessed the effect of NPA on hormone content and cell dynamics variations during leaf expansion of soybeans under shade conditions. The results revealed that the inhibition of soybean leaf area under shade conditions was caused by a reduction in the cell number at the early stages of leaf expansion. The application of NPA under shade conditions inhibited leaf expansion by reducing the cell number. Auxin levels showed an increasing trend during the leaf expansion under shade, while cytokinin was significantly reduced. The application of NPA also reduced cytokinin levels. Cell flow cytometry revealed that reduction of the cell mitotic index by shade and NPA were caused by decreasing cell division at the early stages of leaf expansion. The shade-tolerant variety had a relative larger leaf area than the shade-sensitive variety due to higher cell division. In conclusion, the application of NPA caused a cytokinin reduction at the early stages of leaf expansion, leading to a lower cell division and cell number and inhibiting the leaf area in soybeans under shade. Future works of the function of cytokinin on cell division for selecting a higher leaf area may increase shade tolerance. [ABSTRACT FROM AUTHOR]

Premise: Climate warming has altered the start and end of growing seasons in temperate regions. Ultimately, these changes occur at the individual level, but little is known about how previous seasonal life‐history events, temperature, and plant‐resource state simultaneously influence the spring and autumn phenology of plant individuals. Methods: We studied the relationships between the timing of leaf‐out and shoot senescence over 3 years in a natural population of the long‐lived understory herb Lathyrus vernus and investigated the effects of spring temperature, plant size, reproductive status, and grazing on spring and autumn phenology. Results: The timing of leaf‐out and senescence were consistent within individuals among years. Leaf‐out and senescence were not correlated with each other within years. Larger plants leafed out and senesced later, and size had no effect on growing season length. Reproductive plants leafed out earlier and had longer growing seasons than nonreproductive plants. Grazing had no detectable effects on phenology. Colder spring temperatures delayed senescence in two of three study years. Conclusions: The timing of seasonal events, such as leaf‐out and senescence in plants can be expressed largely independently within and among seasons and are influenced by different factors. Growing season start and length can often be dependent on plant condition and reproductive status. Knowledge about the drivers of growing season length of individuals is essential to more accurately predict species and community responses to environmental variation. [ABSTRACT FROM AUTHOR]

To examine the interactive effect of temperature and photon flux density (PFD) on growth dynamics and gas exchange of young Vitis vinifera L. cv. Shiraz vines, a controlled environment study was conducted by exposing vines to two different temperatures combined with either high or low PFD. Shoot growth was accelerated and the phyllochron of Shiraz leaves was hastened in the low temperature (25/12°C) × low PFD condition (350 μmol m−2 s−1). In early emerging leaves, leaf area was responsive to temperature whereas in later emerging leaves it was dependent on light intensity. The high temperature (32/20°C) × high PFD (700 μmol m−2 s−1) treatment delayed internode extension of early emerging internodes. However, low temperature × high PFD increased leaf gas exchange across the different growth stages. The net shoot carbon balance was greater for the low temperature × high PFD treatment. Dry matter accumulation was also greater in early emerging internodes irrespective of treatment. These results on young Shiraz vines indicate that 25°C is favourable to 32°C, and some growth characteristics are accelerated at low PFD while others favour higher PFD. This study describes the effects of temperature and light combination on young Vitis vinifera L. cv. Shiraz vines. The low temperature and low or high light conditions are favourable for growth characters of young vegetative Shiraz vines. However, high temperature and high light conditions are detrimental. [ABSTRACT FROM AUTHOR]

There are potential sources of alleles and genes currently present in wheat-related species that have the potential to be introduced into wheat breeding programs targeting current and future hot and dry climates. However, to date neither the intra- nor the interspecific diversity of the responses of leaf growth and transpiration to temperature and evaporative demand have been investigated in across a significant range of wheat-related species. By analysing 12 groups of wheat-related species and subspecies, we were able to examine the multi-dimensional structure of the genetic diversity for traits linked to plant vegetative structures and their development, and to leaf expansion and transpiration, together with their responses to 'non-stressing' ranges of temperature and evaporative demand. In addition to providing new insights on how genome type, ploidy level, phylogeny, and breeding pressure act together to structure this genetic diversity, our study also provides new mathematical formalisms and associated parameters for trait responses across a wide range of genetic diversity in wheat-related species. This will potentially allow crop models to predict the impact of this diversity on yield, and thus to indicate potential sources of varietal improvement for modern wheat germplasms through interspecific crosses. [ABSTRACT FROM AUTHOR]

The phenylpropanoid pathway, the source of a large array of compounds with diverse functions, starts with the synthesis of trans-cinnamic acid (t-CA) that is converted by cinnamate-4-hydroxylase (C4H) into p-coumaric acid. We have recently shown that in Arabidopsis, exogenous t-CA promotes leaf growth by increasing cell expansion and that this response requires auxin signaling. We have also shown that cell expansion is increased in C4H loss-of-function mutants. Here we provide further evidence that leaf growth is enhanced by either t-CA or a t-CA derivative that accumulates upstream of C4H. We also show that this growth response pathway has two components: one that requires auxin signaling and another which employs a currently unknown mechanism.

This study analyzed interactions among photon flux density (PPFD), air temperature, root-zone temperature for growth of lettuce with non-limiting water, nutrient, and CO2 concentration. We measured growth parameters in 48 combinations of a PPFD of 200, 400, and 750 μmol m–2 s–1 (16 h daylength), with air and root-zone temperatures of 20, 24, 28, and 32°C. Lettuce (Lactuca sativa cv. Batavia Othilie) was grown for four cycles (29 days after transplanting). Eight combinations with low root-zone (20 and 24°C), high air temperature (28 and 32°C) and high PPFD (400 and 750 μmol m–2 s–1) resulted in an excessive incidence of tip-burn and were not included in further analysis. Dry mass increased with increasing photon flux to a PPFD of 750 μmol m–2 s–1. The photon conversion efficiency (both dry and fresh weight) decreased with increasing photon flux: 29, 27, and 21 g FW shoot and 1.01, 0.87, and 0.76 g DW shoot per mol incident light at 200, 400, and 750 μmol m–2 s–1, respectively, averaged over all temperature combinations, following a concurrent decrease in specific leaf area (SLA). The highest efficiency was achieved at 200 μmol m–2 s–1, 24°C air temperature and 28°C root-zone temperature: 44 g FW and 1.23 g DW per mol incident light. The effect of air temperature on fresh yield was linked to all leaf expansion processes. SLA, shoot mass allocation and water content of leaves showed the same trend for air temperature with a maximum around 24°C. The effect of root temperature was less prominent with an optimum around 28°C in nearly all conditions. With this combination of temperatures, market size (fresh weight shoot = 250 g) was achieved in 26, 20, and 18 days, at 200, 400, and 750 μmol m–2 s–1, respectively, with a corresponding shoot dry matter content of 2.6, 3.8, and 4.2%. In conclusion, three factors determine the “optimal” PPFD: capital and operational costs of light intensity vs the value of reducing cropping time, and the market value of higher dry matter contents.

This study analyzed interactions among photon flux density (PPFD), air temperature, root-zone temperature for growth of lettuce with non-limiting water, nutrient, and CO2 concentration. We measured growth parameters in 48 combinations of a PPFD of 200, 400, and 750 μmol m–2 s–1 (16 h daylength), with air and root-zone temperatures of 20, 24, 28, and 32°C. Lettuce (Lactuca sativa cv. Batavia Othilie) was grown for four cycles (29 days after transplanting). Eight combinations with low root-zone (20 and 24°C), high air temperature (28 and 32°C) and high PPFD (400 and 750 μmol m–2 s–1) resulted in an excessive incidence of tip-burn and were not included in further analysis. Dry mass increased with increasing photon flux to a PPFD of 750 μmol m–2 s–1. The photon conversion efficiency (both dry and fresh weight) decreased with increasing photon flux: 29, 27, and 21 g FW shoot and 1.01, 0.87, and 0.76 g DW shoot per mol incident light at 200, 400, and 750 μmol m–2 s–1, respectively, averaged over all temperature combinations, following a concurrent decrease in specific leaf area (SLA). The highest efficiency was achieved at 200 μmol m–2 s–1, 24°C air temperature and 28°C root-zone temperature: 44 g FW and 1.23 g DW per mol incident light. The effect of air temperature on fresh yield was linked to all leaf expansion processes. SLA, shoot mass allocation and water content of leaves showed the same trend for air temperature with a maximum around 24°C. The effect of root temperature was less prominent with an optimum around 28°C in nearly all conditions. With this combination of temperatures, market size (fresh weight shoot = 250 g) was achieved in 26, 20, and 18 days, at 200, 400, and 750 μmol m–2 s–1, respectively, with a corresponding shoot dry matter content of 2.6, 3.8, and 4.2%. In conclusion, three factors determine the "optimal" PPFD: capital and operational costs of light intensity vs the value of reducing cropping time, and the market value of higher dry matter contents. [ABSTRACT FROM AUTHOR]

Maintenance and recovery of the canopy area when drought stress is relieved may be critical for maintaining high productivity. In this study, experiments were conducted in controlled environments to evaluate leaf expansion and leaf necrosis of five soybean (Glycine max Merr. L.) genotypes undergoing soil-drying, followed by re-watering. Water-deficit stress was imposed by limiting daily watering. When soil water decreased to a severe defined level, full watering resumed for five days. Measurements of leaf expansion and necrosis were taken during water-deficit and recovery periods. Genotypic differences for critical soil-water thresholds at which leaf expansion rates decline were detected. Genotype "Benning" showed the sensitivity of expansion rates to soil-drying while "Geden Shirazu" showed leaf expansion tolerance to soil drying. All genotypes recovered expansion rates within one or two days. During recovery, the recently released cultivar 'USDA-N8002ʹ had the highest leaf expansion rate among genotypes, compared to its well-watered plants. The high recovery potential of USDA-N8002 was largely attributable to high nighttime expansion recovery. This elite drought-tolerant cultivar, along with the commercial cultivar Benning, experienced the lowest levels of leaf necrosis. While all genotypes exhibited rapid recovery in leaf expansion following drought, variation in the extent of recovery and level of leaf necrosis indicates that these characteristics can be exploited to enhance drought resilience. [ABSTRACT FROM AUTHOR]

Phenological variation in spring leafing between and within species can determine plant responses to warmer winter and spring temperatures in the short term. Methods are needed for monitoring canopy development that can be replicated on a large-scale, while retaining fine-scale resolution at the level of individual trees. Citizen science has the potential to provide this, but a range of approaches exist in terms of the phenophase recorded (e.g. budburst or leaf expansion), how the phenophase is characterised (first events or intensity monitoring) and the portion of tree crown assessed and observation frequency. A comparison of spring budburst and leaf expansion of four tree species (Fraxinus excelsior, Fagus sylvatica, Quercus robur and Acer pseudoplatanus) was monitored in one woodland using (1) counts of expanded leaves on three crown sections, (2) percentage estimates of expanded leaves across the whole crown and (3) a greenness index from photography. Logistic growth models were applied to make comparisons. First-event dates were found to be misleading due to high variation in leaf development rates within and between species. Percentage estimates and counts produced similar estimates of leaf expansion timing and rate. The greenness index produced similar estimates of timing, but not rate, and was compromised by practicalities of photographing individual crowns in closed-canopy woodland. Citizen scientists could collect data across the period of spring leafing, with visual counts and/or estimates made every 3–4 days, subject to tests of reliability in pilot citizen science studies. [ABSTRACT FROM AUTHOR]

Surpluses of N are associated with environmental and health problems. To optimise N use and reduce nitrate accumulation in leafy species like spinach, the application of biostimulants is suggested. An experiment in controlled conditions (growth chamber/soilless) evaluated baby-spinach responses to two protein hydrolysates (PHs) from plant (legume, Trainer®) and animal (meat, Isabion®) sources, combined with three N rates: 2 (N2, deficient), 8 (N8, sub-optimal), and 14 (N14, optimal) mM of N. Biometrical and morphological traits of shoots and roots as well as the physio-metabolic (gas exchange, N assimilation, and NUtE), physical, mineral, and antioxidant profiles of leaves were assessed. The legume-PH boosts growth and yield only at the highest N conditions, while there was no effect at lower N rates. The legume-PH modulates root architecture and chlorophylls has positive responses only at optimal N availability, such as an increase in N uptake, leaf expansion, and photosynthetic activity at the canopy level. The PHs do not improve NUtE, leaf colour, consistency, cations, or antioxidants. Neither do PHs have any effect on reducing nitrate accumulation. Legume-PH improves N assimilation only at optimal N availability, while meat-PH does not, reaching the highest nitrate value at the highest N rate (2677 mg kg−1 fw), even if this value is under the EC limits for fresh spinach.

Studying the phenological characteristics of landscape trees can determine the optimal afforestation time for local landscaping, while also providing a theoretical basis for garden design, plant configuration and garden phenology prediction. In order to grasp the leaf pheniological rhythm of common landscape tree species in Nyingchi Prefecture, optimize the garden plant configuration of Nyingchi Prefecture, 53 kinds of landscape tree species were selected as the object for continuous 5a parallel observation and analysis of their leaf phenology. The results showed that: the budding period lasts from early March to mid-April, and that of 20 species concentrates in late March. It is recommended that afforestation be completed before mid-April. The leaf expansion period lasts from early March to mid-June, and the peak period is from mid-April to early May. It is recommended to arrange the seasonal landscape according to the leaf expansion characteristics of the tree species. The 53 tree species were classified into 5 types based on leaf phenological characteristics. Finally, corresponding measures and suggestions were proposed for local garden afforestation and tree arrangement. [ABSTRACT FROM AUTHOR]

The use of thermal time is essential in plant studies and crop growth modeling because correcting time for temperature allows working in fluctuating conditions as if temperature was constant. However, thermal time is often seen as a loose concept because of a multitude of thermal functions and case-specific parameter values. Our hypothesis is that these different formalisms and parameterization could emerge from common principles and a common response of plant development to temperature, but with several counfounding factors which are not taken into account. We first show that these calculations of thermal time are based on sound common principles and mathematical formalisms. We test, via a modelling exercise of nine case studies using maize plants grown in three field sites, how a given "ground truth" response of plant development rate to temperature can be affected if an experimenter either considers or ignores confounding factors. We also show that apparent differences in temperature responses between phenological stages of the growth cycle, between day and night, or between plant genotypes may be due to the confounding effects of evaporative demand, the range of temperatures, and the time interval at which measurements are taken. On the basis of our findings, we propose that the critical point in the use of a given formalism of thermal time calculation is to ensure that the chosen model is compatible with the temporal definition, temperature range, and environmental scenario in the considered dataset. [ABSTRACT FROM AUTHOR]

High‐resolution leaf growth is rarely studied despite its importance as a metric for plant performance and resource use efficiency. This is in part due to methodological challenges. Here, we present a method for in situ leaf growth measurements in a natural environment. We measured instantaneous leaf growth on a mature Avicennia marina subsp. australasica tree over several weeks. We measured leaf expansion by taking time‐lapse images and analysing them using marker tracking software. A custom‐made instrument was designed to enable long‐term field studies. We detected a distinct diel growth pattern with leaf area shrinkage in the morning and leaf expansion in the afternoon and at night. On average, the observed daily shrinkage was 37% of the net growth. Most of the net growth occurred at night. Diel leaf area shrinkage and recovery continued after growth cessation. The amount of daily growth was negatively correlated with shrinkage, and instantaneous leaf growth and shrinkage were correlated with changes in leaf turgor. We conclude that, at least in this tree species, instantaneous leaf growth patterns are very strongly linked to, and most likely driven by, leaf water relations, suggesting decoupling of short‐term growth patterns from carbon assimilation. High‐resolution leaf growth measurements in Avicennia marina showed leaf shrinkage in the morning and expansion mainly during the night, and a strong correlation of leaf area change with turgor, suggesting that growth was driven by plant hydraulic status rather than by the rate of carbon uptake. [ABSTRACT FROM AUTHOR]

The phenylpropanoid pathway, the source of a large array of compounds with diverse functions, starts with the synthesis of trans-cinnamic acid (t-CA) that is converted by cinnamate-4-hydroxylase (C4H) into p-coumaric acid. We have recently shown that in Arabidopsis, exogenous t-CA promotes leaf growth by increasing cell expansion and that this response requires auxin signaling. We have also shown that cell expansion is increased in C4H loss-of-function mutants. Here we provide further evidence that leaf growth is enhanced by either t-CA or a t-CA derivative that accumulates upstream of C4H. We also show that this growth response pathway has two components: one that requires auxin signaling and another which employs a currently unknown mechanism. [ABSTRACT FROM AUTHOR]

This study aimed to characterize the physiological and morphological traits that are associated with adaptation to unflooded soil conditions in rice. Four indica rice cultivars (Puluik Arang, Badari Dhan, Shwe Nang Gyi, and Ratul), which were previously identified as highly or less adaptable to unflooded soil conditions, were grown under flooded and unflooded (soil water potential; －0.10 MPa) soil conditions. Water uptake was measured every day for three weeks, and then the leaf water potential, the stomatal conductance, the dry matter weight, shoot and root morphological traits were measured. Puluik Arang and Badari Dhan exhibited greater leaf area expansion and higher maintenance of root development under the unflooded condition than that by other cultivars. The leaf water potential and stomatal conductance of fully expanded highest leaf in Puluik Arang and Badari Dhan were not affected by unflooded soil regime. Leaf area and root morphological traits were significantly correlated with water uptake regardless of soil moisture regimes. These results suggested that Puluik Arang and Badari Dhan exhibited great water uptake capacity through physiological and morphological adaptation of shoot and root traits to unflooded condition, resulting in great biomass productivity under the condition.

Novel technologies for estimating crop water needs include mainly remote sensing evapotranspiration estimates and decision support systems (DSS) for irrigation scheduling. This work provides several examples of these approaches, that have been adjusted and modified over the years to provide a better representation of the soil–plant–atmosphere continuum and overcome their limitations. Dynamic crop simulation models synthetize in a formal way the relevant knowledge on the causal relationships between agroecosystem components. Among these, plant–water–soil relationships, water stress and its effects on crop growth and development. Crop models can be categorized into (i) water-driven and (ii) radiation-driven, depending on the main variable governing crop growth. Water stress is calculated starting from (i) soil water content or (ii) transpiration deficit. The stress affects relevant features of plant growth and development in a similar way in most models: leaf expansion is the most sensitive process and is usually not considered when planning irrigation, even though prolonged water stress during canopy development can consistently reduce light interception by leaves; stomatal closure reduces transpiration, directly affecting dry matter accumulation and therefore being of paramount importance for irrigation scheduling; senescence rate can also be increased by severe water stress. The mechanistic concepts of crop models can be used to improve existing simpler methods currently integrated in irrigation management DSS, provide continuous simulations of crop and water dynamics over time and set predictions of future plant–water interactions. Crop models can also be used as a platform for integrating information from various sources (e.g., with data assimilation) into process-based simulations.

Premise of the Study: The densities of veins and stomata govern leaf water supply and gas exchange. They are coordinated to avoid overproduction of either veins or stomata. In many species, where leaf area is greater at low light, this coordination is primarily achieved through differential cell expansion, resulting in lower stomatal and vein density in larger leaves. This mechanism would, however, create highly inefficient leaves in species in which leaf area is greater at high light. Here we investigate the role of cell expansion and differentiation as regulators of vein and stomatal density in Rheum rhabarbarum, which produces large leaves under high light. Methods: Rheum rhabarbarum plants were grown under full sunlight and 7% of full sunlight. Leaf area, stomatal density, and vein density were measured from leaves harvested at different intervals. Key Results: Leaves of R. rhabarbarum expanded at high light were six times larger than leaves expanded at low light, yet vein and stomatal densities were similar. In high light‐expanded leaves, minor veins were continuously initiated as the leaves expanded, while an extended period of stomatal initiation, compared to leaves expanded at low light, occurred early in leaf development. Conclusions: We demonstrate that R. rhabarbarum adjusts the initiation of stomata and minor veins at high light, allowing for the production of larger leaves uncoupled from lower vein and stomatal densities. We also present evidence for an independent control of vein and stomatal initiation, suggesting that this adjustment must involve some unknown developmental mechanism. [ABSTRACT FROM AUTHOR]

LED lamps with various combinations of red (R) and blue (B) wavelengths were used to supplement sunlight for the growth of a heat-resistant (HR) and heat-sensitive (HS) recombinant inbred lines (RIL) of lettuce. The RB-LED ratios were 100R:0B (0B), 92R:8B (8B), 84R:16B (16B), and 76R:24B (24B) with an equal PPFD of 100 μmol m−2 s−1. The greatest leaf expansion rates were observed at 8B for both genotypes. All HR-RILs had similar values of growth parameters and specific leaf area (SLA). However, higher values of growth parameters were observed in HS-RIL with 0B, 8B, and 16B than that under 24B and sunlight. Furthermore, HS-RIL had higher SLA under 0B compared to other conditions. Photosynthetic light-use efficiency and maximal oxygen evolution rate were the lowest under 8B for both genotypes. The quality of LED lighting, if provided, seemed to implicate genotype dependence, probably as a result of their different sensitivities to heat stress. [ABSTRACT FROM AUTHOR]

Highlights • Leaf expansion rate (LER) of maize increased along with an increase in temperatureunder low evaporative demand conditions. • Under high evaporative demand conditions, LER reduced at 32 °C due to high VPD. • Stomatal conductance, photosynthesis, and transpiration mirrored the response of LER. • Stomatal traits were affected by VPD. • The response of LER in maize was associated with the differential expression of genes related to leaf development and expansion. Abstract Leaf area affects light interception, carbon assimilation and plant growth. How maize leaf development and expansion is affected by temperature under different evaporative demand conditions is not well understood. Effects of three temperatures (21, 27 and 32 °C) under high and low evaporative demand conditions were tested in growth chambers. Leaf expansion rate (LER), leaf appearance rate (LAR), leaf number, plant height, photosynthesis (A), net assimilation rate (NAR), stomatal conductance (gs), and transpiration (E) increased with increasing temperature under low evaporative demand environments. Under high evaporative demand, while there was an increase with temperature until 27 °C, at 32 °C there was a decrease in LER, plant height, A, NAR, gs, and E. However, the variation in the rate of leaf appearance appears to be linked to temperature but not VPD. The development of stomata and epidermal cells were affected by VPD with large size stomata and more epidermal cells under low VPD. The differential responses of LER to low and high evaporative demands could be attributed to changes in expression of Expansin A2, A4, and B1 genes and XTH23. The significant effect of temperature and VPD on the expression of vacuolar H + pyrophosphatase and teosinte branched gene was detected. Overall, we found a negative effect of high VPD due to high evaporative demand for maize leaf expansion and development. [ABSTRACT FROM AUTHOR]

* Background and Aims Dynamics in branch and leaf growth parameters, such as the phyllochron, duration of leaf expansion, leaf life span and bud mortality, determine tree architecture and canopy foliage distribution. We aimed to estimate leaf growth parameters in adult Arabica coffee plants based on leaf supporter axis order and position along the vertical profile, considering their modifications related to seasonal growth, air [CO2] and water availability. * Methods Growth and mortality of leaves and terminal buds of adult Arabica coffee trees were followed in two independent field experiments in two sub-tropical climate regions of Brazil, Londrina-PR (Cfa) and Jaguariúna-SP (Cwa). In the Cwa climate, coffee trees were grown under a FACE (free air CO2 enrichment) facility, where half of those had been irrigated. Plants were observed at a 15-30 d frequency for 1 year. Leaf growth parameters were estimated on five axes orders and expressed as functions of accumulated thermal time (°Cd per leaf). * Key Results The phyllochron and duration of leaf expansion increased with axis order, from the seond to the fourth. The phyllochron and life span during the reduced vegetative seasonal growth were greater than during active growth. It took more thermal time for leaves from the first- to fourth-order axes to expand their blades under irrigation compared with rainfed conditions. The compensation effects of high [CO2] for low water availability were observed on leaf retention on the second and third axes orders, and duration of leaf expansion on the first- and fourth-order axes. The second-degree polynomials modelled leaf growth parameter distribution in the vertical tree profile, and linear regressions modelled the proportion of terminal bud mortality. * Conclusions Leaf growth parameters in coffee plants were determined by axis order. The duration of leaf expansion contributed to phyllochron determination. Leaf growth parameters varied according the position of the axis supporter along the vertical profile, suggesting an effect of axes age and micro-environmental light modulations. [ABSTRACT FROM AUTHOR]

Storage nitrogen (N) is a buffer pool for maintaining leaf growth and synthesizing photosynthetic proteins, but the dynamics of its forms within the life cycle of a single leaf and how it is influenced by N supply remain poorly understood. A field experiment was conducted to estimate the influence of N supply on leaf growth, photosynthetic characteristics, and N partitioning inthe sixth leaf of winter oilseed rape (Brassica napus L.) from emergence through senescence. Storage N content (Nstore) decreased gradually along with leaf expansion. The relative growth rate based on leaf area (RGRa) was positively correlated with Nstore during leaf expansion. The water-soluble protein form of storage N was the main N source for leaf expansion. After the leaves fully expanded, the net photosynthetic rate (An) followed a linear-plateau response to Nstore, with An stabilizing at the highest value above a threshold and declining below the threshold. Non-protein and SDS (detergent)-soluble protein forms of storage N were the main N sources for maintaining photosynthesis. For the leaf N economy, storage N is used for co-ordinating leaf expansion and photosynthetic capacity. N supply can improve Nstore, thereby promoting leaf growth and biomass. [ABSTRACT FROM AUTHOR]

Young leaves of tropical trees frequently appear red in color, with the redness disappearing as the leaves mature. During leaf expansion, plants may employ photoprotective mechanisms to cope with high light intensities; however, the variations in anthocyanin contents, nonphotochemical quenching (NPQ), and photorespiration during leaf expansion are poorly understood. Here, we investigated pigment contents, gas exchange, and chlorophyll (Chl) fluorescence in Woodfordia fruticosa leaves during their expansion. Young red leaves had significantly lower Chl content than that of expanding or mature leaves, but they accumulated significantly higher anthocyanins and dissipated more excited light energy through NPQ. As the leaves matured, net photosynthetic rate, total electron flow through PSII, and electron flow for ribulose-1,5-bisphosphate oxygenation gradually increased. Our results provided evidence that photorespiration is of fundamental importance in regulating the photosynthetic electron flow and CO assimilation during leaf expansion. [ABSTRACT FROM AUTHOR]

Nitrogen (N) is an important regulator of photosynthetic carbon (C) flow in plants, and an adequate balance between N and C metabolism is needed for correct plant development. However, an excessive N supply can alter this balance and cause changes in specific organic compounds associated with primary and secondary metabolism, including plant growth regulators. In previous work, we observed that high nitrate supply (15 mM) to maize plants led to a decrease in leaf expansion and overall biomass production, when compared with low nitrate supply (5 mM). Thus, the aim of this work is to study how overdoses of nitrate can affect photosynthesis and plant development. The results show that high nitrate doses greatly increased amino acid production, which led to a decrease in the concentration of 2-oxoglutarate, the main source of C skeletons for N assimilation. The concentration of 1-aminocyclopropane-1-carboxylic acid (and possibly its product, ethylene) also rose in high nitrate plants, leading to a decrease in leaf expansion, reducing the demand for photoassimilates by the growing tissues and causing the accumulation of sugars in source leaves. This accumulation of sugars, together with the decrease in 2-oxoglutarate levels and the reduction in chlorophyll concentration, decreased plant photosynthetic rates. This work provides new insights into how high nitrate concentration alters the balance between C and N metabolism, reducing photosynthetic rates and disrupting whole plant development. These findings are particularly relevant since negative effects of nitrate in contexts other than root growth have rarely been studied. [ABSTRACT FROM AUTHOR]

Information on the involvement of elongation-controlling hormones, particularly gibberellin (GA), in UV-B modulation of stem elongation and leaf growth, is limited. We aimed to study the effect of UV-B on levels of GA and indole-3-acetic acid (IAA) as well as involvement of GA in UV-B inhibition of stem elongation and leaf expansion in pea. Reduced shoot elongation (13%) and leaf area (37%) in pea in response to a 6-h daily UV-B (0.45 W m) exposure in the middle of the light period for 10 days were associated with decreased levels of the bioactive GA in apical stem tissue (59%) and young leaves (69%). UV-B also reduced the content of IAA in young leaves (35%). The importance of modulation of GA metabolism for inhibition of stem elongation in pea by UV-B was confirmed by the lack of effect of UV-B in the le GA biosynthesis mutant. No UV-B effect on stem elongation in the la cry-s ( della) pea mutant demonstrates that intact GA signalling is required. In conclusion, UV-B inhibition of shoot elongation and leaf expansion in pea depends on UV-B modulation of GA metabolism in shoot apices and young leaves and GA signalling through DELLA proteins. UV-B also affects the IAA content in pea leaves. [ABSTRACT FROM AUTHOR]

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Many studies investigated temperature effects on leaf initiation and expansion by relating these processes to air temperature or the temperature of a specific organ (e.g. leaf temperature). In reality plant temperature is hardly ever equal to air temperature or spatially uniform. Apical bud temperature ( Tbud), for example, may greatly differ from the temperature of the rest of the plant ( Tplant) dependent on the environment. Recent research in Cucumis sativus showed that Tbud influences leaf initiation independent of Tplant. These findings trigger the question if such spatial temperature differences also influence leaf expansion and plant phenotype. In a 28 day study, we maintained temperature differences between Tbud and Tplant ranging from −7 to +8 °C using a custom-made bud temperature control system. Leaf expansion did not only depend on leaf temperature but also on the difference between bud and leaf temperature. Differences between Tbud and Tplant considerably influenced vertical leaf area distribution over the shoot: increasing Tbud beyond Tplant resulted in more and smaller leaves, while decreasing Tbud below Tplant resulted in less and larger leaves. The trade-off between leaf number and leaf area resulted in phenotypic alterations that cannot be predicted, for example, by crop models, when assuming plant temperature uniformity. [ABSTRACT FROM AUTHOR]

Non-destructive measurement of leaf area (LA) is preferred in growth analysis and plant physiological studies. Many regression-based models have been developed for estimating LA using leaf length (L), leaf width (W), or imaginary rectangle of L x W (LW) as predictor or independent variable. Objective of this study was to develop and validate appropriate regression models for estimating snap bean trifoliate LA using easily measured L, W, or calculated LW. Snap bean used in this research was PV072 cultivar. Trifoliate-leaf samples were purposively collected from different individual plants, to represent wide range of leaf sizes, from the smallest leaf with fully open blade to the largest available leaf. Snap bean trifoliate leaf consists of three leaflets. The sampled leaves were alternately divided into two subgroups, based on length of terminal leaflet, for developing and validating LA estimation models. Linear, quadratic, and power regressions were evaluated for their appropriateness to be used for estimating LA. Intercept (a) was forced to zero to make the models more geometrically realistic. Results of this research indicated that: (1) zero-intercept quadratic and power regression models performed well for length of leaflet (Lt) or width of leaflet (Wt) was used as predictor, whereas zero-intercept linear model was appropriate and geometrically-sound if imaginary rectangular Lt x Wt (LtWt) was used for estimating surface area of both terminal and side leaflets (LtA); (2) for a practical, fast, and accurate estimation of LA, LtWt of terminal leaflet was the recommended option among other single or combination of predictors; and (3) recommended empirical model for LA estimation of snap bean trifoliate leaf is LA = 1.5198 LtWt. [ABSTRACT FROM AUTHOR]