Corrigendum: Foliar application of putrescine alleviates terminal drought stress by modulating water status, membrane stability, and yield- related traits in wheat (Triticum aestivum L.).

[This corrects the article DOI: 10.3389/fpls.2022.1000877.].

Foliar application of putrescine alleviates terminal drought stress by modulating water status, membrane stability, and yield- related traits in wheat (Triticum aestivum L.).

Drought stress is one of the major limitations to the growth and yield productivity of cereal crops. It severely impairs the early growing and grain -filling stages of wheat. Therefore, cost- effective and eco-friendly approaches for alleviating drought stress in cereal crops are in high demand. Polyamines, such as putrescine, have a significant effect on improving crop yield under drought- stress conditions. Therefore, the current study was executed with the aim of exploring the significance of putrescine in alleviating drought stress and improving yield- related traits in wheat. Two distinct wheat cultivars (Fakhar-e-Bhakkar and Anaj-2017) were treated with the foliar application of different concentrations (control, 0.5, 1.0, and 1.5 PPM) of putrescine (put) under two moisture conditions (well- watered and terminal drought stress). The results demonstrate that the imposition of terminal drought stress significantly reduces different physiological and yield- related traits of both wheat cultivars. The reduction of relative water content (RWC%), membrane stability index (MSI), leaf area, tillers per plant, biomass yield, number of spikelets per spike, 100-grain weight, grain yield per plant, and straw yield was greater in Anaj-2017 than in Fakhar-e-Bhakkar cultivar. The results further explain that the foliar application of increased concentrations of putrescine from 0.0 to 1.0 PPM gradually improved physiological and yield traits, whereas these traits declined with the application of putrescine at the highest dose (1.5 PPM). The exogenous application of 1.0 PPM putrescine improved the relative water content (19.76%), specific leaf area (41.47%), and leaf area ratio (35.84%) compared with the controlled treatment. A higher grain yield (28.0 g plant-1) and 100-grain weight (3.8 g) were obtained with the foliar application of 1.0 PPM putrescine compared with controlled treatments. The findings of this study confirm the protective role of putrescine against terminal drought stress. It is therefore recommended to use putrescine at a concentration of 1.0 PPM, which could help alleviate terminal drought stress and attain better wheat yield.

Leaf trait modification in European beech trees in response to climatic and edaphic drought.

Leaf morphological and physiological traits control the carbon and water relations of mature trees and are determinants of drought tolerance, but it is not well understood how they are modified in response to water deficits. We analysed five sun-canopy leaf traits (mean leaf size (LS), specific leaf area (SLA), Huber value (HV), water potential at turgor loss point (Ψtlp ) and foliar carbon isotope signature (δ13 C)) in European beech (Fagus sylvatica L.) across three precipitation gradients sampled in moist (2010), dry (2019) and very dry (2018) summers, and tested their response to short-term water deficits (climatic water balance (CWB) preceding sample collection) and long-term water availability (mean annual precipitation (MAP), plant-available soil water capacity (AWC) and neighbourhood competition). Across the 34 sites, LS varied seven-fold (3.9-27.0 cm2 ), SLA four-fold (77.1-306.9 cm²·g-1 ) and HV six-fold (1.0-6.65 cm2 ·m-2 ). In the 2018 dataset, LS showed a negative and HV a positive relationship to MAP, which contradicts relations found in multi-species samples. Average Ψtlp ranged from -1.90 to -2.62 MPa and decreased across the sites with decreasing CWB in the month prior to measurement, as well as with decreasing MAP and AWC in 2019. Studied leaf traits varied considerably between years, suggesting that mast fruiting and the severe 2018 drought caused the formation of smaller leaves. We conclude that sun-canopy leaf traits of European beech exhibit considerable plasticity in response to climatic and edaphic aridity, and that osmotic adjustment may be an important element in the drought response strategy of this anisohydric tree species.

Functional response of Betula species to edaphic and nutrient stress during restoration of fly ash deposits in the Middle Urals (Russia).

We studied the impact of fly ash produced by the thermal power station in the Middle Urals (Russia) on functional traits of two Betula species naturally colonizing ash dump lagoons. The main limiting factors for tree growth on fly ash deposits were nitrogen deficiency, high alkalinity, and unfavorable mechanical composition of substrate. Leaf area ratio (LAR) and leaf mass ratio (LMR) per tree, leaf area (LA), leaf shape coefficient (LSh), leaf thickness (LT), leaf mass per area (LMA), photosynthesis (Amax) and transpiration rates, chlorophyll (Chl), carotenoid (Car), and nitrogen (N) content were measured in Betula pendula Roth and Betula pubescens Ehrh. growing on the ash dump and in the forest near the dump. Both Betula species showed similar functional response to adverse conditions of the fly ash. We found a 1.5-2-fold increase in LAR and LMR in trees growing on fly ash deposits compared with trees in the forest. In both species, the most significant differences across leaf morphological traits were shown for LT. Higher LT provided an increase in Chl and N content per leaf area that caused the rise in Amax and photosynthetic water use efficiency in the trees on the ash deposit. At the same time, Betula species preserved interspecific differences in values of LA and LT which were larger in B. pubescens whiles B. pendula differed by higher LSh. We concluded that the increase in assimilation activity at both whole-plant and leaf levels provides plant adjustment to edaphic and nutrient stress that allow Betula species to colonize technogenic substrates as fly ash deposits.

Leaf size as a key determinant of contrasting growth patterns in closely related Limonium (Plumbaginaceae) species.

This study aims to analyze the importance of leaf size on plant growth capacity among an array of closely related Limonium species, and its impact on the underlying determinants of growth reduction under extreme water deficit conditions. To do so, thirteen Balearic Limonium species with contrasting leaf size were grown under long-term well-watered (WW) and severe water-deficit (WD) conditions in a common garden experiment. Fundamental growth traits were measured, including relative growth rate (RGR), net assimilation rate (NAR), leaf area ratio (LAR), leaf mass area (LMA) and leaf mass ratio (LMR). WD promoted small changes in leaf size, and species with larger leaves had higher RGR than species with smaller leaves, irrespective of the water treatment. Most RGR variation across species and treatments was explained by NAR, with comparatively much lower importance of LAR. The factorization of LAR underlying components denoted the importance of LMA in explaining RGR, whereas the impact of LMR on RGR was negligible in Limonium. Further, species with larger leaves had higher water consumption but also higher water use efficiency, especially under WD. Therefore, contrary to general trends in species from dry environments, increased leaf size is linked to increased growth capacity and also increased water use efficiency across closely related Limonium species.

The effects of Solidago canadensis water extracts on maize seedling growth in association with the biomass allocation pattern.

BACKGROUND: Solidago canadensis L. is an aggressive exotic plant species in China that has potential allelopathic effects on competing plant species. Effects of hormesis are frequently observed in studies of allelopathy; however, the mechanisms of such effects need to be elucidated. Allelopathic compounds may affect the growth of recipient plants via alteration of biomass allocation patterns or photosynthetic capacity. The aim of this study was to determine how water extracts from S. canadensis affected the shoot and root growth of recipient plants and whether the underlying mechanism was related to the biomass allocation pattern or photosynthetic gas exchange capacity. METHODS: The water extracts from S. canadensis shoots at 12 different concentrations in the range of 0-0.25 g/ml were applied thrice in 9 days to maize seedlings cultivated in silica sand. The growth (shoot height, leaf length and area and root length) and biomass accumulation and allocation (specific leaf area (SLA), leaf area ratio (LAR) and leaf mass ratio (LMR)) were compared among maize seedlings exposed to different treatment concentrations. Gas exchange (photosynthetic light response curve) was measured and compared among maize seedlings exposed to three concentrations of water extract (0, 0.0125 and 0.2 g/ml) before and after the first application, and seedling growth was measured after the third and final application. RESULTS: The growth of seedlings (shoot height, leaf length and area and root length) was promoted at concentrations below 0.125 g/ml and inhibited at concentrations above this level (P < 0.05). The pattern of change in biomass accumulation and allocation was similar to that of shoot growth, but biomass accumulation and allocation was not significantly affected by the water extract treatments (P > 0.05). The water extract treatments did not significantly affect the photosynthetic capacity (P > 0.05), but the dark respiration rate was higher in the low-dose treatment than that in the high-dose treatment. Shoot height was positively correlated with the biomass allocation indicators SLA and LAR (P < 0.05) but not with LMR (P > 0.05). CONCLUSIONS: The results suggested that the effects of the water extracts from S. canadensis were highly dependent on the concentration, with the growth of maize seedlings promoted at low concentrations of water extracts. The effects of the water extracts on the growth of maize seedlings were mainly due to the effects on the LAR, the allocation to leaf area growth, whereas the effects of the water extracts on leaf gas exchange capacity cannot explain variation of seedling growth. Thus, the stimulation of plant growth was very likely due to increased biomass allocation towards the shoot.

Tasa relativa de crecimiento en plántulas de dos poblaciones de Magnolia pugana (Magnoliaceae) en distintos niveles de luz y fertilidad del suelo / Relative growth rate in Magnolia pugana (Magnoliaceae) seedlings from two populations at different light levels and soil fertility

Resumen El estudio de la ecofisiología de las especies en peligro de extinción es clave para el éxito de programas de conservación y restauración ecológica. El objetivo de este trabajo fue conocer el efecto de los factores luz, fertilidad de suelo y procedencia de las plántulas en el crecimiento de plántulas de Magnolia pugana. Se estimó la tasa relativa de crecimiento (TRC) y sus componentes (Tasa de Asimilación Neta: TAN y Cociente del Área Foliar: CAF), así como la relación raíz/vástago (C: R/V). Las plántulas fueron obtenidas de semillas recolectadas de dos localidades en Zapopan, Jalisco, México, la primera es una población silvestre en San Nicolás (SN) y la segunda es una plantación ubicada en los jardines del Centro Universitario de Ciencias Biológicas y Agropecuarias (CUCBA). El experimento se llevó a cabo en condiciones de invernadero. En septiembre 2015, 96 plántulas de tres meses de edad fueron sometidas a los siguientes tratamientos con un experimento factorial (2 × 2 × 2): nivel de luz (alta = 1 120 μmol m-2 s-1 y baja = 136.3 μmol m-2 s-1), procedencia de las plántulas (San Nicolás y CUCBA) y fertilidad del suelo (alta = suelo San Nicolás, baja = suelo del CUCBA) con 12 repeticiones por cada combinación de factores y niveles. El crecimiento se estimó con dos cosechas: la primera a los 30 días de establecido el experimento y la segunda a los 60 días. Los niveles de luz, fertilidad del suelo y la procedencia de las plántulas influyeron en el crecimiento a través de ajustes fisiológicos y morfológicos. En general Magnolia pugana mostró mayor TRC y TAN en la luz alta, mientras que el CAF disminuyó. La fertilidad del suelo y la procedencia de las plántulas no afectaron la TRC ni sus componentes. Sin embargo, si fueron afectados por los niveles de luz, las plántulas de SN crecieron más en luz alta. La altura del tallo varió debido a la fertilidad del suelo y a la procedencia de las plántulas, en el suelo con fertilidad baja, en el suelo del CUCBA las plántulas de SN fueron 35 % más altas que las del CUCBA. El suelo de baja fertilidad en la luz alta ocasionó que las plántulas asignaran mayor biomasa a la raíz. El componente fisiológico (TAN) fue el mayor determinante en la variación intraespecífica de la TRC. Las plántulas de SN mostraron mayor plasticidad fenotípica debido a que es una población silvestre, por lo que posiblemente tiene variación genética más alta que la población cultivada del CUCBA. Los resultados sugieren que Magnolia pugana es una especie con capacidad de adaptarse a diversos ambientes debido a su plasticidad fenotípica frente a los distintos niveles de luz y fertilidad del suelo.

Abstract The study of ecophysiology of endangered species is key to the success of conservation and ecological restoration programs. The objective of this work was to know the effect of light, soil fertility and seed origin on the growth of Magnolia pugana seedlings. The relative growth rate (RGR) and its components (Net Assimilation Rate: NAR and Leaf Area Ratio: LAR), as well as the root-shoot ratio (R/S) were estimated. Seedlings were obtained from seeds collected in two localities in Zapopan, Jalisco, Mexico, the first is a wild population in San Nicolás (SN) and the second is a plantation located in the gardens of the Centro Universitario de Ciencias Biológicas y Agropecuarias (CUCBA). The experiment was conducted under greenhouse conditions. In September 2015, 96 seedlings of approximately three months old were subjected to the following treatments in a factorial experiment (2x2x2): light level (high = 1 120 μmol m-2 s-1 and low = 136.3 μmol m-2 s-1), seedling origin (SN and CUCBA) and soil fertility (high fertility = SN soil, low fertility = CUCBA soil) with 12 replicates for each combination of factors and levels. Growth was estimated in two harvests: the first harvest after 30 days of starting the experiment and the second at 60 days. Light and soil fertility levels, as well as seedling origin influenced growth through physiological and morphological adjustments. In general, Magnolia pugana showed higher RGR and NAR in high light, while LAR decreased. Soil fertility and seedling origin did not affect RGR or its components. However, these were affected by the light level, seedlings from SN grew more in high light. Stem height varied due to soil fertility and seedling origin, in low fertility soil (CUCBA) the seedlings of SN were 35 % higher than those of CUCBA. Low fertility soil under high light caused greater investment in seedling root biomass. The physiological component (NAR) was the major determinant of intraspecific variation in RGR. SN seedlings showed greater phenotypic plasticity due to coming from a wild population, which possibly has higher genetic variation than the cultivated population from CUCBA. The results suggest that Magnolia pugana is a species capable of adapting to diverse environments due to its phenotypic plasticity in response to different light and soil fertility levels. Rev. Biol. Trop. 66(2): 622-633. Epub 2018 June 01.

Salt effects on functional traits in model and in economically important Lotus species.

A common stress on plants is NaCl-derived soil salinity. Genus Lotus comprises model and economically important species, which have been studied regarding physiological responses to salinity. Leaf area ratio (LAR), root length ratio (RLR) and their components, specific leaf area (SLA) and leaf mass fraction (LMF) and specific root length (SRL) and root mass fraction (RMF) might be affected by high soil salinity. We characterised L. tenuis, L. corniculatus, L. filicaulis, L. creticus, L. burtii and L. japonicus grown under different salt concentrations (0, 50, 100 and 150 mm NaCl) on the basis of SLA, LMF, SRL and RMF using PCA. We also assessed effects of different salt concentrations on LAR and RLR in each species, and explored whether changes in these traits provide fitness benefit. Salinity (150 mm NaCl) increased LAR in L. burtii and L. corniculatus, but not in the remaining species. The highest salt concentration caused a decrease of RLR in L. japonicus Gifu, but not in the remaining species. Changes in LAR and RLR would not be adaptive, according to adaptiveness analysis, with the exception of SLA changes in L. corniculatus. PCA revealed that under favourable conditions plants optimise surfaces for light and nutrient acquisition (SLA and SRL), whereas at higher salt concentrations they favour carbon allocation to leaves and roots (LMF and RMF) in detriment to their surfaces. PCA also showed that L. creticus subjected to saline treatment was distinguished from the remaining Lotus species. We suggest that augmented carbon partitioning to leaves and roots could constitute a salt-alleviating mechanism through toxic ion dilution.

Effects of PEG-induced osmotic stress on growth and dhurrin levels of forage sorghum.

Sorghum (Sorghum bicolor L. Moench) is a valuable forage crop in regions with low soil moisture. Sorghum may accumulate high concentrations of the cyanogenic glucoside dhurrin when drought stressed resulting in possible cyanide (HCN) intoxication of grazing animals. In addition, high concentrations of nitrate, also potentially toxic to ruminants, may accumulate during or shortly after periods of drought. Little is known about the degree and duration of drought-stress required to induce dhurrin accumulation, or how changes in dhurrin concentration are influenced by plant size or nitrate metabolism. Given that finely regulating soil moisture under controlled conditions is notoriously difficult, we exposed sorghum plants to varying degrees of osmotic stress by growing them for different lengths of time in hydroponic solutions containing polyethylene glycol (PEG). Plants grown in medium containing 20% PEG (-0.5 MPa) for an extended period had significantly higher concentrations of dhurrin in their shoots but lower dhurrin concentrations in their roots. The total amount of dhurrin in the shoots of plants from the various treatments was not significantly different on a per mass basis, although a greater proportion of shoot N was allocated to dhurrin. Following transfer from medium containing 20% PEG to medium lacking PEG, shoot dhurrin concentrations decreased but nitrate concentrations increased to levels potentially toxic to grazing ruminants. This response is likely due to the resumption of plant growth and root activity, increasing the rate of nitrate uptake. Data presented in this article support a role for cyanogenic glucosides in mitigating oxidative stress.

Leaf area accumulation helps juvenile evergreen trees tolerate shade in a temperate rainforest.

Most knowledge of the physiological correlates of interspecific variation in shade tolerance derives from studies of first-year seedlings in artificial environments. The present study relates growth, allocation, foliage turnover, biomass distribution and gas exchange traits to low-light survival of large seedlings (20-100 cm tall) of eight temperate rainforest evergreens under field conditions. Taxa for which natural mortality was not observed in low light during the 14-month study are referred to here as "shade-tolerant" species, and those which did die in the shade are referred to as "light-demanding" species. In low light (2-5% canopy openness), shade-tolerant species had slightly lower light compensation points than light-demanders. Light-demanding species had more plastic aboveground allocation patterns, generally allocating proportionally less aboveground biomass to foliage production than shade-tolerant associates in high light (>10% canopy openness), but more in low light. Foliage turnover was generally much slower in shade-tolerant species (10-40% year-1) than in light-demanding species (30-190%). As these differences in leaf retention outweighed variation in allocation, shade-tolerant species displayed higher leaf areas at all light levels. Furthermore, all shade-tolerant species gained leaf area in low light during the study period, whereas light-demanding taxa showed leaf area declines. Higher leaf area ratios, plus differences in light compensation points, indicate that large seedlings of shade-tolerant evergreens enjoy net carbon gain advantages over light-demanding associates in low light. However, minimal growth rate differences in low light imply higher storage allocation in shade-tolerant species. This study provides a rather different picture from that which has emerged from recent reviews of first-year seedling data, illustrating the long-term consequences of foliage turnover differences for biomass distribution, and suggesting that shade tolerance in juvenile evergreen trees is associated with a suite of traits which enhance net carbon gain, but not growth, in low light. Accumulation of a large foliage area through long leaf retention times is probably a key mechanism enhancing low-light carbon gain in evergreens.

Light and salinity affect growth of the salt marsh plant Aster laurentianus.

• The effects are reported of substrate salinity and light on the relative growth rate of the annual Aster laurentianus, an endangered species of eastern Canadian salt marshes. • The independent and combined effects of photosynthetically active photon flux density and salinity on the relative growth rate (RGR) and overall plant performance were measured in glasshouse and growth-chamber experiments on seedlings of A. laurentianus. • Low light availability decreased RGR through its negative effect on unit leaf rate. However, specific leaf area and leaf mass ratio varied inversely with changes in light, such that leaf area ratio did not differ greatly among light levels. High salinity decreased RGR by reducing unit leaf rate and leaf area ratio; a reduction in the latter was brought about by a lower leaf mass ratio rather than by a lower specific leaf area. Low light availability combined with high substrate salinity affected A. laurentianus in a strictly additive manner; there was no significant interaction between the two factors on overall plant performance. • Light and salinity are important factors controlling growth of A. laurentianus, and might explain the distribution pattern of the species in the field.

Contribution of physiological and morphological plant traits to a species' competitive ability at high and low nitrogen supply : A hypothesis for inherently fast- and slow-growing monocotyledonous species.

Why do inherently fast-growing species from productive habitats generally have a higher rate of biomass production in short-term low-nitrogen experiments than slow-growing species from unproductive habitats, whereas the opposite is found in long-term experiments? Is this mainly due to inherent differences in biomass allocation, leaf characteristics or the plants' physiology? To analyse these questions we grew five monocotyledonous species from productive and unproductive habitats in a climate chamber at both high and low nitrogen supply. Nitrate was supplied exponentially, enabling us to compare inherent differences in morphological and physiological traits between the species, without any interference due to differences in the species' ability to take up nutrients. At high nitrogen supply, we found major inherent differences in specific leaf area and nitrogen productivity, i.e. daily biomass increment per unit plant nitrogen, where-as there were only small differences in net assimilation rate, i.e. daily biomass increment per unit leaf area, and biomass partitioning. We propose that the higher specific leaf area and nitrogen productivity of inherently fast-growing species are the key factors explaining their high abundance in productive habitats compared with inherently slow-growing ones. At low nitrogen supply, the net assimilation rate was decreased to a similar extent for all species, compared with that at high nitrogen supply. The nitrogen productivity of the inherentlyfast-growing species decreased with decreasing nitrogen supply, whereas that of the inherently slow-growing species remained constant. There were no inherent differences in nitrogen productivity in this treatment. At this low nitrogen supply, the inherently fast-growing species invested relatively more biomass in their roots that the slow-growing ones did. The inherently fast-growing species still had a higher specific leaf area at low nitrogen supply, but the difference between species was less than that at high nitrogen supply. Based on the present results and our optimization model for carbon and nitrogen allocation (Van der Werf et al. 1993a), we propose that the relatively large investment in root biomass of fast-growing species is the key factor explaining their higher biomass production in short-term experiments. We also propose that in the long run the competitive ability of the slow-growing species will increase due to a lower turnover rate of biomass. It is concluded that the plant's physiology (net assimilation rate and nitrogen productivity), only plays a minor role in the species' competitive ability in low-nitrogen environments.

Leaf area ratio and net assimilation rate of 24 wild species differing in relative growth rate.

Which factors cause fast-growing plant species to achieve a higher relative growth rate than slow-growing ones? To answer this question 24 wild species were grown from seed in a growth chamber under conditions of optimal nutrient supply and a growth analysis was carried out. Mean relative growth rate, corrected for possible ontogenetic drift, ranged from 113 to 356 mg g-1 day-1. Net assimilation rate, the increase in plant dry weight per unit leaf area and unit time, varied two-fold between species but no correlation with relative growth rate was found. The correlation between leaf area ratio, the ratio between total leaf area and total plant weight, and relative growth rate was very high. This positive correlation was mainly due to the specific leaf area, the ratio between leaf area and leaf weight, and to a lesser extent caused by the leaf weight ratio, the fraction of plant biomass allocated to the leaves. Differences in relative growth rate under conditions of optimum nutrient supply were correlated with the soil fertility in the natural habitat of these species. It is postulated that natural selection in a nutrient-rich environment has favoured species with a high specific leaf area and a high leaf weight ratio, and consequently a high leaf area ratio, whereas selection in nutrient-poor habitats has led to species with an inherently low specific leaf area and a higher fraction of root mass, and thus a low leaf area ratio.

Growth of Pyrola rotundifolia ssp. maritima in relation to shade.

The maritime race of the larger wintergreen [Pyrola rotundifolia L. ssp. maritima (Kenyon) E. F. Warb.] was investigated in relation to its light environment at Braunton Burrows in south-west England. Measurements made at the site of its greatest abundance indicated that, in July, Pyrola commonly experiences an irradiance which is below 10% of full daylight with some habitats providing less than 1%. The species also occurs in situations receiving up to 100% daylight; at or towards this extreme the foliage is yellowish-green instead of deep green, giving an impression of reduced luxuriance. The mean specific leaf area of plants growing in the field was found to be inversely related to mean percentage irradiance received at each site. However, the slope of this trend was slight. Detached, rooted rosettes were removed from the field and grown for 85 days in a glasshouse under treatments which provided 100, 20.2 and 6.1% daylight. The plants in all treatments appeared normal but growth was slow. Yields and relative growth rates were significantly reduced by shading (P 0-05). The depressing effect of shading on growth rate was very slightly less than on unit leaf rate, the difference being due to slight increases in leaf area ratio. This, in turn, was tracted entirely to small increases in specific leaf area. Leaf weight ratio was not affected significantly, nor were substantial effects recorded in root/shoot ratio or in fresh weight/dry weight ratio. We conclude that the vegetative growth of Pyrola has a low capacity for adjustment to both natural and experimental shading; its growth rate in the field will tend to be lower under a dense leafy canopy than in less shaded habitats. The inherently low growth rate might, however, be an advantageous feature under shade conditions. The evident success of the species in shaded situations is certainly due to factors other than a simple shade requirement for vegetative growth.