Chemical and hydraulic signals regulate stomatal behavior and photosynthetic activity in maize during progressive drought

The objectives of this study were to investigate stomatal regulation in maize seedlings during progressive soil drying and to determine the impact of stomatal movement on photosynthetic activity. In well-watered and drought-stressed plants, leaf water potential (Ψ _leaf), relative water content (RWC), stomatal conductance (g _s), photosynthesis, chlorophyll fluorescence, leaf instantaneous water use efficiency (iWUE_leaf), and abscisic acid (ABA) and zeatin-riboside (ZR) accumulation were measured. Results showed that g _s decreased significantly with progressive drought and stomatal limitations were responsible for inhibiting photosynthesis in the initial stages of short-term drought. However, after 5 days of withholding water, non-stomatal limitations, such as damage to the PSII reaction center, became the main limiting factor. Stomatal behavior was correlated with changes in both hydraulic and chemical signals; however, changes in ABA and ZR occurred prior to any change in leaf water status. ABA in leaf and root tissue increased progressively during soil drying, and further analysis found that leaf ABA was negatively correlated with g _s (R ² = 0.907, p < 0.05). In contrast, leaf and root ZR decreased gradually. ZR in leaf tissue was positively correlated with g _s (R ² = 0.859, p < 0.05). These results indicate that ABA could induce stomatal closure, and ZR works antagonistically against ABA in stomatal behavior. In addition, the ABA/ZR ratio also had a strong correlation with g _s, suggesting that the combined chemical signal (the interaction between ABA and cytokinin) plays a role in coordinating stomatal behavior. In addition, Ψ _leaf and RWC decreased significantly after only 3 days of drought stress, also affecting stomatal behavior.     

Contrasting hydraulic strategies in <Emphasis Type="Italic">Salix psammophila</Emphasis> and <Emphasis Type="Italic">Caragana korshinskii</Emphasis> in the southern Mu Us Desert,China

Salix psammophila and Caragana korshinskii are two common shrubs in the southern Mu Us Desert, China. Their hydraulic strategies for adapting to this harsh, dry desert environment are not yet clear. This study examined the hydraulic transport efficiency, vulnerability to cavitation, and daily embolism refilling in the leaves and stems of these two shrubs during the dry season. In order to gain insight into water use strategies of whole plants, other related traits were also considered, including daily changes in stomatal conductance, leaf mass per area, leaf pressure–volume parameters, wood density and the Huber value. The leaves and stems of S. psammophila had greater hydraulic efficiency, but were more vulnerable to drought-induced hydraulic dysfunction than C. korshinskii. The difference between leaf and stem water potential at 50 % loss of conductivity was 0.12 MPa for S. psammophila and 0.81 MPa for C. korshinskii. Midday stomatal conductance decreased by 74 % compared to that at 8:30 in S. psammophila, whereas no change occurred in C. korshinskii. Daily embolism and refilling occurred in the stems of S. psammophila and leaves of C. korshinskii. These results suggest that a stricter stomatal regulation, daily embolism repair in stems, and a higher stem water capacitance could be partially compensating for the greater susceptibility to xylem embolism in S. psammophila, whereas higher leaf elastic modulus, greater embolism resistance in stems, larger difference between leaf and stem hydraulic safety, and drought-induced leaf shedding in C. korshinskii were largely responsible for its more extensive distribution in arid and desert steppes.     

Shrub Expansion of <Emphasis Type="Italic">Alnus viridis</Emphasis> Drives Former Montane Grassland into Nitrogen Saturation

The N₂-fixing shrub Alnus viridis is currently encroaching on montane grasslands in the Alps as a result of reduced land management and complete abandonment. Alnus introduces large amounts of nitrogen (N) into these formerly N-poor grasslands and restricts the succession to montane forests. We studied pools and fluxes of N and the associated C pools in pastures (controls) and adjacent Alnus shrublands at two elevations (1650 versus 1950 m a.s.l.) in three valleys in the Swiss central Alps. The total N and C pools stored in 50-year-old Alnus shrubland did not exceed those in adjacent pastures with a total of approximately 610 g N m^?2 in phytomass plus soil (down to 30 cm) at both elevations. In Alnus stands, reduced soil N pools balanced the gain in phytomass N pools, a likely result of a faster turnover of soil N. The soil solution under Alnus was continuously enriched with nitrate, with a total N leaching of 0.79 g N m^?2 season^?1 (June–October) under 50-year-old stands at both elevations and the highest flux of 1.76 g N m^?2 season^?1 in 25-year-old shrubland at low elevation, clearly indicating an excess of available N in Alnus shrubland. In contrast, N leaching across all pastures was close to zero (0.08 g N m^?2) throughout the season. At the catchment scale, streamlet water showed increased nitrate concentrations with typical flushing peaks in spring and autumn, provided more than one fifth of the catchment area was covered by Alnus shrubs. We conclude that the expansion of Alnus rapidly converts centuries-old, N-poor grassland into N saturated shrubland, irrespective of elevation, and it reduces the C storage potential of the landscape because the Alnus dominance constrains re-establishment of a natural montane forest.     

Green roof <Emphasis Type="Italic">Petunia</Emphasis>, <Emphasis Type="Italic">Ageratum</Emphasis>, and <Emphasis Type="Italic">Mentha</Emphasis> responses to water stress,seaweeds, and trinexapac-ethyl treatments

The availability of sufficient irrigation water and the development of drought-tolerant species are challenging factors in the design and maintenance of green roofs in modern cities. Green roof plants of Petunia hybrid Headliner^® Red Star, Ageratum hybrid Artist^® blue, and Mentha spicata L. grown in a simulated green roof pot system under controlled greenhouse conditions. The plants were watered every 2 or 6 days (2DWI/6DWI) for 8 weeks accompanied by either a 6-day treatment of seaweed extracts of Ascophyllum nodosum as a soil drench or foliar spray, or two concentrations of trinexapac-ethyl (TE) biweekly sprays. Following treatments, leaf number, leaf area, dry weights, plant height, stomatal conductanse, photosynthetic and transpiration rates and leaf water potential and relative water content were determined in two seasons during 2016 and 2017. The prolonged irrigation intervals reduced plant growth as revealed by morphological and physiological parameters. The application of SWE as drench treatment improved Petunia and Ageratum plant vegetative growth, stomatal conductance, photosynthetic and transpiration rates and leaf water potential and relative water content during prolonged irrigation intervals. TE increased the vegetative growth as well as the physiological performance of Ageratum plants. However, neither SWE nor TE treatments improved the performance of Mentha plants under prolonged irrigation intervals. It was suggested that improved photosynthetic rates were stimulated by enhanced stomatal conductance leading to improved leaf water potential as well as increased relative water content during prolonged irrigation conditions.     

Non-native liana, <Emphasis Type="Italic">Euonymus fortunei</Emphasis>, associated with increased soil nutrients,unique bacterial communities,and faster decomposition rate

Invasive plants have wide-ranging impacts on native systems including reducing native plant richness and altering soil chemistry, microbes, and nutrient cycling. Increasingly, these effects are found to linger long after removal of the invader. We examined how soil chemistry, bacterial communities, and litter decomposition varied with cover of Euonymus fortunei, an invasive evergreen liana, in two central Kentucky deciduous forests. In one forest, E. fortunei invaded in the late 1990s but invasion remained patchy and we paired invaded and uninvaded plots to examine the associations between E. fortunei cover and our response variables. In the second forest, E. fortunei had completely invaded the forest by 2005; areas where it had been selectively removed by 2010 were paired with an adjacent invaded plot. Where E. fortunei had patchily invaded, E. fortunei patches had up to 3.5× nitrogen, 2.7× carbon, and 1.9× more labile glomalin in soils than uninvaded plots, whereas there were no differences in soil characteristics between invaded and removal plots. In the patchily invaded forest, bacterial community composition varied among invaded and non-invaded plots, whereas bacterial communities did not vary among invaded and removal plots. Finally, E. fortunei leaf litter decomposed faster (k = 4.91 year^?1) than the native liana (k = 3.77 year^?1), Vitis vulpina; decomposition of both E. fortunei and V. vulpina was faster in invaded (k = 7.10 year^?1) than removal plots (k = 4.77 year^?1). Our findings suggest that E. fortunei invasion increases the rate of leaf litter decomposition via high-quality litter, alters the decomposition environment, and shifts in the soil biotic communities associated with a dense mat of wintercreeper. Land managers with limited resources should target the densest mats for the greatest restoration potential and remove wintercreeper patches before they establish dense mats.     

Changes in leaf epicuticular wax,gas exchange and biochemistry metabolism between <Emphasis Type="Italic">Jatropha mollissima</Emphasis> and <Emphasis Type="Italic">Jatropha curcas</Emphasis> under semi-arid conditions

Jatropha curcas and Jatropha mollissima plants were evaluated under conditions of high (HSM) and low (LSM) soil moisture in a semi-arid environment, as changes in the content and concentration of epicuticular wax and the leaf metabolism which could have a relationship with drought tolerance. Besides epicuticular wax, gas exchange, antioxidant system and biochemical parameters of the photosynthetic metabolism were measured. The epicuticular wax content increased only in J. mollissima leaves 95 % under LSM, when compared with HSM conditions. Therefore, J. curcas invested less in the production of long-chain n-alkanes than did J. mollissima under LSM conditions. J. mollissima plants showed the highest CO₂ assimilation rate during the HSM period compared to J. curcas. Both species showed high stability in some leaf biochemistry products, highlighting the highest sugar content, free amino acids, total soluble protein, and photosynthetic pigments in the leaves of J. mollissima plants under both of the soil moisture conditions. Moreover, the stability and performance of the different parameters, such as morphologic variables, seem to allow J. mollissima plants to tolerate semi-arid conditions.     

Field assessment of environmental factors constraining the development and expansion of <Emphasis Type="Italic">Schoenoplectus californicus</Emphasis> marsh at a California tidal freshwater restoration site

The effective restoration of wetland habitats requires understanding the establishment requirements, growth responses, and expansion dynamics of targeted plant species. This is particularly true when restoring areas that have been previously managed for other activities, such as agriculture, which can have legacy effects on the local environment. We investigated environmental factors (specifically hydrology and soil physicochemical conditions) that may influence the establishment, growth and expansion of Schoenoplectus californicus in a tidal freshwater marsh restoration site in the Sacramento–San Joaquin Delta, California, USA. This study site was previously leveed, drained, and utilized for agricultural production. A 1997 levee breach restored tidal connectivity and wetland vegetation has re-established in portions of the area. Our approach coupled an intensively-sampled transect study in S. californicus-dominated marshes with a spatially-extensive survey of S. californicus lateral expansion rates and elevation. Lateral expansion of S. californicus marsh edge was significantly less in lower elevation areas (0.61 ± 0.04 m NAVD88), whereas the marsh edge at higher elevations (0.84 ± 0.03 m NAVD88) exhibited greater expansion, often at rates greater than 1.0 m year^?1. These elevation means correspond to percentages of time that the marsh surface was flooded of 100 and 94 %, respectively. Although marsh edge expansion was influenced by elevation and the resultant hydrology, other factors, such as physical exposure of marsh shorelines and compacted agricultural soils also appear to be important. However, once established, S. californicus appears to be able to ameliorate high soil bulk densities over time as the advancing marsh platform develops.     

The interactive effects of created salt marsh substrate type,hydrology, and nutrient regime on <Emphasis Type="Italic">Spartina alterniflora</Emphasis> and <Emphasis Type="Italic">Avicennia germinans</Emphasis> productivity and soil development

Recent salt marsh and barrier island restoration efforts in the northern Gulf of Mexico have focused on optimizing self-sustaining attributes of restored marshes to provide maximum habitat value and storm protection to vulnerable coastal communities. Salt marshes in this region are dominated by Spartina alterniflora and Avicennia germinans, two species that are valued for their ability to stabilize soils in intertidal salt marshes. We conducted a controlled greenhouse study to investigate the influences of substrate type, nutrient level, and marsh elevation on the growth and biomass allocation of S. alterniflora and A. germinans, and the consequent effects on soil development and stability. S. alterniflora exhibited optimal growth and survival at the lowest elevation (? 15 cm below the water surface) and was sensitive to high soil salinities at higher elevations (+ 15 cm above the water surface). A. germinans performed best at intermediate elevations but was negatively affected by prolonged inundation at lower elevations. We found that although there was not a strong effect of substrate type on plant growth, the development of stressful conditions due to the use of suboptimal materials would likely be exacerbated by placing the soil at extreme elevations. Soil shear strength was significantly higher in experimental units containing either S. alterniflora or A. germinans compared to unvegetated soils, suggesting that plants effectively contribute to soil strength in newly placed soils of restored marshes. As marsh vegetation plays a critical role in stabilizing shorelines, salt marsh restoration efforts in the northern Gulf of Mexico and other storm impacted coasts should be designed at optimal elevations to facilitate the establishment and growth of key marsh species.     

Gas exchanges of an endangered species <Emphasis Type="Italic">Syringa pinnatifolia</Emphasis> and a widespread congener <Emphasis Type="Italic">S. oblata</Emphasis>

Net photosynthetic rate (P_N), transpiration rate (E), water use efficiency (WUE), stomatal conductance (g_s), and stomatal limitation (L_s) were investigated in two Syringa species. The saturation irradiance (SI) was 400 µmol m^-2s^-1 for S. pinnatifolia and 1 700 µmol m^-2s^-1 for S. oblata. Compared with S. oblata, S. pinnatifolia had extremely low g _s . Unlike S. oblata, the maximal photosynthetic rate (P_max) in S. pinnatifoliaoccurred around 08:00 and then fell down, indicating this species was sensitive to higher temperature and high photosynthetic photon flux density. However, such phenomenon was interrupted by the leaf development rhythms before summer. A relatively lower P_N together with a lower leaf area and shoot growth showed the capacity for carbon assimilation was poorer in S. pinnatifolia.     

Assessing biodegradation of furfuryl alcohol using <Emphasis Type="Italic">Pseudomonas putida</Emphasis> MTCC 1194 and <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis> MTCC 1034 and its kinetics

The biodegradation of furfuryl alcohol (FA) in shake flask experiments using a pure culture of Pseudomonas putida (MTCC 1194) and Pseudomonas aeruginosa (MTCC 1034) was studied at 30 °C and pH 7.0. Experiments were performed at different FA concentrations ranging from 50 to 500 mg/l. Before carrying out the biodegradation studies, the bacterial strains were acclimatized to the concentration of 500 mg/l of FA by gradually raising 100 mg/l of FA in each step. The well acclimatized culture of P. putida and P. aeruginosa degraded about 80 and 66% of 50 mg/l FA, respectively. At higher concentration of FA, the percentage of FA degradation decreased. The purpose of this study was to determine the kinetics of biodegradation of FA by measuring biomass growth rates and concentration of FA as a function of time. Substrate inhibition was calculated from experimental growth parameters using the Haldane equation. Data for P. putida were determined as µ _max ?=?0.23 h^?1, K _s ?=?23.93 mg/l and K _i ?=?217.1 mg/l and for P. aeruginosa were determined as µ _max ?=?0.13 h^?1, K _s ?=?21.3 mg/l and K _i ?=?284.9 mg/l. The experimental data were fitted in Haldane, Aiba and Edwards inhibition models.     

Early characterization of somatic hybrids from symmetric protoplast electrofusion of <Emphasis Type="Italic">Solanum pinnatisectum</Emphasis> Dun. and <Emphasis Type="Italic">Solanum tuberosum</Emphasis> L.

Variability of 31 somatic hybrids of Solanum pinnatisectum Dun. with Solanum tuberosum L. for leaf morphology, plant vigor, resistance to Phytophthora infestans, ploidy level, and cytoplasm type was evaluated in vitro. The composition of these somatic hybrids was as follows: [S. pinnatisectum Dun. (2n = 2x = 24; cytoplasmic type Wγ) + S. tuberosum L. (2n = 4x = 48; cytoplasmic type Tß)]. Based on leaf morphology and plant growth vigor, plants were divided into three groups, including plants close to tbr parent with unlobed leaves, small plants with scarcely dissected leaves, and vigorous plants with asymmetrically and pinnately lobed leaves. Nine of the somatic hybrids were found to be highly resistant to P. infestans. Somatic hybrids were either tetraploid or hexaploid, with hexaploids being predominant. The cytoplasm of somatic hybrids was either Tßγ or Wßγ, with Tßγ being more common. Overall, in contrast to leaf morphology and growth vigor, level of resistance to P. infestans was not related to either ploidy level or type of cytoplasm. These findings demonstrate that early in vitro selection of promising hybrids can be useful in breeding programs.     

How are anatomical and hydraulic features of the mangroves <Emphasis Type="Italic">Avicennia marina</Emphasis> and <Emphasis Type="Italic">Rhizophora mucronata</Emphasis> influenced by siltation?

Key message

This article provides significant data in the debate on whether siltation might have a negative impact on the hydraulic functioning of two widespread mangrove tree species Avicennia marina and Rhizophora mucronata.

Abstract

Elevated sediment addition, or siltation, within mangrove ecosystems is considered as being negative for trees and saplings, resulting in stress and higher mortality rates. However, little is known about how siltation influences the hydraulic functioning of mangrove trees. Comparing two mangrove tree species (Avicennia marina Vierh. Forsk. and Rhizophora mucronata Lam.) from low and high-siltation plots led to the detection of anatomical and morphological differences and tendencies. Adaptations to high siltation were found to be either mutual among both species, e.g., significant smaller single leaf area (p _A.marina  = 0.058, F1.38 = 3.8; p _R.mucronata  = 0.005, F1.38 = 8.7; n = 20 × 20) and a tendency towards smaller stomatal areas (p _A.marina  = 0.131, F1.8 = 2.8; p _R.mucronata  = 0.185, F1.8 = 2.1, n = 5 × 60), or species-specific trends for A. marina, such as higher phloem band/growth layer ratios (p = 0.101, F1.8 = 3.4, n = 5 × 3) and stomatal density (p = 0.052, F1.8 = 5.2, n = 5 × 4). All adaptations seemingly contributed to a comparable hydraulic conductivity independent of the degree of siltation. These findings indicate that silted trees level off fluctuations in their hydraulic performance as a survival mechanism to cope with this less favourable environment. Most of the trees’ structural adaptations to cope with siltation are similar to known drought stress-imposed adaptations.

     

Biotic factors in induced defence revisited: cell aggregate formation in the toxic cyanobacterium <Emphasis Type="Italic">Microcystis aeruginosa</Emphasis> PCC 7806 is triggered by spent <Emphasis Type="Italic">Daphnia</Emphasis> medium and disrupted cells

Bioassays with the toxic cyanobacterium Microcystis aeruginosa PCC 7806, its non-toxic mutant ΔmcyB, and Daphnia magna as grazer were used to evaluate biotic factors in induced defence, in particular cyanobacterial and grazer-released info-chemicals. Three main questions were addressed in this study: Does Daphnia grazing lead to a loss of cyanobaterial biomass? Is the survival time of Daphnia shorter in a culture of the toxic cyanobacterium? Does direct grazing or the presence of spent Daphnia medium or a high number of disrupted toxic Microcystis cells in the assays lead to an increase in the cellular microcystin content in the remaining intact cells? The biovolume (growth) as well as size and abundance of Microcystis aggregates were determined by particle analysis, while the survival time of Daphnia individuals was recorded by daily observation and counting, with the relative concentration of cell-bound microcystin-LR, was measured by HPLC analysis. Compared to some recent studies in the field of induced defence, in this study, evidence was found for a direct grazing effect, i.e. the loss of biovolume in the toxic culture. In addition, Daphnia magna ingested more non-toxic than toxic cells, and survived longer with non-toxic cells. In terms of increased cell-bound toxin concentration as a means of defence reported in some studies, a higher cell-bound microcystin-LR content was not measured in this study in any of the treatments (P > 0.05). Under low light conditions with impaired growth of Microcystis, and the presence of a high number of particles with less than 1-μm diameter (possibly heterotrophic bacteria), Daphnia medium was associated with a strong reduction in cell-bound toxin concentration (P < 0.05). This study showed no increased cell aggregation under direct grazing (P > 0.05), but increased aggregation with spent Daphnia medium under high light conditions (P < 0.05). Further, the addition of cell-free extract from disrupted toxic Microcystis cells strongly increased the aggregation of the intact cells under low light (P < 0.05). These findings are discussed with the possible role of microcystin and other infochemicals in the expression of proteins and morphology changes in Microcystis.     

Effects of light intensity on leaf photosynthetic characteristics,chloroplast structure,and alkaloid content of <Emphasis Type="Italic">Mahonia bodinieri</Emphasis> (Gagnep.) Laferr.

The variation of light intensity has obvious effects on leaf external morphology, internal anatomy, and physiological characteristics; it even induces changes in secondary metabolite production. The effects of different irradiance levels on biomass, gas exchange parameters, and photosynthetic pigment contents in Mahonia bodinieri (Gagnep.) Laferr. were analyzed here. Combined analyses of physiology, cytology, and HPLC were used to study the differences in leaf morphology, structure, physiological characters, and alkaloid content in response to different irradiances. The results indicated that the highest foliar biomass was observed under I ₅₀ (50 % of full sunlight) followed by I ₃₀ (30 % of full sunlight), the highest net photosynthetic rate, stomatal conductance, transpiration rate values were observed under I ₃₀ followed by I ₅₀, and lower values occurred in I ₁₀ (10 % of full sunlight) and I ₁₀₀ (full sunlight). With increased light intensity, total leaf area and the contents of chlorophyll a (Chl a), chlorophyll b (Chl b), and chlorophyll (Chl a+b) per unit leaf area were clearly reduced, whereas leaf mass per area, carotenoid content, leaf thickness, thickness of palisade and spongy parenchyma, and stomatal density were all significantly increased. Electron microscopic observation revealed that the number of grana, stroma lamellae and the number of starch grains in chloroplasts were decreased, the number of plastoglobuli was increased when irradiance levels increased. The estimated total yield of alkaloids in a single plant was higher under I ₃₀ and I ₅₀ than under I ₁₀ or I ₁₀₀ as a result of the higher biomass of the plants. Therefore, I ₃₀ and I ₅₀ were not only beneficial to increase biomass, but also suitable for the synthesis and accumulation of the major secondary metabolites (alkaloids). Our findings provide valuable data for the determination and regulation of irradiance levels during artificial cultivation of M. bodinieri.     

Histological and cytological studies of plant infection by <Emphasis Type="Italic">Erysiphe euonymi</Emphasis>-<Emphasis Type="Italic">japonici</Emphasis>

Powdery mildew caused by Erysiphe euonymi-japonici (Eej) is an increasingly serious fungal disease on Euonymus japonicus that is an important ornamental plant. However, little is currently known about infection and pathogenesis of Eej on E. japonicus. Here, we report plant infection by Eej at the histological and cytological levels. Eej caused severe disease symptoms with white and snow-like colonies on leaf surfaces of E. japonicus. Microscopic observations were conducted continuously to define infection process of Eej on E. japonicus. Eej conidia germinated to produce appressorial germ tubes on leaf surfaces and formed irregular haustoria in plant epidermal cells at 6 h post-inoculation (hpi) and 12 hpi, respectively. After uptaking nutrients from host cells by haustoria, Eej formed numerous hyphae and extensive colonization on leaf surfaces at 96 hpi and finally produced abundant conidiophores and new conidia on leaf surfaces at 168 hpi. In addition, there was consistently a single nucleus in different Eej infection structures and haustorial development could be divided into three major stages, including formation of penetration peg, formation of haustorial neck and initial haustorium, and maturation of haustorium. These results provide useful information for further determination of Eej pathogenesis and finally controlling the disease.     

Leaf-residing <Emphasis Type="Italic">Methylobacterium</Emphasis> species fix nitrogen and promote biomass and seed production in <Emphasis Type="Italic">Jatropha curcas</Emphasis>

Background

Jatropha curcas L. (Jatropha) is a potential biodiesel crop that can be cultivated on marginal land because of its strong tolerance to drought and low soil nutrient content. However, seed yield remains low. To enhance the commercial viability and green index of Jatropha biofuel, a systemic and coordinated approach must be adopted to improve seed oil and biomass productivity. Here, we present our investigations on the Jatropha-associated nitrogen-fixing bacteria with an aim to understand and exploit the unique biology of this plant from the perspective of plant–microbe interactions.

Results

An analysis of 1017 endophytic bacterial isolates derived from different parts of Jatropha revealed that diazotrophs were abundant and diversely distributed into five classes belonging to α, β, γ-Proteobacteria, Actinobacteria and Firmicutes. Methylobacterium species accounted for 69.1 % of endophytic bacterial isolates in leaves and surprisingly, 30.2 % which were able to fix nitrogen that inhabit in leaves. Among the Methylobacterium isolates, strain L2-4 was characterized in detail. Phylogenetically, strain L2-4 is closely related to M. radiotolerans and showed strong molybdenum-iron dependent acetylene reduction (AR) activity in vitro and in planta. Foliar spray of L2-4 led to successful colonization on both leaf surface and in internal tissues of systemic leaves and significantly improved plant height, leaf number, chlorophyll content and stem volume. Importantly, seed production was improved by 222.2 and 96.3 % in plants potted in sterilized and non-sterilized soil, respectively. Seed yield increase was associated with an increase in female–male flower ratio.

Conclusion

The ability of Methylobacterium to fix nitrogen and colonize leaf tissues serves as an important trait for Jatropha. This bacteria–plant interaction may significantly contribute to Jatropha’s tolerance to low soil nutrient content. Strain L2-4 opens a new possibility to improve plant’s nitrogen supply from the leaves and may be exploited to significantly improve the productivity and Green Index of Jatropha biofuel.

     

Photosynthetic responses to soil water stress in summer in two Japanese urban landscape tree species (<Emphasis Type="Italic">Ginkgo biloba</Emphasis> and <Emphasis Type="Italic">Prunus yedoensis</Emphasis>): effects of pruning mulch and irrigation management

Key message

Stomatal regulation involves beneficial effects of pruning mulch and irrigation on leaf photosynthesis in Prunus yedoensis and Ginkgo biloba under moderate drought. G. biloba showed conservative water use under drought.

Abstract

Leaf photosynthesis is highly sensitive to soil water stress via stomatal and/or biochemical responses, which markedly suppress the growth of landscape trees. Effective irrigation management to maintain leaf photosynthesis and information on species-specific photosynthetic responses to soil water stress are essential for the sustainable management of landscape trees in Japan, in which summer drought often occurs. In order to investigate effective irrigation management, we used plants with moderate soil water stress as controls, and examined the effects of daily irrigation and pruning mulch on leaf photosynthesis in container-grown Ginkgo biloba and Prunus yedoensis, which are the first and second main tall roadside trees in Japan. Stomatal conductance was significantly increased by pruning mulch and daily irrigation, with similar increases in leaf photosynthesis being observed in P. yedoensis and G. biloba. In order to obtain information on species-specific photosynthetic responses to soil water stress, we compared the responses of leaf photosynthesis and leaf water status to reductions in soil water content (SWC) between the two species. G. biloba maintained a constant leaf water potential, leaf water content, maximum carboxylation rate, and electron transport rate with reductions in SWC, whereas reductions were observed in P. yedoensis. We concluded that pruning mulch and irrigation effectively offset the negative impact of moderate water stress on leaf photosynthesis in summer in P. yedoensis and G. biloba via stomatal regulation, and also that G. biloba maintained its photosynthetic biochemistry and leaf water status better than P. yedoensis under severe water stress.

     

Impact of Chemical,Organic and Bio-Fertilizers Application on Bell Pepper, <Emphasis Type="Italic">Capsicum annuum</Emphasis> L. and Biological Parameters of <Emphasis Type="Italic">Myzus persicae</Emphasis> (Sulzer) (Hem.: Aphididae)

Myzus persicae (Sulzer) is a polyphagous aphid that causes chlorosis, necrosis, stunting, and reduce growth rate of the host plants. In this research, the effects of Zinc sulfate and vermicompost (30%), Bacillus subtilis, Pseudomonas fluorescens, Glomus intraradices, G. intraradices × B. subtilis, and G. intraradices × P. fluorescens compared to control was investigated on the growth characters of Capsicum annuum L. and biological parameters of M. persicae. Different fertilizers caused a significant effect on growth characters of C. annuum and biological parameters of M. persicae. The highest plant growth was observed on Zinc sulfate and B. subtilis treated plants, and the lowest was on control. Increase in the amount of specific leaf area (SLA) (0.502 mm² mg^?1) was significantly higher in the B. subtilis than other fertilizer treatments. The longest (10.3 days) and the shortest (5.3 days) developmental times of M. persicae nymphs were observed on 30% vermicompost and Zinc sulfate treatments, respectively. The lowest adult longevity periods of M. persicae (11.2 and 11.3 days) were observed on G. intraradices × B. subtilis and 30% vermicompost treatments, respectively, and the longest ones (16.4 days) on Zinc sulfate. The highest rate of nymphal mortality and the lowest amount of nymphal growth index (NGI) were recorded on 30% vermicompost. The nymphs reared on Zinc sulfate treatment had the lowest rate of nymphal mortality and the highest amount of NGI. Thus, amending the soil with 30% vermicompost had a significantly negative effect on the biological parameters of M. persicae that can be used as an ecological control tactic for this pest.     

Changes in leaf hydraulic conductance correlate with leaf vein embolism in<Emphasis Type="Italic"> Cercis siliquastrum</Emphasis> L.

The impact of xylem cavitation and embolism on leaf (K _leaf) and stem (K _stem) hydraulic conductance was measured in current-year shoots of Cercis siliquastrum L. (Judas tree) using the vacuum chamber technique. K _stem decreased at leaf water potentials (Ψ_L) lower than ?1.0 MPa, while K _leaf started to decrease only at Ψ_L L K _leaf changes. Field measurements of leaf conductance to water vapour (g _L) and Ψ_L showed that stomata closed when Ψ_L decreased below the Ψ_L threshold inducing loss of hydraulic conductance in the leaf. The partitioning of hydraulic resistances within shoots and leaves was measured using the high-pressure flow meter method. The ratio of leaf to shoot hydraulic resistance was about 0.8, suggesting that stem cavitation had a limited impact on whole shoot hydraulic conductance. We suggest that stomatal aperture may be regulated by the cavitation-induced reduction of hydraulic conductance of the soil-to-leaf water pathway which, in turn, strongly depends on the hydraulic architecture of the plant and, in particular, on leaf hydraulics.     

Cadmium tolerance in <Emphasis Type="Italic">Schinus molle</Emphasis> trees is modulated by enhanced leaf anatomy and photosynthesis

Key message

Low concentrations of cadmium cause anatomical responses in leaf chlorenchyma enhancing Schinus molle photosynthesis and tolerance.

Abstract

This work is aimed to evaluate the effects of cadmium (Cd) on leaf anatomy and photosynthesis in Schinus molle, a species that can cope with harsh environments. Seven-month-old S. molle plants were exposed over 90 days to varying Cd concentrations (0, 10, 20, 50, 125 or 250 µM using Cd(NO₃)₂ as the Cd source). The plants were placed in vases containing washed sand and vermiculite as the substrate and nutrient solution. Throughout the experiment, the substrate was maintained at field capacity, and the nutrient solution was replaced at 15-day intervals. After 90 days, leaves were collected and processed for anatomical analysis using typical plant microtechniques. In addition, plant growth, photosynthesis, chlorophyll content and A/Ci curve were evaluated using an infrared gas analyzer. S. molle growth was not affected by Cd. Lower Cd concentrations (10 and 20 µM) resulted in greater net photosynthesis, stomatal conductance and density, Vcmax, Jmax and mesophyll thickness. However, Cd concentrations of 50 µM or greater resulted in a reduction of most of the evaluated characteristics to levels close to control. All of the tested Cd concentrations resulted in reduced chlorophyll content and stomatal size. Therefore, the effect of Cd in a tolerant species such as S. molle is concentration dependent, and at low Cd concentrations, these plants can cope with the toxicity by adjusting leaf structure and function.