Effects of a nitrogen fixing plant Vigna radiata on growth, leaf stomatal gas exchange and hydraulic characteristics of the intercropping Juglans regia seedlings

Aims Our main purposes were to explore effects of phosphorus deficiency and soil acidification on growth, water balance and phosphorus nutrition in Juglans regia seedlings and to investigate the hydraulic mechanism involved in reduced photosynthesis and growth. Methods We measured growth, hydraulic characteristics, and gas exchanges in J. regia seedlings. The effects of phosphorus deficiency and soil acidification on xylem anatomic structure, water balance and photosynthetic characteristics were also analyzed. Important findings Soil acidification inhibited the phosphorous uptake and utilization efficiency in J. regia seedlings. A combination of soil acidification and phosphorous deficiency interrupted water balance, and reduced photosynthesis and growth of J. regia seedlings. Under soil acidification and phosphorus deficiency, non-stomatal factors also played a role in inhibiting photosynthesis.

Abstract. Gas exchange is a parameter needed in stream metabolism and trace gas emissions models. One way to estimate gas exchange is via measuring the decline of added tracer gases such as sulfur hexafluoride (SF6). Estimates of oxygen (O2) gas exchange derived from SF6 additions require scaling via Schmidt number (Sc) ratio, but this scaling is uncertain under conditions of high gas exchange via bubbles because scaling depends on gas solubility as well as Sc. Because argon (Ar) and O2 have nearly identical Schmidt numbers and solubility, Ar may be a useful tracer gas for estimating stream O2 exchange. Here we compared rates of gas exchange measured via Ar and SF6 for turbulent mountain streams in Wyoming, USA. We measured Ar as the ratio of Ar : N2 using a membrane inlet mass spectrometer (MIMS). Normalizing to N2 confers higher precision than simply measuring [Ar] alone. We consistently enriched streams with Ar from 1 to 18 % of ambient Ar concentration and could estimate gas exchange rate using an exponential decline model. The mean ratio of gas exchange of Ar relative to SF6 was 1.8 (credible interval 1.1 to 2.5) compared to the theoretical estimate 1.35, showing that using SF6 would have underestimated exchange of Ar. Steep streams (slopes 11–12 %) had high rates of gas exchange velocity normalized to Sc=600 (k600, 57–210 m d−1), and slope strongly predicted variation in k600 among all streams. We suggest that Ar is a useful tracer because it is easily measured, requires no scaling assumptions to estimate rates of O2 exchange, and is not an intense greenhouse gas as is SF6. We caution that scaling from rates of either Ar or SF6 gas exchange to CO2 is uncertain due to solubility effects in conditions of bubble-mediated gas transfer.

The effect of two sources of nitrogen (nitrogen fixation or nitrate assimilation) and gradual water stress on theelectrophoretic spectra of peroxidase, catalase and superoxide dismutase was studied in soybean leaves. An increase in H2O2production was observed, especially after the prolonged drought treatment. At 50% drought the activity of anionic peroxidase activity for isoenzymes Nos. 2 and 7+8 significantly increased (by 54 and 18%, respectively) in the leaves of nitrate-fed plants compared to the control plants; for nitrogen-fixing plants these values were 31 and 14%, respectively. In the case of cationic peroxidases, the application of 50% drought led to the inhibition of the moderately fast isoenzymes (Nos. 2 and 3, with Rm 0.5 and 0.65, respectively) and the activation of the fastest moving isoenzyme (No. 4, with Rm 0.8) in nitrate-fed soybean. The same tendency was observed in the leaves of nitrogen-fixing plants. The effect of restricted soil humidity on SOD activity was expressed as a change in the activity of some of the isoenzymes. There was a clear tendency for the SOD isoenzyme activity to increase after the exposure of nitrate-fed and nitrogen-fixing soybean plants to 50% drought treatment. high catalase activity was registered in control nitrate-fed plants. Generally the catalase isoenzyme activity in control nitrogen-fixing plants had low values. Both intensities of water stress (30 and 50% drought) caused an increase in the catalase activity, and this increase was much higher for nitrogen-fixing plants. Therefore, soybean plants responded to drought treatment by changes in the antioxidant enzyme activity, as these changes were partially dependent on the source of nitrogen. The results suggested that nitrogen-fixing soybean plants were more resistant to gradual water stress.

In the arid southwest of North America, winter precipitation penetrates to deep soil layers, whereas summer ''monsoon'' precipitation generally wets only surface layers. Use of these spatially separated water sources was determined for three dominant tree species of the pinyon-juniper ecosystem at six sites along a gradient of increasing summer precipitation in Utah and Arizona. Mean summer precipitation ranged from 79 to 286 mm, or from 18% to 60% of the annual total across the gradient. We predicted that, along this summer rainfall gradient, populations of dominant tree species would exhibit a clinal off-on response for use of water from upper soil layers, responding at particular threshold levels of summer precipitation input. This prediction was largely supported by our observations of tree water source use over a two-year period and from irrigation ex- periments. Hydrogen and oxygen stable isotope ratios ( dD and d 18 O) of tree xylem water were compared to that of precipitation, groundwater, and deep and shallow soil water to distin- guish among possible tree water sources. dD-d 18 O relationships and seasonal xylem water potential changes revealed that trees of this ecosystem used a mixture of soil water and recent precipitation, but not groundwater. During the monsoon period, a large proportion of xylem water in Pinus edulis and Juniperus osteospermawas from monsoon precipitation, but use of this precipitation declined sharply with decreasing summer rain input at sites near the regional monsoon boundary in Utah. Quercus gambelii at most sites along the gradient used only deep soil water even following substantial inputs of summer rain. Pop- ulations of Quercus at sites with the highest average summer precipitation input, however, predominantly used water in upper soil layers from recent summer rain events. Soil tem- perature correlated with patterns of summer precipitation use across the gradient; high soil temperatures north of the monsoon boundary may have inhibited surface root activity for some or all of the three tree species. Irrigation experiments with deuterium-labeled water revealed that Quercus gambeliiin northern Arizona and southern Utah did not use water from surface layers. In contrast, Juniperus osteosperma at these sites responded significantly to the irrigations: between 37% and 41% of xylem water originated from irrigations that wetted only the top 30 cm of soil. Responses by Pinus edulis to these irrigations were variable; uptake of labeled water by this species was greater in September at the end of the summer than during the hot midsummer period. Inactivity of Pinus roots in midsummer supports the hypothesis that root activity in this species is sensitive to soil temperature. Seasonal patterns of leaf gas exchange and plant water potential corresponded to the seasonality of rainfall at different sites. However, no correlation between a species' ability to use summer rainfall and its tolerance to water deficits at the leaf level was found. Midday stomatal conductance (gs) for Pinus needles approached zero at predawn water potentials near 22 MPa, whereas gs in Quercus and Juniperus declined to zero at 22.8 and 23.7 MPa, respectively. The relationship between photosynthesis (A) and gs was similar among the three species, although Quercus maintained higher overall rates of gas exchange and tended to operate higher on the A/gs curve than the two conifers. At sites in eastern Arizona where Quercus fully used moisture from summer rains, leaf gas exchange characteristics were similar to those of Pinus and Juniperus.

Physoclist fish are able to regulate their buoyancy by secreting gas into their hydrostatic organ, the swim bladder, as they descend through the water column and by resorbing gas from their swim bladder as they ascend. Physoclists are restricted in their vertical movements due to increases in swim bladder gas volume that occur as a result of a reduction in hydrostatic pressure, causing fish to become positively buoyant and risking swim bladder rupture. Buoyancy control, rates of swim bladder gas exchange and restrictions to vertical movements are little understood in marine teleosts. We used custom-built hyperbaric chambers and laboratory experiments to examine these aspects of physiology for two important fishing target species in southern Australia, pink snapper (Pagrus auratus) and mulloway (Argyrosomus japonicus). The swim bladders of pink snapper and mulloway averaged 4.2 and 4.9 % of their total body volumes, respectively. The density of pink snapper was not significantly different to the density of seawater (1.026 g/ml), whereas mulloway were significantly denser than seawater. Pink snapper secreted gas into their swim bladders at a rate of 0.027 ± 0.005 ml/kg/min (mean ± SE), almost 4 times faster than mulloway (0.007 ± 0.001 ml/kg/min). Rates of swim bladder gas resorption were 11 and 6 times faster than the rates of gas secretion for pink snapper and mulloway, respectively. Pink snapper resorbed swim bladder gas at a rate of 0.309 ± 0.069 ml/kg/min, 7 times faster than mulloway (0.044 ± 0.009 ml/kg/min). Rates of gas exchange were not affected by water pressure or water temperature over the ranges examined in either species. Pink snapper were able to acclimate to changes in hydrostatic pressure reasonably quickly when compared to other marine teleosts, taking approximately 27 h to refill their swim bladders from empty. Mulloway were able to acclimate at a much slower rate, taking approximately 99 h to refill their swim bladders. We estimated that the swim bladders of pink snapper and mulloway ruptured after decreases in ~2.5 and 2.75 times the hydrostatic pressure to which the fish were acclimated, respectively. Differences in buoyancy, gas exchange rates, limitations to vertical movements and acclimation times between the two species are discussed in terms of their differing behaviour and ecology.

In agroecosystems, nitrogen is one of the major nutrients limiting plant growth. To meet the increased nitrogen demand in agriculture, synthetic fertilizers have been used extensively in the latter part of the twentieth century, which have led to environmental challenges such as nitrate pollution. Biological nitrogen fixation (BNF) in plants is an essential mechanism for sustainable agricultural production and healthy ecosystem functioning. BNF by legumes and associative, endosymbiotic, and endophytic nitrogen fixation in non-legumes play major roles in reducing the use of synthetic nitrogen fertilizer in agriculture, increased plant nutrient content, and soil health reclamation. This review discusses the process of nitrogen-fixation in plants, nodule formation, the genes involved in plant-rhizobia interaction, and nitrogen-fixing legume and non-legume plants. This review also elaborates on current research efforts involved in transferring nitrogen-fixing mechanisms from legumes to non-legumes, especially to economically important crops such as rice, maize, and wheat at the molecular level and relevant other techniques involving the manipulation of soil microbiome for plant benefits in the non-legume root environment.

Physiological adaptations of the intertidal rockpool teleost Blennius pholis L., to aerial exposure

The stable isotopes of hydrogen and oxygen in xylem water are often used to investigate tree water sources. But this traditional approach does not acknowledge the contribution of water stored in the phloem to transpiration and how this may affect xylem water and source water interpretations. Additionally, there is a prevailing assumption that there is no isotope fractionation during tree water transport. Here, we systematically sampled xylem and phloem water at daily and subdaily resolutions in a large lysimeter planted with Salix viminalis. Stem diurnal change in phloem water storage and transpiration rates were also measured. Our results show that phloem water is significantly less enriched in heavy isotopes than xylem water. At subdaily resolution, we observed a larger isotopic difference between xylem and phloem during phloem water refilling and under periods of tree water deficit. These findings contrast with the expectation of heavy‐isotope enriched water in phloem due to downward transport of enriched leaf water isotopic signatures. Because of previous evidence of aquaporin mediated phloem and xylem water transport and higher osmotic permeability of lighter hydrogen isotopologues across aquaporins, we propose that radial water transport across the xylem–phloem boundary may drive the relative depletion of heavy isotopes in phloem and their relative enrichment in xylem.

<div class="htmlview paragraph">The Biomass Production Chamber (BPC) Sizing Model has been designed to incorporate plant growth chamber options into NASA’s Advanced Life Support Sizing Analysis Tool. The concept addressed by the model is that the gas exchange from a biomass production chamber, in conjunction with human metabolic data and food consumption rates, can be used to estimate the chamber size necessary for the gas exchange and food production rate required for a specific crew size.</div> <div class="htmlview paragraph">NASA’s baseline design utilizes a 78m<sup>2</sup> (840 ft<sup>2</sup>) plant growth area and a 9.45m (31 ft) center shelf length. Using an iterative comparison method, the center shelf is incremented by 1.5m (5 ft) sections until necessary food production requirements and gas exchange rates are satisfied.</div>

It has been suggested that in plant invasions, species may develop intrinsically higher gas exchange and growth rates, and greater nitrogen uptake and allocation to shoots, in their invasive range than in their native habitat under excess nutrients. In this study, native populations of two old world Phragmites australis phylogeographic groups (EU and MED) were compared with their invasive populations in North America [NAint (M) and NAint (Delta)] under unlimited nutrient availability and identical environmental conditions in a common garden. We expected that both introduced groups would have higher growth, nitrogen uptake and allocation, and gas exchange rates than their native groups, but that these enhanced traits would have evolved in different ways in the two introduced ranges, because of different evolutionary histories. Biomass, leaf area, leaf nitrogen concentrations (NH4 + and NO3 −) and transpiration rates increased in introduced versus native groups, whereas differences in SLA, leaf pigment concentrations and assimilation rates were due to phylogeographic origins. Despite intrinsic differences in the allocation of C and N in leaves, shoots and rhizome due to phylogeographic origin, the introduced groups invested more biomass in above-ground tissues than roots and rhizomes. Our results support the concept that invasive populations develop enhanced morphological, physiological and biomass traits in their new ranges that may assist their competiveness under nutrient-enriched conditions, however the ecophysiological processes leading to these changes can be different and depend on the evolutionary history of the genotypes.

Potted seedlings of Leucadendron xanthoconus (Proteaceae) were grown in native mountain fynbos soil under different nutrient and water regimes. Nutrient treatments comprised addition of nitrogen, phosphorus and a Long Ashton macronutrient solution (LA). Water was applied at three levels, ranging from near drought to maintained saturation. Rates of gas exchange were measured on a subset of the experimental plants under a range of irradiance levels prior to harvesting of all plants at an age of six months. Measurement of biomass and its distribution showed that increasing water had a significantly positive effect on productivity, and that drought reduced root:shoot ratio and leaf specific weight. Total productivity was highest with LA-addition and lowest in the control, whereas phosphorus and nitrogen additions had an intermediate effect. None of the treatments included in the gas exchange work was shown to affect significantly photosynthetic capacity or water use efficiency. Droughted individuals showed an increased ability to reduce carbon dioxide concentration in the substomatal cavity, and a lower stomatal conductance overall. Stomatal conductance was found to be independent of irradiance in all treatments. The relationships investigated are placed in the context of fynbos utilization and the management of natural fynbos landscapes with regard to the reclamation and maintenance of component natural ecosystems.

The filamentous, heterocyst-forming cyanobacteria perform oxygenic photosynthesis in vegetative cells and nitrogen fixation in heterocysts, and their filaments can be hundreds of cells long. In the model heterocyst-forming cyanobacterium Anabaena sp. strain PCC 7120, the genes in the fraC-fraD-fraE operon are required for filament integrity mainly under conditions of nitrogen deprivation. The fraC operon transcript partially overlaps gene all2395, which lies in the opposite DNA strand and ends 1 bp beyond fraE. Gene all2395 produces transcripts of 1.35 kb (major transcript) and 2.2 kb (minor transcript) that overlap fraE and whose expression is dependent on the N-control transcription factor NtcA. Insertion of a gene cassette containing transcriptional terminators between fraE and all2395 prevented production of the antisense RNAs and resulted in an increased length of the cyanobacterial filaments. Deletion of all2395 resulted in a larger increase of filament length and in impaired growth, mainly under N2-fixing conditions and specifically on solid medium. We denote all2395 the fraF gene, which encodes a protein restricting filament length. A FraF-green fluorescent protein (GFP) fusion protein accumulated significantly in heterocysts. Similar to some heterocyst differentiation-related proteins such as HglK, HetL, and PatL, FraF is a pentapeptide repeat protein. We conclude that the fraC-fraD-fraE←fraF gene cluster (where the arrow indicates a change in orientation), in which cis antisense RNAs are produced, regulates morphology by encoding proteins that influence positively (FraC, FraD, FraE) or negatively (FraF) the length of the filament mainly under conditions of nitrogen deprivation. This gene cluster is often conserved in heterocyst-forming cyanobacteria.

Micropropagation enables the efficient clonal propagation of plants, bringing advantages to the Eucalyptus plantlet process. Herein, the influence of gas exchange rates and sucrose concentrations on the development of microstumps of a Eucalyptus urophylla S. T. Blake clone for microcutting production was evaluated. The microstumps were cultured under three gas exchange systems using caps with membrane, caps without membrane or a combination of the above, and also supplemented with 0, 7, 15 and 30 g L-1 sucrose. Gas exchange and sucrose supplementation affected the development of microstumps in vitro and the survival of microcuttings ex vitro. Lower sucrose concentrations were necessary under higher gas exchange rate conditions to improve the development and production of microstumps. Higher survival rates of ex vitro microcuttings were also observed under higher gas exchange rate. Sucrose is important in the initial plant development, but it can be reduced after the culture is established, depending on the gas exchange rate used. Thus, our findings show that reducing sucrose and increasing the gas exchange rates are efficient strategies for establishing microstumps of the Eucalyptus urophylla clone maintained under an in vitro condition. Study Implications: Photoautotrophic micropropagation can promote significant growth of Eucalyptus, and in this system, environmental factors need to be adequately controlled. This study has revealed efficient combinations of sucrose concentrations and gas exchange systems that promote greater in vitro production and greater ex vitro survival of microcuttings. Plants grown under higher gas exchange conditions show better acclimatization with higher survival rate during the ex vitro stage and require lower sucrose concentration during in vitro cultivation. This approach is useful in enhancing micropropagation techniques and indicates its potential application for scaling up large culture vessels to aseptic culture rooms for closed microcutting production systems.

The cyanobacteria are a diverse group of prokaryotes which carry out oxygenic photosynthesis. Some cyanobacteria can also fix nitrogen. Because nitrogenase is sensitive to oxygen, the process of nitrogen fixation in cyanobacteria is separated from oxygenic photosynthesis either temporally or spacially. Under nitrogen deprivation conditions, some filamentous cyanobacteria form thick-walled heterocysts. Heterocysts are terminally differentiated cells which are usually regularly spaced along the filaments (pattern formation). The main function of heterocysts is nitrogen fixation. Differentiation from a vegetative cell to a heterocyst is a complex process and many genes are involved in this process (1-3). Buikema and Haselkorn (4) reported cloning and sequencing of hetRgene from AnabaenaPCC 7120. They showed that the hetRgene was up-regulated when nitrogen was removed from growth medium. A single nucleotide mutation in hetRopen reading frame (S179N) resulted in a totally nonfunctional hetRgene product. The strain with such a mutant gene could not form heterocysts under nitrogen deprivation conditions. On the other hand, presence of multiple copies of hetRled to formation of strings of heterocysts. Black et al. (5) analysed hetRexpression and found that hetRgene expression required the presence of a functional hetRgene product, suggesting that hetRwas positively auto-regulatory. These features of hetRgene and its product led to suggestion that hetRgene is a master switch controlling heterocyst differentiation (2). The function of hetRgene may not be restricted to regulation of heterocyst differentiation. Southern analysis showed that hetRgene may be present in non-heterocystous cyanobacteria such as Plectonemawhile it was not detected in unicellular cyanobacteria (4). Leganes et al. (6) showed that hetRis required for akinete formation in Nostoc ellipsosporum.

This paper presents HydroShoot, a leaf-based functional-structural plant model (FSPM) that simulates gas exchange rates of complex plant canopies under water deficit conditions. HydroShoot is built assuming that simulating both the hydraulic structure of the shoot together with the energy budget of individual leaves is the asset for successfully scaling-up leaf to canopy gas exchange rates. HydroShoot includes three interacting modules: hydraulic, which calculates the distribution of xylem water potential across shoot hydraulic segments; energy, which calculates the complete energy budget of individual leaves; and exchange, which calculates net carbon assimilation and transpiration rates of individual leaves. HydroShoot was evaluated on virtual and real grapevines having strongly contrasted canopies, under well-watered and water deficit conditions. It captured accurately the impact of canopy architecture and soil water status on plant-scale gas exchange rates and leaf-scale temperature and water potential. Both shoot hydraulic structure and leaf energy budget simulations were, as postulated, required to adequately scaling-up leaf to canopy gas exchange rates. Notwithstanding, simulating shoot hydraulic structure was found more necessary to adequately performing this scaling task than simulating leaf energy budget. That is, the intra-canopy variability of leaf water potential was a better predictor of the reduction of whole plant gas exchange rates under water deficit than the intra-canopy variability of leaf temperature. We conclude that simulating the shoot hydraulic structure is a prerequisite if FSPMs are to be used to assess gas exchange rates of complex plant canopies as those of grapevines. Finally, HydroShoot is available through the OpenAlea platform (https://github.com/openalea/hydroshoot) as a set of reusable modules.