Exudation Rate Research Articles

Role of the polycarboxylic compounds in the response of Silene vulgaris to chromium.

This work aims to investigate the nature and the specific mechanisms by which polycarboxylic compounds participate in the tolerance of Silene vulgaris to Cr with special attention given to the rhizosphere system. This knowledge is important to use this species in the implementation of phytoremediation technologies in Cr-polluted soils. According to the results, chromium is chelated and mobilized by the citric and malic acids in plant tissues, while oxalic acid might participate in the reduction and chelation of Cr in the rhizosphere. At the applied doses, the response of both exudation rate and root exudate composition (total polyphenols and quercitin) seems to involve a rearrangement in the lignification of the plant cell wall to immobilize Cr. Quercetin-3-dirhamnosyl-galactoside and apiin (apigenin-7-O-apiosyl-glucoside) have been identified as the major polyphenols in the root exudates of S. vulgaris. The increments found in the apiin concentration in root exudates seem to be related to the protection against Cr toxicity by chelation of Cr or by free radical scavenging. Though earlier response is detected in plant tissues, results from this work together with previous studies in S. vulgaris indicate that exudation might be a regulated mechanism of protection under Cr exposition in S. vulgaris that may involve mainly Cr reduction and chelation.

Temporal differences in plant growth and root exudation of two Brachiaria grasses in response to low phosphorus supply

Exploiting the natural variability of Brachiaria forage germplasm to identify forage grasses adapted to infertile acid soils that contain very low available phosphorus (P) is an important research objective for improving livestock production in the tropics. The objective of this study was to determine the differences in the release of root biochemical markers, i.e. carboxylates and acid phosphatases (APases), during the development of P deficiency in signalgrass and ruzigrass. We used the hydroxyapatite pouch system in hydroponics to simulate conditions of low P supply in acid soils to test the response of well-adapted signalgrass ( Brachiaria decumbens cv. Basilisk, CIAT 606) and less-adapted ruzigrass ( B. ruziziensis cv. Kennedy, CIAT 654). We monitored shoot and root growth and other physiological and biochemical components that are important for root functionality at weekly intervals for 3 weeks. We found that monocarboxylate exudation was not associated with the plant’s physiological P status, while exudation of oxalate and secreted-APases increased with declining plant P concentrations in both grasses. Ruzigrass showed higher exudation rates and grew faster than signalgrass, but could not maintain its initial fast growth rate when P concentrations in plant tissue declined to 1.0 mg P/g dry matter. Oxalate was the dominant exuded carboxylate for signalgrass after 21 days of growth and this response might confer some eco-physiological advantages in signalgrass when grown in low-P acid soils.

Фитохимические и фармакологические векторы применения <i>Malva sylvestris</i> L. в дерматологической практике

Методом ВЭЖХ изучен компонентный состав фенольных соединений листьев мальвы лесной и проведено количественное определение суммы флавоноидов и гидроксикоричных кислот (2,97 ± 0,08) % и (2,84 ± 0,03) % соответственно. Среди фенольных соединений в экстракте доминирует лютеолин, содержание которого составляет 96,12 мг/100 г, а также хлорогеновая кислота (51,04 мг/100 г). Проведена серия фармакологических испытаний (модель острого эксудативного воспаления, ранотензиометрия на модели линейных резаных ран, проба Нестерова). Показано, что применение геля с экстрактом мальвы у животных в условиях патологий воспалительного ґенеза реализуется достоверным уменьшениям величин индекса воспаления и коэффициента эксудации в сравнении с контролем, что можно обусловить присутствием комплекса фенольных соединений. Выявлены также репаративные, капилляропротекторные и гидратантные эффекты фитосубстанции. Результаты, приведенные в данной работе, дают экспериментальное обоснование применения листьев мальвы для лечения патологий, сопровождающихся воспалительным процессом, и использованию данного растения для лечения дерматологических заболеваний, что создает предпосылки для разработки лекарственных форм на основе экстракта мальвы лесной и введения его в официальную медицину.

Morpho-physiological response of Acacia auriculiformis as influenced by seawater induced salinity stress

Aim of the study: To evaluate the morpho-physiological changes of Acacia auriculiformis in response to seawater induced salinity stress along with its tolerance limit.Area of study: Bangabandhu Sheikh Mujibur Rahman Agricultural University, Bangladesh.Material and methods: Three saline treatments (4, 8, 12 dS m-1) were applied to six-month aged Acacia auriculiformis seedlings from January 2014 to June 2014 and the tap water was used as control treatment. To observe salinity effects, the following parameters were measured by using various established techniques: plant height and leaf number, plant biomass, shoot and root distribution as well as shoot and root density, water uptake capacity (WUC), water saturation deficit (WSD) and water retention capacity (WRC), exudation rate, and cell membrane stability.Main results: Diluted seawater caused a notable reduction in shoot and root distribution in addition to shoot and root density, though plant height, leaf number and plant biomass were found to be decreased to some extent compared to control plants. Water status of the plant also altered when plants were subjected to salinity stress. Nevertheless, membrane stability revealed good findings towards salinity tolerance.Research highlights: Considering the above facts, despite salinity exerts some negative effects on overall plant performance, interestingly the percent reduction value doesn’t exceed 50% as compared to control plants, and the plants were successful to tolerate salinity stress till the end of the experiment (150 days) through adopting some tolerance mechanisms.Additional key words: Salt stress; halophytes; growth parameters; WUC; exudation rate; membrane stability.Abbreviations used: BSMRAU (Bangabandhu Sheikh Mujibur Rahman Agricultural University); RCBD (randomized complete block design); DATI (days after treatment imposition); RWC (relative water content); WUC (water uptake capacity); WSD (water saturation deficit); WRC (water retention capacity); FW (fresh weight); DW (dry weight); TW (turgid weight); ROS (reactive oxygen species).

Genotypic Differences in Phosphorus Efficiency and the Performance of Physiological Characteristics in Response to Low Phosphorus Stress of Soybean in Southwest of China.

Southwest of China is one of the major soybean (Glycine max L.) production regions in China with low availability of soil phosphorus (P). Whereas little information is available on P-efficient soybean genotypes in this region, even though using P-efficient soybean genotypes is a sustainable P management strategy for enhancing yield and P use efficiency. To assess the genetic variation on P use efficiency, 274 soybean genotypes were employed to compare the yields and P acquisition potentials in the field. Additionally, 10 representational genotypes (5 P-efficient genotypes and 5 P-inefficient genotypes) were grown in hydroponic media containing low P treatment (0.05 mM L−1) and high P treatment (0.25 mM L−1) to further investigate P assimilation characteristics and the related mechanisms of P-efficient soybean genotypes. In the field trial, the models described the relationships between yield and seed P concentration (R2 = 0.85), shoot P accumulation (R2 = 0.84), HI (R2 = 0.82) well. The yield, seed P concentration and shoot P accumulation ranged from 5.5 to 36.0 g plant−1, from 0.045 to 0.93% and from 0.065 to 0.278 mg plant−1, respectively. In the hydroponic trial, P-efficient genotypes under low P treatment showed significantly better plant growth, P accumulation and root: shoot ratio than P-inefficient genotypes. Simultaneously, total root length, specific root length, root surface area and root volume of P-efficient were significantly greater than P-inefficient under low P treatment. Higher rate of organic acid exudation and acid phosphatase activities was observed in the P-efficient soybean genotypes under low P condition when compared to the P-inefficient soybean genotypes. It indicated that significant genetic variation for P use efficiency existed in this region, and the P-efficient soybean genotypes, especially E311 and E141, demonstrated great tolerance to P deficiency, which could be potential materials using in improving production and P use efficiency in low availability of soil P region.

Efficient acquisition of iron confers greater tolerance to saline-alkaline stress in rice (Oryza sativa L.).

To elucidate the mechanisms underlying tolerance to saline-alkaline stress in two rice genotypes, Dongdao-4 and Jigeng-88, we exposed them to medium supplemented with 10 mM Na2CO3 and 40 mM NaCl (pH 8.5). Dongdao-4 plants displayed higher biomass, chlorophyll content, and photosynthetic rates, and a larger root system than Jigeng-88 under saline-alkaline conditions. Dongdao-4 had a higher shoot Na+/K+ ratio than Jigeng-88 under both control and saline-alkaline conditions. Dongdao-4 exhibited stronger rhizospheric acidification than Jigeng-88 under saline-alkaline conditions, resulting from greater up-regulation of H+-ATPases at the transcriptional level. Moreover, Fe concentrations in shoots and roots of Dongdao-4 were higher than those in Jigeng-88, and a higher rate of phytosiderophore exudation was detected in Dongdao-4 versus Jigeng-88 under saline-alkaline conditions. The Fe-deficiency-responsive genes OsIRO2, OsIRT1, OsNAS1, OsNAS2, OsYSL2, and OsYSL15 were more strongly up-regulated in Dongdao-4 than Jigeng-88 plants in saline-alkaline medium, implying greater tolerance of Dongdao-4 plants to Fe deficiency. To test this hypothesis, we compared the effects of Fe deficiency on the two genotypes, and found that Dongdao-4 was more tolerant to Fe deficiency. Exposure to Fe-deficient medium led to greater rhizospheric acidification and phytosiderophore exudation in Dongdao-4 than Jigeng-88 plants. Expression levels of OsIRO2, OsIRT1, OsNAS1, OsNAS2, OsYSL2, and OsYSL15 were higher in Dongdao-4 than Jigeng-88 plants under Fe-deficient conditions. These results demonstrate that a highly efficient Fe acquisition system together with a large root system may underpin the greater tolerance of Dongdao-4 plants to saline-alkaline stress.

Inoculation with Azospirillum brasilense (Ab-V4, Ab-V5) increases Zea mays root carboxylate-exudation rates, dependent on soil phosphorus supply

We aimed to investigate the effects of root carboxylate exudation in the interaction between Azospirillum brasilense and Zea mays. We hypothesized that root carboxylate exudation is a mechanism that increases colonization of the maize rhizosphere by A. brasilense and that carboxylate exudation would increase at a low soil phosphorus (P) availability. We conducted a greenhouse experiment, using maize seeds inoculated and uninoculated with A. brasiliense. Seeds were planted in pots, supplied with nutrient solution, varying in P concentration. After 45 days we measured total plant biomass, root length and area, plant nutrient status, and the root carboxylate-exudation rate. Inoculation increased the root length and area, and this effect increased with increasing P supply. Inoculated plants also showed an increased root carboxylate-exudation rate. For inoculated treatments, the exudation rate was positively correlated with root architecture parameters; however, it was negatively correlated with leaf manganese concentration, a proxy for the amount of carboxylates in the rhizosphere. Inoculation of A. brasilense stimulated root carboxylate exudation, which was positively correlated with root length and area. These positive correlations are probably mediated by the effect of carboxylates on the rhizosphere microbial community. This indicates a positive feedback in which A. brasilense inoculation stimulates root carboxylate exudation, influencing the rhizosphere microbial community. It results in positive effects on maize root architecture. The root length of inoculated plants was positively correlated with P supply, indicating that P supply positively affects the microbial community, modulating the interaction between A. brasilense and Z. mays.

Drought effects on Helianthus annuus and Glycine max metabolites: from phloem to root exudates

Numerous compounds are exuded by roots that play a central role in microbial decomposition and stabilization of soil carbon. The release of root exudates is sensitive to drought, but it is unclear how compound-specific exudates are related to drought-induced changes in plant metabolism.We investigated drought effects on root exudate quality and quantity for sunflower (Helianthus annuus) and soybean (Glycine max). We analyzed metabolites in phloem and root biomass extracts, to investigate whether root exudation is controlled by above- or below-ground processes.Sunflower and soybean showed different drought responses. Sunflower increased rates of exudation after rewetting (+330% in C) but the composition of metabolites remained unchanged compared to the control (constant moisture). Soybean did not change rates but the composition of metabolites changed with increased concentrations of osmolites (proline and pinitol). For specific groups, positive relationships were observed between exudates and phloem (amino-acids and organic acids) and between exudates and root biomass (sugars).Our results indicate that drought can induce different responses in plant metabolism causing changes in the quantity or composition of root exudates following rewetting. Furthermore, our results suggest that metabolism in shoots can influence exudation of organic acids and amino acids, while roots have a stronger control over exudation of sugars.

Similar outcomes for anti-tumor necrosis factor-α antibody and immunosuppressant following seton drainage in patients with Crohn's disease-related anal fistula.

Anal fistula is common in patients with Crohn's disease (CD) and leads to significant morbidity. The efficacy of seton drainage combined with anti-tumor necrosis factor-α monoclonal antibody (anti-TNF-α) or immunosuppressant in the treatment of CD-related anal fistula remains unclear. The aim of the present study was to compare the efficacy between seton drainage combined with anti-TNF-α and seton drainage combined with immunosuppressant postoperatively on the treatment of CD-related anal fistula. A total of 65 patients with CD-related anal fistula who had received seton drainage combined with postoperative medication were divided into an antibiotics only group, anti-TNF-α group and immunosuppressant group; all patients were treated with antibiotics. Fistula closure, external orifice exudation rate and recurrence rate were assessed among these patients. The duration of follow-up ranged from 3 to 84 months with an average of 25.3 months. There were 11 (16.9%) cases of recurrence after seton drainage, 9 of which underwent a second seton drainage. In the total study group, 34 (52.3%) cases achieved complete fistula closure, and 10 (15.4%) cases showed external orifice exudation. No significant difference was found among these three groups, regarding fistula closure rate, closure time of fistula and recurrence rate. The external orifice exudation rate was significantly higher in the anti-TNF-α group compared with the antibiotics only group and immunosuppressant group (P=0.004 and P=0.026, respectively). Seton drainage is an effective treatment for CD-related anal fistula. The efficacy is similar whether combined with anti-TNF-α or immunosuppressant.

Effects of arbuscular mycorrhizae on tomato yield, nutrient uptake, water relations, and soil carbon dynamics under deficit irrigation in field conditions

Plant strategies to cope with future droughts may be enhanced by associations between roots and soil microorganisms, including arbuscular mycorrhizal (AM) fungi. But how AM fungi affect crop growth and yield, together with plant physiology and soil carbon (C) dynamics, under water stress in actual field conditions is not well understood. The well-characterized mycorrhizal tomato (Solanum lycopersicum L.) genotype 76R (referred to as MYC+) and the mutant nonmycorrhizal tomato genotype rmc were grown in an organic farm with a deficit irrigation regime and control regime that replaced evapotranspiration. AM increased marketable tomato yields by ~25% in both irrigation regimes but did not affect shoot biomass. In both irrigation regimes, MYC+ plants had higher plant nitrogen (N) and phosphorus (P) concentrations (e.g. 5 and 24% higher N and P concentrations in leaves at fruit set, respectively), 8% higher stomatal conductance (gs), 7% higher photosynthetic rates (Pn), and greater fruit set. Stem water potential and leaf relative water content were similar in both genotypes within each irrigation regime. Three-fold higher rates of root sap exudation in detopped MYC+ plants suggest greater capacity for water uptake through osmotic driven flow, especially in the deficit irrigation regime in which root sap exudation in rmc was nearly absent. Soil with MYC+ plants also had slightly higher soil extractable organic C and microbial biomass C at anthesis but no changes in soil CO2 emissions, although the latter were 23% lower under deficit irrigation. This study provides novel, field-based evidence for how indigenous AM fungi increase crop yield and crop water use efficiency during a season-long deficit irrigation and thus play an important role in coping with increasingly limited water availability in the future.

Nodulation control of crack fertilization technique reduced the growth inhibition of soybean caused by short-term waterlogging at early vegetative stage

Waterlogging is the constraint for soybean growth and yield, because soybean is often cultivated in upland fields converted from paddy in Japan. However, efficient cultivation techniques for alleviating the adverse effects have not been developed. We have proposed the new soybean cultivation technique named crack fertilization which enables yield increase due to enhancing new root growth and N acquisition by increasing nodulation. Waterlogging induces N deficiency due to the suppression of nutrient uptake by the inhibition of root growth and nodule activity. Thus, it is hypothesized that crack fertilization would be effective to alleviate the inhibition of soybean growth and yield. The soybean cultivar of Sachiyutaka was planted in 1/5000 a Wagner pots and root boxes. Two separate waterlogging treatments were imposed to soybean plants at different growth stages, V1 and R4, and crack fertilization was done at V3. After these treatments, soybean plants were sampled at R5 in 2012 and 2013 experiments, respectively. Waterlogging at V1 and R4 inhibited the growth and yield of soybean and nodule growth, and the decreases in physiological parameters of soybean such as photosynthesis, chlorophyll content, and xylem sap exudation rate were observed. The adverse effects of waterlogging at V1 were alleviated by crack fertilization at V3, whereas crack fertilization could not alleviate the adverse effects of waterlogging at R4. Thus, crack fertilization after waterlogging at early vegetative stage would be the cultivation technique that enables to alleviate the adverse effects.

Transcript abundance, enzyme activity and metabolite concentration regulates differential carboxylate efflux in soybean under low phosphorus stress

Low phosphorus (P) availability in soil owing to adsorption, precipitation and conversion of organic forms drastically limits plant growth and yield. Among several strategies adopted by plants to cope with P starvation, research on root carboxylate exudation to release fixed P in soil is gaining impetus. Since the rate of exudation is a function of carboxylate synthesis and expression of efflux transporters, our objective was to analyse the expression and activity of genes influencing carboxylate exudation in soybean and the effect of P starvation on biomass and P acquisition efficiency. The relative expression levels and enzyme activity of phosphoenolpyruvate carboxylase, malate dehydrogenase and citrate synthase in soybean roots increased during low-P stress, particularly in genotypes exhibiting higher carboxylate efflux. With the exception of two genotypes (G-2656 and HIMSO-1521), the relative expression of efflux transporters for malate and citrate did not correspond to carboxylate exudation. Carboxylates in root apices were higher in NRC-7, HIMSO-1521 and EC-232019 under low-P as compared to sufficient P. P-efficient soybean genotypes (EC-232019 and HIMSO-1521) exhibiting higher carboxylate exudation showed better P acquisition and biomass under low-P stress. Down regulation of pyruvate kinase at the transcript- and enzyme-level was observed under low-P stress in P-efficient genotypes suggesting an effective glycolytic bypass mechanism to facilitate continued carbon flux from glycolytic pathway to the tricarboxylic acid cycle. Hence, transcript abundance, enzyme activity and internal carboxylate concentration in the root tissues govern carboxylate efflux in soybean, in turn, influencing biomass and P uptake.

The amino acid distribution in rachis xylem sap and phloem exudate of Vitis vinifera ‘Cabernet Sauvignon’ bunches

Amino acids are essential to grape berry and seed development and they are transferred to the reproductive structures through the phloem and xylem from various locations within the plant. The diurnal and seasonal dynamics of xylem and phloem amino acid composition in the leaf petiole and bunch rachis of field-grown Cabernet Sauvignon are described to better understand the critical periods for amino acid import into the berry. Xylem sap was extracted by the centrifugation of excised leaf petioles and rachises, while phloem exudate was collected by immersing these structures in an ethylenediaminetetraacetic acid (EDTA) buffer. Glutamine and glutamic acid were the predominant amino acids in the xylem sap of both grapevine rachises and petioles, while arginine and glycine were the principal amino acids of the phloem exudate. The amino acid concentrations within the xylem sap and phloem exudate derived from these structures were greatest during anthesis and fruit set, and a second peak occurred within the rachis phloem at the onset of ripening. The concentrations of the amino acids within the phloem and xylem sap of the rachis were highest just prior to or after midnight while the flow of sugar through the rachis phloem was greatest during the early afternoon. Sugar exudation rates from the rachis was greater than that of the petiole phloem between anthesis and berry maturity. In summary, amino acid and sugar delivery through the vasculature to grape berries fluctuates over the course of the day as well as through the season and is not necessarily related to levels near the source.

Root exudation of low-molecular-mass-organic acids by six tree species alters the dynamics of calcium and magnesium in soil

Soils in plantations of Cryptomeria japonica in Japan have ∼threefold more exchangeable Ca compared with soils in other types of forest vegetation even in a Ca-poor environment. To explain mechanisms underlying this phenomenon, we determined the effect of root exudation rate of low-molecular-mass organic acids (LMMOAs) on exchangeable cations in soil. We conducted a pot experiment using C. japonica and five dominant tree species in Japan, and measured the root exudation rates of LMMOAs and exchangeable nutrient concentrations in the soils. To estimate whether the root exudation rate of LMMOAs is elevated in response to Ca deficiency, we created variation in Ca availability by adding different amounts of crushed oyster shells. The root exudation rates of LMMOAs were two to five times higher for C. japonica than for other tree species, but did not differ significantly among the different quantities of oyster shell. Exchangeable Ca and Mg were significantly higher in the soils with C. japonica and significantly correlated with the root exudation rate of LMMOAs (R2 > 0.24) at high and moderate quantities of oyster shell. Therefore, variation among species, in terms of root exudation of organic acids, might be one important factor affecting the cation dynamics in soil.

Do warming-induced changes in quantity and stoichiometry of root exudation promote soil N transformations via stimulation of soil nitrifiers, denitrifiers and ammonifiers?

Despite the recognized importance of root exudation to soil biogeochemical processes and soil function in forest ecosystems, few studies have investigated the impact of quantity and stoichiometry of root exudation on soil nitrogen (N) transformations. In addition, the potential mechanism of how climate warming influences soil N cycling via root-soil interactions remains unclear. We performed an experiment in which in situ root exudates were collected from Picea asperata seedling to examine the response of root carbon (C) & N exudation rates and the C: N ratio stoichiometry along with the soil N transformation rates to warming using infrared heaters in the Eastern Tibetan Plateau. The results showed that warming enhanced root C exudation rates (ug C g−1 root biomass h−1), with higher C: N ratio stoichiometry simultaneously. Experimental warming also significantly increased the soil net mineralization rates, net nitrification rates, and denitrification rates. Then, we conducted an in vitro experiment in which three bacterial strains (Bacillus subtilis, Nitrobacter hamburgensis, and Brachymonas denitrificans) representing ammonifiers, nitrifiers, and denitrifiers, respectively, were cultured with exudates as the culture media. The results indicated that root exudates collected in warmed plots significantly stimulated the growth of the three soil N transformation bacteria, compared with the treatments in control plots. Collectively, our results, to some degree, evidence a linkage that climate warming-induced changes in C fluxes and C: N ratio stoichiometry of root exudation stimulated the growth and reproduction of soil N transformation bacteria, consequently accelerating the soil organic matter decomposition and soil N transformations.

Water for Carbon, Carbon for Water

Core Ideas Mucilage exuded by roots modifies the hydraulic properties of the rhizosphere. In turn, the rhizosphere hydraulic properties affect transpiration and photosynthesis. These water–carbon feedbacks in the rhizosphere help plant performance in dry soils. Plant roots exude approximately 10% of the carbon assimilated through photosynthesis into the soil, a process referred to as rhizodeposition. Here, we show that the mucilaginous fraction of the rhizodeposits, referred to as mucilage, plays a crucial role on soil–plant water relation and it has the potential to increase plant drought tolerance. Mucilage is a gel that can absorb large volumes of water, altering the physical properties of the rhizosphere and maintaining the rhizosphere wet and conductive when the soil dries. It is hypothesized that mucilage acts as a hydraulic bridge between roots and the soil, facilitating root water uptake and maintaining transpiration in dry soils. By employing a simplified model of root water uptake coupled with mucilage dynamics, we found that in a sandy soil the benefit of mucilage in maintaining root water uptake commenced to manifest when the soil matric potential dropped below approximately −0.8 MPa. This critical matric potential varied with transpiration rate, root length, and exudation rate. Below the critical potential, mucilage maintained photosynthesis and resulted in a net gain of carbon. In summary, rhizodeposition modifies the physical soil environment and has an impact on transpiration and photosynthesis. In other words: water for carbon, but also carbon for water.

The invasive annual cheatgrass releases more nitrogen than crested wheatgrass through root exudation and senescence.

Plant-soil feedbacks are an important aspect of invasive species success. One type of feedback is alteration of soil nutrient cycling. Cheatgrass invasion in the western USA is associated with increases in plant-available nitrogen (N), but the mechanism for this has not been elucidated. We labeled cheatgrass and crested wheatgrass, a common perennial grass in western rangelands, with (15)N-urea to determine if differences in root exudates and turnover could be a mechanism for increases in soil N. Mesocosms containing plants were either kept moist, or dried out during the final 10days to determine the role of senescence in root N release. Soil N transformation rates were determined using (15)N pool dilution. After 75 days of growth, cheatgrass accumulated 30% more total soil N and organic carbon than crested wheatgrass. Cheatgrass roots released twice as much N as crested wheatgrass roots (0.11 vs. 0.05mgN kg(-1) soil day(-1)) in both soil moisture treatments. This occurred despite lower root abundance (7.0 vs. 17.3g dry root kg(-1) soil) and N concentration (6.0 vs. 7.6gN kg(-1) root) in cheatgrass vs. crested wheatgrass. We propose that increases in soil N pool sizes and transformation rates under cheatgrass are caused by higher rates of root exudation or release of organic matter containing relatively large amounts of labile N. Our results provide the first evidence for the underlying mechanism by which the invasive annual cheatgrass increases N availability and establishes positive plant-soil feedbacks that promote its success in western rangelands.

The Effect of Root Exudate 7,4'-Dihydroxyflavone and Naringenin on Soil Bacterial Community Structure.

Our goal was to investigate how root exudate flavonoids influence the soil bacterial community structure and to identify members of the community that change their relative abundance in response to flavonoid exudation. Using a model system that approximates flavonoid exudation of Medicago sativa roots, we treated a soil with 7,4′-dihydroxyflavone and naringenin in two separate experiments using three different rates: medium (equivalent to the exudation rate of 7,4′-dihydroxyflavone from M. sativa seedlings), high (10× the medium rate), and low (0.1× the medium rate). Controls received no flavonoid. Soil samples were subjected to ATP assays and 16S rRNA gene amplicon sequencing. The flavonoid treatments caused no significant change in the soil ATP content. With the high 7,4′-dihydroxyflavone treatment rate, operational taxonomic units (OTUs) classified as Acidobacteria subdivision 4 increased in relative abundance compared with the control samples, whereas OTUs classified as Gaiellales, Nocardioidaceae, and Thermomonosporaceae were more prevalent in the control. The naringenin treatments did not cause significant changes in the soil bacterial community structure. Our results suggest that the root exudate flavonoid 7,4′-dihydroxyflavone can interact with a diverse range of soil bacteria and may have other functions in the rhizosphere in addition to nod gene induction in legume—rhizobia symbiosis.

Exploring rhizospheric interactions for agricultural sustainability: the need of integrative research on multi-trophic interactions

Large scale exploitation of rhizospheric interactions is essential for enhancing the agroecosystems resilience to climate change and also for adopting inventive adaptation strategies for maximizing the food production under such adverse conditions. Successful exploitation of rhizospheric interactions can be used for improving the soil fertility and organic carbon pool while minimizing the trace gases emission from agrosystems. Most importantly, such knowledge can be used to enhance the plant-microbe interactions, conferring diseases resistance to host plants, bioremediation and restoration of marginal and degraded lands. However, recent studies proved that changing climatic conditions can alter the rhizosphere biology by modifying the root exudation rate, resource availability and biogeochemical cycling. Therefore, strategic and applied researches are essential to explore the rhizosphere biology under changing climatic conditions and harnessing all beneficial interactions as a low-input biotechnology for sustainable agriculture, ecosystem restoration and environmental sustainability.

Plant water relations and canopy temperature depression for assessing water stress tolerance of potato

An experiment was conducted with five potato genotypes at Bangabandhu Sheikh Mujibur Rahman Agricultural University, Gazipur during 2010–2011 under control and water stress conditions to determine the effect of water stress on plant water relations and canopy temperature depression of potato. Of the five genotypes, CIP 393371.58 and CIP 396244.12 maintained higher relative water content (RWC) under both the conditions and showed comparatively less midday depression in RWC. The water stress condition significantly decreased water uptake capacity. Under water stress condition tolerant genotypes CIP 393371.58 and CIP 396244.12 showed highest xylem exudation rate of 0.26 and 0.18 g h−1, respectively and transpiration rate of 36 and 34 µg m−2 s−1, respectively at 50 days after planting, and both were positively and significantly correlated. Greater increases in canopy temperature were observed at noon in Asterix and CIP 391004.18 and lower in CIP 393371.58 and CIP 396244.12 and showed inverse relationship with transpiration rate. The genotypes CIP 393371.58 and CIP 396244.12 showed higher canopy temperature depression value and the genotypes CIP 391004.18 and Asterix showed lower canopy temperature depression value under water stress condition. Among the genotypes, CIP 393371.58 and CIP 396244.12 showed better tolerance to water stress condition.