Root Sap Research Articles

Antitussive effects of Musanga cecropioides in animal models

This study investigates the antitussive effects of Musanga cecropioides, a traditional medicinal plant, using animal models. Musanga cecropioides extracts were prepared from the leaves, roots, and root sap, and their effects were evaluated on mucus expectoration and citric acid-induced cough in mice and guinea pigs, respectively. The results indicated that aqueous and methanol extracts of Musanga cecropioides leaves and roots significantly increased mucus secretion and reduced cough frequency, with the highest effectiveness observed in methanol root extract at 100 mg/kg. These findings suggest that Musanga cecropioides possesses promising antitussive properties, supporting its traditional use in treating cough and respiratory ailments. This natural remedy could offer a safer alternative to conventional cough suppressants, warranting further clinical studies to confirm its efficacy and safety in humans.

Unique root hydraulic and mechanical properties support the resilience of grapevines adapted to the Atacama Desert.

Cortical lacunae caused by drought, especially observed in hybrids originating from Vitis rupestris, disrupt the connection between roots and soil. Yet, the physiological processes behind lacuna formation during drought and its consistency across Vitis species remain unclear. Here, we used a root pressure probe to investigate fine root hydraulic and mechanical properties, in the arid-adapted R-65 and drought-susceptible 101-14Mgt cultivars. We then performed P-V curves, root sap osmolality, and electrolyte leakage (EL) and used fluorescent light microscopy techniques. Only 101-14Mgt showed lacunae formation during drought due to its stiffer cortical tissue, unlike R-65. Lacunae resulted in a notable decline in root hydraulic conductivity during severe drought, with increased EL and root sap osmolality, indicating potential cellular damage. R-65 displayed different and xerophyte-like characteristics featuring a higher turgor loss point and decreased root capacitance, essential for maintaining root structural integrity in arid conditions. Our findings highlight lacuna formation is impacted by root tissue elasticity possibly linked to specific Vitis species favoring deeper rooting. In arid-adapted grapevines, hydraulic regulators such as reduced turgor loss point, and root capacitance could contribute to enhanced drought tolerance.

Biosafety assessment and In vitro antioxidant activity of Musanga cecropioides root sap

The present study evaluated the biosafety and in vitro antioxidant activity of Musanga cecropioides root sap, a traditional remedy known for its health benefits. The sap was found to be rich in bioactive compounds, including alkaloids, tannins, saponins, flavonoids, and phenols, confirming existing literature. Proximate analysis revealed high moisture, fat, and protein content, alongside significant levels of essential vitamins and amino acids, indicating potential nutritional and therapeutic benefits. Acute toxicity assessments in mice demonstrated safety at doses up to 100 ml/kg, while the sub-acute toxicity assessment using rats showed no significant changes in haematological parameters or liver and kidney function markers. Histological examinations showed minor, non-significant alterations in liver and lung tissues. Antioxidant assays (DPPH and ABTS) revealed considerable radical scavenging activities, attributed to the presence of known antioxidant compounds. These findings support the traditional use of Musanga cecropioides root sap, highlighting its potential as a natural therapeutic agent. Further research is recommended to explore its mechanisms and clinical efficacy, paving the way for its development into a standardized natural remedy.

Evaporation-driven internal hydraulic redistribution alleviates root drought stress: Mechanisms and modeling.

Many tree species have developed extensive root systems that allow them to survive in arid environments by obtaining water from a large soil volume. These root systems can transport and redistribute soil water during drought by hydraulic redistribution (HR). A recent study revealed the phenomenon of evaporation-driven hydraulic redistribution (EDHR), which is driven by evaporative demand (transpiration). In this study, we confirmed the occurrence of EDHR in Chinese white poplar (Populus tomentosa) through root sap flow measurements. We utilized microcomputed tomography technology to reconstruct the xylem network of woody lateral roots and proposed conceptual models to verify EDHR from a physical perspective. Our results indicated that EDHR is driven by the internal water potential gradient within the plant xylem network, which requires 3 conditions: high evaporative demand, soil water potential gradient, and special xylem structure of the root junction. The simulations demonstrated that during periods of extreme drought, EDHR could replenish water to dry roots and improve root water potential up to 38.9% to 41.6%. This highlights the crucial eco-physiological importance of EDHR in drought tolerance. Our proposed models provide insights into the complex structure of root junctions and their impact on water movement, thus enhancing our understanding of the relationship between xylem structure and plant hydraulics.

Integrated Management Practices for Canopy-Topsoil Improves the Grain Yield of Maize with High Planting Density.

Inappropriate spatial distribution of canopy and roots limits further improvements to the grain yield of maize with increased planting density. We explored an integrated management practice called strip deep rotary with staggered planting (SRS) which includes comprehensive technology for both canopy layers and topsoil. Here, field experiments were conducted under two maize cropping systems (spring maize and summer maize) to evaluate the effect of SRS on the spatial distribution of the canopy and roots for maize under high planting density (90,000 plants ha-1) and to determine the physiological factors involved in yield formation. Compared with conventional management practices (no-tillage with single planting, NTS), SRS decreased the LAI of the middle to top layers while improving the light distribution of the middle and lower layers by 72.99% and 84.78%, respectively. Meanwhile, SRS increased the root dry weight density and root sap bleeding by 51.26% and 21.77%, respectively, due to the reduction in soil bulk density by an average of 5.08% in the 0-40 cm soil layer. SRS improved the SPAD in the ear and lower leaves and maximized the LAD, which was conducive to dry matter accumulation (DMA), increasing it by 14.02-24.16% compared to that of NTS. As a result, SRS increased maize grain yield by 6.71-25.44%. These results suggest that strip deep rotary combined with staggered planting noticeably optimized the distribution of light in the canopy and reduced the soil bulk density to promote root vitality and growth, to maintain canopy longevity, and to promote the accumulation of dry matter, which eventually increased the grain yield of the maize under high planting density conditions. Therefore, SRS can be considered a better choice for the sustainable high yield of maize under high-density planting conditions in the NCP and similar areas throughout the world.

Suitable fertilization depth can improve the water productivity and maize yield by regulating development of the root system

An undeveloped root system generally leads to low water utilization efficiency and decreases the yield in spring maize (Zea mays L.). Little is known about whether changing the fertilization depth can optimize the root distribution to improve the water productivity and maize yield. During 2019 and 2020, we conducted a field experiment with spring maize and applied the fertilizer at different soil depths of 0.05 m (D5), 0.15 m (D15), 0.25 m (D25), and 0.35 m (D35) to clarify the regulatory effects of the fertilization depth on the root distribution, water productivity at the biomass level (WPb), and maize yield formation. Compared with D5, D25 significantly increased the root length density of the vertical roots, inter-row roots, and within-row roots in the 0–1.0 m soil depth by 18%, 14%, and 24%, respectively, and the root surface area density increased by 39%, 17%, and 22%. Compared with D5, D25 significantly increased the soil water consumption by 28 mm during the maize jointing to silking stage and reduced the soil water content in the 0.4–1.4 m soil depth at the maize silking stage. D25 and D15 also significantly increased the root sap production rate and NO3–-N and NH4+-N concentrations in the root sap compared with D5 and D35 after the maize silking stage. The N uptake and nitrogen use efficiency under D25 were 17% and 39% higher, respectively, compared with D5. The water productivity at the grain yield and biomass level, biomass, and maize yield values under D25 were 23.5 kg ha–1 mm–1, 45.7 kg ha–1 mm–1, 24320 kg ha–1, and 12477 kg ha–1, respectively, which were 10%, 12%, 13%, and 14% higher compared with D5. The different fertilization depths explained 91%, 86%, and 66% of the variations in the maize yield, N uptake, and total evapotranspiration, respectively. Therefore, deep fertilization at a suitable soil depth regulated the distribution of the root system, which improved the capability of soil water and nitrogen utilization, and eventually increased the water productivity and maize yield. The most effective fertilizer depth was 0.25 m and it can be used as an effective water and fertilizer management strategy for the sustainable development of maize.

Diagnóstico nutricional de banana (Musa AAA Simmonds subgrupo Cavendish) com análise de seiva da raiz

ABSTRACT The status of mineral nutrients in the banana crop is commonly determined by foliar and soil analyses, which often do not present a significant relation with its production performance. This study aimed to evaluate whether the root sap analysis determines the nutritional status of plants more accurately in response to fertilization. The experiment was carried out in a completely randomized design, with three treatments (complete fertilization, traditional fertilization and no fertilization), three replicates and four plants per replicate. The contents of macro (N, P, K, Ca and Mg) and micronutrients (B, Zn, Mn, Fe and Cu) were analyzed in the root sap, leaves and soil at the base of the plant. Potassium was the macronutrient found in the highest quantity in the root sap of the fertilized and unfertilized plants, while the predominant micronutrients were Mn in the fertilized plants and Fe in the unfertilized ones. The concentrations of N, P, K, Ca and Mg in the root sap were significantly lower for no fertilization than for complete and traditional fertilization, but did not show significant diferences between the foliar and soil analyses. The root sap analysis was more sensitive than leaf analysis to diagnose the nutritional status of the banana plants.

Genome-wide miRNAs profiles of pearl millet under contrasting high vapor pressure deficit reveal their functional roles in drought stress adaptations.

Pearl millet (Pennisetum glaucum [L.] R. Br.) is an important crop capable of growing in harsh and marginal environments, with the highest degree of tolerance to drought and heat stresses among cereals. Diverse germplasm of pearl millet shows a significant phenotypic variation in response to abiotic stresses, making it a unique model to study the mechanisms responsible for stress mitigation. The present study focuses on identifying the physiological response of two pearl millet high-resolution cross (HRC) genotypes, ICMR 1122 and ICMR 1152, in response to low and high vapor pressure deficit (VPD). Under high VPD conditions, ICMR 1152 exhibited a lower transpiration rate (Tr), higher transpiration efficiency, and lower root sap exudation than ICMR 1122. Further, Pg-miRNAs expressed in the contrasting genotypes under low and high VPD conditions were identified by deep sequencing analysis. A total of 116 known and 61 novel Pg-miRNAs were identified from ICMR 1152, while 26 known and six novel Pg-miRNAs were identified from ICMR 1122 genotypes, respectively. While Pg-miR165, 168, 170, and 319 families exhibited significant differential expression under low and high VPD conditions in both genotypes, ICMR 1152 showed abundant expression of Pg-miR167, Pg-miR172, Pg-miR396 Pg-miR399, Pg-miR862, Pg-miR868, Pg-miR950, Pg-miR5054, and Pg-miR7527 indicating their direct and indirect role in root physiology and abiotic stress responses. Drought responsive Pg-miRNA targets showed upregulation in response to high VPD stress, further narrowing down the miRNAs involved in regulation of drought tolerance in pearl millet.

An undiscovered facet of hydraulic redistribution driven by evaporation-a study from a Populus tomentosa plantation.

Maintaining the activity and function of the shallow root system of plants is essential for withstanding drought stress, but the associated mechanism is poorly understood. By investigating sap flow in 14 lateral roots (LRs) randomly selected from trees of a Chinese white poplar (Populus tomentosa) plantation receiving three levels of irrigation, an unknown root water transport mode of simultaneous daytime bi-directional water flow was discovered. This mode existed in five LRs confined to the surface soil without attached sinker roots. In the longer term, the bi-directional water flow was correlated with the soil water content. However, within the day, it was associated with transpiration. Our data demonstrated that bi-directional root sap flow occurred during the day, and was driven by evaporative demand, further suggesting the existence of circumferential water movement in the LR xylem. We named this phenomenon evaporation-driven hydraulic redistribution (EDHR). A soil-root water transport model was proposed to encapsulate this water movement mode. EDHR may be a crucial drought-tolerance mechanism that allows plants to maintain shallow root survival and activity by promoting root water recharge under extremely dry conditions.

Root sap flow as a tool to establish hydrological thresholds for plant growth and survival

Water saving technologies are important for sustainable agriculture and forestry. Recent research indicates that the plant itself may alternate between several natural water sources to survive drought. Therefore, a key issue is how to establish the boundaries of hydrological conditions important for non-stressed tree growth. The smart decision might be to ask the plant itself. Sap flow represents a suitable language to such a talk: it gives long-term automatic records of plant responses to environmental changes. In this work we illustrate how root sap flow can be used to provide information on the thresholds for two sources of tree root water uptake, superficial soil water and groundwater. With this knowledge, a threshold diagram can be constructed which is species and site specific. Such a diagram may help managers of rain fed plantations to follow the current hydrological conditions and apply irrigation as a preventive treatment to avoid growth loss and tree mortality.

Coordination of stomatal control and stem water storage on plant water use in desert riparian trees

Populus euphratica Oliv. is a relatively ‘conservative’ water user even when growing in favourable water conditions, but the mechanistic understanding of this has received little attention. We undertook an experiment to determine trees water use by measuring stem and root sap flow (Fs), variation in stem diameter (Ds), leaf stomatal gas-exchange (e.g. conductance, gs and transpiration, Tr) and water potential $$\left( {{\psi _{\text{L}}}} \right)$$ during the growing season for P. euphratica. There was a hysteretic ‘apparent feedforward’ of stomatal response to increasing VPD. Mean of gs was not significantly different among months. $${\psi _{\text{L}}}$$ was negatively related to gs and Tr, but in contrast, stem Fs was positively associated to Tr but not to gs. There was no lag in the daily onset and cessation of Fs between the bottom and top of the trunk, possibly due to the short distance between measurement points (about 2 m), however, the lag time in Fs between the bottom of the trunk and roots, approximately 30 min, suggested that stored water was withdrawn first from the trunk and subsequently the roots. Daily contraction of Ds (− Ds) increased with increasing Fs during both day and night, and expansion of Ds (+ Ds) showed a logarithmic rise to a maximum with increasing Fs during the day. Day Fs and − Ds were also logarithmic with respect to VPD, with a correlation coefficient equal to 0.51 and 0.50, respectively (P < 0.001). This suggests that water use of P. euphratica was determined by the stomatal control and stem water storage together, which has great significance for the species buffers xylem water deficit, maintaining high leaf production, and water use efficiency.

Barley CMS detected in Finland in 1976 enabled growing of productive winter-barley F1 hybrids in the European winter-barley zone since 2002

My wide crossing program of barley (Hordeum vulgare s.l.) in 1976 yielded a system which could be used to produce F1 hybrid seeds. The genotypes were designated as msm1 (male sterile, maternal), and Rfm1a (restorer of fertility in msm1). I later found 19 other strains with dominant restorer alleles, which were carriers of a fertile cytoplasm. Hence, the restorer genes probably evolved in advance creating an opportunity for the cytoplasm to mutate to male sterility. Cytological studies revealed an uncontrolled secretion of sporopollenin in the sterile anthers, leading to their starvation and sterility. The Rfm1a gene was shown to cause an increase in the cytokinin activity of Fraction 7 in the root sap of barley, regardless of the cytoplasm type. In 1980, I found another male sterile cytoplasm, msm2, whose anther can also be restored by the Rfm1 alleles. The msm2 strain originally had complementary partial restorer genes and was found to be more responsive to such restorers than msm1. In Germany, the Rfm1 gene was recently translocated to a rye (Secale cereale) chromosome to study its response in CMS rye. The msm2 cytoplasm could be distinguished from msm1 with electron microscopy at the early stages of the anthers. The msm1 cytoplasm is not known to be associated with increased disease susceptibility, unlike the T-sterile cytoplasm formerly used to produce hybrid seeds of maize (Zea mays). Hybrid cvs: Seeds of msm1–Rfm1a were first requested from me by Hilleshög AB in Sweden. Hilleshög later became a part of Syngenta. Hilleshög techniques for sugar-beet hybrids were applied by Syngenta breeders to produce hybrid barley seeds. Syngenta introduced the first commercial winter-barley hybrid in the UK in 2002. Their hybrid cvs were marketed to countries growing winter-barley in Europe. The ha yields of their hybrids exceeded those of conventional cultivars or parental lines by about 1000 kg. In Spain, the winter-barley hybrid yielded 21 percent more than the conventional cultivars in 2015, when grown in the field scale. For the 2016 harvest, hybrids were sown in Germany on more than 140000 ha, which reflects 11.6 percent of the total feed barley area. In 2017, Syngenta launched a cashback scheme for, if their hybrid cultivars did not comfortably out-yield the farmer's conventional counterpart that season. Hybrid seeds must be acquired for each sowing. Unlike conventional monogenic barley cultivars, the hybrids exploit genetic variability and heterozygosity. Hybrid winter-barley is the most competitive of winter cereals with the aggressive weed Alopecurus myosuroides in the UK. Thick stems in new hybrids increase lodging resistance. The winter-barley hybrid ‘Wootan’ gave ha yields up to 6000 kg in Tammisaari, though incompletely winter-hardy in Finland. Maturing a month later than the hybrid ‘Hobbit’ and with optimal winterhardiness, winter-barley hybrids could exceed ha yields of 10000 kg in Finland. Some other breeding companies seem to work for hybrid barley, too.

Depressed hydraulic redistribution of roots more by stem refilling than by nocturnal transpiration for Populus euphratica Oliv. in situ measurement.

During the night, plant water loss can occur either through the roots, as hydraulic redistribution (HR), or through the leaves via the stoma, as nocturnal transpiration (E n), which was methodologically difficult to separate from stem refilling (R e). While HR and E n have been reported across a range of species, ecosystem, and climate zone, there is little understanding on the interactions between E n and/or R e and HR. As water movement at night occurs via gradients of water potential, it is expected that during periods of high atmospheric vapor pressure deficit (VPD), water loss via E n will override water loss via HR. To test this hypothesis, sap flow in stems and roots of Populus euphratica Oliv. trees, growing in a riparian zone in a hyperarid climate, was measured once in a year. Nocturnal stem sap flow was separated into E n and R e using the “forecasted refilling” method. Substantial nocturnal sap flow (38% of 24‐hr flux on average) was observed and positively correlated with VPD; however, the strength of the correlation was lower (R 2 = .55) than diurnal sap flow (E d) (R 2 = .72), suggesting that nocturnal stem sap flow was attributed to both water loss through the canopy and replenishment of water in stem tissues. Partitioning of nocturnal sap flow shows that R e constituted approximately 80%, and E n ~20%, of nocturnal sap flow. The amount of root sap flow attributed to redistribution was negatively related to E d (R 2 = .69) and the amount of acropetally sap flow in stems, R e (R 2 = .41) and E n (R 2 = .14). It was suggested that the magnitude of HR is more strongly depressed by R e that was recharge to the water loss via E d than by E n. It was consistent with whole‐tree water balance theory, that the nighttime upward sap flow to xylem, stem refilling and transpiration, may depress hydraulic redistribution of roots.

Impact of osmoregulation on the differences in Cd accumulation between two contrasting edible amaranth cultivars grown on Cd-polluted saline soils

This study aimed to investigate the difference of osmoregulation between two edible amaranth cultivars, Liuye (high Cd accumulator) and Quanhong (low Cd accumulator), under salinity stress and determine the effects of such difference on Cd accumulation. A pot experiment was conducted to expose the plants to sewage-irrigated garden soil (mean 2.28 mg kg−1 Cd) pretreated at three salinity levels. Under salinity stress, the concentrations of Cd in the two cultivars were significantly elevated compared with those in the controls, and the Cd concentration in Liuye was statistically higher than that in Quanhong (p < 0.05). Salinity-induced osmoregulation triggered different biogeochemical processes involved in Cd mobilization in the rhizosphere soil, Cd absorption, and translocation by the two cultivars. Rhizosphere acidification induced by an imbalance of cation over anion uptake was more serious in Liuye than in Quanhong, which obviously increased soil Cd bioavailability. Salinity-induced injuries in the cell wall pectin and membrane structure were worse in Liuye than in Quanhong, increasing the risk of Cd entering the protoplasts. The chelation of more cytoplasmic Cd2+ with Cl− ions in the roots of Liuye promoted Cd translocation into the shoots. Furthermore, the less organic solutes in the root sap of Liuye than in that of Quanhong also favored Cd translocation into the shoots. Hence, osmoregulation processes can be regarded as important factors in reducing Cd accumulation in crop cultivars grown on saline soils.

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.

Disruption of reproductive behavior of grapevine cicada, Cicadatra alhageos, by acoustic signals playback

AbstractThe grapevine cicada, Cicadatra alhageos (Kolenati) (Hemiptera: Cicadidae), is a key pest of grapevine (Vitis spp., Vitaceae) in the Middle East. The main damage is caused by nymphs that feed on root sap, and adults that oviposit on branches. As males produce sound to attract females, one of the control methods can be disruption of sexual communication. Disruptive effects of acoustic playbacks on singing males were studied. Signals (0.5–10 kHz) were broadcast to disrupt male calling behavior. Playback of acoustic signals interrupted male sexual signalling. To reduce female oviposition behavior in the field, an experiment was conducted based on a completely randomized design with two treatments (control vs. acoustic broadcasting) and four replications over a period of 3 years. Playback of disruption signals in the field reduced female oviposition on grapevine branches that were close to the signal source. Therefore, application of acoustic stimuli may be an effective and low‐cost control method against grapevine cicada.

Root aquaporins contribute to whole plant water fluxes under drought stress in rice (Oryza sativa L.).

Aquaporin activity and root anatomy may affect root hydraulic properties under drought stress. To better understand the function of aquaporins in rice root water fluxes under drought, we studied the root hydraulic conductivity (Lpr) and root sap exudation rate (Sr) in the presence or absence of an aquaporin inhibitor (azide) under well-watered conditions and following drought stress in six diverse rice varieties. Varieties varied in Lpr and Sr under both conditions. The contribution of aquaporins to Lpr was generally high (up to 79% under well-watered conditions and 85% under drought stress) and differentially regulated under drought. Aquaporin contribution to Sr increased in most varieties after drought, suggesting a crucial role for aquaporins in osmotic water fluxes during drought and recovery. Furthermore, root plasma membrane aquaporin (PIP) expression and root anatomical properties were correlated with hydraulic traits. Three chromosome regions highly correlated with hydraulic traits of the OryzaSNP panel were identified, but did not co-locate with known aquaporins. These results therefore highlight the importance of aquaporins in the rice root radial water pathway, but emphasize the complex range of additional mechanisms related to root water fluxes and drought response.

Very low dose gamma irradiation stimulates gaseous exchange and carboxylation efficiency, but inhibits vascular sap flow in groundnut (Arachis hypogaea L.)

Purpose: An experiment was carried out to determine the effect of low dose gamma radiation on germination, plant growth, nitrogen and carbon fixation and carbon flow and release characteristics of groundnut.Materials and methods: Dry seeds of groundnut variety Trombay groundnut 37A (TG 37A), a radio mutant type developed by Bhabha Atomic Research Centre (BARC), Mumbai, India, were subjected to the pre-sowing treatment of gamma radiation within low to high dose physiological range, i.e., 0.0, 0.0082, 0.0164. 0.0328, 0.0656, 0.1312, 5, 25, 100, 500 Gray (Gy) from a cobalt source (60Co). Observations were recorded for the radiation effect on percentage germination, vigour, gas exchange attributes such as photosynthetic rate, stomatal conductance and transpiration rate, chlorophyll content, root exudation in terms of 14C release, vascular sap flow rate and activities of rate defining carbon and nitrogen assimilating enzymes such as ribulose-1,5-bisphosphate carboxylase (rubisco) and nitrate reductase (NR).Results: Seed germination was increased by 10–25% at the lower doses up to 5 Gy while the improvement in plant vigour in the same dose range was much higher (22–84%) than the unirradiated control. For radiation exposure above 5 Gy, a dose-dependent decline in germination and plant vigour was measured. No significant effect was observed on the photosynthesis at radiation exposure below 5 Gy but above 5 Gy dose there was a decline in the photosynthetic rate. Stomatal conductance and transpiration rate, however, were only inhibited at a high dose of 500 Gy. Leaf rubisco activity and NR activities remained unaffected at all the investigated doses of gamma irradiation. Mean root exudation and sap flow rate of the irradiated plants, irrespective of the dose, was reduced over the unirradiated control more so in a dose-dependent manner.Conclusions: Results indicated that a very low dose of gamma radiation, in centigray to gray range, did not pose any threat and in fact stimulated metabolic functions in such a way to aid growth and development of groundnut plants. It further showed that the radiation threshold for the gas exchange traits and rubisco activity, which ultimately determine the plant health and yield, were higher than compared to the other metabolic attributes and were well beyond 500 Gy and that the dose range above 500 Gy should be targeted to measure lethal effects of radiation on carbon assimilation attributes in leguminous crops, in general, and groundnut in particular.

Transpiration inQuercus subertrees under shallow water table conditions: the role of soil and groundwater

Water is one of the major environmental factors limiting plant growth and survival in the Mediterranean region. Quercus suber L. woodlands occupy vast areas in the Iberian Peninsula, frequently under shallow water table conditions. The relative magnitude of soil and groundwater uptake to supply transpiration is not easy to evaluate under these circumstances. We recently developed a conceptual framework for the functioning of the root system in Q. suber that simulates well tree transpiration, based on two types of root behaviour: shallow connected and deep connected. Although this significantly improved knowledge on the functional traits of Mediterranean Q. suber, the approach has the limitation of requiring root sap flow data, which are seldom available. In this work, we present alternative methodologies to assess if trees are connected to groundwater and to estimate the soil and groundwater contributions to tree transpiration. We provide evidence on the tree unrestricted access to groundwater solely based on meteorological, stem sap flow and leaf water potential data. Using a soil mass balance approach, we estimated the yearly soil and groundwater contributions to tree transpiration: 69.7% and 30.3%, respectively. Groundwater uptake became dominant in the dry summer: 73.2% of tree transpiration. Results reproduce extremely well those derived from root modelling. Because of its simplicity both in formulation and data requirements, our approach is potentially liable to be adapted to other groundwater-dependent Mediterranean oak sites, where interactions between land use and water resources may be relevant. Copyright © 2013 John Wiley & Sons, Ltd.

Root functioning, tree water use and hydraulic redistribution in Quercus suber trees: A modeling approach based on root sap flow

Mediterranean evergreen oaks have to survive a long summer drought. Roots may play a relevant role under these conditions. We studied their structure and function in a mature Quercus suber L. tree in central Portugal. The root system was mapped till the lowest water table level (4.5m depth). Xylem anatomy was analyzed in a vertical profile belowground. Sap flow was continuously monitored for 1.5yrs in the stem and roots of this intensively studied tree (heat field deformation method) and in the stem of four trees (Granier method), in relation to environmental variables and predawn leaf water potential. The sources of water uptake were assessed by stable isotope analyses in summer. Results showed a dimorphic root system with a network of superficial roots linked to sinker roots, and a taproot diverting into tangles of deep fine roots submerged for long periods, with parenchyma aerenchyma. Transpiration was not restricted in summer due to root access to groundwater. The isotopic δ18O signature of twig xylem water was similar to that of groundwater in the dry season. Two functional types of superficial roots were identified: shallow connected and deep connected roots. A modeling approach was built considering that each superficial root was linked to a sinker, with part of the root deep connected (between the stem and the sinker) and part shallow connected (between the sinker and topsoil). This conceptual framework simulated tree stem sap flow from root sap flow with a high efficiency (R2=0.85) in four plot trees.On an annual basis, soil water and groundwater contributions were 69.5% and 30.5% of stem flow, respectively. Annual hydraulic lift and hydraulic descent were 0.9% and 37.0% of stem flow, respectively. The trees maximize the exploitation of the environmental resources by using the topsoil water during most of the year, and groundwater together with hydraulic lift (nutrient supply) in the dry summer. This study shows that a dimorphic root system, with roots reaching groundwater, is an efficient strategy of Q. suber trees to cope with seasonal drought. Knowledge of the functional behavior of Q. suber trees under shallow water table conditions may contribute to the definition of better adapted management practices and to anticipate their responses to climate change.