Root Hydraulic Conductivity of Two Cactus Species in Relation to Root Age, Temperature, and Soil Water Status

The effects of root age, temperature, and soil water statuson root hydraulic conductivity (L_P) were investigated for twocactus species, Ferocactus acanthodes and Opuntia ficus-indica.The volumetric flux density of water was measured for excisedroot segments, either using negative hydrostatic pressures appliedto the proximal end or using reverse flow of water from theroot to the soil. For both species, L_P at 20 ?C increased withroot age, average values reaching a maximum of 3.9 ? 10^–7m s^–1 MPa^–1 for F. acanthodes and 5.2 ? 10^–7m s^–1 MPa^–1 for O.ficus-indica at 11 to 17 weeksof age; L_P subsequently declined with increasing root age forboth species. L_P was maximal at a temperature of about 10 ?Cfor the youngest roots (1–3 weeks), this optimum shiftingto 40 ?C for 8-week-old roots of both species. For older roots(up to 1.5-years-old), L_P increased with temperature from 0?C to 50 ?C, with a Q₁₀ of 1.3 between 20 ?C and 30 ?C. At asoil water potential (_soil) of –0.016 MPa, root L_P wasindependent of the direction of water flow for both species.Depending on root age, L_P declined 45- to 500-fold for F. acanthodesand 90- to 800-fold for O.ficus-indica as _soil was reduced from–0.016 to –1.06 MPa, consistent with a rectifier-likebehaviour with respect to water movement between soil and roots.Incorporation of such responses into water uptake models shouldlead to a better understanding of root function. Key words: Ferocactus acanthodes, Opuntia ficus-indica, water potential, tension, reverse flow     

Hydraulic Conductivity and Anatomy for Lateral Roots of Agave deserti During Root Growth and Drought-induced Abscission

Hydraulic conductivity (L_p), radial conductivity (L_R), axialconductance (K_h), and related anatomical characteristics forlateral roots of Agave deserti were investigated during rootgrowth and drought-induced abscission. The elongation rate oflateral roots averaged 5 mm d^–1 under wet conditions andwas reduced 95% by 17 d of drought (     

根径向水流导度测定技术的改进

根系径向流的水力学性质主要是根的径向水流导度,它取决于径向水流通道的状况。利用改进的现有原位的测定根系径向水流导度的蒸腾计技术,设计了一个简便的４室吸水测定装置,可一次性获得根本质部水势和根径向水流导度,缩短测定时间１０ｍｉｎ,确保测定精度。然后用改进的装置测定了生长在不同水分条件下冬小麦（Ｔｒｉｔｉｃｕｍ ａｅｓｔｉｖｕｍＬ．）根系的径向水流导度,结果显示根系的平均径向水流导度为４．６３＊１０＾     

植物根系水分导度及影响因素

根系水分导度（Lpr）是表示根系吸收和运输水分能力的生理指标,文章介绍Lpr的研究进展。     

Changes in Root Hydraulic Conductivity During Wheat Evolution

A better understanding of the mechanisms of water uptake by plant roots should be vital for improving drought resistance and water use efficiency (WUE). In the present study, we have demonstrated correlations between root system hydraulic conductivity and root characteristics during evolution using six wheat evolution genotypes (solution culture) with different ploidy chromosome sets (Triticum boeoticum Bioss., T. monococcum L.: 2n=2x=14;T. dicoccides Koern., T. dicoccon (Schrank) Schuebl.:2n=4x=28;T. vulgare Vill., T. aestivum L. cv. Xiaoyan No. 6:2n=6x=42). The experimental results showed that significant correlations were found between root system hydraulic conductivity and root characteristics of the materials with the increase in ploidy chromosomes (2x→6x) during wheat evolution. Hydraulic conductivity of the wheat root system at the whole-plant level was increased with chromosome ploidy during evolution, which was positively correlated with hydraulic conductivity of single roots, whole plant biomass,root average diameter, and root growth (length, area), whereas the root/shoot ratio had an inverse correlation with the hydraulic conductivity of root system with increasing chromosome ploidy during wheat evolution. Therefore, it is concluded that that the water uptake ability of wheat roots was strengthened from wild to modern cultivated species during evolution, which will provide scientific evidence for genetic breeding to improve the WUE of wheat by genetic engineering.     

Changes in Root Hydraulic Conductivity During Wheat Evolution

A better understanding of the mechanisms of water uptake by plant roots should be vital for improving drought resistance and water use efficiency (WUE). In the present study, we have demonstrated correlations between root system hydraulic conductivity and root characteristics during evolution using six wheat evolution genotypes (solution culture) with different ploidy chromosome sets (Triticum boeoticum Bioss., T. monococcum L.: 2n = 2x = 14; T. dicoccides Koern., T. dicoccon (Schrank) Schuebl.: 2n = 4x = 28;T. vulgare Vill., T. aestivum L. cv. Xiaoyan No. 6: 2n = 6x = 42). The experimental results showed that significant correlations were found between root system hydraulic conductivity and root characteristics of the materials with the increase in ploidy chromosomes (2x→6x) during wheat evolution. Hydraulic conductivity of the wheat root system at the whole-plant level was increased with chromosome ploidy during evolution, which was positively correlated with hydraulic conductivity of single roots, whole plant biomass,root average diameter, and root growth (length, area), whereas the root/shoot ratio had an inverse correlation with the hydraulic conductivity of root system with increasing chromosome ploidy during wheat evolution. Therefore, it is concluded that that the water uptake ability of wheat roots was strengthened from wild to modern cultivated species during evolution, which will provide scientific evidence for genetic breeding to improve the WUE of wheat by genetic engineering.     

Influences of Water Status, Temperature, and Root Age on Daily Patterns of Root Respiration for Two Cactus Species

Daily patterns of root respiration measured as CO₂, efflux werestudied at various soil water potentials, temperatures, androot ages for individual, attached roots of the barrel cactusFerocactus acanthodes and the platyopuntia Opuntia ficus-indica.The daily patterns of root respiration for both establishedroots and rain roots followed the daily patterns of root temperature.Root respiration increased when root temperature was raisedfrom 5 °C to 50 °C for F. acanthodes and from 5 °Cto 55 °C for O. ficus-indica; at 60 °C root respirationdecreased 50° from the maximum for F. acanthodes and decreased25° for O. ficus-indica. Root respiration per unit d. wtdecreased with root age for both species, especially for rainroots. Root respiration rates for rain roots were reduced tozero at a soil water potential (     

氮磷亏缺对玉米根系水流导度的影响

在人工气候室水培条件下,从单根和整株根系两个层次研究了N、P营养与玉米(Zea mays L.)根系水流导度(root hydraulic conductivity,Lpr)间的关系。结果表明：表型抗旱的杂交种F1代户单4号和母本天四的单根水导和整株根系水导均高于不抗旱的父本478,其中天四的单根水导最高,而户单4号的整株根系水导最高。N、P亏缺均使玉米单根水导和整株根系水导降低,但与N亏块相比,P亏缺的植株具有较高的整株根系水导和较低的单根水导。整株根系的水导更能反映植物根系的输水性能。     

Cyanide-Resistant Root Respiration and Tap Root Formation in Two Subspecies of Hypochaeris radicata

Root respiration of the tap root forming species Hypochaeris radicata L. was measured during tap root formation. A comparison was made of two subspecies: H. radicata L. ssp. radicata L., a subspecies from relatively rich soils, and H. radicata L. ssp. ericetorum Van Soest, a subspecies from poor acidic soils. Root respiration was high and to a large extent inhibited by hydroxamic acid (SHAM) before the start of the tap root formation, indicating a high activity of an alternative non-phosphorylative electron transport chain. The rate of root respiration was much lower and less sensitive to SHAM when a considerable tap root was present. However, root respiration was also cyanide-resistant when a tap root was present, indicating that the alternative pathway was still present. A decreased rate of root respiration coincided with an increase of the content of storage carbohydrates, mainly in the tap root. The level of reducing sugars was constant throughout the experimental period, and it was concluded that the activity of the alternative oxidative pathway was significant in oxidation of sugars that could not be utilized for purposes like energy production, the formation of intermediates for growth or for storage. Root respiration decreased after the formation of a tap root. This decrease could neither be attributed to a gradual disappearance of the alternative chain, nor to a decreased level of reducing sugars. No differences in respiratory metabolism between the two subspecies have been observed, suggesting that a high activity of the alternative oxidative pathway is not significant in adaptation of the present two subspecies to relatively nutrient-rich or poor soils.     

Efficiency of Root Respiration in Relation to Growth Rate, Morphology and Soil Composition

Root growth respiration and root maintenance respiration rate of the following species were determined: Hypochaeris radicata L. ssp. radicata L., H. radicata ssp. ericetorum Van Soest, Plantago lanceolata L., P. major L. ssp. major, P. major ssp. pleiosperma Pilgcr, P. maritime L., Senecio viscosus L., S. vulgaris L. and Urtica dioica L. A high root growth respiration (i.e. the amount of oxygen consumed for synthesis of a given weight of root material) implied a high maintenance respiration rate (i.e. the amount of oxygen consumed per unit of time and dry weight, but not connected with growth). High values of both components reflect a low efficiency of root respiratory processes. The efficiency of root respiration, as determined by the values for root growth respiration and root maintenance respiration rate could not be demonstrated to be of advantage in adaptation to soil conditions, as e.g. nitrogen content, moisture content and pH. It is concluded that (he degree of ‘wasteful utilization of sugars’ in roots, i.e. such consumption of sugars as cannot be related to structural growth, storage of carbohydrates or maintenance processes, depends on imbalance of transport of sugars from the shoot to the roots with utilization of sugars for synthesis of root material. The results are discussed in relation to Brouwer's explanation for the equilibrium between the growth of shoots and of roots. Root growth rate in the present species appears limited by a factor produced in the shoot under light conditions, and which factor is distinct from carbohydrates. The evidence presented shows that relatively inefficient root respiration does not imply a low growth rate. In regulation of plant growth the growth rate itself and also the shoot to-root ratio may be more important than the regulation of the efficiency of energy metabolism.     

Aluminium and the Hydraulic Conductivity of Quercus rubra L. Root Systems

Two hydroponic experiments were conducted to determine the effectsof brief and prolonged AI³⁺ exposures on the hydraulic conductivity(Lp) of northern red oak (Quercus rubra L.) root systems. RootLp was determined using the pressure chamber method of Fiscus(1977). In the first experiment, 28- to 40-d-old seedlings weretreated for 4 d with complete nutrient solutions containingone of three Al concentrations (0.04, 1.85 or 3.71 mol m^–3)and either 0 or 50 mmol m^–3 P. Neither Lp nor daily transpirationwas affected by treatment. In Experiment II, seedlings were grown for 48–63 d incomplete solutions containing one of three Al concentrations(0, 0.75 or 2.00 mol m^–3) and either 10 or 250 mmol m^–3Ca. Lp and leaf area to root length ratio (LA/RL) were reducedwhen (AI³⁺/ Ca²⁺), the solution activity ratio, was 2.9 andhigher. Lp and LA/RL were also negatively correlated with Alconcentration and Al/Ca concentration ratio in the roots. Lpwas positively correlated with LA/RL in both experiments. Itis unclear whether Lp in the second experiment was reduced directlyby solution and root chemistry or whether Lp changed in responseto altered leaf/root balance. Key words: Al phytotoxicity, Al x Ca interaction, Quercus rubra, root hydraulic conductivity     

Effects of Cyanide on Respiration, Growth, and Potassium Absorption by Carrot Root Tissue 4

Slowly and rapidly growing carrot root tissue cultures havebeen found to be similarly sensitive to inhibition by cyanideat 10^-4 M in respect of respiration, growth, and potassium absorption.These observations conflict with those of Steward and Millar(1954), who reported that the actively proliferating cultureswere strikingly insensitive to the inhibitor at this level.It is suggested that the failure of these authors to detectany effects of cyanide on their cultures was due to the dilutionof the inhibitor by evaporation.     

Root Respiration,Photosynthesis and Grain Yield of Two Spring Wheat in Response to Soil Drying

The effects of soil water regime and wheat cultivar, differing in drought tolerance with respect to root respiration and grain yield, were investigated in a greenhouse experiment. Two spring wheat (Triticum aestivum) cultivars, a drought sensitive (Longchun 8139-2) and drought tolerant (Dingxi 24) were grown in PVC tubes (120 cm in length and 10 cm in diameter) under an automatic rain-shelter. Plants were subjected to three soil moisture regimes: (1) well-watered control (85% field water capacity, FWC); (2) moderate drought stress (50% FWC) and (3) severe drought stress (30% FWC). The aim was to study the influence of root respiration on grain yield under soil drying conditions. In the experiment, severe drought stress significantly (p < 0.05) reduced shoot and root biomass, photosynthesis and root respiration rate for both cultivars, but the extent of the decreases was greater for Dingxi 24 compared to that for Longchun 8139-2. Compared with Dingxi 24, 0.04 and 0.07 mg glucose m⁻² s⁻¹ of additional energy, equivalent to 0.78 and 1.43 J m⁻² s⁻¹, was used for water absorption by Longchun 8139-2 under moderate and severe drought stress, respectively. Although the grain yield of both cultivars decreased with declining soil moisture, loss was greater in Longchun 8139-2 than in Dingxi 24, especially under severe drought stress. The drought tolerance cultivar (Dingxi 24), had a higher biomass and metabolic activity under severe drought stress compared to the sensitive cultivar (Longchun 8139-2), which resulted in further limitation of grain yield. Results show that root respiration, carbohydrates allocation (root:shoot ratio) and grain yield were closely related to soil water status and wheat cultivar. Reductions in root respiration and root biomass under severe soil drying can improve drought tolerant wheat growth and physiological activity during soil drying and improve grain yield, and hence should be advantageous over a drought sensitive cultivar in arid regions.     

Root Respiration and Carbohydrate Status of Two Wheat Genotypes in Response to Hypoxia

To investigate root respiration and carbohydrate status in relationto waterlogging or hypoxia tolerance, root respiration rateand concentrations of soluble sugars in leaves and roots weredetermined for two wheat (Triticum aestivum L.) genotypes differingin waterlogging-tolerance under hypoxia (5% O₂) and subsequentresumption of full aeration. Root and shoot growth were reducedby hypoxia to a larger extent for waterlogging-sensitive Coker9835. Root respiration or oxygen consumption rate declined withhypoxia, but recovered after 7 d of resumption of aeration.Respiration rate was greater for sensitive Coker 9835 than fortolerant Jackson within 8 d after hypoxia. The concentrationsof sucrose, glucose and fructose decreased in leaves for bothgenotypes under hypoxia. The concentration of these sugars inroots, however, increased under hypoxia, to a greater degreefor Jackson. An increase in the ratio of root sugar concentrationto shoot sugar concentration was found for Jackson under hypoxicconditions, suggesting that a large amount of carbohydrate waspartitioned to roots under hypoxia. The results indicated thatroot carbohydrate supply was not a limiting factor for rootgrowth and respiration under hypoxia. Plant tolerance to waterloggingof hypoxia appeared to be associated with low root respirationor oxygen consumption rate and high sugar accumulation underhypoxic conditions.Copyright 1995, 1999 Academic Press Oxygen consumption rate, sugar accumulation, Triticum aestivum L., waterlogging tolerance     

Root Respiration and Growth in Plantago major as Affected by Vesicular-Arbuscular Mycorrhizal Infection

Effects of vesicular-arbuscular mycorrhizal (VAM) infection and P on root respiration and dry matter allocation were studied in Plantago major L. ssp. pleiosperma (Pilger). By applying P, the relative growth rate of non-VAM controls and plants colonized by Glomus fasciculatum (Thaxt. sensu Gerdemann) Gerdemann and Trappe was increased to a similar extent (55-67%). However, leaf area ratio was increased more and net assimilation rate per unit leaf area was increased less by VAM infection than by P addition. The lower net assimilation rate could be related to a 20 to 30% higher root respiration rate per unit leaf area of VAM plants. Root respiration per unit dry matter and specific net uptake rates of N and P were increased more by VAM infection than by P addition. Neither the contribution of the alternative respiratory path nor the relative growth rate could account for the differences in root respiration rate between VAM and non-VAM plants. It was estimated that increased fungal respiration (87%) and ion uptake rate (13%) contributed to the higher respiratory activity of VAM roots of P. major.     

High-Temperature Preconditioning and Thermal Shock Imposition Affects Water Relations,Gas Exchange and Root Hydraulic Conductivity in Tomato

Potted tomato plants (Lycopersicon esculentum Mill. cv. Amalia) were submitted to three different treatments: control (C) plants were maintained at day/night temperature of 25/18 °C; preconditioned plants (PS) were submitted to two consecutive periods of 4 d each, of 30/23 and 35/28 °C before being exposed to a heat stress (40/33 °C lasting 4 d) and non-preconditioned (S) plants were maintained in the same conditions as the C plants and exposed to the heat stress. The inhibition of plant growth was observed only in PS plants. Heat stress decreased chlorophyll content, net photosynthetic rate and stomatal conductance in both PS and S plants. However, PS plants showed good osmotic adjustment, which enabled them to maintain leaf pressure potential higher than in S plants. Furthermore, at the end of the recovery period PS plants had higher pressure potential and stomatal conductance than in S plants. This revised version was published online in July 2006 with corrections to the Cover Date.     

Changes in Structure and Hydraulic Conductivity for Root Junctions of Desert Succulents as Soil Water Status Varies

Variations in hydraulic conductivity (L_P) and the underlying anatomical and morphological changes were investigated for main root-lateral root junctions of Agave deserti and Ferocactus acanthodes under wet, dry, and rewetted soil conditions. During 21 d of drying, L_P and radial conductivity (L_R) increased threefold to fivefold at junctions of both species. The increase in L_R was accompanied by the formation of an apoplastic pathway for radial water movement from the surface of the junction to the stele for A. deserti and by the rupture of periderm by emerging primordia of secondary lateral roots for F. acanthodes. During 7 d of rewetting, L_R decreased for junctions of A. deserti, as apoplastic water movement was not apparent, but L_R was unchanged for F. acanthodes. Axial conductance (K_h) decreased during drying for both species, largely because of embolism related to the degradation of unlignified cell wall areas in tracheary elements at the root junction. The resulting apertures in the cell walls of such elements would admit air bubbles at pressure differences of only 0.12-0.19 MPa. Rewetting restored K_h for both species, but not completely, due to blockage of xylem elements by tyloses. About 40% of the primary lateral roots of the monocotyledon A. deserti abscised during 21 d of drying. For the dicotyledon F. acanthodes, which can form new conduits in its secondary xylem, only 10% of the primary lateral roots abscised during 21 d of drying, consistent with the much greater frequency of lateral roots that persist during drought in the field compared with the case for the sympatric A. deserti.     

Energy, Respiration, and Growth in Plants

The energy relations and heat production during plant growthare analysed in terms of respiration, dry weight, and growth.Wastage respiration and its relationship to this analysis arediscussed The results of microcalorimetric experiments on wheatseedlings are analysed and interpreted.     

A Periscope Method for Observing Root Growth and Distribution in Field Soil

This paper describes a technique for observing root growth inthe field using glass tubes and a periscope. Roots of two crops(winter wheat and millet) were studied in situ with the periscopeand the results compared with those obtained from washed soilsamples. Generally, both techniques gave similar patterns ofgrowth and distributions of roots although the periscope measurements,when compared with washed soil samples, tended to underestimateroot density close to the soil surface and overestimate densitieslower in the profile. Both methods allowed differences in theroot systems of irrigated and unirrigated crops to be distinguishedbut the periscope method was considerably faster