Phosphorus affects storage root yield of cassava through root numbers

Abstract

The objective of this study was to determine the effect of phosphorus applied through fertigation on growth and root yield of cassava. This was achieved through a greenhouse pot-experiment consisting of 1, 4, 7, 10, 20 and 30?mg?P?L^?1. Increasing P from 1 to 30?mg?P?L^?1 realized a 57.1 and 150.0% increase in leaf blade P in 2014 and 2015, respectively. Similarly, chlorophyll content and shoot growth increased as P concentration in solution increased. However, leaf stomatal conductance and net photosynthesis reached a maximum in 7 and 20?mg?P?L^?1 in 2014 and 2015, respectively. This trend of stomatal conductance and net photosynthesis was consistent with that of dry root yield and storage roots numbers. Regressing dry root yield against storage root numbers showed that R² = 0.80. Phosphorus encourages formation of storage roots and the duration of cassava’s growth affects the amount of P required for maximum root yield.     

Biochar reduced soil extractable Cd but increased its accumulation in rice (Oryza sativa L.) cultivated on contaminated soils

Purpose

This study focused on the effects and mechanisms of biochar amendment to Cd-contaminated soil on the uptake and translocation of Cd by rice under flooding conditions.

Materials and methods

Pot and batch experiments were conducted using Cd-contaminated soil collected from a field near an ore mining area and a cultivar of Oryza sativa ssp. indica. Biochar derived from rice straw under anaerobic conditions at 500 °C for 2 h was mixed with the soil at the rate of 0, 2.5, and 5%.

Results and discussion

The application of 5% biochar reduced CaCl₂-extractable soil Cd by 34% but increased Cd concentration in brown rice by 451%. Biochar amendment decreased water-soluble Fe²⁺ in soils and formation of Fe plaques on roots and weakened the Fe²⁺-Cd²⁺ competition at adsorption sites on the root surface. Biochar increased water-soluble Cd in the soil and consequently Cd uptake by rice roots by releasing water-soluble Cl^?. Biochar application also reduced the proportion of cell wall-bound Cd in the root, which caused easier Cd translocation from the cortex to the stele in the root and up to the shoot.

Conclusions

Rice straw biochar (with high concentration of water-soluble Cl^?) reduced CaCl₂-extractable soil Cd but increased Cd concentration in rice under flooding condition.

     

Effects of Litter and Fine Root Composition on Their Decomposition in a Rhodic Paleustalf under Different Land Uses

Abstract

Plant litter and fine roots are important in maintaining soil organic carbon (C) levels as well as for nutrient cycling. The decomposition of surface‐placed litter and fine roots of wheat (Triticum aestivum), lucerne (Medicago sativa), buffel grass (Cenchrus ciliaris), and mulga (Acacia aneura), placed at 10‐cm and 30‐cm depths, was studied in the field in a Rhodic Paleustalf. After 2 years, ≤10% of wheat and lucerne roots and ≥60% of mulga roots and twigs remained undecomposed. The rate of decomposition varied from 4.2 year^?1 for wheat roots to 0.22 year^?1 for mulga twigs, which was significantly correlated with the lignin concentration of both tops and roots. Aryl+O‐aryl C concentration, as measured by ¹³C nuclear magnetic resonance spectroscopy, was also significantly correlated with the decomposition parameters, although with a lower R ² value than the lignin concentration. Thus, lignin concentration provides a good predictor of litter and fine root decomposition in the field.     

Effect of manganese on endomycorrhizal sugar maple seedlings

Abstract

Manganese (Mn) toxicity may play an important role in the poor survival of seedlings in declining sugar maple (Acer saccharum Marsh.) stands in northern Pennsylvania. To determine the effect of Mn on the growth of sugar maple seedlings, 1‐year‐old seedlings inoculated with vesicular‐arbuscular mycorrhizal (VAM) fungi and growing in sand‐vermiculite‐peat moss medium were irrigated for 7 weeks with nutrient solution (pH 5) containing 0.1 (control), 1, 2, 4, 8, or 16 mg L^?1 Mn. Total seedling dry weight was negatively correlated with Mn, becoming significantly different than the control at 2 mg L^?1 Mn. Stem and root dry weight were reduced by lower Mn levels than leaf dry weight. Manganese had no effect on the root/shoot ratio. The concentration of Mn in roots and leaves increased as the level of Mn in the nutrient solution increased, with the concentration in the leaves 2.2‐ to 3.7‐fold greater than the concentration in the roots. Except for a reduction of P in the roots, Mn had little effect on the concentration of nutrient elements in the roots or leaves. Colonization of the roots by VAM fungi was increased by Mn, with a maximum percentage at 4 mg L^?1 Mn. Manganese toxicity symptoms in the leaves, small discrete chlorotic spots, began to appear at 1 mg L^?1 Mn. The sensitivity of sugar maple seedlings to Mn found in this study supports the hypothesis that Mn may affect regeneration in declining sugar maple stands. However, evaluation of the effects of Mn on seedlings in native soils under field conditions will be necessary before the role of Mn in sugar maple regeneration can be understood.     

Effect of supplying P to a portion of the soybean root system on root growth and P uptake kinetics 1

Abstract

Knowledge of the effect of supplying P to portions of the soybean (Glycine max L. Merr) root system on P influx kinetics and root growth is important in developing P fertilizer placement practices for efficient fertilizer use. The objective of this research was to determine the effect of restricting P supply to portions of the root system on plant P status, root growth, and P influx kinetics. Two solution experiments were conducted in a controlled climate chamber. Phosphorus influx kinetics were determined on 25‐day‐old soybean plants that had been grown with 100, 75, 50, 25, and 12.5% of their roots initially exposed to P. Phosphorus influx kinetics were also measured on 25‐day‐old plants that had been P‐starved for the last 1, 2, 4, and 6 days prior to the determining P influx kinetics in order to relate plant P status to P influx kinetics.

Reducing the portion of the roots supplied with P reduced P uptake. This resulted in a reduction in plant P concentration and was related to a 3.41‐fold increase in maximum P influx measured on 25‐day‐old plants. Restricting the proportion of roots supplied with P had no significant effects on the Michaelis‐Menten constant or on the concentration in solution where net influx was zero. Root growth rate of the roots in the P containing solution was not significantly different from those in the ‐P solution.

Phosphorus uptake was correlated with final root surface area exposed to P (r² = 0.88??). Starving the plants for P reduced P concentration in the shoot and root and this resulted in as much as a 1.68‐fold increase in maximum influx.     

Cluster Root Formation by Lupinus Albus is Modified by Stratified Application of Phosphorus in a Split-Root System

ABSTRACT

Cluster root formation by white lupin (Lupinus albus L. cv. Kiev Mutant) in response to stratified application of hydroxyapatite was examined in a split-root system. The system consisted of two vertical compartments, each divided horizontally into five 60-mm layers. Hydroxyapatite was applied to different layers at 150 mg phosphorus(P) kg^?1 soil. The proportion of dry biomass of cluster roots in the whole root system was significantly reduced when P concentration was high in shoots due to P application, suggesting that cluster root formation was regulated by the shoot P status. However, the cluster root percentage increased in the soil layer supplemented with P, and decreased in other layers, especially when P was applied in a deep layer. The formation of cluster roots is regulated by internal plant P status, but is also greatly affected by localized P supply. Heterogeneous P supply can modify the distribution of cluster roots.     

Phytoavailability of lead altered by two Pelargonium cultivars grown on contrasting lead-spiked soils

Purpose

This study assesses the potential of two contrasted fragrant Pelargonium cultivars to induce pH and dissolved organic carbon (DOC) changes in the soil solution, Pb speciation, and their subsequent effects on rhizosphere phytoavailable Pb.

Materials and methods

Rooted plantlets were grown in special devices, floating on aerated nutrient solution in PVC tanks. This setup allows roots to be physically separated, through a mesh, from a 3-mm soil matrix layer that can be considered as rhizosphere soil. Two contrasted soils, each spiked with Pb-rich particles, emitted from a battery recycling industry, were used at total burdens of 500 and 1500 mg Pb kg^?1 in addition to a control unspiked soil. Soil solution pH, phytoavailable Pb, DOC, Pb adsorption, precipitation on roots, and Pb phases in soil and plant were investigated.

Results and discussion

Attar of Roses (Attar) cultivar acidified its rhizosphere by 0.4 pH units in both spiked soils. Concolor Lace (Concolor) was unable to change soil solution pH on soil-1 and increased it by 0.7 units on soil 2. Concentrations of Pb in soil solution from Attar plants were always higher than those of Concolor ones. DOC contents of both unspiked soil-1 and soil-2 without plants were not significantly different. In the case of spiked samples, DOC contents in the rhizosphere soil were increased by three and two times for Attar and Concolor, respectively, compared to the unspiked soil without plant. Both cultivars were able to increase DOC contents, independent of soil type and level of contamination. Accumulation of Pb in shoots and roots was higher in Attar as compared to Concolor due to enhanced available Pb as a result of pH and DOC modifications of the rhizosphere soil. Significant amounts of Pb were adsorbed on roots of both cultivars. X-ray elemental analysis of precipitates on roots revealed the association of Pb with P in cylinder-like structures. Extended X-ray absorption fine structure (EXAFS) spectroscopy revealed that Pb was present, to a major extent in the inorganic form, mainly as PbSO₄ in the soil, whereas it was complexed with organic species within plant tissues. The conversion of Pb into organic species could decrease toxicity, may enhance plant tolerance, and could increase translocation.

Conclusions

Plant-induced changes were responsible for the modification of lead phases within the soil. Immobile forms present in the source leaded particles as well as in the soils were converted into soluble species, ultimately improving the phytoavailable or soil solubilized Pb.

     

Influence of Mercury on Soybean Plants (Glycine max L.) at Low pH

The influence of Hg on soybean plants under different pH conditions and Hg concentrations was studied. Growth inhibition by Hg was higher in roots than the upper part of the plant, but was highly dependant on pH condition. Growth inhibition of roots was observed when Hg concentration was higher than 1 mg Hg L^?1 for pH 4.0 and 5 mg Hg L^?1 for pH 6.0. Using ²⁰³Hg as a radioactive tracer, the amount of Hg (1 mg Hg L^?1) uptake in root was found to be about 1.5 times higher at pH 4.0 than that at pH 6.0; suggesting that Hg when highly accumulated at the lower pH induced inhibition of root growth. Decreased amounts of Hg due to evaporation during the plant growth were very low, but were higher at pH 6.0 than that at pH 4.0. There was hardly any translocation of Hg from roots to the upper parts through the stem within 24 h.     

Genotypic differences in effects of cadmium on growth and nutrient compositions in wheat

Abstract

A solution culture study was conducted to determine the genotypic difference in the effects of cadmium (Cd) addition on growth and on the uptake and distribution of Cd and other 11 nutrients in wheat plants. Cadmium addition at a rate of 1 mg L^?1 significantly reduced root and shoot dry matter production, shoot height, root length, chlorophyll content, and tillers per plant. On the average of 16 wheat genotypes used in study, Cd concentrations of Cd‐treated plants were 48.1 and 459 μg g^?1 dry weight (DW) in shoots and roots, respectively, and retained 77.91% of total Cd taken up in the roots. On the whole, Cd addition reduced the concentration of sulfur (S), phosphorus (P), magnesium (Mg), molybdenum (Mo), manganese (Mn), and boron (B), and increased iron (Fe), irrespective of the plant parts. The effect of Cd on the concentration of potassium (K), calcium (Ca), and copper (Cu) differed in shoots and roots. The significant difference existed among 16 wheat genotypes in their response to Cd in terms of growth and nutrient concentrations. Genotype E81513, which showed relatively less inhibition in growth, had the lowest shoot Cd concentration and more Cd accumulation in roots, while Ailuyuang had the highest Cd concentration and accumulation in shoot with lower Cd concentration in root. The significant interaction was found between Cd treatment and genotype for all nutrient concentrations in both shoot and root, except S and Zn in root.     

Distribution of exudates of lupin roots in the rhizosphere under phosphorus deficient conditions

Abstract

The distribution of secretory acid phosphatase and organic acids enhanced by phosphorus deficiency in lupin rhizosphere was investigated using a rhizobox system which separated the rhizosphere soil into 0.5 mm fractions. In the soil fraction closest to the root surface, the lupin exudates displayed an acid phosphatase activity of 0.73 u g^?1 dry soil and citrate concentration of 85.2 μmol g^?1 dry soil, respectively. The increase of the acid phosphatase activity-induced an appreciable depletion of organic P in the rhizosphere, indicating that lupin efficiently utilized the organic P from soil through the enzyme activitye The sterile treatments demonstrated that the acid phosphatase in the rhizosphere was mainly derived from lupin root secretions. The secretory organic acids enhanced considerably the solubility of the inorganic P in three types of soil and a sludge. However, the secretory acid phosphatase and organic acids from lupin roots were only detected in a considerable amount in 0-2.5 mm soil fractions from root surface.     

Copper induced iron deficiency in wheat (Triticum aestivum L)

Abstract

A pot experiment was conducted to study the interaction effects of phosphorus and copper on wheat. The soils used were calcareous loamy sand (ls) and non calcareous sandy loam (sl). Four levels of Cu (0, 5, 10 and 20?mg Cu kg^?1 soil) and six levels of P (0, 25, 50, 100, 200 and 400?mg P kg^?1 soil) were applied in all possible combinations with three replications. Soil pH decreased with Cu application while Olsen P increased with P application in both soils. Growth and yield of wheat improved significantly with graded levels of applied P. However, when any level of P was combined with 20?mg Cu kg^?1 soil, severe iron chlorosis of leaves, a drastic reduction in growth and chlorophyll content was observed in calcareous ls only. The results indicated that it was Cu and not P that induced Fe deficiency in wheat grown in alkaline calcareous soil and the Cu requirement of the crop seemed to be much lower in the calcareous ls. Root dry matter, grain and straw yield decreased with increasing levels of applied Cu in ls but in sl maximum increase of 62.5, 74.3 and 63.7 per cent in root, grain and straw yield was observed with a combined application of 400?mg P and 5?mg Cu kg^?1 soil over control. Accumulation of Cu in roots decreased the Fe absorption by roots which indicated that Fe chlorosis of wheat leaves is expected when Cu: Fe concentration ratio in root is > 0.30.     

Significance of Nickel Supply for Growth and Chlorophyll Content of Wheat Supplied with Urea or Ammonium Nitrate

ABSTRACT

Nickel (Ni) is an essential element for activation of urease in higher plants. The effects of Ni as an essential micronutrient on growth and chlorophyll content of wheat plants grew in nutrient solutions supplied either with ammonium nitrate or urea as two different nitrogen (N) sources were investigated. Plants were allowed to grow for six weeks, then leaf chlorophyll content, shoot and root fresh and dry weights, and Ni concentration in shoots and roots were determined. Shoot and root Ni concentration in both urea and ammonium nitrate-fed plants increased significantly with the increase in Ni concentration. Growth and chlorophyll content in leaves of the urea-fed plants increased when Ni concentration in the solution was as high as 0.05 mg L^?1 and decreased at 0.1 mg Ni L^?1. In ammonium nitrate-fed plants, these parameters increased up to 0.01 mg Ni L^?1 and started to decrease with further increase in Ni concentration. Plants that grew in nutrient solutions containing urea had more shoots and roots fresh and dry weight at third and fourth Ni levels (0.05 and 0.1 mg L^?1) than those that grew in media containing ammonium nitrate with similar Ni levels. Total chlorophyll content was also higher in plants supplied with urea plus Ni. The amount of Ni required for optimum wheat growth was dependent on the forms of N used. When supplied with ammonium nitrate or urea, the amount of Ni needed was 0.01 and 0.05 mgL^?1 of nutrient solutions, respectively.     

Decarboxylation of organic anions to alleviate acidification of red soils from urea application

Purpose

Decarboxylation of organic anions in crop straw is recognized as one of the mechanisms for increasing pH in acidified soils. However, the effectiveness of specific compounds in alleviating soil acidification from nitrification has not been well determined. This study examined three organic anions commonly found in crop straws and their effect on soil acidity and N transformation processes following urea application to a red soil (Ferralic Cambisol).

Materials and methods

A 35-day incubation experiment was conducted using soil after receiving 26 years of two different nutrient treatments: (1) chemical nitrogen, phosphorus, and potassium fertilization (NPK, pH 4.30) and (2) NPK plus swine manure (NPKM, pH 5.88). Treatments included three rates (0.25, 0.5, and 1.0 g C kg^?1) of calcium citrate, 0.5 g C kg^?1 calcium oxalate, 0.5 g C kg^?1 calcium malate, urea-only (control) soil, and a non-treated soil as a reference. Soil acidity, mineral N species, decarboxylation, and their correlations were determined.

Results and discussion

All three organic anions significantly increased pH in both soils and the effectiveness was positively correlated with application rate. The change in total exchangeable soil acidity was dominated by aluminum concentration in the NPK soil, but by proton concentration in the NPKM soil. At ≥?0.5 g C kg^?1, the anions decreased soil exchangeable acidity by 25–68% in NPK soil and by 63–88% in NPKM soil as compared with control. Oxalate was the most effective in increasing soil pH by 0.70 and 1.31 units and reducing exchangeable acidity by 3.79 and 0.33 cmol₍₊₎ kg^?1 in NPK and NPKM soils, respectively, and also resulted in the highest CO₂ production rate. Addition of organic anions led to a lower nitrification rate in NPKM soil relative to the NPK soil.

Conclusions

These results imply that crop straws rich in organic anions, especially oxalate, would have a higher potential to alleviate soil acidification.

     

In vivo nitrate reductase activity in carex pseudocyperus L.: The influence of nitrate ‐ ammonium concentration ratios and correlation with growth

Abstract

The influence of the nitrate nutritional status and increasing ammonium concentrations on the nitrate reductase activity of shoots and roots of Carex pseudocyperus L. was investigated. The activity of this enzyme was correlated with the relative growth rates of the plant. Nitrate reductase activity was determined by a modified in vivo test (1). A specially developed test system allowed a large amount of samples to be handled easily.

The optimization procedure of the incubation buffers led to different assay conditions for the shoot and the root, respectively. Enzyme activity in the shoot was dependent on the length of the incubated leaf pieces. Incubation had to take place under dark, anaerobic conditions.

Enzyme activity was influenced by an evident diurnal rhythm with an optimum six hours after starting illumination, so that harvesting occurred always at that day time.

Increasing nitrate concentrations of up to 2.5mM NO₃‐ in the nutrient solution induced an increasing nitrate reductase activity in the shoot. The enzyme activity of the root was already fully induced at 1mM NO₃ ^?. A nitrate concentration above 5mM NO₃ ^? inhibited enzyme activity in shoots as well as in roots. The addition of increasing amounts of ammonium to a solution containing 2mM NO₃ ^? led to a significant inhibition of the enzyme activity in both parts of the plant.

Relative growth rates of the shoot, as a function of increasing nitrate concentrations in the nutrient solution, were highly positively correlated to the corresponding nitrate reductase activity, but only a slight, negative correlation was observed between these two parameters in the root.     

Boron nutrition and mobility,and its relation to the elemental composition of greenhouse grown root crops I. Rutabaga

Abstract

The nutrition and mobility of B, and its relation to the elemental composition of two cultivars of rutabaga (Brassica napus ssp. rapifera cv. Laurentian and Wilhelmsberger) plants were investigated in greenhouse experiments. Laurentian exhibited a greater response than Wilhelmsberger to continuing B deficiency as indicated by the severity in the roots of brown heart, of external roughness and elongation and of the decrease in B concentration. Signs of B deficiency were not found when the B contents of the root and young leaves were 27 and 56 ug g‐1 DM respectively. Root B levels of 14 and 17–20 μg g^‐1 gave moderate and slight internal signs of brown discoloration. Foliar applications of B partially restored the B concentrations of the roots; however, the mechanism of movement was unclear. The Mg, Mn and Zn contents of roots were the only elements that consistently increased and accumulated under B deficiency. The relative element composition of the root compared to the mature leaves is consistent with the root being supplied predominantly with nutrients by the phloem. Nutrient retranslocation was assessed from the ratio of element concentration in the roots or young leaves to that in the mature leaves. Although Mg, Mn and B exhibited limited mobility under adequate B nutrition they were translocated from mature leaves to younger tissues under B starvation. It is concluded that Wilheimsberger is by virtue of its greater capacity for the retranslocation of B to roots, less sensitive to B deficiency and the brown heart disorder.     

Overcoming the Stressful Effect of Low pH on Soybean Root Hair Curling using Lipochitooligosacharides

Abstract

Signal molecules are among the major factors required for the legume–bacteria symbiosis. The excretion of signal molecules by plants stimulates the bacterial Nod genes resulting in the production of lipochitooligosacharides (LCOs). LCOs cause root hair deformation (RHD) and induction of nodule cells division, leading to the formation of nodules. The chemical structure of LCOs determines their biochemical activities; for example, removal of the sulfate group can significantly reduce the morphogenic activities of LCOs. Stressful conditions interrupt the excretion of signal molecules by the legumes' roots and consequently the inhibition of LCO production by the bacteria. This research has studied the effect of different concentrations of LCOs on RHD of two soybean [Glycine max (L.) Merr] cultivars, AC Bravour and Maple Glen, under acidity stress. In the first experiment, two different concentrations of LCO (10^?7 and 10^?6M) and in the second experiment, three different concentrations of LCO (10^?7, 10^?6, and 10^?5M) were added to the soybean roots subjected to the pH levels of 4, 5, 6, and 7 for 24 h. By microscopy observation, the ratios of RHD were determined. Addition of LCOs resulted in RHD in both cultivars. Maple Glen roots responded similarly to different concentrations of LCO, whereas roots of AC Bravour responded differently. The concentration of 10^?5M LCO could inhibit the stressful effect of pH 4 on RHD compared with pH 7 in both cultivars. The significant interaction between LCO and pH suggests that the effect of LCO on RHD may be more significant under higher levels of acidity.     

Responses of Bougainvillea spectabilis to elevated atmospheric CO2 under galaxolide (HHCB) pollution and the mechanisms of its rhizosphere metabolism

Purpose

Due to the discovery of synthetic musks in soil and the gradual increase in atmospheric carbon dioxide (CO₂), it is important to reveal the potential implications of these compounds for bioremediation systems. Hence, this study was conducted to investigate the combined influence of galaxolide (HHCB) and elevated CO₂ on an ornamental remediation plant.

Materials and methods

We conducted pot experiments with Bougainvillea spectabilis, an ornamental remediation plant, in which the biomass, HHCB and chlorophyll contents, and rhizosphere metabolism of the plants were analyzed.

Results and discussion

We showed that B. spectabilis exhibited high tolerance under combined HHCB and elevated CO₂ stresses. The addition of HHCB alone to the soil did not significantly reduce the biomass components of B. spectabilis, whereas the presence of elevated CO₂ (750 μL L^?1) alone showed a relatively strong ability to increase plant biomass, especially that of the leaves. An elevated CO₂ concentration stimulated the absorption of low doses of HHCB by the roots. Regarding the root metabolites of B. spectabilis, carbohydrates and organic acids were highly correlated with HHCB concentration, and amino acids were well correlated with CO₂ concentration.

Conclusions

Our study indicates that B. spectabilis may be well suited to remove HHCB from contaminated soil under elevated CO₂ levels, and the root metabolism of this plant provides information about HHCB contamination and elevated CO₂ conditions.

     

Phosphorus effects on zinc translocation in maize

Abstract

Interactions of P and Zn in roots and shoots of maize were studied in greenhouse using three different type of Egyptian soils (one alluvial and two calcareous). No Zn deficiency symptoms were seen in maize. The concentration of Zn in shoots was reduced due to P application. Its concentration in roots was hardly influenced by added P. Added P increased its concentration in the shoots much more than in the roots. Added Zn increased its concentration in roots more than in shoots. These findings suggest that applied P had no effect on Zn absorption by the roots. The main effect was a physiological inhibition in the translocation of Zn from roots to shoots, probably due to the indirect effect on increasing salt concentration in the root medium added as CaH₂PO₄. This may have depolarized the xylem potential resulting in increasing the anion influx and decreasing that of the cation into the relatively less negatively charged xylem vessels. As the xylem potential appears to be in the stele at the interface between the xylem vessels and the pericycle cells. Results of the calcareous soils suggest that excess of CaCO₃ influences P‐Zn relationship within the plant by decreasing the translocation of Zn and increasing that of P from roots to shoots.     

Simple method for 14C‐labelling root material for use in root decomposition studies

Abstract

A method was devised in which plant roots can be easily and uniformly radiolabelled with ¹⁴C for use in soil decomposition studies. The roots were labelled from an exogenous sugar solution for a total period of 48 hours after which root decomposition studies could be performed. The method offers distinct advantages over the existing constant ¹⁴C‐CO₂ atmosphere labelling method.     

The effect op several enzymes on cation exchange in roots

Abstract

Commercial protease and cellulase treatment of dried and milled plant roots decreased their cation exchange capacity to varying degrees, indicating that protein and cellulose contribute to the exchange mechanism in addition to pectin. Membranes isolated from two roots proved to be epidermal cells; these had a significant cation exchange capacity when thought of as an interface between the soil and the root, but not when compared to the root as a whole. Methylation of the membranes reduced their exchange capacity to zero.