Effect of zinc,phosphorus and nitrogen on tryptophan concentration in rice grains grown on limed and unlimed soils

Summary The effects of Zn, P, N and CaCO₃ on tryptophan concentration in rice grain were studied in greenhouse at Haryana Agricultural University. Zinc application upto 20 ppm increased tryptophan concentration in rice grain. Zn-EDTA gave highest increase followed by ZnSO₄ and then ZnO. Liming at the rate of 4 and 8 per cent decreased tryptophan concentration significantly. Phosphorus application upto 100 ppm also decreased tryptophan significantly but Zn in combination with P increased tryptophan and overcame negative effect of P. Nitrogen application upto 120 ppm increased tryptophan concentration. There was positive interaction between Zn and N. Ammonium sulphate gave highest tryptophan followed by ammonium nitrate and then urea. The tryptophan concentration ranged between 766 ppm and 2011 ppm in paddy grain. The lowest tryptophan concentration was in the plants treated with 8 per cent lime in absence of added Zn and highest with 10 ppm Zn through Zn-EDTA. Department of Soils.     

Effect of zinc sources and levels on the growth and Zn nutrition of soybean (Glycine max. L.) in the presence of chloride and sulphate salinity

A study was conducted in a screen house in pots on a sandy loam soil deficient in Zn. Salinity was induced by adding 44, 88 and 132 me/l of chloride and sulphate salts in the saturation extract. To these treatments, 0, 5 and 10 ppm Zn were added as ZnSO₄·7H₂O or Zn-EDTA. The results indicated that the yield of soybean shoot was lowest at the highest salinity level and highest at the lowest level. Shoot yield improved markedly with Zn application. Both sources of Zn were equally effective in augmenting crop yields. Yields were low in Cl-salinity when compared with equivalent levels of SO₄-salinity. Application of ZnSO₄·7H₂O produced higher yields in SO₄-dominant salinity. Zinc content increased and Zn uptake decreased with increase in Cl-salinity regardless of Zn sources. In SO₄-salinity, ZnSO₄·7H₂O did not influence the Zn content, but uptake was suppressed with increase in SO₄-salinity. Increasing rates of SO₄-salinity enhanced Zn content in the presence of Zn-EDTA.     

Zn、B配施对鸡血藤黄酮类化合物积累的影响

为探讨Zn、B配施对鸡血藤(Spatholobus suberectus)黄酮类化合物积累的影响,采用营养液叶面喷施,对其总黄酮含量、可溶性蛋白质和PAL活性的变化进行研究。结果表明,Zn、B配施的鸡血藤总黄酮含量、可溶性蛋白质含量、PAL活性增加,其中施用50 mg L–1 Zn SO4+10 mg L–1 Na_2B_4O_7·10H_2O鸡血藤的可溶性蛋白质含量最高,达0.89%;施用25 mg L–1Zn SO4+50 mg L–1 Na2B4O7·10H2O鸡血藤的总黄酮含量和PAL活性最高,分别为4.65%、29.47 U g–1min–1。因此,合理配施Zn、B能促进鸡血藤黄酮类化合物的积累。     

Effect of zinc on biological half-lives of 65Zn in whole body and liver and on distribution of 65Zn in different organs of rats following nickel toxicity

This study was designed to determine the effect of zinc on the biological half-lives of ⁶⁵Zn in whole body and liver and on distribution of ⁶⁵Zn in different organs of rats following nickel toxicity. Sprague-Dawley (SD) rats received either nickel in the form NiSO₄·6H₂O at a dose of 800 mg/L in drinking water, zinc in the form of ZnSO₄·7H₂O at a dose of 227 mg/L in drinking water, and nickel plus zinc or drinking water alone for a total duration of 8 wk. All of the rats were injected with a tracer dose of 0.37 MBq ⁶⁵Zn at the end of the treatment period. The effects of different treatments were studied on biological half-lives of ⁶⁵Zn in whole body and liver and on the distribution of ⁶⁵Zn in different organs of rats. In the present study, we have noted that nickel treatment to normal rats caused a significant decrease in the slow component (Tb₂) in liver, which improved following zinc supplementation. Nickel administration to normal-diet-fed animals caused significant lowering in the percentage uptake of ⁶⁵Zn values in the brain, liver, and intestine. However, the administration of zinc to nickel-treated rats improved the status of ⁶⁵Zn in different organs. The Tb₂ in the liver and the percentage uptake of ⁶⁵Zn values elevated following zinc supplementation to nickel-treated rats.     

Fertilizer nitrogen budget of Na15NO3 and (15NH4)2SO4 split-applied to winter wheat in microplots on a loam soil

Labelled fertilizer N applied to winter wheat as Na¹⁵NO₃ and (¹⁵NH₄)₂SO₄ at a total N dressing of 100kg ha⁻¹ was used in a microplot balance study to investigate the fate of each split fraction at three growth stages: end of tillering, heading and beginning of flowering. Results indicated that while the percentage utilization of the applied N by the grain and total crop increased considerably from the first to the third split application, these values diminished steadily in the straw. Grain recovery values for the first, second and third split applications were 34.2%, 51.5% and 55.7% for the NO₃ and 32.3%, 48.4% and 52.5% for the NH₄ carrier, respectively. The corresponding recovery values for the whole plant were 54.6%, 67.8% and 69.9% for the NO₃ and 51.7%, 63.5% and 66.1% for the NH₄ carrier. A greater proportion of the fertilizer N applied at the end of tillering stage was found in the vegetative plant components as compared with the grain. The reverse occurred for the N applied at the heading and at the beginning of the flowering stages. The residual fertilizer N found in the soil amounted to 18.0%, 10.4% and 11.6% of the applied NO₃−N and to 22.5%, 12.7% and 15.2% of the applied NH₄−N for the respective split applications. No differences were found for each split application between the two carriers as far as the unaccounted fertilizer N was concerned. The losses were 26.6%, 22.3% and 18.6% of the applied N for the three split applications, respectively. The application of fertilizer N did not lead to any increase in soil N uptake by the crop.     

Characterization of natural variation for zinc, iron and manganese accumulation and zinc exposure response in Brassica rapa L.

Brassica rapa L. is an important vegetable crop in eastern Asia. The objective of this study was to investigate the genetic variation in leaf Zn, Fe and Mn accumulation, Zn toxicity tolerance and Zn efficiency in B. rapa. In total 188 accessions were screened for their Zn-related characteristics in hydroponic culture. In experiment 1, mineral assays on 111 accessions grown under sufficient Zn supply (2 μM ZnSO₄) revealed a variation range of 23.2–155.9 μg g⁻¹ dry weight (d. wt.) for Zn, 60.3–350.1 μg g⁻¹ d. wt. for Fe and 20.9–53.3 μg g⁻¹ d. wt. for the Mn concentration in shoot. The investigation of tolerance to excessive Zn (800 μM ZnSO₄) on 158 accessions, by using visual toxicity symptom parameters (TSPs), identified different levels of tolerance in B. rapa. In experiment 2, a selected sub-set of accessions from experiment 1 was characterized in more detail for their mineral accumulation and tolerance to excessive Zn supply (100 μM and 300 μM ZnSO₄). In this experiment Zn tolerance (ZT) determined by relative root or shoot dry biomass varied about 2-fold. The same six accessions were also examined for Zn efficiency, determined as relative growth under 0 μM ZnSO₄ compared to 2 μM ZnSO₄. Zn efficiency varied 1.8-fold based on shoot dry biomass and 2.6-fold variation based on root dry biomass. Zn accumulation was strongly correlated with Mn and Fe accumulation both under sufficient and deficient Zn supply. In conclusion, there is substantial variation for Zn accumulation, Zn toxicity tolerance and Zn efficiency in Brassica rapa L., which would allow selective breeding for these traits.     

Effect of zinc and phosphorus on the grain yield of corn (Zea mays L.) grown on a calcareous soil

Summary In a field experiment, more than 22% increase in the grain yield of corn was obtained by the application of 50 kg ZnSO₄/ha. Grain yields were also increased by increasing the level of applied phosphorus. Positive relationship was obtained between Zn and P, the phosphorus treatment increased Zn uptake by grains and vice versa.     

‘On-farm’ seed priming with zinc in chickpea and wheat in Pakistan

A series of on-station trials was implemented between 2002 and 2006 to assess the response of wheat (Triticum aestivum L.) and chickpea (Cicer arietinum) to zinc (Zn) added by soaking seeds (priming) in solutions of ZnSO₄ before sowing. Wheat seed was primed for 10 h in 0.3% Zn and chickpea for 6 h in 0.05% Zn. Seed treatments increased the seed concentration in wheat from 27 to 470 mg/kg and in chickpea from 49 to 780 mg/kg. Priming wheat seeds with 0.3% Zn significantly increased the mean shoot dry mass, Zn concentration and Zn uptake of 15-day-old seedlings relative to non-primed controls and seeds primed with water alone. Using 0.4% Zn further increased shoot Zn concentration but depressed shoot dry mass to the level of the non-primed control. In seven trials, mean grain yield of wheat was significantly increased from 2.28 to 2.42 t/ha (6%) by priming with water alone and to 2.61 t/ha (14%) by priming with 0.3% Zn. Mean grain yield of chickpea in seven trials was increased significantly from 1.39 to 1.65 t/ha (19%) by priming seeds with 0.05% Zn. The effect of priming chickpea seeds with water was intermediate (1.49 t/ha) and not statistically separable from the non-primed and zinc-primed treatments. Increased grain yield due to priming in both crops was associated with increases in total biomass but there was no significant effect of priming on harvest index. In addition to increasing yield, priming seeds with Zn also significantly increased grain zinc concentration, by 12% in wheat (mean of three trials) and by 29% in chickpea (one trial) and the total amount of Zn taken up by the grain (by 27% in wheat and by 130% in chickpea). Using ZnSO₄ to prime seeds was very cost-effective, with net benefit-to-cost ratios of 75 for wheat and 780 for chickpea. An erratum to this article can be found at     

Uptake and transport of foliar applied zinc (65Zn) in bread and durum wheat cultivars differing in zinc efficiency

Using two bread wheat (Triticum aestivum) and two durum wheat (Triticum durum) cultivars differing in zinc (Zn) efficiency, uptake and translocation of foliar-applied ⁶⁵Zn were studied to characterize the role of Zn nutritional status of plants on the extent of phloem mobility of Zn and to determine the relationship between phloem mobility of Zn and Zn efficiency of the used wheat cultivars. Irrespective of leaf age and Zn nutritional status of plants, all cultivars showed similar Zn uptake rates with application of ⁶⁵ZnSO₄ to leaf strips in a short-term experiment. Also with supply of ⁶⁵ZnSO₄ by immersing the tip (3 cm) of the oldest leaf of intact plants, no differences in Zn uptake were observed among and within both wheat species. Further, Zn nutritional status did not affect total uptake of foliar applied Zn. However, Zn-deficient plants translocated more ⁶⁵Zn from the treated leaf to the roots and remainder parts of shoots. In Zn-deficient plants about 40% of the total absorbed ⁶⁵Zn was translocated from the treated leaf to the roots and remainder parts of shoots within 8 days while in Zn-sufficient plants the proportion of the translocated ⁶⁵Zn of the total absorbed ⁶⁵Zn was about 25%. Although differences in Zn efficiency existed between the cultivars did not affect the translocation and distribution of ⁶⁵Zn between roots and shoots. Bread wheats compared to durum wheats, tended to accumulate more ⁶⁵Zn in shoots and less ⁶⁵Zn in roots, particularly under Zn-deficient conditions. The results indicate that differences in expression of Zn efficiency between and within durum and bread wheats are not related to translocation or distribution of foliar-applied ⁶⁵Zn within plants. Differential compartementation of Zn at the cellular levels is discussed as a possible factor determining genotypic variation in Zn efficiency within wheat.     

Contribution of inoculation with azolla combined with nitrogen,phosphorus and zinc to rice in Nile Delta

Rice performance, in terms of plant height, productive tillering, yield and N-contents of grain and straw, harvest index (grain yield as a percentage of grain plus straw yields) and relative fertilizer N-use efficiency (kg grain yield/kg fertilizer-N) was enhanced by urea, ZnSO₄ and green manuring withAzolla caroliniana. Unlike urea fertilizer, calcium superphosphate increased the rate of azolla field colonization and promoted a thick, healthy dark-green mat of the fern. Response to ZnSO₄ was higher in the azolla-free sub-subplots. Application of ZnSO₄ corrected symptoms of Zn deficiency in rice but the addition of calcium superphosphate in the absence of Zn intensified the symptoms of Zn deficiency.     

Effects of Amendments on Growth and Uptake of Cd and Zn by Wetland Plants,Typha angustifolia and Colocasia esculenta from Contaminated Sediments

A pot study was conducted to compare the effects of amendments (CaHPO₄ and cow manure) on growth and uptake of Cd and Zn from contaminated sediments by two wetland plant species, Typha angustifolia and Colocasia esculenta. Contaminated sediments (Cd 33.2 mg kg^–1 and Zn 363 mg kg^–1) were collected from Mae Tao basin, Mae Sot district, Tak province, Thailand. The experiment consisted of 4 treatments: control (uncontaminated sediment), Cd/Zn, Cd/Zn + 5% CaHPO₄, and Cd/Zn + 10% cow manure. Plants were grown for 3 months in the greenhouse. The addition of CaHPO₄ resulted in the highest relative growth rate (RGR) and highest Cd accumulation in both T. angustifolia and C. esculenta while the lowest RGR was found in C. esculenta grown in the cow manure treatment. Both plant species had higher concentrations of metals (Cd, Zn) in their belowground parts. None of the amendments affected Zn accumulation. C. esculenta exhibited the highest uptake of both Cd and Zn. The results clearly demonstrated the phytoremediation potential of C. esculenta and the enhancement of this potential by CaHPO₄ amendment.     

Impact of ZnSO and ZnO Nanoparticles on Seed Germination and Seedling Growth of Lettuce

Micronutrient nanoparticles (NPs) are currently an option for chemical fertilization and biostimulation in crops. However, there is little information on the phytotoxic or biostimulatory effects of NPs at low concentrations of some elements, such as Zn. In this study, the effect of low concentrations of Zn oxide (ZnO) NPs on germination, growth variables, and nutritional attributes of lettuce (Lactuca sativa L.) was evaluated in comparison to Zn sulfate. Romaine lettuce seeds were treated with ZnSO₄^-- × 7H₂O and ZnO NPs at Zn molar concentrations of 1 × 10⁻³, 5 × 10⁻³, 1 × 10⁻⁴, 5 × 10⁻⁴, 1 × 10⁻⁵, 5 × 10⁻⁵, 1 × 10⁻⁶, and 5 × 10⁻⁶. The seeds treated with ZnSO₄⁻ at 5 × 10⁻⁶ registered the highest radicle length, 73% more than the control treatment. The seeds treated with ZnSO₄⁻ at 5 × 10⁻³ registered the lowest values, with 50% less than the control treatment. ZnO NPs at 5 × 10⁻⁶ significantly increased content of chlorophyll A and B and total phenolics. These results indicate the possible existence of a mechanism related to the intrinsic nanoparticle properties, especially at low concentrations.

     

Effects of elevated CO2 on plant growth and nutrient partitioning of rice (Oryza sativa L.) at rapid tillering and physiological maturity

Abstract

This work investigates the relationship between plant growth, grain yield, nutrient acquisition and partitioning in rice (Oryza sativa L.) under elevated CO₂. Plants were grown hydroponically in growth chambers with a 12-h photoperiod at either 370 or 700 µmol CO₂ mol^?1 concentration. Plant dry mass (DM), grain yield and macro- and micronutrient concentrations of vegetative organs and grains were determined. Elevated CO₂ increased biomass at tillering, and this was largely due to an increase in root mass by 160%. Elevated CO₂ had no effect on total nutrient uptake (N, P, K, Mg and Ca). However, nutrient partitioning among organs was significantly altered. N partitioning to leaf blades was significantly decreased, whereas the N partitioning into the leaf sheaths and roots was increased. Nutrient use efficiency of N, P, K, and Mg in all organs was significantly increased at elevated CO₂. At harvest maturity, grain yield was increased by 27% at elevated CO₂ while grain (protein) concentration was decreased by a similar magnitude (28%), suggesting that critical nutrient requirements for rice might need to be reassessed with global climate change.     

Compensation concentration as critical variable for regulating the flux of trace gases between soil and atmosphere

The flux of a trace gas between soil and atmosphere is usually the result of simultaneously operating production and consumption processes. The compensation concentration is the concentration at which the rate of production equals the rate of consumption so that the net flux between soil and atmosphere is zero. Production and uptake may be due to different processes, which are at least partially known for some of the trace gases, and which may be differently regulated. The direction and the magnitude of the flux between soil and atmosphere is a function of both the compensation concentration and the trace gas concentration in the ambient atmosphere. Compensation and/or ambient concentrations may fluctuate and thus may have a strong impact on the flux of CO, NO and NO₂, and to a smaller extent also on that of H₂. Compensation concentrations also exist for N₂O and OCS, but are too high to affect the flux under field conditions. Compensation concentrations have so far not been demonstrated for the flux of CH₄. However, the uptake of CH₄ by soil exhibits a threshold concentration below which no uptake occurs.Article invited in celebration of tenth anniversary ofBiogeochemistry.     

Oxytetracycline production by Streptomyces rimosus in solid-state fermentation of corncob

Corn-cob was used as a substrate in the production of oxytetracycline by Streptomyces rimosus TM-55 in a solidstate fermentation. Oxytetracycline was detected on day 4, and reached its maximum on day 8. Optimal conditions for oxytetracycline production were an initial pH of 5.2 to 6.3, an initial moisture content of 64% to 67%, supplementation with 20% (w/w) rice bran or 1.5% to 2.5% (w/w) (NH₄)₂SO₄ as sole N source, 1.0% (w/w) CaCO₃, 2% (w/w) MgSO₄.7H₂O, and 0.5% (w/w) KH₂PO₄, with incubation for 8 days at 25 to 30°C. Each g substrate produced 7 to 8 mg oxytetracycline.     

Biofortification and Bioavailability of Rice Grain Zinc as Affected by Different Forms of Foliar Zinc Fertilization

Background

Zinc (Zn) biofortification through foliar Zn application is an attractive strategy to reduce human Zn deficiency. However, little is known about the biofortification efficiency and bioavailability of rice grain from different forms of foliar Zn fertilizers.

Methodology/Principal Findings

Four different Zn forms were applied as a foliar treatment among three rice cultivars under field trial. Zinc bioavailability was assessed by in vitro digestion/Caco-2 cell model. Foliar Zn fertilization was an effective agronomic practice to promote grain Zn concentration and Zn bioavailability among three rice cultivars, especially, in case of Zn-amino acid and ZnSO₄. On average, Zn-amino acid and ZnSO₄ increased Zn concentration in polished rice up to 24.04% and 22.47%, respectively. On average, Zn-amino acid and ZnSO₄ increased Zn bioavailability in polished rice up to 68.37% and 64.43%, respectively. The effectiveness of foliar applied Zn-amino acid and ZnSO₄ were higher than Zn-EDTA and Zn-Citrate on improvement of Zn concentration, and reduction of phytic acid, as a results higher accumulation of bioavailable Zn in polished rice. Moreover, foliar Zn application could maintain grain yield, the protein and minerals (Fe and Ca) quality of the polished rice.

Conclusions

Foliar application of Zn in rice offers a practical and useful approach to improve bioavailable Zn in polished rice. According to current study, Zn-amino acid and ZnSO₄ are recommended as excellent foliar Zn forms to ongoing agronomic biofortification.     

Nanoporous CaCO3 Coatings Enabled Uniform Zn Stripping/Plating for Long‐Life Zinc Rechargeable Aqueous Batteries

Zn‐based batteries are safe, low cost, and environmentally friendly, as well as delivering the highest energy density of all aqueous battery systems. However, the application of Zn‐based batteries is being seriously hindered by the uneven electrostripping/electroplating of Zn on the anodes, which always leads to enlarged polarization (capacity fading) or even cell shorting (low cycling stability). How a porous nano‐CaCO₃ coating can guide uniform and position‐selected Zn stripping/plating on the nano‐CaCO₃‐layer/Zn foil interfaces is reported here. This Zn‐deposition‐guiding ability is mainly ascribed to the porous nature of the nano‐CaCO₃‐layer, since similar functionality (even though relatively inferior) is also found in Zn foils coated with porous acetylene black or nano‐SiO₂ layers. Furthermore, the potential application of this strategy is demonstrated in Zn|ZnSO₄+MnSO₄|CNT/MnO₂ rechargeable aqueous batteries. Compared with the ones with bare Zn anodes, the battery with a nano‐CaCO₃‐coated Zn anode delivers a 42.7% higher discharge capacity (177 vs 124 mAh g^?1 at 1 A g^?1) after 1000 cycles.     

Cultivar differences in leaf photosynthesis of rice bred in Japan

The grain yield of rice (Oryza sativa L.), as well as of other cereal crops, is limited to a large extent, by the supply of photosynthates produced during grain filling period. In this study, flag leaf photosynthesis (LPS) after heading was compared among 32 cultivars bred during the past century in Japan, to determine if the improvement of LPS has occurred with the breeding advance of high yielding cultivars. Measurement of LPS was made for 5 consecutive years in the paddy field, on the flag leaf of the main stem, at heading (LPS-0), and 2 weeks (LPS-2) and 4 weeks (LPS-4) after heading. LPS decreased with advance of leaf senescence from LPS-0 to LPS-2, and then to LPS-4. However, if nitrogen was top-dressed at the heading time, high LPS-2 was maintained, particularly in the newer cultivars. A significant positive correlation between LPS and the released year of cultivar was found at LPS-2, especially in the nitrogen top-dressed plot, but not at LPS-0 or LPS-4. Cultivar difference in LPS of the senescing leaves were not stable through the different years, whereas LPS-0 was stable over years, suggesting that the LPS in the senescent leaf is susceptible to the environmental variation due to the effects on leaf senescence. Cultivar difference in LPS at any stage was closely associated with mesophyll conductance to CO₂, and stomatal conductance was also associated with cultivar difference in such a high LPS as LPS-0 and nitrogen top-dressed LPS-2. Significant correlation between LPS and specific leaf weight was not observed at any stage of the flag leaf.Abbreviations CV coefficient of variation - g_m mesophyll conductance - g_s stomatal conductance - LPS apparent photosynthetic rate per unit leaf area (leaf photosynthesis) - LPS-0 LPS at heading - LPS-2 LPS at active grain filling - LPS-4 LPS at maturity of grain - NT non-top dressed plot - PPFD photosynthetic photon flux density - r_m mesophyll resistance - r_s stomatal diffusion resistance against CO₂ - r_s(H₂O) stomatal diffusion resistance against H₂O - RuBisCO ribulose-1,5-bisphosphate carboxylase/oxygenase - SLW specific leaf weight - TD nitrogen top-dressed plot     

Ammonium uptake by Chondrus crispus Stackhouse (Gigartinales,Rhodophyta) in culture

Cultivated Chondrus crispus was used in N-NH₄ uptake experiments in the laboratory. An elevation of temperature increased the apparent rate of uptake, especially up to 11 °C. Uptake in the dark was found to be 83 % of that in the light. The apparent uptake decreased with increasing internal N pool; rates were 26.5, 22.2 and 20.2 µg N g dry wt^–1 min^–1 for internal N pools of 2.7, 3.5 and 4.6%, respectively. Apparent uptake increased with the substrate N concentration. The resulting curve has two components: an active uptake and a diffusion component at high (> 5000 µg N L^–1) external N levels. Ks and V _max were calculated by deducting the diffusion component from the uptake curve: these were of 497 µg N L ^–1 and 14.4 µg N g dry wt^–1 min^–1. respectively, and reflect a low substrate affinity. This could be the result of 10 years of continuous culture of C. crispus. Uptake was similarly followed in the culture tanks and showed comparable results; nighttime would be the most appropriate time to supply nutrients.     

Test of soil extractants for their suitability in predicting Ca/Sr ratios in leaves and stems of sugar maple seedlings

Differential uptake and translocation of Ca and Sr in organisms have been reported, calling into question the use of Sr to track Ca cycling in the environment. We investigated the relationship between Ca/Sr ratios in soil extracts of various strengths (H₂O, NH₄Cl, and NH₄EDTA) and seedlings of sugar maple (Acer saccharum Marsh.) grown from natural regeneration on 37 sites. Our objectives were to determine if Ca/Sr ratios in soil extracts are correlated with those in sugar maple tissues, and what soil extractant best duplicate plant tissue Ca/Sr ratios. Leaves had higher Ca/Sr ratios than stems and the extractants did not produce equal Ca/Sr ratios: H₂O had the lowest Ca/Sr, and NH₄EDTA the highest. The relationships between soil extract Ca/Sr ratios and leaf and stem Ca/Sr ratios were significant and linear, but the slopes differed among extractants. The lowest slope (0.45) was observed for the water extract/leaves and the highest (2.15) for the NH₄EDTA extract/stem with discrimination factors ranging from 0.22 with NH₄EDTA to 1.59 for water. Leaf extracts were more strongly correlated with soil Ca/Sr than stem extracts (R ² of 0.57–0.7 vs. R ² of 0.45–0.6, respectively). These findings support the use of Ca/Sr ratios in plants to track their source of soil Ca, but they highlight the need to calibrate the relationships for the plant tissue and soil extractant used.