Calcium Availability Research Articles

Nutrient composition, starch microstructure and thermal properties, and in vitro availability of selected minerals of nixtamalized Philippine quality protein maize variety IPB Var 6 and the production of healthy loaf bread using nixtamalized corn–wheat flour blends

Corn is one of the most important food crops globally providing at least 30% of the food calories in developing countries. This study aimed to determine the nutritional content and starch properties of nixtamalized Philippine quality protein maize (QPM) variety and its potential as a flour substitute in loaf bread production. The nixtamalized Philippine QPM flour had a significant increase in moisture and calcium contents. In vitro availability of calcium, iron, and zinc was relatively lower and associated with phytate content. The developed loaf bread utilizing the optimum nixtamalized corn–wheat flour blend had improved nutritional value and had no significant difference in sensory characteristics compared with the control loaf bread made from wheat flour. The use of nixtamalized IPB Var 6 flour as an ingredient in loaf bread making improved its crude fiber, calcium, and iron levels and can be a nutritious potential substitute ingredient for baked products. Novelty impact statement The process of nixtamalization can improve the nutritional content of corn and has the potential to improve the quality of a food staple such as loaf bread. Incorporating nixtamalized QPM flour into loaf bread resulted in increased fiber, protein, and calcium contents, and it was also acceptable to the consumers in terms of sensory characteristics and general acceptability. Data on the nutritional content and availability of selected minerals of nixtamalized QPM flour can be used as basis for future researches to optimize the method to maximize its potential effects in the improvement of the nutritional value of QPM, thereby providing a healthier alternative staple for the consumers.

Nutrient management in salt affected soils for sustainable crop production

ABSTRACT Soil salinity and sodicity are the global problems and pose a serious threat to agriculture sustainability. The distribution of salt affected soils exist mostly under arid and semi-arid climates where rainfall is inadequate to leach salts from/out of the root zone. These soils have poor fertility, generally with low availability of nitrogen, calcium, zinc, iron and manganese. Therefore, judicious nutrients management on the principle of INM in these soils is as important as their reclamation. In these soils, crops respond differently to applied nutrients due to their diverse chemical composition impacting precipitation-dissolution reactions and adsorption-desorption kinetics. Nutrient transformation and loss mechanisms of applied nutrients are also affected by the magnitude of soil salinity and sodicity. The paper aims at discussing efficient nutrient management in salt affected soils for sustainable crop production.

OXALATE-CALCIUM RATIOS OF COMMON CEREALS CONSUMED IN EASTERN NIGERIA

The importance of Oxalate content of an individual plant in limiting total dietary calcium availability is of significance when the ratio oxalic to calcium (oxa:cal.) is greater than one. Food with oxal: cal ratio greater than two, have no utilizable calcium and contain excess oxalate while foodstuff with oxal:cal. of about one provides little calcium but do not inhibit the utilization of calcium provided by other products. The study analysed three commonly consumed cereals of oxalic acids and calcium by rigorous classical quantitative method of precipitation/titration and atomic absorption spectrophotometry, respectively. The result should oxal:cal. ratios>1 for all the cereals indicating that the cereals have no utilizable calcium, thus contain excess oxalate which not only complex the calcium contained in the food but also that derived from other food sources eaten together with it. This can result in deficiency of such an essential mineral as calcium in the body and even render the body prone to bone diseases and possibility of developing kidney stones due to calcium oxalate formation (calcium oxalate being the most common component of kidney stone).

Low soil fertility impairs cotton yield in the early years of no-tillage over degraded pasture

No-till is one of the main techniques for soil conservation and the mitigation of negative climate impacts. The objective of this study was to evaluate soil fertility, nutrition, cotton yield, and the fiber quality of cotton under different soil tillage systems. The study was carried out in the field in the 2017/2018 and 2018/2019 crop seasons. The experimental design was a complete randomized block with five replications. No-till (NT) and conventional tillage (CT) farming were used in the 2017/2018 and 2018/2019 crop seasons. NT resulted in higher soil bulk density (0-35 cm) than CT. When compared to NT, the availability of calcium, magnesium, potassium, phosphorous, cation exchange capacity, base saturation, zinc, and pH were 120, 90, 43, 135, 49, 110, 41, and 8% higher in areas with CT, respectively. Boron content was 14% higher with NT (0-20 cm) than CT. Leaf concentrations of nitrogen, Ca, and Mg were higher with CT in both seasons, and B was higher with NT. However, in the second season (2018/2019), leaf concentrations of P, K, and sulfur were higher with NT than CT. When compared to NT, fiber yields were 75% and 32% higher with CT in the 2017/2018 and 2018/2019 seasons, respectively; this corresponded to a difference of 757 and 420 kg ha-1 of fiber. However, no effects on fiber quality parameters were observed. NT limits the availability of most nutrients in soil in the early years of cotton cultivation; this reduces plant nutrition and fiber yield but has no effect on quality.

Landscape acidification has trophic-mediated effects on Ovenbirds (Seiurus aurocapilla)

Acid deposition from fossil fuel combustion caused calcium depletion in eastern North America during the 20th century, and calcium is a critical resource for birds during both the egg laying and nesting periods. The effects of acid deposition on animals have largely acted through trophic relationships, with reduced calcium availability in prey possibly being a limiting factor for forest songbirds. Following 21 years of experimental whole-watershed acidification at the Bear Brook Watershed in Maine, we investigated Ovenbird (Seiurus aurocapilla) territory size and potential prey (leaf litter arthropod) abundance, assemblage, and calcium concentration during one breeding season. We delineated and estimated the area of 8 Ovenbird territories in an acidified and a control watershed, but found that territory size did not differ between watersheds. However, while calcium concentrations of potential prey also did not differ between watersheds, territory size decreased as calcium concentrations of potential prey increased, regardless of watershed. Our results suggest that calcium limitation can be a determinant of territory size in some landscapes, and this provides further support to importance of the role of calcium in the lives of passerines.

The hydration of fast setting spray binder versus (aluminum sulfate) accelerated OPC

The (early) hydration mechanisms of two different binder systems used for shotcrete were investigated: the so far almost unexplored low sulfate binder (spray binder), used in the field of dry-mix shotcrete; and ordinary Portland cement, accelerated by aluminum sulfate, widely used for wet-mix shotcrete. The basis for the fast setting of the spray binder is the rapid dissolution of C3A and the subsequent formation of flaky CO3-AFm phases. Thereby induced high aluminum concentrations in the pore solution lead to a blockage of alite dissolution during the first hours of hydration. At later stages, higher amounts of portlandite are formed in the dry-mix, compared to the wet-mix system. The lower calcium availability for portlandite formation in the wet-mix system is explained by an enhanced formation of C–A–S–H phases with a higher Ca:Si ratio. Additionally, wet-mix systems show lower porosity and higher compressive strength after 1 d of hydration and beyond.Graphical abstract

Calcium supply of adolescent girls and sucrose-lactose imbalance in nutrition

Ensuring calcium homeostasis is a complex metabolic process. Its impairment, especially in childhood and adolescence, is manifested by numerous changes in the functioning of most organism systems, which are difficult to restore in later periods of life. The goal of this research was to study the characteristics of calcium and disaccharide consumption by adolescent girls and to identify the physiological and biochemical mechanisms of the influence of sucrose-lactose imbalance on calcium supply. Material and methods. A multicenter cross-sectional study was conducted. In this study, teen girls aged 11-14 years without an established diagnosis of lactase insufficiency, living in urban areas, took part on a voluntary basis in the autumn period (n=136, of which 40 were Adyghes, 45 Chechens, other nationalities, mainly Russian - 51). Three-day diets were analyzed, physiological manifestations of calcium deficiency and taste sensitivity to sucrose were evaluated, the CFRt indices (sum of carious, filled and removed permanent teeth) were calculated, and calciuria was studied according to the Sulkovich test in the morning portion of urine. Results. It has been established that the consumption of milk and dairy products by adolescents does not meet physiological standards, which leads to the 2.2 fold decrease in their contribution to calcium provision and to the risk of insufficient milk calcium consumption (RIC Camilk). In the nutrient status of adolescents, regardless of nationality and region of residence, the syndrome of sucrose-lactose imbalance (SLI) was revealed: the 1.4 fold excess of sucrose consumption and 2.1 fold decrease in lactose consumption compared with optimal values. For further analysis, the children were divided into groups, variable in the combination of RIC Camilk and SLI of varying severity: group 1LL - low RIC Camilk and low SLI; group 2LM - low RIC Camilk and moderate SLI, group 3MM - moderate RIC Camilk and moderate SLI; group 4MH - moderate RIC Camilk and high SLI, and group 5HH - high RIC Camilk and high SLI. The analysis of the data showed that higher levels of SLI (groups 2LM and 4MH) at the same levels of RIC Camilk (groups 1LL and 3MM) reduce calcium bioavailability, impair calcium metabolism and increase the prevalence and severity of physiological manifestations of calcium insufficiency by 1.5 and 1.4 fold, and dental diseases estimated using the CFRt index - by 1.2 and 1.6 fold. The prevalence of low taste sensitivity to sucrose in 5HH group was 1.4 fold higher compared to 4MH group. Against the background of excessive consumption of added sugars, calciuria didn't significantly differ in groups with different levels of calcium intake. Conclusion. Based on the assessment of nutrition, teen girls showed SLI syndrome and high RIC Camilk. SLI reduces calcium availability, increasing the prevalence of calcium insufficiency symptoms in adolescent girls with moderate and high RIC Camilk.

Integrated View on the Role of Vitamin D Actions on Bone and Growth Plate Homeostasis.

ABSTRACT1,25(OH)2D3, the biologically active form of vitamin D3, is a major regulator of mineral and bone homeostasis and exerts its actions through binding to the vitamin D receptor (VDR), a ligand‐activated transcription factor that can directly modulate gene expression in vitamin D‐target tissues such as the intestine, kidney, and bone. Inactivating VDR mutations or vitamin D deficiency during development results in rickets, hypocalcemia, secondary hyperparathyroidism, and hypophosphatemia, pointing to the critical role of 1,25(OH)2D3‐induced signaling in the maintenance of mineral homeostasis and skeletal health. 1,25(OH)2D3 is a potent stimulator of VDR‐mediated intestinal calcium absorption, thus increasing the availability of calcium required for proper bone mineralization. However, when intestinal calcium absorption is impaired, renal calcium reabsorption is increased and calcium is mobilized from the bone to preserve normocalcemia. Multiple cell types within bone express the VDR, thereby allowing 1,25(OH)2D3 to directly affect bone homeostasis. In this review, we will discuss different transgenic mouse models with either Vdr deletion or overexpression in chondrocytes, osteoblasts, osteocytes, or osteoclasts to delineate the direct effects of 1,25(OH)2D3 on bone homeostasis. We will address the bone cell type–specific effects of 1,25(OH)2D3 in conditions of a positive calcium balance, where the amount of (re)absorbed calcium equals or exceeds fecal and renal calcium losses, as well as during a negative calcium balance, due to selective Vdr knockdown in the intestine or triggered by a low calcium diet. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Chemical interactions among caseins during rennet coagulation of milk

Rennet milk curds were prepared under 4 different temperature and acidity conditions. The development of different types of inter-protein chemical bonds (disulfide, hydrophobic, electrostatic, hydrogen, and calcium bridges) was monitored for 60 min after curd cutting. Hydrophobic inter-protein interactions originally present in casein micelles in milk were substituted by electrostatic, hydrogen, and calcium bonds throughout the curd curing period. Disulfide bonds were not disturbed by the experimental conditions employed in the study, remaining at a constant level in all studied treatments. Acidification of curds increased the availability of soluble ionic calcium, increasing the relative proportion of calcium bridges at the expense of electrostatic-hydrogen bonds. Although pH defined the nature of the interactions established among proteins in curd, temperature modified the rate at which such bonds were formed.

The Rhizobium and calcium fertilizer application to peanut plant in dry land

One of the main problems of peanut planting in dry land is a lack of nitrogen and calcium availability. Efforts to increase the nitrogen and calcium availability for peanut farming in dry land is needed and one possible approach is by application of Rhizobium and calcium fertilizers. This research was conducted to determine the effect of the application of Rhizobium (Nodulin) and calcium fertilizers on growth and yield of peanut plants in dry land. Two experiments were conducted, one in a greenhouse using a completely randomized design and another experiment in the field using a randomized block design. The treatments were with the application of Nodulin, without Nodulin, with calcium fertilizer and without calcium fertilizer. The results showed that the application of calcium and Nodulin was able to increase the number of root nodules and peanut growth. Nodulin and calcium fertilizers increased the dry pod weight of 2.177 g per 6 m2 or 3.7 tons.ha-1. The application of Nodulin and calcium was also able to increase the nitrogen and calcium content of leaf tissue up to 18.9% and 20.9%, respectively.

Increased myofilament calcium sensitivity is associated with decreased cardiac troponin I phosphorylation in the diabetic rat heart.

What is the central question of this study? In Zucker Diabetic Fatty rats, does cardiomyocyte myofilament function change through the time course of diabetes and what are the mechanisms behind alterations in calcium sensitivity? What is the main finding and its importance? Zucker Diabetic Fatty rats had increased myofilament calcium sensitivity and reduced phosphorylation at cardiac troponin I without differential O-GlcNAcylation. The diabetic heart has impaired systolic and diastolic function independent of other comorbidities. The availability of calcium is altered, but does not fully explain the cardiac dysfunction seen in the diabetic heart. Thus, we explored if myofilament calcium regulation of contraction is altered while also categorizing the levels of phosphorylation and O-GlcNAcylation in the myofilaments. Calcium sensitivity (pCa50 ) was measured in Zucker Diabetic Fatty (ZDF) rat hearts at the initial stage of diabetes (12weeks old) and after 8weeks of uncontrolled hyperglycaemia (20weeks old) and in non-diabetic (nDM) littermates. Skinned cardiomyocytes were connected to a capacitance-gauge transducer and a torque motor to measure force as a function of pCa (-log[Ca2+ ]). Fluorescent gel stain (ProQ Diamond) was used to measure total protein phosphorylation. Specific phospho-sites on cardiac troponin I (cTnI) and total cTnI O-GlcNAcylation were quantified using immunoblot. pCa50 was greater in both 12- and 20-week-old diabetic (DM) rats compared to nDM littermates (P=0.0001). Total cTnI and cTnI serine 23/24 phosphorylation were lower in DM rats (P=0.003andP=0.01, respectively), but cTnI O-GlcNAc protein expression was not different. pCa50 is greater in DM rats and corresponds with an overall reduction in cTnI phosphorylation. These findings indicate that myofilament calcium sensitivity is increased and cTnI phosphorylation is reduced in ZDF DM rats and suggests an important role for cTnI phosphorylation in the DM heart.

On-site urine treatment combining Ca(OH)2 dissolution and dehydration with ambient air

We present the results of three field tests and three laboratory tests of a new physical-chemical urine treatment system, which can recover all nutrients, while pathogens are inactivated. The system consists of two steps. In the first reactor, biological processes including urea hydrolysis are prevented by mixing fresh urine with calcium hydroxide (Ca(OH)2). Due to the high pH value and the high availability of calcium, phosphate can be recovered by precipitation. The high pH value also fosters the inactivation of microorganisms, including pathogens. In the second reactor, water is evaporated at low energy consumption by blowing unheated ambient air over the stabilized urine. Stabilization in the first reactor was successful in all field and laboratory tests. The pH value remained between 12 and 13, except for short dips due to shortages of Ca(OH)2. Nearly all phosphorus (92-96%) precipitated and could be recovered as calcium phosphate in the first reactor, while nitrogen and potassium overflowed with the urine into the evaporation reactor. The efficiency of the second treatment step was very different for field and laboratory experiments and depended on the duration of the experiment. During a four-day laboratory test, nitrogen recovery was 98%. In contrast, nitrogen recovery was only around 20% in the long-term field experiments. The high nitrogen losses occurred, because biological urea hydrolysis was not inhibited anymore, when the pH value in the second reactor decreased due to the dissolution of high amounts of carbon dioxide from the ambient air. Potassium was not subject to any significant loss, and the measured recovery in the solid evaporation product was 98%. Evaporation rates ranged between 50 g m−2 h−1 (RH = 82±13%, T = 12±6°C) and 130 g m−2 h−1 (RH = 60±19%, T = 24±5°C) in the three field tests. Apart from some disturbances due to low supply of Ca(OH)2, the urine module functioned without any substantial failures and was simple to maintain. The minimum consumption of Ca(OH)2 at full capacity was 6 g·L−1 urine and the electricity demand was 150 Wh kg−1 water evaporated from urine, resulting in operational costs of 0.05 EUR pers−1 d−1.

Zinc-substituted hydroxyapatite produced from calcium precursor derived from eggshells

The availability of natural calcium derived from biowaste materials is an inexpensive alternative to commercial calcium reagents used to produce calcium phosphate bioceramics. This approach is more ecofriendly, cost effective and sustainable owing to its abundant availability. In this study, zinc-substituted hydroxyapatite (ZnHA-Es) was synthesised using calcium precursor derived from eggshells through precipitation method. Zn concentration was varied from 1 mol% to 5 mol% during the synthesis, and the derived powders were calcined at 700 °C in air atmosphere. XRD analysis revealed that ZnHA-Es powders were highly crystalline and comprised biphasic mixtures of HA as the major phase and β-tricalcium phosphate as the minor phase. FTIR examination indicated that all ZnHA-Es samples had a similar structure to pure HA as evidenced by the presence of frequency bands corresponding to phosphate, carbonate and hydroxyl functional groups. The disappearance of vibrational bands of carbonate groups became more apparent with increased Zn concentration. Microstructure analysis revealed that the derived nanostructured particles were spherical (approximately 40–100 nm in diameter) regardless of Zn substitution.

Promoting adaptive bone formation to prevent stress fractures in military personnel

ABSTRACT Mechanical loading leads to adaptive bone formation – the formation of new bone on existing skeletal surfaces – which increases bone strength and fatigue resistance. The same mechanical loading can also cause microdamage to bone and development of a stress fracture through targeted remodelling. Stress fractures are common in military recruits and cause significant morbidity, lost training time, and discharge from military service. This narrative review proposes strategies to promote adaptive bone formation as a novel approach to mitigate the risk of stress fracture injuries during arduous military training. Exercise that is unaccustomed, dynamic, high-impact, multidirectional, intermittent, and includes extended rest periods to restore bone mechanosensitivity, is most osteogenic. New bone formation can take up to one year to mineralize, and so new exercise training programmes should be initiated well in advance of military activities with high risk of stress fracture. Bone mechanosensitivity is highest in adolescence, before puberty, and so increasing physical activity in youth is likely to protect skeletal health in later life, including for those in the military. Recent data show that adaptive bone formation takes place during initial military training. Adaptive bone formation can also be supported with adequate sleep, vitamin D, calcium, and energy availability. Further evidence on how strategies to promote adaptive bone formation affect stress fracture risk are required. Adaptive bone formation can be optimized with a range of training and nutritional strategies to help create a resilient skeleton, which may protect against stress fracture throughout military service.

Effect of Phosphorus and Calcium Availability as Influenced by Manure, Rock Phosphate, and Dolomite on Soybean Yield

Soybean (Glycine max) contains nutritional components such as high protein which support health needs and improve the quality of life. However, to achieve this standard, soybean productivity needs to be increased. Manure, rock phosphate, and dolomite are potential alternatives in improving soybean production. This study aims to examine phosphorus and calcium availability as Influenced by manure, rock phosphate, and dolomite to increase soybean yield. The experiment consisted of six treatments groups with four replications using a completely randomized block design. Furthermore, the groups include T0 (Control), T1 (5 t ha− 1 manure + 2.5 t ha−1 rock phosphate), T2 (5 t ha−1 manure + 5 t ha−1 rock phosphate), T3 (5 t ha− 1 + 2.5 t ha−1 dolomite), T4 (5 t ha−1 manure + 5 t ha−1 dolomite), and T5 (5 t ha−1 manure + 5 t ha− 1 rock phosphate + 5 t ha−1 dolomite). The results showed that phosphorus and calcium availability were significantly influenced by manure, rock phosphate, dolomite, and simultaneously increase soybean yield. Also, the best number of filled pods, 100-seed weight and yield were obtained with the application of 5 t ha−1 manure + 5 t ha−1 rock phosphate + 5 t ha−1 dolomite (20 pods plot−1, 0.62 g, and 260.89 g plot−1 respectively). Therefore, based on the results, phosphorus and calcium obtained from manure, rock phosphate and dolomite potentially increase soybean yield.

Thomas H. Kunz

Thomas H. Kunz

Influence of calcium channel modulators on the production of serotonin, gentisic acid, and a few other biosynthetically related phenolic metabolites in seedling leaves of salt tolerant rice variety Nonabokra

ABSTRACT Rice, a most salt-sensitive cereal plant, adopts diverse pathways to withstand sodium chloride–induced salinity-related adversities. During the present study, attempt was made to understand the role of calcium on metabolite profile of the leaves of salt tolerant rice seedlings of variety of Nonabokra under sodium chloride induced salinity, by Gas Chromatography–Mass Spectrometry-based metabolomics approach. Calcium availability in the seedlings was reduced or enhanced applying inhibitors (vanadyl sulfate, lanthanum chloride, and verapamil) or promoters of calcium influx (calcimycin also known as calcium ionophore A23187) in the sodium chloride (100 mM) supplemented growth medium. Growth medium of ten-day-old seedlings was replaced by sodium chloride supplemented hydroponic solution with promotor or inhibitors of calcium channel. Fifteen days old seedlings were harvested. It was observed that depletion of calcium availability increased the level of serotonin and gentisic acid whereas increased calcium level decreased these metabolites. It was concluded from the results that production of the signaling molecules serotonin and gentisic acids was elevated in calcium-deficient seedlings under salt stress the condition that was considered as control during the experiment. The two signaling molecules probably help this tolerant rice variety Nonabokra to withstand the salt-induced adversities.

Can use of substrates affect water quality in aquatic organism culture?

The choice of suitable substrates has received special attention in aquaculture and fishkeeping ventures. The aim of this study was to evaluate the influence of different substrates on water quality and the development of lambari fish (Astyanax bimaculatus) and freshwater shrimp (Macrobrachium potiuna). Two experiments were performed sequentially, one with fish and the other with shrimp. In both experiments, three different substrates were evaluated (shell gravel, river gravel, and dolomite), and the control was without any substrate. The water parameters evaluated were as follows: dissolved oxygen, saturation, oxide-reduction potential, temperature, pH, alkalinity, conductivity, ammonia, nitrite, nitrate, and phosphorus. It was observed that both dolomite and shell gravel interfered with the parameters that are related to the acid-base balance of the water and the availability of calcium and magnesium. The productive performance of lambari fish was not affected considering the different substrates evaluated; however, the productive performance of freshwater shrimp was lower in the absence of substrates in relation to the other treatments.

In situ evaluation of desensitizing toothpastes for protecting against erosive tooth wear and its characterization

This five-phase, single-blind, crossover in situ trial evaluated the effects of desensitizing or anti-erosive toothpastes on dentin erosive wear and tubule occlusion. Some characteristics such as relative dentin abrasivity (RDA), viscosity (V), cytotoxicity, and fluoride and calcium (Ca) availability of the toothpastes were also tested. Samples were positioned on removable intraoral appliances from 15 volunteers (n=4), according to the groups, C-control (0 ppm fluoride), F-sodium monofluorophosphate (MFP), A-MFP and arginine+calcium carbonate, CSP-calcium sodium phosphosilicate, and CS-MFP and calcium silicate+sodium phosphate. Erosion-abrasion cycling was performed (1% citric acid, 2min, 6×/day; toothbrushing, 5s, 2×/day). Surface loss (SL) was evaluated by optical profilometry. Environmental scanning electron microscopy images (ESEM) counted the number of open dentin tubules (ODTs). Data were statistically analyzed (α=0.05). There were no significant differences in SL among groups (p=0.468). The ODT for CSP, CS, and A groups were significantly lower than the control. CSP and CS presented significantly less ODT than F, but they did not significantly differ from A. F and CS were more abrasive than all the other toothpastes; CSP was more abrasive than A, and C was the least abrasive. CSP presented higher V (p<0.05). All toothpastes presented lower cell viability than the control without toothpaste exposure. F and A presented significantly higher values of F- (p<0.05). All fluoride toothpastes had similar amount of Ca, differing from the control (p<0.05). Although the toothpastes caused similar degree of erosive wear, CSP and CS were able to occlude the dentin tubules. Desensitizing toothpastes containing calcium, sodium, phosphate, and silicate could be a suitable option for treating dentin hypersensitivity.

Ectomycorrhizal symbioses increase soil calcium availability and water use efficiency of Quercus acutissima seedlings under drought stress

Ectomycorrhizal fungi (EMF) can enhance drought resistance of host plants by increasing nutrient and water absorption. Calcium (Ca) plays a central role in drought stress adaptation, yet it remains unclear how EMF influence Ca uptake of plants under drought stress. We carried out a pot experiment in which Quercus acutissima seedlings were inoculated with or without the ectomycorrhizal (EM) fungus Xerocomus chrysenteron under control and water stress soil moisture conditions in order to investigate how soil Ca availability and plant Ca uptake are modulated by EMF and how this may contribute to drought resistance of the seedlings. We found that soil water-extractable Ca was significantly reduced by drought in non-ectomycorrhizal treatment, while EM treatment significantly increased soil Ca availability and Ca uptake of Quercus acutissima seedlings under drought conditions. Furthermore, seedling water use efficiency (WUE) was positively correlated with soil Ca availability and plant Ca content. Calcium uptake promotion seems to be involved in the mechanisms of drought tolerance enhancement by EMF.