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Mycorrhizal Fungi and Water Use

Dr. Efren Cazares – MycoRoots

Consulting to verify statements regarding mycorrhizal fungi and water use™.

The objective of this consulting was to read and examine mycorrhizal research papers published referee journals to determine the existent evidence that support the statements that mycorrhizal fungi reduce watering needs. The statements to verify were that mycorrhizal plants use up to 30% less water. These research studies were published from 1981-2006 from a wide range of conditions, plants and geographies. All papers presented sections on material and methods including experimental design, results and discussions. The studies were performed in diverse environments that range from complete sterile systems, to greenhouse and nurseries to agricultural soils. The arbuscular mycorrhizal fungal species used were: Acaulospora scrobiculata, Glomus intraradices, G. deserticola, G. clarum, G. mosseae, G. monosporum, G. fasciculatum, G. etunicatum, G. caledonium, G. occultum, G. aggregatum, G.versiforme, and G. macrocarpum.


Auge, R. M., Kurt A. Schekel and R.L. Wample. 1987. Leaf water and carbohydrate status of VA mycorrhizal rose exposed to drought stress. Plant and Soil 99:291-302.

This paper looked at the impact of drought and P nutrition on shoot water relation, carbohydrate and chlorophyll levels of VA mycorrhizal on rose. The mycorrhizal fungi used were Glomus intraradices and Glomus deserticola. Regardless of phosphorus (P) fertilization, leaf and osmotic and bulk water potentials were higher in mycorrhizal than nonmycorrhizal plants. Leaf starch, chlorophyll and water contents were higher in G. intraradices-colonized plants than in the high-phosphorus nonmycorrhizal plants, while fructose, glucose and other carbohydrates were lower. Level of P fertilization had no effect on water relations or soluble carbohydrate content of nonmycorrhizal roses. The water status of water-stressed rose was improved more by G. intraradices (leaf diffusive conductance 55%, leaf water status 20%) and than by G. deserticola. Under dry soil conditions, the influence of the fungus became more pronounced than under moist conditions, at least in the case of the high-P G. intraradices-colonized roses. The root and plant P content increased with increased P fertilization in mycorrhizal roses, without producing effect on most water status parameters.


Al-Karaki, G.N. 1998. Benefit, cost and water-use efficiency of arbuscular mycorrhizal durum wheat grown under drought stress. Mycorrhiza 8:41-45.

This study determined the effects of arbuscular mycorrhizal fungal (AMF) inoculation on growth, benefit/cost and water-use efficiency (grams dry matter produced per kilogram water evapotranspired) in two wheat genotypes (drought sensitive and drought tolerant) under water-stressed and well-watered conditions. Shoot and root dry matter and root AMF colonization were higher for well watered than for water-stressed plants. The mycorrhizal plants were more water-use efficient than nonmycorrhizal plants. Shoot Dry matter differences between mycorrhizal and nonmycorrhizal plants represent the benefit derived by plants from Arbuscular mycorrhizal fungal -root associations. The mycorrhizal plants used less water to produce one unit of shoot of Dry matter (WUE-Water Use Efficiency) than nonmycorrhizal plants, but water-stressed and well-watered plants did not differ in Water Use Efficiency. Also, these plants had higher shoot and root dry matter than nonmycorrhizal plants regardless of water stress level. AMF colonization increased total P uptake by both genotypes regardless of water-stress level. This likely occurred because mycorrhizal plants had enhanced root growth and thus a greater P absorption surface area. Enhanced growth effects on mycorrhizal plants have been attributed to improved water relations resulting from enhanced P nutrition. The calculated benefit/cost values of arbuscular mycorrhizal fungi on host plant dry matter were higher for wheat grown under water-stressed than under well-watered conditions.


Al-Karaki, G.N. and R. B. Clark. 1998. Growth, mineral acquisition, and water use by mycorrhizal wheat grown under water stress. Journal of Plant Nutrition 21:263-276.

This study determined effects of water stress vs. no water stress and the arbuscular mycorrhizal (AM) fungi Glomus monosporus on growth, acquisition of phosphorus (P), zinc (Zn), copper (Cu), manganese (Mn), and iron (Fe), and water use in two wheat cultivars exhibiting differences in resistance to water stressed (WS). Shoot and root dry matter, leaf areas, total root length and root colonization with AM for plants grown under non-WS were higher than for plants grown under WS. Much of the reduction in dry matter was Overcome by AM plants grown under WS. Nutrients contents were greater under WS than under non-WS conditions. The AM plants had higher water efficiency values than non-AM plants when grown under WS. Their results of this study indicated that AM plants had greater tolerance to drought stress than non-

AM plants.


Al-Karaki, G.N. and R. B. Clark. 1999. Varied rates of mycorrhizal inoculums on growth and nutrient acquisition by barley grown with drought stress. Journal of Plant Nutrition 22:1775-1784.

The objective of this research was to determine effects of varied rates of arbuscular mycorrhizal fungi (AMF) inoculums on plant growth and acquisition of phosphorus (P), zinc (Zn), copper ( Cu), and manganese (Mn) by barley grown with and without drought stress. Root AMF colonization increased as inoculum rate increased in plants grown with water stress (WS) and non-water stressed (NWS). Leaf area and shoot, root dry matter, and plant contents of P, Zn, Cu and Mn increased as inoculum rate increased up to 240 spores of Glomus mosseae per 100 g dry soil regardless of soil moisture. The response of barley to different rates of AMF inoculum depended on soil moisture.


Al-Karaki, G.N., B. McMichael and John Zak. 2004. Field response of wheat to arbuscular mycorrhizal fungi and drought stress. Mycorrhiza14:263-269.

This study was to determine the effects of arbuscular mycorrhizal (AM) fungi inoculation on growth, grain yield and mineral acquisition of two winter wheat cultivars grown in the field under well-watered and water-stressed conditions. Water management treatments were 1) water-stressed (WS) plants grown under rainfed` conditions with 50 mm irrigation applied at planting, and 2) well-watered (WW) plants grown under rainfed conditions with irrigation scheduled to prevent symptoms of water stress. The total seasonal irrigation for the WW treatment was 408.5 mm. Therefore, the water stress treatment was equivalent to 72% less water than well water treatment. Mycorrhizal colonization was higher in well-watered plants colonized with AM fungi than water-stressed plants. Biomass and grain yields were higher in mycorrhizal than nonmycorrhizal plots irrespective of soil moisture, and G. eutunicatum inoculated plants generally had higher biomass and grain yields than those colonized by G. mosseae under either soil moisture condition. The mycorrhizal plants had higher shoot P and Fe concentration than nonmycorrhizal plants at all samplings regardless of soil moisture conditions. Enhanced plant growth and yield following AM fungal inoculation was related to improved uptake of P and Cu, especially under WS conditions. Mycorrhizal fungi may improve nutrient uptake by increasing the exploration of the soil pore space. The improved growth, yield and nutrient uptake in wheat plants reported here demonstrate the potential of mycorrhizal inoculation to reduce the effects of drought stress on wheat grown under field conditions in semiarid areas of the world.


Bethlenfalvay, G.J. M.S. Brown, R.N. Ames and R.S. Thomas. 1988. Effects of drought on host and endophyte development in mycorrhizal soybeans in relation to water use and phosphate uptake. Physiologia plantarum 72:565-571.

The aim of this study was to test the hypothesis of P as the major factor in VAM response to drought, and to determine the relationship between unavailable soil water and the response of the host plant to colonization by VAM fungi under drought stress. They found that the dry weights of VAM plants were greater at severe stress and smaller at no stress than those of non-VAM plants. Colonization of roots by G. mosseae did not vary with stress, but the biomass and length of the extraradical mycelium was greater in severely stressed than in non-stressed plants. Growth enhancement of VAM plants relative to P-fertilized non-VAM plants under severe stress was attributed to increased uptake of water as well as to more efficient P uptake. The ability of VAM plants to deplete soil water to a greater extent than non-VAM plants suggests lower permanent wilting potentials for the former.


Borkowska, B. 2002. Growth and photosynthetic activity of micropropagated strawberry plants inoculated with endomycorrhizal fungi (AMF) and growing under drought stress. Acta Physiologiae Plantarum 24:365-370.

This study found that mycorrhization strongly affected growth and tolerance to water deficiency of the plants cultivated in greenhouse. Mycorrhizal plants showed higher biomass accumulation (crowns and roots) and larger leaf area. The mycorrhizal plants fully recovered their photosynthetic activity when watering was restored. Their results suggest positive role of AMF in protecting photochemical systems against water deficiency.


Amico, J.D., A. Torrecillas, P. Rodrigiez, A. Morte and M.J. Sanchez-Blanco. 2002. Responses of tomato plants associated with the arbuscular mycorrhizal fungus Glomus clarum during drought and recovery. Journal of Agricultural Science 138:387-393.

This study tested whether Glomus clarum could enhance tomato plant growth and improve the water relations affecting the ability of the plant to extract water from the soil under well watered and waterstressed conditions, and to examine the ability of water-stressed tomato plants to recover. They concluded that under the growth conditions used in this study, and in spite of a relatively low level of root colonization, mycorrhizal symbiosis had a beneficial effect on tomato plant water status, enhancing water uptake by improving root hydraulic conductivity and increasing leaf conductance and photosynthetic activity.


Fidelibus M.W., C.A. Martin and J.C. Stutz. 2001. Geographic isolates of Glomus increase root growth and whole-plant transpiration of Citrus seedlings grown with high phosphorus. Mycorrhiza 10:231-236.

This study tested the hypothesis that growth and water-use characteristic of AM plants would differ from those of non-AM plants that were well supplied with P. They used AM fungal isolates of different geographic origins, therefore they also tested that inoculation of citrus seedlings with Glomus isolates from arid, semi-arid or mesic areas would result in different patterns of plant growth and water use. AM plants and non-AM plants had similar shoot size (dry weight and canopy area), but all AM fungus treatments stimulated root growth (dry weight and length). Leaf P concentration were 12-56% higher in AM plants than non-AM plants. Enhanced root growth was positively correlated with leaf concentration. In general, AM plants had greater whole-plant transpiration than non-AM plants under well-watered conditions, under mild water stress and during recovery from moderate and severe soil drying. This suggests a faster recovery from moisture stress by AM plants. AM plants had lower leaf conductance than non-AM plants when exposed to severe soil drying. Although the greatest differences were between AM and non-AM plants, plants treated with Glomus isolates differed in colonization level, leaf P concentration, root length, transpiration flux and leaf conductance. Also, they suggested that Glomus isolates that increase root growth and whole-plant transpiration might improve the field performance if young citrus rootstock and mitigate against desiccation after soil drying by amplifying the potential for root exploration of soil for water.


Hardie, K. and L. Leyton. 1981. The influence of vesicular-arbuscular mycorrhizal on growth and water relations of red clover. I. In phosphate deficient soil. New Phytologist 89:599-608.

This study found that VA mycorrhizal colonization of red clover grown in phosphate deficient soils enhanced the concentration of P in the tissues, stimulated growth of root and shoot but reduced the root/shoot ratio. Addition of phosphate to well below the optimum level also stimulated growth and enhanced P status of non-mycorrhizal plants, but their yields and P concentrations were much smaller than those of mycorrhizal plants and their root/shoot ratios were unaffected. The hydraulic conductivities of the root systems were much higher in mycorrhizal than non-mycorrhizal plants. The conductivities of the mycorrhizal roots were still two to three times higher, suggesting that this was mainly due to hyphal growth in the soil. Mycorrhizal plants were able to extract soil moisture down to lower water potentials than non-mycorrhizal plants and recovered turgor more rapidly than non-mycorrhizal plants when soil water was restored. Thus, the mycorrhizal habit is an advantage to the host plant in times of moisture stress.


Tobar, R.M., R. Azcon, J.M. Barea. 1994. The improvement of plant N acquisition from an ammonium-treated, drought-stressed soil by the fungal symbiont in arbuscular mycorrhizae. Mycorrhiza 4:105-108.

The objective of this study was to determine that mycorrhizal activity on N uptake under water-stressed conditions and effects on plant growth. They used a neutral agricultural soil and the arbuscular fungi were Glomus mosseae and G. fasciculatum. They found that under water-stressed conditions both fungal species increased the 15N enrichment of plant tissues. This indicates a direct effect of arbuscular mycorrhizal fungi on N acquisition in relatively dry soils. G. mosseae had more effect on N uptake than G. fasciculatum on P uptake under water-stressed conditions, but both fungi improved plant biomass production relative to nonmycorrhizal plants.


Ruiz-Lozano, J.M., R. Azcon and M.Gomez. 1995. Effects of Arbuscular-Mycorrhizal Glomus species on drought tolerance: Physiological and nutritional plant responses. Applied and Environmental Microbiology 61:456-460.

This study compared seven Glomus species to determine their effects on plant growth, mineral uptake, the CO2 exchange rate, water use efficiency, transpiration, stomatal conductance, photosynthetic P use efficiency, and proline accumulation under well-watered and drought stress conditions. AM fungal species showed diverse effectiveness at increasing host plant drought tolerance. The different effects of these fungi on alleviating stress appeared to be based on physiological processes rather than nutrient uptake by the host. The protection of mycorrhizal plants against water stress was related to the effects that the endophytes had on increasing leaf conductance and transpiration as well as P and K uptake. Glomus deserticola was the most adapted and aggressive colonizer as well as the most effective species for increasing drought tolerance of the host plant both in terms of maintaining growth under stress conditions and in permitting more efficient use of water. Also, they observed that plant nutrient uptake was strongly influenced by the fungal symbiont involved in the association. The differences in shoot and root growth stimulation between the least effective fungal isolate (G. occultum) and the most effective fungal isolate (G. deserticola) ranged from 270% under well-watered conditions to more than 821% under drought stress conditions. They concluded that selection of AM fungi for introduction into dry environments to address specific problem situations is a promising but usually neglected strategy.


Nikolaou, N., K. Angelopoulos, and N. Karagiannidis. 2003. Effects of drought stress on mycorrhizal and non-mycorrhizal cabernet sauvignon grapevine, grafted onto various rootstocks. Expl. Agric 39:241-252.

The objective of this study was to assess the effects of drought stress on leaf photosynthesis and water relations of Cabernet Sauvignon grapevine scion grafted onto eight different rootstocks. Foliar growth, leaf phosphorus concentrations and drought tolerance were greater in the inoculated than in the non-inoculated plants. Some drought-sensitive rootstocks colonized with mycorrhizal fungi and subjected to drought for eight days showed much-improved drought resistance compared with noninfected rootstocks of the same varieties. They concluded that mycorrhizal colonization may improve the water status of non-irrigated vines.


Subramanian, K.S., C. Charest, L.M. Dwyer and R.I. Hamilton. 1995. Arbuscular mycorrhizas and water relations in maize under drought stress at tasselling. New Phytologist 129:643 650.

This study hypothesized that under drought conditions inoculation of AM fungi in maize improves water relations that may play an important role in drought tolerance of the host plant. They measured leaf water potential, stomatal resistance, transpiration rate and green leaf area in mycorrhizal and non-mycorrhizal plants of drought sensitive and resistant maize cultivars when irrigation was withheld for 3 weeks following tasselling. Mycorrhizal inoculation had a significant effect in improving water relations and in retaining more green leaf area, leaf water potential and stomatal resistance and transpiration rates in drought-stressed maize plants. The response was more pronounced in drought sensitive than the drought-resistant cultivars. These findings suggest that AM association improves plant water relations and contributes to drought tolerance in maize.


Subramanian, K.S., C. Charest. 1999. Acquisition of N by external hyphae of an arbuscular mycorrhizal fungus and its impact on physiological response in maize under drought-stressed and well-watered conditions. Mycorrhiza 9:69-75.

This study examined the uptake of nitrogen by external hyphae of an arbuscular mycorrhizal (AM) fungus (Glomus intraradices) and its impact on physiological response in maize plants subjected to well-watered or drought-stressed conditions. Mycorrhizal colonization by G. intraradices improved nutritional status and N assimilation in maize plants exposed to moderate drought stress. The increased capacity for N acquisition and assimilation may enable the host plant to sustain moderate drought stress conditions. Glutamine synthetase activity in AM plants increased by 30% under drought conditions, which may be attributed to the hyphal transport of N in the form of NO3 or NH4. They also found that AM colonization conferred a higher P status under drought conditions. In summary, they suggested a positive relationship between N hyphal contribution and metabolic/nutritional status of the host plant. These changes may assist the host plant to withstand drought conditions.


Subramanian, K.S., P. Santhanakrishnan, P. Balasubramanian. 2006. Responses of field grown tomato plants to arbuscular mycorrhizal fungal colonization under varying intensities of drought stress. Scientia Horticulturae 107:245-253.

The objective of this study was to examine the effects of mycorrhizal inoculation with AM fungus on the growth, reproductive behavior, water status, nutrient content, fruit yield and quality attributes of field grown tomatoes drought under stress conditions. Their 2 year- field study suggested that the inoculation with Glomus intraradices improves drought tolerance of tomato plants as secondary consequence of enhanced nutritional status of the host plant, especially N and P. Mycorrhizal association improved tomato fruit quality by enhancing ascorbic acid content and reducing the acidity. Drought impact on deteriorating fruit quality can be lessened through mycorrhizal colonization. Their data revealed that AM colonization enhances nutritional status and leaf relative water content and enables the host plant to withstand varying intensities of drought stress under field conditions.


Runjin, L. 1989. Effects of vesicular-arbuscular mycorrhizas and phosphorus on water status and growth of apple. Journal of Plant Nutrition 12:997-1017.

The objective of this study was to determine the influence of VAM fungi on the water status, mineral uptake, and growth of the seedlings of apple and to establish the probable mechanism by which arbuscular mycorrhiza (AM) changes water relations of their host plant under ample moisture supply and water stress conditions. The found that sterilized soil inoculated with Glomus versiforme and G. macrocarpum enhanced element uptake, improved water status, drought tolerance and growth of the plants. Colonized plants grew rapidly two months after inoculation. Phosphorus added to the soil had a negative effect on the development and function of AM. In sterilized soil, AM colonization increased the transpiration rate of the leaves, reduced the stomatal resistance and the permanent wilting as well enhanced the rate of recovery of the plant from the water stress and the plant growth. This was probably due to enhancing absorption and translocation of water by the external hyphae. It also increased absorption of most minerals, especially Zn and Cu by the roots and weakened the P-Cu and P-Zn interactions. Under natural conditions, growth, mineral nutrition, water relations are interlinked with the effects of soil microorganisms that includes AM fungi.


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