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Mycorrhizal Fungi and Root Biomass

Dr. Efren Cazares – MycoRoots

Consulting to verify statements regarding mycorrhizal fungi and root biomass™.

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 increase root biomass. 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. aggregatum, and G. macrocarpum


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 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 that 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. 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. 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.


Aguilera-Gomez, L., F.T. Davies, Jr., V. Olalde-Portugal, S.A. Duray and L. Phavaphutanon. 1999. Influence of phosphorus and endomycorrhiza (Glomus intraradices) on gas exchange and plant growth of chile ancho pepper (Capsicum annum L. cv. San Luis).

The objectives of this research were: 1) to determine the influence of endomycorrhizal in alleviating low P effects of mycorrhizal chile ancho pepper plants based on plant growth and gas exchange characteristics and 2) to evaluate the influence of P on mycorrhizal development of arbuscules, vesicles, and intraradical and extraradical hyphae formation. Their long-term goal is to demonstrate the usefulness of mycorrhizal for more efficient utilization of P fertilization in sustainable production systems for this pepper variety. Mycorrhizal colonization increased leaf number, leaf area, shoot, root and fruit mass at low P rates compared to non-VAM plants. Reproductive growth was enhanced by 450% in mycorrhizal plants at high P levels. The enhanced growth and gas exchange of mycorrhizal plants was in part due to greater uptake of P and greater extraradical hyphae development.


Brejeda, J.J., L.E. Moser and K.P. Vogel. 1998. Evaluation of Switchgrass rhizosphere microflora for enhancing seedling yield and nutrient uptake. Agron. J. 90:753-758.

Seedlings inoculated with rhizosphere microflora produced up to 15-fold greater shoot and root yields, and recovered up to 6-fold more N and 36-fold more P than seedlings inoculated with rhizosphere bacteria only. These responses were consistent for all four cultivars and were probably due to arbuscular mycorrhizal fungi. Seedlings inoculated with rhizosphere populations from seeded switchgrass stands averaged 1.5-fold greater shoot and root yields than seedlings inoculated with rhizosphere populations from native prairies. Plant growth promoting rhizosphere, AM fungi and nonmycorrhizal fungi may be responsible for the large increases in shoot and root weights and in N and P uptake following inoculation of seedlings with rhizosphere microflora.


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 P 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. The mycorrhizal effects reported in this study may have been a secondary consequence of AM-enhanced host P nutrition because root growth was highly correlated with leaf P concentration.


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.


Corkidi, L., E.B. Allen, D. Merhaut, M.F. Allen, J. Downer, J. Bohn and M. Evans. 2005. Effectiveness of commercial mycorrhizal inoculants on the growth of Liquidambar styraciflua in plant nursery conditions. J. Environ. Hort. 23:72-76.

In this study, several products were selected to evaluate their effect on the growth and development of Liquidambar styraciflua, an important commercial hardwood in the southern United States, which is highly dependent on mycorrhizal fungi. The growth response of mycorrhizal and nonmycorrhizal plants was analyzed at two harvest times. Significant differences were found in the growth of sweetgum seedlings to mycorrhizal colonization with the different commercial products. Some products enhanced the growth of sweetgum relative to the nonmycorrhizal plants after fourteen weeks of transplanting.


Scagel, C.F., K. Reddy and J.M. Armstrong. 2003. Mycorrhizal fungi in rooting substrate influences the quantity and quality of roots on stem cuttings of hick’s yew. Hortechnology 13:62-66.

The objectives of this study were to determine if the addition of AM fungal (Glomus intraradices) inoculum into the rooting substrate during cutting propagation increases rooting of hick’s yew and how the quantity of AM fungal inoculum influences the rooting of hick’s yew under nursery production conditions. Adding AM fungal inoculum into the rooting substrate significantly influenced the number of initial roots their dry weight and size per cutting compared to controls. However, the highest level of inoculum tested increased adventitious root initiation without increased root growth. Also, they determined that adding inoculum into the rooting substrate of cuttings treated with rooting hormones is equal to or better than the rooting response obtained by using hormone under nursery production conditions.


Yano-Melo, A.M., O.J. Saggin Jr., J.M. Lima-Filho, N.F. Melo and L.C. Maia. 1999. Effect of arbuscular mycorrhizal fungi on the acclimatization of micropropagated banana plantlets. Mycorrhiza 9:119-123.

This study evaluated the effects of the inoculation of three native AM fungal species isolated from irrigated banana plantations of the Brazilian semiarid region on growth, nutrition and physiology of banana plantlets developed in vitro. After three months of acclimatization, statistically significant differences in plant height, leaf area, fresh and dry matter of shoot, and fresh weight of roots between inoculated and non-inoculated plants were recorded. Leaf area and height of inoculated plants were approximately 57% and 32% higher, respectively, than non-inoculated plants. Dry matter of shoots increased 45-64% in mycorrhizal plants. Plants inoculated with Glomus clarum showed an increment of around 45% in the fresh weights of shoots and roots over non-inoculated plants. Inoculation with AM fungi increased growth of micropropagated banana plantlets during acclimatization period, and this may benefit rates of photosynthesis and also nutrient transport by mass flow.


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