Fungal Growth Responses to Osmotic as Compared to Matric Water Potential

Abstract

The osmotic and matric water potential characteristics of Phytophthora cinnamomi and Alternaria tenuis, fungi of widely different tolerance to water stress, were evaluated using agar media of varying nutritional status and three texturally different soils. The water potential of the agar media was controlled osmotically with KCl or sucrose. For the osmotic soil system, soil water content was maintained approximately constant and the desired water potential range was achieved by adding KCl solutions of different concentrations to air‐dry soil samples at a level equivalent to the water content of the field moist soils; for the matric system, decreases in water potential were achieved by adding decreasing volumes of water to air‐dry soil according to the moisture retention characteristics of the soils. Fungal growth was determined by measuring changes in colony diameter with time.Osmotic water potentials for optimum fungal growth in agar and soil systems were similar to the water potentials for optimum growth in soils of matric‐controlled water potential. However, with decreasing water potential both fungi were much less tolerant to matric than to osmotic stress, emphasizing that fungal response to decreasing soil water cannot be explained solely on a water potential basis, but must include consideration also of changes in other water‐related soil properties such as solute transport. Fungal responses to matric and osmotic water potential differences were not related to soil texture.From a practical standpoint, the matric potentials at which growth extinction occurred were numerically one‐half to two‐thirds of the corresponding osmotic potentials at which growth ceased. If this relationship holds for other fungi and other soils, fungal growth responses to water potential obtained using simple agar systems of osmotic‐controlled water potential should provide useful approximations of the matric water potential relations of fungi in soil, thereby facilitating prediction of the maximum soil water potential range within which specific fungi may develop competitively in natural soils.

The Water Relations of the Alga Cyanidium caldarium in Soil

“…As discussed by Griffin (1969), matric reduction of water potential has indirect effects not directly related to water potential, the most important being that the removal of bulk water reduces solute diffusion as a result of the interruption of previously continuous water pathways. A greater effect of matric than of osmotic stress on growth has been found by Adebayo & Harris (1971) in Phytophthora cinnamomi and Alternaria tenuis although Cook, Papendick & Griffin (1972) found virtually identical responses to both kinds of water stresses in the fungus Ophiobolus graminis. As discussed by Adebayo, Harris & Gardner (1971), organisms can compensate for osmotic water stress by accumulating solute so that its concentration inside the cell is greater than outside, thus allowing for inward diffusion of water.…”

“…There have been a number of studies on the effects of varied availability of soil water on fungi (Griffin, 1969;Adebayo & Harris, 1971 ; Sommers, Harris, Dalton & Gardner, 1970) and bacteria (Clark, 1967), but no similar detailed examination has been made of any soil algal population. The work described here bears upon the problem of water availability for populations of the alga, Cyanidium caldarium, in hot, acid soils of Yellowstone National Park, Wyoming, U.S.A.…”

Use of osmotic solutions for inhibition of sunflower seed germination in blotter test

“…In this study, there was no effect of A. alternata isolates. According to earlier reports, fungal development may be stimulated at potentials varying from -0.3 to -2.0 MPa (Adebayo & Harris, 1971;Wearing & Burgess, 1979;Subbarao et al, 1993;Gao & Shain, 1995;Whiting & Rizzo, 1999;Carvalho et al, 2001;Farias et al, 2004;Teixeira et al, 2005;Machado et al, 2008). On the other hand, at more negative potentials than -1.0 MPa the growth of some fungi can be affected by some of the solutes used (Alam et al, 1996).…”

“…At potentials in the range of -0.3 to -2.0 MPa, the growth of Botrytis cinerea, Alternaria alternata, Aspergillus niger, Cryphonectria parasitica, Fusarium moniliforme and Fusarium graminearum was actually stimulated (Adebayo & Harris, 1971;Wearing & Burgess, 1979;Subbarao et al, 1993;Gao & Shain, 1995;Alam et al, 1996). Growth of Colletotrichum lindemunthianum, Bipolaris sorokiniana, Acremonium strictum, Drechslera oryzae, Phoma sorghina, Pyricularia grisea, Gerlachia oryzae, Fusarium oxysporum f.sp.…”

Effects of Combined Water Potential and Temperature Stresses on Cryptosporidium parvum Oocysts

“…We tested the effects of water potential, temperature, and freeze-thaw cycling on rates of oocyst degradation with a full-factorial approach. Our design included three replicate trials at each combination of three lengths of exposure (1,15, and 29 days), three temperatures (Ϫ14, 4, and 30°C), and three levels of water potential (Ϫ4, Ϫ12, and Ϫ33 bars). We also examined the effects of freeze-thaw cycling at the three levels of water potential.…”