Differentiation of soil properties related to the spatial association of wheat roots and soil macropores

Under certain soil conditions, e.g. hardsetting clay B-horizons of South-Eastern Australia, wheat plants do not perform as well as would be expected given measurements of bulk soil attributes. In such soils, measurement indicates that a large proportion (80%) of roots are preferentially located in the soil within 1 mm of macropores. This paper addresses the question of whether there are biological and soil chemical effects concomitant with this observed spatial relationship. The properties of soil manually dissected from the 1–3 mm wide region surrounding macropores, the macropore sheath, were compared to those that are measured in a conventional manner on the bulk soil. Field specimens of two different soil materials were dissected to examine biological differentiation. To ascertain whether the macropore sheath soil differs from rhizosphere soil, wheat was grown in structured and repacked cores under laboratory conditions. The macropore sheath soil contained more microbial biomass per unit mass than both the bulk soil and the rhizosphere. The bacterial population in the macropore sheath was able to utilise a wider range of carbon substrates and to a greater extent than the bacterial population in the corresponding bulk soil. These differences between the macropore sheath and bulk soil were almost non-existent in the repacked cores. Evidence for larger numbers of propagules of the broad host range fungus Pythium in the macropore sheath soil were also obtained.

[1]  E. Bååth,et al.  The use of phospholipid and neutral lipid fatty-acids to estimate biomass of arbuscular mycorrhizal fungi in soil , 1995 .

[2]  A. Richardson,et al.  Soil microorganisms and phosphorus availability. , 1994 .

[3]  J. B. Passioura,et al.  Soil structure and plant growth: Impact of bulk density and biopores , 1996, Plant and Soil.

[4]  D. Reuter,et al.  An appraisal of soil phosphorus testing data for crops and pastures in South Australia , 1995 .

[5]  P. Grace,et al.  Soil Biota: Management in Sustainable Farming Systems , 1996 .

[6]  E. Bååth,et al.  Shifts in the structure of soil microbial communities in limed forests as revealed by phospholipid fatty acid analysis , 1993 .

[7]  V. Römheld,et al.  Root‐induced changes of nutrient availability in the rhizosphere , 1987 .

[8]  Walter J. Horst,et al.  Root-induced changes in the rhizosphere: Importance for the mineral nutrition of plants , 1986 .

[9]  P. Curtis,et al.  Soil Microbial Communities Beneath Populus Grandidentata Grown Under Elevated Atmospheric CO2 , 1996 .

[10]  L. J. Lennox.  An automated procedure for the determination of phosphorus , 1979 .

[11]  J. F. Dormaar.  EFFECT OF PLANT ROOTS ON CHEMICAL AND BIOCHEMICAL PROPERTIES OF SURROUNDING DISCRETE SOIL ZONES , 1988 .

[12]  G. Gobran,et al.  A conceptual model for nutrient availability in the mineral soil-root system , 1996 .

[13]  M. Mccully,et al.  How Do Real Roots Work? (Some New Views of Root Structure) , 1995, Plant physiology.

[14]  P. Kuikman,et al.  Protease and deaminase activities in wheat rhizosphere and their relation to bacterial and protozoan populations , 1996, Biology and Fertility of Soils.

[15]  M. Ali-Shtayeh,et al.  An improved method and medium for quantitative estimates of populations of Pythium species from soil , 1986 .

[16]  G. B. Schaalje,et al.  Chemical and biochemical changes in the rhizospheres of wheat and canola , 1995 .

[17]  W. R. Gardner.  DYNAMIC ASPECTS OF WATER AVAILABILITY TO PLANTS , 1960 .

[18]  A. Jongerius,et al.  Handbook for Soil Thin Section Description , 1987 .

[19]  J. Kirkegaard,et al.  Effect of Brassica break crops on the growth and yield of wheat , 1994 .

[20]  D. Robinson.  The responses of plants to non-uniform supplies of nutrients. , 1994, The New phytologist.

[21]  G. Robertson,et al.  Fatty acid methyl ester (FAME) profiles as measures of soil microbial community structure , 1995, Plant and Soil.

[22]  M. Watt,et al.  Formation and Stabilization of Rhizosheaths of Zea mays L. (Effect of Soil Water Content) , 1994, Plant physiology.

[23]  E. Bååth,et al.  The use of phospholipid fatty acid analysis to estimate bacterial and fungal biomass in soil , 1996, Biology and Fertility of Soils.

[24]  J. Passioura.  Roots and Water Economy of Wheat , 1985 .

[25]  K. Volkmar.  Effects of biopores on the growth and N-uptake of wheat at three levels of soil moisture , 1996 .