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1

Biological Soil Crusts, Plant Functional Groups, and Soil Parameters in Arid Areas of Iran

Bashtian M. H., Sepehr A., Farzam M., Bahreini M.

Polish Journal of Ecology

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2018

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Vol. 66, nr 4

337--351

EN

Biological soil crusts (BSCs) have a vital role regarding vegetation and soil development in arid and semi-arid areas in the world, and apparently in Iran, where they comprise more than 85% of the land. In this research, the relationship between BSCs and plant functional groups, considering soil parameters along an arid alluvial fan located in Khorasan Razavi province in northeastern Iran, was examined. The sampling carried out in summer, systematically from apex towards base part of alluvial fan, using a 0.25 m2 quadrat over a 5-cm thick soil surface. Surface levels were classified into three categories: apex, middle, and base. At each level, 16 samples were taken; in total 48 samples were collected along the alluvial fan from the apex point to the base district. The results showed a strong relationship between BSCs and the soil surface features, and a weak correlation between the plant functional group and soil parameters. BSCs indicated an ecological evolution from apex to the base geomorphic level by soil development; so that BSCs are more developed on the base of alluvial fan, but their diversity is reduced.

2

Effect of patchy distribution of soil nutrients on root morphology and biomass allocation of selected grassland species: experimental approach

Zaller J.

Polish Journal of Ecology

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2007

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Vol. 55, nr 4

731-746

EN

Nutrient distribution in natural habitats is usually patch in space and time, however most knowledge about plant growth and behaviour is based on experiments conducted under spatially homogenous conditions. Evidence has accumulated that the growth and competitive interaction of plant species are strongly affected by heterogeneous resource distribution, even when the total resource supply remains similar. For this study it is hypothesized that infestations of grasslands with the nitrophilous weed Rumex obtusifolius L. (broadleaved dock) are partially the consequence of its ability to exploit spatial nutrient heterogeneity. This was tested in a full-factorial pot experiment with homogeneously or heterogeneously distributed nitrogen and/or potassium at either normal or increased soil moisture where R. obtusifolius was grown together with three other grassland species (grass: Arrhenatherum elatius L., non-leguminous herb: Taraxacum officinale Weber, leguminous herb: Trifolium repens L.). The species differed significantly in their root morphology (root length and diameter, specific root length, number of root tips) and biomass allocation response to nutrient distribution, as well as to the nutrient type used to create patches and to soil moisture (e.g., significant species x treatment interactions). Generally, the root system of A. elatius showed the highest plasticity to imposed treatments, followed by T. officinale, R. obtusifolius and T. repens. Unexpectedly, root morphology of R. obtusifolius was unresponsive to soil heterogeneity and less responsive to nutrient type and irrigation than that of the other species. Nutrient type used to create patches influenced the biomass allocation to the root system of R. obtusifolius while nutrient distribution and irrigation showed no effect on biomass allocation. Exploitation of soil nitrate-nitrogen and potassium was similar among species but exploitation was individually affected by nutrient type, nutrient distribution and irrigation suggesting that species-specific differences in nutrient storage capacities in roots or adjustments regarding root nutrient uptake kinetics may play an important role. Results from this study show that R. obtusifolius does not seem to have superior traits to utilize soil nutrient heterogeneity, certain nutrient types or higher soil moisture that differentiates it from the other grassland species tested. The observed effects might have consequences for the long-term competitive relationships between species in the grassland community suggesting that cultural and biological management measures oriented towards the improvement of the competitive ability of co-occurring grassland species might also be important in heterogeneous soils.

3

Calculating effective conductivity of heterogeneous soils by homogenization

Szymkiewicz A.

Archives of Hydro-Engineering and Environmental Mechanics

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2005

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Vol. 52, nr 2

111-130

EN

The paper concerns effective conductivity of a heterogeneous soil composed of two materials characterized by different hydraulic conductivities. According to the homogenization theory the effective conductivity is obtained from the solution of an elliptic equation for a single representative elementary volume. A numerical algorithm to solve this equation is described. Examples of calculations for periodic media with inclusions of various shapes are presented. Influence of volumetric fraction, arrangement, continuity and conductivity ratio of the two materials on the effective conductivity is investigated. Numerical results are compared with some analytical estimations available in the literature.