Root decisions

Root systems have recognizable developmental plans when grown in solution or agar; however, these plans often must be modified to cope with the prevailing conditions in the soil environment such as the avoidance of obstacles and the exploitation of nutrient-rich patches or water zones. The modular structure of roots enables them to respond to their environment, and roots are very adaptive at modifying growth throughout the root system to concentrate their efforts in the areas that are the most profitable. Roots also form associations with microorganisms as a strategy to enhance resource capture. However, while the responses of roots in nutrient patches are well-recognized, overall 'rules of response' and variation in strategy among plant species that can be applied in a number of different environments are still lacking. Finally, there is increasing evidence that root-root interactions are much more sophisticated than previously thought, and the evidence for roots to identify self from non-self roots will be briefly discussed.

Plastic plants and patchy soils

Soil nutrients are distributed in a non-uniform or 'patchy' manner. It is well established that the modular nature of root systems allows them to show both morphological and/or physiological plasticity upon encountering nutrient-rich patches. These plastic responses are widely believed to be foraging mechanisms by the plant to enhance nutrient resource capture. Although morphological plasticity has traditionally been viewed as the more expensive option as it requires new root construction, more recent evidence suggests this may not necessarily be the case. Moreover, plants may be able to recapture most of the initial outlay involved in new root construction, again lowering the overall cost to the plant. Under natural conditions the roots of most plant species have an additional nutrient acquisition mechanism namely mycorrhizal symbiosis. However, the impact of these important symbiotic associations upon the host plant's response to nutrient patches has received relatively little attention. The mycorrhizal fungal symbiont should, in theory, be better able to compete directly with the rest of the microbial community for the nutrients in the patch. This could potentially be important to the host plant, as generally, root proliferation responses are more important for interspecific plant, than plant-microbial, competition.

Morphological and molecular diversity and abundance of tomentelloid ectomycorrhizae in broad-leaved forests of the Hungarian Plain

The most common representatives of tomentelloid ectomycorrhizae (EM) collected in broad-leaved forests (Populus and Quercus) of the Hungarian Plain during a 4-year project are demonstrated. Eighteen specimens of nine tomentelloid EM morphotypes were investigated. Five of these, introduced here for the first time, were characterized by microscopical-morphological and anatomical methods. Molecular identification was carried out using sequence analysis of the nrDNA ITS region. Altogether, 54 ITS sequences (6 previously published and 12 new sequences from our mycorrhizae and 36 from GenBank derived from fruitbodies) were compared by phylogenetic analyses using neighbor-joining, maximum parsimony and maximum likelihood methods. Identification to species level was successful in the case of six EM morphotypes (Tomentella galzinii, T. subtestacea, T. sublilacina, T. pilosa, T. ferruginea and T. stuposa), and the possible taxonomic position of the remaining three was approached. These results are supported by morphology, as compared with literature data. Relative abundance of the EM morphotypes within the soil samples was estimated. Our results confirm that tomentelloid EM are constant, diverse and abundant members of the EM communities in temperate-continental broad-leaved forests.