Thesis (Ph. D.)--Oregon State University, 1961. / Typescript. Includes bibliographical references (leaves 80-83). Also available on the World Wide Web.

The response of arsenate tolerant and non-tolerant Holcus lanatus L. phenotypes, where tolerance is achieved through suppression of high affinity phosphate/arsenate transporters, was investigated under different growth regimes to investigate why there is a polymorphism in tolerance found in populations growing on uncontaminated soil. The growth of tolerant plants differed from non-tolerants in response to phosphate (P) fertilization when grown on the uncontaminated soil from the population's origin: non-tolerants put more resources into tiller production and down regulated investment in root production while tolerants tillered less effectively and did not alter resource allocation to shoot biomass under P fertilization. The two phenotypes also differed in their shoot element status having greater concentrations of manganese (Mn) and selenium (Se), while suppressed uptake of arsenic (As) and phosphorus in tolerant phenotypes. Enrichment of As-amended soil with P induced growth of tolerant phenotypes, particularly the root biomass and did not alter As influx, but increased As uptake of non-tolerants compared to their corresponding status in As-amended soil. Growth and nutrition of tolerant and non-tolerant phenotypes did not differ in response to fertilization with nitrogen (N). By contrast, iron (Fe) addition affected root biomass production, shoot-root ratio, and As influx. Fe fertilization decreased the uptake of As in both tolerant and non-tolerant phenotypes. When tolerant and non-tolerant phenotypes were grown in different contrasting local soils, there was a significant interaction between soil and phenotype for tillering and root biomass production. Sometimes tolerants out performed non-tolerants, and vice versa, or there were no differences. Therefore, variation in growth matrix response could be the basis of the maintenance of polymorphism in H. lanatus population. The polymorphism was also widely present (40%) in other wild grass species suggesting an important ecological role for this gene that can be screened through plant root response to arsenate and can be transplanted to other crops to harvest safe agricultural products from As contaminated sites.

This thesis contains a literature review of Holcus lanatus and records studies on both the growth and spread of the species and the response of it and of Lolium perenne to several management and edaphic factors. Holcus lanatus is an adaptable, competitive species with ecotypes growing in a wide range of environments. It is valuable on hill land, acid, low nutrient soils and to prevent erosion. Beef cattle grazing it have made greater liveweight gains than on L. perenne. Experiments used plants growing in pots and small field plots. A growth study of spaced H. lanatus plants showed they can produce up to 240,000 seeds, most of which germinated shortly after being shed onto moist soil. Seedlings established poorly in a closed sward. Spaced plants produced runners in autumn whose plantlets established better when plants were cut regularly in spring. Holcus lanatus plants needed vernalization in order to flower. This was enhanced by and to a small extent replaced by short days. When H. lanatus plants in bud were cut, useful summer vegetative regrowth resulted. The New Zealand cultivar Massey Basyn was more productive than Oxfordshire H. lanatus in a pot trial. Holcus lanatus dominated a mixture with L. perenne in a glasshouse experiment, especially under high or infrequent cutting, but it was not so dominant in a field experiment. Cattle treading damaged H. lanatus more than it did L. perenne. Holcus lanatus responded to a high water table by producing adventitious and surface roots. Propyzamide at 2.24 and linuron at 1.12 kg a.i./ha in early summer and asulam at 1.12 or 2.24 kg a.i./ha in early September gave good control of established H. lanatus in L. perenne in preliminary trials. The agricultural significance of these results is discussed.

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Les interactions entre les végétaux et les organismes telluriques sont déterminantes pour la décomposition des matières organiques et la nutrition minérale des plantes. L’objectif général de la thèse était de comprendre comment les interactions multi-trophiques dans la rhizosphere agissent sur la disponibilité en azote minéral et l’allocation en carbone dans la plante. Nous avons mis au point des dispositifs de culture de plante, permettant de contrôler l’environnement biotique des racines (inoculation par des espèces symbiotiques modèles : un protozoaire bactériophage et/ou une espèce mycorhizienne à arbuscules). Nous avons utilisé l’azote 15N et le carbone 13C pour tracer le cheminement de l’azote du sol vers la plante et le carbone assimilé par photosynthèse, de la plante vers le sol et les microorganismes du sol. L’allocation de C vers les racines et la rhizosphère est dépendante de la qualité de la litière foliaire enfouie. La structure de la communauté microbienne déterminée par l’analyse des profils d’acides gras (PLFA) est modifiée par la présence de protozoaires pour la litière à C/N élevé. Les mycorhizes à arbuscules et les protozoaires présentent une complémentarité pour l’acquisition du C et de N par la plante. Les protozoaires remobilisent l’azote de la biomasse microbienne par leur activité de prédation. Les hyphes fongiques transportent du C récent issu de la plante vers des sites riches en matière organique non accessibles aux racines. Ainsi, l’activité de la communauté microbienne est stimulée et la disponibilité en N augmentée lorsque des protozoaires sont présents. Les perspectives de ce travail sont de déterminer si (i) les interactions étudiées dans ce dispositif modèle peuvent être généralisées à d’autres interactions impliquant d’autres espèces de champignons mycorhiziens et de protozoaires (ii) la phénologie de la plante et la composition des communautés végétales influence la nature et l’intensité des réponses obtenues / Plants interact with multiple root symbionts for fostering uptake of growth-limiting nutrients. In turn, plants allocate a variety of organic resources in form of energy-rich rhizodeposits into the rhizosphere, stimulating activity, growth and modifying diversity of microorganisms. The aim of my study was to understand how multitrophic rhizosphere interactions feed back to plant N nutrition, assimilate partitioning and growth. Multitrophic interactions were assessed in a single-plant microcosm approach, with arbuscular mycorrhizal fungi (Glomus intraradices) and bacterial feeding protozoa (Acanthamoeba castellanii) as model root symbionts. Stable isotopes enabled tracing C (13C) and N (15N) allocation in the plant and into the rhizosphere. Plant species identity is a major factor affecting plant-protozoa interactions in terms of N uptake and roots and shoot morphology. Plants adjusted C allocation to roots and into the rhizosphere depending on litter quality and the presence of bacterial grazers for increasing plant growth. The effect of protozoa on the structure of microbial community supplied with both, plant C and litter N, varied with litter quality added to soil. AM-fungi and protozoa interact to complement each other for plant benefit in C and N acquisition. Protozoa re-mobilized N from fast growing rhizobacteria and by enhancing microbial activity. Hyphae of AM fungi acted as pipe system, translocating plant derived C and protozoan remobilized N from source to sink regions. Major perspectives of this work will be to investigate whether (i) multitrophic interactions in our model system can be generalized to other protozoa-mycorrhiza-plant interactions (ii) these interactions are depending on plant phenology and plant community composition