One of Du Rietz's professors at Uppsala University was
Rutger Sernander, a popular lecturer who pioneered the study of plant ecology at the institution. One of Du Rietz's earliest publication was on the material collected by Sernander in Norway. Du Rietz later continued Sernander's work. From 1917 to 1923, Du Rietz served as an associate assistant professor at the Department of Plant Biology. He then transitioned to the role of
curator at the
Botanical Museum in Uppsala, a position he held from 1924 to 1927. Du Rietz was also the leader of the biological geological work at
Abisko Scientific Research Station, and general secretary of the international plant geographical excursion through Scandinavia in 1925. Du Rietz undertook several study trips within and outside Sweden, scientific expeditions to New Zealand and Australia and in his research mainly devoted on plant sociology and
lichenology. In 1929 he co-founded the (). Having been a
docent since 1921, in 1934 Du Rietz was appointed as both professor of plant ecology at Uppsala University (
emeritus in the early 1960s), and as the director of the institute. He had served temporarily in this latter position since Sernander's retirement in November 1931. Sernander established the "Uppsala school", known for treating plant communities as tangible entities rather than abstract constructs and for advocating an empirical, inductive approach that emphasised life forms, stratification, dominance, and the significance of smaller non-flowering plants and fungi (
cryptogams). This approach was primarily analytical, focusing on the analysis, characterisation, and classification of vegetation independently of habitat factors, which were to be considered subsequently. Du Rietz would later carry on the research traditions of the "Uppsala school". Du Rietz taught high-level material without being difficult to understand, and became popular among botany students. Under his supervision, the plant biology seminar flourished. According to his biographer, the Swedish plant ecologist Hugo Sjörs, Du Rietz was regarded as an inspiring academic teacher. It is reported that his students were inclined to undertake large and challenging projects, often requiring considerable time to complete. Du Rietz valued thorough documentation and comprehensive reporting of research materials. The scope of plant groups and environments studied by the students was diverse, predominantly involving field research. Although Du Rietz insisted on formal accuracy, he reportedly did not often intervene directly with the content of students' dissertations. This approach is said to have fostered a supportive environment that contributed to the development of doctoral students into independent researchers. A few of his students,
Sten Ahlner,
Gunnar Degelius,
Torsten Hasselrot, and
Rolf Santesson, later became notable lichenologists.
Stig Waldheim and
Ove Almborn were also influenced by the Uppsala school of phytogeography even though they were associated with
Lund University. Du Rietz resumed his international contacts on a large scale during the first major
International Botanical Congress after the Second World War, in
Stockholm in 1950. Einar was then responsible for the plant geography section as well as for its excursions and the many guide books for these that were published. He personally led a series of excursions: from
Västergötland to
Uppland, an
archipelago excursion, and a very frequently visited mountain excursion in the
Abisko area; in the latter, he brought a
megaphone so his voice could be heard over the wind. Sjörs regarded these events as the fourth pinnacle in Du Rietz's professional career, following his doctoral dissertation, the 1925 field trip, and achieving his professorial qualifications. After this phase of his career, Du Rietz started researching the plant genus
Euphrasia (eyebrights), both local and foreign species. ==Personal==