g., Ingestad, 1979, Ingestad, 1982, Ingestad, 1987, Linder, 1987 and Linder, 1995). Carl Olof followed progress in science across a wide range of fields. After the discovery of the radiocarbon method for dating of organic material by Willard

Libby, who received the Nobel Prize in Chemistry in 1960, Carl Olof applied the method to dating of the organic matter in the soil profile. He found that the organic matter in the illuvial (Bs) horizon in podzol (Spodosol) FK228 soils could be several hundred years old (Tamm and Östlund, 1960), and subsequent work demonstrated even older organic matter (>1000 years old) in this horizon in northern boreal forest (Tamm and Holmen, 1967). These novel studies were made long before today’s widespread interest in soil C turnover. Carl Olof also became very engaged in problems related to deposition of sulphur

and N (e.g., Tamm and Cowling, 1977). He had already established field scale experiments in the late 1960s and early 1970s with annual additions of dilute sulphuric acid and nitrogen, providing strong experimental evidence as concerns over acid deposition developed in the following decades. His experiments demonstrated that Scots pine (Pinus sylvestris L.) was quite tolerant of soil acidification induced by sulphuric acid, but that very high additions of N, which also acidified soil, reduced tree growth where moderate N additions increased growth ( Tamm, 1989 and Tamm, 1991). The field experiments ranged from small with few treatments Phosphoribosylglycinamide formyltransferase and replicate Afatinib datasheet plots to very large ones, like the long-term experiments at Norrliden, Lisselbo, and Stråsan. For example, at Norrliden, there were four separate experiments, with altogether

102 plots, each 30 × 30 m. In the N addition experiments at Norrliden, Lisselbo, and Stråsan, nitrogen was added annually for decades. These ambitious experiments were established as early examples of dedication to long-term ecological investigation. The experiments continue today with low-to-moderate additions of N, and the plots that received the highest doses no longer receive treatment and are being monitored for recovery (e.g., Högberg et al. 2006). Carl Olof and his student Leif Hallbäcken revisited plots established five decades earlier by Olof Tamm to provide one of the longest-term records of change in forest soils. They carefully remeasured soil pH using the same old-fashioned method and found the upper mineral soil acidified as forests aged, with a larger decline in soil pH in Southwest Sweden than in Northwest Sweden, matching the gradient in acid deposition (Hallbäcken and Tamm, 1986 and Tamm and Hallbäcken, 1988). Carl Olof was very active as Swedish representative in discussions about forest decline and soil acidification (cf. Schulze et al., 1989) and his pioneering studies influenced the environmental policies in Europe during the 1980s and the 1990s.