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| Influences of Phytophthora pathogens on gas exchange and root growth of beech grown under different CO2 and nitrogen regimes |
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Fleischmann, F.(1.), Matyssek, R.(2), Oßwald W.(1)
(1)TU-München, Center of Life and Food Sciences, Department of Ecology, Section Phytopathology, Am Hochanger 13, 85354 Freising
(2)TU-München, Center of Life and Food Sciences, Department of Ecology, Chair of Forest Botany, Am Hochanger 13, 85354 Freising
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We investigated the influence of Phytophthora citricola, P. cambivora, P. syringae and P. undulata on root development, net CO2 assimilation and transpiration of beech seedlings and young saplings. Shortly after inoculation photosynthesis and transpiration of seedlings, grown under ambient CO2 and infected with either P. citricola or P. cambivora were strongly reduced. Three weeks after infection all seedlings were dead showing severe wilt and root rot symptoms. Remarkably, P. syringae and P. undulata infected seedlings did not differ from controls regarding photosynthesis and transpiration, although their root systems were damaged.
A significant influence on photosynthesis and transpiration of P. citricola and P. cambivora infected two year old beech was visible after bud break. Some days before plants started to wilt, photosynthesis and transpiration of P. citricola infested plants were reduced to almost zero levels. Water use efficiency data clearly indicated that infected plants suffered from severe drought stress. Again P. syringae and P. undulata infected beech did not differ from control plants regarding photosynthesis and transpiration, whereas their fine root system was reduced to about 50%. Remarkably, these plants showed the same root mass as control plants, indicating that defence reactions such as cellulose or lignin synthesis might have been induced.
In an other experiment we inoculated three year old beech, grown under different CO2 and nitrogen regimes for two years, with P. citricola. Susceptibility of these plants was much lower compared to two year old plants and seedlings. Remarkably only plants grown under elevated CO2 (ambient + 300ppm) and low nitrogen fertilisation showed the highest susceptibility towards this root rot pathogen. These plants were characterized by the lowest nitrogen content and the highest C/N- ratio in leaves. Seventeen per cent of these plants had died already two weeks after inoculation started.
These first results clearly indicate that elevated CO2 together with ambient nitrogen favours susceptibility of beech towards the root rot pathogen P. citricola.
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