## Recovery from photoinhibition in sycamore (Acer pseudoplatanus L.) is altered by the form of nitrogen nutrition ## Bartak, M., Hajek, J. Department of Plant Physiology and Anatomy, Masaryk University, Kotlarska 2, 61137 Brno, Czech Republic. Fax: 41211214, E-mail: mbartak@sci.muni.cz, http://www.sci.muni.cz /kfar Abstract Presented study compares the functioning of photosystem II (PS II) and its sensitivity to photoinhibition in sycamore (Acer pseudoplatanus) seedlings cultivated for 4 weeks in growh medium with either nitrate (NO3) or ammonium (NH4) as the sole source of nitrogen and exposed to two levels of irradiance: (1) HL=400 (mol m-2 s-1), (2) LL= 35 (mol m-2 s-1). Nitrate compared to ammonium nutrition led to an increase in chlorophyll content The effect of nitrogen nutrition on chlorophyll fluorescence parameters was apparent only in HL plants. NO3 nutrition decreased Fv/Fm, photochemical quenching (qP) but increased non-photochemical quenching (qN). When exposed to strong light, both NO3 and NH4 plants exhibited photoinhibition expressed as an decrease in Fv/Fm, qP, and an increase in qN, especially in qT+I component related to photoinhibitory changes in PS II. During recovery from photoinhibition, NO3-cultivated HL plants showed faster recovery of Fv/Fm than NH4-cultivated plants. qT+I component of total qN recovered faster in NH4 than NO3 plants. LL plants showed more pronounced drop of Fv/Fm after photoinhibitory treatment than HL plants. No difference was found between NO3- and NH4-cultivated LL plants in their recovery from photoinhibition. The differences in chlorophyll fluorescence parameters and sensitivity to photoinhibition between NO3- and NH4-cultivated plants found in this study are discussed as a consequences of altered nitrogen metabolism. It is concluded that long-term cultivation of plants in NH4 nutrition leads to the enhancement of qN but accelerates recovery from photoinhibition. Keywords: tree seedlings, nitrogen, nitrate reductase, chlorophyll fluorescence quenching

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