Climate effects on the nitrogen balance of beech (Fagus sylvatica) at its south-eastern distribution limit in Europe.

Owing to its wide European distribution and drought sensitivity, beech (Fagus sylvatica L.) has captured the attention of researchers in the context of climate change. Contrary to central European beech ecosystems, little is known about the nitrogen (N) balance of beech at its south-eastern European distribution limit. Here we studied the seasonal variation of key N-related parameters during the period 2003-2004, and tested whether climatic differences between the years affected the N balance of beech in north-western Greece. The warmer and drier climate of 2003 was characterised by lower soil N availability, compared to 2004. The pool of total soluble non-protein nitrogen (TSNN) was more sensitive than total N to interannual differences in growth conditions, as reflected particularly in the TSNN concentrations, and in the composition of phloem and xylem sap in early spring. In 2003, the N demands of expanding leaves were covered mainly by stored N remobilisation, as indicated by elevated TSNN levels in phloem and xylem sap, and by increased loading of arginine and glutamine, major N-storage compounds, in these N-exchange and transport pools. By contrast, the more favourable growth conditions of 2004 supported new growth also by current root N uptake, as indicated by increased asparagine levels in phloem and xylem sap. [ABSTRACT FROM AUTHOR]