NEEDLE RESPIRATION AND NITROGEN CONCENTRATION IN SCOTS PINE POPULATIONS FROM A BROAD LATITUDINAL RANGE - A COMMON GARDEN TEST WITH FIELD-GROWN TREES

1. Models of tree function and forest ecosystem carbon budgets often a ssume that potential global changes in temperature and/or other factor s may alter tissue nitrogen (N) and dark respiration rates (R(d)). How ever, little is known of patterns of co-variation in tissue N and R(d) among intraspecific populations originating along climatic gradients, and of whether an N-based model of R(d) can link these two variables. To address these issues, we studied N and R(d) in fully expanded need les of 10-year-old trees of 14 Scots Pine (Pinus sylvestris) populatio ns of wide-ranging origin (43 degrees to 60 degrees N), grown under co mmon garden conditions. 2. For 11 lowland populations (elevation <200 m) from the contiguous part of the species range (48 degrees to 60 deg rees N) grown at a field site in Kornik, western Poland (52 degrees N) , there were greater needle %N in populations from increasing latitude of origin or decreasing mean annual temperature (r greater than or eq ual to 0.93, P<0.01). Similar %N and latitude of origin correlations w ere observed in another year at this site and in retrospective analyse s of published data for different sets of Scots Pine populations grown in common gardens at 48 degrees, 52 degrees C and 62 degrees N latitu des. Needle R(d) rates of the 11 lowland populations growing at Kornik and measured at a common temperature (20 degrees C) were greater, by as much as 50%, for more northerly than southerly populations. Mean R( d) rates were positively correlated to latitude of origin and to mean annual temperature (P<0.05, r=0.7 to 0.8). R(d) and needle %N were pos itively correlated (P<0.01, r=0.75), with one relationship fitting all data. Across the entire range from 1.15 to 1.55 needle %N, R(d) incre ased from 4.5 to 6.9 nmol g(-1) s(-1). 3. Mean needle %N and R(d) valu es for two montane southern populations (43 degrees and 44 degrees N, elevation greater than or equal to 885 m) growing in the same common g arden at Kornik were consistent with the relationships between mean an nual temperature, needle %N and R(d) observed for the more northerly p opulations but did not fit the latitudinal patterns. This suggests tha t temperature and/or associated climate variables are likely the drivi ng force for observed genetic variation in Scots Pine needle %N and R( d) across latitudinal and altitudinal gradients. 4. Results of these c ommon garden studies support the idea of a general relationship betwee n needle dark respiration and N concentration, and indicate that there is intraspecific genetic variation in physiology that is selected by climate that persists in a common environment, resulting in higher nee dle %N and respiration in plants originating from colder habitats. Suc h patterns need to be better understood and quantified, and merit cons ideration in modelling of current and potential global change effects on plant function and global carbon cycles.