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 assume that potential global changes in temperature and/or other factors may alter tissue nitrogen (N) and dark respiration rates (R(d)). However, 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 needles of 10-year-old trees of 14 Scots Pine (Pinus sylvestris) populations of wide-ranging origin (43 degrees to 60 degrees N), grown under common garden conditions. 2. For 11 lowland populations (elevation <200 m) from the contiguous part of the species range (48 degrees to 60 degrees 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 equal to 0.93, P<0.01). Similar %N and latitude of origin correlations were observed in another year at this site and in retrospective analyses of published data for different sets of Scots Pine populations grown in common gardens at 48 degrees, 52 degrees C and 62 degrees N latitudes. 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 positively 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) increased from 4.5 to 6.9 nmol g(-1) s(-1). 3. Mean needle %N and R(d) values for two montane southern populations (43 degrees and 44 degrees N, elevation greater than or equal to 885 m) growing in the same common garden at Kornik were consistent with the relationships between mean annual temperature, needle %N and R(d) observed for the more northerly populations but did not fit the latitudinal patterns. This suggests that temperature and/or associated climate variables are likely the driving force for observed genetic variation in Scots Pine needle %N and R(d) across latitudinal and altitudinal gradients. 4. Results of these common garden studies support the idea of a general relationship between 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 needle %N and respiration in plants originating from colder habitats. Such patterns need to be better understood and quantified, and merit consideration in modelling of current and potential global change effects on plant function and global carbon cycles.