assessment of changes in the phosphorus status of forest ...

2.6 Changes in P concentrations in the foliage and leaf litter during the last
Foliage
10 years at Level II sites in Lower Saxony (NS)
It has been previously pointed out that P data obtained by one time sampling of
foliage may not provide useful information about the P status of a forest stand. The
main reason for that is the substantial temporal variation owing to many factors
outlined previously in the review. Thus repeatedly taken samples over a number of
years provide better information of any change in the foliar status. To assess, whether
there may be a decline in foliar P nutrition, the temporal dynamics in P concentrations
in the current year needles and mature foliage of 27 long-term monitoring plots in
Lower Saxony were assessed statistically. For each site, annual or biannual Pconcentration
values were analysed using mixed linear models, which were fitted to
all data for each species for a 10-year period. There were 10 spruce sites, for which
the mean P concentrations of 1-year old needles and the relative proportion of 3-year
and 5-year needles are given in Table 5. In addition, there were three pine sites, 8
beech sites and 6 oak sites (Fig 7-10). The older spruce needles had lower
concentrations of P, 66-82 % in 3-yr old and 47–70% in 5-yr old needles when
compared to 1-yr old needles. This represents a significant amount of P withdrawal,
assuming the weights of 3- and 5-yr old needles have not increased, which is unlikely.
Table 5: Mean P foliar values in the current year old (1-yr) needles, and relative
concentrations in 3-yr and 5-yr old needles to 1-yr old needles. Mean
values represent 10 years of measurements.
Site P in 1-yr old Percent of P contained Percent of P contained
needles in 3-yr old needles in 5-yr old needles
mg/g % %
HiKA 1.11 67 59
HiMA 1.18 70 57
HIMJ 1.31 82 70
LBKA 1.33 75 56
LBNH 1.39 77 70
LBSH 1.22 78 70
SLF1 1.38 74 62
SLFD 1.32 70 61
SPFi 1.36 72 55
WIFi 1.47 66 47
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