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2.6 Changes <strong>in</strong> P concentrations <strong>in</strong> <strong>the</strong> foliage and leaf litter dur<strong>in</strong>g <strong>the</strong> last<br />

Foliage<br />

10 years at Level II sites <strong>in</strong> Lower Saxony (NS)<br />

It has been previously po<strong>in</strong>ted out that P data obta<strong>in</strong>ed by one time sampl<strong>in</strong>g <strong>of</strong><br />

foliage may not provide useful <strong>in</strong>formation about <strong>the</strong> P <strong>status</strong> <strong>of</strong> a <strong>forest</strong> stand. The<br />

ma<strong>in</strong> reason for that is <strong>the</strong> substantial temporal variation ow<strong>in</strong>g to many factors<br />

outl<strong>in</strong>ed previously <strong>in</strong> <strong>the</strong> review. Thus repeatedly taken samples over a number <strong>of</strong><br />

years provide better <strong>in</strong>formation <strong>of</strong> any change <strong>in</strong> <strong>the</strong> foliar <strong>status</strong>. To assess, whe<strong>the</strong>r<br />

<strong>the</strong>re may be a decl<strong>in</strong>e <strong>in</strong> foliar P nutrition, <strong>the</strong> temporal dynamics <strong>in</strong> P concentrations<br />

<strong>in</strong> <strong>the</strong> current year needles and mature foliage <strong>of</strong> 27 long-term monitor<strong>in</strong>g plots <strong>in</strong><br />

Lower Saxony were assessed statistically. For each site, annual or biannual Pconcentration<br />

values were analysed us<strong>in</strong>g mixed l<strong>in</strong>ear models, which were fitted to<br />

all data for each species for a 10-year period. There were 10 spruce sites, for which<br />

<strong>the</strong> mean P concentrations <strong>of</strong> 1-year old needles and <strong>the</strong> relative proportion <strong>of</strong> 3-year<br />

and 5-year needles are given <strong>in</strong> Table 5. In addition, <strong>the</strong>re were three p<strong>in</strong>e sites, 8<br />

beech sites and 6 oak sites (Fig 7-10). The older spruce needles had lower<br />

concentrations <strong>of</strong> P, 66-82 % <strong>in</strong> 3-yr old and 47–70% <strong>in</strong> 5-yr old needles when<br />

compared to 1-yr old needles. This represents a significant amount <strong>of</strong> P withdrawal,<br />

assum<strong>in</strong>g <strong>the</strong> weights <strong>of</strong> 3- and 5-yr old needles have not <strong>in</strong>creased, which is unlikely.<br />

Table 5: Mean P foliar values <strong>in</strong> <strong>the</strong> current year old (1-yr) needles, and relative<br />

concentrations <strong>in</strong> 3-yr and 5-yr old needles to 1-yr old needles. Mean<br />

values represent 10 years <strong>of</strong> measurements.<br />

Site P <strong>in</strong> 1-yr old Percent <strong>of</strong> P conta<strong>in</strong>ed Percent <strong>of</strong> P conta<strong>in</strong>ed<br />

needles <strong>in</strong> 3-yr old needles <strong>in</strong> 5-yr old needles<br />

mg/g % %<br />

HiKA 1.11 67 59<br />

HiMA 1.18 70 57<br />

HIMJ 1.31 82 70<br />

LBKA 1.33 75 56<br />

LBNH 1.39 77 70<br />

LBSH 1.22 78 70<br />

SLF1 1.38 74 62<br />

SLFD 1.32 70 61<br />

SPFi 1.36 72 55<br />

WIFi 1.47 66 47<br />

37

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