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

More documents

Recommendations

Info

From this it can be concluded that the serious situation in relation to P nutrition of German forests is described adequately. 3. Due to many plant and site factors outlined in the review, one time foliage sampling is not considered adequate to assess the P status of individual sites. Therefore a data set from the intensive monitoring sites from Lower Saxony, where repeated foliage samples were taken, was included in the analysis. Temporal dynamics in P concentrations in the current year needles and mature foliage of 27 long-term monitoring plots in Lower Saxony (Level II sites), for which annual or biannual P-concentration values existed, were analysed for a ten year period using mixed linear models. Foliar P concentrations at these sites revealed a decline in P concentrations across all sites for spruce and pine over a ten-year period from the mid 90s to 2004 or 2005. The decline over a ten-year period equated to a reduction in P concentrations in the youngest needles of 0.06 mg g -1 in spruce and 0.15 mg g -1 in pine. In both species, the decline was more pronounced in older needles. For beech, no decline in P concentrations could be observed. Similar results of a decrease in P foliage levels of periodically collected samples during the last 20 years have been reported in the literature from different parts of Europe and North America as described in detail in the review. 4. In order to assess the general validity of the results reported above for Lower Saxony, there is a need to carry out further evaluations for additional Level II sites covering a wider range of site conditions. It is therefore recommended that additional analysis be carried out to evaluate data from Level II sites across different German States. 5. A number of reasons have been provided in the reviewed literature for this decreasing trend in foliar P values. In most cases, this decreasing trend has been related to high inputs of N and acidity to forest stands. These changes in N inputs and soil acidity can affect the P status of forest ecosystems in a number of ways: (a) High N inputs have resulted in higher growth rates, thereby causing additional demand for P uptake and causing increased levels of P retention in the woody components. This would decrease the fraction of P turnover. (b) High N inputs may decrease the rate of litter decomposition and thereby the associated organic P mineralisation. This would further decrease the amount of P turnover present in the recycled organic matter. (c) P uptake may be impaired due to high soil acidity and associated reduction in fine-root and mycorrhizal activity. (d) Under high acidity conditions, the amount of easily desorbed P may decrease due to an increase in P fixation by soils. (e) High N inputs usually causes high nitrate levels in soils which may compete with the uptake of phosphate (anion competition). (f) 6
High N inputs and uptake by plants may cause an imbalance of N to P ratios, affecting plant vitality. The review provides examples for the different possible processes described here. To what extent the different mechanisms captured by these hypotheses are responsible for the current situation for different sites and tree species remains unknown. 6. To analyse whether the variation in foliar P concentrations, soil P content, or forest floor P content may be explained by the large set of independent parameters determined in the nationwide forest soil survey, a regression tree approach was used. This data mining approach is often used to generate hypotheses from large data sets with a multitude of independent variables. The explorative analysis of the nationwide inventory (BZE1) data set did not provide an explanation for the variation in foliar P levels. The absence of any pattern in relation to soil P was assigned to the lack of sensitive methods to determine long term changes in plantavailable P content of forest soils. 7. The exploratory analysis of the data set indicated that P content in forest floors was more closely related to their N content than to the C content, which suggests that P accumulation in the forest floor may not be a simple function of organic matter accumulation, but may be related to the accumulation of organic matter with lower C/N ratios, such as in OH layers. 8. Analysis of total P in soils (as was done in the samples from the BZE I ) does not relate to the amount of plant available P in soils. Total P occurs in many organic and inorganic forms in forest soils. Labile and mineralisable fractions can be described using chemical extraction procedures but their availability in forest soils is not appropriately defined. Moreover, chemical extraction procedures are highly resource intensive and cannot be employed directly to national survey samples. Given appropriate pedo-transfer functions which may involve analysis of forest soils for total P and other easy to measure parameters, it may be possible to assess the amount of different fractions of P in soils. However, the pedo-transfer functions developed so far are based on a limited set of samples from forest sites and they appear to be site and bedrock specific. Presently available pedo-transfer functions cannot be used to determine P fractions in a wide range of samples collected on a large grid based inventory. Due to high variation in estimating the pedo-transfer functions, the small changes expected in the estimated amount of labile P fractions may not be detectable. Therefore the use of pedo-transfer functions to determine the amount of P fractions in forest soils is unlikely to be a useful assessment technique. 7
Page 1 and 2: ASSESSMENT OF CHANGES IN THE PHOSPH
Page 3 and 4: RECOMMENDATIONS 1. The results of t
Page 5: EXECUTIVE SUMMARY 1. The first nati
Page 9 and 10: 12. It is recommended that a series
Page 11 and 12: Below, these hypotheses are being d
Page 13 and 14: Douglas fir which suffered from abs
Page 15 and 16: easons of such results. Another rea
Page 17 and 18: The frequency and the amount of mas
Page 19 and 20: usually present in the leaves. In v
Page 21 and 22: level class are given in brackets.
Page 23 and 24: 2.3 Factors influencing the foliage
Page 25 and 26: example the compiled data from BZE-
Page 27 and 28: mostly during periods of active gro
Page 29 and 30: Table 3: Number of cases included f
Page 31 and 32: P % 0.1 0.2 0.3 0.4 Kiefer 4 4,5 5
Page 33 and 34: P % 0.1 0.2 0.3 0.4 0.5 Eiche 4 4,5
Page 35 and 36: 19.84 n=144 NVHU< 1228 | CMENGE< 38
Page 37 and 38: 2.6 Changes in P concentrations in
Page 39 and 40: in section 1 of this report. In sum
Page 41 and 42: Fig 8: Mixed linear model describin
Page 43 and 44: Fig 10: . Mixed linear model descri
Page 45 and 46: Table 6: Concentration of P (mg/g)
Page 47 and 48: (Nilsen and Abrahmsen 2003) reporte
Page 49 and 50: 3. PHOSPHRUS IN FOREST SOILS 3.1 In
Page 51 and 52: sequential extraction scheme of ext
Page 53 and 54: Table 8 : Sequential extraction pro
Page 55 and 56: phosphates at pH values
Page 57 and 58:
3.2.2 Inorganic forms of P - desorp
Page 59 and 60:
Mineralisation of organic P does no
Page 61 and 62:
enhances the dissolution of Ca-phos
Page 63 and 64:
water, and sodium bicarbonate metho
Page 65 and 66:
Table 10. Estimated transfers and c
Page 67 and 68:
3.3 Use of pedo-transfer functions
Page 69 and 70:
the amount taken up at each site. T
Page 71 and 72:
is commonly saturated with HCO3 is
Page 73 and 74:
assess P status or any changes in P
Page 75 and 76:
Forest Ecol. Manage. 92, 119-152. B
Page 77 and 78:
Rev. Plant Physiol.Plant Mol. Biol.
Page 79 and 80:
and N-free-fertilisation. Plant Soi
Page 81 and 82:
Sparling GP, Hart PBS, August JA. (
show all

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

Create successful ePaper yourself

Delete template?

Save as template?