Changes in soil phosphatase activity and P transformation rates induced by application of N- and S-containing acid-mist to a forest canopy
J.A. Carreira
a,
, R. Garcı´a-Ruiz
a
, J. Lie´tor
a
, A.F. Harrison
b
a
Area de Ecologı´a, Universidad de Jae´n, Campus Las Lagunillas B-3, 23071 Jae´n, Spain
b
Merlewood Research Station, Institute of Terrestrial Ecology, Grange-over-Sands LA11 6JU, UK Accepted 30 May 2000
Abstract
The indirect effects of acid-misting applied to tree canopies, on soil P availability, phosphatase activity and P mineralisation rates in a Sitka spruce Picea sitchensis Bong. Carr stand have been investigated. The treated trees, grouped according to five height classes, had for four
years previously received acid mist consisting of a mixture of H
2
SO
4
and NH
4
NO
3
pH 2.5 at concentrations of 3.2 mM H
1
and 1.6 mM each of NH
1 4
; NO
2 3
and SO
22 4
: These simulate cloudwater composition in uplands affected by acidic deposition. Another group of mixed height-
class trees, received a double dose of acid mist. Control — no acid-misted-trees received only the usual precipitation inputs. The acid mist treatments had previously been found to induce a significant reduction in stem diameter growth, but no canopy visible injury symptoms were
observed. Root bioassays had demonstrated the induction of P nutritional stress in acid-misted versus no acid-misted trees. Soil chemical analysis showed that acidifying inputs induced changes in the inorganic P subcycle by: i increasing acidity and P sorption capacity of the
soils; and ii decreasing the concentration of labile inorganic P. We report here on changes in the organic P subcycle phosphatase activity and gross mineralisation rates. We used a method which applies independent treatments to soil samples control, HgCl
2
-addition, HgCl
2
- addition 1 autoclaving to separate mineral solubilisation, organic mineralisation and immobilisation of solution P. Soil phosphatase activity
was significantly lower under acid-misted trees 263.9 mg pNP h
21
g
21
than under control trees 382.0 mg pNP h
21
g
21
. Soils beneath double-dose acid-misted trees showed a 42 reduction in the labile inorganic P pool-size, and a 33 increase in the labile organic P pool-
size, compared to soils under control trees. A pattern of decreasing net P solubilisation and gross P mineralisation rates with increasing acid- mist dose-level was also found. Thus, the combined effects of acid-misting on the inorganic and organic P subcycles, in addition to the
suggested effect of N saturation enhancing demand for P by the trees, may have induced P deficiency and reduced tree growth. The effects described are considered to be important factors in the forest decline syndrome. q 2000 Elsevier Science Ltd. All rights reserved.
Keywords : Picea sitchensis; Acidic deposition; Soil acidification; Phosphorus availability; Gross P mineralisation; Net P solubilisation; Immobilisation;
Phosphatase activity
1. Introduction
Much research has concentrated on the acidifying effects of atmospheric pollutant inputs on soils and their roles in
forest decline Schulze, 1989, as this has become a signifi- cant economic and environmental problem in Europe.
Forest damage both in Europe and in North America is frequently associated with acute nutritional unbalances
Hu¨ttl, 1988; Tomlinson, 1990, often caused by base cations Mg and K leaching from the soil Ulrich et al.,
1980; Van Breemen et al., 1983 and induced cation defi- ciencies Van Dick and Roelofs, 1988; Kazda, 1990. The
induction of phosphorus deficiency has also been proposed as a possible effect of acidic deposition Foy et al., 1978,
but there is a lack of studies specifically addressing the question Binkley et al., 1989. A limited number of reports
have indicated that pollutant inputs are inducing phosphorus deficiency in forest trees, at least in some sensitive areas
both in North America Pare´ and Bernier, 1989a and in Europe Mohren et al., 1986; Van Dick and Roelofs,
1988; Houdijk and Roelofs, 1993. Phosphorus deficiency is known to be a key limiting factor in forest production
across Europe Harrison, 1989. However, little research has been carried out on changes in soil P cycling induced
by pollutant inputs and in the balance between N and P nutrition of trees.
Our working hypothesis is that acidifying inputs, and the induced changes in soil acidity, decrease the availability of
P in soil by reducing both soil solution P due to increased P
Soil Biology Biochemistry 32 2000 1857–1865
0038-071700 - see front matter q 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 0 3 8 - 0 7 1 7 0 0 0 0 1 5 9 - 0
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Corresponding author. Tel.: 134-9-53-212551; fax: 134-9-53-212141. E-mail address:
jafuenteujaen.es J.A. Carreira.
adsorption capacity and the rate of organic phosphorus mineralisation. In addition, associated N saturation creates
enhanced demand for P by the trees relative to the supply from the soil. The combination of these two factors will
induce P deficiency and reduce tree growth Fig. 1.
To test this hypothesis, the effects of acid-mist applied to tree canopies, on tree P nutrition, and soil P cycling and
availability, were assessed in a field manipulation experi- ment in Scotland. Acid-mist treatments had been applied for
four consecutive years to a Sitka spruce plantation and had caused a significant reduction in stem diameter growth
compared to non-acid-misted trees Sheppard et al., 1995. Foliar analysis were carried out in an attempt to relate such
reduction in stem area to the induction of nutrient deficien- cies including P, but results were inconclusive Sheppard
et al., 1995. However, Carreira et al. 1997 applied a more sensitive root bioassay technique based on the metabolic
uptake of
32
P by excised roots and demonstrated that acid- mist treated trees were under P nutritional stress relative to
non-acid-misted trees. Additionally, acid-mist treatments were found to affect soil acidity lower pH and marked
changes in the cation exchange complex composition and processes involved in the inorganic P subcycle higher soil P
adsorption capacity Carreira et al., 1997. Here, we report on changes in processes involved in the soil organic P
cycling phosphatase activity and organic P mineralisation.
2. Materials and methods
