The fate of fertiliser P in soil under pasture and uptake by subterraneum clover – a field study using <Superscript>33</Superscript>P-labelled single superphosphate

Background and aims

Single superphosphate (SSP) is a major source of phosphorus (P) used in grazing systems to improve pasture production. The aim of this experiment was to determine the fate of fertiliser P in clover pastures under field conditions.

Methods

A procedure was developed to radiolabel SSP granules with a ³³P radiotracer, which was then applied to the soil surface (equivalent to ~12 kg P ha^?1) of a clover pasture. Recovery of fertiliser P was determined in clover shoots, fertiliser granules and soil fractions (surface layer: 0–4 cm and sub-surface layer: 4–8 cm).

Results

The P diffusion patterns of the ³³P-labelled SSP granules were not significantly different to those of commercial SSP granules (P?>?0.05). Recovery of fertiliser P in clover shoots was 30–35 %. A considerable proportion of the fertiliser P (~28 %) was recovered in the surface soil layer and was largely inorganic P.

Conclusions

Recovery of fertiliser P by clover plants was up to 35 % in the year of application. Much of the fertiliser P in soil fractions was inorganic P, which highlights the importance of inorganic P forms and dynamics in soils under clover pasture on a single season timeframe at these sites.

     

Embedded rock fragments affect alpine steppe plant growth,soil carbon and nitrogen in the northern Tibetan Plateau

Background and Aims

Rock fragments within topsoil have important effects on soil properties and plant growth. This study mainly aimed to investigate the relationships between rock fragments, soil carbon (C) and nitrogen (N) densities and vegetation biomass in an alpine steppe.

Methods

Rock fragments, plant and soil samples were collected from four topographic positions (top, upper, lower, and bottom) on a hillslope.

Results

Volumetric rock fragment content within the 0–30 cm soil profile varied from 17.8 to 30.5%, the upper position value was significantly greater (P < 0.05) than those at other positions. The highest aboveground biomass was observed at the lower position (921 kg ha^?1), while the highest belowground biomass within the 0–30 cm profile was found at the upper position (4460 kg ha^?1). More fine earth and plant litter input accompanied by lower C and N losses induced by rainfall erosion resulted in higher soil organic C and total N densities (28.6 Mg C ha^?1 and 2.87 Mg N ha^?1) at the lower position.

Conclusions

Rock fragments may promote root growth but limit aboveground biomass production, and can therefore change the biomass distribution pattern. Our findings provide more evidence for scientifically assessing alpine steppe productivity.

     

Modelling facilitation or competition within a root system: importance of the overlap of root depletion and accumulation zones

Background and aims

Relevant soil properties and nutrient distributions influencing crop root growth might be different under no-till (NT) and mouldboard plough (MP) management. The possible different root systems within different managements might have key impact on crop nutrient uptake and consequently crop production. Our objective was to assess the long-term combined effects of tillage and phosphorus (P) fertilization on corn (Zea mays L.) root distribution and morphology.

Methods

Corn root and soil samples were collected during the silking stage at five depths (0–5, 5–10, 10–20, 20–30 and 30–40 cm) and three horizontal distances perpendicular to the corn row (5, 15 and 25 cm) under MP and NT with three P fertilizations (0, 17.5, and 35 kg P ha^?1) for a long-term (22 years) experiment in eastern Canada. Root morphology and soil properties were determined.

Results

NT practice decreased corn root biomass by ?26 % compared to MP, mainly by decreasing the primary and secondary roots. Additionally, corn roots in NT tend to be more expansive on the surface layer with higher root length and surface densities for the depth of 0–5 cm at two sampling distances of 15 and 25 cm. The 35 kg P ha^?1 rate increased the root biomass by 26 and 41 % compared to the 0 and 17.5 kg P ha^?1 rates.

Conclusions

No-tillage practice and low rates of P fertilization reduce corn roots. This is probably caused by the weed competition in NT and the continued downward P status with low P rates over 22 years.

     

<Emphasis Type="Italic">Gluconacetobacter diazotrophicus</Emphasis> exopolysaccharide protects bacterial cells against oxidative stress in vitro and during rice plant colonization

Aims

Increasing the input and turnover of root tissue is considered to be one method that may increase carbon (C) inputs and storage in soil. The use of herbicide during pasture renewal (periodic re-sowing of pasture) is expected to increase root inputs and turnover as plants die. The objective of this study was to quantify the short-term impact of pasture renewal on root turnover and C input to soil of ryegrass-clover pastures.

Methods

Pastures were labelled in the field using a ¹³C isotope pulse labelling method within 1 m² clear chambers. Five daily labelling events were carried out during one week in paired treatment plots within 3 replicate paddocks. One plot per paddock was sprayed with herbicide and then the pasture was renewed by direct drilling of seed. The ¹³C of roots and soil (0–100 mm) was measured at regular intervals over an 89-day period.

Results

Herbicide application caused an initial rapid turnover time of 17 days followed by a slower turnover time of 524 days, compared to unsprayed pasture which had a root turnover of 585 days. Faster root turnover following herbicide application resulted in greater cumulative C input to soil over 89 days with approximately double the C input in the sprayed treatment (3238 ± 378 kg C ha^?1) compared to the unsprayed treatment (1726 ± 540 kg C ha^?1).

Conclusions

The use of glyphosate during pasture renewal increased root turnover and resulted in a greater short term cumulative C input to soil. This study provides the first values of root turnover and C input to soil during a pasture renewal event in New Zealand pasture systems and contributes to the understanding of how pasture roots may influence the soil C input following plant death in grassland systems.

     

Intensive ground vegetation growth mitigates the carbon loss after forest disturbance

Aims

Slow or failed tree regeneration after forest disturbance is increasingly observed in the central European Alps, potentially amplifying the carbon (C) loss from disturbance. We aimed at quantifying C dynamics of a poorly regenerating disturbance site with a special focus on the role of non-woody ground vegetation.

Methods

Soil CO₂ efflux, fine root biomass, ground vegetation biomass, tree increment and litter input were assessed in (i) an undisturbed section of a ~ 110 years old Norway spruce stand, (ii) in a disturbed section which was clear-cut six years ago (no tree regeneration), and (iii) in a disturbed section which was clear-cut three years ago (no tree regeneration).

Results

Total soil CO₂ efflux was similar across all stand sections (8.5 ± 0.2 to 8.9 ± 0.3 t C ha^?1 yr.^?1). The undisturbed forest served as atmospheric C sink (2.1 t C ha^?1 yr.^?1), whereas both clearings were C sources to the atmosphere. The source strength three years after disturbance (?5.5 t C ha^?1 yr.^?1) was almost twice as high as six years after disturbance (?2.9 t C ha^?1 yr.^?1), with declining heterotrophic soil respiration and the high productivity of dense graminoid ground vegetation mitigating C loss.

Conclusions

C loss after disturbance decreases with time and ground vegetation growth. Dense non-woody ground vegetation cover can hamper tree regeneration but simultaneously decrease the ecosystem C loss. The role of ground vegetation should be more explicitly taken into account in forest C budgets assessing disturbance effects.

     

Pig slurry acidification,separation technology and thermal conversion affect phosphorus availability in soil amended with the derived solid fractions,chars or ashes

Aims

The aim was to study effects of slurry acidification, separation technology and thermal processing on the availability of P in soil amended with the solid fraction of pig slurry.

Methods

Acidified and non-acidified slurry were separated using different technologies: screw press (SCR), decanting centrifuge (DEC) and drainage after chemical pretreatment (CHE). Solids and pyrolysed (400 °C or 600 °C, char) or combusted (625 °C, ash) solids were applied to two soils, with triple superphosphate (TSP) as a reference. Soil P availability was determined over 12 weeks using diffusive gradients in thin films (DGT).

Results

The initial availability of P from DEC and CHE solids was similar to TSP in both soils. After 6 weeks no significant difference was observed between DEC solids and DEC chars. Acidification did not significantly affect P availability in the solids-amended soils over time, but it did affect P availability with the thermally processed materials.

Conclusions

Application of separated pig slurry solids generally increased soil P availability initially, but declining with time, indicating soil P fixing reactions. Chars and ashes on the other hand showed lower initial P availability, but remained constant or increased slightly with chars yielding P availability similar to solids after 12 weeks.

     

Linking root traits and competitive success in grassland species

Background and aims

Measures of phosphorus (P) in roots recovered from soil underestimate total P accumulation below-ground by crop species since they do not account for P in unrecovered (e.g., fine) root materials. ³³P-labelling of plant root systems may allow more accurate estimation of below-ground P input by plants.

Methods

Using a stem wick-feeding technique ³³P-labelled phosphoric acid was fed in situ to canola (Brassica napus) and lupin (Lupinus angustifolius) grown in sand or loam soils in sealed pots.

Results

Recovery of ³³P was 93 % in the plant-soil system and 7 % was sorbed to the wick. Significantly more ³³P was allocated below-ground than to shoots for both species with 59–90 % of ³³P measured in recovered roots plus bulk and rhizosphere soil. ³³P in recovered roots was higher in canola than lupin regardless of soil type. The proportion of ³³P detected in soil was greater for lupin than canola grown in sand and loam (37 and 73 % lupin, 20 and 23 % canola, respectively). Estimated total below-ground P accumulation by both species was at least twice that of recovered root P and was a greater proportion of total plant P for lupin than canola.

Conclusion

Labelling roots using ³³P via stem feeding can empower quantitative estimates of total below-ground plant P and root dry matter accumulation which can improve our understanding of P distribution in soil-plant systems.

     

Impact of plant growth-promoting bacteria on grain yield,protein content,and urea-<Superscript>15</Superscript> N recovery by maize in a Cerrado Oxisol

Background and aims

The inoculation of cereal crops with plant growth-promoting bacteria (PGPB) is a potential strategy to improve fertilizer-N acquisition by crops in soils with low capacity to supply N. A study was conducted to assess the impact of three inoculants on grain yield, protein content, and urea-¹⁵ N recovery in maize (Zea mays L.) under Cerrado soil and climate conditions.

Methods

The main treatments included inoculants containing (i) Azospirillum brasilense strain Sp245, (ii) A. brasilense strains AbV5 + AbV6, (iii) Herbaspirillum seropedicae strain ZAE94, and (iv) a non-inoculated control. The subtreatments were (i) urea-N fertilization (100 kg N ha^?1) at 30 days after sowing and (ii) no N addition at the stage. To determine fertilizer-N recovery, ¹⁵N–labelled urea was applied in microplots.

Results

Inoculants carrying A. brasilense improved urea-¹⁵ N acquisition efficiency in maize and also improved grain yield compared to the non-inoculated control, while urea-N fertilization enhanced grain quality by providing higher protein content.

Conclusion

Our results suggest that the inoculation of maize grains with PGPB represents a strategy to improve fertilizer-N recovery and maize yield in Cerrado soil with a low capacity to supply N.

     

Root morphology acclimation to phosphorus supply by six cultivars of <Emphasis Type="Italic">Trifolium subterraneum</Emphasis> L

Aims

Trifolium subterraneum L. is the predominant annual pasture legume in southern Australia. Cultivars with improved phosphorus (P) foraging ability would improve the P-use efficiency of agricultural systems. We therefore investigated variation in root traits related to P-uptake among six cultivars.

Methods

Micro-swards were grown at six levels of P in field soil with indigenous arbuscular mycorrhizal (AM) fungi for six weeks. Dry matter yield, tissue P concentration, rhizosphere carboxylates, AM fungal colonisation and root morphological traits were measured.

Results

The cultivars showed similar shoot and root yield responses to P supply. Average root diameter did not change, specific root length (SRL) increased and root tissue density (RTD) decreased with increased P supply. Amounts of total rhizosphere carboxylates were low (<1.2 nmol cm^?1 root). The percentage of root length colonised by AM fungi was greatest (29–43 %) at an intermediate level (8 mg kg^?1 dry soil) of P supply.

Conclusions

Most differences among cultivars were reasonably consistent across P supply levels, indicating greater numbers of lines could be screened reliably at a single P level. Low colonisation by AM fungi at low P supply deserves consideration when selecting soils for cultivar comparisons. Increased SRL and decreased RTD at high P supply likely result from self-shading within the micro-swards and warrant further investigation.

     

Taxonomic and ecological patterns in root traits of <Emphasis Type="Italic">Carex</Emphasis> (Cyperaceae)

Background and aims

In Malawi, strategies are being sought to boost maize production through improvements in soil fertility. This study assessed the impact of intercropping maize (Zea mays) with pigeon pea (Cajanus cajan) in Lixisols of Malawi on yield, biological N fixation, soil aggregation, and P forms within soil aggregates.

Methods

Maize and pigeon pea were grown intercropped in pots, with varying degrees of root interaction in order to understand the relative importance of biochemical versus physical rhizospheric interactions. Following harvest, soils were separated into aggregate fractions using wet-sieving, and the nutrient content of all fractions was assessed.

Results

The proportion of macroaggregates and microaggregates increased by 52 and 111%, respectively, in the intercropping treatment compared to sole maize, which significantly increased organic P storage in the microaggregates of intercropped compared to sole maize (84 versus 29 mg P kg^?1, respectively). Biologically fixed N increased from 89% in the sole pigeon pea to 96% in the intercropped system.

Conclusions

Intercropping maize with pigeon pea can have a significant and positive impact on soil structure as well as nutrient storage in these high P-sorbing soils. This is caused primarily by physical root contact and to a lesser degree by biochemical activities.

     

Corneal Collagen Cross-Linking for the Management of Mycotic Keratitis

Purpose

To evaluate the efficiency of corneal collagen cross-linking (CXL) in addition to topical voriconazole in cases with mycotic keratitis.

Design

Retrospective case series in a tertiary university hospital.

Participants

CXL was performed on 13 patients with mycotic keratitis who presented poor or no response to topical voriconazole treatment.

Methods

The clinical features, symptoms, treatment results and complications were recorded retrospectively. The corneal infection was graded according to the depth of infection into the stroma (from grade 1 to grade 3). The visual analogue scale was used to calculate the pain score before and 2 days after surgery.

Main Outcome Measures

Grade of the corneal infection.

Results

Mean age of 13 patients (6 female and 7 male) was 42.4 ± 17.7 years (20–74 years). Fungus was demonstrated in culture (eight patients) or cytological examination (five patients). Seven of the 13 patients (54%) were healed with topical voriconazole and CXL adjuvant treatment in 26 ± 10 days (15–40 days). The remaining six patients did not respond to CXL treatment; they initially presented with higher grade ulcers. Pre- and post-operative pain score values were 8 ± 0.8 and 3.5 ± 1, respectively (p < 0.05).

Conclusions

The current study suggests that adjunctive CXL treatment is effective in patients with small and superficial mycotic ulcers. These observations require further research by large randomized clinical trials.

     

Acid and calcareous soils affect nitrogen nutrition and organic nitrogen uptake by beech seedlings (<Emphasis Type="Italic">Fagus sylvatica</Emphasis> L.) under drought,and their ectomycorrhizal community structure

Aims

The role of different soil types for beech productivity and drought sensitivity is unknown. The aim of this experimental study was to compare mycorrhizal diversity between acid sandy and calcareous soils and to investigate how this diversity affects tree performance, nitrogen uptake and use efficiency (NUE).

Methods

Beech trees were germinated and grown in five different soil types (pH 3.8 to 6.7). One-and-a-half-year-old plants were exposed for 6 weeks to sufficient or low soil humidity. Tree biomass, root tip mycorrhizal colonization and community structure, root tip mortality, leaf area, photosynthesis, nitrogen concentrations, NUE and short-term ¹⁵N uptake from glutamine were determined.

Results

Soil type did not affect photosynthesis or biomass formation, with one exception in calcareous soil, where root mortality was higher than in the other soil types. Beech in acid soils showed lower mycorrhizal colonization, higher nitrogen tissue concentrations, and lower NUE than those in calcareous soils. Drought had no effect on nitrogen concentrations or NUE but caused reductions in mycorrhizal colonization. Mycorrhizal species richness correlated with nitrogen uptake and NUE. Nitrogen uptake was more sensitive to drought in calcareous soils than in acid soils.

Conclusions

Beech may be more drought-susceptible on calcareous sites because of stronger decrease of organic nitrogen uptake than on acid soils.

     

Fertilization,soil and plant community characteristics determine soil microbial activity in managed temperate grasslands

Background and aims

Contaminated soils can impede germination and growth of selected plant species, restricting effective phytoremediation strategies. The purpose of the present study was to enhance the germination and growth of saltgrass [Distichlis spicata (L.) Greene] by evaluating the efficacy of certain seed pretreatments and soil amendments.

Methods

Ten seed pretreatment methods, two amendments, three soil depths and five saline levels were tested under greenhouse conditions.

Results

Saltgrass germination and growth were negatively correlated with increasing salinity levels when NaCl > 85.6 mM. Among ten seed pretreatments (stratification + Proxy 24 h, hot water + Proxy 24 h, stratification, hot water + Proxy 48 h, Proxy 48 h, Proxy 24 h, hot water, scarification, gibberellins, and KMnO₄), the two best methods were stratification + Proxy 24 h and hot water + Proxy 24 h for enhancing saltgrass germination, with the latter pretreatment being especially useful because of its shorter preparation time and high germination rates. Proxy is a commercial ethephon product. Potting soil (5.0 cm depth) was found to be the best amendment for saltgrass germination and growth in hydrocarbon-contaminated soils.

Conclusion

We conclude that direct seeding of saline soils contaminated with petroleum hydrocarbons is a feasible phytoremediation strategy provided that appropriate seed pretreatments and amendments are utilized.

     

Simulated nitrogen deposition significantly suppresses the decomposition of forest litter in a natural evergreen broad-leaved forest in the Rainy Area of Western China

Background and aims

Litter, an essential component of forest ecosystems, plays an important role in maintaining soil fertility, sequestering carbon (C) and improving soil biodiversity. However, litter decomposition is affected by increased nitrogen (N) deposition. Numerous reports have presented N deposition experiments in different forest ecosystems to investigate the effects of N deposition on litter decomposition, but the effects remain unclear, especially in ecosystems receiving increasingly higher levels of ambient N deposition. To address this gap, we performed a litterbag experiment to understand the effects of increasing N deposition on the litter decomposition process in natural evergreen broad-leaved forest in the Rainy Area of Western China.

Methods

A 2-year field litter decomposition experiment was conducted using the litterbag method. Four levels of N deposition were established: control (CK; 0 kg·N·ha^?1·year^?1), low N deposition (LN; 50 kg·N·ha^?1·year^?1), medium N deposition (MN; 150 kg·N·ha^?1·year^?1), and high N deposition (HN; 300 kg·N·ha^?1·year^?1). The simulated N depositions ranged from 50% to 320% of the ambient rate of wet N deposition.

Results

Simulated N deposition significantly increased the remaining mass, C, N, lignin and cellulose of the litter. The LN treatment decreased the remaining phosphorus (P); conversely, the HN treatment increased it. In the late stage of the study period, the mass remaining was positively closely correlated to the lignin and cellulose remaining during the decomposition process.

Conclusions

Simulated N deposition significantly suppressed the litter decomposition in the natural evergreen broad-leaved forest, despite the high rate of ambient N deposition, and the inhibitory effects increased with the N deposition levels. The suppressive effect of N deposition on litter decomposition may be primarily explained by the inhibition of lignin and cellulose degradation by the exogenous inorganic N. With ongoing N deposition in future, N deposition may have a potentially significant impact on C and N cycles in such forest ecosystems.

     

Dynamics of soil carbon,nitrogen, and phosphorus in calcareous soils after land-use abandonment – A chronosequence study

Aims

The objective of this study was to investigate changes in soil total organic C (TOC), total nitrogen (TN), phosphorus (P) fractions, and microbial community structure during secondary succession after abandonment of vineyards on calcareous soils.

Methods

Two chronosequences covering 200 years and differing in aspect and slope were established in Hungary, and the upper 10 cm of the mineral soils were studied.

Results

We found strong increases in TOC concentrations after land-use abandonment, especially at the south-exposed sites. The TOC/TN ratio increased by a factor of 1.3 in the south-west exposed chronosequence and by a factor of 1.6 in south exposed chronosequence. The concentration of labile P (NaHCO₃-extractable P) diminished during the first 50 years after land-use abandonment, leading to low P availability at the later stages of the succession. The total organic P (TOP) concentration increased during the first 40 years after abandonment. At the later stages of succession, TOP concentrations decreased again, while the ratio of TOC/TOP increased continuously over 200 years. The ratio of arbuscular-mycorrhizal-fungi-to-bacteria (AMF/bacteria) increased strongly during the first decade after abandonment of the vineyards.

Conclusions

Our study indicates that impacts of former cultivation on secondary ecosystems persisted for more than a century, and that especially P concentrations showed long lasting legacy effects.

     

Phosphorus availability from bone char in a P-fixing soil influenced by root-mycorrhizae-biochar interactions

Aims

The objectives of this study were to evaluate (1) the fertilizer potential of bone char, (2) the effects of wood biochar on plant-available phosphorus (P), and (3) the role of root-mycorrhizae-biochar interactions in plant P acquisition from a P-fixing soil.

Methods

Incubation and pot experiments were conducted with a P-fixing soil and maize with or without root hairs and arbuscular mycorrhizae (AM) inoculation. Olsen-, resin-P and plant P accumulation were used to estimate P availability from bone char, co-pyrolyzed bone char-wood biochar, and separate bone char and wood biochar additions produced at 60, 350 and 750 °C, and Triple Superphosphate (TSP).

Results

Maize inoculated with AM showed similar P accumulation when fertilized with either 750 °C bone char or TSP. Pyrolyzing bone did not increase extractable P in soil in comparison to unpyrolyzed bone, apart from a 67 % increase in resin-extractable P after additions of bone char pyrolyzed at 350 °C. Despite greater Olsen-P extractability, co-pyrolysis of bone with wood reduced maize P uptake. Wood biochars reduced resin-P from bone char by 14–26 %, whereas oven-dried wood increased resin-P by 23 %.

Conclusions

Bone char is an effective P fertilizer, especially if root-AM interactions are simultaneously considered. Biochar influences plant access to soil P and requires careful management to improve P availability.

     

Roles of shoots and roots in cadmium uptake and distribution in tubers of potato (<Emphasis Type="Italic">Solanum tuberosum</Emphasis> L)

Aims

We investigated whether density fractionation can be used to determine the distribution of organic phosphorus (OP) between free and mineral-associated soil organic matter (SOM).

Methods

We performed density fractionations using sodium polytungstate solution (specific gravity 1.6 g cm^?3) on 20 soils from UK semi-natural and pasture ecosystems, to obtain a light fraction (LF) and a heavy fraction (HF) for each soil. The fractions were quantified by weight, and analysed for organic carbon (OC), total N (TN), total P (TP), inorganic P (IP), and OP (by difference).

Results

Good recoveries of soil mass (96%), OC and TN (both ~ 90%) were obtained, but recovery of OP only averaged 56%. The average P:C ratio of HF SOM exceeded that of LF SOM by a factor of six, greater than the factor of two obtained for TN:OC. For the soils studied, the elements of SOM were predominantly in the HF, with averages of 75% for C, 82% for N, and 90% for P.

Conclusions

The incomplete recovery of OP demands further work. Nonetheless, the results show that HF SOM is much richer in P than LF SOM.

     

Responses of switchgrass soil respiration and its components to precipitation gradient in a mesocosm study

Aims

The objective of this study was to investigate the effects of the precipitation changes on soil, microbial and root respirations of switchgrass soils, and the relationships between soil respiration and plant growth, soil moisture and temperature.

Methods

A mesocosm experiment was conducted with five precipitation treatments over two years in a greenhouse in Nashville, Tennessee. The treatments included ambient precipitation, ?50%, ?33%, +33% and +50% of ambient precipitation. Soil, microbial, and root respirations were quantified during the growing seasons.

Results

Mean soil and root respirations in the +50% treatment were the highest (2.48 and 0.93 μmol CO₂ m^?2 s^?1, respectively) among all treatments. Soil microbial respiration contributed more to soil respiration, and had higher precipitation sensitivity mostly than root respiration. Increases in precipitation mostly enhanced microbial respiration while decreases in precipitation reduced both microbial and root respirations. Across precipitation treatments, soil respiration was significantly influenced by soil moisture, soil temperature, and aboveground biomass.

Conclusions

Our results showed that microbial respiration was more sensitive to precipitation changes, and precipitation regulated the response of soil respiration to soil temperature. The information generated in this study will be useful for model simulation of soil respiration in switchgrass fields under precipitation changes.

     

Phosphorus dynamics in a tropical forest soil restored after strip mining

Background and aims

We hypothesized that successful early ecosystem and soil development in these P-deficient soil materials will initially depend on effective re-establishment of P storage and cycling through organic matter. This hypothesis was tested in a 26-year chronosequence of seven lightly fertilized, oxidic soil materials restored to eucalypt forest communities after bauxite mining.

Methods

Total P (Pt) status, Hedley P fractions and partial chemical speciation (NaOH-EDTA extraction and analysed using solution ³¹P NMR spectroscopy) were determined in the restored soils.

Results

Concentrations of Pt and most Hedley fractions changed with restoration period, declined with depth and were strongly positively correlated with C and N concentrations. Biological P dominated the Labile and Intermediate P fractions while Long-term P was dominantly inorganic. Organic P concentrations in NaOH-EDTA extracts and their chemical natures were similar in restored and unburned native forest sites. Phosphomonoesters were the dominant class of organic P.

Conclusions

Surprisingly rapid P accretion and fractional changes occurred over 26 years, largely in the surface soils and closely associated with organic matter status. Alkaline hydrolysis products of phosphodiesters and pyrophosphate indicated the importance of microbial P cycling. The important consequences for long-term ecosystem development and biological diversity require further study.