Accelerating ecological restoration of drastically disturbed land by

Accelerating ecological restoration of drastically disturbed land by promoting early establishment of microbial function Julie Williamson, Davey Jones, Mark Nason, Edwin Rowe. Institute of Environmental Science, University of Wales Bangor, WALES. LL 57 2 UW. Introduction Quarries and minesites are examples of extreme disturbance. Frequently, soil-forming material is scarce and ecological restoration is the only viable option. Establishing soil microbial function is critical and a key objective of our study. At Penrhyn slate quarry in North Wales we examined soil microbial function under populations of naturally established birch (Betula pubescens) with that under young planted birch. Hypotheses • microbial biomass and nutrient cycling capability increase with tree size in natural tree populations • organic amendments promote earlier establishment of microbial function than inorganic ones in planted trees • organic amendments result in a ‘soil’ similar in microbial and biochemical properties to soil under naturally established trees. The effect of amendment type and time on soil properties under planted small birch was tested by Anova. • Soil mineral N (NH 4 N + NO 3 N) was much higher in the amended plots than the control; potentially- mineralisable N and microbial N were far greater in the sewage-paper mix treatment and increased over time, compared with the other treatments. Basal respiration was also stimulated by the organic mix. A decrease in mineral N and basal respiration over time was consistent with ecological succession. Actinomycete CFUs were similar in all treatments (Table 2). • Soil properties under planted birch amended with sewage-paper mix most closely resembled those of large natural birch trees; relative to total C in each case, microbial biomass and basal respiration quotients were very similar. The range of actinomycete CFUs was similar in natural and planted birch (Tables 1, 2). Table 2. Soil biochemical properties of small birch trees planted in slate waste amended with organic or mineral amendments, sampled after 1, 7 and 13 months. Numbers followed by the same letter within a row are not significantly different (P > 0. 05). n = 9. Methods • Naturally established groves of similar-sized birch (Fig. 1) growing in undisturbed slate waste were selected and ranked according to tree height (range 20 - 1000 cm). Six replicate groves were selected for each tree height class. • Nearby, seedling birch were planted into slate waste with 1) no amendment, 2) slow-release NPK (15: 10) fertiliser prills or 3) digested sewage cake + de-inked paper pulp mix. NPK fertiliser was applied to deliver N at a rate equivalent to the predicted N-mineralisation of sewage in the first year. Slate was sampled after one, seven and 13 months. There were nine replicate plots for each fertiliser level. • Soil samples were taken from 0 -15 cm depth. Results The effect of tree size in natural populations on soil properties was tested in two ways: • Anova showed that soil organic matter (total C), microbial biomass and microbial activity (basal respiration and amino acid mineralisation rates) all increased dramatically in large trees compared with small trees. Similarly, actinomycete (late-succession bioindicator) phospholipid fatty acid (PLFA) levels also increased (Table 1). • Individual tree heights were closely related to their basal stem area (R 2 =90%, data not shown). • Regression analysis showed that variations in soil organic matter, microbial biomass and microbial activity, and actinomycete PLFA were closely related to the summed basal stem areas for each grove of naturally established trees. Actinomycete colony-forming units (CFU) correlated weakly with PLFA data (P = 0. 048) but were highly variable and not significantly related to tree size (Table 1). Table 1. Influence of size of birch trees naturally established in slate waste on selected biochemical properties. Tree height class was used for Anova and the summed stem basal areas of each grove used for regression analysis. Numbers followed by the same letter within a row are not significantly different (P>0. 05). n = 6. Fig. 1 A grove of medium-sized naturally established birch trees. Conclusions • Soil organic matter, microbial biomass and activity increased with tree size in natural tree populations. Naturally established birch provided a model against which we compared soil function under planted birch. • The organic amendment effectively immobilised N in slate waste as microbial N and potentially-mineralisable N, whilst providing mineral N at a similar rate to NPK fertiliser. Immobilisation ensured a continued slow release of nutrients to sustain tree growth. The organic amendment was therefore suitable for ecological restoration. • Soil properties under birch planted in slate waste amended with the organic mix were similar to those existing in slate naturally colonised by large birch. The organic amendment accelerated the process of soil genesis. • Actinomycete PLFA proved a successful indicator of soil genesis in naturally established trees but actinomycete CFUs were too variable. Acknowledgements This is an EU LIFE Environment funded project, with industry sponsors A. Mc. Alpine Slate Ltd. Thanks to Dr R. Bardgett (Lancaster University) and Dr P. Hobbs (Institute for Grassland Environmental Research) for PLFA extraction and analysis.