Interactive effects of composted green waste and earthworm activity on tree growth and reclaimed soil quality: a mesocosm experiment

On reclaimed landfill sites, the addition of organic matter such as composted green waste (CGW) to soil-forming materials can support tree survival and growth. CGW addition may also assist the establishment of sustainable earthworm populations, and in turn these organisms can promote further soil development through their burrowing and feeding activity. Despite such potentially mutual benefits, little research has been carried out into CGW and earthworm interactions with trees on reclaimed land. A twelve month, open field nursery experiment revealed the responses of the interactions between two tree species; Alnus cordata (Betulaceae) and Acer platanoides (Sapindaceae), CGW and the earthworms Aporrectodea longa (Lumbricidae) and Allolobophora chlorotica (Lumbricidae) in reclaimed soil. Controlled mesocosm conditions permitted a detailed investigation into the factors affecting tree growth and nutrient uptake, soil nutrient cycling and earthworm population dynamics. Results revealed that A. cordata growth was unaffected by CGW or earthworm addition. There was, however, a significant positive synergistic effect of earthworm activity and CGW addition on A. platanoides growth. CGW addition significantly increased levels of organic carbon and essential plant macro-nutrients in reclaimed soil while earthworm activity assisted decomposition of both leaf litter and CGW. Findings showed that CGW may serve as a suitable early source of organic matter to support earthworm population establishment on reclaimed sites. This experiment demonstrates that CGW improves reclaimed soil quality, thereafter supporting tree establishment and growth on reclaimed landfill

A New Approach Using Modeling to Interpret Measured Changes in Soil Organic Carbon in Forests : The Case of a 200 Year Pine Chronosequence on a Podzolic Soil in Scotland

Discounted APC via the Frontiers Open Access Agreement Acknowledgments: Andy Kennedy for teaching about the podzolic soil sampling and horizon recognition. Rothiemurhus estate owners and the forest manager–Piers Voisey. Forest Research agency Soil Sustainability Research and Forest Mensuration, Modeling and Forecasting Science groups for consultations, practical and financial support. Ron Summers and Samantha Broadmeadow for help with GIS maps. Dr Robert Wilson for the help with finding ancient pine woodland locations in Scotland. We acknowledge the E-OBS dataset from the EU-FP6 project ENSEMBLES (http://ensembles-eu.metoffice.com) and the data providers in the ECA&D project (http://www.ecad.eu). This work contributes to the UKRI-funded Soils-R-GRREAT project (NE/P019455/1). We thank to two reviewers for their insightful comments. Funding: The research was funded by the University of Aberdeen and Forest Research joint PhD training grant. James Hutton Institute provided help in kind. The NERC (Natural Environmental Resources Council) grant NE/P019455/1 was used to pay publishing fees.Peer reviewedPublisher PD

Effects of composted green waste on soil quality and tree growth on a reclaimed landfill site

The addition of composted green waste (CGW) into soil-forming materials during land reclamation can benefit tree growth by improvement of soil properties and provide an effective waste management solution. CGW addition may also assist the establishment of earthworm populations, which in turn aid soil development through their burrowing and feeding activities. An experiment was set up on a reclaimed landfill site, to measure the effects of CGW addition on soil physical and chemical quality and subsequently on the survival and growth of two tree species (Acer platanoides and Alnus cordata). A further objective was to measure the influence of earthworm (Aporrectodea longa) addition on the above. CGW addition led to significantly greater A. cordata growth (height and diameter) and increased survival rate. No benefits from CGW addition were observed on A. platanoides growth or survival, although this is likely due to soil drought conditions during establishment. CGW addition significantly increased levels of organic carbon and essential plant macro-nutrients in the reclaimed soil. Soil pH rose slightly across all treatments, with highest final pH under the control treatment. Earthworm inoculation, as used, was unsuccessful at increasing population density of A. longa. This experiment showed that CGW application can effectively improve tree establishment and soil quality on reclaimed landfill; however tree species selection is an important consideration, based on individual species tolerance and sensitivity to certain soil conditions. These findings will be informative to decisions on soil amendment and afforestation activities on similar reclaimed landfill sites

Developing a systematic sampling method for earthworms in and around deadwood

Background: The ecological importance of deadwood is widely acknowledged, however popular forestry practices may reduce deadwood from a site, and most European forests now fall below recommended targets, putting deadwood-associated species at risk. There is increasing evidence that earthworm species which live in alternative habitats such as deadwood can be missed by traditional sampling methods, which can lead to false classifications regarding species distributions and conservation status and value. Resolving the current lack of a systematic and quantitative methodology for surveying earthworms in microhabitats such as deadwood may therefore lead to valuable insights into earthworm species ecologies in forest ecosystems. The main aim of this research was to develop and trial a systematic method for surveying deadwood-associated earthworms, with potential future application to other invertebrates. Sampling of earthworms within soil, deadwood and soil beneath deadwood was carried out across a chronosequence of unmanaged oak forest stands. The results were then used to investigate the influence of soil and deadwood environmental factors and woodland age on the earthworm populations of oak-dominated broadleaf woodlands. Results: Results from our surveys successfully show that in oak woodland habitats with deadwood, omitting deadwood microhabitats from earthworm sampling can lead to underestimates of total earthworm species richness, abundance and biomass. We also found a significantly greater proportion of juveniles within the earthworm communities of broadleaf deadwood, where temperature and moisture conditions were more favourable than surrounding open soil habitats. Conclusions: The systematic method presented should be considered as additional and complementary to traditional sampling protocols, to provide a realistic estimate of earthworm populations in woodland systems. Adopting this quantitative approach to surveying the biodiversity value of deadwood may enable forest management practices to more effectively balance wood production against ecological and conservation values. Opportunities for further development of the sampling methodology are proposed

Soil organic matter stabilization and carbon-cycling enzyme activity are affected by land management

Increasing carbon (C) storage in soil is a key aspect of climate change mitigation strategies and requires an understanding of the impacts of land management on soil C cycling. The primary aim of this study is to investigate how land management impacts key soil organic matter stabilization and cycling processes affecting soil C storage. Soil sampling was undertaken across seven transects crossing the boundary between agriculture and forestry. The transects covered 3 pasture (AP) and 4 arable (AA) fields combined with 3 young secondary woodlands (50-60 years old - WY) and 4 mature/ancient semi-natural woodlands (110 to >400 years old - WM). Physical fractionation of soil organic matter pools was performed, together with pH, carbon and nitrogen content, as well as activity of four enzymes associated with C transformation in the soil. Woodland soils were associated with significantly higher content of light fraction C and greater enzyme activity in comparison to agricultural soils. Enzyme activity and soil organic C decreased with soil depth regardless of land-use type. We did not, however, observe any effect of the distance from the land use boundary on either enzyme activity and soil C pools. Our results indicate that analysis of soil organic matter (SOM) fractions can act as an indicator of decomposition rates of SOM in forest and agricultural ecosystems

Looking for Earthworms in Deadwood

Fallen branches, logs, and tree stumps are a valuable habitat in forests, giving food and shelter to many organisms, including earthworms. Unfortunately, deadwood is often removed from forests because its value is not fully appreciated. We wanted to overcome this by developing a sampling method for earthworms living in deadwood in forests. By testing our new sampling method in oak forests, we found that including deadwood in earthworm surveys improves our knowledge of forest earthworm populations. We also found a greater number of young earthworms in deadwood, where conditions were warmer and moister than in the soil. By surveying deadwood for invertebrates, such as earthworms, we can better understand the important role that deadwood in forests plays in maintaining biodiversity

Fine-scale temporal characterization of trends in soil water dissolved organic carbon and potential drivers

Long-term monitoring of surface water quality has shown increasing concentrations of Dissolved Organic Carbon (DOC) across a large part of the Northern Hemisphere. Several drivers have been implicated including climate change, land management change, nitrogen and sulphur deposition and CO2 enrichment. Analysis of stream water data, supported by evidence from laboratory studies, indicates that an effect of declining sulphur deposition on catchment soil chemistry is likely to be the primary mechanism, but there are relatively few long term soil water chemistry records in the UK with which to investigate this, and other, hypotheses directly. In this paper, we assess temporal relationships between soil solution chemistry and parameters that have been argued to regulate DOC production and, using a unique set of co-located measurements of weather and bulk deposition and soil solution chemistry provided by the UK Environmental Change Network and the Intensive Forest Monitoring Level II Network . We used statistical non-linear trend analysis to investigate these relationships at 5 forested and 4 non-forested sites from 1993 to 2011. Most trends in soil solution DOC concentration were found to be non-linear. Significant increases in DOC occurred mostly prior to 2005. The magnitude and sign of the trends was associated qualitatively with changes in acid deposition, the presence/absence of a forest canopy, soil depth and soil properties. The strongest increases in DOC were seen in acidic forest soils and were most clearly linked to declining anthropogenic acid deposition, while DOC trends at some sites with westerly locations appeared to have been influenced by shorter-term hydrological variation. The results indicate that widespread DOC increases in surface waters observed elsewhere, are most likely dominated by enhanced mobilization of DOC in surficial organic horizons, rather than changes in the soil water chemistry of deeper horizons. While trends in DOC concentrations in surface horizons have flattened out in recent years, further increases may be expected as soil chemistry continues to adjust to declining inputs of acidity

Relationships between nitrogen cycling microbial community abundance and composition reveal the indirect effect of soil pH on oak decline

Tree decline is a global concern and the primary cause is often unknown. Complex interactions between fluctuations in nitrogen (N) and acidifying compounds have been proposed as factors causing nutrient imbalances and decreasing stress tolerance of oak trees. Microorganisms are crucial in regulating soil N available to plants, yet little is known about the relationships between soil N-cycling and tree health. Here, we combined high-throughput sequencing and qPCR analysis of key nitrification and denitrification genes with soil chemical analyses to characterise ammonia-oxidising bacteria (AOB), archaea (AOA) and denitrifying communities in soils associated with symptomatic (declining) and asymptomatic (apparently healthy) oak trees (Quercus robur and Q. petraea) in the United Kingdom. Asymptomatic trees were associated with a higher abundance of AOB that is driven positively by soil pH. No relationship was found between AOA abundance and tree health. However, AOA abundance was driven by lower concentrations of NH4+, further supporting the idea of AOA favouring lower soil NH4+ concentrations. Denitrifier abundance was influenced primarily by soil C:N ratio, and correlations with AOB regardless of tree health. These findings indicate that amelioration of soil acidification by balancing C:N may affect AOB abundance driving N transformations, reducing stress on declining oak trees

Impact of pollen on throughfall biochemistry in European temperate and boreal forests

Pollen is known to affect forest throughfall biochemistry, but underlying mechanisms are not fully understood. We used generalized additive mixed modelling to study the relationship between long-term series of measured throughfall fluxes in spring (April–June) at forest plots and corresponding airborne pollen concentrations (Seasonal Pollen Integral, SPIn) from nearby aerobiological monitoring stations. The forest plots were part of the intensive long term monitoring (Level II) network of the UNECE International Co-operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests) with dominant tree genera Fagus, Quercus, Pinus and Picea, and were distributed all across Europe. We also conducted a 7-day laboratory dissolution experiment with bud scales and flower stalks of European beech (Fagus sylvatica L.), pollen of beech, common oak (Quercus robur L.), silver birch (Betula pendula L.), Scots pine (Pinus sylvestris L.), Corsican pine (Pinus nigra Arnold ssp. laricio (Poiret) Maire), Norway spruce (Picea abies (L.) Karst.) and sterilized pollen of silver birch in a nitrate (NO3--N) solution (11.3 mg N L-1). Throughfall fluxes of potassium (K+), ammonium (NH4+-N), dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) showed a positive relationship with SPIn whereas NO3--N fluxes showed a negative relationship with SPIn. In years with massive seed production of beech and oak SPIn and throughfall fluxes of K+ and DOC were higher, but fluxes of NO3--N were lower. The experiment broadly confirmed the findings based on field data. Within two hours, pollen released large quantities of K+, phosphate, DOC and DON, and lesser amounts of sulphate, sodium and calcium. After 24-48 hours, NO3--N started to disappear, predominantly in the treatments with broadleaved pollen, while concentrations of nitrite and NH4+-N increased. At the end of the experiment, the inorganic nitrogen (DIN) was reduced, presumably because it was lost as gaseous nitric oxide (NO). There was no difference for sterilized pollen, indicating that the involvement of microbial activity was limited in above N transformations. Our results show that pollen dispersal might be an overlooked factor in forest nutrient cycling and might induce complex canopy N transformations, although the net-impact on N throughfall fluxes is rather lo

Combining multiple isotopes and metagenomic to delineate the role of tree canopy nitrification in European forests along nitrogen deposition and climate gradients

Forest canopies influence our climate through carbon, water and energy exchanges with the atmosphere. However, less investigated is whether and how tree canopies change the chemical composition of precipitation, with important implications on forest nutrient cycling. Recently, we provided for the first time isotopic evidence that biological nitrification in tree canopies was responsible for significant changes in the amount of nitrate from rainfall to throughfall across two UK forests at high nitrogen (N) deposition [1]. This finding strongly suggested that bacteria and/or Archaea species of the phyllosphere are responsible for transforming atmospheric N before it reaches the soil. Despite microbial epiphytes representing an important component of tree canopies, attention has been mostly directed to their role as pathogens, while we still do not know whether and how they affect nutrient cycling. Our study aims to 1) characterize microbial communities harboured in tree canopies for two of the most dominant species in Europe (Fagus sylvatica L. and Pinus sylvestris L.) using metagenomic techniques, 2) quantify the functional genes related to nitrification but also to denitrification and N fixation, and 3) estimate the contribution of NO3 derived from biological canopy nitrification vs. atmospheric NO3 input by using \u3b415N, \u3b418O and \u3b417O of NO3in forest water. We considered i) twelve sites included in the EU ICP long term intensive forest monitoring network, chosen along a climate and nitrogen deposition gradient, spanning from Fennoscandia to the Mediterranean and ii) a manipulation experiment where N mist treatments were carried out either to the soil or over tree canopies. We will present preliminary results regarding microbial diversity in the phyllosphere, water (rainfall and throughfall) and soil samples over the gradient. Furthermore, we will report differences between the two investigated tree species for the phyllosphere core microbiome in terms of relative abundance of bacterial and Archaea classes and those species related to N cycling. Finally we will assess whether there are differences among tree species and sites in the number of functional genes related to N cycling and how they are related to the N deposition and/or climate. [1] Guerrieri et al. 2015 Global Change and Biology 21 (12): 4613-4626