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Biochar, a solid product from thermical conversion of biomass, can be used as a climate change mitigation strategy, since it can sequester carbon from the atmosphere and store it into the soil. The aim of this study is to assess the potential of biochar as mitigation strategy in the long-term, by modelling the results obtained from a field experiment, over 8 years. As far as we know, this is the first time that a model for biochar degradation has been validated with long-term field data

The work concerns the study of the hydrochar from digestate and hydrochar co-compost characterization as amendments. The processes for hydrochar and co-compost production were described in Part 1 of this work (Scrinzi et al., 2022). The amendment properties of hydrochar (produced at 180-200-220 °C for 3 h) and co-composts (25%, 50%, and 75% hydrochar percentage of digestate substitution) were assessed by phytotoxicity, plant growth bioassay, and soil effect. Different seeds species (Lepidium sativum, Cucumis sativus, and Sorghum bicolor sp.) were dosed at increased concentrations using both wet raw amendments and their water extracts. The chemical characterization showed phytotoxic compounds content depending on both the initial feedstock (digestate) and the HTC process; at the same time, the analysis highlighted the reduction of these compounds by composting (organic acid, polyphenols, salt concentration). The dose-response was analyzed by the Cedergreen-Streibig-Ritz model and the half-maximal effective concentration (EC50) was calculated based on this equation. The soil properties and GHG emissions measurements (CH

In the context of climate change mitigation, technologies for removing the CO2 from the atmosphere are key challenges. Most recent scenarios from integrated assessment models require large-scale deployment of negative emissions technologies (NETs) to reach the 2 °C target. Among them, technologies for increasing organic carbon content in soils (SOC) have been developed. In the 15th IPCC special report on Global Warming of 1.5 °C, biochar and pyrogenic carbon capture and storage have been credited as promising negative emission technology. In fact, soil carbon sequestration (SCS) and biochar have a large negative emission potential (each 0.7 GtCeq. yr-1) and they are expected to have lower impact on land, water use, nutrients, albedo, energy requirement and cost, and thus fewer disadvantages than many other NETs.SCS can be assessed using soil carbon dynamic models, such as RothC, as suggested by IPCC. However, studies on the inclusion of biochar in RothC are still scarce. Furthermore, most of these studies are based on the results of laboratory experiments and do not account for the effects of biochar on SOC degradation (the priming effect). The use of laboratory data can be problematic, since they may not adequately represent field conditions, especially due to the lack of long-term field studies.The aim of this work was to assess and predict how biochar influences the soil C dynamics, by modifying the RothC model to simulate the findings of a long-term field experiment on biochar application to a short coppice rotation in Italy. We first modified the model to include two stocks of C input into the soil: the labile and the recalcitrant biochar pools. We also included a parametrized function to account for the priming effect on SOC dynamics in the soil. Secondly, we calibrated the model parameters with the data obtained from the field experiment. Finally, we validated the model results by estimating the remaining biochar amount in the site after 10 years from application, using an isotopic mass balance.The results confirm that biochar degradation can be faster in field conditions in comparison to laboratory experiments; nevertheless, it can contribute to substantially increase the C stock in the long-term. Moreover, the modified RothC model allowed to assess the SCS potential of biochar application in soils, at least in the specific conditions examined, and could represent a flexible tool to assess the effect biochar as a SCS strategy in the long-term. We are exploring the possibility to use data from other long-term field experiment to move in that direction. The results of this study could be added to the Italian biochar database, providing new knowledge about a topic that needs to be explored.

Biochar production and application as soil amendment is a promising carbon (C)-negative technology to increase soil C sequestration and mitigate climate change. However, there is a lack of knowledge about biochar degradation rate in soil and its effects on native soil organic carbon (SOC), mainly due to the absence of long-term experiments performed in field conditions. The aim of this work was to investigate the long-term degradation rate of biochar in an 8-year field experiment in a poplar short-rotation coppice plantation in Piedmont (Italy), and to modify the RothC model to assess and predict how biochar influences soil C dynamics. The RothC model was modified by including two biochar pools, labile (4% of the total biochar mass) and recalcitrant (96%), and the priming effect of biochar on SOC. The model was calibrated and validated using data from the field experiment. The results confirm that biochar degradation can be faster in field conditions in comparison to laboratory experiments; nevertheless, it can contribute to a substantial increase in the soil C stock in the long term. Moreover, this study shows that the modified RothC model was able to simulate the dynamics of biochar and SOC degradation in soils in field conditions in the long term, at least in the specific conditions examined. Biochar production and application as soil amendment is a promising carbon (C) negative technology to increase soil C sequestration and mitigate climate change. However, there is a lack of knowledge about biochar degradation rate in soil and its effects on native soil organic carbon (SOC), mainly due to the absence of long term experiments performed in field conditions. The aim of this work was to investigate the long term degradation rate of biochar in a field experiment of 8 years in a poplar short rotation coppice plantation in Piedmont (Italy), and to modify the RothC model to assess and predict how biochar influences soil C dynamics. The RothC model was modified by including two biochar pools, labile (4 % of the total biochar mass) and recalcitrant (96 %), and the priming effect of biochar on SOC. The model was calibrated and validated using data from the field experiment. The results confirm that biochar degradation can be faster in field conditions in comparison to laboratory experiments; nevertheless, it can contribute to substantially increase the soil C stock in the long-term. Moreover, this study shows that the modified RothC model was able to simulate the dynamics of biochar and SOC degradation in soils in field conditions in the long term, at least in the specific conditions examined.

Biochar production and application as soil amendment is a promising carbon (C) negative technology to increase soil C sequestration and mitigate climate change. However, there is a lack of knowledge about biochar degradation rate in soil and its effects on native soil organic carbon (SOC), mainly due to the absence of long term experiments performed in field conditions. The aim of this work was to investigate the long term degradation rate of biochar in a field experiment of 8 years in a poplar short rotation coppice plantation in Piedmont (Italy), and to modify the RothC model to assess and predict how biochar influences soil C dynamics. The RothC model was modified by including two biochar pools, labile (4 % of the total biochar mass) and recalcitrant (96 %), and the priming effect of biochar on SOC. The model was calibrated and validated using data from the field experiment. The results confirm that biochar degradation can be faster in field conditions in comparison to laboratory experiments; nevertheless, it can contribute to substantially increase the soil C stock in the long-term. Moreover, this study shows that the modified RothC model was able to simulate the dynamics of biochar and SOC degradation in soils in field conditions in the long term, at least in the specific conditions examined.

To understand the main determinants of soil respiration (SR), we investigated the changes of soil respiration and soil physicochemical properties, including soil carbon (C) and nitrogen (N), root C and N, litter C and N, soil bulk densities and soil pH at five forest sites, along an elevation/temperature gradient (404 to 2101 m a.s.l) in Northern Italy, where confounding factors such as aspect and soil parent material are minimized, but an ample variation in forest structure and composition is present. Our result indicated that SR rates increased with temperature in all sites, and about 55% - 76% of SR was explained by temperature. Annual cumulative SR, ranging between 0.65 and 1.40 kg C m-2 yr-1, declined along the elevation gradient, while temperature sensitivity (Q10) of SR increased with elevation. However, a high SR rate (1.27 kg C m-2 yr-1) and low Q10 were recorded in the old conifer forest stand at 1731 m a.s.l., characterized by a complex structure and high productivity, introducing nonlinearity in the relations with elevation and temperature. Reference SR at the temperature of 10°C (SRref) was not related to elevation. A significant linear negative relationship was found for bulk density with elevation. On the contrary, soil C, soil N, root C, root N, pH and litter mass were better fitted by nonlinear relations with elevation. However, it was not possible to confirm a significant correlation of SR with these parameters once the effect of temperature has been removed (SRref). These results show how the main factor affecting SR in forest ecosystems along this Alpine elevation gradient is temperature, but its regulating role can be strongly influenced by site biological characteristics, particularly vegetation type and structure. This study also confirms that high elevation sites are rich in C stored in the soil and also more sensitive to climate change, being prone to high carbon losses as CO2. Conversely, forest ecosystems with a complex structure, with high SRref and moderate Q10, can be more resilient.

Atmospheric nitrogen (N) depositions have increased sharply since the industrial revolution. Numerous authors forecasted severe impacts on forest ecosystem services and functioning when new N input exceeds both biotic and abiotic holding capacity, in what is known as the N saturation process. However, most of the studies performed so far to quantify these impacts have largely neglected the potential role of the canopy and associated biota in biogeochemical processes. The present review collects and summarizes the existing literature about all the interactions of atmospheric N deposition and the canopy, evidencing different processes that may interfere with them. By summarizing the research of the last three decades, we found that a share of both wet and dry N deposition can be retained within the canopy, partially absorbed by the leaves or other aerial parts and utilized for plant metabolism, substantially changing the fate of N in the ecosystem. Focusing on canopy-associated biota, we analyzed how this compartment can represent a highly reactive layer and have an active role in different processes involved in the N cycle such as nitrification, fixation and volatilization. It emerges clearly that the canopy hosts a complex network of processes; however, despite this, most of the manipulative experiments failed to include the canopy into the studies. The documented manipulative experiments which included the canopy are mainly short-term and represent very few forest types. Moreover, we highlighted a lack of research concerning the interaction between the complex network of canopy processes, atmospheric N deposition and other global change factors, such as increasing atmospheric CO2 concentration, increasing temperature and drought events.

The amount of nitrogen (N) deposition onto forests has globally increased and is expected to double by 2050, mostly because of fertilizer production and fossil fuel burning. Several studies have already investigated the effects of N depositions in forest soils, highlighting negative consequences on plant biodiversity and the associated biota. Nevertheless, the impact of N aerial inputs deposited directly on the tree canopy is still unexplored. This study aimed to investigate the influence of increased N deposition on the leaf-associated fungal and bacterial communities in a temperate forest dominated by Sessile oak [Quercus petraea (Matt.) Liebl.]. The study area was located in the Monticolo forest (South Tyrol, Italy), where an ecosystem experiment simulating an increased N deposition has been established. The results highlighted that N deposition affected the fungal beta-diversity and bacterial alpha-diversity without affecting leaf total N and C contents. We found several indicator genera of both fertilized and natural conditions within bacteria and fungi, suggesting a highly specific response to altered N inputs. Moreover, we found an increase of symbiotrophic fungi in N-treated, samples which are commonly represented by lichen-forming mycobionts. Overall, our results indicated that N-deposition, by increasing the level of bioavailable nutrients in leaves, could directly influence the bacterial and fungal community diversity.

In the last decades, the effects of nitrogen (N) deposition on temperate forests have received much interest. Studies recorded several changes in soil carbon (C) and N cycles due to extra reactive N available. For instance, past studies reported that N deposition, may influence CO2 emission, lower CH4 consumption by the soil and increase the emission of N2O. Nevertheless, the mechanistic understanding of these ecological responses is still far to be reached. However, most of the studies neglected to include the canopy interception in the experiments simulating N addition, notwithstanding tree canopy have shown to change both the amount and the chemical composition of the N deposition. Hence, experiments simulating this process by applying fertilization above the canopy are needed.The aim of this study is to explore how N deposition influences greenhouse gas (GHG) emissions in a temperate oak forest (Quercus petraea Liebl.) located in Monticolo (Bolzano, Italy). In this site, a set of three plots was created and replicated three times. Each set includes a control plot, a plot with below-canopy fertilization (NBL) and a plot with above-canopy fertilization (NAB). The fertilization is applied, since 2015, from May to September, for a total annual N addition of 20 kg N ha-1.Since April 2018, CO2 emission has been monthly measured with a portable infrared gas analyzer. Measurements were performed on three points per plot, for a total of 27 measurement points. During measurements, soil moisture and soil temperature at 10 cm depth were measured as well.The measurements of CH4 and N2O started during the growing season in 2019 and are performed on a monthly basis by a static chamber method. Three chambers were installed per plots, for a total of 27 chambers.We will present the preliminary results of this study. The results showed that the 5-year N fertilization did not lead to significant differences between plots in terms of GHG fluxes. The sensitivity of CO2 emission to temperature was not influenced by extra N. The differences were not significant between fertilized and unfertilized plots, nor between the two fertilization methods.

Abstract. Forests ability to store carbon is strongly connected with the amount of nitrogen (N) that forest ecosystems can retain; N is indeed considered the most limiting nutrient for terrestrial ecosystem's net primary productivity. Since the industrial revolution, human activities have more than doubled the rate of N input into the nitrogen cycle and this could alleviate N limitation thus stimulating plant growth. However, it has been suggested that when N availability exceeds biotic demand and abiotic sinks, additional N can trigger a negative cascade effect: nutrient imbalance, reduced productivity, increased losses of N, eutrophication and acidification of soil and water, leading toward forest decline and net greenhouse gases emissions. The consequences of increased N deposition on forest depend in large share on the fate of N in the ecosystem, which can be simulated and quantified by a fertilization at a known isotopic signature. Nevertheless, most of the tracer experiments performed so far added the fertilizer directly to the forest floor, neglecting the potential role of N uptake by the forest canopy. In the Italian Alps, we are conducting an experiment where both types of N additions (above and below the canopy layer) are performed in two different forest stands, to understand if canopy fertilization better simulates ecological consequences of increased atmospheric N deposition. These field-scale manipulation experiments are willing to test two different hypotheses: i) the N uptake by trees in the above-canopy N addition experimental sites is higher than under-canopy N addition ii) forest growth rate varies with the type of treatment. To describe the fate of the applied N, stable isotope techniques have been adopted: the forest sites, fertilized with NH4NO3 at a known isotopic signature, are sampled for all the ecosystem components (plant, soil and water) periodically to determine the total N content and its isotopic signature. The δ15N values permit to calculate the recovery of N-fertilizer in tree tissues, soil and leaching-water, allowing us to understand how N allocation varies under these two fertilization strategies and how this affects C sequestration potential. Results regarding the short-term effects over the first 6 years of data collection will be presented.

Biochar is a carbonaceous material produced through the pyro-gasification of biomass. In the last decade, biochar has been proposed as a soil amendment because it can improve soil physico-chemical properties and carbon stocks, contributing to climate change mitigation.In the framework of the Wood-Up project (Optimization of WOOD gasification chain in South Tyrol to prodUce bioenergy and other high-value green Products to enhance soil fertility and mitigate climate change, FESR1028), we studied the impact of conifer wood biochar on the emissions of the main greenhouse gases (GHGs) from the soil: carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4), as well as on the soil carbon stock of agricultural fields in South Tyrol.In May 2017, 25 and 50 t ha-1 of pure biochar and biochar mixed with compost (45 t ha-1), were applied to the soil of a vineyard near Merano (South-Tyrol, northern Italy) following a randomized block experimental design with four replicates per treatment.Soil GHGs fluxes were monitored from June 2017 until December 2019. Fluxes were measured, in real time, with a high-resolution portable multi-gas analyzer based on cavity ring-down spectroscopy technology (Picarro inc., Santa Clara, CA, USA) connected to an automated dynamic chambers system (Eosense Inc., Dartmouth, NS, Canada). Gas emissions were measured monthly and were related to soil temperature and moisture to evaluate the impact of treatments on the sensitivity of GHGs fluxes to environmental parameters. The stability of conifer wood biochar in soil was assessed through the quantification of the Benzene PolyCarboxylic Acids (BPCA), specific biomarkers of black carbon, over time. The BPCA content in the soil was measured before the application of biochar and compost, three weeks after the application and two years later.During the first year of experiment, in biochar-amended soils, we observed a reduction of the temperature sensitivity of all GHGs fluxes in comparison to treatments without biochar (control and compost alone). In the second and third year an opposite trend was observed, with an increase of temperature sensitivity of GHGs fluxes in biochar-treated soil. The change of biochar effect over time might be linked to biochar ageing in soil. However, a role of soil moisture cannot be excluded, as it was higher in the first year of experiment. The experimental results will be presented in the broader context of the Wood-Up project.

Biochar has been shown to improve soil quality and crop yields. Furthermore, thanks to its high carbon content (C) and stable chemical structure, biochar can sequester C in the soil for a long time, mitigating climate change. However, the variability in published biochar stability in the soil makes verifying this trait under different environmental and agricultural conditions necessary. Moreover, most of the published literature refers to short-term incubation experiments, which are considered to not adequately represent long-term dynamics under field conditions. This article reports the results of a field experiment carried out in a vineyard near Merano, northern Italy, where the stability of woodchips biochar in soil, its impact on the total soil C stocks as well as on the original soil organic C (priming effect) were studied over two years. Vineyard soil (Dystric Eutrochrept) was amended with biochar (25 and 50 t ha−1) alone or together with compost (45 t ha−1) and compared with unamended control soil. Two methods assessed the stability of biochar in soil: the isotopic mass balance approach and the quantification of Benzene PolyCarboxylic Acids (BPCAs), molecular markers of biochar. The amount of C in the soil organic matter (SOM-C) was determined in the amended plots by subtracting the amount of biochar-C from the total soil organic C stock, and the occurrence of priming effect was verified by comparing SOM-C values at the beginning and at the end of the experiment. Results did not show any significant biochar degradation for both application rates, but results were characterized by a high variation. The application of 50 t ha−1 of biochar significantly increased soil C stock while no effect of biochar on the degradation of SOM-C was observed. Results were confirmed in the case of biochar application together with compost. It can be concluded that the use of woodchips biochar as a soil amendment can increase soil C content in the medium term. However, further analyses are recommended to evaluate the impact of biochar on climate change mitigation in the long term.

Relative biomass of tree compartments is dependent on plant size and stand density, with stand density being an important predictor, especially for belowground biomass and at high stand densities. Estimation of biomass production is an important issue against the background of climate change and carbon storage. Even though many studies investigated the biomass productivity of trees or single compartments, only few considered the belowground biomass. Further, there is a lack of studies focusing on young trees and considering further influencing factors such as the prevailing stand density. In the present study, young Quercus robur trees were sampled on Nelder trials, which comprise different stand densities, on four European sites differing in climatic conditions. Besides the estimation of logarithmically transformed power equations, Dirichlet regressions were applied for deriving biomass functions for the single compartments leaves, branches, stem and roots. Thereby, the dependence of total and compartment biomass allocation on diameter at root collar (d 0), tree height and stand density is tested. The results show that besides d 0, the local Stand Density Index (SDIl) is an important predictor for biomass. Especially, the belowground biomass shows a significant relation to the SDIl, which is less the case for the aboveground biomass. Not considering the SDIl leads to an overestimation of the biomass productivity, especially when the stand density is high. Furthermore, the results show that the belowground biomass is lower than the aboveground biomass, but with 50–80% of the aboveground biomass still of considerable size. This indicates the importance of including stand characteristics when estimating above- and belowground tree biomass in future studies.

Acknowledgements This work contributes to the ELUM (Ecosystem Land Use Modelling & Soil Carbon GHG Flux Trial) project, which was commissioned and funded by the Energy Technologies Institute (ETI), and to Carbo-BioCrop (http://www.carbobiocrop.ac.uk; a NERC funded project; NE/H010742/1), UKERC Phase II and III (NERC; NE/H013237/1), MAGLUE (http://www.maglue.ac.uk; an EPSRC funded project; EP/M013200/1) and as part of the Seventh Framework For Research Programme of the EU, within the EUROCHAR project (N 265179) and EXPEER within WU FP7-Infrastructures. We acknowledge the use of 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). We thank two anonymous reviewers and Dr William van Dijk for their valuable suggestions.

Research Highlights: Biochar is the carbonaceous product of pyrolysis or the gasification of biomass that is used as soil amendment to improve soil fertility and increase soil carbon stock. Biochar has been shown to increase, decrease, or have no effect on the emissions of greenhouse gases (GHG) from soil, depending on the specific soil and biochar characteristics. However, the temperature sensitivity of these gas emissions in biochar-amended soils is still poorly investigated. Background and Objectives: A pot experiment was set up to investigate the impact of woodchips biochar on the temperature sensitivity of the main GHG (CO2, CH4, and N2O) emissions from soil. Materials and Methods: Nine pots (14 L volume) were filled with soil mixed with biochar at two application rates (0.021 kg of biochar/kg of soil and 0.042 kg of biochar/kg of soil) or with soil alone as the control (three pots per treatment). Pots were incubated in a growth chamber and the emissions of CO2, CH4, and N2O were monitored for two weeks with a cavity ring-down gas analyzer connected to three closed dynamic chambers. The temperature in the chamber increased from 10 &deg, C to 30 &deg, C during the first week and decreased back to 10 &deg, C during the second week, with a daily change of 5 &deg, C. Soil water content was kept at 20% (w/w). Results: Biochar application did not significantly affect the temperature sensitivity of CO2 and N2O emissions. However, the sensitivity of CH4 uptake from soil significantly decreased by the application of biochar, reducing the CH4 soil consumption compared to the un-amended soil, especially at high soil temperatures. Basal CO2 respiration at 10 &deg, C was significantly higher in the highest biochar application rate compared to the control soil. Conclusions: These results confirmed that the magnitude and direction of the influence of biochar on temperature sensitivity of GHG emissions depend on the specific GHG considered. The biochar tested in this study did not affect soil N2O emission and only marginally affected CO2 emission in a wide range of soil temperatures. However, it showed a negative impact on soil CH4 uptake, particularly at a high temperature, having important implications in a future warmer climate scenario and at higher application rates.

The atmospheric concentrations of greenhouse gases have increased to unprecedented levels during last decades, raising concerns about their effect on climate change. Agriculture and land use change play an important role in atmospheric CO2 emission and fixation, especially by affecting the soil carbon (C) storage. In this context, agroforestry systems (AFSs) could play an important role contributing to climate change mitigation. Given the importance of olive cultivation in the Mediterranean region, it is important to investigate soil C stock in olive groves, and to assess which agronomic practices could improve the soil C stock in these systems. For this reason, a study was conducted in different olive groves, including conventional and organic management, and a typical silvopastoral AFS. Furthermore, an abandoned olive grove and nearby forest were examined as a comparison. Soil samples were collected in each farm and analysed for C content and physico-chemical characteristics. This study indicates that, irrespective of the management, olive groves in the Umbria region of Italy are characterised by a high level of soil C stock if compared to those growing in other areas and to forest ecosystems, indicating that the practices adopted in the area are not negatively affecting soil C storage. A slightly lower soil C stock was measured in the silvopastoral AFS in comparison to the other farms, while high soil C stock was associated with the use of pomace, suggesting that this practice can be used to further increase soil C stock in olive orchards.

Knowledge about the stand structure and dynamics of subalpine forests is crucial to preserve their multifunctionality. In the present study, we reconstructed the spatiotemporal dynamics of a subalpine Pinus cembra forest in the eastern Italian Alps in response to natural disturbances and forest management. We adopted a concurrent point pattern, dendroecological and growth dominance (GD) analysis. We mapped and measured all trees of Pinus cembra and Larix decidua in a 1 ha plot. We analyzed intra- and interspecific spatial patterns and spatial autocorrelation of tree size and age. We explored establishment dynamics and shifts in competition by analyzing growth suppression/release patterns and GD trends. Results showed a clumped, uneven-aged, multilayered structure where pine was dominant. The synergic action of ecological and human-induced factors is discussed to explain the prevalence of pine over time. Spatial pattern and autocorrelation analyses suggest a different colonization strategy of the t...

Soil respiration ( R soil ) partitioning into its components is pivotal to understand C cycling in ecosystems. Notwithstanding the importance of mycorrhizal fungi in the belowground C cycle, their respiration ( R myc ) is poorly studied in agricultural ecosystems. In this study, we applied a modified trenching method and the 13 C natural abundance technique to distinguish R myc from root respiration ( R root ) and from the respiration due to soil organic matter (SOM) degradation ( R som ) in an apple orchard ( Malus domestica Borkh.) located in Northern Italy. Membranes with different mesh size were used to physically exclude roots or mycorrhizae from soil cores with a different δ 13 C than the orchard average value. The CO 2 efflux from soil cores was determined with an infrared gas analyser, and isotopic measurements were performed on the soil-emitted CO 2 . The different R soil components were determined both by difference and by the isotopic mass balance. Mycorrhizal contribution to soil respiration (11 ± 6%) was of similar magnitude to that of roots (12 ± 4%) while R som accounted for 73 ± 3% of R soil . In presence of apple roots, respiration of SOM and mycorrhizae ( R som+myc ) significantly increased in late summer and autumn, likely because of a priming effect of roots on SOM degradation or to a stimulation of mycorrhizal respiration. Our results suggest that respiration of mycorrhizal fungi can significantly contribute to R soil , and need to be considered to correctly partition soil respiration. Furthermore, as roots increased R som+myc , the root exclusion method for soil respiration partitioning may overestimate R root .

We performed a series of experiments in controlled conditions to assess the potential of hardwood- derived biochar either as a source or as a removing additive of macronutrients [nitrate-nitrogen (NO3-N), ammonium-N (NH4-N), potassium (K), phosphorus (P), and magnesium (Mg)] in solution. In addition, a 3-year field trial was carried out in a commercial nectarine orchard to evaluate the effect of increasing soil-applied biochar rates on tree nutritional status, yield, fruit quality, soil pH, soil NO3-N, and NH4-N concentration and soil water content. In controlled conditions, the concentrations of K, P, Mg, and NH4-N in solution were significantly increased and positively correlated with biochar rates. Biochar was ineffective in removing NO3-N, K, P, and Mg from enriched solutions, while at the rate of 40 g L–1 biochar removed almost 52% of the initial NH4-N concentration. In a mature, irrigated, fertilized, commercial nectarine orchard (Big Top/GF677) on a sandy-loam soil in the Italian Po Valley, soil-applied biochar at the rates of 5, 15, and 30 t ha–1 were effective in reducing the leached amount of NH4-N in the top 0.25 m soil layer over 13 months, as estimated by ion exchange resin lysimeters. Nevertheless, independent of the rate, biochar did not affect soil pH, soil N mineral availability, soil moisture, tree nutritional status, yield, and fruit quality. We conclude that, unless an evident constraint is identified, in non-limiting conditions (e.g., water availability and soil fertility), potential benefits from biochar application in commercial orchards are hidden or negligible

The present study assesses the stability of biochar, its effect on original soil organic matter (SOM) decomposition, and the interactions with plant roots over a 3-year period in a short rotation coppice plantation in Northern Italy. Biochar produced from gasification of maize silage (δ13C of biochar ≈ − 13.8‰) was applied into the soil of the plantation (δ13C of SOM ≈ −23.5‰). Total and heterotrophic respirations were measured in control and biochar-treated plots, and the amount of biochar-derived carbon dioxide (CO2) was calculated using an isotopic mass balance method. Biochar mean residence time (MRT) was assessed using exponential decay models. The remaining amount of biochar at the end of the experiment was estimated by a soil isotopic mass balance. In the absence of plant roots, MRT of the more recalcitrant biochar fraction (96% of the total) was 24.3 years, significantly lower than expected from previous shorter-term studies or laboratory incubations. In the presence of plant roots, MRT decreased to 12.6 years, confirming the previously observed positive effect of roots on biochar decomposition. However, in the absence of roots, the biochar decreased the decomposition of original SOM by 16%, indicating long-lasting protective effect on SOM (negative priming effect). The soil isotopic mass balance suggested that part of the applied biochar could have been lost by downward migration. This study provides the first estimation of the biochar stability and priming effect on SOM in field conditions in the medium term.

The increasing importance of short rotation coppice (SRC) plantations for bioenergy production makes it crucial to evaluate their carbon (C) sink potential and to understand which sustainable practices could increase productivity and C sequestration. This study examined the combined effect of woody ash and nitrogen (N) fertilization on the productivity, net C balance (NECB) and soil C sink capacity of a poplar SRC plantation established on a former arable land in northern Italy. Above- (ANPP) and below-ground (BNPP) primary productivity, including both root litter and rhizodeposition (Croot litter), were estimated by a combination of inventory methods, soil respiration measurements and C budgeting approaches. NECB was estimated as changes in both plant and soil C pools, and the portion of soil organic carbon (SOC) derived from poplar leaf and root litter was estimated using a combination of in-growth cores and isotopic measurements. Nitrogen application at 100kgha−1 increased ANPP in terms of C accumulation only in the first year, while NECB was not affected by treatments and was 9.96MgCha−1year−1 on average. Irrespective of the treatment, the plantation accumulated on average 0.7MgCha−1year−1 of SOC and the poplar-derived soil C input was 3.0Mgha−1year−1. Positive NECB shows that the studied SRC resulted in an important C sink even in the first years after the establishment. However, long-term studies are needed to better assess the effect of N and ash application on C and nutrient cycles over more than one rotation period.

While it has been recently recognized that freshwater ecosystems may significantly offset the terrestrial carbon sink through emissions of carbon dioxide (CO2) and methane (CH4), empirical data on the magnitude of these sources are still scarce, in particular in temperate regions. In this study, we measured the near-surface dissolved concentrations of CH4 and CO2 from 40 lakes in the Alpine area to estimate their potential for greenhouse gas (GHG) emissions. We hypothesized (1) a temperature-driven gradient of dissolved gas concentrations in terms of elevation and latitude of the lakes and (2) that lower concentrations would be measured in man-made reservoirs compared to natural lakes. Average CH4 and CO2 surface dissolved concentrations amounted to 1.10 ± 1.30 and 36.23 ± 31.15 µmol L−1, respectively. All the lakes, except for one, were supersaturated, exceeding ambient atmospheric CH4 and CO2 concentrations by a factor of 400 ± 424 and 2.43 ± 2.29, respectively. Consistent with our hypothesis, we found lower surface dissolved GHG concentrations in man-made reservoirs compared to natural lakes, which was shown to be related to their greater depth. Even though temperature is known to affect multiple physico-chemical and biological processes governing the strength of the uptake, release and conversion of CH4 and CO2, and temperature is inversely related to elevation, no relationship between dissolved GHG concentrations and elevation could be determined. This is believed to be the result of the overriding importance of lake depth for near-surface CH4 concentrations and the lack of explanatory variables related to lake carbon cycling. Overall, this study suggests that lakes in the Alpine region act as sources of CO2 and CH4 to the atmosphere and that further research should be carried out to quantify the actual GHG emissions from Alpine freshwater bodies and how these are affected by ongoing changes in climate and land use.

Leaf litter and deadwood have important roles in the forest ecosystems, providing shelter for several organisms, preventing erosion and microclimate fluctuations. Their decomposition is a key process of biogeochemical cycles in forest. Microorganisms are the primary agents of decomposition. Particularly, fungi are considered the major contributors due to their ability to produce specific enzymes and the possibility to access new substrates through hyphae. In this review, we highlighted the role of fungi in decomposition and reconsider the role of bacteria, neglected in the past, identifying key research needs and knowledge. Particular attention is given to the succession of different taxa with different ecological role that are able to use a substrate that undergoes to chemical and structural modifications. The quality of substrates is a critical factor that influences the microbial community together with environmental variables, such as temperature and moisture. However, the microbial community is also able to influence the substrate characteristics. Litter nitrogen content is influenced by the uptake of exogenous N by decomposers to meet their metabolic requirements. The complex interactions among microbial communities, ecosystem attributes and chemical composition of fine litter and woody debris remain unclear and almost exclusively referred to boreal and temperate forests.

Summary Biochar addition to soil has been suggested as a promising strategy to increase soil carbon storage with important side-effects on soil fertility and crop productivity. Understanding the effect of biochar on soil respiration partitioning into rhizosphere-derived (Fr) and soil organic carbon-derived (Fsoc) components and on plant root dynamics and microbial activity is a crucial issue in the prediction of the impact of biochar on soil organic carbon and nutrient cycles. Within this framework, an experiment was carried out in an apple (Malus domestica Bork) orchard located in the experimental farm of the Bologna University (Italy). In spring 2009, 10 t of biochar per hectare were incorporated into the surface 20-cm soil layer by soil ploughing. The trenching method was used in order to partition total soil respiration (Fs) into Fr and Fsoc components in both biochar-treated and control soil. Soil respiration measurements were performed from June 2009 to March 2011. To study root dynamics, polycarbonate boxes were built and buried into the soil. Soil profile pictures were collected fortnightly with a CCD sensor scanner inserted in the boxes and analysed with the WinRHIZO Tron MF software. Biochar addition increased Fsoc and reduced Fr, even if the root length intensity (La) increased in biochar-treated soils relative to that in the control. A decrease in root metabolic activity was postulated to explain these contrasting results.

International audience; Wide-scale application of biochar to soil has been suggested as a mechanism to offset increases in CO 2 emissions through the long-term sequestration of a carbon rich and inert substance to the soil, but the implications of this for soil diversity and function remain to be determined. Biochar is capable of inducing changes in soil bacterial communities, but the exact impacts of its application are poorly understood. Using three European sites [UK SRC, short rotation coppice, French grassland (FR) and Italian SRF, short rotation forestry (IT)] treated with identical biochar applications, we undertook 16S and ITS amplicon DNA sequencing. In addition, we carried out assessments of community change over time and N and P mobilization in the UK. Significant changes in bacterial and community structure occurred due to treatment, although the nature of the changes varied by site. STAMP differential abundance analysis showed enrichment of Gemmatimonadete and Acidobacte-ria in UK biochar plots 1 year after application, whilst control plots exhibited enriched Gemmataceae, Isosphaer-aceae and Koribacteraceae. Increased mobility of ammonium and phosphates was also detected after 1 year, coupled with a shift from acid to alkaline phosphomonoesterase activity, which may suggest an ecological and functional shift towards a more copiotrophic ecology. Italy also exhibited enrichments, in both the Proteobacte-ria (driven by an increase in the order Rhizobiales) and the Gemmatimonadetes. No significant change in the abundance of individual taxa was noted in FR, although a small significant change in unweighted UNIFRAC occurred, indicating variation in the identities of taxa present due to treatment. Fungal β diversity was affected by treatment in IT and FR, but was unaffected in UK samples. The effects of time and site were greater than that of biochar application in UK samples. Overall, this report gives a tantalizing view of the soil microbiome at several sites across Europe and suggests that although application of biochar has significant effects on microbial communities, these may be small compared with the highly variable soil microbiome that is found in different soils and changes with time.

Nitrogen leaching in croplands is a worldwide problem with implications both on human health and on the environment. Efforts should be taken to increase nutrient use efficiency and minimize N losses from terrestrial to water ecosystems. Soil-applied biochar has been reported to increase soil fertility and decrease nutrient leaching in tropical soils and under laboratory conditions. Our objective was to evaluate the effect of biochar addition on short-term N leaching from A soil horizon in a mature apple orchard growing on subalkaline soils located in the Po Valley (Italy). In spring 2009, 10 Mg of biochar per hectare was incorporated into the surface 20-cm soil layer by soil plowing. Cumulative nitrate (NO3 -) and ammonium (NH4 +) leaching was measured in treated and control plots 4 mo after the addition of biochar and the following year by using ion-exchange resin lysimeters installed below the plowed soil layer. Cumulative NO3 - leaching was not affected by biochar after 4 mo. whereas in the following year it was significantly (p < 0.05) reduced by 75% over the control (from 5.5 to 1.4 kg ha-1). Conversely, NH4 + leaching was very low and unaffected by soil biochar treatment. The present study shows that soil biochar addition can significantly decrease shortterm nitrate leaching from the surface layer of a subalkaline soil under temperate climatic conditions.

Background and aims Fruit orchards potential as carbon (C) sinks is virtually unknown. Moreover, despite their importance in the Mediterranean area, few data are available about the effect of the reduction in water availability on fruit tree productivity. Here we report the effect of two different irrigation regimes on net primary (NPP) and net ecosystem (NEP) productivities of an apple orchard in northern Italy in 2006.

Sustainable management of mineral nutrition in vineyards, as well as in other fruit plantations, should aim at exploiting the use of internal sources of nutrients, in order to reduce the need for external nutrient inputs. In this paper we explore the potential of the grassed alleys to provide nutrients to the vines. We followed for one vegetative season the decomposition of ryegrass and clover, frequently present as floor vegetation in vineyards, using litter bags filled with 15N-enriched grass material. In addition, we quantified the amount of nitrogen (N) transferred from the decomposing litter to field-grown grapevines. Ryegrass and clover had a relatively rapid decomposition rate, with a loss of C approaching 80% in only 16 weeks. The release of nutrients was particularly fast for potassium (95% in 16 weeks) followed by nitrogen (80%), calcium (70–80%), phosphorous (65–85%), magnesium (70–75%), and sulfur (60–70%). In spite of the rapid release of N from decomposing material, the N uptake by grapevines was on average less than 4% of the initial amount of N present in the litter of ryegrass and clover. Even if N release during the decomposition of mowed perennial ryegrass and white clover little contributed to the N nutrition of grapevine in the same growing season, most N from mowed grassed was still recovered in the soil.

We identified the role of various soil parameters and root density as drivers of soil respiration (Rs) in an apple orchard, measured during different periods of the year and at a range of distances from trees, in plots with a different history of nutrient supply. Rs was measured in April, May, August and December and studied in relation to soil temperature and moisture, total soil C and N, as well as to fine root density and medium-, and large-sized root density and root N concentration. The study also aimed to partition Rs by applying the root regression technique. Rs ranged from 0.06 in December to 1.49 g CO2 m−2 h−1 in August. Average soil temperature alone explained up to 71% of the annual variability of Rs, while soil water content was negatively correlated to Rs. Fertilization, soil C and N concentration and root N had negligible effects on Rs. Fine root density, but not medium- and large-sized root density, contributed to explaining part of the yearly variability of Rs and proved to be a good predictor in December, when the statistical significance of the regression made it possible to estimate the autotrophic component of Rs as being about 35% of total soil respiration.

Modern agriculture requires both, attention to crop yield and quality and to environmental issues. Among farmers' practices, fertilization can play a pivotal role in alleviating environmental pressure without affecting the production. In this work we present the study of nutrients budget spanning six years of apple trees cultivation and we propose a model for tree nutrient uptake as a tool to guide fruit trees fertilization. The survey has been carried on a typical apple orchard of the Po Valley, Italy, with Gala/M9 planted in February 1997 at a density of 2632 trees/ha. Each year trunk diameter, fruit yield and pruning wood production were recorded. The biomass of abscised leaves was estimated. A sample of 3 trees was excavated in November 2002. Nutrient concentration has been obtained for fruits, pruning wood, leaves and the whole excavated trees. In 6 years from planting, trees accumulated 16 Mg ha -1 of dry biomass in the framework, 8.5 in the pruning wood, 28 in fruits, and 8.3 in the abscised leaves. Nutrients absorbed in higher amounts were Ca (462 kg ha -1 ) and K (406 kg ha -1 ), but most of them returned to soil by abscised leaves and pruning wood. Potassium was mostly partitioned to fruits. Nitrogen was also absorbed in high amounts (345 kg ha ). The results of this study have been integrated in an electronic spreadsheet (www.isafruit.org) able to estimate apple tree nutrient uptake.

The decomposition of plant residues has a pivotal role in carbon and nutrient cycles in agricultural ecosystems, where it can contribute to the sustainable management of the crops. In this paper we report a study on the release of C and nutrients during the decomposition of peach abscised leaves in northern Italy. Litter bags containing a representative amount of leaf material were installed under tree canopies either on the soil surface under open field conditions or on the soil surface in pots under partially controlled conditions. Potted leaf litter was pre-labelled with 15N. We observed that in 3 years, peach leaves lost 85% of their initial mass mostly attributable to cellulose decomposition, while new lignin or lignin-like compounds were synthesised during the first stages of the decomposition process. Nutrient dynamics differed depending on the considered element. Nitrogen and sulphur were initially immobilized into the litter to be released only starting after 44 weeks from the beginning of the decomposition. Potassium and magnesium were rapidly released in the winter following leaf abscission, reaching an amount that remained constant up to the end of the trial. Calcium and phosphorus release was slow, but constant throughout the three-year study period. With the only exception of Mg, 80–90% of initial amounts of mineral elements had released from decomposing peach leaves after 3 year from leaf abscission. Since in mature stands leaf litters of different ages coexist on the soil surface 80–90% of the nutrients contained in the abscised leaves are expected to return annually to the soil and potentially be available for subsequent root and/or microbial uptake.

Sustainable agriculture requires assessments of nitrogen fluxes and monitoring of potential nitrate losses. Watershed studies are particularly valuable to calculate nitrogen balances and quantify the relative importance of different sources of inputs and outputs. A nitrogen balance was calculated from September 2004 to October 2006 in an agricultural watershed named Valle Volta (Northern Italy) located in a Nitrate Vulnerable Zone. The area, consisting of 17.4 km 2 of arable land, with limited presence of urban areas and roads, is entirely below the sea level (3 m b.s.l. in average). Soils are typically Vertic Cambisols and Thionic Fulvisols with fine texture (silty clay or silty clay loam). About 45% of the agricultural soil is pipe-drained. The ground water level is maintained at 4.6 m b.s.l. by the activity of pumps that raise excess waters into a river. Water fluxes in and out from the basin were daily registered, and dissolved inorganic nitrogen concentration (N–NO 3 + N–NH 4 ) analyzed periodically. Data about fertilizers applications, seeds and crop yield were obtained from farmers’ interviews. Biological nitrogen fixation (BNF) was estimated on the base of dry matter yield. Major N inputs derived from fertilizers (174–188 Mg watershed −1 year −1 ), followed by BNF (126–131 Mg watershed −1 year −1 ). Maize was the crop receiving the highest fertilization rates, accounting for more than 40% of total fertilizer inputs. Saleable products were the main form of N leaving the watershed (317–338 Mg watershed −1 year −1 ). Nitrate was the main N form in irrigation and efflux water; its concentration was higher from autumn to spring, with peaks of 10–20 mg N L −1 in efflux water, while it was low in summer. Nitrogen losses with efflux water were higher in spring and in autumn. Overall, losses of nitrate by efflux water were limited if compared with literature data. Water balance in the area remained near zero at the beginning and the end of the first year, confirming the suitability of the area for this kind of study. The potential net contribution of each hectare of agricultural soil of Valle Volta basin to the N load toward the Adriatic sea is about 5.5 kg N. Our study demonstrated that in the Valle Volta watershed, total N outputs and inputs are of similar magnitude, indicating that crop management and especially N fertilization techniques has reached good levels of ecological sustainability.

International audience; As studies on biochar stability in field conditions are very scarce, the carbon sequestration potential of biochar application to agricultural soils remains uncertain. This study assessed the stability of biochar in field conditions, the effect of plant roots on biochar stability and the effect of biochar on original soil organic matter (SOM) decomposition in two (Italy and United Kingdom) short rotation coppice systems (SRCs), using continuous soil respiration monitoring and periodic isotopic ((CO2)-C-13) measurements. When root growth was excluded, only 7% and 3% of the biochar carbon added was decomposed after 245 and 164days in Italy and United Kingdom sites respectively. In the presence of roots, this percentage was increased to 9% and 8%, suggesting a small positive priming effect of roots on biochar decomposition. A decreased decomposition rate of original SOM was observed at both sites after biochar incorporation, suggesting a protective effect of biochar on SOM. This study supports the carbon sequestration potential of biochar and highlights the role of root activity on biochar decomposition, questioning the applicability of laboratory incubation studies to assess biochar stability.

Background Most current approaches in forest science and practice require information about structure and growth of individual trees rather than - or in addition to - sum and mean values of growth and yield at forest stand level as provided by classic experimental designs. By inventing the wheel design, Nelder provided the possibility to turn to the individual tree as basic information unit. Such trials provide valuable insights into the dependency of growth on stand density at particular sites. Methods Here, we present an extension of the original design and evaluation by Nelder. (i) We established Nelder wheels along an environmental gradient through Europe in atlantic climate in Belgium and Germany, Mediterranean climate in Italy, continental climate in Hungary as well as on high land climate in Mexico. Such disjunct Nelder wheels along an environmental gradient can be regarded and analysed as a two-factor design with the factors of site condition and stand density. (ii) We present an advanced statistical approach to evaluate density dependent growth dynamics of trees planted in form of the Nelder design, which considers spatio-temporal autocorrelation. (iii) We prove the usefulness of the methods in improving ecological theory concerning density related productivity, trade-offs between facilitation and competition, and allometric relations between size variables. Results First evaluations based on remeasured Nelder wheels in oak (Quercus roburL.) show a size growth differentiation during the first observation period. In particular, height growth is accelerated under higher competition indicating facilitation effects. We detect furthermore a high variability in allometric relations. Conclusions The proposed design, methods, and results are discussed regarding their impact on forest practice, model building, and ecological theory. We conclude that the extended Nelder approach is highly efficient in providing currently lacking individual tree level information.

The viability of a near infrared (NIR) method based on a dual-beam, fibre-optic portable spectrophotometer was tested to determine soluble solids non-destructively in apples ( Malus domestica Borkh.). A total of 340 apples (190 of cv. `Golden Delicious' and 150 of cv. `Jonagold') sampled from two positions in the canopy to increase variation in soluble solids concentration, were measured after 5-months storage and the measurements randomly assigned to a calibration data set and a prediction data set. Thus the calibration set and the prediction set represented exactly the same distribution. The calibration data set was used to select the wavelengths best correlated with °Brix and to fit a multiple linear regression (MLR) equation that was applied to calculate the °Brix value in the prediction data set. The most significant R 2 (0.56) was found with the first derivative of log(1/ R ) (where R =reflectance), yielding standard error of calibration (S.E.C.)=1.01 °Brix, standard error of prediction (S.E.P.)=1.14 °Brix and bias=−0.13 °Brix. When MLR was carried out separately on each cultivar, the R 2 value was higher for `Golden Delicious' (0.65), but not for `Jonagold' fruit. Analysis of variance performed on the actual and the predicted °Brix showed no difference in statistical significance, although the bias was higher (±5% of actual °Brix) at the extremities of the °Brix range. The scoring of the fruits according to soluble solids content measured by NIR enabled correct classification of 72 and 76% of the fruits, with a threshold of 12 and 13 °Brix, respectively. This NIR method seems reliable for determining soluble solids contents non-destructively, and could prove useful in the orchard.

Treatments differing from each other for the type of tube closure (i.e., cotton plug for free gas exchange, airtight rubber cap, and rubber cap with ethysorb) and/or rooting culture medium (i.e., enriched or not by 25 to 100 µM acetylsalicylic acid) were compared for their effects on gaseous composition of the culture atmosphere and microcutting rooting of the GF 677 (Prunus persica × Prunus amygdalus) hybrid. Rubber capping, which leads to rapid ethylene accumulation inside tubes, strongly reduced rooting time and in some cases enhanced final rooting percentage over that of cotton plugs. Ethysorb almost completely absorbed ethylene produced by shoots, which showed lower rooting percentages within 9 d than microcuttings cultured in the absence of ethysorb. In contrast, no significant difference in rooting was found between the two treatments after 14 d. Carbon dioxide concentration was similar in all treatments within 5 to 9 d and seemed to be ineffective for rooting. The influence of acetylsalicylic acid on rooting was unclear. Root number and length were not significantly influenced by the treatments. These results demonstrate that the use of airtight closures, leading to rapid ethylene accumulation, can reduce time of rooting expression for GF 677 microcuttings. However, free gas exchange towards the end of the rooting period (from Day 9 to Day 14) is advisable to prevent leaf yellowing. No significant difference in plantlet survival and growth after transfer ex vitro was found among treatments.

Rhizodeposition plays an important role in nitrogen (N) cycling within ecosystems, but it is understudied in agroecosystems, especially in orchards. In this study, we quantified N flux from peach root to soil in two soils with different texture. Seedlings were grown for 1 year in sand and fertilized with 15N-enriched ammonium nitrate. Trees were then transplanted into pots filled with a coarse-textured (CT) or a fine-textured (FT) soil with natural 15N abundance. The isotopic mass balance technique was applied to quantify the uptake and the release of N by roots. At the end of the experimental year tree growth was 431 g tree−1 in CT soil and 188 g tree−1 in FT soil, and root N concentration was 0.98% in CT soil and 0.73% in FT soil. Leaf chlorophyll was always higher in trees grown in CT than in FT soil. Nitrogen uptake in CT soil was more than double that in FT soil (4471 mg tree−1 vs. 2106 mg tree−1), but its allocation was not affected by soil texture (57% aboveground and 43% belowground). Nitrogen flux from roots to soil was 453 and 412 mg N tree−1 year−1 for trees in CT and in FT soil, respectively, 70% of which transferred in the winter. Our data suggest that root mortality is more important than root exudation in N transfer from roots to soil. Rhizodeposition was similar for both soils but tree growth was greater in CT soil than in FT soil. As a consequence, trees in FT soil allocated belowground (root biomass and rhizodeposition) a higher proportion of the absorbed N compared to trees in CT soil. Data also indicate that rhizodeposition can account for a major fraction (25–41%) of the photosynthate flux to the root system and therefore it should be considered to accurately estimate BNPP. A deeper knowledge of the belowground orchard processes is necessary to understand a balanced tree nutrient uptake. Rhizodeposition can also contribute to nutrient mobilization, heavy metal detoxification, root exploitation of soil, and drought tolerance. This work can thus provide information enabling horticulturists to develop management practices to optimise tree growth.