Giustino Tonon

Effect of NaCl and mannitol iso-osmotic stresses on proline and free polyamine levels in embryogenic Fraxinus angustifolia callus.

With the aim to differentiate the ionic and osmotic components of salt stress, short and long-term changes in free polyamines and proline induced by iso-osmotic concentrations of NaCl (0.1 mol/L and 0.2 mol/L) and mannitol (0.2 mol/L and 0.4 mol/L) were determined in Fraxinus angustifolia callus. The peculiarities of the short-term responses were: i) a very early (30 min) and temporary increase in Putrescine (Pu) and Spermine (Spm) as a consequence of salt treatment, and ii) a continuous accumulation of Spermidine (Spd) and Spm in response to mannitol. The changes of Proline (Pro) were quite limited both in the short and in the long term, and generally occurred later than Polyamine (PAs) changes took place, suggesting a regulatory mechanism of PAs metabolism on Pro biosynthesis. In the long-term, no drastic accumulations of Pro or PAs in response to NaCl and mannitol were observed, suggesting that their physiological role is unlikely to be that of osmo-compatible solutes in this plant system. The salt induced a higher callus growth inhibition effect than did mannitol and this inhibition was associated with the reduction of endogenous levels of PAs, especially Pu. However, while a diverging time course was observed under lethal salt concentration (0.2 mol/L NaCl), a high parallelism in the endogenous changes of Pro and Pu was observed under all non-lethal conditions (control--0.2 and 0.4 mol/L mannitol--0.1 mol/L NaCl). Therefore the synchronous changes of Pro and Pu can be considered as a physiological trait associated with cell survival. These results indicate a strong metabolic co-ordination between PAs and Pro pathways and suggest that the metabolic fluxes through these pathways start competing only when the stress level is high enough to be lethal for cells.

Biochar mineralization and priming effect on SOM decomposition in two European short rotation coppices.

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 (δ13CO2) measurements. When root growth was excluded, only 7% and 3% of the biochar carbon added was decomposed after 245 and 164 days 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.

Biochar alters the soil microbiome and soil function: results of next‐generation amplicon sequencing across Europe

Wide‐scale application of biochar to soil has been suggested as a mechanism to offset increases in CO2 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 Acidobacteria in UK biochar plots 1 year after application, whilst control plots exhibited enriched Gemmataceae, Isosphaeraceae 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 Proteobacteria (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.

Fate of 15N derived from soil decomposition of abscised leaves and pruning wood from apple (Malus domestica) trees

Abstract The fate of nitrogen (N) derived from soil incorporating 15N-labeled apple (Malus domestica) leaves and wood from pruning (hereafter referred to as “pruning wood”) was studied in an 8-month pot experiment. The net mineralization of N was measured as 15N recovery in perennial ryegrass (Lolium perenne) that was allowed to grow in soils amended with residues < 2 mm in size (litter : soil ratio, w/w, 1:250 for leaves and 1:330 for wood). The immobilization of native soil N as a consequence of residue addition was measured by comparing the amount of total N taken up by ryegrass in residue-amended soil and in control soil. Net immobilization of soil N occurred during the first 2 months after litter addition and was especially high in the soil amended with leaf litter. During the period of soil N immobilization, the amount of soil microbial N was high in the soils treated with both types of residues, while that of mineral N was markedly reduced only in the leaf-litter-amended soil. Net N uptake from the control soil almost stopped after 3 months of plant growth, while ryegrass in the litter-amended soil continued to take up N, indicating a likely release of previously immobilized N. Net mineralization of the 15N from apple residues was slow during the first 2 months after their incorporation and then increased. In total, 6% (leaves) and 12% (wood) of the N added via residues underwent mineralization, while 67% (leaves) and 85% (wood) were found in the extractable soil N pool (humic and fulvic acids and non-humified fractions). The data indicated that, even if N was incorporated into the soil, apple leaves and pruning wood did not mineralize significant amounts of N in the short term. The evidence suggested that during the decomposition of both types of apple residues the N originally present was incorporated into the stable soil N pool.

Seasonal changes in microbial nitrogen in an old broadleaf forest and in a neighbouring young plantation

Soil microorganisms are actively involved in many processes of the soil N cycle and are strong competitors with plants for soil N. Therefore, microbial dynamics are important factors in controlling forest productivity. Nevertheless, they are poorly studied especially in relation to forest age, which can produce strong effects on the microbial community by affecting the forest floor environment. In the present study, seasonal variations of soil microbial N (Nmic) were monitored in an old floodplain hardwood forest (270 years) and in a young hardwood plantation (19 years) in two soil horizons (0–15 and 15–30 cm). Although the differences according to time of sampling and soil horizon were statistically significant, Nmic was significantly higher in old than in young forest, especially for the deeper soil layer. However, the highest percentage of total N (Ntot) immobilised in microbial biomass was found in the surface soil layer of the young plantation. Soil organic C (Corg) explained 23% of the spatial–temporal variation of Nmic over all sampling periods in the old forest, whereas the linear combination of Ntot, total extractable soil N (Ntotex) and the C/N ratio explained 59% of variation in Nmic when considering only the growing season. In contrast, Corg and Ntotex explained 59% of variation in Nmic in the young stand when considering all sampling periods and 75% when the analysis was limited to growing season. Soil moisture did not show any significant correlation with Nmic in either site. The sensitivity of Nmic to variation in Corg and Ntot seems to be affected by forest age, being higher in young than in old forest. Finally our results indicate that during the growing season, when the Ntotex availability is low, the dynamics of Nmic and Ntotex are temporally interdependent, suggesting the existence of a reciprocal control whose mechanisms deserve to be elucidated.

The increase of atmospheric CO 2 affects growth potential and intrinsic water-use efficiency of Norway spruce forests: insights from a multi-stable isotope analysis in tree rings of two Alpine chronosequences

Key messageRelevant CO2increase affects iWUE and growth potential of Alpine Norway spruce forests due to triggering of photosynthetic capacity. Minor effect on iWUE of tree size/age ontogenetic factors.AbstractAn increase in European forest productivity has been widely reported, but evidences on its causal relationship with climate change are still scarce, though they are crucial to understand the mitigation potential of forests and their future dynamics. In the present study, we first assessed the changes in forest productivity of two even-aged Norway spruce forests. Consequently, we investigated the role of several environmental drivers, such as atmospheric CO2 levels, temperature, and precipitation regimes on the intrinsic water-use efficiency (iWUE) temporal patterns of the above-mentioned forests. We applied a chronosequence approach, combining it with a multi-stable isotope analysis, including δ13C and δ18O, to infer tree responses to climate change over time in terms of iWUE changes. By this innovative methodology, we were able to separate environmental and age/size-related factors on iWUE changes. Results showed an increase in forest productivity in both sites, paralleled by a significant increase of iWUE, mainly triggered by a CO2-driven increase in photosynthetic capacity, rather than by a reduction of stomatal conductance. The paramount role of the increase in photosynthetic capacity was confirmed by a strong correlation between atmospheric CO2 concentration and iWUE temporal patterns. The effect of size/age of trees on iWUE temporal changes resulted to be less defining than that of climate change.

Biochars in soils: towards the required level of scientific understanding

Key priorities in biochar research for future guidance of sustainable policy development have been identified by expert assessment within the COST Action TD1107. The current level of scientific understanding (LOSU) regarding the consequences of biochar application to soil were explored. Five broad thematic areas of biochar research were addressed: soil biodiversity and ecotoxicology, soil organic matter and greenhouse gas (GHG) emissions, soil physical properties, nutrient cycles and crop production, and soil remediation. The highest future research priorities regarding biochar’s effects in soils were: functional redundancy within soil microbial communities, bioavailability of biochar’s contaminants to soil biota, soil organic matter stability, GHG emissions, soil formation, soil hydrology, nutrient cycling due to microbial priming as well as altered rhizosphere ecology, and soil pH buffering capacity. Methodological and other constraints to achieve the required LOSU are discussed and options for efficient progress of biochar research and sustainable application to soil are presented.

Isotopic discrimination during litter decomposition and δ13C and δ15N soil profiles in a young artificial stand and in an old floodplain forest

In the present study, rates of litter decomposition and microbial biomass nitrogen were monitored over an 8-month period in a young broadleaf plantation (18 y) and in an old floodplain forest. Moreover, δ13C and δ15N temporal variations within soil profiles were evaluated at both sites. Rates of litter decomposition were higher in spring and autumn than in summer, in both forests. At the end of the observation period the percentage of original litter remaining was not statistically different between the young and the old forest and accounted for 60–70% of the original amount. Microbial biomass nitrogen in the remaining litter and the percentage of litter mass lost during decomposition were positively correlated. The difference in litter quality affected the decomposition rate and also the changes in carbon isotopic composition during the decomposition process. In contrast, 15N isotopic signatures showed a similar trend in the litter of the two forests irrespective of the litter quality. Although δ13Csoil and δ15Nsoil showed considerable temporal variation they increased with depth in the soils of both sites but their seasonal changes did not reflect those of the decomposing litter. Within the same soil horizon, both δ13C and δ15N showed similar seasonal trends in the soils of the two forests, suggesting the involvement of environmental factors acting at regional level, such as soil temperature and rainfall variations, in regulating seasonal δ13C and δ15N soil variations. # Revised version of a paper presented at the 1st Joint European Stable Isotope Users Group Meeting (JESIUM), August, 30 to September, 3, 2004, Vienna, Austria.

Stand density sensitive biomass functions for young oak trees at four different European sites

Key messageRelative 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.AbstractEstimation 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 (d0), tree height and stand density is tested. The results show that besides d0, 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.

Evaluation of the ECOSSE model to predict heterotrophic soil respiration by direct measurements

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.