Elena Vanguelova

Variation in fine root biomass of three European tree species: Beech (Fagus sylvatica L.), Norway spruce (Picea abies L. Karst.), and Scots pine (Pinus sylvestris L.)

Abstract Fine roots (<2 mm) are very dynamic and play a key role in forest ecosystem carbon and nutrient cycling and accumulation. We reviewed root biomass data of three main European tree species European beech, (Fagus sylvatica L.), Norway spruce (Picea abies L. Karst.) and Scots pine (Pinus sylvestris L.), in order to identify the differences between species, and within and between vegetation zones, and to show the relationships between root biomass and the climatic, site and stand factors. The collected literature consisted of data from 36 beech, 71 spruce and 43 pine stands. The mean fine root biomass of beech was 389 g m−2, and that of spruce and pine 297 g m−2 and 277 g m−2, respectively. Data from pine stands supported the hypothesis that root biomass is higher in the temperate than in the boreal zone. The results indicated that the root biomass of deciduous trees is higher than that of conifers. The correlations between root biomass and site fertility characteristics seemed to be species specific. There was no correlation between soil acidity and root biomass. Beech fine root biomass decreased with stand age whereas pine root biomass increased with stand age. Fine root biomass at tree level correlated better than stand level root biomass with stand characteristics. The results showed that there exists a strong relationship between the fine root biomass and the above-ground biomass.

Tree fine root Ca/Al molar ratio – Indicator of Al and acidity stress

Abstract High soil acidity and elevated soil Al concentrations limit plant growth in many terrestrial ecosystems. Aluminium toxicity can be ameliorated by Ca. Thus, Ca/Al molar ratios in soil solution and in plant tissues have been proposed as superior indicators than Al concentration itself for evaluating the Al toxicity stress to trees (Cronan & Grigal, J Environ Qual 1995;24:209 – 226). This article presents an overview of publications since 1995 where the reduced Ca/Al ratio in fine tree roots has been used as an indicator of stress for Al and/or soil acidity. The main aim of this review was to evaluate the use and the critical threshold of the fine root Ca/Al ratio as a potential indicator for Al toxicity stress to trees in acid soils. Based on the reviewed literature, the fine root Ca/Al molar ratio was strongly negatively related to Al stress in small tree seedlings in controlled environments, whereas the response was not clear under field conditions where other environmental factors interact. Fine root Ca/Al ranged from 0.03 to 17 in tree seedlings and from 0.1 to 18 in mature trees depending on experimental and site conditions, as well as the tolerance and uptake mechanisms of the different tree species. Fine root Ca/Al was positively related to the soil solution Ca/Al molar ratio. Fine root Ca/Al ratios were related positively to fine root length, growth, specific root length, and biomass, and negatively to root diameter, callose formation, respiration chain activity, starch concentration, and root necromass. A number of relationships have been also found between the fine root Ca/Al and above-ground seedling and/or mature tree growth and nutrient uptake. The critical thresholds for the Ca/Al fine root ratio of 0.2 suggested by Cronan and Grigal (1995) is estimated to represent 90% risk of inverse impact on root and above-ground tree growth. Values of Ca/Al molar ratio in the fine roots of mature trees were only rarely determined below the critical 0.2. The caveats for the use and the interpretation of Ca/Al ratio in fine roots have been addressed in detail. A protocol for root processing and elemental analysis to obtain reliable and comparable results of Ca and Al concentrations in roots is also provided. The article concludes with recommendations for a wider use of the Ca/Al ratio in roots as a bioindicator of Al toxicity to trees in acid soils.

Exceedance of critical loads and of critical limits impacts tree nutrition across Europe

Key messageExceedance of critical limits in soil solution samples was more frequent in intensively monitored forest plots across Europe with critical loads for acidity and eutrophication exceeded compared to other plots from the same network. Elevated inorganic nitrogen concentrations in soil solution tended to be related to less favourable nutritional status.ContextForests have been exposed to elevated atmospheric deposition of acidifying and eutrophying sulphur and nitrogen compounds for decades. Critical loads have been identified, below which damage due to acidification and eutrophication are not expected to occur.AimsWe explored the relationship between the exceedance of critical loads and inorganic nitrogen concentration, the base cation to aluminium ratio in soil solutions, as well as the nutritional status of trees.MethodsWe used recent data describing deposition, elemental concentrations in soil solution and foliage, as well as the level of damage to foliage recorded at forest plots of the ICP Forests intensive monitoring network across Europe.ResultsCritical loads for inorganic nitrogen deposition were exceeded on about a third to half of the forest plots. Elevated inorganic nitrogen concentrations in soil solution occurred more frequently among these plots. Indications of nutrient imbalances, such as low magnesium concentration in foliage or discolouration of needles and leaves, were seldom but appeared more frequently on plots where the critical limits for soil solution were exceeded.ConclusionThe findings support the hypothesis that elevated nitrogen and sulphur deposition can lead to imbalances in tree nutrition.

Sources of errors and uncertainties in the assessment of forest soil carbon stocks at different scales—review and recommendations

Spatially explicit knowledge of recent and past soil organic carbon (SOC) stocks in forests will improve our understanding of the effect of human- and non-human-induced changes on forest C fluxes. For SOC accounting, a minimum detectable difference must be defined in order to adequately determine temporal changes and spatial differences in SOC. This requires sufficiently detailed data to predict SOC stocks at appropriate scales within the required accuracy so that only significant changes are accounted for. When designing sampling campaigns, taking into account factors influencing SOC spatial and temporal distribution (such as soil type, topography, climate and vegetation) are needed to optimise sampling depths and numbers of samples, thereby ensuring that samples accurately reflect the distribution of SOC at a site. Furthermore, the appropriate scales related to the research question need to be defined: profile, plot, forests, catchment, national or wider. Scaling up SOC stocks from point sample to landscape unit is challenging, and thus requires reliable baseline data. Knowledge of the associated uncertainties related to SOC measures at each particular scale and how to reduce them is crucial for assessing SOC stocks with the highest possible accuracy at each scale. This review identifies where potential sources of errors and uncertainties related to forest SOC stock estimation occur at five different scales—sample, profile, plot, landscape/regional and European. Recommendations are also provided on how to reduce forest SOC uncertainties and increase efficiency of SOC assessment at each scale.

The cycling of pollutants in nonurban forested environments

Forests are complex ecosystems which respond to external inputs of pollutants in a variety of ways. Quantifying changes in the storage of pollutants within ecosystem pools and the biogeochemical fluxes between them provides a means of calculating the overall pollutant balance of a forest ecosystem as an indicator of its sustainability and health. This chapter focuses on pollutant cycling in nonurban forest ecosystems with specific attention on quantification of external inputs, pollutant fluxes and pools within forests and exports to adjacent systems (Fig. 34.1). Selected case studies are used to exemplify the approach and illustrate the importance of location, forest type, management practices such as harvesting and soil conditions. Direct pollutant impacts on forest ecosystem functioning, the effects of intensified biomass utilization, and interactions between climate and pollutant cycling are also discussed.

Environment and host as large-scale controls of ectomycorrhizal fungi

Explaining the large-scale diversity of soil organisms that drive biogeochemical processes—and their responses to environmental change—is critical. However, identifying consistent drivers of belowground diversity and abundance for some soil organisms at large spatial scales remains problematic. Here we investigate a major guild, the ectomycorrhizal fungi, across European forests at a spatial scale and resolution that is—to our knowledge—unprecedented, to explore key biotic and abiotic predictors of ectomycorrhizal diversity and to identify dominant responses and thresholds for change across complex environmental gradients. We show the effect of 38 host, environment, climate and geographical variables on ectomycorrhizal diversity, and define thresholds of community change for key variables. We quantify host specificity and reveal plasticity in functional traits involved in soil foraging across gradients. We conclude that environmental and host factors explain most of the variation in ectomycorrhizal diversity, that the environmental thresholds used as major ecosystem assessment tools need adjustment and that the importance of belowground specificity and plasticity has previously been underappreciated.Analyses of data from 137 forest plots across 20 European countries show that ectomycorrhizal fungal diversity is strongly influenced by environmental and host species factors and provide thresholds to inform ecosystem assessment tools

Author Correction: Environment and host as large-scale controls of ectomycorrhizal fungi

Change history: In the HTML version of this Article, author ‘Filipa Cox’ had no affiliation in the author list, although she was correctly associated with affiliation 3 in the PDF. In addition, the blue circles for ‘oak’ were missing from Extended Data Fig. 1. These errors have been corrected online.