The response of forest ecosystems to increased atmospheric CO₂is constrained by nutrient availability. It is thus crucial to account for nutrient limitation when studying the forest response to ...climate change. The objectives of this study were to describe the nutritional status of the main European tree species, to identify growth‐limiting nutrients and to assess changes in tree nutrition during the past two decades. We analysed the foliar nutrition data collected during 1992–2009 on the intensive forest monitoring plots of the ICP Forests programme. Of the 22 significant temporal trends that were observed in foliar nutrient concentrations, 20 were decreasing and two were increasing. Some of these trends were alarming, among which the foliar P concentration in F. sylvatica, Q. Petraea and P. sylvestris that significantly deteriorated during 1992–2009. In Q. Petraea and P. sylvestris, the decrease in foliar P concentration was more pronounced on plots with low foliar P status, meaning that trees with latent P deficiency could become deficient in the near future. Increased tree productivity, possibly resulting from high N deposition and from the global increase in atmospheric CO₂, has led to higher nutrient demand by trees. As the soil nutrient supply was not always sufficient to meet the demands of faster growing trees, this could partly explain the deterioration of tree mineral nutrition. The results suggest that when evaluating forest carbon storage capacity and when planning to reduce CO₂emissions by increasing use of wood biomass for bioenergy, it is crucial that nutrient limitations for forest growth are considered.
We evaluated trends (2005–2013) and patterns of dissolved organic nitrogen (DON) and its ratio with dissolved organic carbon (DOC), DOC:DON in atmospheric deposition and soil solution of five Level ...II plots of the International Co-operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests) in Flanders, Northern Belgium. The primary aim was to confirm positive postulated trends in DON levels and DOC:DON under on-going recovery from acidification. The DON concentrations (0.95–1.41mgL−1) and fluxes (5.6–8.3kgha−1y−1) in throughfall were about twice as high compared to precipitation in the open field (0.40–0.48mgL−1, 3.0–3.9kgha−1y−1). Annual soil profile leaching losses of DON varied between 1.2 and 3.7kgha−1y−1. The highest soil DON concentrations and fluxes were observed beneath the O horizon (1.84–2.36mgL−1, 10.1–12.3kgha−1y−1). Soil solution concentrations and fluxes of DON showed significant increasing trends. Temporarily soil solution DOC:DON rose following an exceptionally long spring drought in 2007, suggesting an effect of drying and rewetting on DOM composition. Further research is needed to test the dependence of DON and DOC:DON on factors such as latitude, forest cover, length of the growing season, hydrology and topography. Nonetheless, even with considerable variation in soil type, level of base saturation, and soil texture in the five included ICP Forests Level II plots, all data revealed a proportionally larger positive response of DON flux than DOC to recovery from acidification.
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•DON concentrations increased under acidification recovery.•DON fluxes showed similar increasing trends.•DOC:DON peaked after drying and rewetting.
Resource allocation to different plant tissues is likely to be affected by high investment into fruit production during mast years. However, there is a large knowledge gap concerning species-specific ...differences in resource dynamics. We investigated the influence of mast years on stem growth, leaf production, and leaf carbon (C), nitrogen (N), and phosphorus (P) concentrations and contents in
Fagus sylvatica
,
Quercus petraea
, and
Q. robur
at continental and climate region scales using long-term data from the International Co-operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests) and similar datasets. We discussed the results in the light of opposing resource dynamics hypotheses: (i) resource accumulation before mast years and exhaustion after mast years (
resource storage hypothesis
), (ii) shifting resources from vegetative to generative compartments (
resource switching hypothesis
), and (iii) investing resources concurrently in both vegetative and generative compartments (
resource matching hypothesis
). Linear mixed-effects modelling (LMM) showed that both stem growth and leaf production were negatively influenced by weather conditions which simultaneously lead to high fruit production. Thus, the impact of generative on vegetative growth is intermixed with effects of environmental factors. Superposed epoch analyses and LMM showed that for mast behaviour in
F. sylvatica
, there are indicators supporting the
resource storage
and the
resource switching hypotheses
. Before mast years, resources were accumulated, while during mast years resources switched from vegetative to generative tissues with reduced stem and leaf growth. For the
Quercus
species, stem growth was reduced after mast years, which supports the
resource storage hypothesis
. LMM showed that leaf C concentrations did not change with increasing fruit production in neither species. Leaf N and P concentrations increased in
F. sylvatica
, but not in
Quercus
species. Leaf N and P contents decreased with increasing fruit production in all species, as did leaf C content in
F. sylvatica
. Overall, our findings suggest different resource dynamics strategies in
F. sylvatica
and
Quercus
species, which might lead to differences in their adaptive capacity to a changing climate.
Despite the importance of vegetation uptake of atmospheric gaseous elemental mercury (Hg(0)) within the global Hg cycle, little knowledge exists on the physiological, climatic, and geographic factors ...controlling stomatal uptake of atmospheric Hg(0) by tree foliage. We investigate controls on foliar stomatal Hg(0) uptake by combining Hg measurements of 3569 foliage samples across Europe with data on tree species' traits and environmental conditions. To account for foliar Hg accumulation over time, we normalized foliar Hg concentration over the foliar life period from the simulated start of the growing season to sample harvest.
Throughout Europe and the USA, forest ecosystem functioning has been impacted by long-term excessive deposition of acidifying compounds. In this study, we report on trends in stand deposition and ...soil solution fluxes of inorganic nitrogen (N) and sulphur (S) compounds over a 17-year period (1994–2010) in five ICP Forests monitoring plots in Flanders, northern Belgium. Deposition was dominated by N, and primarily NH₄ ⁺. Deposition of SO₄ ²⁻ and NH₄ ⁺ declined by 56–68% and 40–59% respectively. Deposition of NO⁻ ₃ decreased by 17–30% in deciduous forest plots, but remained stable in coniferous forest plots. The decrease of N and S deposition was parallelled by a simultaneous decline in base cation (BC = Ca²⁺ + K⁺ + Mg²⁺) deposition, resulting in a 45–74% decrease of potentially acidifying deposition. Trends in soil solution fluxes of NH₄ ⁺, NO₃ ⁻, SO₄ ²⁻ and BC mirrored declining depositions. Nitrate losses below the rooting zone were eminent in both coniferous forest plots and in one deciduous forest plot, while net SO₄ ²⁻ release was observed in two deciduous forest plots. Critical limits for BC/Al ratio were exceeded at the three plots on sandy soils with lower cation exchange capacity and base saturation. Soil solution acid neutralizing capacity increased but remained negative, indicating that soil acidification continued, as the start of recovery was delayed by a simultaneous decrease of BC depositions and short-term soil buffering processes. Despite substantial reductions, current N deposition levels still exceed 4–8 times the critical load for safeguarding sensitive lichen species, and are still 22–69% above the critical load for maintaining ground vegetation diversity.
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•Changes in soil solution chemistry indicate an improvement in forest N status.•Biotic recovery appeared to be lagging behind according to tree nutritional status.•Insight in recovery ...from N saturation requires a multiple indicator approach.
Nitrogen (N) depositions in Europe are decreasing, but this could not explain faster than expected improvement of N saturation indicators in temperate forests. Alongside there were local signs of initial recovery from acidification during the past three decades and enhanced leaching of dissolved organic carbon and nitrogen (DOC, DON). These two global change processes both affect total dissolved nitrogen (TDN) levels and often occur simultaneously, hence complicating mechanistic explanations for changing European forest N status. We aimed to test the hypothesis that forest N status in northwest Europe has started to improve. If this hypothesis is confirmed, we wanted to investigate to what extent such improvement is due to reduced N deposition. We evaluated the evolution of multiple N saturation indicators in five ICP Forests Level II plots in northern Belgium, using long-term soil solution and foliage datasets. The DON:TDN ratio (molar) in soil solution increased overall in the O horizon (mean 0.279–0.463, slope 0.023–0.037 yr−1) and in the mineral soil (mean 0.134–0.78, slope 0.007–0.051 yr−1) between 2005 and 2014. The DOC:NO3− ratio (molar) in soil solution increased in three plots in the O horizon (mean 6.84–22.15, slope 0.58–1.92 yr−1) and in four plots in the mineral soil (mean 2.07–25.32, slope −0.06–5.76 yr−1) between 2002 and 2014. The ratio of N and phosphorus (P) concentrations in foliage (mgg−1) and the ratio of base cations (Bc=Ca+K+Mg) and N concentrations in foliage (molar) remained unaltered between 1999 and 2013. Changes in the soil solution chemical composition thus confirmed an improvement in forest N status, despite sustained high NO3− concentrations, but biotic recovery appeared to be lagging behind. This demonstrates that insight in forest recovery from N saturation requires a multiple indicator approach, and further monitoring of tree nutritional status alongside soil processes is needed to monitor the evolution of European forest N status.
Dissolved organic carbon (DOC) in the soil solution of forests originates from a number of biologically and/or biochemically mediated processes, including litter decomposition and leaching, soil ...organic matter mineralization, root exudation, mucilage and microbial activity. A variable amount of DOC reaches the forest floor through deposition, but limited information is available about its impact on soil solution DOC. In this study, trends and patterns of soil solution DOC were evaluated in relation to deposition of DOC over an 11-year period (2002–2012) at five ICP Forests intensive monitoring plots in Flanders, northern Belgium. Trend analysis over this period showed an increase of soil solution DOC concentrations for all observed depth intervals. Fluxes of DOC increased in the organic layer, but were nearly stable in the mineral soil. Annual leaching losses of DOC were higher in coniferous (55–61 kg C ha−1) compared to deciduous plots (19–30 kg C ha−1) but embody less than 0.05% of total 1-m soil organic C stocks. Temporal deposition patterns could not explain the increasing trends of soil solution DOC concentrations. Deposition fluxes of DOC were strongly correlated with soil solution fluxes of DOC, but their seasonal peaks were not simultaneous, which confirmed that air-borne or canopy-derived DOC has a limited impact on soil solution DOC.
•Soil solution DOC concentrations in Flanders forests increased (2002–2012).•Soil solution DOC fluxes showed less systematic trends.•Deposition could not explain the increase of soil solution DOC concentrations.•Stand deposition had a rather limited impact on soil solution DOC.
KEY MESSAGE : Exceedance 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. CONTEXT : Forests 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. AIMS : We 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. METHODS : We 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. RESULTS : Critical 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. CONCLUSION : The findings support the hypothesis that elevated nitrogen and sulphur deposition can lead to imbalances in tree nutrition.
In transnational monitoring programmes, a balance between international reference methods, which improve spatial comparability, and national analysis methods that favour temporal comparability, by ...their use and testing over many years, needs to be sought. Prior to the next Pan-European Forest Soil Survey, a third interlaboratory comparison of soil analysis methods was organised. All participating laboratories were requested to use the same reference methods. Fifty-two soil laboratories from 27 European countries analysed a total of 48 soil parameters on three soil samples which were typical for European forest soils. The results of the statistical analysis showed a high interlaboratory and intralaboratory variability, especially for the acid oxalate extractions, particle size distribution, exchangeable elements and total carbonates. The intercomparability of the test results did not improve compared to the previous ring test. As the exercise aimed primarily at comparing the performance of the laboratories, it was not powerful enough to find cause–effect relationships between the meta information provided by the laboratories and the variability of the test results.
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