Comment on "In defense of plants as biomonitors of soil quality".
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Ecosystem↗
Biomedical subjects
Sebastiaan Luyssaert
Publications and source records attributed to Sebastiaan Luyssaert.
Acidification of forested podzols in North Belgium during the period 1950-2000.
Acidification of forest soils in Europe and North America has been an important concern over the last decades. The last area-covering survey of forest soil acidification in Flanders (North Belgium) goes back to 1985 [Ronse A, De Temmerman L, Guns M, De Borger R. Evolution of acidity, organic matter content, and CEC in uncultivated soils of North Belgium during the past 25 years. Soil Sci; 146, (1988), 453-460] and highlighted a significant acidification of the upper layer (0.3-0.4 m) of forested podzols during the period 1950-1985. The present study aimed to assess (1) to what extent further acidification of forested podzols occurred during the period 1985-2000 at different depths and (2) whether the average annual acidification rate accelerated or slowed down between 1985 and 2000 compared to the period 1950-1985. Average soil pH-KCl values of podzols in northern Belgium dropped during the period 1985-2000. This decline extends to a depth of about 50 cm but was most pronounced and significant in the A horizon. In the A(0), A(1) and A(2) horizons, average pH dropped with 0.2, 0.3 and 0.1 units, and in the B(ir) and C horizons with 0.1 units. No change in average pH value occurred in the B(h) horizon. Average annual acidification rate of the A(1) horizon was significantly higher in the period 1985-2000 than in the period 1950-1985. Changes in pH occurred in the entire soil profile during the period 1950/67-1985 likely because sulphate was the major form of acid deposition before 1985. After 1985, acid sulphur deposition decreased with more than 50% in North Belgium. In contrast, ammonium deposition almost doubled between 1950 and 1980, which may explain why soil acidification between 1985 and 2000 has been restricted to the upper soil horizons.
Acid Rain↗
Does the commonly used estimator of nutrient resorption in tree foliage actually measure what it claims to?
A descriptive temporal model is considered to be the best available estimator for accretion, resorption and proportional nutrient resorption. However, ecological studies rarely collect sufficient data for applying such a model. A less-demanding and commonly used estimator for proportional resorption (PR) calculates PR as the percentage of the nutrient pool that is withdrawn from mature foliage before leaf abscission. Data from an intensive sampling campaign of the aboveground nutrient pools and fluxes of two Betula pendula Roth. stands were used. We showed that the commonly used estimator is not an accurate estimator for accretion, resorption and proportional resorption. The commonly used estimator underestimated the proportional resorption of N on the average by 3-10%, and the proportional resorption of P by 20-25%. The low accuracy of the estimations was shown to be caused by a lack of selectiveness of the commonly used estimator. In other words, the commonly used estimator does not measure the underlying processes in specific nutrient accretion and resorption at the stand level. However, when a sufficiently high sampling density with several samples at a given point in time is used, then the commonly used estimator preserves the ranking relationship between the PR of different sites for N in 97% of the cases and for P in 71%. The commonly used estimator can thus be used in comparative studies as an index for proportional nutrient resorption only. The quantitative results should not be taken literally, as they are based on only two sets of observations. However, the results show that the commonly used estimator should no longer be used as a measure for accretion, resorption or PR whenever the plant accretes nutrients in the foliage as a compensation for nutrient losses due to foliar leaching and litterfall during the growing season.
Betula↗
Use and abuse of trace metal concentrations in plant tissue for biomonitoring and phytoextraction.
Some plant species accumulate trace metals from the soil in their aboveground biomass. Therefore, some scientists have concluded that these species are suitable for biomonitoring trace metal concentrations in the soil or for removing excessive trace metals from the soil by means of phytoextraction. A significant correlation between the chemical composition of foliage and soil is not a sufficient condition for using the chemical composition of foliage as a biomonitor for the quality of the soil. The chemical composition of foliage can, however, provide additional information to the traditional soil samples. The phytoextraction potential of a plant species cannot solely be evaluated on the basis of the trace metal concentrations in the plant and soil tissue. Data on the depth of the rooting zone, the density of the soil and the harvestable biomass should also be taken into account. Although plant tissue analysis is a useful tool in a wide range of studies and applications, trace metal concentrations in plant tissue cannot be viewed in isolation. Instead it should be analysed and interpreted in relation to other information such as soil concentrations, rooted zone, biomass production, etc.
Biodegradation, Environmental↗
Are N and S deposition altering the mineral composition of Norway spruce and Scots pine needles in Finland?
Data from a large-scale foliar survey were used to calculate the extent to which N and S deposition determined the mineral composition of Scots pine and Norway spruce needles in Finland. Foliar data were available from 367 needle samples collected on 36 plots sampled almost annually between 1987 and 2000. A literature study of controlled experiments revealed that acidifying deposition mediates increasing N and S concentrations, and decreasing Mg:N and Ca:Al ratios in the needles. When this fingerprint for N and S elevated deposition on tree foliage was observed simultaneously with increased N and S inputs, it was considered sufficient evidence for assuming that acidifying deposition had altered the mineral composition of tree needles on that plot in the given year. Evidence for deposition-induced changes in the mineral composition of tree foliage was calculated on the basis of a simple frequency model. In the late eighties the evidence was found on 43% of the Norway spruce and 27% of Scots pine plots. The proportion of changed needle mineral composition decreased to below 8% for both species in the late nineties.
Acid Rain↗
Metal uptake by young trees from dredged brackish sediment: limitations and possibilities for phytoextraction and phytostabilisation.
Five tree species (Acer pseudoplatanus L., Alnus glutinosa L. Gaertn., Fraxinus excelsior L., Populus alba L. and Robinia pseudoacacia L.) were planted on a mound constructed of dredged sediment. The sediment originated from a brackish river mouth and was slightly polluted with heavy metals. This preliminary study evaluated the use of trees for site reclamation by means of phytoextraction of metals or phytostabilisation. Although the brackish nature of the sediment caused slight salt damage, overall survival of the planted trees was satisfactory. Robinia and white poplar had the highest growth rates. Ash, maple and alder had the highest survival rates (>90%) but showed stunted growth. Ash, alder, maple and Robinia contained normal concentrations of Cd, Cu, Pb and Zn in their foliage. As a consequence these species reduce the risk of metal dispersal and are therefore suitable species for phytostabilisation under the given conditions. White poplar accumulated high concentrations of Cd (8.0 mg kg(-1)) and Zn (465 mg kg(-1)) in its leaves and might therefore cause a risk of Cd and Zn input into the ecosystem because of autumn litter fall. This species is thus unsuitable for phytostabilisation. Despite elevated metal concentrations in the leaves, phytoextraction of heavy metals from the soil by harvesting stem and/or leaf biomass of white poplar would not be a realistic option because it will require an excessive amount of time to be effective.
Acer↗
Evaluation of forest nutrition based on large-scale foliar surveys: are nutrition profiles the way of the future?
This paper introduces the use of nutrition profiles as a first step in the development of a concept that is suitable for evaluating forest nutrition on the basis of large-scale foliar surveys. Nutrition profiles of a tree or stand were defined as the nutrient status, which accounts for all element concentrations, contents and interactions between two or more elements. Therefore a nutrition profile overcomes the shortcomings associated with the commonly used concepts for evaluating forest nutrition. Nutrition profiles can be calculated by means of a neural network, i.e. a self-organizing map, and an agglomerative clustering algorithm with pruning. As an example, nutrition profiles were calculated to describe the temporal variation in the mineral composition of Scots pine and Norway spruce needles in Finland between 1987 and 2000. The temporal trends in the frequency distribution of the nutrition profiles of Scots pine indicated that, between 1987 and 2000, the N, S, P, K, Ca, Mg and Al decreased, whereas the needle mass (NM) increased or remained unchanged. As there were no temporal trends in the frequency distribution of the nutrition profiles of Norway spruce, the mineral composition of the needles of Norway spruce needles subsequently did not change. Interpretation of the (lack of) temporal trends was outside the scope of this example. However, nutrition profiles prove to be a new and better concept for the evaluation of the mineral composition of large-scale surveys only when a biological interpretation of the nutrition profiles can be provided.
Algorithms↗
Support, shape and number of replicate samples for tree foliage analysis.
Many fundamental features of a sampling program are determined by the heterogeneity of the object under study and the settings for the error (alpha), the power (beta), the effect size (ES), the number of replicate samples, and sample support, which is a feature that is often overlooked. The number of replicates, alpha, beta, ES, and sample support are interconnected. The effect of the sample support and its shape on the required number of replicate samples was investigated by means of a resampling method. The method was applied to a simulated distribution of Cd in the crown of a Salix fragilis L. tree. Increasing the dimensions of the sample support results in a decrease in the variance of the element concentration under study. Analysis of the variance is often the foundation of statistical tests, therefore, valid statistical testing requires the use of a fixed sample support during the experiment. This requirement might be difficult to meet in time-series analyses and long-term monitoring programs. Sample supports have their largest dimension in the direction with the largest heterogeneity, i.e. the direction representing the crown height, and this will give more accurate results than supports with other shapes. Taking the relationships between the sample support and the variance of the element concentrations in tree crowns into account provides guidelines for sampling efficiency in terms of precision and costs. In terms of time, the optimal support to test whether the average Cd concentration of the crown exceeds a threshold value is 0.405 m3 (alpha = 0.05, beta = 0.20, ES = 1.0 mg kg(-1) dry mass). The average weight of this support is 23 g dry mass, and 11 replicate samples need to be taken. It should be noted that in this case the optimal support applies to Cd under conditions similar to those of the simulation, but not necessarily all the examinations for this tree species, element, and hypothesis test.
Cadmium↗
Sampling procedure for the foliar analysis of deciduous trees.
Sampling can be the source of the greatest errors in the overall results of foliar analysis. This paper reviews the variability in heavy metal concentrations in tree crowns, which is a feature that should be known and understood when designing a suitable leaf sampling procedure. The leaf sampling procedures applied in 75 articles were examined. Most of the environmental studies used a closely related form of the UN/ECE-EC leaf sampling procedure, which was developed for the long-term monitoring of forest condition. Studies with objectives outside the UN/ECE-EC field of application should utilize a sampling procedure that is in accordance with the objectives of the study and based on the observed variation in pilot and similar studies. The inherent sources of heavy metal variability inside the stand, i.e. the crown class, stand management, site properties, crown dimensions, infections, seasons, etc. were discussed, but the underlying causes of this variability are rarely understood. The inherent variability in tree crowns is the reason for using leaf sampling as a tool in pollution studies. The objectives of a pollution study determine which sources of variability are utilized by the researcher.
Environmental Monitoring↗