Plant and Soil 242: 171–182, 2002. © 2002 Kluwer Academic Publishers. Printed in the Netherlands.
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Tree species mediated soil chemical changes in a Siberian artificial afforestation experiment Tree species and soil chemistry Oleg V. Menyailo1,4, Bruce A. Hungate2 & Wolfgang Zech3 1 Institute of Forest SB RAS, Krasnoyarsk 660036, Russia. 2
Department of Biological Sciences and Merriam Powell Center for Environmental Research, Northern Arizona University, AZ 86001, USA. 3 Institute of Soil Science and Soil Geography, University of Bayreuth, Bayreuth 95447, Germany. 4 Corresponding author∗
Key words: artificial afforestation, forest ecosystems, grassland conversion, soil acidity, soil solution, tree species effect Abstract Natural and human-induced changes in the composition of boreal forests will likely alter soil properties, but predicting these effects requires a better understanding of how individual forest species alter soils. We show that 30 years of experimental afforestation in Siberia caused species-specific changes in soil chemical properties, including pH, DOC, DON, Na+ , NH4 + , total C, C/N, Mn2+ , and SO4 2− . Some of these properties — pH, total C, C/N, DOC, DON, Na+ — also differed by soil depth, but we found no strong evidence for species-dependent effects on vertical differentiation of soil properties (i.e., no species × depth interaction). A number of soil properties — NO3 − , N, Al3+ , Ca2+ , Fe3+ , K+ , Mg2+ and Cl− — responded to neither species nor depth. The six studied species may be clustered into three groups based on their effects on the soil properties. Scots pine and spruce had the lowest pH, highest C/N ratio and intermediate C content in soil. The other two coniferous species, Arolla pine and larch, had the highest soil C contents, highest pH values, and intermediate C/N ratios. Finally, the two deciduous hardwood species, aspen and birch, had the lowest C/N ratio, intermediate pH values, and lowest C content. These treemediated soil chemical changes are important for their likely effects on soil microbiological activities, including C and N mineralization and the production and consumption of greenhouse gases.
Introduction The influence of tree species on soil chemical properties is a critical question in soil science and biogeochemistry, especially given increasing artificial afforestation in Europe, North America and Russia as a way to reduce net CO2 emissions. Additionally, the species composition of boreal forests will likely change in response to climate and atmospheric change. Pastor and Post (1988) suggested that changes in temperature and precipitation resulting from increasing atmospheric CO2 concentrations will cause a northward migration of the hardwood-conifer forest border in North America. Such migration of hardwood forests will likely take also place in Russian Siberia. Thus, a better understanding of the effects of different species on ∗ E-mail:
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soil properties is needed to predict how such humaninduced and natural changes in species composition will alter ecosystem processes. However, there are no published data on the direct effects of Siberian tree species on soil chemical properties. The effects of tree species on soil chemistry have been studied in temperate and boreal forests of Northern America and Europe (Finzi et al., 1998b; Muys and Lust, 1992; Priha and Smolander, 1997), yet such responses may not represent well how species alter soil properties in Siberian forests. First, Larix sibirica (larch) and Pinus sylvestris (Scots pine) are dominant species in Siberian forests; Larix sibirica is absent in North American and European boreal forests, while Pinus sylvestris is a dominant species in European boreal forests. Second, as species effects may interact with nutrient availability and acid deposition, the low rate of N deposition in Siberia (less than 2 kg
172 ha−1 year−1 ) may lead to qualitatively different species effects in Siberia compared to Europe and North America. Thus, the responses of soil chemical variables to different tree species in Siberia may differ from those reported in literature for European and American forests. One of the potential problems in examining plantinduced soil changes is the confounding effects of site variability and land-use history. For a study to assess how plants influence soil, more precise estimates can be made if experiments are established on an initially homogeneous substrate (Binkley, 1994). If soils are initially uniform, then any differences in soil variables that arise over time among experimental treatments (between species) can be fully attributed to species effects (Wedin and Tilman, 1990). Experiments to test the effects of individual tree species on soil properties are difficult to set up compared to those for agricultural or herbaceous plants, and require long-term maintenance in order to be able to observe species effects on soil properties. Thus, there are few artificial afforestation experiments around the world (Priha and Smolander, 1997) and little data on the effects of forest species on soil properties. Here, we report results from the only artificial afforestation experiment in Russian Siberia, investigating the effects of single tree species on soil chemical properties after 30 years of stand development. The primary aim of our work was to discern the effects of the six most commonly dominant tree species in Siberian forests on soil chemical variables, including total carbon and nitrogen, dissolved organic carbon and nitrogen (DOC and DON), acidity, and the major ions in soil solution. Second, we wanted to discern the effect of soil depth on these properties, and the interaction between depth and species. A third goal was to elucidate the effect of grassland conversion to forestry.
properties prior to planting, and subsequently returned to the site prior to experimental planting. In 1971– 1972, 2–3-year-old seedlings of spruce (Picea abies), birch (Betula pendula), Scots pine (Pinus sylvestris), aspen (Populus tremula), larch (Larix sibirica) and Arolla pine (Pinus cembra) were sown into individual plots, each occupying 2400 m2 (Figure 1). An area of 9600 m2 was left for grassland as a control, and the soil under grass was not mechanically homogenized. The region is characterized by continental climatic conditions: average rainfall is 500 mm year−1, average summer temperature is 20 ◦ C, depth to permafrost is 70–170 cm, and soil temperature at 20 cm depth in winter is −4 to −14 ◦ C and 10 to 12 ◦ C in summer. The soil is the gray forest type according to Russian Soil Classification System and Greyzem according to FAO (1990). In August 1999, each plot was sub-divided into three parts: A, B and C. From each sub-plot, two trees were randomly chosen and four soil samples were taken at 50 cm apart of the stem of each tree. In grassland, three sub-plots (each of 2 m2 ) were chosen along the forest plantation; at each subplot six soil samples were taken at each depth. Soil samples were taken at three depth (0–10, 10–20 and 20–30 cm) and soils from one depth and one sub-plot were mixed. Thus, one species resulted in nine soil samples, three sub-plots versus three soil depths. The total number of soil samples was 63: six species plus grassland by three subplots by three depths. Because each species occupies only a single plot, subsamples within these plots are not independent, and the design of this experiment thus suffers from pseudoreplication (sensu Hurlbert, 1984). Nevertheless, because such long-term artificial afforestation experiments are rare, we felt that use of inferential statistics in this experiment would provide useful estimates of the effects of single tree species on soil properties. Study of soil chemical properties
Materials and methods Research sites The research plots are located 50 km Northwest from Krasnoyarsk and were established by the laboratory of soil science of the Institute of Forest, Siberian Branch of the Russian Academy of Sciences. The upper 0– 50 cm of soil of a 1.5-ha area were removed, mechanically homogenized to minimize vertical and spatial heterogeneity of chemical, physical and biological
All samples were analyzed for pH in water solution (1:2.5). The major ions in water solution (1:5) — Na+ , K+ , Ca2+ , Mg2+ , Mn2+ , Fe3+ , and Al3+ — were measured by atomic absorption spectrometry (AAS 4100, Perkin-Elmer), NH4 + , NO3 − , Cl− and SO4 2− by a flow injection analyzer (Lachat), and DOC as CO2 by infrared detection after persulfate oxidation. Total dissolved nitrogen was also determined in the water extract using a Total Nitrogen Analyzer (TN-05, Mitsubishi Kasei Corp.). Dissolved organic nitrogen (DON) was determined as the difference
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Figure 1. Schema of the Siberian artificial afforestation experiment, organized by laboratory of soil science of the Institute of Forest SB RAS in 1971–1972.
between total dissolved N and inorganic N. Total C, N and C/N were determined by Dumas combustion and gas chromatography (Heraeus elemental analyzer). All chemical characteristics (except pH, C and N) were determined in the central analytical laboratory of BITÖK (Bayreuth Institute of Terrestrial Ecosystem Research). Total C, N and pH were analyzed at the Department of Soil Science of the University of Bayreuth. Statistical data analysis All variables were tested for normality of distribution and were log-transformed when necessary. The effects of tree species and soil depth were determined by two-way analysis of variance (ANOVA) with three replicates. First, the main effects of species and soil depth were determined for forest plots only (without grassland, n=54). When significant main effects were detected, post hoc comparisons with the Tukey’s honest significant difference (HSD) test were performed to discern which species and at what depths differences were significant. To determine the effect of grassland conversion to forests, one-way ANOVA was computed with species as a main factor including grassland (n=63) without regard to soil depth. We considered effects significant at P
