Mineral Soil Layers Research Articles

Forest Continuity as a Key Determinant of Soil Carbon and Nutrient Storage in Beech Forests on Sandy Soils in Northern Germany

Forest (or tree) age has been identified as an important determinant of the carbon (C) storage potential of forest soils. A large part of Central Europe’s current forested area was affected by land use change with long periods of cultivation in past centuries suggesting that the organic C stocks in the soil (SOC) under recent forest may partly be legacies of the past and that stand age effects have to be distinguished from forest continuity effects (that is, the time since re-afforestation). We examined the influence of mean tree age and forest continuity on the SOC pool and the stores of total N and available P, Ca, Mg, and K in the soil (mineral soil and organic layer) across a sample of 14 beech (Fagus sylvatica) forests on sandy soil with variable tree age (23–189 years) and forest continuity (50-year-old afforestation to ancient (‘permanent’) forest, that is, >230 years of proven continuity). Ancient beech forests (>230 years of continuity) stored on average 47 and 44% more organic C and total N in the soil than recent beech afforestation (50–128 years of continuity). Contrary to expectation, we found large and significant C and N pool differences between the forest categories in the mineral soil but not in the organic layer indicating that decade- or century-long cultivation has reduced the subsoil C and nutrient stores while the organic layer element pools have approached a new equilibrium after only 50–128 years. PCA and correlation analyses suggest that forest continuity cannot be ignored when trying to understand the variation in soil C stocks between different stands. Forest clearing, subsequent cultivation, and eventual re-afforestation with beech resulted in similar relative stock reductions of C and N and, thus, no change in soil C/N ratio. We conclude that the continuity of forest cover, which may or may not be related to tree age, is a key determinant of the soil C and nutrient stores of beech forests in the old cultural landscape of Central Europe.

Effects of long-term fertilisation on soil properties in Scots pine and Norway spruce stands

The response of surface soil after 45- to 52-years to repeated nitrogen and phosphorus fertilisation was studied. This study included 30 factorial experiments established in young (5- to 30-year-old) stands using plots of 900 m, on average, and by randomising treatments within each experiment. Total amount of N added varied from 534 to 1908 kg ha and that of P from 69 to 193 kg ha, repeated at every second N fertilisation. Liming was performed twice; in total, 6000 kg ha of dolomite was applied. Nitrogen fertilisation increased the mass of the organic layer and the amount of carbon and consequently the amounts of most of the elements in the organic layer. In both the organic layer and the 0–10 cm layer of mineral soil, nitrogen fertilisation decreased the C/N ratio and tended to lower pH, although only slightly. Phosphorus fertilisation increased the amounts of P and Ca. Liming increased the total amounts of most elements in the organic layer, except for C and N. We were able to derive models to describe how changes in the chemical properties of the surface soil depended on doses of elements and on site and stand properties.2–1–1–1

Assessment of organic matter changes in the soil of the Brdo plot under different climate change scenarios through the Yasso07 model application

The forest soil can act as an important sink for CO2 and in that respect also appears in the national Kyoto reports, where a distinction is made between carbon accumulated in litter and organic soil horizons and carbon accumulated in mineral soil layers. There is a multitude of dynamic models of organic carbon (Corg) change in the soil particularly due to different environmental and anthropogenic factors. The purpose of this paper is the Yasso07 model application on the “Brdo” plot, which is part of the ICP Forest Level II plots of Slovenia. The Yasso07 model describes the decomposition of organic matter in the forest soil by dividing litter inputs into different components with varying decomposition rates. Here, the temporal change of soil Corg in various scenarios of future climate change (increase in air temperature, change in precipitation) was predicted. The difference between the measured amount and the model-predicted amount of Corg in the soil for the current climate on the Brdo plot is 6.4 t C ha-1 (88.6 t C ha-1 measured vs. 95.0 t C ha-1 predicted). Taking into consideration the climate change scenarios for Slovenia, Corg stock is expected to decrease in the future according to Yasso07 projections in all scenarios of climate change. The estimate of 100-year decrease of Corg is the largest for scenario, when large increase of both temperature and precipitation is expected (18.2%) and smallest when small temperature increase and precipitation decrease are predicted (9.3%). Assuming stable litter input, larger influence on Corg decrease was predicted for the temperature change compared to precipitation change. However, many uncertainties are included in model estimates ranging from litter input estimates, climate change uncertainties, climate-litter production feedbacks, starting value estimates, etc. The determination of the uncertainty of model calculations is a requirement for conducting simulations and their interpretation.

Effects of repeated whole-tree harvesting on soil properties and tree growth in a Norway spruce (Picea abies (L.) Karst.) stand

Increased demand for forest-derived biomass has resulted in changes in harvest intensities in Finland. Conventional stem-only harvest (SOH) has to some extent been replaced with whole-tree harvest (WTH). The latter involves a greater removal of nutrients from the forest ecosystem, as all the above ground biomass is exported from the site. This has raised concerns that WTH could result in large changes in the nutrient dynamics of a forest stand and could eventually lower its site productivity.The objective of this study was to assess the effects of repeated SOH and WTH on surface soil properties and stand growth in a fertile Norway spruce (Picea abies (L) Karst.) stand. The studied stand is part of a series of whole-tree thinning experiments established in Southern Finland.Ten years after the final harvest it was evident that repeated WTH had a decreasing effect on total C and N pools in the combined organic+mineral soil layer compared to the SOH treatment. The response of soil chemical properties to the treatments was more apparent in the mineral soil layer than in the organic layer. Treatment did not have a significant effect on pH or on the C/N-ratio of the soil. The results suggest that although the stand possesses significant pools of nutrients at present, WTH, if continued, could have long-term effects on site productivity.Harvesting intensity and fertilization had no effect on Norway spruce volume increment during 20years before clear-felling. Ten years after final felling, no evidence was found that WTH had affected the growth of the new generation of planted Norway spruce seedlings.

Investigating the role of moisture as an environmental constraint in the decomposition of shallow and deep mineral soil organic matter of a temperate coniferous soil

Temperature and moisture are primary environmental drivers of soil organic matter (SOM) decomposition, and an improved understanding of how they interact to control SOM cycling processes in temperate forest soils is needed. Intact soil cores from shallow (0–25 cm) and deep (25–50 cm) mineral soils were incubated under constant and/or diurnal temperature regimes, and subjected to a series of moisture manipulations within a climate-controlled facility. Soil temperature, moisture, and CO2 efflux were monitored daily for all intact cores and monitored continuously on a subset of cores in order to establish predictive relationships between these variables. Moisture constraints upon the decomposition of SOM were observed below 0.20 and above 0.60 water filled pore space (WFPS) for all shallow mineral soils, and below 0.40 WFPS for shallow soils that had been recently rewet. These thresholds were also evidenced in phase lags between respiration and temperature at 5 cm at high moisture contents, suggesting that while biological responses drive soil respiration at low moisture contents, diffusivity limits the response at high soil moisture. While the shallow mineral soil dominated the contribution to CO2 flux and consistently generated short term responses to rewetting events, deep mineral soil layers respired an order of magnitude lower than shallow layers (per gram C) with no short term measured response to rewetting events. The temperature sensitivity, measured using a Q10 function, was close to 2 for all soil cores, regardless of soil depth or (steady state) moisture content. The exclusion of fluxes collected following precipitation events from field-derived estimates of CO2 flux–temperature relationships, improved these relationships. This study provides insights into how we consider the role of moisture in evaluating SOM decomposition-temperature responses for temperate forest soils.

Stability of soil organic carbon in agro and forest ecosystems on Arenosol

The aim of the study was to assess the stability of soil organic carbon (SOC) in Arenosol (AR) under three different land uses: 1) continuous arable land, 2) abandoned for the last 15 years arable land, and 3) 50 years ago afforested with Scots pine (Pinus sylvestris L.) or silver birch (Betula pendula Roth) arable land. In the 0–10, 10–20 and 20– 40 cm mineral soil layers the following was determined: 1) total SOC and humus fractional composition in bulk soil, 2) unprotected SOC (water extractable SOC and soil microbial biomass carbon (C bio )), and 3) in physical fractions unprotected and protected from microbial decomposition SOC. Mean C bio was the lowest in pine plantations, the highest in birch plantations and intermediate in arable or abandoned arable land. The highest concentrations of fulvic and humic acids and unprotected water extractable SOC were found in forest plantations. However, mineral topsoil after the afforestation, especially with birch, contained the highest concentrations of total SOC and the concentrations of SOC protected in soil organic matter (SOM) of silt + clay sized (<53 µm) fraction. Our results confirmed the Kyoto Protocol’s provision that the afforestation of nutrient-poor sandy arable soils with birch could be relevant for soil carbon sequestration.

Long-term effects of stump harvesting on soil properties and tree growth in Scots pine and Norway spruce stands

Effects of stump harvesting on the properties of surface soil and on the density, structure and growth of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) stands were estimated in a field trial in western Finland. The experiment was established in 1977 and measured in 2010. Stems and logging residues were harvested after clear-cutting, and stumps were lifted and removed from half of the experimental area. Sixteen plots were planted with pine seedlings and 16 with spruce. The main effects of stump harvesting were improved survival of planted trees and an increase in natural regeneration. No clearly negative effects were noted in the stand development. Stump harvesting had no or minimal effects on the properties of the organic layer and those of the 0- to 10-cm mineral-soil layer. Soil properties did not differ between tree species. Pine production was higher on plots with stump removal compared to plots without soil treatment.

Plot Level Spatial Variability of Soil Organic Carbon, Nitrogen, and Their Stable Isotopic Compositions in Temperate Managed Forest Soils of Atlantic Canada

Spatial variability of soil organic matter is known to influence ecosystem processes at various scales. The aims of this study were to assess this variability in two paired managed forests differing in age and use the information to propose future sampling plans for these and similar forest soils. The two paired sites (Hattie Lake and Melrose) consisted of adjacent young (10–13 years) and mid-age (45–57 years) black spruce (Picea mariana Mill. BSP)–dominated forest plots. Soil samples were collected from the organic (forest floor (FF)) and mineral soil layers (0- to 15- and 15- to 30-cm depths) at 49 points on a square grid using 62 × 62–m area established at each of the four plots. Soil samples were analyzed for organic C, total N concentrations, and their stable isotopes. We used conventional statistics and geostatistics to evaluate the spatial variability of these soil properties. We also evaluated if mean values varied in relation to stand age. The young plot at Hattie Lake site contained areas of poor drainage compared with the other plots. Only this plot exhibited a very high coefficient of variation (CV, 81–92%) of C and N concentrations and a wider range of δN in the mineral soil layers compared with those of the other plots. Also moderate spatial dependence of C and N concentrations and mass was associated with the poorly drained plot while the other plots showed weak to no spatial dependence for these soil properties. Variability of C and N mass was very high (CV, 82–89%) in the FF, whereas intermediate variability (CV, 19–53%) was shown for mineral soil layers that did not consistently relate to stand age. Mean total soil C mass within the top 30 cm including the FF was significantly higher for the poorly drained plot (7.7 ± 0.9; mean ± 99% confidence interval) than the other plots (pooled mean, 5.3 ± 0.6). More intensive sampling is required for the FF than the mineral soil to estimate mean soil C mass. Although generalizations about spatial autocorrelation of forest soil properties studied could not be made in relation to stand age at the scale of our study, site drainage status was an important factor that needs to be considered in future sampling designs of these and similar managed forests.

Contributions of microbial and physical–chemical processes to phosphorus availability in Podzols and Arenosols under a temperate forest

The objective of the present study was to assess the relative contributions of microbial (mineralization of non-microbial organic phosphorus and microbial phosphorus) and physical–chemical (diffusion of phosphate ions at the solid-to-solution interface) processes involved in replenishing the soil solution with phosphate ions. This assessment was carried out across soil depths and subsystems in a forest ecosystem. Major differences in the contribution of microbial processes (CMP%) were found between soil layers and subsystems, corresponding with differences in soil organic matter and Al and Fe oxide contents. CMP% significantly decreased with increasing soil depth (from 87–100% in the forest floor to 2–16% in the 90–120cm mineral soil layer). Tree fine roots were mostly concentrated in the top soil layers where microbial processes dominated. Consequently, estimates of CMP% in the entire soil profile were also affected by the vertical distribution of tree fine roots. We assumed that including fine root densities leads to a more correct estimation of the role of microbial processes (CMP%=31–52% in the entire soil profile, up to 75% in one particular site). To our knowledge, this is the first assessment of the relative contributions of the different processes involved in replenishing the soil solution with phosphate ions based on soil properties and fine root distribution.

Tree species is the major factor explaining C:N ratios in European forest soils

The C:N ratio is considered as an indicator of nitrate leaching in response to high atmospheric nitrogen (N) deposition. However, the C:N ratio is influenced by a multitude of other site-related factors. This study aimed to unravel the factors determining C:N ratios of forest floor, mineral soil and peat top soils in more than 4000 plots of the ICP Forests large-scale monitoring network. The first objective was to quantify forest floor, mineral and peat soil C:N ratios across European forests. Secondly we determined the main factors explaining this C:N ratio using a boosted regression tree analysis (BRT), including fifteen site and environmental variables.Ninety-five percent of the C:N ratios were between 16 and 44 in the forest floor, between 13 and 44 in the peat topsoil and between 10 and 32 in the mineral topsoil. Within the aerated forest floor and the mineral soil, the C:N ratios decreased with depth, while in the hydromorphic forest floor and the peats no clear trend with depth was observed.Tree species was clearly the most important explanatory variable for the C:N ratio in both forest floors and topsoils, while it was soil type in the deeper mineral soil layers. The lowest C:N ratios both in the forest floor and the top mineral soil were found in black locust (Robinia pseudoacacia L.) and black alder (Alnus glutinosa L.) stands, both N fixing tree species. While in the forest floor the highest C:N ratios were found in evergreen species like pine, cork oak (Quercus suber L.) and eucalyptus, the pine species and Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) showed the highest C:N ratios in the mineral soil. The second most important explanatory variable in the forest floor and mineral topsoil was the biogeographical zoning (ecoregion). In the peat topsoil and in the deeper mineral soil layers it was the humus type. Deposition and climatic variables were of minor importance at the European scale.Further analysis for eight main forest tree species individually, showed that the influence of environmental variables on C:N ratios was tree species dependent. For Aleppo pine (Pinus halepensis Miller) and holm oak (Quercus ilex L.), both with a typical Mediterranean distribution, the relationship between N and S deposition and C:N ratio appeared to be positive. This study suggests that applying C:N ratios as a general indicator of the N status in forests at the European level, without explicitly accounting for tree species, is too simplistic and may result in misleading conclusions.

Above- and below-ground N stocks in coniferous boreal forests in Finland: Implications for sustainability of more intensive biomass utilization

Nitrogen (N) is typically the growth-limiting factor in boreal forest ecosystems. Therefore, knowledge on forest N stocks and fluxes is crucial in order to predict and evaluate the effects of different anthropogenic factors (e.g. climate change, air pollutant deposition, forest management practices) on the condition, development and sustainability of boreal forests. In this study, we evaluated the amount and distribution of N and biomass in different compartments of forest ecosystem, including not only tree stand and soil, but also such rarely reported N stocks as litter layer, ground vegetation and fine and small roots. We also calculated the theoretical export of N in three forest harvest regimes of different intensity (stem-only harvest, whole-tree harvest, whole-tree harvest and stump uplifting) and assessed the time required for N deposition to compensate the N losses occurring in them. The study included seven Scots pine and eight Norway spruce dominated stands belonging to the UN-ECE ICP Forests Level II programme in Finland. The average effective temperature sum and stand age of the sites ranged 658–1351 d.d. and 55–200 yrs, respectively. Among the study sites, the total biomass (needles, living and dead branches, stems, bark, stumps, coarse roots, fine and small roots, understory, litter, humus and mineral soil layers) ranged from 178Mg ha−1 to 541Mg ha−1, the respective range for N stock being 1890–7530kg ha−1. The two largest pools of N in forest ecosystem were mineral soil (depth 0–40cm; mean=70%) and humus layer (mean=16%). The largest living biomass N stock was in stems in pine stands (88kg ha−1) and in needles in spruce stands (134kg ha−1). Nstored in tree biomass accounted for 7–19% of the total ecosystem N stock. The proportion of N stored in potential logging residues or biofuel (needles, living and dead branches, stumps and coarse roots) was 67±4% and 53±5% of the tree N stock in northern spruce stands and in southern pine stands, respectively. The understory vegetation N stock was the largest in northern spruce stands, and the lowest in southern spruce stands. Our results supported the hypothesis that in boreal coniferous forests, inputs of N by deposition accumulating during the following rotation period will be able to replenish the export of N caused by conventional stem-only-harvest in final cutting, but the sustainability of the site productivity will be challenged when more intense whole tree harvest regimes are practiced, especially in Norway spruce stands.

Carbon cycling and sequestration in a Japanese red pine (Pinus densiflora) forest on lava flow of Mt. Fuji

AbstractBiometric‐based carbon flux measurements were conducted in a pine forest on lava flow of Mt. Fuji, Japan, in order to estimate carbon cycling and sequestration. The forest consists mainly of Japanese red pine (Pinus densiflora) in a canopy layer and Japanese holly (Ilex pedunculosa) in a subtree layer. The lava remains exposed on the ground surface, and the soil on the lava flow is still immature with no mineral soil layer. The results showed that the net primary production (NPP) of the forest was 7.3 ± 0.7 t C ha−1 year−1, of which 1.4 ± 0.4 t C ha−1 year−1 was partitioned to biomass increment, 3.2 ± 0.5 t C ha−1 year−1 to above‐ground fine litter production, 1.9 t C ha−1 year−1 to fine root production, and 0.8 ± 0.2 t C ha−1 year−1 to coarse woody debris. The total amount of annual soil surface CO2 efflux was estimated as 6.1 ± 2.9 t C ha−1 year−1, using a closed chamber method. The estimated decomposition rate of soil organic matter, which subtracted annual root respiration from soil respiration, was 4.2 ± 3.1 t C ha−1 year−1. Biometric‐based net ecosystem production (NEP) in the pine forest was estimated at 2.9 ± 3.2 t C ha−1 year−1, with high uncertainty due mainly to the model estimation error of annual soil respiration and root respiration. The sequestered carbon being allocated in roughly equal amounts to living biomass (1.4 t C ha−1 year−1) and the non‐living C pool (1.5 t C ha−1 year−1). Our estimate of biometric‐based NEP was 25 % lower than the eddy covariance‐based NEP in this pine forest, due partly to the underestimation of NPP and difficulty of estimation of soil and root respiration in the pine forest on lava flows that have large heterogeneity of soil depth. However, our results indicate that the mature pine forest acted as a significant carbon sink even when established on lava flow with low nutrient content in immature soils, and that sequestration strength, both in biomass and in soil organic matter, is large.

Soil C and N sequestration in organic and mineral layers of two coeval forest stands implanted on pyroclastic material (Mount Vesuvius, South Italy)

Tree species influence organic matter sequestration in forest soil. We explored the pattern of soil organic carbon (SOC) and soil organic nitrogen (SON) sequestration in two 40-year-old, adjacent forest stands, one with Black pine (Pinus nigra Arn.) and one with Black locust (Robinia pseudoacacia L.). We compared the patterns of annual carbon (C) and nitrogen (N) sequestration in the organic and mineral soil layers of the two forests with literature data for <100years old deciduous and coniferous forests from different climatic zones.Carbon and N inputs, with aboveground litter fall, were significantly higher in the Black pine than in the Black locust stand. In the soil profile of the Black pine stand, the amount of SOC was significantly higher and that of SON significantly lower than in the Black locust stand. The average annual sequestration rates were 41.3 and 75.0gCm−2, and 2.9 and 2.6gNm−2, respectively, in the Black locust and the Black pine stands. In both forests most of SOC and SON were stored in the organic layers (OL and OF+OH). In the mineral soil layers the amount of SOC was similar for the two stands whereas the amount of SON was significantly higher in the Black locust stand (23.7 vs 14.6gNm−2). In all soil layers, the concentrations of water soluble organic matter (WSOM) were higher in the Black locust stand compared to that with Black pine. Manganese accumulated in the OF+OH layer of the Black pine stand.The results suggest different sequestration patterns, with higher SOC sequestration rates in the Black pine stand and higher SON sequestration rates in the Black locust stand. Comparison with literature data suggests this to be a generality in C and N sequestration patterns for coniferous and deciduous forests.

New decomposition rate functions based on volumetric soil water content for the ROMUL soil organic matter dynamics model

The ROMUL decomposition model describes the flux of soil organic matter through the soil decomposition process separately for the organic layer (forest floor) and mineral soil. In the original ROMUL the effect of soil moisture on soil organic matter decomposition was described by using gravimetric soil water content, a parameter that is often difficult to obtain when the model is applied using continuous weather data. The new decomposition rate functions based on a soil respiration model use volumetric soil water content, replacing the original moisture functions with new ones. This paper also describes the development of a simple volumetric soil water model, with separate water storage compartments for the organic and mineral soil layers to better correspond with the structure of the ROMUL model. A volumetric soil model is also easier to adapt to various locations than the gravimetric soil water model.The new decomposition rate functions employing the new soil water model were tested by re-simulating a previous application of the ROMUL model to a forest site representing conditions in Southern Finland. Whereas the original ROMUL model underestimated the steady-state soil carbon stock of the site, the new model structure considerably reduced the decomposition rates, and the revised soil carbon storage estimates are now in good agreement with the measured data.

Nitrogen availability in the taiga forest ecosystem of northeastern Siberia

The inorganic nitrogen (N) cycle and its dynamics in the soil were observed in the ecosystem at the Spasskaya Pad experimental forest near Yakutsk in northeastern Siberia in order to estimate the N availability for the larch (Larix cajanderi Mayr.) The soil pool of bulk N in the forest accounted for up to 866 g N m−2 (0–50 cm), whereas up to 1.7% (14.6 g N m−2) was potassium chloride (KCl)-extractable inorganic N. Ammonium was a dominant form of inorganic N. The size of the soil inorganic N pool fluctuated seasonally. It was small in the beginning of the summer and increased rapidly once the cumulative degree day of the soil temperature at 20 cm reached more than 300 (°C days), indicating that active N mineralization began at some point from the middle of July to the beginning of August. This soil pool of inorganic N that had accumulated at the end of the previous summer was consumed by the beginning of the next summer through microbial immobilization, which may have begun in September. Recycling of N in the soil was important because the input of inorganic N by deposition was very small (48 mg N m−2 year−1). A tracer 15N experiment showed that larch did not uptake organic N in the form of amino acid (alanine); rather, it used ammonium and nitrate as N sources. The amount of available N for plants was assessed as water-extractable inorganic N in the soil solution that was transported to the rooting area by mass flow driven by plant transpiration, and it accounted for 1.9 × 103 (1.2 × 103 for trees) mg N m−2 during the growing season−1 (0–50 cm of the mineral soil layer in June, July, and August). Microorganisms in the soil are also expected to be competing for this available N. Our results show that despite a large amount of inorganic N production, N availability for plants is low as the soil pool of inorganic N is built up at the same rate as larch senescence.

Buried soil organic inclusions in non‐sorted circles fields in northern Sweden: Age and Paleoclimatic context

AbstractAlthough burial of surface organic soil horizons into deeper mineral soil layers helps drive the long‐term buildup of carbon in arctic soils, when and why buried horizons formed as result of cryoturbation in northern Sweden remain unclear. In this study, we used 14C and 210Pb dating to assess when organic matter was buried within non‐sorted circles fields near Abisko in northern Sweden. In addition, we used aerial photos from 1959 and 2008 to detect eventual trends in cryogenic activities during this period. We found that organic matter from former organic horizons (stratigraphically intact or partly fragmented) corresponds to three major periods: 0–100 A.D., 900–1250 A.D., and 1650–1950 A.D. The latter two periods were indicated by several dated samples, while the extent of the oldest period is more uncertainty (indicated by only one sample). The aerial photos suggest a net overgrowth by shrub vegetation of previously exposed mineral soil surfaces since 1959. This overgrowth trend was seen in most of the studied fields (92 out of 137 analyzed fields), indicating that the cryogenic activity has mainly decreased in studied non‐sorted circles fields since the 1950s. This latter interpretation is also supported by the absence of buried organic layers formed during the last decades. We suggest that the organic matter was buried during the transition from longer cold periods to warmer conditions. We believe these climatic shifts could have triggered regional scale burial of soil organic matter and thus affected how these soils sequestered carbon.

Seasonal dynamics of soil fauna in the subalpine and alpine forests of west Sichuan at different altitudes

The climate (especially temperature) often plays an important role in the structure, function as well as composition of soil organisms in different latitudes and altitudes. As one of the essential components of soil ecosystem, soil faunal community not only lays their roles as soil engineer in material cycling and energy flow, but also acts as the sensitive bio-indicator to environmental change. However, little information has been available on the responses of soil faunal community to the changed environment at different altitudes and seasons. In order to understand the seasonal dynamics of soil faunal diversity under different forests with varying altitudes, three fir (Abies faxoniana) forests were selected covering a 600m vertical transition zone. The primary fir forest at 3600m (A1) of altitude, mixed fir and birch forest at 3300m (A2) of altitude, and secondary fir forest at 3000m (A3) of altitude are representative forests in the subalpine and alpine region of west Sichuan. A 2years study was conducted in the three subalpine and alpine forests from May in 2009 until October in 2010. Soil samples were collected in both the soil organic layer and mineral soil layer. Soil macro-fauna were picked up by hand in the fields. Meso/micro-fauna and damp living fauna were separated and collected from the soil samples by Baermann and Tullgren methods in laboratory, respectively. A total of 74,827 individuals were collected in the 2years, belonging to seven phyla, 16 classes, 31 orders and 125 families by preliminary identification. Similar dominant groups were detected in different forests at different altitudes, consisting of Spirostreptida, Formicidae, Staphylinidae, Hesperinidae, Onychiuridae, Isotomidae, Oribatuloidae, Alicoragiidae, Secernentea, and Adenophorea. In contrast, the ordinary species of macro-fauna and the ratios of Acarina to Collembolan were obviously different. For instance, the ordinary species were dominated by Cydmaenidae and Mycetophilidae at the A1, Scaphidiidae and Helicinidae at the A2, and Lumbricida and Agelenidae at the A3, respectively. Both the individual density and the number of soil faunal groups were significantly higher in soil organic layer than those in mineral soil layer. The density and group of macro-, meso- and micro-fauna in different forests showed the order as A2>A1>A3, but the density of damp living fauna showed the order as A1>A2>A3. The functional groups of macro-fauna were mainly dominated by saprozoic. The highest density and group of macro-fauna was observed in August, while the highest value of meso/micro-fauna was detected in October. In addition, the Jacard similarity indices showed that the composition and structure of soil fauna were similar in the different forests varied with altitudes, but the Shannon–Wiener indices were significantly different. The highest values of Shannon–Wiener indices were observed in October at both the A1 and A3, and in August at the A2. The results suggested that soil faunal community kept a high diversity in the subalpine and alpine forests of west Sichuan, and their structures were significantly affected by the variation of altitudes, which provided important scientific evidences for understanding the ecological processes in the subalpine and alpine coniferous forests.

Dynamics of soil and root C stocks following afforestation of croplands with poplars in a semi-arid region in northeast China

Background and aims Afforestation on croplands can help sequester atmospheric CO2 through increased carbon (C) storage in the soil and vegetation. However, the dynamics of soil organic C (SOC) and rootC stocks, particularlythose inthedeepersoillayers, following afforestation are not well documented for semi-arid regions. The aim of this study was to investigate the dynamics of soil and root C stocks to 1 m depth following afforestation with poplar (Populus×xiaozhuanica W. Y. Hsu & Liang) on croplands at the Keerqin Sandy Lands in northeast China. Methods Forest floor, root and mineral soil samples were collected from 23 paired plots of poplar plantations with different stand basal areas (SBA, ranging from 0.2 m 2 ha �1 to 32.6 m 2 ha �1 ) and reference croplands using a paired-site design. Changes of SOC concentration and content, and root C content were analyzed using paired t tests, and the relationships between forest floor C content, soil and root ΔC (ΔC refers to the difference in C stocks between a poplar plantation and the paired cropland) and SBA were tested with a polynomial regression analysis. Results Afforestation resulted in linear increases of ΔC in the forest floor and 0–10 cm mineral soil with SBA (R 2 =0.67, p<0.001 and R 2 =0.34, p=0.003, respectively), but there were no clear relationships between SOC stocks in the soil deeper than 10 cm and SBA. The fine root C stock increased by afforestation across all the soil layers (p<0.05), and root ΔC had a quadratic curve (the first two mineral soil layers) or linear (the other mineral soil layers) relationship with SBA. About 73 % of the variance of ΔC in the top soil was explained by changes in the forest floor C stock, but changes in plant derived C stocks did not explain the variance of soil ΔC in the deeper layers very well. Conclusions Our study suggest that afforestation increased C sequestration in the forest floor and surface mineral soil, and C stocks in the forest floor and surface mineral soil and roots were strongly controlled by the SBA, which changes with stand development, in the studied semiarid region in northeast China.

Impact of land-use management on nitrogen transformation in a mountain forest ecosystem in the north of Iran

Soil inorganic N is one of the most important soil quality indexes, which may be influenced by land-use change. The historical conversion of land-use from native vegetation to agriculture resulted in sharp declines in soil N dynamics. This study was conducted to determine the soil inorganic N concentrations and net N mineralization rate in four common types of land-uses in the mountain forest area in the north of Iran, namely arable land, pine plantation, ash plantation, and beech stand. The soil samples were taken from top mineral soil layer (5 cm) in each site randomly (n=6) during August- September 2010. Beech stand and ash plantation showed significantly higher total nitrogen compared with arable land and pine plantation, while extractable NH4+-N concentration was significantly greater in Beech stand compare to arable soils (p<0.05). No significantly difference was found in Net N mineralization, net nitrification and net ammonification rates among different land-uses. Results showed that net N mineralization and ammonification were occurred just in the soil of Ash plantation during the incubation time. Our findings suggested that conversion of Hyrcanian forests areas to pine plantation and agricultural land can disrupt soil natural activities and affect extremely soil quality.

Factors affecting vertical distribution of Fukushima accident-derived radiocesium in soil under different land-use conditions

The Fukushima Dai-ichi nuclear power plant accident in Japan, triggered by a big earthquake and the resulting tsunami on 11 March 2011, caused a substantial release of radiocesium (137Cs and 134Cs) and a subsequent contamination of soils in a range of terrestrial ecosystems. Identifying factors and processes affecting radiocesium retention in these soils is essential to predict how the deposited radiocesium will migrate through the soil profile and to other biological components. We investigated vertical distributions of radiocesium and physicochemical properties in soils (to 20cm depth) at 15 locations under different land-use types (croplands, grasslands, and forests) within a 2km×2km mesh area in Fukushima city. The total 137Cs inventory deposited onto and into soil was similar (58.4±9.6kBqm−2) between the three different land-use types. However, aboveground litter layer at the forest sites and herbaceous vegetation at the non-forested sites contributed differently to the total 137Cs inventory. At the forest sites, 50–91% of the total inventory was observed in the litter layer. The aboveground vegetation contribution was in contrast smaller (<35%) at the other sites. Another remarkable difference was found in vertical distribution of 137Cs in mineral soil layers; 137Cs penetrated deeper in the forest soil profiles than in the non-forested soil profiles. We quantified 137Cs retention at surface soil layers, and showed that higher 137Cs retention can be explained in part by larger amounts of silt- and clay-sized particles in the layers. More importantly, the 137Cs retention highly and negatively correlated with soil organic carbon content divided by clay content across all land-use types. The results suggest that organic matter inhibits strong adsorption of 137Cs on clay minerals in surface soil layers, and as a result affects the vertical distribution and thus the mobility of 137Cs in soil, particularly in the forest ecosystems.