Soil Organic Layer Research Articles

Constraining the organic matter decay parameters in the CBM-CFS3 using Canadian National Forest Inventory data and a Bayesian inversion technique

Forests are an important component of the global carbon (C) cycle: they can capture and retain large amounts of C annually, depending on stand characteristics, climate, and disturbance regimes. With climate and disturbance regimes shifting, it is important to be able to accurately represent the corresponding changes in forest C dynamics with well-calibrated models. The Carbon Budget Model of the Canadian Forest Sector (CBM-CFS3) is a widely used model for simulating C dynamics in managed forests at stand, regional, and national levels. Here, we use a Bayesian Markov Chain Monte Carlo (MCMC) technique to calibrate the parameters in the CBM-CFS3 by assimilating C stocks of six deadwood and soil pools estimated from data collected from 635 plots within the Canadian National Forest Inventory. Calibration led to most improvement in the simulation of C stocks in small and fine woody debris, reducing RMSE by 54.3%, followed by the snag stems (RMSE reduced by 23.2%), and coarse woody debris (13%). The calibrated parameters resulted in increased rates of C cycling in fine and coarse woody debris and the soil organic layer, distinct C dynamics in hardwood and softwood dominated stands, and increased temperature sensitivity of the C contained in the mineral soil. While parameter calibration considerably improved the simulation of the small and fine woody debris and snags stem pools, model representation of the branch snag, coarse woody debris, soil organic layer, and mineral soil pools were not substantially improved. Lack of substantial improvements in the calibrated model performance indicated the need for including additional processes in C dynamics simulation or a change in the modelling paradigm. We illustrate the potential need to include a lignin effect on deadwood decay and suggest further exploration of the effects of tree species, soil types, and mosses on performance of the CBM-CFS3.

Alterations to the fuel bed after single and repeated prescribed fires in an Appalachian hardwood forest

To manage upland oak forests across the central and southern Appalachian mountain and plateau regions, prescribed fire is applied more frequently and across larger areas than in the recent past. The often stated objective is to reduce fuels, but there is a paucity of information on the impacts of repeated burning on fuels, including woody materials and the soil organic layer. These are complex components of forest ecosystems with significant impacts on nutrient and carbon cycling, forest successional dynamics, and soil protection from loss via erosion. Thus, understanding fuel bed response to prescribed fire is essential for predicting future forest function. Using study sites distributed across a range of landscape positions in the Daniel Boone National Forest on the Cumberland Plateau of eastern Kentucky, we examined changes to the fuel bed over six years in response to a single fire (burned once in six years), repeated fire (burned four times in six years), and fire-excluded treatments to determine prescribed fire impacts on fuel loads and mineral soil exposure. Prior to burning, fuel loads were generally similar among landscape positions, although the duff layer was lowest on sub-mesic and greatest on sub-xeric positions. A single fire reduced duff depth by 50%, whereas repeated burning led to depth reductions of >60%. Repeated burning also significantly increased mineral soil exposure (25%) compared to single burn and fire-excluded (2–4%) treatments, with the greatest effects on sub-mesic and intermediate landscape positions. Repeated burning significantly reduced fine woody (1-h) fuels, but only after three burns, whereas fine fuel mass on sites burned once was similar to those where fire was excluded. There were no statistically significant effects of burning on large woody fuels (100- and 1000-h fuels). Overall, the primary impact of prescribed fire on the fuel bed was to consume the organic horizon and expose mineral soil, which has the potential to reduce fuel continuity for subsequent burns. Fire behavior in this region is driven primarily by fine fuels (litter and duff) and fuel continuity, both of which recover in relatively short periods of one to several years. Reduction of woody fuels is more intractable under a prescribed fire regime.

Temporal changes in the radiocesium distribution in forests over the five years after the Fukushima Daiichi Nuclear Power Plant accident

To elucidate the temporal changes in the radiocesium distribution in forests contaminated by the Fukushima Daiichi Nuclear Power Plant accident, we monitored the 137Cs concentration and inventory within forests from 2011 to 2015 across nine plots containing variable tree species and different contamination levels. The 137Cs concentrations in needles and branches decreased exponentially at all coniferous plots, with effective ecological half-lives of 0.45–1.55 yr for needles and 0.83–1.69 yr for branches. By contrast, the 137Cs concentration in deciduous konara oak leaves did not change over the five years. The concentration of 137Cs in oak wood increased by 37–75%, whereas that in Japanese red pine decreased by 63% over the five years. In Japanese cedar and hinoki cypress, the 137Cs concentration in wood showed an increasing trend in half of the plots. The changes in 137Cs in the organic and mineral soil layers were not strongly related to the tree species or contamination level. Our multi-site, multi-species monitoring results revealed that the pattern of temporal changes in radiocesium in the 9 forest plots was similar overall; however, changes in 137Cs in needles/leaves and wood differed among tree species.

Retention of dead standing plant biomass (marcescence) increases subsequent litter decomposition in the soil organic layer

We evaluated the impact of retaining dead standing biomass (marcescence) on subsequent litter decomposition in the soil organic layer. Litter of plants that naturally keep dead standing biomass in various extents, Calamagrostis epigeios (keeps most of its dead biomass standing), Quercus robur (keeps some dead leaves on the tree), and Alnus glutinosa (all litter falls to the ground after senescence), were either exposed to environmental climate (ambient) conditions for one year or kept in a dry dark place. After a year, both litter treatments were placed in the soil organic layer for another year. We monitored the mass loss and chemical changes during decomposition. Changes in the chemical composition of aromatic components in C. epigeios litter and decreasing amounts of aromatic compounds in Q. robur and C. epigeios litter during exposure to ambient conditions indicate an effect of photodegradation on these compounds. The litter of Q. robur also exhibited accelerated subsequent litter decomposition in the soil organic layer. In contrast, an increase of aliphatic and aromatic compounds and a decrease of carbohydrates in A. glutinosa litter during exposure to ambient conditions rather points to leaching or microbial decay of labile compounds than an effect of photodegradation. Moreover, the subsequent decomposition of A. glutinosa litter in the soil organic layer was decelerated as compared to the unexposed litter. Our results suggest that litter with comparably low quality (Q. robur and C. epigeios), as compared to litter with a high quality (A. glutinosa), is prone to photodegradation. This process facilitates subsequent decomposition in soil.

Seasonal and Long-Term Changes to Active-Layer Temperatures after Tall Shrubland Expansion and Succession in Arctic Tundra

Vegetation, active-layer soils, and snow cover regulate energy exchange between the atmosphere and permafrost. Therefore, interactions between changes to tundra vegetation and soil thermal regime will fundamentally affect permafrost in a warmer world. We recorded soil temperatures for approximately 1 year in a Siberian Low Arctic landscape with a known history of alder (Alnus) shrub expansion on disturbed microsites in patterned ground. We recorded near-surface soil temperatures and measured physical properties of soils and vegetation on sorted-circle microsites in four stages of shrubland development: (1) tundra lacking tall shrubs; (2) shrub colonization zones; (3) mature shrublands; and (4) paludified, long-established shrublands with thick soil organic layers. Summer soil temperatures declined with increasing shrub cover and soil organic thickness; shrub colonization suppressed cryoturbation, facilitating the development of continuous vegetation and a surface organic mat on circles. Compared to open tundra, mature shrubs cooled soils by up to 9 °C during summer, but warmed soils by greater than 10 °C in winter presumably because they developed highly insulative snowpacks. Paludified shrublands had the coldest summer active layers, but winter soil temperatures were much colder than mature shrublands and were similar to earlier stages. Our results indicate that although tall shrub establishment dramatically warms winter soils within decades, much of this warming is transient at paludification-prone sites because the buildup of wet peat favors cooling in winter and the stature and snow-trapping capacity of shrubs diminish over time. In the ecosystem we studied, shrub expansion has contrasting effects on active-layer temperatures both seasonally and over longer timescales due to successional processes.

Characterizing hydrologic changes of the Great Dismal Swamp using SAR/InSAR

The Great Dismal Swamp (GDS), one of the largest, northernmost peatlands on the Atlantic Coastal Plain, is underlain by a thick water-logged organic soil layer (peat) made up of dead and decaying plant material. The peatland functions as a main sink for a large amount of soil derived organic carbon. The disturbance of this wetland has negatively impacted the ecosystem and contributed to climate change through the release of the stored greenhouse gases. Surface water level and soil moisture conditions are critical information about peatlands, but monitoring these hydrologic changes has been a challenging task. With a lack of in situ soil moisture measurements, we first explored yearlong Soil Moisture Active Passive (SMAP) data to find the close relationship (R-squared value: 0.80) between soil moisture and groundwater table from March 2015 to March 2016. Based on synthetic aperture radar (SAR) backscattering returns and interferometric SAR (InSAR) phase measurements from C-band Radarsat-1 and L-band ALOS PALSAR datasets, we then analyzed the hydrologic changes in the peatlands. We compared averaged C/L-band SAR backscattering intensity (mid 1998–early 2008 for Radarsat-1, late 2006–early 2011 for ALOS PALSAR) with groundwater level changes and found that the SAR backscattering is significantly responsive (R-squared value: 0.76 and 0.67 for Radarsat-1 and ALOS PALSAR, respectively) to soil moisture changes through a three-way correlated relationship of soil moisture, groundwater level, and SAR intensity. Using InSAR coherence observations, we delineated the inundated area (western and northern regions of GDS) during the wet season, subject to double-bounce backscattering. We measured the relative water level changes in the inundated areas through the InSAR phase measurements, and estimated the groundwater level changes corresponding to soil moisture changes using time-series InSAR analysis. Our comprehensive study has demonstrated that time-series SAR backscattering returns and InSAR analysis can be used to gauge soil moisture conditions and to monitor the hydrologic and vegetation changes in the GDS.

The fate of nitrogen inputs in a warmer alpine treeline ecosystem: a 15N labelling study

Summary Global warming may accelerate nitrogen (N) transformations in the soil, with potentially large effects in N‐poor high‐elevation ecosystems. To gain insight into the partitioning of inorganic and organic N inputs within the plant–soil system and how warming influences these patterns, we applied a 15N label (15NH4Cl or 15N‐glycine) shortly after snowmelt during the sixth year of experimental soil warming (+4 °C) at treeline in the Swiss Alps. Seven weeks after labelling, approximately 60% of the applied label remained in the soil organic layer to 10 cm depth, whereas label recovery summed over all measured plant pools was <10% of the added label. Soil warming led to a weaker Δ15N signal in plants and no change in the amount of added label recovered in plants. This 15N dilution resulted from a greater N pool size of some plant species in warmed plots as well as enhanced availability of (unlabelled) N under warming. Temporal dynamics of foliar Δ15N in dominant dwarf shrub species suggested that these plants primarily take up N early in the season. In a subset of plots labelled with 13C‐enriched glycine (U‐13C2‐15N‐glycine), the labelled glycine was mineralized rapidly, with approximately 50% of the applied 13C respired as CO2 during the first 99 h, suggesting that effects of warmer soils on N dynamics in this treeline system are only slightly modulated by the preferences of different plant species for inorganic and organic N forms. Synthesis. Plants growing in warmer soils acquired more unlabelled, soil‐derived N in the sixth year of treatment, implying a sustained increase in N mineralization and availability in alpine treeline ecosystems with higher soil temperatures predicted for the future. Wide variation in the ability of plant species and functional groups to compete for early‐summer N inputs means that there is a feedback between plant community shifts and N dynamics under environmental change at the treeline.

Metalleinträge in terrestrische Ökosysteme: Analyse von Daten aus Modellierung und Biomonitoring

Metal deposition into terrestrial ecosystems: evaluating data from modelling and biomonitoring In Germany, atmospheric deposition of heavy metals derived by modelling and measurements using biological and technical samplers are used to spatially differentiate respective European data. However, a comparative analysis is still missing. Therefore, this article compares results from deposition modelling derived by LOTOS-EUROS and EMEP with data on heavy metals concentrations in leaves, needles and organic surface soil collected by intensive forest monitoring (ICP Forests Level II) and the Environmental Specimen Bank (ESB). The concentrations in leaves and needles collected during the years 2007–2011 for the specimen bank revealed clear correlations with the modelled values. They were specific for the matrices sampled and, in case of Cd concentrations in one year old spruce needles, for ecosystem types. Thereby, the correlations with LOTOS-EUROS were stronger than those with EMEP. Yet, these differences could not be proved to be significant. Most data retrieved from ICP Forests Level II monitoring showed stronger correlations with EMEP. They are lower than those calculated from specimen bank data. The advantage of IPC Forests Level II data is that it yields concentrations for different age groups of needles. Rather high correlations were found especially between LOTOS-EUROS results and Pb concentrations in two year old needles collected from pine and spruce. Additionally to leaves and needles, Forests Level II data were used to analyze heavy metal concentrations in organic soil layers. Significant correlations were computed for Cd between the modelled total deposition and respective concentrations in OH soil layers and for Pb between modelled total deposition and OL and OH soil layers. The different biomonitoring networks should be connected more tightly to enhance the spatial significance of their common data.

Patterns of canopy and surface layer consumption in a boreal forest fire from repeat airborne lidar

Fire in the boreal region is the dominant agent of forest disturbance with direct impacts on ecosystem structure, carbon cycling, and global climate. Global and biome-scale impacts are mediated by burn severity, measured as loss of forest canopy and consumption of the soil organic layer. To date, knowledge of the spatial variability in burn severity has been limited by sparse field sampling and moderate resolution satellite data. Here, we used pre- and post-fire airborne lidar data to directly estimate changes in canopy vertical structure and surface elevation for a 2005 boreal forest fire on Alaska’s Kenai Peninsula. We found that both canopy and surface losses were strongly linked to pre-fire species composition and exhibited important fine-scale spatial variability at sub-30 m resolution. The fractional reduction in canopy volume ranged from 0.61 in lowland black spruce stands to 0.27 in mixed white spruce and broadleaf forest. Residual structure largely reflects standing dead trees, highlighting the influence of pre-fire forest structure on delayed carbon losses from aboveground biomass, post-fire albedo, and variability in understory light environments. Median loss of surface elevation was highest in lowland black spruce stands (0.18 m) but much lower in mixed stands (0.02 m), consistent with differences in pre-fire organic layer accumulation. Spatially continuous depth-of-burn estimates from repeat lidar measurements provide novel information to constrain carbon emissions from the surface organic layer and may inform related research on post-fire successional trajectories. Spectral measures of burn severity from Landsat were correlated with canopy (r = 0.76) and surface (r = −0.71) removal in black spruce stands but captured less of the spatial variability in fire effects for mixed stands (canopy r = 0.56, surface r = −0.26), underscoring the difficulty in capturing fire effects in heterogeneous boreal forest landscapes using proxy measures of burn severity from Landsat.

Tropical Montane Cloud Forests in the Orinoco river basin: The role of soil organic layers in water storage and release

The Tropical Montane Cloud Forest (TMCF) is a hydrologically unique and highly vulnerable ecosystem to changes in land-use and climate. Assessing the impacts of these changes needs to consider soil-water dynamics. In particular, the organic layer and its functioning requires attention because its difference in water retention characteristics and root density compared to the underlying mineral soils. A higher root density and a higher water storage capacity of the organic layer compared to the mineral soils suggests that most nutrient and water uptake occurs in this layer. However, hydraulic properties of mineral soils and their impact on hydrology of TMCFs have been poorly studied. Here we provide organic layer water retention curves for TMCF soils that were measured in the laboratory. With these data we assessed the potential land-use and climate change impacts on TMCF soil moisture dynamics. From the land-use change perspective, we estimated the water storage capacity loss by slash-and-burn deforestation practices. These estimates show that the storage loss ranges from 35 to 59mm when TMCFs are converted to pastures. This is several times higher than the estimated TMCF canopy storage capacity (2 to 5mm). Therefore, the higher peak flow observations in deforested catchments might not only be explained by a decreasing canopy water storage but also likely due to a decreasing soil water storage. From the climate change perspective, we evaluated the effect of contrasting dry season conditions on soil moisture and transpiration using a 1-D water-flow model, and assessed the sensitivity of these hydrological variables to uncertainties in saturated hydraulic conductivity. Although transpiration was not limited by soil moisture during the mild dry season, it was affected during the severe dry season and continued to decline under expected climate change with the prolongation of dry spells. Our results show that the organic layer is a key element in TMCF's hydrological functioning and call for an increased focus on the role of organic soils when evaluating effects of land-use change.

Impacts of twenty years of experimental warming on soil carbon, nitrogen, moisture and soil mites across alpine/subarctic tundra communities

High-altitude and alpine areas are predicted to experience rapid and substantial increases in future temperature, which may have serious impacts on soil carbon, nutrient and soil fauna. Here we report the impact of 20 years of experimental warming on soil properties and soil mites in three contrasting plant communities in alpine/subarctic Sweden. Long-term warming decreased juvenile oribatid mite density, but had no effect on adult oribatids density, total mite density, any major mite group or the most common species. Long-term warming also caused loss of nitrogen, carbon and moisture from the mineral soil layer in mesic meadow, but not in wet meadow or heath or from the organic soil layer. There was a significant site effect on the density of one mite species, Oppiella neerlandica, and all soil parameters. A significant plot-scale impact on mites suggests that small-scale heterogeneity may be important for buffering mites from global warming. The results indicated that juvenile mites may be more vulnerable to global warming than adult stages. Importantly, the results also indicated that global warming may cause carbon and nitrogen losses in alpine and tundra mineral soils and that its effects may differ at local scale.

Effects of simulated warming on soil ammonia-oxidizing bacteria and archaea communities in an alpine forest of western Sichuan, China

Ongoing climate change, characterized by winter warming, snow cover decline and extreme weather events, is changing terrestrial ecosystem processes in high altitude and latitude regions. Winter soil processes could be particularly sensitive to climate change. In fact, winter warming and snow cover decline are interdependent in cold biomes, and have a synergistic effect on soil processes. Soil microorganisms not only play crucial roles in material cycling and energy flow, but also act as sensitive bio-indicators of climate change. However, little information is available on the effect of winter warming on forest soil ammonia-oxidizing bacteria (AOB) and archaea (AOA). The alpine and subalpine forest ecosystems on the eastern Tibet Plateau have important roles in conserving soil, holding water, and maintaining biodiversity. To understand the changes in AOB and AOA communities under climate change scenarios, an altitudinal gradient experiment in combination with soil column transplanting was conducted at the Long-term Research Station of Alpine Forest Ecosystems, which is situated in the Bipeng Valley of Lixian County, Sichuan, China. Thirty intact soil columns under an alpine forest at an altitude of 3582m were transplanted and incubated at 3298m and 3023m forest sites, respectively. Compared with the 3582m, we expected air temperature increases of 2°C and 4°C at the 3298m and 3023m, respectively. However, the temperatures in the soil organic layer (OL) and mineral soil layer (ML) increased by 0.27°C and 0.13°C, respectively, at 3023m and −0.36°C and −0.35°C at 3298m. Based on a previous study and with simultaneous monitoring of soil temperature, the abundances of AOB and AOA communities in both the OL and ML were measured by qPCR in December 2010 (i.e., the onset of the frozen soil period) and March 2011 (i.e., the late frozen soil period). The soil columns incubated at 3023m had relatively higher AOB abundances and lower AOA/AOB ratios than those at 3298m, while higher AOA abundances and AOA/AOB ratios were observed at 3298m. The abundance of the microbial community at the late frozen period was higher than that at the onset of frozen soil, and the changes in microbial community abundance at the late frozen period were more substantial. Furthermore, the nitrate nitrogen (N) concentrations in both the OL and ML were significantly higher than ammonia N concentrations, implying that soil nitrate N is the primary component of the inorganic N pool in the alpine forest ecosystem. Additionally, the responses of AOA and AOB in the soil OL to soil column transplanting were more sensitive than the responses of those in ML. In conclusion, climate warming alters the abundance of the ammonia-oxidizing microbial community in the alpine forest ecosystem, which, in turn, might affect N cycling.

Effect of clear-cutting on soil CO2 emission

An experimental study to estimate the effect of clear-cutting on CO2 emission from the soil surface was performed using the chamber method. For field measurements, several experimental plots within the clear-cut with different degrees of damage of the upper organic soil layer and different amounts of litter and logging residue on the surface were selected. Soil CO2 fluxes were simultaneously measured both on the clear-cutting plots and on two plots within the spruce forest stand located close to the clear-cut area. The results show a significant seasonal and diurnal variability of soil CO2 emission. It was found that the soil respiration rate varies significantly among plots and depends on the damage to the upper soil layer and the availability of litter and logging residue on the soil surface. It was found that the rate of CO2 emission from soil surface is strongly dependent on the air and soil temperature and moisture of the upper soil layer. Different rates of soil respiration are also revealed on the plots located at different distances from tree trunks within the control forest stand.

Monitoring soil carbon pool in the Hyrcanian coastal plain forest of Iran: Artificial neural network application in comparison with developing traditional models

Iran is categorized under Low Forest Cover Countries and the Nour Forest Park is the largest coastal plain forest in the country. As forest soils contain higher carbon than plant biomass and play a key role in the global carbon cycle, this study aimed to assess highly accurately usable models for monitoring soil organic carbon (SOC) based on plant- species diversity in the forest. For measuring plant-species diversity indices and taking soil samples at two depths (0–20 and 20–40cm), a total of 75 plots based on a randomized complete block (RCB) design which included three naturally different stand types were outlined in the forest. Traditional models based on multiple linear regression and curve estimation regression analyses, and artificial neural network (ANN) type of multi-layer perception on the basis of back-propagation training algorithm were used for predicting the SOC. According to the Pearson's correlation, the traditional functions and ANN models including Abundance and evenness (J′) of herbs layer, and dominance (D) of trees layer, Abundance andJ′of herbs layer in turns were developed for predicting the SOC in the soil top and subsoil layer. The findings showed that the power-law models based on validation parameters among the traditional models were the best predictors for SOC in the different soil layers. Designing the topology of each model in the ANN on the basis of training algorithm and testing data set indicated that the best architectures in the optimum models in turns were composed of one hidden layer with 15 neurons including tangent sigmoid function (A3) for predicting the SOC in the soil organic layer, and two hidden layers with 35 neurons in each layer including the same function (A6) for predicting the subsoil (mineral) layer. Also, the optimum models in the ANN including A3 (R2=0.87,RMSE%=8.17) and A6 (R2=0.93,RMSE%=3.73), in comparison with the traditional models, predicted the SOC with a higher accuracy. Since the optimum models in the ANN predicted the response values with the highest accuracy and without major concerns for statistical issues and uncertainty, the ANN technique is suggested for monitoring SOC in the forest.

Analysis of Carbon Dioxide Emission from Lawn Ecosystem with Contrasting Soil Profiles

Land-use change is among the main factors contributing to climate change. Urbanization is a land-use change pathway, conjugate with a rapid growth of urban territory and irreversible change of soil features and functioning. Greenhouse gases’ emissions (primarily CO2 emission) and carbon sequestration are among important soil functions. Ecological risks of increased CO2 emissions in urban soils are determined by different factors of anthropogenic impact. This paper aims to analyze the impact of different soil constructions on CO2 emissions from urban lawns. The research plot is situated in northern Administrative district of Moscow (NAD) and included urban soil constructions with organic layers of different genesis (turf, sand-turf mixtures and soils-sand mixtures) and of different depth (5, 10 and 20 cm). As a result an average CO2 emission from turf (20 cm dept of organic layer) was 22 g/m2 day, whereas the sand-turf mixture (10 cm of the organic layer) emitted 16.15 and peat soil (5 cm of organic layer) - 19.23 g/m2 day respectively. Therefore, was observed dependence of CO2 emissions on genesis and depth of soil organic layers. Also was revealed dependence of CO2 emissions on climate conditions for nine-months of observations.

Radiocaesium partitioning in Japanese cedar forests following the "early" phase of Fukushima fallout redistribution.

Our study focused on radiocaesium (137Cs) partitioning in forests, three vegetation periods after the Fukushima Daiichi nuclear power plant accident. 137Cs distribution in forest components (organic and mineral soil layers as well as tree compartments: stem, bark, needles, branches and roots) was measured for two Japanese cedar stand ages (17 and 33 years old). The results showed that around 85% of the initial deposit was found in the forest floor and topsoil. For the youngest stand almost 70% of the deposit is present in the forest floor, whereas for the oldest stand 50% is present in the 0–3 cm mineral soil layer. For trees, old and perennial organs (including dead and living needles and branches, litter fall and outer bark) directly exposed to the fallout remained the most contaminated. The crown concentrated 61–69% of the total tree contamination. Surprisingly the dead organs concentrated 25 ± 9% (young cedars) to 36 ± 20% (mature cedar) of the trees’ residual activity, highlighting the importance of that specific compartment in the early post-accident phase for Japanese cedar forests. Although the stem (including bark) represents the highest biomass pool, it only concentrates 3.3% and 4.6% of the initial 137Cs deposit for mature and young cedars, respectively.

Biomass and morphology of fine roots in eight Cryptomeria japonica stands in soils with different acid-buffering capacities

Cryptomeria japonica, which is one of the main silvicultural species in Japan, accumulates calcium (Ca) in soils with high acid buffering capacity (ABC) but has depleted Ca in soils with low-ABC over the past two decades. However, the contribution of fine roots in C. japonica to the accumulation or depletion of Ca in soils with different ABCs has not been evaluated. The aim of this study was to clarify the responses of C. japonica fine roots in terms of biomass and morphology in eight plantation stands to soils with two contrasting ABCs, which have different trends of soil acidification. We evaluated the biomass and specific root length (SRL) of fine roots divided into three diameter classes (<0.5, 0.5–1.0, and 1.0–2.0mm), obtained from the organic layer and two mineral soil layers from 0 to 10 and 10 to 20cm depths, in soils with high- and low-ABCs. We also investigated root traits of seedlings grown in soil monoliths in-situ in a greenhouse condition to compare the response of mature trees in stands. The biomass of fine roots (<2.0mm) in mature C. japonica was significantly higher and the SRL was significantly lower in low-ABC soils than in high-ABC soils. In the organic layer, the biomass of very fine roots (<0.5mm) at the organic soil layer in low ABC soils was higher than that in high ABC soils. However, the SRL and the dry weight of the seedlings in the greenhouse condition showed no differences between the soils with two contrasting ABCs. We concluded that fine roots of C. japonica stands could have changed and contributed differently to soils with contrasting ABCs. The conflicting root responses of mature trees in stand and seedlings under controlled conditions suggest that careful caution should be taken to extrapolate in-situ mature trees from the results of seedlings, particularly when evaluating the effects of soil degradation such as soil acidifications on sustainable C. japonica plantation forests.

Aboveground and belowground arthropods experience different relative influences of stochastic versus deterministic community assembly processes following disturbance.

BackgroundUnderstanding patterns of biodiversity is a longstanding challenge in ecology. Similar to other biotic groups, arthropod community structure can be shaped by deterministic and stochastic processes, with limited understanding of what moderates the relative influence of these processes. Disturbances have been noted to alter the relative influence of deterministic and stochastic processes on community assembly in various study systems, implicating ecological disturbances as a potential moderator of these forces.MethodsUsing a disturbance gradient along a 5-year chronosequence of insect-induced tree mortality in a subalpine forest of the southern Rocky Mountains, Colorado, USA, we examined changes in community structure and relative influences of deterministic and stochastic processes in the assembly of aboveground (surface and litter-active species) and belowground (species active in organic and mineral soil layers) arthropod communities. Arthropods were sampled for all years of the chronosequence via pitfall traps (aboveground community) and modified Winkler funnels (belowground community) and sorted to morphospecies. Community structure of both communities were assessed via comparisons of morphospecies abundance, diversity, and composition. Assembly processes were inferred from a mixture of linear models and matrix correlations testing for community associations with environmental properties, and from null-deviation models comparing observed vs. expected levels of species turnover (Beta diversity) among samples.ResultsTree mortality altered community structure in both aboveground and belowground arthropod communities, but null models suggested that aboveground communities experienced greater relative influences of deterministic processes, while the relative influence of stochastic processes increased for belowground communities. Additionally, Mantel tests and linear regression models revealed significant associations between the aboveground arthropod communities and vegetation and soil properties, but no significant association among belowground arthropod communities and environmental factors.DiscussionOur results suggest context-dependent influences of stochastic and deterministic community assembly processes across different fractions of a spatially co-occurring ground-dwelling arthropod community following disturbance. This variation in assembly may be linked to contrasting ecological strategies and dispersal rates within above- and below-ground communities. Our findings add to a growing body of evidence indicating concurrent influences of stochastic and deterministic processes in community assembly, and highlight the need to consider potential variation across different fractions of biotic communities when testing community ecology theory and considering conservation strategies.

Responses of soil microbial community structure and function to simulated warming in alpine forest.

Soil samples were collected from an alpine coniferous forest. Soil cores with soil organic layer above and mineral soil layer below were incubated in plant growth chambers during 10 weeks. Taking the annual average soil temperature in the alpine forest as the control, and other two levels of temperature were increased 2 and 4 ℃, respectively, to investigate the responses of soil microbial community and soil enzyme activity to warming. The results showed that warming significantly reduced PLFAs content of bacteria in soil organic layer and PLFAs content of G- in the mineral soil layer, whereas soil fungi was slightly influenced by warming. Warming caused the G+/G- increasing and changed the microbial community structure, but had no significant effect on soil enzymes activity, i.e., laccase (Lac), β-1,4-glucoside (BG), acid phosphate (AP), β-1,4-N-acetylglucosaminidase (NAG). There were significantly positive correlations between fungi, bacteria, G+ and G-, showing the coordinated growth trend between soil microbial communities. There was significantly negative correlation between BG and bacteria, showing the BG competing for carbon source utilization with soil microbial community. In consequence, the soil microbe types responded differently to warming. Bacteria were more sensitive to temperature than fungi, and fungi had stronger ability to tolerate warming in the alpine forest.

More frequent burning increases vulnerability of Alaskan boreal black spruce forests

Much recent research has investigated the effects of burning on mature black spruce (Picea mariana) forests in interior Alaska, however little research has focused on how frequent reburning affects soil organic layer (SOL) vulnerability in these ecosystems. We compared organic soil layer characteristics in black spruce stands that burned after two fire-free intervals (FFI), including an intermediate-interval (37–52 years) and a more typical long-interval (70–120 years). We found that depth of burn varied significantly between intermediate-interval and long-interval sites, and as there was less material available to burn in intermediate-interval stands, percent depth reduction was greater in these stands (78.9% ± 2.6%) than in long-interval stands (62.9% ± 1.5%). As a result, less residual organic soil carbon remained post-fire in intermediate-interval than long-interval stands. Post-fire organic soil carbon stocks averaged 0.51 ± 0.08 kg C m−2 in the intermediate-interval sites, which is less than estimates of soil carbon stock for long-interval fire events (ranging from 2.07 to 5.74 kg C m−2). In addition to altering soil carbon storage, a depletion of the SOL during more frequent fire events will likely delay the recovery of permafrost and could trigger a change in the possible successional trajectory of a site, from black spruce dominated to deciduous or even shrub dominated ecosystems in the future.