Deeper Soil Horizons Research Articles

Clay mineral evolution and formation of intermediate phases during pedogenesis on picrite basalt bedrock under temperate conditions (Yunnan, southwestern China)

In order to better understanding clay mineral evolution coupled with geochemical changes during weathering of igneous rocks under temperate conditions, the picrite basalt-derived soil in Dali (South China) was investigated using X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscope (SEM), and high-resolution transmission electron microscopy (HRTEM) methods. Our results show that smectite and mixed-layer clays occur throughout the weathered soil profile, while discrete kaolinite and illite phases are absent in the soil. From saprolite to topsoil, smectite decreases sharply, while mixed-layer kaolinite/smectite (K/S) and illite/smectite (I/S) clays increase markedly. Clay minerals in the saprolite consist of both dioctahedral and trioctahedral species, while those of the middle to upper profile display a uniform dioctahedral structure. I/S phases are characterized by interstratification of 12-Å smectite and 10-Å illite layers, and K/S phases by interstratification of 12-Å smectite and 7-Å kaolinite layers, with I/S/K clays containing all three layer types. Kaolinization of smectite occurs at the initial stage of weathering, earlier than that of smectite illitization. Desilication and K-fixation of smectite take place simultaneously during advanced weathering, resulting in formation of illitic and kaolinitic phases continuously throughout the developmental history of the soil. Notably high K concentrations in the weathering profile may be related to K-fixing in the interlayer of illite due to smectite illitization in response to more advanced weathering and pedogenic processes, while the increasing K content in the topsoil may be ascribed to fertilizer in land use and uptake of K by plants from deeper soil horizons. Fe2O3 and TiO2 accumulation in the topsoil is probably mediated by microorganisms.

Characteristics and controls of inorganic and organic phosphorus transformation during long-term paddy soil evolution

Information on phosphorus (P) transformation during long-term paddy soil evolution is important for maintaining rice yield and nutrient management. This study was aimed to reveal the characteristics and controls of inorganic and organic P transformation during paddy soil evolution over a millennial time scale using both sequential chemical extraction and solution 31P nuclear magnetic resonance spectroscopy. Results show that the rate and trajectory of P evolution in the topsoil differ markedly from that of the illuvial horizon. The amount of apatite P, non-occluded P, occluded P and total P in the topsoils increased rapidly during the early stage of paddy soil evolution (< 50 yrs) due to anthropogenic P additions, but declined in the older paddy soils due to the leaching loss of P sorbents (CaCO3 and Fe/Al oxides); thus, the added P cannot be efficiently retained by the older paddy soils. Total organic P including phosphate monoester in the topsoils reached maximum in the 300-yr paddy soil and declined thereafter. However, the phosphate diester pool (including DNA) and its proportion in the topsoil increased continuously across the paddy soil chronosequence, suggesting that long-term paddy cultivation promoted labile organic P accumulation. In the deeper soil horizons with less human impacts, the temporal trends in inorganic and organic P across the paddy soil chronosequence can be fully predicted by previous established P transformation models during natural pedogenesis, although the rates of P changes differ among different sites. Our study demonstrates that long-term paddy cultivation alters the rate and trajectory of inorganic and organic P transformation in the topsoils over a millennial time scale, and highlights the importance of labile organic P activation for nutrient supply in the older paddy soils.

Glyphosate and aminomethyphosphonic (AMPA) contents in Brazilian field crops soils

Because of a lack of direct measurements, the presence and persistence of glyphosate and its main metabolite aminomethylphosphonic acid (AMPA) in agricultural soils of Brazil remains unknown. This paper aims at reporting glyphosate and AMPA contents in Brazilian field crop soils at the country scale from southern states to eastern Amazon. Brazilian field crop farmers are among the highest users of glyphosate-based herbicides (GBH) in the world. Soybean and corn field crop soils from 17 sites were collected at two depths (i.e. 0-20 cm and 20-40 cm) in 2016 and 2018. The study area encompasses three regions of Brazil: southern Brazil, central-west Brazil and eastern Amazon, all having in common intensive, conventional, large-scale grain farming. ßGlyphosate and AMPA contents were measured using a GC-ECD following soil extraction. Both chemicals were ubiquitously detected in soils cultivated under various agricultural practices ranging from ploughing to no-till ones. Average measured glyphosate and AMPA contents were 0.08 ± 0.09 µg/g and 0.17 ± 0.16 µg/g respectively with maximum values of 0.57 µg/g and 0.98 µg/g. Glyphosate plus AMPA contents in the top 40 cm of soils presented cumulated amounts exceeding the annual glyphosate inputs via GBH. This is interpreted as a multiannual persistence of these chemicals in Brazilian agricultural soils. Downward migration of glyphosate and AMPA is also suspected with regard to the vertical distribution of these chemicals along with deeper soil horizons. This study highlights the backlash of conservation agriculture as far as glyphosate and AMPA presence in agricultural soils are concerned. These compounds persistence in Brazilian soils appear to be longer than what is usually reported in the literature, especially so for tropical environments. The worldwide concern about the ubiquitous presence of glyphosate and AMPA in the environment needs a broader screening in Brazilian field crop soils since the majority of the available data comes from Argentina, Europe and to a lesser extent North America.

Carbon Stock Assessment in Gypsum-Bearing Soils: The Role of Subsurface Soil Horizons

With the aim of contributing to the knowledge of soil organic carbon stocks in dry areas, this work is based on a quantification of SOC stocks in gypsum-bearing soils whose vertical and spatial heterogeneity greatly limits inferring the total SOC stocks solely from soil surface information. Public databases of soil profiles were key to this quantification, through which it was estimated which amounts of organic carbon can potentially be excluded from calculations associated with soil C cycle models in the absence of information regarding deep soil horizons. These databases include two key factors in the quantification of SOC stocks, which are often excluded: the volume of coarse fragments and the thickness of all sampled soil horizons where SOC concentration was determined. The observed average value of SOC stocks in the studied subsurface horizons reaches 73% of the whole soil. Climate, relief, and land use influence the quantity and heterogeneity of SOC stocks in these soils. Information based on the mere surface of the soil is not relevant to quantify the total SOC; however, the calculation of stocks through soil pits of medium depth (30 cm) has proven to be potentially useful as a complementary approach to these stocks.

Environmental selection dominates over dispersal limitation in shaping bacterial biogeographical patterns across different soil horizons of the Qinghai-Tibet Plateau

Soil microbial biogeographical patterns have been widely explored from horizontal to vertical scales. However, studies of microbial vertical distributions were still limited (e.g., how soil genetic horizons influence microbial distributions). To shed light on this question, we investigated soil bacterial communities across three soil horizons (topsoil: horizon A; midsoil: horizon B; subsoil: horizon C) of 60 soil profiles along a 3500 km transect in the Qinghai-Tibet Plateau. We found that bacterial diversity was highest in the topsoil and lowest in the subsoil, and community composition significantly differed across soil horizons. The network complexity decreased from topsoil to subsoil. There were significant geographical/environmental distance-decay relationships (DDR) in three soil horizons, with a lower slope from topsoil to subsoil due to the decreased environmental heterogeneity. Variation partitioning analysis (VPA) showed that bacterial community variations were explained more by environmental than spatial factors. Although environmental selection processes played a dominant role, null model analysis revealed that deterministic processes (mainly variable selection) decreased with deeper soil horizons, while stochastic processes (mainly dispersal limitation) increased from topsoil to subsoil. These results suggested that microbial biogeographical patterns and community assembly processes were soil horizon dependent. Our study provides new insights into the microbial vertical distributions in large-scale alpine regions and highlights the vital role of soil genetic horizons in affecting microbial community assembly, which has implications for understanding the pedogenetic process and microbial responses to extreme environment under climate change.

Biochar-induced changes in the soil diazotroph community abundance and structure in a peanut field trial

Biological nitrogen fixation (BNF) can help replenish available nitrogen (N) in cropland and reduce the use of chemical N fertilizers, with diazotrophs playing an important role. However, the response of diazotroph community and BNF activity in biochar amendment soil, especially in the deep soil horizon, are poorly understood. In this study, soil samples were collected from topsoil (0–20 cm) and subsoil (20–40 cm) in the field experiment (established in 2013) comprising treatments with no chemical fertilizer (CK), chemical fertilizer (NPK), biochar (BC), and biochar plus chemical fertilizers (BNPK). Here, we investigated the diazotroph community using real-time PCR and high-throughput sequencing of the nifH gene, and assessed the soil N2 fixation rate (RNfix) using acetylene reduction assay (ARA). Results showed that in the topsoil, the treatments with biochar significantly increased nifH gene copies and RNfix, which was consistent with the increased soil organic matter (SOM), total carbon-to-nitrogen ratio (C/N), dissolved organic carbon (DOC) and pH. In the subsoil, applying chemical fertilizers (NPK) strongly decreased RNfix, but had no effect on diazotroph abundance; in contrast, biochar application (BC) had no effect on RNfix, but suppressed the growth of bacteria and diazotrophs while increasing the abundance of Rhizobiales order. Diazotroph and bacterial gene copies were significantly and positively correlated in both top- and sub-soil, and they were mainly influenced by SOM and total nitrogen (TN). In addition, soil nitrate nitrogen (NO3−–N) was the major factor in shaping the vertical stratification of diazotroph community structure. Although nifH gene abundance was significantly correlated with RNfix in the topsoil, the structure equation modeling (SEM) showed the highest correlation between diazotroph community structure and RNfix. Hence, we suggested that soil carbon and nitrogen sources were the key factors correlated with changes in the vertical pattern of diazotroph abundance. Biochar induced the dominant diazotroph community succession and increased soil carbon content and pH, which contributed to the BNF activity. Changes in the BNF activity were driven by the variation in diazotroph community structure.

Ecological Stoichiometry in Pinus massoniana L. Plantation: Increasing Nutrient Limitation in a 48-Year Chronosequence

Stoichiometric ratios of carbon (C), nitrogen (N), and phosphorus (P) are considered indicators of nutrient status and ultimate ecosystem health. A detailed investigation of these elements in the leaves, branches, forest layer vegetation and soil, depending on stand age, was carried out. We investigated the effects of stand age (9-, 18-, 28-, and 48-year) on the aboveground plant parts (leaf, branch, herb, shrub, plant litter) and belowground pools (soil, roots) of P. massoniana plantations. The CNP stoichiometry of trees was affected by stand age. Mean N content in the aboveground parts in the nine-yr stand was greater than the other stands (18-, 28-, 48-yr), which decreased with increasing stand age. As stands aged, the nutrient demands of the plantations increased as well as their N:P ratios in soil. C content in the soil ranged from 30 to 105, the total N was 0.06 to 1.6, and the total P content ranged from 3.3–6.4 g kg−1. Soil C, N and P contents were greatly influenced by both stand age and soil depth, because surface soil sequester C and N more actively compared to deeper horizons, and more nutrients are released to the topsoil by the plant litter layer. Similarly, the ratios of other layers had a similar pattern as CNP because more nutrients were taken up by the plantations, decreasing nutrient supply in the deeper soil horizons. The green leaves N:P ratios (16) indicate limited growth of P. massoniana, as the range for global nutrient limitation for woody plants oscillated between 14–16, indicating N and P limitation. Young stands were observed to have greater P content and P resorption efficiency (56.9%–67.3%), with lower C:P and N:P ratios (704.4; 14.8). We conclude that with stand development, the nutrient demands of the plantations also increase, and soil N:P stoichiometry shows that these improve soil quality.

Soil health, soil genetic horizons and biodiversity#

AbstractMaintaining or recovering soil health is becoming a goal of many policies carried out at national, continental and global scales to promote global health. This viewpoint is aimed at stressing the relevance of a holistic approach to soil health assessment and monitoring, which is not only related to soil functional biodiversity but also considers the genetic horizons of the soil profile and not just the topsoil. We highlight that soil health has different connotations depending on the environmental setting and may show high spatial and temporal dynamics. Although the biological activity is often concentrated in the surficial horizon, we report increasing evidence that deep soil horizons host relevant biological communities, which are regulated by soil conditions that are usually different from those present in the topsoil. The processes responsible for the formation of surface and subsurface soil genetic horizons produce soil features that select the presence of organisms. The natural self‐organization of soil features is at the basis of the soil classification systems and of their ability to differentiate soil taxa and appreciate pedodiversity. Examples are reported of surface and deep soil genetic horizons as an important interpretative tool of soil functional biodiversity and soil health. Therefore, the assessing and monitoring of soil health should not be carried out at fixed depth, but according to soil genetic horizons. We conclude that the loss of the natural self‐organization of genetic horizons is a form of soil health degradation.

Impacts of Climate Change on Blue Carbon Stocks and Fluxes in Mangrove Forests

Mangroves store blue carbon (693 Mg CORG ha−1) disproportionate to their small area, mainly (74%) in deep soil horizons. Global stock estimates for mangroves (5.23–8.63 Pg CORG) are equivalent to 15–24% of those in the tropical coastal ocean. Carbon burial in mangrove soils averages 184 g CORG m−2 a−1 with global estimates (9.6–15.8 Tg CORG a−1) reflecting their importance in carbon sequestration. Extreme weather events result in carbon stock losses and declines in carbon cycling and export. Increased frequency and ferocity of storms result in increasingly negative responses with increasing strength. Increasing temperatures result in increases in carbon stocks and cycling up to a critical threshold, while positive/negative responses will likely result from increases/decreases in rainfall. Forest responses to sea-level rise (SLR) and rising CO2 are species- and site-specific and complex due to interactive effects with other drivers (e.g., temperature, salinity). The SLR critical threshold is ≈ 6 mm a−1 indicating survival only under very low-low CO2 emissions scenarios. Under low coastal squeeze, landward migration could result in sequestration and CO2 losses of 1.5 and −1.1 Pg C with net stock gains and losses (−0.3 to +0.5 Pg C) and CO2 losses (−3.4 Pg) under high coastal squeeze.

Application of the Chow method for evaluation of morphometric parameters of the sunflower root system

When growing sunflower, great importance is provided to the issue of accumulation and preservation of moisture in deep soil horizons, which in turn affects the productivity of crops. In arid regions, providing plants with moisture is of particular importance. The technologies of conservation agriculture in relation to sunflower cultivation allow varying the depth of autumn tillage from 17 to 33 cm, which, in combination with the metered use of mineral fertilizers and considering the difference in moisture consumption for the growing season from a meter layer of soil, provide an increase in yield compared to the traditional main autumn tillage. Moreover, the ratio of income from the sale of sunflower seeds grown in an arid steppe to production costs depends on the combination of the depth of strip processing and the dose of fertilization. Wherein, in the main zones of commercial sunflower production, high yield increases are provided by the application of nitrogen-phosphorus fertilizers, which contribute to the intensive formation of underground vegetative organs, which has unlimited growth in length and positive geotropism. The article presents the results of the application of multivariate regression analysis to study the morphobiological features of formation of the root system of sunflower grown using Strip-Till technology on the experimental field of the Povolzhye Educational and Scientific Production Association of the Saratov State Agrarian University named after N.I. Vavilov. The results of the morphometric assessment indicate a better development of the root system of plants in the treated strips compared to traditional types of basic tillage. To determine the limits of applicability of the piecewise linear regression model and develop practical recommendations for implementation of resource-saving potential of the Strip-Till technology in the dry steppe zone of the South-East of Russia used a reliable and sensitive criterion based on the method of J. Chow.

Dynamic Hillslope Soil Moisture in a Mediterranean Montane Watershed

AbstractVariations in hillslope soil moisture control forest hydrologic fluxes and storage pools, yet sparse observations combined with the complexity and heterogeneity of water movement and storage in the vadose zone can make temporal and spatial patterns and processes difficult to predict. We used two years of field observations of volumetric soil moisture at three depths (15, 30, and 100 cm) across five topographic positions (riparian, toeslope, sideslope, shoulder, and ridge) along three hillslope transects to better understand how soil moisture changes with hillslope position and through time. As expected, we found higher values of soil moisture at all depths at the riparian and toeslope positions. Unexpectedly, we found that ridges were particularly wet during the wet winter months and dried quickly during the summer months, indicating that topography alone cannot account for mean wet season soil moisture in our Mediterranean climate field site. The variability in soil moisture across all soil depths and topographic positions was greatest when soils were dry and decreased under wet soil conditions; this variability remained high in the deeper soil horizons, regardless of season. Lastly, event analysis suggests that the response to early season rainfall was highly variable along the hillslopes and was likely dominated by localized controls such as microtopography and vegetation as well as soil texture, antecedent moisture conditions, and rainfall characteristics. Our results suggest that the drivers of wet and dry season soil moisture dynamics can vary across topographic positions along a hillslope and do not always follow topographic controls.

PSXI-21 Soil emission of carbon dioxide and behavior of microorganisms in soils of Western Kazakhstan

Abstract Kazakhstan Western ecosystems are intensively used in agricultural production. Assessing greenhouse gas emissions from soils, especially CO2, is important. In the upper stages, microbiology, characteristics and condition of the soil change. Biological intensity indicators are soil respiration processes, numerous microbiocenoses species composition. Soil CO2 emissions were measured 5 times monthly during three years. The CO2 flow rate from soil surface is measured by a closed dynamic chamber method with Li-8100A field respirometer. Metagenomic soil testing used bacteria DNA, archaea, real-time PCR, 16SrRNA sequencing. The soil CO2 monthly dynamics fluxes varied among the lands, within the season. In 2020, the CO2 emissions soil peak noted in the pasture. There is a slight decline in summer with a decrease towards the cold season. Comparison between the CO2 flux pasture soils is less in virgin soil. The minimum CO2 flux was recorded in November - February; in the spring, the flux increases. The above CO2 emissions were recorded in summer. In soils, there is wide variety of microorganisms with opposite and incompatible properties for one habitat. The microbial communities structure identified at the family level. The taxonomic samples structure ominated by phylae - Actinobacteria, Proteobacteria, Chloroflexi, Acidobacteria, Gemmatimonadetes, Firmicutes, Actinobacteria. The spread explained by increased actinomycetes resistance characteristic to low moisture content with long dry period. For comparative evaluation microbial communities results comparing by cenoses of upper horizons with dark chestnut soil indicators. This violation caused microorganisms resistance to disturbing factors. On anthropogenically disturbed saline soils, the bacteria found were specific and resistant to critical conditions. CO2 emission in soil varied cenosis type. The CO2 intensity factors were precipitation deficit, high temperature. The profile microorganisms distribution corresponded to the soil horizons humus content. During summer soil drying, the deep soil horizons abundance occurred where moisture is retained.

Dynamics of organic matter in soils formed on limestone and sandstone in the karst area in southwestern China: δ 13C and δ 15N approaches

To better understand biogeochemical processes associated with the dynamics of soil organic matter (SOM), the δ 13C and δ 15N values were analyzed in the SOM of limestone soil (developed on limestone) and sandstone soil (developed on sandstone), as well as in dominant plant species and litter samples collected on the studied soil profiles in karst areas of Southwest China. In general, the content of soil organic carbon (SOC) and soil organic nitrogen (SON) is highest in the surface soil layer and decreases downward in both types of soil profiles. In addition, the content of SOM (including both SOC and SON) in the limestone is much higher than in sandstone soil. The higher pH values, as well as the content of calcium, magnesium, and clay minerals, are probably the reasons for the higher SOM content in the limestone soil compared to the sandstone soil.In the SOM of the upper layers of yellow sandstone and limestone soil δ 13C values range from 2.6‰ to 6.3‰ and δ 15N values from 5.1‰ to 8.1‰, which is larger than in litters. Yellow sandstone soils have smaller differences between δ 13C and δ 15N values of SOM from litter and topsoil than the limestone soil. The δ 13C and δ 15N values of SOM increase with depth in yellow sandstone soil profiles, but not in the limestone soil profiles. An increase in the values of δ 13C and δ 15N with a decrease in the SOM content in the yellow sandstone soil significantly substantiates the decomposition of SOM, which causes higher values of δ 13C and δ 15N values in the deeper soil horizons. By contrast, the limestone soil has complex depth profiles of δ 13C and δ15N, which can be mainly attributed to land-use changes and organic and mineral interactions between soil accumulations.

Soil erodibility in European mountain beech forests

Forests in Europe are currently not endangered by soil erosion. However, this can change with climate change or with intensified forest management practices. Using a newly established network of plots in beech forests across Europe, the aims of this study were to (i) distinguish soil properties and erodibility indices in relation to bedrock, (ii) determine geochemical properties and organic carbon (Corg) influencing erodibility, and (iii) assess the effect of soil depth on erodibility indices. Seventy-six soil samples from 20 beech forests were collected in 11 countries to quantify soil properties influencing erodibility indices: clay ratio, modified clay ratio, sodium adsorption ratio, and oxides ratio. The results indicate that the dominant soil properties, determined by bedrock, that correlate with forest soil erodibility indices are Corg, pH, electrical conductivity, calcium and sodium ions concentrations, total water-soluble cations, and the percentage of sand. According to the tested indices, soil susceptibility to erosion follows the order granite &gt; andesite &gt; sandstone &gt; quartzite &gt; limestone. Deeper soil horizons on granite are more susceptible to erosion than surface horizons are, but this is not the case for soils on limestones. In conclusion, forest management should consider the predisposition of different soil types to erosion.

Bioturbation by black soldier fly larvae-Rapid soil formation with burial of ceramic artifacts.

Bioturbation involves the incorporation of residues from the surface soil into the subsoil; however, common small soil ‘bioengineers’, such as earthworms or termites, are unlikely to transport human artifacts to deeper soil horizons. However, such artifacts occur in the deeper soil horizons within Amazonian Anthrosols (Terra Preta). Here we test the assumption that such tasks could be carried out by fly larvae, which could thus play a crucial role in waste decomposition and associated soil mixing under tropical conditions. We performed two greenhouse experiments with sandy substrate covered with layers of organic waste, ceramic fragments, and black soldier fly larvae (BSFL) (Hermetia illucens (L.) (Dipt.: Stratiomyidae)). We used in-situ images to assess the rate of bioturbation by BSFL, and then designed our main study to observe waste dissipation (reduction of organic carbon and phosphorus contents from waste model trials with and without charcoal) as related to larval-induced changes in soil properties. We found that the bioturbation of macroinvertebrates like BSFL was able to bury even large (> 5 cm) ceramic fragments within hours, which coincided with high soil growth rates (0.5 cm h-1). The sandy soil was subsequently heavily enriched with organic matter and phosphorus originating from organic waste. We conclude that BSFL, and possibly other fly species, are important, previously overlooked soil ‘bioengineers’, which may even contribute to the burial of artifacts in Anthrosols and other terrestrial waste dumps.

Leaching of Phosphomonoesterase Activities in Beech Forest Soils: Consequences for Phosphorus Forms and Mobility

Phosphomonoesterases play an important role in the soil phosphorus (P) cycle since they hydrolyze P monoester to phosphate. Their activity is generally measured in soil extracts, and thus, it remains uncertain how mobile these enzymes are and to which extent they can be translocated within the soil profile. The presence of phosphomonoesterases in soil solutions potentially affects the share of labile dissolved organic P (DOP), which in turn would affect P leaching. Our study aimed at assessing the production and leaching of phosphomonoesterases from organic layers and topsoil horizons in forest soils and its potential effect on dissolved P forms in leachates obtained from zero-tension lysimeters. We measured phosphomonoesterase activities in leached soil solutions and compared it with those in water extracts from litter, Oe/Oa, and A horizons of two beech forests with a contrasting nitrogen (N) and P availability, subjected to experimental N × P fertilization. In addition, we determined phosphate and DOP. In soil solutions leached from litter, Oe/Oa, and A horizons, phosphomonoesterase activities ranged from 2 to 8 μmol L–1 h–1 during summer, but remained below detection limits in winter. The summer values represent 0.1–1% of the phosphomonoesterase activity in soil extracts, indicating that enzymes can be translocated from organic layers and topsoils to greater soil depths. Activities of phosphomonoesterases obtained by water extracts were greater in the organic layer of the P-poor site, while activities of those in soil solutions were similar at the two sites. Nitrogen addition increased phosphomonoesterase activities in leached soil solutions of the organic layer of the N- and P-poor soil. Using a modeling approach, we estimated that approx. 76% of the initial labile DOP was hydrolyzed to dissolved inorganic P within the first 24 h. Back calculations from measured labile DOP revealed an underestimation of approx. 15% of total dissolved P, or 0.03 mg L–1. The observed leaching of phosphomonoesterases implies that labile organic P could be hydrolyzed in deeper soil horizons and that extended sample storage leads to an underestimation of the contribution of DOP to total dissolved P leaching. This has been neglected in the few field studies measuring DOP leaching.

Fine-root functional trait responses to experimental warming: a global meta-analysis.

Whether and how warming alters functional traits of absorptive plant roots remains to be answered across the globe. Tackling this question is crucial to better understanding terrestrial responses to climate change as fine-root traits drive many ecosystem processes. We carried out a detailed synthesis of fine-root trait responses to experimental warming by performing a meta-analysis of 964 paired observations from 177 publications. Warming increased fine-root biomass, production, respiration and nitrogen concentration as well as decreased root carbon : nitrogen ratio and nonstructural carbohydrates. Warming effects on fine-root biomass decreased with greater warming magnitude, especially in short-term experiments. Furthermore, the positive effect of warming on fine-root biomass was strongest in deeper soil horizons and in colder and drier regions. Total fine-root length, morphology, mortality, life span and turnover were unresponsive to warming. Our results highlight the significant changes in fine-root traits in response to warming as well as the importance of warming magnitude and duration in understanding fine-root responses. These changes have strong implications for global soil carbon stocks in a warmer world associated with increased root-derived carbon inputs into deeper soil horizons and increases in fine-root respiration.

Field calibrations of a Diviner 2000 capacitive soil water content probe on a shallow groundwater site and the application in a weighable groundwater lysimeter

The determination of the volumetric soil water content θv by means of capacitive profile probes is often applied to investigate the soil water storage change ΔS that serves as basis for decisions in agricultural water management. The soil properties have a big effect on the accuracy of the θv measurements. The use of only one calibration function, often provided by the manufacturers of the probes, cannot fulfil the requirements of all site conditions. Therefore, many individual calibration functions have in the past been determined for different soils and sensors. A literature review of existing calibration functions of the capacitive profile probe Diviner 2000 shows the broad range of available functions. The review makes it clear that there is a lack of functions for organic soils. These soils are typical soils of wet sites with shallow groundwater tables. The soil moisture is of big importance for many ecological processes of these sites and therefore an exact determination of θv is important. A Diviner 2000 profile probe was calibrated on such a shallow groundwater site in a classic field calibration procedure and the determined functions were applied to the soil profile of a weighable groundwater lysimeter. The soil water storage change ΔS was estimated with the measured θv values and compared with the measured mass change Δm of the lysimeter. The mean error (bias) between ΔS with the field calibration function and Δm was 7.8 kg and the root mean squared error (RMSE) 19.9 kg. An iterative adaptation of the calibration functions to the measured Δm values of the lysimeter reduced the bias to 0.9 kg and the RMSE to 14.0 kg. The investigations illustrate the problems of a classic field calibration under the conditions of a shallow groundwater site with low θv changes in deeper soil horizons and soils with high Corg contents as well as the inaccuracy in the determination of ΔS based on θv measurements with capacitive profile probes.

Soil Microbiome Composition along the Natural Norway Spruce Forest Life Cycle

Stand-replacing disturbances are a key element of the Norway spruce (Picea abies) forest life cycle. While the effect of a natural disturbance regime on forest physiognomy, spatial structure and pedocomplexity was well described in the literature, its impact on the microbiome, a crucial soil component that mediates nutrient cycling and stand productivity, remains largely unknown. For this purpose, we conducted research on a chronosequence of sites representing the post-disturbance development of a primeval Norway spruce forest in the Calimani Mts., Romania. The sites were selected along a gradient of duration from 16 to 160 years that ranges from ecosystem regeneration phases of recently disturbed open gaps to old-growth forest stands. Based on DNA amplicon sequencing, we followed bacterial and fungal community composition separately in organic, upper mineral and spodic horizons of present Podzol soils. We observed that the canopy opening and subsequent expansion of the grass-dominated understorey increased soil N availability and soil pH, which was reflected in enlarged bacterial abundance and diversity, namely due to the contribution of copiotrophic bacteria that prefer nutrient-richer conditions. The fungal community composition was affected by the disturbance as well but, contrary to our expectations, with no obvious effect on the relative abundance of ectomycorrhizal fungi. Once the mature stand was re-established, the N availability was reduced, the pH gradually decreased and the original old-growth forest microbial community dominated by acidotolerant oligotrophs recovered. The effect of the disturbance and forest regeneration was most evident in organic horizons, while the manifestation of these events was weaker and delayed in deeper soil horizons.

Phosphorus adsorption characteristics in forested and managed podzolic soils

AbstractDespite the agricultural expansion into Canada's boreal ecoregion, little is known about the phosphorus (P) adsorption capacity in natural and managed Podzols' soil profiles. This information is critical for informing management decisions for P use efficiency and mitigating related environmental risks. Thus, this study aimed to evaluate P adsorption characteristics of podzolic horizons in natural and managed soil using nonlinear Langmuir and Freundlich adsorption models. A batch adsorption experiment was conducted using soils collected from distinct horizons of forested and managed fields in eastern and central Newfoundland, Canada. Nonlinear Langmuir and Freundlich fitted models had r values &gt;.99 regardless of horizons, locations, and management history. The organic LFH, a surface horizon typical for forested Podzols, and a long‐term managed Ap horizon had the highest P retention capacities when compared to either newly converted soils or soils used as tree nursery following conversion from natural forest. A significant linear correlation and multiple regression models (p &lt; .05) were established between P adsorption parameters and selected soil properties. Results suggest that following conversion from forest to agricultural use, long‐term management that includes tillage and lime and fertilizer application creates an Ap horizon with strong adsorption capacity, which could still fix P and serve as a source of P. The newly converted soils and the deeper soil horizons, for both natural and converted lands, do act mainly as P sinks; hence, crops may need larger quantities of P fertilizer increasing fertilizer expenses and also increasing future legacy P.