High-resolution soil sampling reveals the pattern of biological weathering and soil formation under trees.

Trees contribute to bedrock weathering in a variety of ways. However, evaluating their full impact is complicated by a lack of direct observation of unexposed root systems of individual trees, especially when the scale of the analysis goes down to the level of microbiomes. In the present study, we investigated the contribution of tree root systems to bioweathering and soil production at the macro- and microscale. Soil profiles developed under trees on granite bedrock were investigated in two parts of the Sudety Mountains, SW Poland: the Rudawy Janowickie Mountains, and the Stolowe Mountains. Soil profiles were gradually excavated and soil samples collected from pre-defined positions of the root zone: 1) bulk soil, 2) rhizosphere, 3) cracks, 4) topsoil, and 5) control positions. In total, we analyzed 103 samples for soil chemistry and microbiological activity. In addition, we analyzed 19 samples using XRF (X-ray Fluorescence). Four parent rock samples, in the form of thin-sections, were the subject of mineralogical evaluation. Soil analyses included: total organic carbon (C) and nitrogen (N) content, soil pHH2O, soluble iron (Fed), and aluminum (Ald), non-crystalline (amorphous) iron (Feox), and aluminum (Alox). For microbiological analyses, we used a Biolog (EcoPlate) system to determine the functional diversity of soil microorganisms. We evaluated the results on soil chemistry and microbiological activity statistically by principal component analysis (PCA) and redundancy analysis (RDA). Differences between soil sampling positions were assessed using a non-parametric Kruskal-Wallis (K-W) rank sum test and a post-hoc pairwise Dunn test. Trees developed different root architectures, likely shaped by the depth to bedrock and its pre-existing net of fractures and fissures. Tree roots were able to enter bedrock cracks at one study site (at Pstrazna, Stolowe Mountains). The soil profile was too deep for root system penetration at the second study site (Mt Janska, Rudawy Janowickie Mountains, RJM). The rhizospheric soil along the roots had significantly different chemical properties compared to non-rhizospheric soil types. At Mt. Janska, soil differed from the crack soil in terms of Alox (pHolm-adj. < 0.0006) and Feox (pHolm-adj. < 0.004), and from the bulk soil (pHolm-adj. < 0.02) and topsoil (pHolm-adj. < 0.007). In addition, at Pstrazna, the soil differed from the control soil in terms of C (pHolm-adj. < 0.009) and soil pHH2O (pHolm-adj. < 0.0008) and from the topsoil in terms of soil pHH2O. The highest metabolic activity was in cracks at Mt. Janska and in control samples from Pstrazna. In general, the spatial distribution of soil microbial activity, and the weathering that results from that portion of the soil biome, is spatially heterogeneous and appears to be partially determined by the interaction of root growth and bedrock fracture patterns.

Effect of warming on ground vegetation in Carpathian Norway spruce stands, exemplified by European blueberry (Vaccinium myrtillus L.) nutrient stoichiometry.

Despite its small share of total forest biomass, ground vegetation plays an important role in biogeochemical cycles, being able to modify carbon (C) and nutrients fluxes. Global climate warming may affect plant nutrient uptake and the carbon:nitrogen:phosphorus (C:N:P) stoichiometry, the release of nutrients from the soil and soil organic matter, as well as significantly influence the tree stand nutrient supply. In this context, the response of Norway spruce (Picea abies (L.) H.Karst) stands' ground vegetation to warming is uncertain. An open-top chamber soil-warming simulation, lasting two growing seasons, was conducted in a spruce forest. At the end of each of the two growing seasons, before leaf senescence, European blueberry (Vaccinium myrtillus L.) aboveground biomass (leaves and stems) and mineral topsoil samples were collected from the plots. The C, N, P, micronutrient, and macronutrient concentrations were estimated in the samples. Warming caused significant decreases in C, N, and P in the soil. Warming also decreased the C:P and N:P stoichiometric ratios in the soil and increased the C:P ratio in plant stems. Significant increase in foliar C and decrease in foliar P in warmed plots were observed. The most evident effect was reduction of N and P in the soil, which directly affected the plant C:P and soil N:P stoichiometry. Our results show that warming has caused a significant decrease in the content of some nutrients in the aboveground plant tissues of blueberries. Given that N is a limiting factor of ecosystems productivity, its reduction in the soil caused by warming may be a serious threat to proper nutrient uptake and cause disruption of biogeochemical cycles. The decrease in nutrient content in aboveground tissues due to warming can result in disruptions to physiological processes.

Weathering and soil production under trees growing on sandstones - The role of tree roots in soil formation.

Rock weathering drives both landform formation and soil production/evolution. The less studied biological component of weathering and soil production caused by tree root systems is the main focus of the present study. Weathering by trees, which likely has been important in soil formation since the first trees emerged in the middle and late Devonian, is accomplished through both physical and biological means, like acids excreted by plants and exudates from associated bacterial communities. However, these processes are relatively poorly known. We assessed the impact of tree roots and associated microbiota on the potential level of biological weathering. Three research plots were selected in two sandstone regions in Poland. Two plots were in the Stolowe Mountains (Zlotno, Batorów), a tableland built of Cretaceous sandstones. The third plot (Zegiestów) was in the Sacz Beskidy Mountains, the Carpathians. Soil samples were taken from tree root zones of Norway spruces from predefined sampling positions. Soils from non-tree control positions were also sampled. Soil samples were a subject of laboratory analyses which included the content of Fe and Al (amorphous and labile forms), carbon (C), nitrogen (N), and soil pH. The microbial functional diversity of soil microorganisms was determined using the Biolog (EcoPlate) system. Rock fragments were collected for mineralogical and a subject of optical microscopy and cathodoluminescence analyses in order to examine their mineralogical composition. Significant differences (pHolm-corrected < 0.05) between sample locations were found mostly for the Zegiestów plot: Soils at control positions differed from the crack and bulk soil sample positions in terms of C, N, C/N, and pH. Tree roots were able to develop a great variety of sizes and forms by following the existing net of bedrock discontinuities and hillslope microrelief. They developed along the most accessible surfaces, and caused rockcliff retreat and scree slope formation. These two features can be considered as initial stages of soil production. Trees add to the complexity of the soil system and allow formation of rhizospheric soils, and horizons rich in organic matter which are zones of a high microbial activity. However, as our study shows, rock cracks with roots cannot be considered as zones of microbial weathering. In addition, C content and microbial activity decreases with depth but can stay on a high level along living and dead roots. When entering rock fractures, they change the intensity of biomechanical weathering and soil properties. The highest biological activity of microorganisms was found in the control samples. Overall, tree roots do change the pattern of soil formation and explain the existing pattern of soil chemical properties, microbial activity, and potentially biological weathering intensity, and the intensity of those processes in correlation with root presence varies in space.

Short-term impact of different doses of spent coffee grounds, salt, and sand on soil chemical and hydrological properties in an urban soil.

Natural and human activities have deteriorated urban soil's health and ecological functions as compared to forest soils. Therefore, we hypothesized that any intervention in poor quality soil in urban area will change their chemical and water retention properties. The experiment was conducted in Krakow (Poland) in completely randomized design (CRD). The soil amendments used in this experiment consisted of control, spent coffee grounds (SCGs), salt, and sand (1 and 2 t ha-1) in order to evaluate the impact of these soil amendments on the urban soil chemical and hydrological properties. Soil samples were collected after 3 months of soil application. The soil pH, soil acidity (me/100 g), electrical conductivity (mS/cm), total carbon (%), CO2 emission (g m-2 day-1), and total nitrogen (%) were measured in laboratory condition. The soil hydrological properties like volumetric water content (VWC), water drop penetration time (WDPT), current water storage capacity (Sa), water storage capacity after 4 and 24 h (S4 and S24), and capillary water Pk (mm) were also determined. We noted variations in soil chemical and water retention properties in urban soil after the application of SCGs, sand, and salt. It was observed that SCGs (2 t ha-1) has reduced soil pH and nitrogen (%) by 14 and 9%, while the incorporation of salt resulted in maximum soil EC, total acidity, and soil pH. The soil carbon (%) and CO2 emission (g m-2 day-1) were enhanced and declined by SCGs amendment. Furthermore, the soil hydrological properties were significantly influenced by the soil amendment (spent coffee grounds, salt, and sand) application. Our results showed that spent coffee grounds mixing in urban soil has considerably enhanced the soil VWC, Sa, S4, S24, and Pk, whereas it decreased the water drop penetration time. The analysis showed that the single dose of soil amendments had not improved soil chemical properties very well. Therefore, it is suggested that SCGs should be applied more than single dose. This is a good direction to look for ways to improve the retention properties of urban soil and you can consider combining SCGs with other organic materials like compost, farmyard manure, or biochar.

Application of Near-Infrared Spectroscopy to Detect Modification of the Cation Exchange Properties of Soils from European Beech and Silver Fir Forest Stands in Poland.

This study investigated changes in the composition of the cation exchange capacity of soil samples caused by the acid leaching of soil cations under laboratory conditions. Furthermore, near-infrared (NIR) spectroscopy was used to evaluate the properties of forest soils. The potential influence of the species composition of stands (beech and fir) was also investigated. Eighty soil samples from the topsoil of plots located in central Poland were analyzed. Soil samples were leached 0 (non-leached), 5, 10, and 15 times and then analyzed to determine the contents of cations (Al3+, Ca2+, K+, and Mg2+), the total carbon content, and the pH. From NIR spectra obtained by scanning 54 samples and measurement results for soil sample properties, a calibration model was developed. The model was validated using 26 independent samples. The results showed that acid leaching decreased the pH of soil solutions and the carbon content. The amounts of Al3+, Ca2+, K+, and Mg2+ decreased with an increasing number of leaching treatments, but most leaching had occurred after five treatments. Data analysis showed that leaching with hydrochloric acid depleted alkaline cations and Al3+ in the soil, which reduced the stability of organic matter, causing its release. Modification of ion exchange properties is observable based on the analysis of the NIR spectra. Good calibration results were achieved for all tested parameters (R2C ≥ 0.89). The best validation results were obtained for Al3+ and C contents under fir stands, and for the pH and Al3+ content of soils under beech stands (R2V > 0.8). However, the differences between the measured and estimated mean values of the investigated soil were relatively small (no significant difference, p > 0.05). The species composition of stands (beech and fir) had no impact on the developed mathematical models. Soil assessment using NIR spectroscopy allowed calibration models to be obtained, which were successfully used to calculate soil properties at a much lower cost and in a much shorter time compared with other laboratory methods. The results of the paper affirmed that using a relatively small number of samples (3-4) to calculate an average of soil content properties provided satisfactory results.

The proximity of a highway increases CO2 respiration in forest soil and decreases the stability of soil organic matter.

Roadways traverse many forest areas and they often have harmful effects on forest soils, including the modified stability of soil organic matter (SOM). Soil CO2 respiration is an important indicator of SOM biological stability. The aim of this study was to test the hypotheses that a roadway will (1) modify the composition of the cation exchange capacity of adjacent forest soils, and (2) significantly decrease the stability of SOM. Two study sites were established in Scots pine and Silver fir stands, located close to the S7 highway in central Poland, which was opened to traffic in 1984. From each site, samples were taken at 2, 12 and 22 m from the forest edge. Soil CO2 respiration was determined using closed chamber incubation with an alkali trap. We also conducted a comprehensive analysis of soil chemical properties. The stoichiometric ratios of chosen chemical parameters to total carbon (Ct) were calculated. In both sites, we observed increased soil pH and CO2 respiration in the vicinity of the highway, as well as increased ratios of exchangeable calcium (Ca), magnesium (Mg) and sodium (Na) to Ct. In the fir site, the humic and fulvic acids, the dissolved organic carbon (DOC) content and aluminum (Al) to Ct ratio were depleted in close proximity to the highway. We suggest that the combined effect of Ca and Na ions, originating from winter de-icing, caused the depletion of Al and hydrogen (H) in the soil close to the forest edge and, therefore, resulted in lower SOM stability expressed as the decreased DOC and pyrophosphate-extractable carbon content, as well as the release of CO2. We conclude that the changes of SOM stability with distance were the effect of modification of ion-exchange relationships (particularly base cations versus Al3+ with H+) rather than forest stand species or intrinsic SOM properties (like functional groups, the recalcitrance of bindings etc.). Our work supports earlier studies, confirming the significant impact of Al and H on SOM stability.

Sequestration of Mercury in Soils under Scots Pine and Silver Fir Stands Located in the Proximity to a Roadway.

Forest soils are the main source of mercury (Hg) in stream water. Stocks of Hg in forest soils are related to several factors, including forest species composition. In this study, the potential source of Hg pollution was a relatively new roadway traversing forested areas. We compared Hg accumulation in soils of two coniferous species: Scots pine (Pinus sylvestris L.) and silver fir (Abies alba Mill.). The experimental plots were located near the S7 expressway in Central Poland. The stands differed in the length of time they had been exposed to Hg, because different parts of the roadway were built and opened to traffic at different times. We analyzed 480 soil samples from organic horizons (O) and the top 10 cm of mineral soil (A) sampled from six plots. The overall average Hg concentrations (irrespective of forest stand, n = 240) was 0.225 mg kg-1 in the O horizons and 0.075 mg kg-1 in the mineral horizons. The Hg concentration in the O horizons was more than three times greater in fir stands than that in pine stands. The average Hg:C ratios in the O and A horizons were 1.0 and 2.3 mg Hg kg-1 C, respectively. Our data does not clearly show the effect of road on Hg accumulation near the road. The concentrations of Hg in investigated soils adjacent to the roadway were only slightly higher than ranges reported for unpolluted areas, and no clearly affected by the vicinity of roadway. In contrast to the other reports, our data indicate a significant impact of tree species on Hg concentrations in both the O and A horizons. Moreover, the average Hg:C ratio was strongly dependent on the tree species.