Determining landscape-level drivers of variability for over fifty soil chemical elements

Climate and Soil Properties Drive the Distribution of Minor and Trace Elements in Forest Soils of the Winter Olympic Core Area

Minor and trace elements in soil play a crucial role in regulating ecological processes that sustain the functionality of forest ecosystems. In this study, we have selected three conifer forests (Pinus sylvestris, Picea asperata, Larix principis-rupprechtii), one broadleaf forest (Betula Platyfilla) and one mixed forest of Betula Platyfilla and Larix principis-rupprechtii in the Winter Olympic core area and determined the pattern of 12 typical elements (B, Fe, V, Cr, Ni, Co, Mn, As, Cu, Zn, Sn and Se) in soils and their main drivers in the three different soil layers (A, B and C horizon) in each soil profile. Our results showed that the concentrations of B, Fe, Cr, Cu, Ni and Sn were mainly enriched in the broadleaf forest and mixed broadleaf-conifer forest zones, and the average concentrations of Co, Mn, V, Zn, As and Se were mainly enriched in coniferous forest zones in contrast. We have observed that the mean concentrations of Fe, Cr, Ni, Zn, As, Sn and Co increase with soil depth in the BP forest. The concentrations of Se and Cu were higher in the A layer than the C layer. The piecewise structural equation modeling (piecewiseSEM) results visualized a direct and negative effect on B, Fe, V, Cr and Ni concentrations due to soil temperature, while the concentrations of Se is mainly influenced by soil temperature and soil properties.

Climate and soil properties regulate the vertical heterogeneity of minor and trace elements in the alpine topsoil of the Hengduan Mountains

Soil minor and trace elements are vital regulators of ecological processes that sustain alpine ecosystem functions. In this study, the vertical pattern and driving factors of element concentrations in alpine soils of the Tibetan Plateau were investigated. Three snow mountains (Meili, Baima, and Haba) part of the Hengduan Mountain range, were selected as the study area to determine the vertical distribution of 12 typical elements (Cr, Ni, Cu, Fe, Mn, Zn, Cd, Pb, Ca, Sr, As, and Se) in topsoil with increasing and decreasing elevation, as well as the dominant driving factors of their spatial heterogeneity. Results showed that all elements, except Se, showed strong vertical heterogeneity, among which Cr, Ni, Cu, and Fe showed peak concentrations at 2700-3000 m; the highest concentrations of Mn and Zn were at 3200 m and 2700 m, with Cd and Pb at 2500 m. Ca and Sr levels gradually decreased with increasing elevation. According to the structural equation model and random forest analysis, the vertical heterogeneity of soil elements is directly regulated by the variability of climate and soil properties due to changes in elevation. A three-way PERMANOVA further quantized the contributions of climate and soil properties on vertical heterogeneity of all soil elements, which were 35.2 % and 50.5 %, respectively. This study used various statistical tools to reveal the dominant factors affecting the vertical heterogeneity of soil elements. These findings provided a scientific overview of element distribution on the Tibetan Plateau and significant references for the vertical distribution of elements in the topsoil of other snow mountains worldwide.

Concentrations and bioconcentration factors of leaf microelements in response to environmental gradients in drylands of China

Determining response patterns of plant leaf elements to environmental variables would be beneficial in understanding plant adaptive strategies and in predicting ecosystem biogeochemistry processes. Despite the vital role of microelements in life chemistry and ecosystem functioning, little is known about how plant microelement concentrations, especially their bioconcentration factors (BCFs, the ratio of plant to soil concentration of elements), respond to large-scale environmental gradients, such as aridity, soil properties and anthropogenic activities, in drylands. The aim of the present study was to fill this important gap. We determined leaf microelement BCFs by measuring the concentrations of Mn, Fe, Ni, Cu and Zn in soils from 33 sites and leaves of 111 plants from 67 species across the drylands of China. Leaf microelement concentrations were maintained within normal ranges to satisfy the basic requirements of plants, even in nutrient-poor soil. Aridity, soil organic carbon (SOC) and electrical conductivity (EC) had positive effects, while soil pH had a negative effect on leaf microelement concentrations. Except for Fe, aridity affected leaf microelement BCFs negatively and indirectly by increasing soil pH and SOC. Anthropogenic activities and soil clay contents had relatively weak impacts on both leaf microelement concentrations and BCFs. Moreover, leaf microelement concentrations and BCFs shifted with thresholds at 0.89 for aridity and 7.9 and 8.9 for soil pH. Woody plants were positive indicator species and herbaceous plants were mainly negative indicator species of leaf microelement concentrations and BCFs for aridity and soil pH. Our results suggest that increased aridity limits the absorption of microelements by plant leaves and enhances leaf microelement concentrations. The identification of indicator species for the response of plant microelements to aridity and key soil characteristics revealed that woody species in drylands were more tolerant to environmental changes than herbaceous species.

Changes in soil micronutrients along a temperature gradient in northern China

How climate warming affected terrestrial ecosystems received considerable attention. Soil micronutrients play a vital role in regulating the growth of all living organisms and thus make a significant contribution to plant production. However, the responses of soil micronutrients to climate warming still remained unclear. While soil sampling along a temperature gradient could reveal the long-term influence of climate warming on soil nutrient dynamics, the variations of soil micronutrients with temperature might be interfered by the effect of precipitation due to the collinearity between temperature and precipitation. Moreover, changes in soil micronutrients over broad geographical scale could be affected by soil texture. Hence, this study conducted a soil investigation across a temperature transect along the 400 mm isohyet in northern China to examine the responses of soil micronutrients to changing temperature and soil texture when the effect of precipitation was minimized. We observed that soil copper (Cu), manganese (Mn) and zinc (Zn) contents all decreased along the temperature gradient. Soil Cu, Mn and Zn contents were positively correlated with soil clay and silt contents and negatively correlated with soil sand content. Temperature and soil texture together accounted for 72.0 % of the variations in soil micronutrient contents. Temperature and soil texture individually explained 10.4 % and 48.0 %, and their shared variation explained 13.6 % of the variations in soil micronutrient contents. Moreover, soil parent material also exerted an effect on soil micronutrient contents. Our results suggested that climate warming might cause a decrease in soil micronutrient contents.

Spatial variability and delineation of management zones based on soil micronutrient status in apple orchard soils of Kashmir valley, India

Knowledge and up-scaling of status, availability, and distribution of soil micronutrients are hugely significant for enhancing crop productivity and profitability. However, regional database entailing spatial variability of key micronutrients for a major apple-producing region like the Kashmir Himalayan Region (KHR) is missing. We investigated 588 topsoil samples between 2016 and 2017 (to 30 cm depth) to estimate spatial variability of extractable Zn, Cu, Mn, and Fe; develop spatial maps; and delineate potential management zones (MZs) in apple orchards using geo-statistical methods. Soil sampling was performed post-harvest season. Principal component analysis and fuzzy c-mean clustering were performed to develop MZs. Results exhibited wide variation, with high coefficient of variation (%) for Mn and Cu (123.9 and 114.4, respectively) and low (71.6) and medium (104) variability for Fe and Zn. Mean concentrations followed the order: Fe > Mn > Cu > Zn, with deficiencies evident towards central and northern regions of the study area. The best-fitted model was exponential. The nugget/sill ratio values were 0.41, 0.08, 0.37, and 0.38 for Zn, Cu, Mn, and Fe, respectively, indicating strong spatial dependence for Cu and moderate dependence for Fe, Zn, and Mn. Correlations between elevation, slope, and soil pH with micronutrients were negative, whereas with soil organic carbon and electrical conductivity positive relationships were identified. Three principal components accounted for 67·18% data variance. Based on the fuzzy performance index and modified partition entropy, five MZs were delineated, which exhibited variations from each other. These MZs highlighted the need for specific supplemental provisions in increasing soil fertility and apple productivity.

Surface soil metal elements variability affected by environmental and soil properties

Identifying the factors controlling the spatial variability of soil metal elements could be a challenge task due to the interaction of environmental attributes and human activities. This study aimed to investigate the critical explanatory variables controlling total Ca, Cd, Cr, Cu, Zn, Fe, Mn, Mg, Pb, and Zn variations in the arable topsoil using classical statistics, principal component analysis, and random forest techniques. The work was conducted in the core region of the Three Gorges Reservoir of China. The explanatory variables included soil, topography, climate, vegetation, land use type, and distance-related parameters. Average concentrations of the metal elements were in order of Fe > Mg > Ca > Mn > Zn > Cr > Ni > Pb > Cu > Cd. Soil Cr, Fe, and Pb showed low variability while others presented medium variability. Average concentrations of Cr, Fe, Cd, and Mg exceeded their corresponding background values. There were highly positive correlations between all metal elements except Pb, Cd and Cr. The principal component analysis further demonstrated that the sources of Pb, Cd, and Cr differed with other elements. The results of random forest suggested that soil properties followed by topography were critical parameters affecting the variations of Ca, Mg, Mn, Fe, Ni, Zn, and Cu. Agricultural activities and soil properties were major factors controlling the variations of Pb, Cr, and Cd. Further study should be conducted to understand the relations between the metal elements and soil properties.

Dynamics of soil metallic nutrients across a 6000-km temperature transect in China

Global warming has exerted profound effects on terrestrial ecosystems. Soil metallic nutrients, an integrated part of soil nutrient fertility, play a significant role in the maintenance of ecosystem functions. However, how soil metallic nutrients respond to global warming remains poorly understood. Spatial observations across a temperature gradient provide a solid evidence in clarifying the long-term responses of soil metallic nutrients to global warming. But due to the collinearity between temperature and precipitation in the geographical patterns, the influence of temperature on soil metallic nutrients might be interfered by the precipitation effect. To minimize the precipitation effect, this study conducted a soil sampling over broad geographical scale along the 400 mm isohyet in China, which extends about 6000 km. Variations in soil potassium (K), calcium (Ca), magnesium (Mg) and iron (Fe) concentrations across the temperature transect were investigated. These four elements all increased until mean annual temperature (MAT) increased to about 2 °C and then decreased with increasing MAT. Temperature, soil property and vegetation type were responsible for the changes of soil metallic nutrients at MAT below 2 °C; altitude, soil property, vegetation type and soil parent material were dominant influential factors of soil metallic nutrients at MAT above 2 °C. Temperature exerted an indirect influence on soil metallic nutrients through its effects on soil property, vegetation type, rock weathering, microbial decomposition and plant growth. It could be expected based on our results that the effects of global warming on soil K, Ca, Mg and Fe might depend on local MAT. Different regions with different climates should adopt different strategies to cope with the effect of global warming on soil metallic nutrients so that ecosystems maintain stable.

Metal contamination of river otters in North Carolina

Aquatic apex predators are vulnerable to environmental contaminants due to biomagnification. North American river otter (Lontra canadensis) populations should be closely monitored across their range due to point and nonpoint pollution sources. Nonetheless, no information exists on environmental contaminants in the North Carolina otter population. Metals and metalloids occur naturally across the landscape, are essential for cellular function, and become toxic when concentrated unnaturally. We conducted our study across the three Furbearer Management Units (FMU) and 14 river basins of North Carolina. We determined the concentrations of arsenic, cadmium, calcium, cobalt, copper, iron, lead, magnesium, manganese, mercury, molybdenum, selenium, thallium, and zinc in liver and kidney samples from 317 otters harvested from 2009 to 2016. Arsenic, lead, and thallium samples were tested at levels below the limit of detection. With the exception of cadmium, we detected all other elements at higher levels in the liver compared with the kidney. Specifically, cadmium, cobalt, copper, iron, magnesium, manganese, mercury, molybdenum, and zinc levels differed by tissue type analyzed. Most element concentrations remained stable or increased with otter age. We detected higher levels of mercury and selenium in the Lower Pee Dee and Cape Fear river basins. River basins within the Mountain FMU were higher in cadmium, copper, iron, lead, and zinc, whereas the Coastal Plain FMU was lower in cobalt and manganese. None of the elements occurred at toxic levels. Our research establishes baseline concentration levels for North Carolina, which will benefit future monitoring efforts and provide insight into future changes in the otter population.