Dynamics of sediment-associated nitrogen export from intermittent streams in subtropical forests of southeast China.

The significance of intermittent streams in nutrient loss within forest ecosystems is becoming increasingly critical due to changes in precipitation patterns associated with global climate change. However, few studies have focused on nutrient export from intermittent streams. We conducted continuous sediment collection from intermittent streams from March 2022 to February 2023 to investigate the export pattern and mechanism of sediment-associated nitrogen (N) from intermittent streams of different forest types (composed forest of Castanopsis carlesii (Cas. carlesii) and Cunninghamia lanceolata (C. lanceolata) forests, compared to Cas. carlesii forests). We measured the N concentrations and calculated the export amounts of four common forms of N associated with sediments: total N (TN), dissolved N (DN), nitrate, and ammonia. Our results showed that (1) the annual average exports of TN, DN, nitrate, and ammonia associated with sediments from intermittent streams from both forest types were 273, 1.62, 0.26, and 0.84 kg ha-1, respectively; (2) N export was significantly higher in composite forests of Cas. carlesii and C. lanceolata, compared to Cas. carlesii forests; (3) stream sediment export amount positively affected N export both in composite forests and Cas. carlesii forests; and (4) N export was also controlled by rainfall amount and stream characteristics. Our study quantified sediment-associated N export from intermittent streams among different subtropical forest types, which will enhance our understanding of N dynamics associated with stream hydrological processes in subtropical forests.

Effects of vegetation restoration on the concentrations of multiple metal elements in post-mining soils.

Vegetation restoration is vital for soil ecological restoration in post-mining areas, but a global-scale quantitative assessment of its effects on soil metal elements is lacking. Here, we conducted a meta-analysis with 2308 paired observations collected from 137 publications to evaluate vegetation restoration effects on the concentrations of 17 metal elements, namely K, AK (available K), Ca, Na, Mg, Fe, Mn, Zn, Cu, Al, Cr, Co, Ni, Cd, Sb, Hg, and Pb in post-mining soils. We found that (1) vegetation restoration significantly increased the concentrations of K, AK, Ca, Mg and Co by 43.2, 42.5, 53.4, 53.7, and 137.2%, respectively, but did not affect the concentrations of Na, Fe, Mn, Zn, Cu, Al, Cr, Ni, Cd, Sb, Hg, and Pb; (2) the effects of vegetation restoration on soil metal concentration were seldom impacted by vegetation type, while soil depth only affected the responses of AK, Cd, and Pb concentrations to vegetation restoration, and leaf type only impacted the responses of Ca and Ni concentrations to vegetation restoration; (3) latitude, elevation, restoration year, climate, and initial soil properties were also important moderator variables of vegetation restoration effects, but their impacts varied among different metals. Overall, our results clearly showed that vegetation restoration in posting-mining areas generally have a positive effect on the concentrations of nutrient elements but did not influence that of toxic elements, which provides useful information for the restoration and reconstruction of soil ecosystem in post-mining areas.

Global patterns and determinants of the initial concentrations of litter carbon components.

Plant litter is an important carbon (C) and nutrient pool in terrestrial ecosystems. The C components in plant litter are important because they regulate plant litter decomposition rate, but little is known on the global patterns and determinants of their concentrations in freshly fallen plant litter. Here, we quantified the concentrations of leaf litter C components (i.e., carbohydrate, polyphenol, tannin, and condensed tannin) with 864 measurements from 161 independent publications. We found that (1) the mean concentrations of leaf litter carbohydrate, polyphenol, tannin and condensed tannin were 27.7, 6.08, 8.84 and 5.7 %, respectively; (2) the concentrations of leaf litter C components were affected by taxonomic division, mycorrhizal association, life form, and/or leaf shedding strategy; (3) soil property had similar impacts on the concentrations of the four C compounds, while the influence of mean annual temperature and precipitation varied; and (4) elevation had opposing effects on carbohydrate and polyphenol concentrations, but not on that of tannin and condensed tannin, and only carbohydrate concentration was strongly affected by absolute latitude. In general, our results clearly show the global patterns and drivers of the concentrations of litter C compounds, providing new insights into the role of litter decomposition in global C dynamics.

[Meta-analysis of plant restoration impacts on soil microbial community structure in mining areas]. / 植被恢复对矿区土壤微生物群落结构影响的整合分析.

Mining causes severe damage to soil ecosystems. Vegetation restoration in abandoned mine areas is an inevitable requirement for sustainable development. Soil microbes, as the most active component of soil organic matter, play a crucial role in the transformation of carbon, nitrogen, phosphorus, and other elements. They are often used as indicators to assess the extent of vegetation restoration in ecologically fragile areas. However, the impacts of vegetation restoration on soil microbial community structure in mining areas at the global scale remains largely unknown. Based on 310 paired observations from 44 papers, we employed the meta-analysis approach to examine the influence of vegetation restoration on soil microbial abundance and biomass in mining area. The results indicated that vegetation restoration significantly promotes soil microbial biomass in mining areas. In comparison to bare soil, vegetation restoration leads to a significant 95.1% increase in soil microbial biomass carbon and a 87.8% increase in soil microbial biomass nitrogen. The abundance of soil bacteria, fungi, and actinomycetes are significantly increased by 1005.4%, 472.4%, and 177.7%, respectively. Among various vegetation restoration types, the exclusive plan-ting of trees exhibits the most pronounced promotion effect on soil microbial biomass and population, which results in a significant increase of 540.3% in soil fungi and 104.5% in actinomycetes, along with a respective enhancement of 110.3% and 106.4% in microbial biomass carbon and nitrogen. Model selection results revealed that soil satura-ted water content and vegetation restoration history contribute most significantly to the abundance of soil bacteria and fungi. Soil available nitrogen has the most significant impact on the abundance of actinomycetes and microbial biomass carbon, while soil available phosphorus emerges as a crucial factor affecting microbial biomass nitrogen. This research could contribute to understanding the relationship between vegetation restoration and the structure of soil microbial communities in mining areas, and providing scientific support for determining appropriate vegetation restoration types in mining areas.

The types of microplastics, heavy metals, and adsorption environments control the microplastic adsorption capacity of heavy metals.

Anthropogenic development has released large amounts of microplastics (MPs), which are carriers of migratory heavy metals, into the environment, and heavy metal adsorption by MPs may have strong combined toxic effects on ecosystems. However, until now, a comprehensive understanding of the factors influencing these adsorption capacities of MPs has been lacking. Thus, we used 4984 experimental data points to systematically assess the factors influencing the adsorption strength of 8 types of MPs on 13 types of heavy metals. We found that (1) the types of MPs, heavy metals, and adsorption environments significantly impacted the heavy metal adsorption capacities of MPs; (2) polyvinyl alcohol (PVA) showed a higher adsorption capacity for lead (Pb) and cadmium (Cd) than did other MPs, by 2810.62 mg/kg and 2732.84 mg/kg, respectively; (3) the adsorption capacities of MPs for heavy metal were regulated by multiple variables, with heavy metal concentration, MP quality, solution amount, adsorption time, and pH being the most important; and (4) MPs had a higher adsorption capacity in aquatic environments (except for seawater) than which in soil environments. Overall, our study clearly showed that the types of heavy metals, adsorption environments, and MPs influenced the heavy metal adsorption capacities of MPs and may exacerbate their combined environmental toxicity, which would help better characterize the severity of MP pollution.

Global characteristics and drivers of sodium and aluminum concentrations in freshly fallen plant litter.

Plant litter is not only the major component of terrestrial ecosystem net productivity, the decomposition of which is also an important process for the returns of elements, including sodium (Na) and aluminum (Al), which can be beneficial or toxic for plant growth. However, to date, the global characteristics and driving factors of Na and Al concentrations in freshly fallen litter still remain elusive. Here, we evaluated the concentrations and drivers of litter Na and Al with 491 observations extracted from 116 publications across the globe. Results showed that (1) the average concentrations of Na in leaf, branch, root, stem, bark, and reproductive tissue (flowers and fruits) litter were 0.989, 0.891, 1.820, 0.500, 1.390, and 0.500 g/kg, respectively, and the concentrations of Al in leaf, branch, and root were 0.424, 0.200 and 1.540 g/kg, respectively. (2) mycorrhizal association significantly affected litter Na and Al concentration. The highest concentration of Na was found in litter from trees associated with both arbuscular mycorrhizal fungi (AM) and ectomycorrhizal fungi (ECM), followed by litter from trees with AM and ECM. Lifeform, taxonomic, and leaf form had significant impacts on the concentration of Na and Al in plant litter of different tissues. (3) leaf litter Na concentration was mainly driven by mycorrhizal association, leaf form and soil phosphorus concentration, while leaf litter Al concentration was mainly controlled by mycorrhizal association, leaf form, and precipitation in the wettest month. Overall, our study clearly assessed the global patterns and influencing factors of litter Na and Al concentrations, which may help us to better understand their roles in the associated biogeochemical cycles in forest ecosystem.

Global patterns and drivers of lead concentration in inland waters.

Water bodies are important carriers for lead (Pb) biogeochemical cycling, which is a key pathway of Pb transport. Although existing studies on Pb loading in inland waters have developed rapidly, a quantitative assessment of the distribution patterns and drivers of Pb concentration in inland waters at the global scale remains unclear. Here, by analyzing 1790 observations collected from 386 independent publications, we assessed the spatial distribution and drivers of Pb concentration in inland waters worldwide. We found that (1) globally, the median of Pb concentration in inland waters was 5.81 µg L-1; (2) among different inland water types, Pb concentration was higher in rivers, and the highest Pb concentration was in industrial land in terms of land use type; (3) Pb concentration in inland waters were positively driven by potential evapotranspiration, elevation and road density; and (4) Pb concentration showed a negative relationship with absolute latitude, decreasing from tropic to boreal regions. Overall, our global assessment of the patterns and drivers of Pb concentration in inland waters contributed to a better understanding of the natural and anthropogenic attributions of Pb in the inland hydrological cycling.

Global patterns and driving factors of plant litter iron, manganese, zinc, and copper concentrations.

Plant litter decomposition is not only the major source of soil carbon and macronutrients, but also an important process for the biogeochemical cycling of trace elements such as iron (Fe), manganese (Mn), zinc (Zn), and copper (Cu). The concentrations of plant litter trace elements can influence litter decomposition and element cycling across the plant and soil systems. Yet, a global perspective of the patterns and driving factors of trace elements in plant litter is missing. To bridge this knowledge gap, we quantitatively assessed the concentrations of four common trace elements, namely Fe, Mn, Zn, and Cu, of freshly fallen plant litter with 1411 observations extracted from 175 publications across the globe. Results showed that (1) the median of the average concentrations of litter Fe, Mn, Zn, and Cu were 0.200, 0.555, 0.032, and 0.006 g/kg, respectively, across litter types; (2) litter concentrations of Fe, Zn, and Cu were generally stable regardless of variations in multiple biotic and abiotic factors (e.g., plant taxonomy, climate, and soil properties); and (3) litter Mn concentration was more sensitive to environmental conditions and influenced by multiple factors, but mycorrhizal association and soil pH and nitrogen concentration were the most important ones. Overall, our study provides a clear global picture of plant litter Fe, Mn, Zn, and Cu concentrations and their driving factors, which is important for improving our understanding on their biogeochemical cycling along with litter decomposition processes.

Vegetation restoration effects on soil carbon and nutrient concentrations and enzymatic activities in post-mining lands are mediated by mine type, climate, and former soil properties.

Vegetation restoration is a widely used, effective, and sustainable method to improve soil quality in post-mining lands. Here we aimed to assess global patterns and driving factors of potential vegetation restoration effects on soil carbon, nutrients, and enzymatic activities. We synthesized 4838 paired observations extracted from 175 publications to evaluate the effects that vegetation restoration might have on the concentrations of soil carbon, nitrogen, and phosphorus, as well as enzymatic activities. We found that (1) vegetation restoration had consistent positive effects on the concentrations of soil organic carbon, total nitrogen, available nitrogen, ammonia, nitrate, total phosphorus, and available phosphorus on average by 85.4, 70.3, 75.7, 54.6, 58.6, 34.7, and 60.4 %, respectively. Restoration also increased the activities of catalase, alkaline phosphatase, sucrase, and urease by 63.3, 104.8, 125.5, and 124.6 %, respectively; (2) restoration effects did not vary among different vegetation types (i.e., grass, tree, shrub and their combinations) or leaf type (broadleaved, coniferous, and mixed), but were affected by mine type; and (3) latitude, climate, vegetation species richness, restoration year, and initial soil properties are important moderator variables, but their effects varied among different soil variables. Our global scale study shows how vegetation restoration can improve soil quality in post-mining lands by increasing soil carbon, nutrients, and enzymatic activities. This information is crucial to better understand the role of vegetation cover in promoting the ecological restoration of degraded mining lands.

Mycorrhizal association and life form dominantly control plant litter lignocellulose concentration at the global scale.

Lignocellulose is a major component of plant litter and plays a dominant role in regulating the process of litter decomposition, but we lack a global perspective on plant litter initial lignocellulose concentration. Here, we quantitatively assessed the global patterns and drivers of litter initial concentrations of lignin, cellulose, and hemicellulose using a dataset consisting of 6,021 observations collected from 795 independent publications. We found that (1) globally, the median concentrations of leaf litter lignin, cellulose, and hemicellulose were 20.3, 22.4, and 15.0% of litter mass, respectively; and (2) litter initial concentrations of lignin, cellulose, and hemicellulose were regulated by phylogeny, plant functional type, climate, and soil properties, with mycorrhizal association and lifeform the dominant predictors. These results clearly highlighted the importance of mycorrhizal association and lifeform in controlling litter initial lignocellulose concentration at the global scale, which will help us to better understand and predict the role of lignocellulose in global litter decomposition models.

Effects of short-term grazing prohibition on soil physical and chemical properties of meadows in Southwest China.

BACKGROUND: Grassland plays an important role in the ecosystem, but overgrazing harms the grassland system in many places. Grazing prohibition is an effective method to restore grassland ecosystems, and it plays a great role in realizing the sustainable development of grassland systems. Therefore, it is necessary to carry out research on the influence of regional grazing prohibition on the physical and chemical properties of different grassland systems. METHODS: In Potatso National Park, Southwest China, we selected experimental plots in the artificial grazing meadow area to study the effects of grazing prohibition on plant and soil indexes in subalpine meadows and swamp meadows. We investigated the biomass and species diversity of grazing prohibition treatment and grazing treatment plots and sampled and tested the soil index. The variation percentage was used to remove the original heterogeneity and yearly variation, allowing us to compare differences in plant index and soil index values between grazing prohibition and grazing treatments. RESULTS: Grazing prohibition increased the aboveground biomass, total biomass, total meadow coverage, average height, richness index, Shannon diversity index and evenness index and reduced the belowground biomass and root/shoot ratio in the subalpine meadow and swamp meadow. Additionally, grazing prohibition reduced the pH and soil bulk density and increased the soil total carbon, soil organic carbon, soil total nitrogen, soil hydrolyzable nitrogen, soil total phosphorus and soil available phosphorus in the subalpine meadow and swamp meadow. Nonmetric multidimensional scaling (NMDS) analysis showed that both plant indexes and soil indexes were significantly different between grazing and grazing prohibition treatments and between meadow types. Short-term grazing prohibition had a great impact on improving the fertility of meadow soil in the study area. We suggest that long-term and extensive research should be carried out to promote the restoration and sustainable development of regional grassland systems.

Soil warming increases soil temperature sensitivity in subtropical Forests of SW China.

BACKGROUND: Soil respiration (R S ) plays an important role in the concentration of atmospheric CO2 and thus in global climate patterns. Due to the feedback between R S and climate, it is important to investigate R S responses to climate warming. METHODS: A soil warming experiment was conducted to explore R S responses and temperature sensitivity (Q 10) to climate warming in subtropical forests in Southwestern China, and infrared radiators were used to simulate climate warming. RESULTS: Warming treatment increased the soil temperature and R S value by 1.4 °C and 7.3%, respectively, and decreased the soil water level by 4.2% (%/%). Both one- and two-factor regressions showed that warming increased the Q 10 values by 89.1% and 67.4%, respectively. The effects of water on Q 10show a parabolic relationship to the soil water sensitivity coefficient. Both R S and Q 10 show no acclimation to climate warming, suggesting that global warming will accelerate soil carbon release.