Soil organic matter,nutrient distribution,fungal and microbial biomass and enzyme activities in a forest beech stand on the Apennines of southern Italy

The aim of this study was to analyse the amount and qualitative characteristics of organic matter (OM) in the litter horizon (considering leaf litter at different decomposition stages) and underlying soil to a 30-cm depth in a beech stand on the Apennines in southern Italy. Distribution of major nutrients as well as fungal and microbial biomass were also evaluated, in addition to beech leaf nutrient content monitor from full expansion to abscission in order to estimate annual nutrient input to soil from litterfall and nutrient retranslocation before abscission. OM was significantly higher in leaf litter. C/N ratio and the Na, Mn, Fe levels also decreased along the decomposition continuum, whereas N and S contents slowly decreased with soil depth. Generally, leaf nutrient content was also significantly lower in dead leaves, indicating efficient retranslocation to persistent organs. Fungal biomass was the highest in leaf layers, with no significant changes between spring and autumn samplings. Enzyme activities did not differ significantly along the decomposition continuum but marked decreases were found in the upper soil layer; these remained relatively constant, with the exception of laccase, at deeper soil depths. No seasonal effect on enzyme activities and OM content was found.     

根据孢粉资料确定伏尔加地区弗拉阶和法门阶界线

俄罗斯伏尔加格勒伏尔加地区上泥盆统弗拉阶和法门阶的界线以3种剖面类型为代表。第一种类型的界线剖面广泛分布于俄罗斯地台,但两阶之间有沉积间断。第二种类型剖面地层发育较完整,即Volgogradian层直覆于Livendian层之上。前者以Corbulispora viminea-Geminospora vasjamica孢子组合带为特征。第三种类型剖面存在于前里海(Pre-Caspian)凹陷的西侧,是最近根据孢粉资料确定的;地层剖面不完整,在中弗拉阶的Semilukian层有剥蚀面,上覆以不同时代的(弗拉期或法门期)盖层。     

Water use by woody plants on contrasting soils in a savanna parkland: assessment with δ2H and δ18O

In savanna parklands of southern Texas, patches of grassland and discrete clusters of small trees and shrubs occur on sandy loam surface soils underlain by an argillic horizon (claypan) at 40 cm. Large trees and shrubs in groves occur on deep (2 m) sandy loam soils without an argillic horizon. 2H and 18O of rainfall, groundwater, and soil and plant water were measured to: (1) determine if coexistence in woody patches occurs via vertical stratification of soil water uptake; (2) document differences in plant water acquisition on contrasting soil types; and (3) evaluate recharge and evaporative losses of soil moisture from grassland vs. wooded landscape elements. Groundwater was isotopically similar to weighted rainfall, suggesting local recharge at this site. Linear regressions of soil water 2H on 18O yielded slopes less than the meteoric water line, indicating significant evaporative losses of soil moisture in all landscape elements. Interspecific differences in root density distribution were significant; some woody species had roots well below 1.6 m, while others had few roots below 0.8 m. 2H and 18O values of stem water from all plants in groves were lower than those of soil water in the upper 1.5 m of the profile, suggesting all species obtained their water from depths >1.5 m. Deep roots of trees and shrubs at this savanna parkland site thus appeared to have a functional significance that was not revealed by biomass or density determinations. Root densities of species in discrete clusters (claypan present) were typically greater than those of the same species in groves (claypan absent), especially in the upper 80 cm of the soil profile. Consistent with rooting profiles, 2H and 18O values of plant water indicated that trees and shrubs in discrete clusters with fine- textured subsoils obtained most of their water at depths <1.5 m. As with groves, there was no indication of water resource partitioning between species. In summary, we saw no isotopic evidence that co- occurring woody plants at this savanna parkland site were partitioning soil moisture vertically during late summer/early fall, despite marked differences in their root density distributions. This supports other lines of evidence which indicate that species interactions in tree/shrub clumps are competitive, and that species composition is therefore unstable in those landscape elements.     

A horizon scanning assessment of current and potential future threats to migratory shorebirds

We review the conservation issues facing migratory shorebird populations that breed in temperate regions and use wetlands in the non‐breeding season. Shorebirds are excellent model organisms for understanding ecological, behavioural and evolutionary processes and are often used as indicators of wetland health. A global team of experienced shorebird researchers identified 45 issues facing these shorebird populations, and divided them into three categories (natural, current anthropogenic and future issues). The natural issues included megatsunamis, volcanoes and regional climate changes, while current anthropogenic threats encompassed agricultural intensification, conversion of tidal flats and coastal wetlands by human infrastructure developments and eutrophication of coastal systems. Possible future threats to shorebirds include microplastics, new means of recreation and infectious diseases. We suggest that this review process be broadened to other taxa to aid the identification and ranking of current and future conservation actions.     

Limit values for plant litter decomposing in two contrasting soils—influence of litter elemental composition

The decomposition dynamics of four types of needle litter and three types of leaf litter were followed for 3 years at two very contrasting coniferous forest systems, a nutrient-rich silver fir (Abies alba Mill.) forest in south Italy (Monte Taburno) and a nutrient-poor Scots pine (Pinus sylvestris L.) forest in central Sweden (Jädraås). Decomposition of the same litter type at the two sites did not differ in the early stages but proceeded further at the nutrient-rich forest site than at the nutrient-poor one. Limit values for decomposition were calculated and the differences for the same litter type between the two contrasting coniferous systems were investigated. At both sites six of the seven litter types gave significant (asymptotic) limit values for decomposition, which varied with litter type. For four litter types out of six the limit values differed significantly between the two sites and were always higher at the nutrient-rich site (Monte Taburno). Using all available data for litters incubated at the two sites revealed that at the nutrient-poor site (Jädraås) there was a significant negative relationship between litter N levels and limit values and there was also a significant negative relationship between initial concentrations of heavy metals (e.g. Zn, Cd, Cu) and limit values. In contrast, at the site Monte Taburno, rich in nutrients and in heavy metals, there was no such relationship.     

Soil Profile Arsenic Concentration Distributions in Missouri Soils Having Cambic and Argillic Soil Horizons

Understanding of the pedogenic pathways associated with arsenic (As) transformations in soil is important to understanding arsenic soil chemistry and discriminating between natural background and anthropogenic arsenic (As). Twenty-one soil series, some with multiple pedons, were assessed to determine if the As distributions in soil profiles exhibit discrete maxima that correspond to the presence of agrillic horizons. The majority of pedons exhibiting argillic horizon expression show a Fe-oxyhydroxide and As maxima corresponding precisely with the argillic horizon. Pearson correlation coefficients verify the close correspondence of Fe and As. Soil profiles having cambic horizons, and lacking argillic horizons, may also show As and Fe accumulations at soil depths. Some coarse-textured, well-drained to moderately well-drained Entisols and Inceptisols have Fe-oxyhydroxide accumulation in their cambic horizons, promoting As accumulation. Conversely, silty-textured and poorly drained to somewhat poorly drained Entisols and Inceptisols have C and Cg horizons that show somewhat uniform Fe and As concentrations throughout their soil profiles. Analysis of selected pedons having well-drained to moderately well-drained soil profiles demonstrates that clay fraction Fe and As concentrations are closely correlated and that the As and Fe concentrations are greater than those from the corresponding whole soil. The somewhat poorly drained Crowley pedon exhibited cohesive masses of Fe and Mn accumulation (sand separate) that had greater arsenic concentrations than those of the clay and silt separates. These pedogenic nodules with enhanced arsenic concentrations reveal alternative pathways involving arsenic transformation.     

Biogeochemical controls on aluminum chemistry in the O horizon of a red spruce (Picea rubens Sarg.) stand in central Maine,USA

This study examined the biotic and abiotic processes controlling solution chemistry and cycling of aluminum (Al) in the organic horizons of a northern coniferous forest ecosystem. A mass balance budget indicated that aboveground inputs of Al to the O horizon averaged 0.9 kg ha^–1 1 yr^–1, with major inputs accounted for by litterfall (69%), followed by precipitation (21%), and net canopy throughfall plus stemflow (10%). Estimated leaching losses of Al from the O horizon averaged 2.1 kg Al ha^-1 yr1. We hypothesize that the difference between measured Al inputs and outputs can be accounted for by Al release from weathering of soil minerals admixed into the O horizon. Variations in O horizon solution Al chemistry were influenced by a number of factors, including pH, Al equilibria with different solid-phase organic exchange sites, and Al complexation with humic ligands in soil solution.