Long-term Succession Research Articles

Nutrient limitation of litter decomposition with long-term secondary succession: evidence from controlled laboratory experiments

Understanding ecosystem processes such as litter decomposition in response to dramatic land-use change is critical for modeling and predicting carbon (C) cycles. However, the patterns of litter decomposition along with long-term secondary succession (over 100 years) are not well reported, especially concerning nutrient limitations on litter decomposition. To clarify the response of litter decomposition to changes in soil nutrient availability, we conducted four incubation experiments involving soil and litter and nutrient addition from different successional stages and investigated the changes in microbial respiration and litter mass loss. Our results revealed that microbial respiration increased with succession without any litter addition (1.19~1.73 mg C g−1 soil), and litter addition significantly promoted microbial respiration (16.5~72.9%), especially in the early successional stage (grassland and shrubland). The decomposition rate of the same litter decreased with succession. In addition, nitrogen (N) and phosphorus (P) addition showed significant effects on litter decomposition and microbial respiration; P addition promoted litter decomposition (2.4~15.3%) and microbial respiration (10.1~34.5%) in all successional stages, while N addition promoted litter decomposition (4.0~10.3%) and microbial respiration (5.4~27.2%) in all except the last stage of succession, which showed a negative effect on litter decomposition (− 7.5%) and microbial respiration (− 6.1%), indicating possible N saturation of litter decomposition and microbial respiration. This work highlights that soil nutrient availability and successional stages need to be taken into account to predict the changes to litter decomposition in response to global changes.

Dynamics of soil microbial metabolic activity during grassland succession after farmland abandonment

Secondary succession has a major influence on vegetation and soil biogeochemical processes, however, the dynamics of microbial metabolic activity and the driving factors during grassland succession after farmland abandonment remain unclear. Therefore, we examined variations in microbial biomass carbon (Cmic), soil basal respiration (BR), microbial quotient (Cmic:Corg), and metabolic quotient (qCO2) in sloping farmlands that had been abandoned for 0, 3, 8, 13, 18, 23 and 30 years on the Loess Plateau in China. Moreover, the plant, soil and microbial properties were determined to reveal the forces driving soil microbial metabolic activity. The results showed that compared to those of farmland, the Cmic significantly increased by 104.7% and 168.0%, while the qCO2 significantly decreased by 54.3% and 70.5%, respectively, in the late succession stages (23 and 30 years). Long-term succession (30 years) significantly enhanced the Cmic:Corg by 51.4%. In contrast, except for a decrease at 8 years, the BR changed little during grassland succession following farmland abandonment. These changes in microbial metabolic activity indicators were associated with shifts in litter biomass, soil organic carbon, available nitrogen, and soil fungi. Litter biomass and fungi were strongly affected the changes in microbial metabolic activity. This study provided new information regarding the dynamics of microbial metabolic activity during long-term secondary succession and enhanced our understanding of the linkages among plant, soil and microorganisms in semiarid ecosystems.

Simulating Variations in Reservoir Eutrophication Level by Reproducing Biogeochemical Cycles

The prediction of qualitative effects of long-term succession of aquatic organism communities with possible responses of the ecosystem to disturbances of the natural homeostasis becomes possible with the structure of the ecosystem taken into account. Among the possible lines of its development, analyzed is the one that maximizes a thermodynamic characteristic—exergy, which reflects how far the ecosystem stands from the state of “dead” matter. The results of calculations by a modified model of biogeochemical cycles in a series of dry years are in agreement with the expert estimates for the development of eutrophication process in the Novosibirsk reservoir in the recent years. A nonmodified model fails to provide such agreement.

Succession of microbial populations and nitrogen-fixation associated with the biodegradation of sediment-oil-agglomerates buried in a Florida sandy beach

The Deepwater Horizon (DWH) oil spill contaminated coastlines from Louisiana to Florida, burying oil up to 70 cm depth in sandy beaches, posing a potential threat to environmental and human health. The dry and nutrient-poor beach sand presents a taxing environment for microbial growth, raising the question how the biodegradation of the buried oil would proceed. Here we report the results of an in-situ experiment that (i) characterized the dominant microbial communities contained in sediment oil agglomerates (SOAs) of DWH oil buried in a North Florida sandy beach, (ii) elucidated the long-term succession of the microbial populations that developed in the SOAs, and (iii) revealed the coupling of SOA degradation to nitrogen fixation. Orders of magnitude higher bacterial abundances in SOAs compared to surrounding sands distinguished SOAs as hotspots of microbial growth. Blooms of bacterial taxa with a demonstrated potential for hydrocarbon degradation (Gammaproteobacteria, Alphaproteobacteria, Actinobacteria) developed in the SOAs, initiating a succession of microbial populations that mirrored the evolution of the petroleum hydrocarbons. Growth of nitrogen-fixing prokaryotes or diazotrophs (Rhizobiales and Frankiales), reflected in increased abundances of nitrogenase genes (nifH), catalyzed biodegradation of the nitrogen-poor petroleum hydrocarbons, emphasizing nitrogen fixation as a central mechanism facilitating the recovery of sandy beaches after oil contamination.

Long-term forest succession improves plant diversity and soil quality but not significantly increase soil microbial diversity: Evidence from the Loess Plateau

Many studies have focused on the processes of vegetation succession, however, the dynamics of soil microbes and the synergy between vegetation and soil are still poorly understood following vegetation succession. This study focused on a forest succession sequence including farmland, grassland, shrubland (i.e., Hippophae rhamnoides), pioneer forest (i.e., Populus davidiana), and climax forest (i.e., Quercus liaotungensis) on the Loess Plateau of China, to explore plant and soil changes, as well as soil microbial community dynamics. The results showed that litter biomass, soil organic carbon (SOC), total nitrogen (TN) and the ratio of SOC to TN exhibited an increasing trend in the whole process of the forest succession, and NH4+, microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), and the ratio of dissolved organic carbon (DOC) to dissolved organic nitrogen (DON) had significantly increased before the shrubland stage, and then they were going to be stable. During the forest succession, the main bacterial phyla present were Proteobacteria, Actinobacteria, and Acidobacteria, and the predominant fungal phyla were Ascomycota and Basidiomycota. The soil microbial community composition was stable and did not change significantly, but the bacteria and fungal communities were associated with specific plant or soil properties. It was proved that the change of soil microbial community was closely related to vegetation and soil community changes. The results suggested that long-term forest succession not only improves plant diversity, but also improves soil biology and quality, even though it does not significantly increase soil microbial diversity. The findings enhance the understanding of the impact of soil microbial ecological characteristics and provide an important guidance for the sustainable management of forest ecosystems following long-term natural vegetation restoration.

The importance of coarse woody debris in dynamic phases exposure in the beech (Fagus orientalis L.) stands of Hyrcanian forests

In a natural forest, phases of different dynamics are gradually replaced to create sustainability in the stands. Coarse woody debris is among the most significant structural elements of natural stands that perform an influential position in the identification of dynamic phases. Therefore, the focus of this study is on dead wood conditioning as one of the major structural components in determining the various dynamic phases in the northern forests of Iran as part of the temperate forests. For this study, compartment 326 of Gorazbon District was considered as one of the control parcels of Kheyroud Forest. In this parcel, 25 one-hectare sample plots were selected as permanent plots for a long-term forest structure and succession studies. The coarse woody debris by 100% sampling method was measured. The results showed that there are 8 main phases in this area (gap formation, understorey initiation, stem exclusion, volume accumulation, volume degradation, multiple, lighting, old-growth). The extensive forest area (52%) is located in the understorey initiation and stem exclusion phases. The results also showed that the total average volume of snags and logs was 41.5 m<sup>3</sup>·ha<sup>–1</sup>. Furthermore, the mean dead wood volume in decay classes 1, 2, 3 and 4 was 10.33, 12.22, 9.15 and 83.9 m<sup>3</sup>·ha<sup>–1</sup>, respectively. The average frequency of dead trees in the diameter classes smaller than 25 cm, 25–50 cm and in the diameter class more than 50 cm is 25.79, 6.93, and 4.88. The significance analysis results obtained by ANOVA test showed that there is a significant difference between volume, snag and log stock and the shape of dead wood in various dynamic phases. Therefore, in general, dead wood in the forest differs according to habitat, evolutionary stage (dynamic phases), standing volume and species diversity of the tree species.

Roles of fishing and climate change in long-term fish species succession and population dynamics in the outer Beibu Gulf, South China Sea

A prevailing, controversial hypothesis is that fishing pressure has played a greater role than climatic and environmental drivers, in changing fish species succession and biomass fluctuation in the South China Sea (SCS). Based on otter trawl survey data from 1959 to 2010 in the outer Beibu Gulf (OBG), northern SCS, large seasonal and interannual variation is reported for fish species composition, the proportional abundances of dominant taxa, and fish biomass. Generalized additive models are developed to quantify relationships between fish biomass and the external factors of fishing pressure and climate change. Fishing pressure proved to be the main driver of sharp declines in demersal fish stocks, with high-value species being replaced by low-value ones over time. Abrupt decreases in fish biomass during the years of 1993 and 1998 correspond to El Nino events, with climate change possibly the main driver of proportional representation of pelagic species in fisheries trawl catch. The need to differentiate impacts of fishing and environmental drivers on fish species with different life history strategies is stressed to better understand fish community dynamics.

Need for a global map of forest naturalness for a sustainable future.

There is a growing need to assess and monitor forest cover and its conservation status over global scales to determine human impact on ecosystems and to develop sustainability plans. Recent approaches to measure regional and global forest status and dynamics are based on remotely sensed estimates of tree cover. We argue that tree cover should not be used to assess the area of forest ecosystems because tree cover is an undefined subset of forest cover. For example, tree cover can indicate a positive trend even in the presence of deforestation, as in the case of plantations. We believe a global map of forest naturalness that accounts for the bio-ecological integrity of forest ecosystems, for example, intact forests, old-growth forest patches, rewilding forests (exploited forest landscapes undergoing long-term natural succession), and managed forests is needed for global forest assessment.

Different Stages of Aquatic Vegetation Succession Driven by Environmental Disturbance in the Last 38 Years

In recent years, investigating the trend of aquatic plant diversity in response to different disturbance events has received increasing interest. However, there is limited knowledge of the different stages of aquatic vegetation succession over a long period in eutrophic lakes. In this study, we analyzed aquatic plant species richness and its relation to the physical and chemical characteristics of water in Chenghai Lake for the period of 1980–2018. This study shows that the richness and distribution of aquatic vegetation in Chenghai Lake are related to chlorophyll-a concentration, dissolved nutrients, base cations, and micronutrients. The results show that the long-term succession of aquatic plants in this lake classified in different stages: (I) A peak in species richness occurred at an intermediate stage that lasted from 1980 to 1992, and this was caused by more aquatic species being able to coexist since the competition for resources was lower; (II) after 26 years of secondary succession (1992–2018), the diversity and distribution area of aquatic plants gradually declined because pioneer species or human activities may have altered habitat conditions to render habitats less beneficial to pioneer species and more suitable for new aquatic plant species. Thus, species diversity and growth performance of aquatic plants in their communities may be useful indicators of Chenghai Lake’s trophic status, especially during the transition period from a mesotrophic lake to a eutrophic one.

Higher temporal turnover of soil fungi than bacteria during long-term secondary succession in a semiarid abandoned farmland

Microorganisms play critical roles in soil biogeochemical processes and the establishment of vegetation communities. However, their long-term successional patterns and associations with environmental factors are not well understood, especially in semiarid areas where plant community composition and species diversity change rapidly. We investigated changes in soil (Cambisol) microbial communities across a chronosequence of abandoned farmland comprising six successional stages (0, 11, 35, 60, 100, and 150-years) in the semiarid Loess Plateau of China. We aimed to reveal the long-term patterns and succession rates of microbial communities, and to reveal the driving forces. Bacterial and fungal communities were characterized by sequencing bacterial 16S ribosomal RNA genes and fungal internal transcribed spacers (ITS), respectively. Temporal turnover of microbial succession was investigated using the slope (w value) of linear regression of log-transformed microbial community similarity over time. Succession rate of fungi was approximately three times higher (w = 0.1477, P < 0.0001) than that of bacteria (w = 0.0549, P < 0.0001). Bacterial succession was affected by changes in soil NH4+-N, total N, organic C, water content, bulk density, and pH, whereas fungi were more susceptible to changes in NO3−-N, available phosphorus, and C:N ratio. Bacterial communities transitioned from slow-growing oligotrophic groups (Gemmatimonadetes, Chloroflexi) to fast-growing copiotrophic groups (Alpha- and Betaproteobacteria). Basidiomycota showed the highest temporal turnover (w = 0.2000, P < 0.0001), followed by Armatimonadetes, Firmicutes, Verrucomicrobia, Chloroflexi, and Proteobacteria. These results provide new insights into microbial community dynamics during long-term secondary succession, and enhance our understanding of associations between soil factors and microbes in semiarid ecosystems.

Long-term insect successional patterns on pig carcasses in central Spain

Baseline data on the insect successional patterns on carcasses can be a valuable estimation tool in the investigations of suspicious deaths, particularly when the post-mortem interval is longer than months or years. However, although carrion insect succession is a recurrent topic in forensic science research, the duration of the published studies is typically shorter than 1year, with only one published study from central Europe documenting successional patterns beyond the first year of decomposition. We provide here the first data on the long-term insect successional patterns in southern Europe, using pig carcasses exposed in the four seasons of the year and documenting the carrion entomofauna during the second and third year of decomposition. Our results confirmed previous observations from central Europe that several Coleoptera species are able to recolonize cadavers during the second and third year after death, with their larvae residing on the remains for long periods. The season of cadaver exposure appears to be a main factor determining the composition of the insect fauna that exploits the remains during subsequent years. Our results suggest that it might be possible to estimate the year and season of death analyzing the composition of the insect fauna occurring on a cadaver. The present data highlight the need for further studies on the long-term insect succession on cadavers in different seasons and geographical areas, in order to fully understand its patterns and ensure its proper application in PMI estimations.

Soil Abiotic Properties and Plant Functional Traits Mediate Associations Between Soil Microbial and Plant Communities During a Secondary Forest Succession on the Loess Plateau.

In the context of secondary forest succession, aboveground-belowground interactions are known to affect the dynamics and functional structure of plant communities. However, the links between soil microbial communities, soil abiotic properties, plant functional traits in the case of semi-arid and arid ecosystems, are unclear. In this study, we investigated the changes in soil microbial species diversity and community composition, and the corresponding effects of soil abiotic properties and plant functional traits, during a ≥150-year secondary forest succession on the Loess Plateau, which represents a typical semi-arid ecosystem in China. Plant community fragments were assigned to six successional stages: 1–4, 4–8, 8–15, 15–50, 50–100, and 100–150 years after abandonment. Bacterial and fungal communities were analyzed by high-throughput sequencing of the V4 hypervariable region of the 16S rRNA gene and the internal transcribed spacer (ITS2) region of the rRNA operon, respectively. A multivariate variation-partitioning approach was used to estimate the contributions of soil properties and plant traits to the observed microbial community composition. We found considerable differences in bacterial and fungal community compositions between the early (S1–S3) and later (S4–S6) successional stages. In total, 18 and 12 unique families were, respectively, obtained for bacteria and fungi, as indicators of microbial community succession across the six stages. Bacterial alpha diversity was positively correlated with plant species alpha diversity, while fungal diversity was negatively correlated with plant species diversity. Certain fungal and bacterial taxa appeared to be associated with the occurrence of dominant plant species at different successional stages. Soil properties (pH, total N, total C, NH4-N, NO3-N, and PO4-P concentrations) and plant traits explained 63.80% and 56.68% of total variance in bacterial and fungal community compositions, respectively. These results indicate that soil microbial communities are coupled with plant communities via the mediation of microbial species diversity and community composition over a long-term secondary forest succession in the semi-arid ecosystem. The bacterial and fungal communities show distinct patterns in response to plant community succession, according to both soil abiotic properties and plant functional traits.

Long-term succession of closed boreal forests at their range limit in eastern North America shows resilience to fire and climate disturbances

The distribution of vegetation zones in northeastern North America forms a gradual transition from closed to open forests, and to tundra. Closed forests near the open forest/tundra boundary generally correspond to residual patches of a once larger forest community. Whether these forest patches have survived as untouched, fire-free communities or as resilient communities during the Holocene remains unknown. To answer to this question, we reconstructed the successional history of two black spruce closed-crown forests and one jack pine forest near the northern limit of closed forest ecosystems. Stand-scale postfire succession was analysed based on charcoal macrofossils. Extensive 14C dating and botanical identification of charcoal fragments located at the organic soil surface and buried in the mineral podzolic solum were used to reconstruct the successional pathways of the sites. The forest sites developed in a context of continuous fire disturbance, except for a short interval of several centuries. The fire history of the three sites is similar with a fire frequency of 34–37 fires over the last 5000–5800 years, which corresponds to a mean fire interval of 150–180 years. Based on parametric and non-parametric estimators, the regional fire regime of the Laforge area (combined fire data of two sites located about 7 km from each other) was most likely characterized by 38 fires over the last 5000–5800 years, i.e., at an interval of about 150–160 years. Birch (Betula papyrifera) was present in the spruce sites between 5800 and 3000 cal. years BP. Jack pine arrived at the pine site about 3000 cal. years BP, at the time when birch was extirpated from the spruce forests. The closed-crown forests near the open forest/tundra boundary are resilient postfire ecosystems which regenerated successfully since mid-Holocene. Compositional change of these forests, which led to the decline of birch but maintained the dominance of conifers, appears related to cooler and wetter conditions of late Holocene. Climatic conditions also slowed the eastward migration of jack pine, which explains the late arrival of this species at its northeastern range. Our data suggest that fire disturbance in these sites of the boreal biome has been a continuous and positive regenerative process since mid-Holocene despite the influence of climatic change on the tree flora.

Soil particle composition, fractal dimension and their effects on soil properties following sand-binding revegetation within straw checkerboard in Tengger Desert, China

This study aims to elucidate the effects of soil particle composition and fractal dimension on soil physical and chemical properties following sand-binding revegetation within straw checkerboard in south-eastern Tengger Desert. Three afforested plantations in the year of 2016 (i.e., 1 year), 2013 (i.e., 4 years) and 1987 (i.e., 30 years) were selected as study sites, with the adjacent mobile sand land as control (CK). We measured soil particle composition, soil fractal dimension, and the changes of soil physical and chemical properties. The relationship between soil particle composition, soil fractal dimension, and soil properties was analyzed. The results showed that contents of soil particle with the size of both 100-250 μm and 250-500 μm were greater than that of 50-100 μm, ranging from 42.5% to 80.1% and from 12.5% to 42.2% relative to that ranging from 0.2% to 20.8%. Contents of soil particle with the size of <2 μm and 2-50 μm were remarka-bly lower than that of 100-250 μm, 250-500 μm and 50-100 μm, ranging from 0 to 1.3% and from 0 to 22.7%, respectively. However, contents of soil particle at the size of 500-1000 μm was the lowest occupying <0.3% of soil particle composition. Soil particle with the size of <2 μm and 2-50 μm were found in the 30-year sites only. Soil particle distribution at the size of 50-100 μm, 100-250 μm, and 250-500 μm followed the order of 30 a>1 a>4 a＞CK, 4 a>1 a>CK>30 a, and CK>1 a>4 a> 30a, respectively. Soil particle with the size of 500-1000 μm occupied little of soil particle composition, with no significant difference between each site. The fractal dimension of soil particles ranged from 0.54 to 2.59. There was significantly greater soil fractal dimension in 30 a in comparison to 4 a, 1 a and CK, with the intermediate values in 4 a and 1 a, and the lowest values in CK. There was a significantly positive correlation of fractal dimension of soil particles with soil particle content of clay, silt, very fine sand, and a significantly negative correlation of fractal dimension of soil particles with soil particle content of medium sand. Fractal dimension of soil particles was positively correlated with soil electrical conductivity, organic carbon, total nitrogen, and carbon-nitrogen ratio, but with no correlation with soil pH and soil water content. Soil particle content at the size of <2 μm, 2-50 μm, and 50-100 μm had a significant positive correlation with soil electrical conductivity, organic carbon, total nitrogen, and carbon-nitrogen ratio, whereas soil particle content at the size of 250-500 μm had a negative correlation with the former four soil indices and soil water content. In addition, there was a significant negative correlation of soil particle content at the size of 500-1000 μm with soil water content. It was concluded that the sand-binding reve-getation within straw checkerboard in Tengger Desert could facilitate the fine soil particles by ameli-orating stressful soil conditions. Long-term succession of revegetation on mobile sand land could enhance soil clay and silt content as well as soil fractal dimension, thus be beneficial for the improvement of soil physical and chemical properties and desertification control.

Taxonomic relatedness and environmental pressure synergistically drive the primary succession of biofilm microbial communities in reclaimed wastewater distribution systems

Compared to drinking water, the higher bacterial abundance, diversity, and organic matter concentration in reclaimed wastewater suggest that it is more likely to form biofilms. Nevertheless, little is known regarding many important aspects of the biofilm ecology in reclaimed wastewater distribution systems (RWDS), such as the long-term microbial community succession and the underlying driving factors. In the present study, by sampling and analysing microbial compositions of pipe wall biofilms from six frequently used pipe materials under NaClOdisinfection (sodium hypochlorite-treated), NONdisinfection (without disinfection), and UVdisinfection (UV-treated) treatments over one year, it was found that the succession of microbial community structure followed a primary succession pattern. This primary succession pattern was reflected as increases in live cell number and α-diversity, along with metagenic succession in taxonomic composition. Proteobacteria, Nitrospirae, Bacteroidetes, Acidobacteria, Planctomycetes, Actinobacteria, and Verrucomicrobia comprised the dominant phyla in biofilm samples. Compared to biofilms in the NaClOdisinfection reactor, the bacterial communities of biofilms in NONdisinfection and UVdisinfection reactors were distributed more evenly among different bacterial phyla. Principal component analysis revealed a clear temporal pattern of microbial community structures in six kinds of pipe wall biofilms albeit a difference in microbial community structures among the three reactors. Adonis testing indicated that the microbial community composition variation caused by disinfection methods (R2 = 0.283, P < 0.01) was more pronounced than that from the time variable (R2 = 0.070, P < 0.01) and pipe material (R2 = 0.057, P < 0.01). Significantly positive correlation between average local abundance and occupancy was observed in biofilm communities of the three reactors, suggesting that the ‘core-satellite’ model could be applied to identify biofilm-preferential species under specific disinfection conditions in RWDS. The prevalence of family Sphingomonadaceae, known to show chlorine tolerance and powerful biofilm-forming ability in NaClOdisinfection reactors, evidenced the habitat filtering consequent to environment pressure. Correlation-based network analysis revealed that taxonomic relatedness such as similar niches, cooperation, taxa overdispersion, and competition all functioned toward driving the bacterial assembly succession in RWDS.

Generation effects? Evolution of independence–unification views in Taiwan, 1996–2016

The landslide victory of the Democratic Progressive Party in Taiwan's 2016 presidential and legislative elections is often interpreted as a persistent swing in attitudes toward cross-strait relations and Taiwan independence. Popular as this interpretation may be, it still runs the risk of mistaking a short-term reaction to a lame duck president's policy performance for a long-term change in attitudes.This study analyzes the evolution of independence–unification (IU) views in the Taiwan population from 1996 to 2016. After reviewing the literature on political generations in Taiwan, I hypothesize that a long-term cohort succession replacing older prounification generations accounted for the evolution toward proindependence views. By pooling six independent face-to-face surveys into repeated cross-sectional data, this study applies a comprehensive multilevel cross-classified random-effect model of age–period–cohort analysis. Markov chain Monte Carlo estimation results confirm that, besides age and period effects, younger cohorts and the 1999 Taiwan-centered high school curriculum have had significant effects on the change in trends in IU views.

Succession of soil macro-faunal biodiversity in forests converted from croplands after long-term coastal reclamation

The long-term succession of the soil macro-faunal community after reclamation at coastal areas is not well understood, especially at the time scale of centuries. The objective of this work was to analyze soil development by measuring its principal physico-chemical properties and study the macro-faunal biodiversity succession along the successional trajectory created by intermittent reclamation. We hypothesized that soil macro-faunal taxonomic and functional diversity, richness, and density would increase after long-term reclamation, and that macro-faunal succession was related to dike age. In July 2014, sites of varying dike age (30, 50, 100, and 200 years) were used to represent a successional trajectory of Fluvisol soils at a reclaimed coast at Yancheng, China. The selected habitats were planted with 14–17 years old poplar (Populus euramericana) or dawn redwood (Metasequoia glyptostroboides) trees. With increasing dike age, soil nutrient status improved over the successional trajectory, as indicated by the increased soil organic carbon (SOC) concentration, total nitrogen (TN), and total phosphorous (TP). Soil salt concentration (SSC), pH, and carbon-nitrogen (C/N) ratio continuously decreased, as did soil bulk density (BD), the latter of which had a smaller coefficient of variation than the other properties did. Over the first 100 years of macro-faunal succession, taxonomic richness, abundance, Margalef’s richness index, and the Shannon-Weaver diversity index increased significantly, but did not differ significantly between the habitats with dike ages of 100 and 200 years. Significant differences in the measured communities’ characters were detected between forests planted with different trees when the dike age was 50 years but not when it was 30 years. Differences in macro-faunal community structure were primarily related to SOC and SSC, which were considerably related to dike age. The taxonomic richness and abundance of functional groups varied significantly among habitats and was related to changes in food resources in the soil environment. The abundance and taxonomic richness of phytophagous and saprophagous species increased with increasing dike age; no significant differences were noted in taxonomic richness of omnivorous species and predator abundance. The results thus supported our hypotheses. In conclusion, long-term macro-faunal community succession was affected by dike age, land use, and soil development after reclamation, and the soil macro-faunal biodiversity tended to increase with increasing dike age.

Long-term succession in a coal seam microbiome during in situ biostimulation of coalbed-methane generation

Despite the significance of biogenic methane generation in coal beds, there has never been a systematic long-term evaluation of the ecological response to biostimulation for enhanced methanogenesis in situ. Biostimulation tests in a gas-free coal seam were analysed over 1.5 years encompassing methane production, cell abundance, planktonic and surface associated community composition and chemical parameters of the coal formation water. Evidence is presented that sulfate reducing bacteria are energy limited whilst methanogenic archaea are nutrient limited. Methane production was highest in a nutrient amended well after an oxic preincubation phase to enhance coal biofragmentation (calcium peroxide amendment). Compound-specific isotope analyses indicated the predominance of acetoclastic methanogenesis. Acetoclastic methanogenic archaea of the Methanosaeta and Methanosarcina genera increased with methane concentration. Acetate was the main precursor for methanogenesis, however more acetate was consumed than methane produced in an acetate amended well. DNA stable isotope probing showed incorporation of 13C-labelled acetate into methanogenic archaea, Geobacter species and sulfate reducing bacteria. Community characterisation of coal surfaces confirmed that methanogenic archaea make up a substantial proportion of coal associated biofilm communities. Ultimately, methane production from a gas-free subbituminous coal seam was stimulated despite high concentrations of sulfate and sulfate-reducing bacteria in the coal formation water. These findings provide a new conceptual framework for understanding the coal reservoir biosphere.

Secrets to success: human capital management strategy

PurposeThe purpose of this paper is to detail four elements that drive human capital management (HCM) strategies that get business results.Design/methodology/approachAnalysis of APQC’s Open Standards Benchmarking® data and human capital management best practices case studies reveals how to establish the groundwork and successfully execute an HCM strategy.FindingsA successful HCM strategy requires specific groundwork and execution to support workforce performance. In terms of groundwork, HR must display strategic competence and business insight. Then, HR must establish a solid implementation infrastructure and follow-up with a comprehensive results assessment.Originality/valueMany HR professionals understand what needs to go into an HCM plan for compensation and benefits, long-term workforce strategy, succession, diversity, learning, retention and HR technology updates and upgrades. This paper details how best-practice organizations successfully build and implement such plans and what tangible results an HR function can expect from adopting the four detailed best practices.

Changes of soil carbon in five land use stages following 10 years of vegetation succession on the Loess Plateau, China

Changes in land use caused by natural vegetation succession can enhance the soil organic carbon (SOC) and carbon (C) stock of terrestrial ecosystems, as reported in many studies throughout the world. However, the dynamics of SOC and soil C stocks and their changes in each succession stage are not clearly following restoration age. Additionally, whether litter and fine roots have positive effects on SOC and soil C sequestration is unclear. We simultaneously studied litter and fine root production and SOC and C stocks along a natural vegetation succession – abandoned farmland, grassland, shrubland, pioneer woodland to natural climax forest – in 2005 and 2015 on the Loess Plateau of China. This allowed a better understanding of the variations of SOC and soil C stock in different land use stages in relation to soil layers and effects of litter and fine roots following vegetation restoration. The land use stages and soil layers significantly affected the rates of SOC and soil C sequestration change. The SOC and soil C stocks in the 0–60 cm soil profile rapidly increased over the course of the long-term natural vegetation succession. During 2005 to 2015, the topsoils (0–20 and 20–40 cm) had higher rates of SOC change (from 0.06 to 0.55 and from 0.23 to 0.51 g kg−1 yr−1, respectively) and soil C sequestration rates (from 0.37 to 1.09 and from 0.40 to 1.16 Mg ha−1 yr−1, respectively) than subsoils (40–60 cm, from 0.04 to 0.36 and from 0.05 to 1.16 Mg ha−1 yr−1). The litter and fine root production increased with age of the natural vegetation succession, and had significant positive effects on changes in SOC and soil C sequestration. Therefore, long-term natural vegetation restoration improved the SOC accumulation, and increased litter and fine root inputs were probably the main factors contributing to soil C sequestration.