Effect of Altitude Gradients on the Spatial Distribution Mechanism of Soil Bacteria in Temperate Deciduous Broad-Leaved Forests.

Soil bacteria are an important part of the forest ecosystem, and they play a crucial role in driving energy flow and material circulation. Currently, many uncertainties remain about how the composition and distribution patterns of bacterial communities change along altitude gradients, especially in forest ecosystems with strong altitude gradients in climate, vegetation, and soil properties. Based on dynamic site monitoring of the Baiyun Mountain Forest National Park (33°38'-33°42' N, 111°47'-111°51' E), this study used Illumina technology to sequence 120 soil samples at the site and explored the spatial distribution mechanisms and ecological processes of soil bacteria under different altitude gradients. Our results showed that the composition of soil bacterial communities varied significantly between different altitude gradients, affecting soil bacterial community building by influencing the balance between deterministic and stochastic processes; in addition, bacterial communities exhibited broader ecological niche widths and a greater degree of stochasticity under low-altitude conditions, implying that, at lower altitudes, community assembly is predominantly influenced by stochastic processes. Light was the dominant environmental factor that influenced variation in the entire bacterial community as well as other taxa across different altitude gradients. Moreover, changes in the altitude gradient could cause significant differences in the diversity and community composition of bacterial taxa. Our study revealed significant differences in bacterial community composition in the soil under different altitude gradients. The bacterial communities at low elevation gradients were mainly controlled by stochasticity processes, and bacterial community assembly was strongly influenced by deterministic processes at middle altitudes. Furthermore, light was an important environmental factor that affects differences. This study revealed that the change of altitude gradient had an important effect on the development of the soil bacterial community and provided a theoretical basis for the sustainable development and management of soil bacteria.

Carbon pools in forest systems and new estimation based on an investigation of carbon sequestration.

Forests, the ancient wooden giants, are both symbols of natural beauty and reservoirs of carbon stocks. The current climate crisis has created an urgent need for an in-depth study of forest ecosystems and carbon stocks. Based on forest inventory data from field surveys and four bioclimatic zones [Zone 1 (Z1, humid forest), Zone 2 (Z2, semi-humid forest), Zone 3 (Z3, semi-humid to semi-arid forest-grassland), and Zone 4 (Z4, semi-arid typical grassland)], two methods [Method 1 (M1) and Method 2 (M2)] were used to estimate carbon stocks in forest ecosystems in Shaanxi Province, China, and explored the spatial patterns of carbon pools and potential influences. The total forest ecosystem carbon pool amounted to 520.80 Tg C, of which 53.60% was stored aboveground, 17.16% belowground, and 29.24% in soil (depth of 0-10 cm). Spatially, there were marked north-south gradients in both biomass (Z2 > Z3 > Z1 > Z4) and soil organic carbon densities (Z1 > Z2 > Z3 > Z4). The differences between aboveground and belowground biomass carbon density across broadleaf, needle-leaf, and broadleaf and needle-leaf mixed forest were not pronounced, while soil organic carbon density had the order of broadleaf (18.38 Mg C/ha) > needle-leaf (11.29 Mg C/ha) > broadleaf and needle-leaf mixed forest (10.33 Mg C/ha). Under an ideal scenario that excludes external factors, mainly forest growth, the sequestration potential of forest biomass by 2032 was estimated by M1 as 85.43 Tg, and by M2 to be substantially higher at 176.21 Tg. As of 2062, M1 estimated 155.97 Tg of sequestration potential for forest biomass. The spatial patterns of forest biomass and soil carbon density were closely related to climatic factors, and these relationships allowed the spatial division into two distinct climatic regions. Moreover, biomass carbon density was significantly correlated with the normalized difference vegetation index, soil silt, and elevation. This study provides key information for promoting the strategic shift from light-green to deep-green forest systems in Shannxi Province and updates the estimation methods of forest ecosystems' carbon pools based on field surveys.

Relationship between negative air ion and PM2.5 in Quercus variabilis under natural conditions.

In recent years, PM2.5 pollution has become a most important source of air pollution. Prolonged exposure to high PM2.5 concentrations can give rise to severe health issues. Negative air ion (NAI) is an important indicator for measuring air quality, which is collectively known as the 'air vitamin'. However, the intricate and fluctuating meteorological conditions and vegetation types result in numerous uncertainties in the correlation between PM2.5 and NAI. In this study, we collected data on NAI, PM2.5, and meteorological elements through positioning observation during the period of June to September in 2019 and 2020 under the condition of relatively constant leaf area in Quercus variabilis forest, a typical forest in warm temperate zones. We investigated the spatiotemporal variation of PM2.5 and NAI under consistent meteorological conditions, established the correlation between PM2.5 and NAI, and explicated the impact mechanism of PM2.5 on NAI in natural conditions. The results showed that NAI decreased exponentially with the increases in natural PM2.5, with a significant negative correlation (y=1148.79x-0.123). The decrease rates of NAI in PM2.5 concentrations of 0-20, 20-40, 40-80, 80-100 and 100-120 µg·m-3 were 40.1%, 36.2%, 9.4%, 2.4%, 5.1% and 6.8%, respectively. Results of the sensitivity analysis showed that the PM2.5 concentration range of 0-40 µg·m-3 was the sensitive range that affected NAI. Our findings could provide a scientific basis for better understanding the response mechanisms of NAI to environmental factors.

Nitrogen deposition caused higher increases in plant-derived organic carbon than microbial-derived organic carbon in forest soils.

Plant- and microbial-derived organic carbon, two components of the soil organic carbon (SOC) pool in terrestrial ecosystems, are regulated by increased atmospheric nitrogen (N) deposition. However, the spatial patterns and driving factors of the responses of plant- and microbial-derived SOC to N deposition in forests are not clear, which hinders our understanding of SOC sequestration. In this study, we explored the spatial patterns of plant- and microbial-derived SOC, and their responses to N addition and elucidated their underlying mechanisms in forest soils receiving N addition at four sites with various soil and climate conditions. Plant- and microbial-derived SOC were quantified using lignin phenols and amino sugars, respectively. N addition increased the total microbial residues by 20.5% on average ranging from 9.4% to 34.0% in temperate forests but not in tropical forests, and the increase was mainly derived from fungal residues. Lignin phenols increased more in temperate forests (average of 63.8%) than in tropical forests (average of 15.7%) following N addition. The ratio of total amino sugars to lignin phenols was higher in temperate forests than in tropical forests and decreased with N addition in temperate forests. N addition mainly regulated soil microbial residues by affecting pH, SOC, exchangeable Ca2+, gram-negative bacteria biomass, and the C:N ratio, while it mainly had indirect effects on lignin phenols by altering SOC, soil C:N ratio, and gram-negative bacteria biomass. Overall, our findings suggested that N deposition caused a greater increase in plant-derived SOC than in microbial-derived SOC and that plant-derived SOC would have a more important role in sequestering SOC under increasing N deposition in forest ecosystems, particularly in temperate forests.

Year-round dynamics of arbuscular mycorrhizal fungi communities in the roots and surrounding soils of Cryptomeria japonica.

Arbuscular mycorrhizal fungi (AMF) live simultaneously inside and outside of host plant roots for a functional mycorrhizal symbiosis. Still, the year-round dynamics and relationships between soil properties and AMF communities of trees in forest ecosystems remain unclear. We collected paired root and soil samples of the same Cryptomeria japonica trees at two forest sites (five trees at each site) every 2 months over a year. Total DNA was extracted from roots and soil separately and soil physicochemical properties were measured. With Illumina's next-generation amplicon sequencing targeting the small subunit of fungal ribosomal DNA, we clarified seasonal dynamics of soil properties and AMF communities. Soil pH and total phosphorus showed significant seasonality while total carbon, nitrogen, and C/N did not. Only pH was a good predictor of the composition and dynamics of the AMF community. The total AMF community (roots + soil) showed significant seasonality because of variation from May to September. Root and soil AMF communities were steady year-round, however, with similar species richness but contained significantly different AMF assemblages in any sampling month. Despite the weak seasonality in the communities, the top two dominant OTUs showed significant but different shifts between roots and soils across seasons with strong antagonistic relationships. In conclusion, few dominant AMF taxa are dynamically shifting between the roots and soils of C. japonica to respond to seasonal and phenological variations in their microhabitats. AMF inhabiting forest ecosystems may have high environmental plasticity to sustain a functional symbiosis regardless of seasonal variations that occur in the soil.

Mixed plantations do not necessarily provide higher ecosystem multifunctionality than monoculture plantations.

Forest stand transformation is a crucial strategy for enhancing the productivity and stability of planted forest ecosystems and maximizing their ecosystem functions. However, understanding forest ecosystem multifunctionality responses to various stand transformation methods remains limited. In this study, we assessed ecosystem multifunctionality, encompassing nutrient cycling, carbon stocks, water regulation, decomposition, wood production, and symbiosis, under different stand transformation methods (Chinese fir monoculture, mixed conifer and broad-leaf, broad-leaf mixed, and secondary forests). We also identified key factors contributing to variations in ecosystem multifunctionality. The results showed that Chinese fir plantations were more conducive to carbon stock creation, while broad-leaved mixed plantations excelled in water regulation. Secondary forests exhibited higher ecosystem multifunctionality than other plantation types, with Chinese fir plantations displaying the highest multifunctionality, significantly surpassing mixed coniferous and broad-leaved plantations. Our findings further revealed that soil nutrients and plant diversity have significant impacts on ecosystem multifunctionality. In summary, stand transformation profoundly influences ecosystem multifunctionality, and mixed plantations do not necessarily provide higher ecosystem multifunctionality than monoculture plantations.

Optimizing functional zoning for Dalingshan Forest Park in China through microcosmic human disturbance evaluation.

Human disturbance stands as a prominent factor influencing the ecological environment within natural protected areas. Presently, the issue of balancing human activities and ecological preservation has emerged as a critical concern in the construction of China's natural protected area system. Functional zoning serves as the cornerstone of natural protected area management and represents a pivotal tool in achieving this equilibrium. This study endeavors to introduce a set of functional zoning methods for natural protected areas based on human disturbance assessments. Utilizing Dalingshan Forest Park in Dongguan city which is known for its significant human disturbances as a case study, field surveys were conducted to identify various types of small-scale and understory-hidden human disturbances, such as residential areas, roads, tourist areas, forestry areas, and energy facilities. Subsequently, a microcosmic human disturbance model tailored to forested areas was developed using the analytic hierarchy process. By integrating the findings of macrocosmic human disturbance assessments conducted concurrently by the research group, a functional zoning plan for Dalingshan Forest Park was proposed. The results show that ecological conservation zones within the park should be established in three specific areas, primarily in regions with low-level microcosmic human disturbance (levels 1 and 2) and terrain fluctuations ≥110 m. In contrast, the rational use zone is notably influenced by tourist infrastructure and road networks, predominantly located in regions with high human activity, such as popular tourist destinations and areas with road classifications and vehicular traffic. The microcosmic human disturbance assessment method proposed in this study enhances the rationality and accuracy of natural protected area functional zoning. It provides a more scientifically grounded research approach for similar studies concerning natural protected area functional zoning and contributes valuable insights for the further advancement of China's efforts in the integration and optimization of natural protected areas.

Linking Forest Ecosystem Services to the SDGs: Semi-quantitative Mapping of Perceptions towards Integrated Decision-making.

With this study, we test and present the results of a reproducible semi-quantitative methodological approach, which enables us to map perceptions of complex systems, linking the forest ecosystem services (FES) of a given spatial level to the wider policy domains represented by the 2030 Agenda and its Sustainable Development Goals (SDGs). Through a participative process, we used integrated forest management and FES as entry point concepts to support and inform dialog towards a normative desired future as framed by the SDGs, taking into account interdependencies across sectors and policy domains. The scales used in the test were national (Switzerland) and international but it is possible to use the approach at any level of integration, especially the landscape one in the case of forest or other ecosystem issues to be transdisciplinary solved. We stress that the semi-quantitative aspects of the approach - be it the ranking of the importance of FES across the different SDGs, or the positive or negative weighting of interactions among these FES in cross-impact matrices - enable the perceptions held by actors to be more explicit and significant for governance or goal prioritization. The results illustrate the perceptions of selected actors on the effects of integrated forest management and provide a basis for multi-actor deliberation on emerging potential synergies or conflicts, thereby genuinely supporting science-policy-practice dialog, which is crucial to foster integrated decision-making.

Evaluating the impact of land use and land cover changes on forest ecosystem service values using landsat dataset in the Atwima Nwabiagya North, Ghana.

This study investigated land use and land cover (LULC) changes and its impact on forest ecosystem service values for 20 years in the Atwima Nwabaiagya North District using Landsat images of 2002, 2012 and 2022. Supervised classification with Maximum Likelihood Algorithm was used to classify the Landsat images. Five LULC types (high-dense forest, low-dense forest, water, bare-ground, and Built-up area) were successfully classified, with overall accuracies of 99.0 % and Kappa coefficients of 0.99. The result of the study showed a reduction of high-dense forest to 23.87 %, low-dense forest to 26.53 %, and water areas as 1.16 % whereas built-up (21.44 %) and bare-ground (27 %) experienced an expansion in their land areas. Related literatures and ecological assets value table with adjusted price value were used to evaluate ecosystem service values in response to LULC changes. The study discovered that ecosystem service value for high and low-dense forests have declined from USD 22.68 million and USD 8.75 million to USD 14.56 million and USD 5.2 million respectively. The overall total ecosystem service value declined by USD 33.73 million in 2002 to USD 21.91 million in 2022. It was revealed that the most notable feature to changes in forest ecosystem service values was the expansion of built-up and bare-grounds. There is a need to curb the current drivers of LULC changes in the Atwima Nwabiagya North to stop further forest degradation for optimum delivery of forest ecosystem service values in the district. For land use planners and decision makers who need site-specific information on the effects of LULC alterations on values of forest ecosystem services, the study's findings are essential. This will make it easier to track past environmental changes and obtain quick, accurate results for use in decision-making.

Assessment of Forest Ecosystem Variations in the Lancang-Mekong Region by Remote Sensing from 2010 to 2020.

Five countries in the Lancang-Mekong region, including Myanmar, Laos, Thailand, Cambodia, and Vietnam, are facing the threat of deforestation, despite having a high level of forest coverage. Quantitatively assessing the forest ecosystem status and its variations based on remote sensing products for vegetation parameters is a crucial prerequisite for the ongoing phase of our future project. In this study, we analyzed forest health in the year 2020 using four vegetation indicators: forest coverage index (FCI), leaf area index (LAI), fraction of green vegetation cover (FVC), and gross primary productivity (GPP). Additionally, we introduced an ecosystem quality index (EQI) to assess the quality of forest health. To understand the long-term trends in the vegetation indicators and EQI, we also performed a linear regression analysis from 2010 to 2020. The results revealed that Laos ranked as the top-performing country for forest ecosystem status in the Lancang-Mekong region in 2020. However, the long-term trend analysis results showed that Cambodia experienced the most significant decline across all indicators, while Vietnam and Thailand demonstrated varying degrees of improvement. This study provides a quality assessment of forest health and its variations in the Lancang-Mekong region, which is crucial for implementing effective conservation strategies.

Fine root decomposition in forest ecosystems: an ecological perspective.

Fine root decomposition is a physio-biochemical activity that is critical to the global carbon cycle (C) in forest ecosystems. It is crucial to investigate the mechanisms and factors that control fine root decomposition in forest ecosystems to understand their system-level carbon balance. This process can be influenced by several abiotic (e.g., mean annual temperature, mean annual precipitation, site elevation, stand age, salinity, soil pH) and biotic (e.g., microorganism, substrate quality) variables. Comparing decomposition rates within sites reveals positive impacts of nitrogen and phosphorus concentrations and negative effects of lignin concentration. Nevertheless, estimating the actual fine root breakdown is difficult due to inadequate methods, anthropogenic activities, and the impact of climate change. Herein, we propose that how fine root substrate and soil physiochemical characteristics interact with soil microorganisms to influence fine root decomposition. This review summarized the elements that influence this process, as well as the research methods used to investigate it. There is also need to study the influence of annual and seasonal changes affecting fine root decomposition. This cumulative evidence will provide information on temporal and spatial dynamics of forest ecosystems, and will determine how logging and reforestation affect fine root decomposition.

Effects of bacteria on early-stage litter decomposition in Wudalianchi volcanic forest.

To understand the role of microorganisms in litter decomposition and nutrient cycling in volcanic forest ecosystem, we conducted in-situ litterbag decomposition experiment and used Illumina MiSeq high-throughput sequencing to analyze the response of bacterial community structure and diversity during the decomposition of litters from Larix gmelinii, Betula platyphylla and Populus davidiana, the dominant tree species in volcanic lava plateau of Wudalianchi. The results showed that mass remaining percentage of litters of three species after 18-month decomposition was 63.9%-68.1%. Litter of B. platyphylla decomposed the fastest, with significant difference in N, C:N, and N:P before and after decomposition. The richness of bacterial species and diversity index differed significantly among the three litters. Proteobacteria, Actinomycetes, and Bacteroidetes were the dominant bacterial groups at the phylum level, while Rhizobium, Sphingomonas, and Pseudomonas were the dominant groups at the genus level, with significant difference among the three litters. After 18 months, the dominant bacterial groups in litter tended to be consistent with those in volcanic lava platform soil. In the volcanic forest ecosystem, bacterial diversity and community structure were mainly affected by P, C:N, and N:P in the litter.

Air kerma rate from radionuclides distributed in forest ecosystem.

This study evaluates the air kerma rate in radioactively contaminated forests. The air kerma rates created by plane sources of monoenergetic photons in the energy range 0.02-3 MeV located at different depths in soil up to 50 g cm-2 and at different heights in the forest medium from 0.05 to 50 m were calculated using numeric solution of the transport (Boltzmann) equation. To simplify the practical use of the results obtained by solving the Boltzmann equation, the study additionally includes approximation formulae for calculating air kerma rate separately from contaminated soil, crowns and trunks of trees in a forest ecosystem for 20 radionuclides - fission products that significantly contribute to the external dose. Biomaterial of trunks and crowns was modeled as uniformly distributed in corresponding layers and homogeneously mixed with air. Different distributions of radionuclides in soil were considered including plane source located at different depths, exponential and uniform distribution. Based on the results, the effect of forest biomass presence as an absorbing and scattering medium on the air kerma rate at 1 m above soil was evaluated. The estimated relative difference in air kerma rate at 1 m above soil in the forest medium and in free air for monoenergetic photon sources with energies 0.1 MeV, 0.66 MeV and 3 MeV did not correlate significantly with the energy of photons. Its maximum value in forest medium with biomass density of 5 kg m-3 was 15-20% for the source at soil depth ∼0.3 g cm-2, decreasing to less than 5% when it is at soil depth greater than 7 g cm-2. An example calculation of the air kerma rate dynamics is presented for the initial period after radioactive fallout considering weathering processes (rainfall and wind action) that contribute to the transfer of activity from the canopies to the forest floor. The differences in air kerma rate values, as an integral characteristic of the gamma radiation field from a radioactive cloud in the forest and in the open area, were evaluated.

Learning ensembles of process-based models for high accurately evaluating the one-hundred-year carbon sink potential of China's forest ecosystem.

China's forests play a vital role in the global carbon cycle through the absorption of atmospheric CO2 to mitigate climate change caused by the increase of anthropogenic CO2. It is essential to evaluate the carbon sink potential (CSP) of China's forest ecosystem. Combining NDVI, field-investigated, and vegetation and soil carbon density data modeled by process-based models, we developed the state-of-the-art learning ensembles model of process-based models (the multi-model random forest ensemble (MMRFE) model) to evaluate the carbon stocks of China's forest ecosystem in historical (1982-2021) and future (2022-2081, without NDVI-driven data) periods. Meanwhile, we proposed a new carbon sink index (CSindex) to scientifically and accurately evaluate carbon sink status and identify carbon sink intensity zones, reducing the probability of random misjudgments as a carbon sink. The new MMRFE models showed good simulation results in simulating forest vegetation and soil carbon density in China (significant positive correlation with the observed values, r = 0.94, P < 0.001). The modeled results show that a cumulative increase of 1.33 Pg C in historical carbon stocks of forest ecosystem is equivalent to 48.62 Bt CO2, which is approximately 52.03% of the cumulative increased CO2 emissions in China from 1959 to 2018. In the next 60 years, China's forest ecosystem will absorb annually 1.69 (RCP45 scenario) to 1.85 (RCP85 scenario) Bt CO2. Compared with the carbon stock in the historical period, the cumulative absorption of CO2 by China's forest ecosystem in 2032-2036, 2062-2066, and 2077-2081 are approximately 11.25-39.68, 110.66-121.49 and 101.31-111.11 Bt CO2, respectively. In historical and future periods, the medium and strong carbon sink intensity regions identified by the historical CSindex covered 65% of the total forest area, cumulative absorbing approximately 31.60 and 65.83-72.22 Bt CO2, respectively. In the future, China's forest ecosystem has a large CSP with a non-continuous increasing trend. However, the CSP should not be underestimated. Notably, the medium carbon sink intensity region should be the priority for natural carbon sequestration action. This study not only provides an important methodological basis for accurately estimating the future CSP of forest ecosystem but also provides important decision support for future forest ecosystem carbon sequestration action.

Climatic water availability modifies tree functional diversity effects on soil organic carbon storage in European forests.

Forest stand and environmental factors influence soil organic carbon (SOC) storage, but little is known about their relative impacts in different soil layers. Moreover, how environmental factors modulate the impact of stand factors, particularly species mixing, on SOC storage, is largely unexplored. In this study, conducted in 21 forest triplets (two monocultures of different species and their mixture on the same site) distributed in Europe, we tested the hypothesis that stand factors (functional identity and diversity) have stronger effects on topsoil (FF + 0-10 cm) C storage than environmental factors (climatic water availability, clay + silt content, oxalate-extractable Al-Alox) but that the opposite occurs in the subsoil (10-40 cm). We also tested the hypothesis that functional diversity improves SOC storage under high climatic water availability, clay + silt contents, and Alox. We characterized functional identity as the basal area proportion of broadleaved species (beech and/or oak), and functional diversity as the product of broadleaved and conifer (pine) proportions. The results show that functional identity was the main driver of topsoil C storage, while climatic water availability had the largest control on subsoil C storage. Functional diversity decreased topsoil C storage under increasing climatic water availability, but the opposite was observed in the subsoil. Functional diversity effects on topsoil C increased with increasing clay + silt content, while its effects on subsoil C were negative at increasing Alox content. This suggests that functional diversity effect on SOC storage changes along gradients in environmental factors and the direction of effects depends on soil depth.

Contribution of tree species to the co-occurrence network of the leaf phyllosphere and soil bacterial community in the subtropical forests.

The underlying mechanisms of the interactions between bacterial communities and tree species are still unknown, primarily attributed to a focus on the soil system while ignoring the leaf phyllosphere, which is a complex and diverse ecosystem that supports microbial diversity in the forest ecosystem. To gain insights into the mechanisms, the effects of seven common subtropical tree species, involving Pinus massoniana Lamb., Mytilaria laosensis Lecomte., Ilex chinensis Sims., Michelia macclurei Dandy., Liquidambar formosana Hance., Quercus acutissima Carruth., and Betula luminifera H.Winkler on the bacterial communities were investigated in the leaf phyllosphere and soil systems. We found that the bacterial community was dominated by Proteobacteria in the leaf phyllosphere (63.2-84.7%), and was dominated by Proteobacteria (34.3-45.0%) and Acidobacteria (32.5-40.6%) in soil. Mycorrhizal types and leaf phenology had no apparent effects on the bacterial abundance in the bacterial diversity in the leaf phyllosphere and soil. The bacterial community composition was greatly influenced by tree species in the leaf phyllosphere rather than in soil, with soil parameters (soil pH and C/N) and litter N identified as the most important factors. Ectomycorrhizal trees exerted positive effects on the complexity of the bacterial community at the expense of decreasing the robustness of the soil bacterial community, potentially threatening ecosystem stability. Evergreen trees decreased the network robustness of bacterial community by 21.9% higher than this of deciduous trees in the leaf phyllosphere. Similarly, evergreen trees decreased soil bacterial abundance by 50.8% and network robustness by 8.0% compared to deciduous trees, indicating the adverse impacts of leaf phenology on the bacterial stability in both leaf and soil. Overall, our results highlight the need for studies of leaf-associated bacteria to comprehensively understand the potential effects of tree species on microbial diversity and stability in subtropical forests.

[Response of Forest Ecosystems to Decreasing Atmospheric Nitrogen Deposition].

Nitrogen deposition has serious consequences to global change. Excessive nitrogen deposition leads to nitrogen saturation in forests, resulting in soil acidification, nitrate leaching, an increase in nitrous oxide emissions, and a decrease in plant species diversity and vegetation productivity. Under the reduction of atmospheric nitrogen deposition in Europe, North America, and China, summarizing the response of forests to decreasing nitrogen deposition can not only improve the knowledge framework of the impact of nitrogen deposition on forests, but also evaluate the effects of emission abatement actions, as well as provide scientific basis for future air pollution control. This study reviewed the response of soil, surface water, nitrogen cycle, and vegetation of temperate forests in Europe and North America and subtropical forests in southwest China to the reduction in atmospheric nitrogen pollution gases and thus nitrogen deposition. The soil water nitrogen concentration responded rapidly to the nitrogen deposition reduction, although the trend was inconsistent. The soil acidification and nitrogen cycles showed a delayed response of recovery from high nitrogen deposition. The nitrogen mineralization and immobilization, soil carbon retention, and net primary production might take decades to respond to the nitrogen deposition reduction. However, the soil inorganic nitrogen pool and nitrogen leaching decreased with the decline in nitrogen deposition, although a one-or two-year lag existed. The surface water nitrogen concentration was closely related to nitrogen status in forests. After the nitrogen deposition decreased, the nitrogen leaching and thus the surface water nitrogen concentration decreased in the areas with historically high nitrogen deposition. However, the low surface water nitrogen concentration in the nitrogen-limited forests was not significantly affected by the nitrogen deposition changes. The recovery of surface water acidification was affected by soil sulfur desorption/mineralization and nitrification/denitrification. The foliar nitrogen concentration decreased with the decline in nitrogen deposition. The nitrogen-saturated forests and regional surface water in southwest China showed a recovery trend from high nitrogen deposition, as a consequence of the implementation of the Total Emissions Control of Air Pollutants and later the Action Plan of Air Pollution Prevention and Control.

Long-term exclusion of invasive ungulates alters tree recruitment and functional traits but not total forest carbon.

Forests are major carbon (C) sinks, but their ability to sequester C and thus mitigate climate change, varies with the environment, disturbance regime, and biotic interactions. Herbivory by invasive, nonnative ungulates can have profound ecosystem effects, yet its consequences for forest C stocks remain poorly understood. We determined the impact of invasive ungulates on C pools, both above- and belowground (to 30 cm), and on forest structure and diversity using 26 paired long-term (>20 years) ungulate exclosures and adjacent unfenced control plots located in native temperate rainforests across New Zealand, spanning 36-41° S. Total ecosystem C was similar between ungulate exclosure (299.93 ± 25.94 Mg C ha-1 ) and unfenced control (324.60 ± 38.39 Mg C ha-1 ) plots. Most (60%) variation in total ecosystem C was explained by the biomass of the largest tree (mean diameter at breast height [dbh]: 88 cm) within each plot. Ungulate exclusion increased the abundance and diversity of saplings and small trees (dbh ≥2.5, <10 cm) compared with unfenced controls, but these accounted for ~5% of total ecosystem C, demonstrating that a few, large trees dominate the total forest ecosystem C but are unaffected by invasive ungulates at a timescale of 20-50 years. However, changes in understory C pools, species composition, and functional diversity did occur following long-term ungulate exclusion. Our findings suggest that, although the removal of invasive herbivores may not affect total forest C at the decadal scale, major shifts in the diversity and composition of regenerating species will have longer term consequences for ecosystem processes and forest C.

Enantioselective terpene emission signifies forest climate response mechanism.

Forest vegetation produces terpene enantiomers, but atmospheric emission mechanisms and ecological functions remain poorly understood. In a study on the tropical rainforest ecosystem, Byron et al. noticed distinct diel trends and sources of enantiomer emission, and a striking change in (-)-α-pinene emission under severe drought, which might favor cloud formation.