Forest Ecotone Research Articles

I want to climb to the tops of trees! Factors facilitating the development of ivy vines in central European forests

Abstract Lianas, which are considered to form tree-related microhabitats, are known as important elements of tropical forests; however, their ecological function and relationships with host trees (phorophytes) in temperate forests are poorly known. This gap in knowledge stems from a low species diversity and abundance of lianas in temperate forests. An exception is common ivy (Hedera helix), which is widely distributed and is currently increasing its abundance in temperate forests. In this study, we examined the relationships between ivy vines with features of their phorophytes, using Central European upland mixed forests as an example. We assess the presence and density of ivy within 69 study plots, established in the forest interior and ecotone. We use generalized linear mixed-effects models to assess drivers of ivy’s presence and its density, while accounting for the tree diameter at breast height, bark roughness, and the canopy light transmittance. We show that ivy is able to grow on nearly all tree species, although it prefers phorophytes with rough bark and a large diameter. Large generative individuals (ivy vines that produce fruits) were found mostly on veteran trees (usually oaks, alders, or pines). For its growth, ivy requires tree phorophytes with only a moderate transparency of light through the tree crowns, which is likely related to evergreen leaves that enable ivy vines to also develop during leaf-off periods. The features of phorophytes preferred by ivy indicate that the vine finds optimal conditions for development in old patches of tree stand, often in areas inaccessible or unprofitable for forest management. We propose using large and fruiting ivy vines as indicators of old-growth forests that deserve protection, which would be in line with the current policy of sustaining and restoring close-to-natural forests in Europe.

Interactions between soil and other environmental variables modulate forest expansion and ecotone dynamics in humid savannas of Central Africa.

Forest expansion into savanna is a pervasive phenomenon in West and Central Africa, warranting comparative studies under diverse environmental conditions. We collected vegetation data from the woody and grassy components within 73 plots of 0.16 ha distributed along a successional gradient from humid savanna to forest in Central Africa. We associated spatially collocated edaphic parameters and fire frequency derived from remote sensing to investigate their combined influence on the vegetation. Soil texture was more influential in shaping savanna structure and species distribution than soil fertility, with clay-rich soils promoting higher grass productivity and fire frequency. Savanna featuring woody aboveground biomass surpassing 40 Mg ha-1 could escape the grass-fire feedback loop, by depressing grass biomass below 4 Mg ha-1. This thicker woody layer also favoured the establishment of fire-tolerant forest pioneers, which synergically contributed to the expansion of forests. Conversely, savannas below this fire suppression threshold sustained a balance between trees and grasses through the grass-fire feedback mechanism. This hysteresis loop, particularly pronounced on clayey soils, suggests that the contrast between grassy savanna and young forests might represent alternative ecosystem states, although savannas with low woody biomass remained vulnerable to forest edge encroachment.

Contrasting foliar nitrogen nutrition of coexisting temperate and boreal trees across a modest temperature cline

The temperate-boreal forest ecotone represents a transition zone from temperate to boreal forest where nitrogen (N) is frequently limiting tree growth, which is highly sensitive to climate change. However, the spatial patterns and potential drivers of plant N nutrition and soil N availability remain poorly understood. To address this, we conducted a field investigation along a temperate-boreal forest ecotone in northeastern China, characterized by a modest mean annual temperature gradient (∼1°C) within the range of current climate warming. Our goal was to evaluate the spatial variation in foliar N nutrition and soil N availability, and the potential driving factors for Mongolian oak (Quercus mongolica) and Dahurian larch (Larix gmelinii), the dominant trees of the local temperate and adjacent boreal forests, respectively. Our results revealed no significant spatial trend in topsoil N availability across the sampling transect. Overall, foliar N concentration was significantly higher, but foliar δ15N was lower, for Mongolian oak than Dahurian larch. More important, foliar N concentration for Mongolian oak increased significantly toward the boreal forest, driven by lower mean annual temperatures and mean annual precipitation, with no significant trend observed for Dahurian larch. Additionally, foliar Δδ15N (foliar δ15N−soil δ15N) decreased significantly for Mongolian oak as it approached the boreal forest, while it increased significantly for Dahurian larch toward the temperate forest. Furthermore, the foliar N concentration, δ15N, and Δδ15N for Dahurian larch were all higher with an increasing basal area proportion of Mongolian oak. Our findings reveal contrasting patterns of foliar N nutrition between co-occurring temperate and boreal trees across a temperate-boreal forest ecotone which experiences a modest climatic gradient. These results underscore the importance of incorporating interspecific interactions to enhance our understanding of future N cycling in southern boreal forests in the context of climate warming.

Effects of burning and nitrogen addition on foliar stoichiometry and nutrient resorption in a subtropical–temperate ecotonal forest

Fire disturbances and atmospheric nitrogen (N) deposition can significantly soil nutrient dynamics and plant nutrient uptake, thereby influencing on biogeochemical cycles within forest ecosystems. Despite these known effects, the combined impact of burning and N addition on leaf nutrient characteristics and the underlying mechanisms remains largely unexplored, particularly within forest ecosystems. This study presents a three-year field experiment designed to assess the responses of leaf N and phosphorus (P) concentrations, N:P ratios, and nutrient resorption in six dominant species (comprising two tree species and four understory species) to burning and N addition in a coniferous-broadleaved mixed forest located within a subtropical-warm temperate transition zone in Central China. The findings revealed that burning did not affect N concentrations in either green or senesced leaves, nor did it influence N or P resorption across any of the tree or shrub species. However, it did increase P concentrations in green leaves and reduce N:P ratios in shrub species. N addition elevated the N concentrations and N:P ratio in green and/or senesced leaves (with the exception of Quercus acutissima Carruth.), without affecting N or P resorption. These results suggest that shrubs enhanced P uptake due to increased soil P availability but maintain consistent internal P cycling (i.e., nutrient resorption) following low-severity fires. Additionally, most shrub species exhibited lower N:P ratios compared to tree species post-burning, indicating distinct nutrient requirements and fire responses based on life form. This study provides essential insights, demonstrating that burning mitigates P limitation on plant growth in subtropical–warm temperate ecotonal forests. Furthermore, the differential responses of leaf nutrient traits and associated stoichiometry across diverse life forms to environmental disturbances may influence plant diversity and community composition within these forests.

Plants, fungi, and carabid beetles in temperate forests: both observed and dark diversity depend on habitat availability in space and time

ContextThe loss of ancient forests threatens many species. Effective nature conservation needs information on how forest availability in the surrounding landscape in space and time determines the diversity of multiple taxa.ObjectivesWe explored the relationship between forest availability at different spatiotemporal scales and the diversity of various groups: vascular plants (woody species, ground layer), epiphytes (bryophytes and lichens), fungi (ectomycorrhizal, arbuscular mycorrhizal, pathogenic, saprotrophic), and carabid beetles. Besides the observed diversity, we also estimated dark diversity, i.e. suitable but absent species. Dark diversity is theoretically a sensitive metric in detecting ecosystem conditions as it is typically relatively large and contains susceptible species.MethodsWe recorded the observed diversity by field sampling and soil DNA in 100 temperate ancient old-growth forest sites in southern Estonia; dark diversity was estimated for the same sites using species co-occurrence data. Forest availability estimates were obtained from four topographic maps (1900s-2010s) at the 0.5–5 km radius.ResultsThe biodiversity of forest specialists was higher at larger historical forest availability at the spatial scale of 2–5 km radius. The diversity of light-demanding forest ecotone taxa mainly had negative relationships with young forests on previous agricultural lands (at 0.5–2 km radius). Dark diversity models were often more strongly associated with forest availability than observed diversity models.ConclusionsDark diversity enhances our understanding of how current and historical forest availability affects local biodiversity. As young forests cannot provide suitable habitats for many forest-dwelling species, stable forest habitats must be preserved as source areas to enhance biodiversity.

Taller trees exhibit greater hydraulic vulnerability in southern Amazonian forests

Potential increases in drought frequency and vapour pressure deficit pose a risk to the future function of tropical trees. Previous studies have found that taller tropical trees show a stronger increase in mortality than shorter trees in response to dry anomalies, but the mechanisms behind this are unclear. Here we investigate whether canopy branches of taller tropical trees have different hydraulic traits compared to shorter conspecifics. We determined xylem resistance to embolism (P50), hydraulic safety margin (HSM), xylem functional traits and xylem theoretical hydraulic conductivity for canopy branches of four tree species across a range of tree heights (sapling to maximum tree height) in an ecotonal forest near the Amazonia-Cerrado transition. We found that canopy branches of taller trees within each species have lower HSM, suggesting that they are more susceptible to hydraulic failure under drought than smaller conspecifics. Height-related trends in HSM were driven by variation in P50 with height and not by variation in leaf water potential which did not vary with height. We find that canopy branches with greater xylem vessel diameters are generally more vulnerable to embolism, suggesting a potential role for a diameter-safety linkage in explaining observed patterns of decreasing HSM with height. However, we find no evidence of a branch-level trade-off between theoretical hydraulic conductivity and hydraulic vulnerability. The greater hydraulic vulnerability of larger trees provides a potential explanation for the higher drought-induced mortality observed in taller tropical trees. The consistency of the height-P50 relationship across species opens the door to a more accurate prediction of southern Amazon forest responses to future droughts. Whether the findings for forests in southern Amazonia can be generalized to other Amazonian regions remains an open question.

Paleosol charcoal: 12,700 years of high-altitude mediterranean vegetation history in relation to forest fires in the southwestern baetic cordillera (Spain)

Mountain forests are sensitive ecosystems. This is why in recent years the dynamics of these forest ecotones have been researched from several different approaches. One of these has been the paleoecological perspective, which is particularly interesting in the mountainous areas of the Mediterranean region, where interactions between climate, vegetation and anthropic activities have been documented for millennia. This is the case of the Sierra de las Nieves Natural Park (southwestern Baetic Cordillera), a mountainous area that constitutes an important refuge for flora in southern Iberian Peninsula. At present, endemic trees such as Abies pinsapo and Quercus faginea subs. alpestris are found. However, its strategic geographical location may also have served in the past as a refuge for other tree taxa. In order to reconstruct the vegetation history in this protected natural area, this research aims to use pedoanthracological analysis in an unexplored area of this mountainous system. The results obtained have allowed to identify a new paleopopulation of Abies, a finding that provides new keys on the paleobiogeography of this species. This is the oldest evidence of this genus and at the highest altitude of those found to date in the southwestern Baetic Cordillera, which would confirm that this fir tree was present in high elevations of the Sierra de las Nieves during the Pleistocene-Holocene transition. Likewise, the first anthracological evidence of Pinus nigra/sylvestris type in the southwestern end of the Baetic Cordillera has been obtained. Forest fires could have been one of the main factors which would be determined the shaping and evolution of the vegetation landscape, as suggested by the fire events identified from the soil analysis. This information can be useful for the conservation and adaptive management of the most threatened forests and their habitats in the face of global change.

Assessing ecological risks and spatial distribution of potentially toxic elements in soils from anthropized environments in a watershed at the caatinga-Atlantic forest ecotone in Brazil

Understanding the processes of mobility and availability of potentially toxic elements in soil is crucial for informed decision-making in the development of public policies aimed at minimizing environmental impacts. Monitoring, in combination with the determination of natural concentrations, can provide effective tools for controlling pollution sources. In this study, enrichment, pollution, and ecological risk indices were used for some potentially toxic elements in an anthropogenically influenced watershed in southwestern Bahia, Brazil. The study involved 63 composite surface soil samples collected from areas with natural forest, crops, pastures, and urbanization. The samples were analyzed for fertility and particle size. Metal extraction followed the EPA 3051A method, and element determination was carried out via ICP-OES. The soils in the Verruga River watershed exhibit a high variability in fertility and granulometric attributes. The Kruskal-Wallis test at a 5% significance level was employed to assess the impact of land management on the availability of elements (As, Co and Pb), while Spearman's correlation, along with hierarchical clustering analysis, was used to comprehend element dynamics. Geostatistics were applied to identify pollution hotspots. Consequently, it became evident that potentially toxic elements can accumulate in the soil depending on land use and management practices (As, Co, and Pb), as well as the weathering process linked to the type of source material, such as diamictite deposits (Ni and Co). Soils in the Verruga River watershed qualify as having minimal enrichment, low pollution levels, and individual ecological risk concerning Cd. The percentage of samples enriched with Cu, As, Zn, and Cd exceeded 67%, with agricultural activities being the primary source of pollution. Meanwhile, in pasture and urban areas, Co and Pb were notably prominent, respectively.

Revealing floristic and structural variation in regenerating areas in the Cerrado-Caatinga transition: an analysis across seres

Abstract In the savanna-seasonally dry tropical forest ecotone in Northeastern Brazil, we studied variations in flora and structure within old growth and two sites in secondary succession (10 and 25 years). We sampled 2,127 trees and shrubs with a diameter at ground level of 3 cm or more, excluding cacti, palm trees, and vines. Old growth contained 478 plants from 29 species, the 25-year site had 819 plants from 27 species, and the 10-year site had 829 plants from 25 species, totaling 38 species across the sites. Regarding the regenerating stratum, we found 2,776 individuals, with the largest and smallest number of individuals for 10 and 25 years regeneration, respectively. Rarefaction and Jacknife richness showed greater tree richness in old growth, whereas 10 and 25 years regeneration presented similar richness estimates; furthermore, the highest richness in the regenerating stratum was observed in 10 years and the lowest in old growth. Our results reveal that changes in composition are caused by species replacement, demonstrating that even in areas deforested for traditional agriculture, turnover causes significant changes in composition and results in the requirement of a long time for reestablishment, similar to the old growth.

Almond consumption by Red Squirrel (Sciurus vulgaris Linnaeus, 1758) in Montes de Málaga Natural Park (south of Spain)

We studied the consumption of almonds by Red Squirrel (Sciurus vulgaris) in a nature park in southern Spain where the species coexists with the crop. For two years, we collected weekly samples of almonds consumed by the species and analyzed its spatial and temporal patterns. We also compared almonds consumed with the production of the crop to assess possible damages. The results reveal a marked seasonal pattern of almond consumption, which begins in mid-June, peaks in mid-July and declines towards the beginning of the harvest season in early October. The mean number of almonds consumed was 1.3 ± 0.4 almonds/m2, and consumption was restricted to a 20-metre-wide band in the ecotone of the pine forest to the crop. We appreciate that this amount of consumption is insignificant when compared to the crop production in large cultivation plots, but the damage may be important in small ones. We discuss different hypotheses (edge effect and refuge-distance effect) to explain why almond consumption occurs only in the ecotone. Finally, we propose almonds consumption as a new presence index of this species in areas where red squirrels coexist with the crop.

Lire le passé forestier dans un bourbier : histoire écologique et dynamique contemporaine d’une population marginale nordique d’érable rouge (Acer rubrum)

ABSTRACT Populations at the edge of a species range are vulnerable to climate change. Studying their ecological history helps understanding resilience processes acting at the limit of the species’ tolerance envelope. In the mixedwood forest ecotone, several thermophilic species, such as white pine and red maple, reach the northern limit of their geographical range. Here we rely on macrofossil analysis of charcoal particles and plant macroremains of a forest hollow to reconstruct the local history of thermophilic species in a marginal red maple stand isolated within the mixedwood forest ecotone. Taxonomic identification and radiocarbon dating of charred particles and wood remains extracted along the peat accumulation profile indicated dominance of white pine during the Holocene Climate Optimum (6200 to 4300 cal yr BP). The fossil assemblage suggests the transition of a black spruce - feathermoss (>9500 to 6200 cal yr BP) to a balsam fir forest that developed after the decline of white pine (since 4300 cal yr BP). Red maple is not detected in the fossil assemblage suggesting a late arrival and/or expansion on the site, likely favored by anthropogenic activities and the climate warming ongoing since the end of the Little Ice Age.

Effects of urban ecosystem under the diversity and structure of two forest ecotones in Maranhão state

Effects of urban ecosystem under the diversity and structure of two forest ecotones in Maranhão state

Analysis of the Potential Range of Mountain Pine-Broadleaf Ecotone Forests and Its Changes under Moderate and Strong Climate Change in the 21st Century.

Climatic changes have a significant impact on the composition and distribution of forests, especially on ecotone ones. In the Southern Ural, pine-broadleaf ecotone forests were widespread during the early Holocene time, but now have persisted as relic plant communities. This study aimed to analyze the current potential range and to model changes in habitat suitability of relic pine-broadleaf ecotone forests of the suballiance Tilio-Pinenion under scenarios of moderate (RCP4.5) and strong (RCP8.5) climate change. For modelling, we used MaxEnt software with the predictors being climate variables from CHELSA Bioclim, the global digital soil mapping system SoilGrids and the digital elevation model. In the Southern and Middle Urals, climate change is expected to increase the areas with suitable habitat conditions of these forests by the middle of the 21st century and decrease them in the second half of the century. By the middle of the 21st century, the eastern range boundary of these forests will shift eastward due to the penetration of broad-leaved tree species into coniferous forests of the Southern Ural. In the second half of the century, on the contrary, it is expected that climate aridization will again shift the potential range border of these forests to the west due to their gradual replacement by hemiboreal coniferous forests. The relationship between the floristic composition of pine-broadleaf forests and habitat suitability was identified. In low and medium habitat suitability, pine-broadleaf forests contain more nemoral species characteristic of deciduous forests of the temperate zone, and can be replaced by broadleaf forests after thinning and removal of pine. In the Volga Upland, suitable habitats are occupied by pine-broadleaf forests of the vicariant suballiance Querco robori-Tilienion cordatae. Projected climatic changes will have a significant impact on these ecotone forests, which remained completely unaltered for a long time.

Changes in Leaf Functional Traits Driven by Environmental Filtration in Different Monsoon Tropical Forest Types

Disturbances have created heterogeneous habitats for secondary and old-growth forests. Under the assumption that ecologically similar species have similar functional traits, numerous studies have attempted to use trait-based approaches to infer the abiotic and biotic factors that drive variations in community composition across different forests. However, the relative importance of these drivers in monsoon forests remains poorly understood. In this study, we randomly selected 86 plots and classified them into three forest types according to environmental factors: 1—secondary forests: secondary forest habitats at high elevation; 2—ecotone forests: general recovery and elevation; and 3—old growth forests: old growth at low elevations. We then compared the species and six leaf functional trait variations across the three forests and assessed their relationships with 15 environmental factors. The results showed that secondary and ecotone forests with a conservative strategy, exhibiting high dry matter content and leaf carbon content, tended to persist in stressful habitats, such as nutrient-poor soil, whereas old growth forests invested in trait values related to rapid resource acquisition with high specific leaf area, leaf nitrogen content, leaf phosphorous content, and leaf potassium content. Species with functional trait values between the secondary, ecotone, and old growth forests had clear signatures of their different strategies to persist in assemblages under distinct and opposite environmental filters. These plots were classified into three forest types according to environmental factors: (1) secondary forest at high elevation; (2) ecotone forests at general elevation; and (3) old growth forests at low elevation. Recovery time and elevation, followed by soil nutrients and light capture, were the most important factors shaping species and functional trait variations across forests. These results have demonstrated that environmental filters select plant species with distinct traits and ecological strategies. Acquisitive traits indicate higher competitive ability and faster resource acquisition for forest species that occur in areas with high soil fertility. Meanwhile, conservative traits promote the resistance of secondary species to environmental stressors in low soil fertility, suggesting that analyzing leaf functional-based trait variations to understand plant ecological strategies along an environmental gradient may improve understanding of forest dynamics in tropical monsoon forests.

Diversity in Landscape Management Affects Butterfly Distribution

The aim of the study was to determine the influence of differentiated landscape management on the distribution and abundance of butterfly species. The question was raised with regard to which land use type benefited butterflies, and which affected them, that is: under which management type does biodiversity increase, and under which is it depleted? The spatial and abundance distributions of the examined butterfly species diverged considerably. The observed differences between the abundance distributions may be due to diverse conditions in the small-scale environments or specific food preferences of individual species. The diversified management of the “Krzywda” landscape fosters the abundance of mesophilic and ubiquitous butterfly species, whereas xerotermophilic and hygrophilous species are not fostered. The transects established on the fallow land with harvested biomass as well as that with unharvested biomass and in the forest ecotone showed that the fallows were characterized by the highest abundance of butterflies, and the greatest number of plant species was recorded there. Mown fallow lands with not harvested biomass as well as forested areas fostered polyphagous and monophagous butterfly species. Oligophagous butterfly species were fostered by mown fallow lands with not harvested biomass. Unmown meadows, the ecotone marshland and fallow, as well as unmown fallow lands did not foster butterfly abundance. This most likely means that land management can influence the food base of butterflies, and consequently, their abundance. The stage of succession as well as the homogeneity of the area in terms of vegetation had the strongest filtering effect on the occurrence and distribution of butterflies among the analyzed variables. The number of species as well as their abundance was higher on transects classified as young successional stages on which successional processes were artificially inhibited by mowing and biomass removal. Advanced environmental engineering enables humans to influence species composition in a given ecosystem to achieve a desired result. There is no doubt that human activity will be successful when the needs of individual species in a given environment are accurately understood.

Mangrove forest encroachment by Nypa frutican, Derris trifoliata, and Acanthus spp. in Segara Anakan Lagoon

Based on phytosociological methods and land cover change analysis, previous studies in Segara Anakan Lagoon (SAL) indicated the spreading of mangrove species living in the forest margin ecotone into the forest interior, encroaching the other mangrove communities. This current study aims to quantify the spreading pattern of those mangrove species, assess the effect of the spreading of those mangrove species to the other mangrove communities, and identify the location of the spreading pattern relative to the newly emerged islands. The spreading pattern can be demonstrated by analyzing landscape structures quantified by landscape metrics. It was done using multi-temporal mangrove maps, representing the changes in mangrove communities over four periods with a decade interval. The landscape metrics used were the aggregation index, the size of community patches, and the distance between the patches. These metrics were extracted by using landscape metrics, an R package. The changes in the metrics over time were compared namely 1990, 2000, 2010, and 2020. The results showed that the small patches of the forest margin species became more aggregated into a larger patch, while the mangrove forests became more fragmented. This condition occurred most in the west part of SAL where the new islands emerged.

Utilizing a top predator to prioritize site protection for biodiversity conservation

Ongoing global change makes it ever more urgent to find creative solutions for biodiversity preservation, but prioritizing sites for protection can be challenging. One shortcut lies in mapping the habitat requirements of well-established biodiversity indicators, such as top predators, to identify high-biodiversity sites. Here, we planned site protection for biodiversity conservation by developing a multi-scale species distribution model (SDM) for the raptorial Northern Goshawk (Accipiter gentilis; goshawk) breeding in an extensive megacity region of Japan. Specifically, we: (1) examined the determinants of top predator occurrence and thus of high-biodiversity value in this megacity setting, (2) identified the biodiversity hotspots, (3) validated whether they actually held higher biodiversity through an independent dataset, and (4) evaluated their current protection by environmental laws. The SDM revealed that goshawks preferred secluded sites far from roads, with abundant forest within a 100 m radius and extensive forest ecotones suitable for hunting within a 900 m radius. This multi-scale landscape configuration was independently confirmed to hold higher biodiversity, yet covered only 3.2% of the study area, with only 44.0% of these sites legally protected. Thus, a rapid biodiversity assessment mediated by a top predator quickly highlighted: (1) the poor development of biodiversity-friendly urban planning in this megacity complex, an aspect overlooked for decades of rapid urban sprawl, and (2) the extreme urgency of extending legal protection to the sites missed by the current protected area network. Exigent biodiversity indicators, such as top predators, could be employed in the early or late stages of anthropogenic impacts in order to proactively incorporate biodiversity protection into planning or flag key biodiversity relics. Our results confirm and validate the applied reliability of top predatory species as biodiversity conservation tools.

Different responses of soil fungal and bacterial communities to nitrogen addition in a forest grassland ecotone.

Continuous nitrogen deposition increases the nitrogen content of terrestrial ecosystem and affects the geochemical cycle of soil nitrogen. Forest-grassland ecotone is the interface area of forest and grassland and is sensitive to global climate change. However, the structure composition and diversity of soil microbial communities and their relationship with soil environmental factors at increasing nitrogen deposition have not been sufficiently studied in forest-grassland ecotone. In this study, experiments were carried out with four nitrogen addition treatments (0 kgN·hm-2·a-1, 10 kgN·hm-2·a-1, 20 kgN·hm-2·a-1 and 40 kgN·hm-2·a-1) to simulate nitrogen deposition in a forest-grassland ecotone in northwest Liaoning Province, China. High-throughput sequencing and qPCR technologies were used to analyze the composition, structure, and diversity characteristics of the soil microbial communities under different levels of nitrogen addition. The results showed that soil pH decreased significantly at increasing nitrogen concentrations, and the total nitrogen and ammonium nitrogen contents first increased and then decreased, which were significantly higher in the N10 treatment than in other treatments (N:0.32 ~ 0.48 g/kg; NH4+-N: 11.54 ~ 13 mg/kg). With the increase in nitrogen concentration, the net nitrogen mineralization, nitrification, and ammoniation rates decreased. The addition of nitrogen had no significant effect on the diversity and structure of the fungal community, while the diversity of the bacterial community decreased significantly at increasing nitrogen concentrations. Ascomycetes and Actinomycetes were the dominant fungal and bacterial phyla, respectively. The relative abundance of Ascomycetes was negatively correlated with total nitrogen content, while that of Actinomycetes was positively correlated with soil pH. The fungal community diversity was significantly negatively correlated with nitrate nitrogen, while the diversity of the bacterial community was significantly positively correlated with soil pH. No significant differences in the abundance of functional genes related to soil nitrogen transformations under the different treatments were observed. Overall, the distribution pattern and driving factors were different in soil microbial communities in a forest-grassland ecotone in northwest Liaoning. Our study enriches research content related to factors that affect the forest-grassland ecotone.

The elevational patterns and key drivers of soil microbial communities strongly depend on soil layer and season

AbstractKnowledge about the elevational patterns of soil microbial biomass and communities can facilitate accurate prediction of the responses of soil biogeochemical processes to climate change. However, previous studies that have considered intra‐ and inter‐annual variations have reported inconsistent results on the one hand, and they have paid little attention to the effect of soil layer on the other hand. We, therefore, conducted a 4‐year in situ soil core incubation experiment along a 2431‐m elevational gradient across the dry valley shrubland, valley‐montane ecotone forest, subalpine coniferous forest, alpine coniferous forest, and alpine meadow in an ecologically fragile alpine‐gorge region on the eastern edge of the Qinghai‐Tibetan Plateau. Soil microbial biomass and community composition in the organic and mineral layers were measured using the phospholipid fatty acids (PLFA) method at five critical periods each year. Our results indicated that soil microbial biomass in the organic layer was the highest in the subalpine coniferous forest, followed by the alpine meadow, alpine coniferous forest, and valley‐montane ecotone forest. In contrast, soil microbial biomass in the mineral layer was significantly higher in the alpine meadow than in the other sites. Soil microbial biomass exhibited differential seasonal fluctuations at different elevations, resulting in their elevational patterns being strongly intra‐annual and inter‐annual dependent. Our results revealed that elevation and seasonality significantly affected soil microbial communities. Seasonality had a more substantial effect than elevation on soil microbial communities during the first 3 years of incubation, whereas the relative importance of seasonal and elevational effects on microbial communities was reversed in the organic layer with incubation time. These results are mainly attributed to the magnitude and direction of effect of environmental variables on soil microbial biomass and communities vary with elevation, soil layer, and sampling time. Briefly, the elevational patterns and dominant factors of soil microbial biomass and communities have intense soil layer and temporal specificity, implying that differential responses of soil biochemical processes to climate change might be observed at different elevations.

Climate change–induced stress disrupts ectomycorrhizal interaction networks at the boreal–temperate ecotone

The interaction networks formed by ectomycorrhizal fungi (EMF) and their tree hosts, which are important to both forest recruitment and ecosystem carbon and nutrient retention, may be particularly susceptible to climate change at the boreal-temperate forest ecotone where environmental conditions are changing rapidly. Here, we quantified the compositional and functional trait responses of EMF communities and their interaction networks with two boreal (Pinus banksiana and Betula papyrifera) and two temperate (Pinus strobus and Quercus macrocarpa) hosts to a factorial combination of experimentally elevated temperatures and reduced rainfall in a long-term open-air field experiment. The study was conducted at the B4WarmED (Boreal Forest Warming at an Ecotone in Danger) experiment in Minnesota, USA, where infrared lamps and buried heating cables elevate temperatures (ambient, +3.1 °C) and rain-out shelters reduce growing season precipitation (ambient, ~30% reduction). EMF communities were characterized and interaction networks inferred from metabarcoding of fungal-colonized root tips. Warming and rainfall reduction significantly altered EMF community composition, leading to an increase in the relative abundance of EMF with contact-short distance exploration types. These compositional changes, which likely limited the capacity for mycelial connections between trees, corresponded with shifts from highly redundant EMF interaction networks under ambient conditions to less redundant (more specialized) networks. Further, the observed changes in EMF communities and interaction networks were correlated with changes in soil moisture and host photosynthesis. Collectively, these results indicate that the projected changes in climate will likely lead to significant shifts in the traits, structure, and integrity of EMF communities as well as their interaction networks in forest ecosystems at the boreal-temperate ecotone.