Piecewise Structural Equation Modeling Research Articles

Plant traits modulate grassland stability during drought and post‐drought periods

Abstract Grasslands are subject to climate change, such as severe drought, and an important aspect of their functioning is temporal stability in response to extreme climate events. Previous research has explored the impacts of extreme drought and post‐drought periods on grassland stability, yet the mechanistic pathways behind these changes have rarely been studied. Here, we implemented an experiment with 4 years of drought and 3 years of recovery to assess the effects of drought and post‐drought on the temporal stability of above‐ground net primary productivity (ANPP) and its underlying mechanisms. To do so, we measured community‐weighted mean (CWM) of six plant growth and nine seed traits, functional diversity, population stability and species asynchrony across two cold, semiarid grasslands in northern China. We also performed piecewise structural equation models (SEMs) to assess the relationships between ANPP stability and its underlying mechanisms and how drought and post‐drought periods alter the relative contribution of these mechanisms to ANPP stability. We found that temporal stability of ANPP was not reduced during drought due to grasses maintaining productivity, which compensated for increased variation of forb productivity. Moreover, ANPP recovered rapidly after drought, and both grasses and forbs contributed to community stability during the post‐drought period. Overall, ANPP stability decreased during the combined drought and post‐drought periods because of rapid changes in ANPP from drought to post‐drought. SEMs revealed that the temporal stability of ANPP during drought and post‐drought periods was modulated by functional diversity and community‐weighted mean traits directly and indirectly by altering species asynchrony and population stability. Specifically, the temporal stability of ANPP was positively correlated with functional divergence of plant communities. CWMs of seed traits (e.g. seed width and thickness), rather than plant growth traits (e.g. specific leaf area and leaf nutrient content), stabilized grassland ANPP. Productivity of plant communities with large and thick seeds was less sensitive to precipitation changes over time. These results emphasize the importance of considering both the functional trait distribution among species and seed traits of dominant species since their combined effects can stabilize ecosystem functions under global climate change scenarios. Read the free Plain Language Summary for this article on the Journal blog.

Tree size variation induced by stand age mainly regulates aboveground biomass across three major stands of temperate forests in South Korea

Forest biomass and biodiversity are the most important elements of forest functions and ecosystem services. In this study, we explore the possibilities and ways to enhance ecosystem functions and services related to biomass and biodiversity. Biotic drivers (i.e., species, phylogenetic and functional diversity, stand structural attributes, and community-weighted mean of trait values), abiotic drivers (i.e., topography and climate), and stand age were extracted as independent variables to explain aboveground biomass (AGB). Using South Korea’s 7th National Forest Inventory data, we analyzed 2,070 plots belonging to the natural forests consisting of 394 plots (19.0%) of coniferous stands, 829 plots (40.0%) of broadleaved stands, and 847 plots (40.9%) of mixed stands. Multimodel inference test and model-averaging approaches were conducted to determine the most significant control variables on AGB in each stand type, and piecewise structural equation modeling was conducted to quantify the relationships and directions between the variables. Abiotic drivers, including stand age and climate moisture index, control tree size variation in all stand types, but biotic drivers control AGB through different mechanisms depending on the stand type. Our results show that there were differences in the composition of variables for controlling AGB among stand types. Across all forest types and total stands, we found that increasing the tree size variation is the key driver of increasing AGB as stand age increases. Our study suggests that forest carbon accumulation by stand type can be enhanced if the key drivers of each stand type are properly managed across forest succession, and different forest management plans that consider different regulation factors among stand types are required. Moreover, it is important to adapt resource use patterns for each stand type with considering environmental conditions to maintain healthy and sustainable forests.

Dendrochemical indicators of tree rings reveal historical soil acidification in Swiss forest stands

The deposition of acidifying nitrogen and sulphur compounds from agriculture and fossil fuel combustion has drastically altered the chemical balance of forest soils in many regions of the world, leading to soil acidification with negative impacts on nutrient availability and thus also on tree vitality. The change of nutrient concentrations in the soil solution can be assessed by long-term investigations, however meaningful indicators, reflecting environmental changes, are needed to compare the current nutrient status with past values. We used dendrochemical indicators in stem wood of different tree species to access the impact of acidifying depositions on soil quality and tree nutrition. We selected 328 stem wood samples from 96 trees of Norway spruce (Picea abies), European beech (Fagus sylvatica), Sessile oak (Quercus petrea) and English oak (Quercus robur) from 22 forest sites, which are part of the long-term Intercantonal Forest Observation Program in Switzerland. Four time periods of 20 years were defined according to the emissions of air pollutants between 1910 and 2017. Our results showed a trend of increasing Al concentrations in tree rings of spruce peaking in the most recent time period (2000–2017). Mn and Ca concentrations in spruce and beech wood have decreased significantly throughout the time period 1910–2017. These dendrochemical indicators depended on the soil pH, with higher Al and lower Mn and Ca concentrations for soils with a low pH (pH<4.2). In oak trees the observed dendrochemical changes are confounded with dendrochemical differences between heartwood and sapwood. K and Mg showed inconsistent patterns in all three tree species, which are probably caused by translocation within the stem discs. With the use of piecewise structural equation models (SEM) we highlighted the direct and indirect influences of N deposition on element concentrations in stem wood. The data suggest a relation between increased N deposition and lower base saturation values in the forest soils for all three tree species, which were linked to higher Al concentrations in spruce and lower Mn concentrations in spruce and beech. The relation between Al concentrations in tree rings of Norway spruce and measured base saturation was used to reconstruct past soil base saturation values. It revealed a progressive soil acidification in the long-term forest observation sites. These reconstructed base saturation values were further used to validate modelled values from dynamic biogeochemical models such as SAFE/ForSAFE. This comparison pointed out possible shortcomings such as the lack of organic complexation in those models. Taken together, our analyses showed that element concentrations of Al, Mn, Ca in Norway spruce and European beech stem wood were suitable dendrochemical indicators of environmental change due to soil acidification, as they reflect both direct and indirect effects of air pollutants and chemical soil properties.

The responses of soil microbial characteristics to nitrogen addition and biochar amendment in a Larix kaempferi plantation

Nitrogen (N) deposition is an important environmental factor that can change soil chemical properties. It can also alter the characteristics of microbial communities. The incorporation of biochar into soils is considered a potential strategy to enhance carbon (C) storage in soil and modify the impacts of N deposition. However, the impacts of biochar on the microbial characteristics of soil after short-term N deposition in subtropical plantations remain poorly understood. Here, we investigated the effects of biochar application (0, 5, 10 t ha−1) on soil chemical traits and microbial characteristics (extracellular enzyme activities, microbial community and microbial biomass) in a Larix kaempferi plantation in Shennongjia, China, under N addition (0, 50, 100 kg N ha−1 yr−1) during two growing seasons. We found that simulated N deposition significant increased soil total nitrogen (TN), nitrate nitrogen (NO3−-N) and total phosphorus (TP) concentrations, while heavy N deposition (100 kg N ha−1 yr−1) significant decreased soil microbial biomass nitrogen (MBN) concentration and β-glucosidase (β-GC) activity. Biochar amendment significantly increased soil microbial biomass, TN and soil organic carbon (SOC) concentrations. Both N addition and biochar amendment significantly altered Ascomycota and Basidiomycota relative abundance, with biochar amendment increasing Ascomycota relative abundance and decreasing Mortierellomycota relative abundance under heavy N deposition. Fungal diversity showed a positive correlation to TN, TP and NO3−-N concentrations, but a negative correlation to MBN. Biochar addition inhibited the increase in soil NO3−-N concentration caused by high N addition in the plantation, and influenced the change in the composition of microbial community caused by N addition. Our piecewise structural equation model suggested that N addition affected MBN and fungal diversity directly or indirectly via its effects on soil enzyme activities and properties. In contrast, there were no significant direct or indirect effects on bacterial diversity among all factors. These results improve our understanding of the influence and mechanisms of N addition and biochar amendment on soil microbial characteristics in subtropical coniferous plantations in the short term, and can provide a valuable reference for predicting the future effects of N deposition on soils in this region’s plantation.

Landscape and Marine Environmental Factors Jointly Regulate the Intertidal Species Richness and Community Structure in the Islands of South Korea

Most studies on island biogeography have focused on the terrestrial taxa; however, there are few studies on the drivers of diversity and community structure of intertidal organisms on islands. We evaluated the effect of landscape and marine environmental factors on the species richness (SR), functional diversity (FD), and community structure (SES.MFD) of intertidal invertebrates among the overall, inhabited, and uninhabited islands. Using the data on the intertidal organisms from 78 islands in South Korea, we implemented variable selection and piecewise structural equation modeling to determine the causal relationships between the SR, FD, and SES.MFD with four landscapes (i.e., island area, coastline length, distance from the mainland, and structural connectivity) and three marine environment factors (i.e., mean annual sea surface temperature variation, wind speed, and evapotranspiration). The coastline length had a positive effect on the SR and SES.MFD in the overall islands including inhabited and uninhabited islands. The SR and FD were negatively affected by the variation in sea surface temperature. The relative importance of the landscape and marine environmental factors differed between the inhabited and uninhabited islands. That is, the inhabited islands were mainly affected by the coastline length, whereas uninhabited islands were regulated by marine environmental factors. Our results demonstrated that the biotic factors of the island intertidal ecosystems are controlled by the interactions between the biotic and various environmental factors. Moreover, the results emphasize that the water stress on the intertidal organisms due to climate change may lead to a loss of biodiversity and functional clustering.

Ultraviolet light affects the color vocabulary: evidence from 834 languages.

It has been suggested that people living in regions with a high incidence of ultraviolet light, particularly in the B band (UV-B), suffer a phototoxic effect during their lifetime. This effect, known as lens brunescence, negatively impacts the perception of visible light in the "blue" part of the spectrum, which, in turn, reduces the probability that the lexicon of languages spoken in such regions contains a word specifically denoting "blue." This hypothesis has been recently tested using a database of 142 unique populations/languages using advanced statistical methods, finding strong support. Here, this database is extended to 834 unique populations/languages in many more language families (155 vs. 32) and with a much better geographical spread, ensuring a much better representativity of the present-day linguistic diversity. Applying similar statistical methods, supplemented with novel piecewise and latent variable Structural Equation Models and phylogenetic methods made possible by the much denser sampling of large language families, found strong support for the original hypothesis, namely that there is a negative linear effect of UV-B incidence on the probability that a language has a specific word for "blue." Such extensions are essential steps in the scientific process and, in this particular case, help increase our confidence in the proposal that the environment (here, UV-B incidence) affects language (here, the color lexicon) through its individual-level physiological effects (lifetime exposure and lens brunescence) amplified by the repeated use and transmission of language across generations.

Multiple mechanisms drive biodiversity-ecosystem service multifunctionality but the dominant one depends on the level of multifunctionality for natural forests in northeast China

Biodiversity plays a key role in maintaining and regulating ecosystem multifunctionality (EMF). However, there remains a knowledge gap on the ecological mechanisms behind the relationship between biodiversity and EMF (BEMF), and how these mechanisms vary with EMF gradients, especially at large scale. We used the dataset of 2224 permanent sample plots in Jilin Province, northeast China to test three BEMF mechanisms and their variations with EMF, including mass ratio, ecological niche complementarity and the green soup hypotheses. Biodiversity metrics were taxonomic, structural, phylogenetic, functional diversity and functional identity. EMF was composed of five services: water retention, soil conservation, carbon storage, stand productivity and soil fertility maintenance. EMF was measured using both the averaging (as the average of the standardized values of all services) and threshold (as the number of services passed a threshold) approach. Totally 23 piecewise structural equation models (pSEMs) were developed for EMF with the threshold level ranging from 5% to 95% by an interval of 5%. Results showed that stand biomass had strong positive effect on EMF. Stand structural diversity had significant direct and indirect effects on EMF, but taxonomic, functional diversity and functional identity only had significant direct and indirect effects on EMF at low thresholds. Stand age had significant direct effects on EMF and indirectly enhanced EMF through stand structural diversity and biomass. Our results provided strong evidence that EMF was driven simultaneously by mass ratio, niche complementarity and green soup hypotheses, but the dominant mechanism was dependent on EMF level. Generally, the green soup hypothesis played more important role in explaining EMF. Recommendations for maintaining high functional and structural diversity and large biomass for maximizing EMF were discussed for forest management.

Importance of Bark Physicochemical Properties in an Epiphytic Bryophyte Community within a Temperate Deciduous Broadleaf Forest

Epiphytic bryophytes are important components of forest ecosystems and play important roles in maintaining biodiversity and ecosystem function. However, the main factors driving epiphytic bryophyte diversity remain unclear. We collected the tree epiphytic bryophytes from a one-hectare plot within a temperate deciduous broadleaf forest (China). Canonical correspondence analyses and Mantel tests were used to establish linear regression models and thus dissect the effects of environmental variables (topography, light and bark physicochemical properties) on the species diversity, functional diversity, and phylogenetic diversity of epiphytic bryophytes. The relationship between environmental variables and epiphytic bryophyte diversity was analyzed using piecewise structural equation modeling. Results showed that the physicochemical properties of the bark directly influenced the species diversity and phylogenetic diversity of the epiphytic bryophytes. The physical and chemical properties of bark also indirectly affected the functional diversity of the epiphytic bryophytes. Elucidation of the factors driving epiphytic bryophyte diversity provides insights into their conservation.

Destabilizing Effects of Environmental Stressors on Aquatic Communities and Interaction Networks across a Major River Basin.

Human-driven environmental stressors are increasingly threatening species survival and diversity of river systems worldwide. However, it remains unclear how the stressors affect the stability changes across aquatic multiple communities. Here, we used environmental DNA (eDNA) data sets from a human-dominated river in China over 3 years and analyzed the stability changes in multiple communities under persistent anthropogenic stressors, including land use and pollutants. First, we found that persistent stressors significantly reduced multifaceted species diversity (e.g., species richness, Shannon's diversity, and Simpson's diversity) and species stability but increased species synchrony across multiple communities. Second, the structures of interaction networks inferred from an empirical meta-food web were significantly changed under persistent stressors, for example, resulting in decreased network modularity and negative/positive cohesion. Third, piecewise structural equation modeling proved that the persistent stress-induced decline in the stability of multiple communities mainly depended upon diversity-mediated pathways rather than the direct effects of stress per se; specifically, the increase of species synchrony and the decline of interaction network modularity were the main biotic drivers of stability variation. Overall, our study highlights the destabilizing effects of persistent stressors on multiple communities as well as the mechanistic dependencies, mainly through reducing species diversity, increasing species synchrony, and changing interaction networks.

Species asynchrony stabilizes productivity over 20 years in Northeast China.

The stability of forest productivity can reflect the functioning of forest ecosystems. It is a crucial topic to understand the relationship between biodiversity and ecosystem functions in ecology. Although previous studies have made great progress in understanding the effects of diversity, species asynchrony, and other factors on community biomass and productivity, few studies have explored how these factors affect the temporal stability of productivity. In this study, we hypothesized that diversity, species asynchrony, and topography would directly or indirectly impact the temporal stability of productivity. To test this hypothesis, we used a multiple regression model and a piecewise structural equation model based on the inventory data over 20 years (5-year intervals) from 1992 to 2012 at Jingouling Forest Farm in Northeast China. Our results showed that species asynchrony was the main driving factor affecting the temporal stability of productivity. Structural diversity significantly decreased community stability, while species diversity had a nonsignificant effect on it. We found the combination of a multiple regression model and a piecewise structural equation model is an effective method for evaluating the factors that influence community stability. The effect of species asynchrony is crucial for understanding the ecological mechanisms underlying the diversity-stability relationship in mixed forests.

Increasing stand stature weakens the positive effects of tree richness and structural imbalance on aboveground biomass in temperate forests: The stand stature hypothesis

Irrespective of whether niche complementarity or selection effects enhance aboveground biomass (AGB) due to tree diversity in natural forests, these effects are confounding due to the roles of tree structural imbalance (i.e., either individual tree height or diameter inequality). Here, we hypothesize that increasing stand stature weakens the positive effects of tree richness and structural imbalance on AGB (i.e., we term ‘the stand stature hypothesis’). Using data from 365 plots of natural temperate forest of the Karakoram mountains in the Gilgit-Baltistan region of Pakistan, we tested several piecewise structural equation models (pSEMs) to disentangle the relative impacts of topographic elevation, stand density and tree richness or structural imbalance on AGB across short-statured (mean tree height < 15 m at stand level) and tall-statured (height ≥ 15 m) forests, and across species mixture (i.e., dominated by either single- or multi-species). We found that tree richness and structural imbalance had significant positive effects on AGB in short-statured (β = 0.30 to 0.33, P < 0.001) as compared to tall-statured (β = 0.02 to −0.06, P = 0.635 to 0.088) stands, irrespective of species mixture. In contrast, tree structural imbalance (β = -0.11 to −0.12, P = 0.015 to < 0.001) rather than tree richness (β = 0.01, P = 0.949) declined AGB in multi-species tall-statured stands but these effects were positive (β = 0.01 to 0.32, P = 0.866 to < 0.001) in single-species stands. Meanwhile, increasing topographic elevation declined AGB (β = -0.09 to −0.42, P = 0.151 to < 0.001). We show that increasing stand stature declines the positive effects of tree richness and structural imbalance on AGB, irrespective of the ubiquitous positive influence of stand density on AGB (i.e., the stand stature effect). Thus, we suggest that tall-statured and short-statured forests should be treated separately during the work plan of forest management and biodiversity conservation.

Piecewise Structural Equation Modeling of the collective implicature in child language

ABSTRACT We test children’s distributive and collective sentence interpretations and the variables that predict them. In our first experiment, we establish that adult English collective sentences with the or some in the subject are categorically collective in their interpretations. We further demonstrate that children’s collective and distributive interpretations are predicted by an independent measure of lexical growth, consistent with the lexical refraction hypothesis, and that their collective interpretations are predicted by their distributive interpretations, consistent with the pragmatic scale hypothesis. Furthermore, the distributive interpretations produce complete mediation between lexicon and collective interpretations in a mediation analysis. In our second experiment, we take independent measures of Spanish-speaking children’s knowledge of the Approximate Number System, inhibition, lexicon and phrasal syntax. We then fit a Piecewise Structural Equation Model with these variables, with high statistical power and showing high goodness-of-fit. We consider the contrast between this model of collective interpretations, which are putatively conversational implicatures, and quantity implicature models from previous studies.

Cascading effects of management and landscape on insect pollinators, pollination services and yield in apple orchards

Recent insect pollinator declines, mainly due to the expansion and intensification of agricultural land use, are jeopardizing ecosystem service provisioning in agroecosystems. Organic farming has been suggested as a biodiversity-friendly alternative to conventional farming, but additional insights evaluating its effectiveness in perennial cropping systems are needed. Here, we provide a comprehensive analysis of local and landscape effects on the provided pollination services and yield in apple crops. We first used mixed models to disentangle effects of agricultural management and landscape effects on both taxonomic and functional diversity of wild bees and hoverflies during bloom in both organic and integrated pest management (IPM) apple orchards in Belgium, and then compared these biodiversity indicators with semi-natural grasslands as a benchmark. Next, we applied piecewise structural equation modeling to quantify the direct and indirect effects of orchard management type and landscape on fruit set, seed set and ultimately on crop yield. Orchards, regardless of their type of management, hosted lower taxonomic and functional pollinator diversity compared to the semi-natural benchmark. Yet, pollinator abundance and diversity were higher in orchard edges and increased with small-scale landscape diversity, which was positively associated with the presence of semi-natural habitat, as well as arable and urban land. Investigating the cascading effects on apple yield, we found that yield levels were not shaped by the observed pollinator diversity or by the measured pollination services, but were lower in organic orchards. Overall, we conclude that apple yield was likely not pollinator limited in our study system, but that conserving and restoring semi-natural habitats, maintaining and expanding orchard edges through reducing field sizes and promoting landscape diversity are the most promising avenues for pollinator conservation in orchard landscapes.

Relative influence of inter- and intraspecific competition in an ungulate assemblage modified by introduced species.

Interspecific competition from introduced and naturally colonizing species has potential to affect resident populations, but demographic consequences for vertebrates have rarely been tested. We tested hypotheses of interspecific and intraspecific competition for density, body mass, and fertility of adult female Roe Deer (Capreolus capreolus) across a heterogeneous forest landscape occupied by two introduced deer species: Mediterranean Fallow Deer (Dama dama); and subtropical Reeve's Muntjac (Muntiacus reevesi). Species-specific deer densities in buffers around culling locations of 492 adult female Roe Deer, sampled over seven years, were extracted from spatially explicit models calibrated through annual nocturnal distance sampling. Roe Deer fertility and body mass were related to species-specific deer densities and extent of arable lands using piecewise structural equation models. Reeve's Muntjac density was lower at higher Fallow Deer densities, suggesting interspecific avoidance via interference competition, but greater when buffers included more arable land. Roe Deer body mass was marginally greater when buffers included more arable land and was independent of deer densities. However, Roe Deer fertility was unrelated to female body mass, suggesting that fertility benefits exceeded an asymptotic threshold of body condition in this low-density population. However, Roe Deer fertility was slightly greater rather than reduced in areas with greater local Roe Deer density, suggesting negligible intraspecific competition. In contrast, Roe Deer was less fertile in areas with greater Reeve's Muntjac densities; thus, interspecific exceeded intraspecific competition in this assemblage. In contrast, we found no support for any effects of Fallow Deer density on Roe Deer density, body mass, or fertility. Complex networks of interspecific competition operating in this deer assemblage include: interspecific interference from Fallow Deer exceeded habitat effects for Reeve's Muntjac; and interspecific competition from introduced, smaller sedentary Reeve's Muntjac reduced fertility, unlike intraspecific, or potential competition with larger, more mobile, Fallow Deer for native Roe Deer. Mechanisms driving Roe Deer fertility may include interspecific behavioral interference or stress-resource depletion is considered less likely because Roe Deer fertility was independent of body mass. Findings emphasize the importance of ensuring appropriate management strategies for controlling invasive species.

Characterization of biophysical contexts leading to severe wildfires in Portugal and their environmental controls

Characterizing the fire regime in regions prone to extreme wildfire behavior is essential for providing comprehensive insights on potential ecosystem response to fire disturbance in the context of global change. We aimed to disentangle the linkage between contemporary damage-related attributes of wildfires as shaped by the environmental controls of fire behavior across mainland Portugal. We selected large wildfires (≥100 ha, n = 292) that occurred during the 2015–2018 period, covering the full spectrum of large fire-size variation. Ward's hierarchical clustering on principal components was used to identify homogeneous wildfire contexts at landscape scale on the basis of fire size, proportion of high fire severity, and fire severity variability, and their bottom-up (pre-fire fuel type fraction, topography) and top-down (fire weather) controls. Piecewise Structural Equation Modeling was used to disentangle the direct and indirect relationships between fire characteristics and fire behavior drivers. Cluster analysis evidenced severe and large wildfires in the central region of Portugal displaying consistent fire severity patterns. Thus, we found a positive relationship between fire size and proportion of high fire severity, which was mediated by distinct fire behavior drivers involving direct and indirect pathways. A high fraction of conifer forest within wildfire perimeters and extreme fire weather were primarily responsible for those interactions. In the context of global change, our results suggest that pre-fire fuel management should be targeted at expanding the fire weather settings in which fire control is feasible and promote less flammable and more resilient forest types.

Altitudinal gradients and body size variation among Chinese lizards in different terrains

AbstractSpatial patterns of body size are associated with environmental factors like temperature, seasonality, precipitation, resources, and altitude, among the most relevant. Latitudinal size patterns have been extensively studied. Studies on altitudinal gradients of body size, however, are relatively few. Besides, it is still unclear whether there is variation in the relationship between environmental factors and body size of species, or correlations within different altitudes. China provides a good opportunity to assess the altitudinal gradients of body size, because the entire terrain of China changes from high altitude in the west to low altitude in the east, with three natural terrain stages (low: less than 660 m.a.s.l.; medium: 660–2600 m.a.s.l.; and high: more than 2600 m.a.s.l.). Similarly, lizards are distributed across a wide altitudinal range (from −154.31 m to ~6000 m above sea level). We examined 211 lizard species in China and assessed the altitudinal gradients of Chinese lizard body sizes at assemblage and interspecific levels. Piecewise structural equation models (pSEM) were used to investigate the direct and indirect relationships between body size and environmental factors within different terrains (low, medium, and high altitudes). Overall, we found that body size in Chinese lizards decreases with increasing altitude. However, there were variations in the altitudinal gradients and drivers within the three terrain stages. Altitude has both direct (medium and low stages) and indirect (high stages) effects in shaping lizard size. We established that body size increased with increasing altitudes in the low and medium terrain stages. Seasonality had different effects on body size in medium (positively) and low (negatively) stages. However, among the three terrain stages, temperature was consistently negatively correlated with lizard size. Overall, we identified complex patterns and drivers of altitudinal gradients of body size within the three terrain stages, probably due to the different environmental conditions across altitudes.

Shrub and precipitation interactions shape functional diversity of nematode communities on the Qinghai-Tibet Plateau.

Land use and climate change alter biodiversity patterns and ecosystem functioning worldwide. Land abandonment with consequent shrub encroachment and changes in precipitation gradients are known factors in global change. Yet, the consequences of interactions between these factors on the functional diversity of belowground communities remain insufficiently explored. Here, we investigated the dominant shrub effects on the functional diversity of soil nematode communities along a precipitation gradient on the Qinghai-Tibet Plateau. We collected three functional traits (life-history C-P value, body mass, and diet) and calculated the functional alpha and beta diversity of nematode communities using kernel density n-dimensional hypervolumes. We found that shrubs did not significantly alter the functional richness and dispersion, but significantly decreased the functional beta diversity of nematode communities in a pattern of functional homogenization. Shrubs benefited nematodes with longer life-history, larger body mass, and higher trophic levels. Moreover, the shrub effects on the functional diversity of nematodes depended strongly on precipitation. Increasing precipitation reversed the effects shrubs have on the functional richness and dispersion from negative to positive but amplified the negative effects shrubs have on functional beta diversity of nematodes. Benefactor shrubs had stronger effects on the functional alpha and beta diversity of nematodes than allelopathic shrubs along a precipitation gradient. A piecewise structural equation model showed that shrubs and its interactions with precipitation indirectly increased the functional richness and dispersion through plant biomass and soil total nitrogen, whereas it directly decreased the functional beta diversity. Our study reveals the expected changes in soil nematode functional diversity following shrub encroachment and precipitation, advancing our understanding of global climate change on nematode communities on the Qinghai-Tibet Plateau.

Soil microbial and macroinvertebrate functional diversity in response to Zokor disturbance in Tibetan alpine meadow

Soils contain a remarkable diversity of organisms that are important regulators of ecosystem functions. However, the knowledge of how the environment shapes biodiversity patterns below ground remains limited in alpine areas of the Tibetan Plateau. Here, we conducted a microhabitat scale study (400 m2 plot) integrating data on soil and plant community characteristics to explore the driving forces of functional diversity of soil microbial and macroinvertebrate communities under disturbance by plateau zokor (Eospalax baileyi), a subterranean rodent inhabiting the Tibetan Plateau. The results show that plateau zokor disturbance led to a decline in the belowground biomass of grasses, whereupon the total belowground plant biomass and soil organic carbon decreased significantly. The functional diversity of soil microbial and macroinvertebrate communities was significantly increased under plateau zokor disturbance. Redundancy analysis indicated that soil moisture, temperature and compaction, in combination with plant species richness and belowground biomass of forb were the most important factors in driving soil microbial and macroinvertebrate functional diversity. Piecewise structural equation modeling (SEM) revealed that plateau zokor mound disturbance had positive effects on the functional diversity of soil microbial and macroinvertebrate communities by regulating soil physical properties (moisture, temperature, and compaction) and plant species richness within the habitat. Further, zokor disturbance affected the functional diversity of soil microbial and macroinvertebrate communities indirectly via regulating soil organic carbon. Our study provides evidence that the functional diversity of microbes is more driven by environmental changes than those of macroinvertebrates.

Island biogeography of soundscapes: Island area shapes spatial patterns of avian acoustic diversity

AbstractAimThe equilibrium theory of island biogeography predicts the positive species–area relationship and the negative species–isolation relationship, resulting in higher species richness on large and close islands. Unlike species richness, soundscape diversity integrates sound from various sources (e.g. biophony, geophony and anthrophony). However, how soundscape diversity varies with island area and isolation still needs to be tested. Here, we explored the island biogeography of bird soundscapes and the determinants of island attributes in shaping bird diversity and soundscape diversity.LocationThousand Island Lake, Zhejiang, China.TaxonBirds.MethodsWe recorded avian soundscapes by audio recorders and censused bird diversity by line transects on 20 land‐bridge islands. We calculated four acoustic indices (acoustic complexity index, bioacoustic index, acoustic evenness index and acoustic entropy index) to assess acoustic richness, evenness and heterogeneity to explore the soundscape diversity of birds. We used multiple linear regressions, spatial autoregressions and piecewise structural equation models to examine the relationships between bird richness and acoustic diversity, and island attributes.ResultsWe found positive diversity–area relationships for avian soundscapes. Larger islands had more vocal species and higher habitat diversity, which led to an increment in the richness and unevenness of avian soundscapes on large islands. Acoustic evenness decreased with increasing isolation (distance to the mainland).Main ConclusionsSoundscapes on large islands are more diverse than those on small islands. Rich acoustic assemblages and heterogeneous habitats promote increased soundscape diversity on islands. Conversely, the lack of vocal contributors, resulting in a decrement in the communication of acoustic signals, can create a lower soundscape diversity on small and remote islands. Our study emphasizes the necessity of examining both species and habitat diversity in island biogeography for better understanding the underlying mechanisms determining biological soundscapes on islands.

Enrichment of organic carbon increases the flux of phosphorus from sediment in mariculture ponds

Environmental pollution associated with aquaculture activities is one of the major bottlenecks encountered in the sustainable development of fisheries. Accumulating organic carbon (org-C) is an inevitable but undesirable consequence of aquaculture activities, and its degradation influences nutrient flux. However, neither the variations in org-C accumulation nor its impact on phosphorus (P) dynamic has been clearly untangled and reliably quantified so far. Therefore, we carried out a field survey to examine the influences of org-C accumulation on sediment P release in mariculture ponds. The results suggested that org-C contents varied considerably between ponds, being significantly lower in monoculture ponds with bivalve shellfish than in polyculture ponds with bivalve shellfish, shrimp, crab, and fish, likely due to the less-artificial-feeding practice and the function of bivalve shellfish as “environmental cleaners.”Sediment P in mariculture ponds mainly occurred in iron-bound P (44%) and organic-P (hot NaOH-extractable organic + acid-soluble organic P = 56%), while calcium-bound P (CaP) only contributed a tiny proportion of about 1%. The positive correlation between P-flux from sediment and org-C suggested that org-C enrichment can stimulate sediment P release. Further analysis of the linear mixed model combined with piecewise structural equation modeling indicated that the two main forces driving P release - enzymatic hydrolysis release and anoxic desorption - operate with sediment org-C being a significant factor (accounted for 75% of the variation in P-flux). At the same time, other factors such as alkaline phosphatase activity, pH, and CaP may play minor roles in affecting P release. Our findings indicated that org-C accumulated in the aquaculture ponds might trigger sediment P release, posing a potential risk of contaminating the downstream water bodies during tailwater discharge.