β-diversity in temperate grasslands is driven by stronger environmental filtering of plant species with large genomes

Elucidating mechanisms underlying community assembly and biodiversity patterns is central to ecology and evolution. Genome size (GS) has long been hypothesized to potentially affect species' capacity to tolerate environmental stress and might therefore help drive community assembly. However, its role in driving β-diversity (i.e., spatial variability in species composition) remains unclear. We measured GS for 161 plant species and community composition across 52 sites spanning a 3200-km transect in the temperate grasslands of China. By correlating the turnover of species composition with environmental dissimilarity, we found that resource filtering (i.e., environmental dissimilarity that includes precipitation, and soil nitrogen and phosphorus concentrations) affected β-diversity patterns of large-GS species more than small-GS species. By contrast, geographical distance explained more variation of β-diversity for small-GS than for large-GS species. In a 10-year experiment manipulating levels of water, nitrogen, and phosphorus, adding resources increased plant biomass in species with large GS, suggesting that large-GS species are more sensitive to the changes in resource availability. These findings highlight the role of GS in driving community assembly and predicting species responses to global change

Nitrogen addition regulates soil nematode community composition through ammonium suppression

Nitrogen (N) enrichment resulting from anthropogenic activities has greatly changed the composition and functioning of soil communities. Nematodes are one of the most abundant and diverse groups of soil organisms, and they occupy key trophic positions in the soil detritus food web. Nematodes have therefore been proposed as useful indicators for shifts in soil ecosystem functioning under N enrichment. Here, we monitored temporal dynamics of the soil nematode community using a multi-level N addition experiment in an Inner Mongolia grassland. Measurements were made three years after the start of the experiment. We used structural equation modeling (SEM) to explore the mechanisms regulating nematode responses to N enrichment. Across the N enrichment gradient, significant reductions in total nematode abundance, diversity (H' and taxonomic richness), maturity index (MI), and the abundance of root herbivores, fungivores and omnivores-predators were found in August. Root herbivores recovered in September, contributing to the temporal variation of total nematode abundance across the N gradient. Bacterivores showed a hump-shaped relationship with N addition rate, both in August and September. Ammonium concentration was negatively correlated with the abundance of total and herbivorous nematodes in August, but not in September. Ammonium suppression explained 61% of the variation in nematode richness and 43% of the variation in nematode trophic group composition. Ammonium toxicity may occur when herbivorous nematodes feed on root fluid, providing a possible explanation for the negative relationship between herbivorous nematodes and ammonium concentration in August. We found a significantly positive relationship between fungivores and fungal phospholipid fatty acids (PLFA), suggesting bottom-up control of fungivores. No such relationship was found between bacterivorous nematodes and bacterial PLFA. Our findings contribute to the understanding of effects of N enrichment in semiarid grassland on soil nematode trophic groups, and the cascading effects in the detrital soil food web

Highly Sensitive and Selective Fluorescence “Turn-On” Detection of Pb (II) Based on Fe3O4@Au–FITC Nanocomposite

New nanocomposites, Fe3O4@Au–FITC, were prepared and explored to develop a fluorescent detection of Pb2+. The Fe3O4@AuNPs–FITC nanocomposites could be etched by Pb2+ in the presence of Na2S2O3, leading to fluorescence recovery of FITC quenched by Fe3O4@Au nanocomposites. With the increase of Pb2+ concentration, the fluorescence recovery of Fe3O4@AuNPs–FITC increased gradually. Under optimized conditions, a detection limit of 5.2 nmol/L of Pb2+ with a linear range of 0.02–2.0 µmol/L were obtained. The assay demonstrated negligible response to common metal ions. Recoveries of 98.2–106.4% were obtained when this fluorescent method was applied in detecting Pb2+ spiked in a lake-water sample. The above results demonstrated the high potential of ion-induced nanomaterial etching in developing robust fluorescent assays

Nitrogen enrichment affects the competition network of aboveground species on the Inner Mongolia steppe

Nitrogen(N) enrichment changes the community structure of terrestrial ecosystems. However, the patterns and structural functions of species interaction networks under N-enrichment conditions are still unclear. We compared and analysed data from 13 years of N deposition experiments in the Inner Mongolia temperate steppe in China. We found that spatial association effectively detected intransitive networks, the structure of which was occasionally changed by species with low biomass but high-frequency occurrence, as an especially vital intermediary for forming a large network. The peak value of the network complexity was maintained at 2 gNm(-2) year(-1). In the third year after fertilization at 50 gNm(-2) year(-1), the species interaction changed to transitivity, which lasted for 8 years. Then, the environment completely replaced species interactions as the main factor affecting community composition. Surprisingly, the negative effect of N enrichment on the species network was counteracted by mowing and precipitation, which increased the probability of intransitive network formation. In the intransitive network, species diversity was not only maintained but also increased under low N-addition rates from 0 gNm(-2) year(-1) to 3 gNm(-2) year(-1). These studies indicated that N enrichment reduced the complexity of the species network and increased hierarchical differences among species competition. Intransitive competition is highly prevalent and a key driver of species coexistence and diversity maintenance in the typical steppe. Moreover, environmental factors directly affect plant intransitive competition, resulting in changes in species diversity

Sampling Date, Leaf Age and Root Size: Implications for the Study of Plant C:N:P Stoichiometry

Plant carbon : nitrogen : phosphorus (C:N:P) ratios are powerful indicators of diverse ecological processes. During plant development and growth, plant C:N:P stoichiometry responds to environmental conditions and physiological constraints. However, variations caused by effects of sampling (i.e. sampling date, leaf age and root size) often have been neglected in previous studies. We investigated the relative contributions of sampling date, leaf age, root size and species identity to stoichiometric flexibility in a field mesocosm study and a natural grassland in Inner Mongolia. We found that sampling date, leaf age, root size and species identity all significantly affected C:N:P stoichiometry both in the pot study as well as in the field. Overall, C:N and C:P ratios increased significantly over time and with increasing leaf age and root size, while the dynamics of N:P ratios depended on species identity. Our results suggest that attempts to synthesize C:N:P stoichiometry data across studies that span regional to global scales and include many species need to better account for temporal variation

Environmental filtering rather than phylogeny determines plant leaf size in three floristically distinctive plateaus

Leaf is essential for plant growth and development; however, the relative importance of environmental filtering and phylogeny in determining leaf size across different spatial scales in grassland ecosystems remains poorly explored. We used transect methodology to explore the spatial variation in leaf size and its underlying mechanisms in grasslands along three topographically and floristically distinctive plateaus in northern China. We measured leaf size of a total of 1192 grassland species in the Tibetan Plateau (TP, temperature limited), Loess Plateau (LP, soil-nutrient limited), and Mongolia Plateau (MP, precipitation limited) along three transects encompassing meadow, typical, and desert steppes. Leaf size ranged from 0.01 to 258.16 cm2, with an average of 5.54 cm2. The smallest leaves were measured in the TP. At the vegetation association level, the largest leaves were present in the meadow steppe, followed by those in typical and desert steppes, irrespective of the plateau. Unexpectedly, phylogeny had a negligible effect on the spatial variation in leaf size in the grasslands. Leaf size was positively correlated with growing-season temperature and precipitation but negatively correlated with ultraviolet (UV) radiation, suggesting that environmental filtering plays a more important role in affecting leaf size than phylogeny. Furthermore, leaf size in the TP and MP was mainly affected by precipitation and UV radiation, respectively, whereas that in the LP was affected by temperature, precipitation, soil nutrients and UV light. Specifically, our results underscored the importance of environmental filtering rather than phylogeny in determining plant leaf size and shed light on the unexpected role of UV radiation in contributing to leaf size variations in these plateaus. Our study provides novel insights into the response of plants to global change, especially in plateaus, alpine zone, and high-latitude areas

5300-year-old soil carbon is less primed than young soil organic matter

Soils harbor more than three times as much carbon (C) as the atmosphere, a large fraction of which (stable organic matter) serves as the most important global C reservoir due to its long residence time. Litter and root inputs bring fresh organic matter (FOM) into the soil and accelerate the turnover of stable C pools, and this phenomenon is termed the “priming effect” (PE). Compared with knowledge about labile soil C pools, very little is known about the vulnerability of stable C to priming. Using two soils that substantially differed in age (500 and 5300 years before present) and in the degree of chemical recalcitrance and physical protection of soil organic matter (SOM), we showed that leaf litter amendment primed 264% more organic C from the young SOM than from the old soil with very stable C. Hierarchical partitioning analysis confirmed that SOM stability, reflected mainly by available C and aggregate protection of SOM, is the most important predictor of leaf litter-induced PE. The addition of complex FOM (i.e., leaf litter) caused a higher bacterial oligotroph/copiotroph (K-/r-strategists) ratio, leading to a PE that was 583% and 126% greater than when simple FOM (i.e., glucose) was added to the young and old soils, respectively. This implies that the PE intensity depends on the chemical similarity between the primer (here FOM) and SOM. Nitrogen (N) mining existed when N and simple FOM were added (i.e., Glucose+N), and N addition raised the leaf litter-induced PE in the old soil that had low N availability, which was well explained by the microbial stoichiometry. In conclusion, the PE induced by FOM inputs strongly decreases with increasing SOM stability. However, the contribution of stable SOM to CO2 efflux cannot be disregarded due to its huge pool size

A Review of Thin-Film Magnetoelastic Materials for Magnetoelectric Applications

Since the revival of multiferroic laminates with giant magnetoelectric (ME) coefficients, a variety of multifunctional ME devices, such as sensor, inductor, filter, antenna etc. have been developed. Magnetoelastic materials, which couple the magnetization and strain together, have recently attracted ever-increasing attention due to their key roles in ME applications. This review starts with a brief introduction to the early research efforts in the field of multiferroic materials and moves to the recent work on magnetoelectric coupling and their applications based on both bulk and thin-film materials. This is followed by sections summarizing historical works and solving the challenges specific to the fabrication and characterization of magnetoelastic materials with large magnetostriction constants. After presenting the magnetostrictive thin films and their static and dynamic properties, we review micro-electromechanical systems (MEMS) and bulk devices utilizing ME effect. Finally, some open questions and future application directions where the community could head for magnetoelastic materials will be discussed

Spatial patterns and ecological drivers of soil nematode beta-diversity in natural grasslands vary among vegetation types and trophic position

Understanding biogeographic patterns of community assemblages is a core objective in ecology, but for soil communities these patterns are poorly understood. To understand the spatial patterns and underlying mechanisms of beta-diversity in soil communities, we investigated the beta-diversity of soil nematode communities along a 3,200-km transect across semi-arid and arid grasslands. Spatial turnover and nested-resultant are the two fundamental components of beta-diversity, which have been attributed to various processes of community assembly. We calculated the spatial turnover and nested-resultant components of soil nematode beta-diversity based on the beta-partitioning framework. Distance matrices for the dissimilarity of soil nematode communities were computed using the 'Sorensen' method. We fitted negative exponential models to compare the distance decay patterns in nematode community similarity with geographic distance and plant community distance in three vegetation types (desert, desert steppe and typical steppe) and along the whole transect. Variation partitioning was used to distinguish the contribution of geographic distance and environmental variables to beta-diversity and the partitioned components. Geographic distance and environmental filtering jointly drove the beta-diversity patterns of nematode community, but environmental filtering explained more of the variation in beta-diversity in the desert and typical steppe, whereas geographic distance was important in the desert steppe. Nematode community assembly was explained more by the spatial turnover component than by the nested-resultant component. For nematode feeding groups, the beta-diversity in different vegetation types increased with geographic distance and plant community distance, but the nested-resultant component of bacterial feeders in the desert ecosystem decreased with geographic distance and plant community distance. Our findings show that spatial variation in soil nematode communities is regulated by environmental processes at the vegetation type scale, while spatial processes mainly work on the regional scale, and emphasize that the spatial patterns and drivers of nematode beta-diversity differ among trophic levels. Our study provides insight into the ecological processes that maintain soil biodiversity and biogeographic patterns of soil community assemblage at large spatial scales

Mean C:N, C:P, N:P ratios for foliage of different ages (young = emerging; medium = fully expanded at midpoint of plant; old = fully expanded at base of plant) (left) and roots in different size categories (small = Φ ≤2 mm; medium = 2 mm <Φ<5 mm; large = Φ≥5 mm) (right).

<p>Error bars are SEM.</p