•CuO-NiO core-shell microspheres with p-p heterojunction were prepared through a simple two-step hydrothermal method.•CuO-NiO core-shell microspheres exhibited enhanced gas sensing properties ...compared with bare CuO microspheres.•The enhanced gas sensing of CuO-NiO core-shell microspheres may be in relation to catalytic effect of NiO flower-like shell and formation of heterojunction.
CuO-NiO core-shell microspheres were prepared through a simple two-step hydrothermal method. The crystal structure, valence state and morphology of the CuO-NiO core-shell were studied by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The surface characteristic of the microspheres was investigated by the nitrogen adsorption method. To demonstrate the use of CuO-NiO core-shell materials, a chemical gas sensor has been fabricated and investigated. The results revealed that core-shell microspheres sensor exhibited enhanced H2S sensing properties compared with bare CuO microspheres. The enhanced gas responses were discussed in relation to catalytic effect of NiO flower-like shell as well as formation of heterojunction.
The effect of biodiversity on primary productivity has been a hot topic in ecology for over 20 years. Biodiversity-productivity relationships in natural ecosystems are highly variable, although ...positive relationships are most common. Understanding the conditions under which different relationships emerge is still a major challenge. Here, by analyzing HerbDivNet data, a global survey of natural grasslands, we show that biodiversity stabilizes rather than increases plant productivity in natural grasslands at the global scale. Our results suggest that the effect of species richness on productivity shifts from strongly positive in low-productivity communities to strongly negative in high-productivity communities. Thus, plant richness maintains community productivity at intermediate levels. As a result, it stabilizes plant productivity against environmental heterogeneity across space. Unifying biodiversity-productivity and biodiversity-spatial stability relationships at the global scale provides a new perspective on the functioning of natural ecosystems.
Ecology Letters (2011)
Observational evidence increasingly suggests that the Janzen–Connell effect extends beyond the species boundary. However, this has not been confirmed experimentally. Herein, we ...present both observational and experimental evidence for a phylogenetic Janzen–Connell effect. In a subtropical forest in Guangdong province, China, we observed that co‐occurring tree species are less phylogenetically related than expected. The inhibition effects of neighbouring trees on seedling survival decreased with increasing phylogenetic distance between them. In a shade‐house experiment, we studied seedling survival of eight species on soil collected close to Castanopsis fissa relative to their survival on soil close to their own adult trees, and found that this relative survival rate increased with phylogenetic distance from C. fissa. This phylogenetic signal disappeared when seedlings were planted in fungicide‐treated soil. Our results clearly support negative effects of phylogenetically similar neighbouring trees on seedling survival and suggest that these effects are caused by associated host‐specific fungal pathogens.
Numerous grassland experiments have found evidence for a complementarity effect, an increase in productivity with higher plant species richness due to niche partitioning. However, empirical tests of ...complementarity in natural forests are rare. We conducted a spatially explicit analysis of 518 433 growth records for 274 species from a 50‐ha tropical forest plot to test neighborhood complementarity, the idea that a tree grows faster when it is surrounded by more dissimilar neighbors. We found evidence for complementarity: focal tree growth rates increased by 39.8% and 34.2% with a doubling of neighborhood multi‐trait dissimilarity and phylogenetic dissimilarity, respectively. Dissimilarity from neighbors in maximum height had the most important effect on tree growth among the six traits examined, and indeed, its effect trended much larger than that of the multi‐trait dissimilarity index. Neighborhood complementarity effects were strongest for light‐demanding species, and decreased in importance with increasing shade tolerance of the focal individuals. Simulations demonstrated that the observed neighborhood complementarities were sufficient to produce positive stand‐level biodiversity–productivity relationships. We conclude that neighborhood complementarity is important for productivity in this tropical forest, and that scaling down to individual‐level processes can advance our understanding of the mechanisms underlying stand‐level biodiversity–productivity relationships.
•Field and greenhouse trials were conducted to assess the allelopathic effects of Eucalyptus.•The effects derived from various mechanisms of allelopathic chemical release were detected.•Allelopathy ...in the E. urophylla plantation was selective.•The introduced tree species, Albizia lebbeck, can be planted in the Eucalyptus plantation.
Allelopathy is widely considered to be one of the causes of biodiversity reduction in Eucalyptus plantations. However, most research conducted on the allelopathic effects of Eucalyptus is performed in the laboratory with weeds and crops as receptors, which fail to fully reflect natural ecosystems. In this study, we conducted two field trials and a greenhouse trial to assess the influence of soil allelopathy, allelochemical volatilization, and foliage litter decomposition on seed germination and seedling growth of three native (Acmena acuminatissima, Cryptocarya concinna and Pterospermum lanceaefolium) and one introduced (Albizia lebbeck) tree species in a Eucalyptus urophylla and Pinus elliottii plantation. In order to avoid confounding factors relating to management strategies and environmental influences, only one plantation of each species was used for experimentation. In the allelopathy experiment, the root length of the three native species was significantly inhibited in the E. urophylla plantation compared with that in the P. elliottii plantation. In the volatilization experiments, the seedling survival rate of the three native species was greater in the E. urophylla plantation, but significant differences were found for A. acuminatissima and C. concinna. Root length and dry weight of P. lanceaefolium increased significantly in the E. urophylla plantation, in the foliage litter decomposition experiments. There was no significant difference between the two plantations for A. lebbeck, except that the seedling survival rate was greater in the E. urophylla plantation in the foliage litter decomposition experiment. We concluded that allelopathy in the E. urophylla plantation was selective, which inhibited the growth of the native tree species but had no significant influence on the introduced A. lebbeck species. Allelopathy from volatilization and foliage litter decomposition contributed little to the inhibitory effects. We suggest that the introduced nitrogen-fixing species, A. lebbeck could be a potential choice for the establishment of mixed stands with Eucalyptus.
BACKGROUND AND AIMS: Volatile organic compounds (VOCs) released into the air from eucalyptus have putative roles in chemical communications. But the types and concentrations released in nature, as ...well as the ecological functions of VOCs in soil water, have not been adequately investigated to date. METHODS: We developed some effective methods for the extraction of VOCs released by root exudation, foliage and leaf litter leaching, and leaf litter decomposition, into water extracts in the laboratory or from field soil around Eucalyptus urophylla. The VOCs were determined by GC-MS. Lolium multiflorum Lam. (annual ryegrass) and Bidens pilosa (cobbler’s pegs) were selected to test the phytotoxic effects of VOCs in soil water released from E. urophylla grown under natural conditions. RESULTS: Fourteen VOCs in soil water, released by foliage and leaf litter leaching and leaf litter decomposition, were identified and quantified. But we did not identify any VOCs from root exudates. When the concentrations of VOCs were reconstituted to mimic the soil conditions, the laboratory bioassays showed that seed germination and seedling growth of the tested plants were significantly inhibited. CONCLUSIONS: VOCs in soil water were phytotoxic when they had been released by foliage and leaf litter leaching and leaf litter decomposition from E. urophylla.
Because the frequency of heterospecific interactions inevitably increases with species richness in a community, biodiversity effects must be expressed by such interactions. However, little is ...understood how heterospecific interactions affect ecosystem productivity because rarely are biodiversity ecosystem functioning experiments spatially explicitly manipulated. To test the effect of heterospecific interactions on productivity, direct evidence of heterospecific neighborhood interaction is needed. In this study we conducted experiments with a detailed spatial design to investigate whether and how heterospecific neighborhood interactions promote primary productivity in a grassland community. The results showed that increasing the heterospecific: conspecific contact ratio significantly increased productivity. We found there was a significant difference in the variation in plant height between monoculture and mixture communities, suggesting that height-asymmetric competition for light plays a central role in promoting productivity. Heterospecific interactions make tall plants grow taller and short plants become smaller in mixtures compared to monocultures, thereby increasing the efficiency of light interception and utilization. Overyielding in the mixture communities arises from the fact that the loss in the growth of short plants is compensated by the increased growth of tall plants. The positive correlation between species richness and primary production was strengthened by increasing the frequency of heterospecific interactions. We conclude that species richness significantly promotes primary ecosystem production through heterospecific neighborhood interactions.
Density dependence has long been considered an important mechanism for species coexistence in forests. Density‐dependent processes can be important mechanisms driving differences in species diversity ...across latitudes. Here we examined the decline in strength of density dependence with increasing latitude, and particularly how density dependence affected both conspecifics and heterospecifics. Conspecific individuals within a species were predominantly aggregated at the three different latitudes of the three study sites in China. The percentage of aggregated species declined with increasing spatial scale and growth stages, which confirmed the overall importance of density dependence. Compared with a latitudinal gradient, the intensity of aggregation in the most northerly temperate (Changbaishan) plot was significantly higher than that in the tropical (Bawangling) or subtropical (Heishiding) plots. This showed that the strength of density dependence among conspecific individuals at low latitudes was stronger than that for high latitudes. We found that the more closely related species were more spatially adjacent in the temperate plot, while the opposite was true in the tropical and subtropical plots at most scales. After calculating the recruitment probability of all species of mature trees, we found that 19 of the 32 species in the tropical plot and 7 of the 12 species in the subtropical plot were less likely to recruit near closely related species. In the northern temperate plot, only one species demonstrated this phenomenon. These results therefore suggest that latitudinal variation in the intensity of negative density‐dependent recruitment resulting from specialist natural enemies (the Janzen–Connell hypothesis) may contribute to the latitudinal gradient of diversity in trees. The strength of density dependence at low latitudes was stronger than at high latitudes, regardless of whether this dependence was measured between only conspecific individuals or between individuals of closely related species.
Community compensatory trend (CCT) is thought to facilitate persistence of rare species and thus stabilize species composition in tropical forests. However, whether CCT acts over broad geographical ...ranges is still in question. In this study, we tested for the presence of negative density dependence (NDD) and CCT in three forests along a tropical-temperate gradient. Inventory data were collected from forest communities located in three different latitudinal zones in China. Two widely used methods were used to test for NDD at the community level. The first method considered relationships between the relative abundance ratio and adult abundance. The second method emphasized the effect of adult abundance on abundance of established younger trees. Evidence for NDD acting on different growth forms was tested by using the first method, and the presence of CCT was tested by checking whether adult abundance of rare species affected that of established younger trees less than did abundance of common species. Both analyses indicated that NDD existed in seedling, sapling and pole stages in all three plant communities and that this effect increased with latitude. However, the extent of NDD varied among understory, midstory and canopy trees in the three communities along the gradient. Additionally, despite evidence of NDD for almost all common species, only a portion of rare species showed NDD, supporting the action of CCT in all three communities. So, we conclude that NDD and CCT prevail in the three recruitment stages of the tree communities studied; rare species achieve relative advantage through CCT and thus persist in these communities; CCT clearly facilitates newly established species and maintains tree diversity within communities across our latitudinal gradient.
Soilborne pathogens can contribute to diversity maintenance in tree communities through the Janzen-Connell effect, whereby the pathogenic reduction of seedling performance attenuates with distance ...from conspecifics. By contrast, arbuscular mycorrhizal fungi (AMF) have been reported to promote seedling performance; however, it is unknown whether this is also distance dependent. Here, we investigate the distance dependence of seedling performance in the presence of both pathogens and AMF. In a subtropical forest in south China, we conducted a four-year field census of four species with relatively large phylogenetic distances and found no distance-dependent mortality for newly germinated seedlings. By experimentally separating the effects of AMF and pathogens on seedling performance of six subtropical tree species in a shade house, we found that soil pathogens significantly inhibited seedling survival and growth while AMF largely promoted seedling growth, and these effects were host specific and declined with increasing conspecific distance. Together, our field and experimental results suggest that AMF can neutralize the negative effect of pathogens and that the Janzen-Connell effect may play a less prominent role in explaining diversity of nondominant tree species than previously thought.
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