Multiple abiotic and biotic drivers of long-term wood decomposition within and among species in the semi-arid inland dunes:A dual role for stem diameter

Litter decomposition in sunny, semi-arid and arid ecosystems is controlled by both biotic factors including litter traits and abiotic factors including UV light, but for wood decomposition it still remains uncertain which of these environmental factors are the predominant controls among different woody species. In these dry ecosystems, it is likely that the stem diameter and spatial position of the dead wood are of particular importance especially where wood can be buried versus exposed due to substrate displacement by wind. Here we focus on the fact that stem diameter can affect decomposition rates both via the relative surface exposure to sunlight or soil and via higher resource quality of narrower stems to decomposers. In a field manipulation experiment, we investigated the relative importance of litter position (sand burial vs. surface vs. suspended above the surface), UV radiation (block versus pass) and stem diameter class (<2, 2–4, 4–8, 8–13 and 13–20 mm) on the mass loss of woody litters of four shrub species in an inland dune ecosystem in northern China. We found that after 34 months of in situ incubation, the mass loss of buried woody litters was three times faster than those of suspended and surface woody litters (53.5 ± 2.7%, 17.0 ± 1.0% and 14.4 ± 1.2%, respectively). In surface and suspended positions, litter decomposition rates were almost equally low and most mass loss was during the first 2 years, when bark was still attached and UV radiation had no significant effect on woody litter mass loss. These findings suggest that sand burial is the main environmental driver of wood decomposition via its control on microbial activity. Moreover, wood N and diameter class were the predominant factors driving woody litter decomposition. A key finding was that wider stems had slower litter decomposition rates not only directly (presumably via greater relative surface exposure) but also indirectly via their higher wood dry matter content or lower wood N; these effects were modulated by litter position. Our findings highlight a dual role of stem diameter on wood decomposition, that is, via relative surface exposure and via wood traits. The accuracy and confidence of global carbon cycling models would be improved by incorporating the different effects of stem diameter on woody litter decomposition and below-ground wood decomposition processes in drylands

Genetic divergence and gene flow among Mesorhizobium strains nodulating the shrub legume Caragana

Although the biogeography of rhizobia has been investigated extensively, little is known about the adaptive molecular evolution of rhizobia influenced by soil environments and selected by legumes. In this study, microevolution of Mesorhizobium strains nodulating Caragana in a semi-fixing desert belt in northern China was investigated. Five core genes-atpD, glnII, gyrB, recA, and rpoB, six heat-shock factor genes-clpA, clpB, dnaK, dnaf, grpE, and hlsU, and five nodulation genes-nodA, nodC, nodD, nodG, and nodP, of 72 representative mesorhizobia were studied in order to determine their genetic variations. A total of 21 genospecies were defined based on the average nucleotide identity (ANI) of concatenated core genes using a threshold of 96% similarity, and by the phylogenetic analyses of the core/heat-shock factor genes. Significant genetic divergence was observed among the genospecies in the semi-fixing desert belt (areas A-E) and Yunnan province (area F), which was closely related to the environmental conditions and geographic distance. Gene flow occurred more frequently among the genospecies in areas A-E, and three sites in area B, than between area F and the other five areas. Recombination occurred among strains more frequently for heat-shock factor genes than the other genes. The results conclusively showed that the Caragana-associated mesorhizobia had divergently evolved according to their geographic distribution, and have been selected not only by the environmental conditions but also by the host plants. (C) 2015 Elsevier GmbH. All rights reserved

Microstructure and dielectric properties of BZT-BCT/PVDF nanocomposites

In this paper, the 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 nanofibers (BZT-BCT NFs) with high aspect ratio were synthesized by electrospinning technique, and the PVDF-based composites filled with the BT NPs or BZT-BCT NFs were fabricated. Obviously, compared to the BT NPs/PVDF composite, the dielectric properties of BZT-BCT NFs/PVDF composites are improved at given volume fraction. The electric modulus formalism indicated that the BZT-BCT NFs could effectively enhance the interfacial polarization of the BZT-BCT NFs/PVDF composites than that of the BT NPs/PVDF composite. In addition, the BZT-BCT NFs with large aspect ratio can make the composites polarize at a higher field strength, thus the composites obtain higher polarization strength. The energy density of 3 vol% BZT-BCT NFs/PVDF composite is 3.08 J/cm3 at 240 kV/mm, which is 2.01 times higher enhancement than the BT NPs/PVDF composite (1.53 J/cm3 at 180 kV/mm). These results also provide a simple but effective method to achieve the materials with high capacitance for energy storage. Keywords: Powders, Nanocomposites, Interfaces, Dielectric properties, Energy storage densit

Plant Interactions with Changes in Coverage of Biological Soil Crusts and Water Regime in Mu Us Sandland, China

Plant interactions greatly affect plant community structure. Dryland ecosystems are characterized by low amounts of unpredictable precipitation as well as by often having biological soil crusts (BSCs) on the soil surface. In dryland plant communities, plants interact mostly as they compete for water resources, and the direction and intensity of plant interaction varies as a function of the temporal fluctuation in water availability. Since BSCs influence water redistribution to some extent, a greenhouse experiment was conducted to test the hypothesis that the intensity and direction of plant interactions in a dryland plant community can be modified by BSCs. In the experiment, 14 combinations of four plant species (Artemisia ordosica, Artemisia sphaerocephala, Chloris virgata and Setaria viridis) were subjected to three levels of coverage of BSCs and three levels of water supply. The results show that: 1) BSCs affected plant interaction intensity for the four plant species: a 100% coverage of BSCs significantly reduced the intensity of competition between neighboring plants, while it was highest with a 50% coverage of BSCs in combination with the target species of A. sphaerocephala and C. virgata; 2) effects of the coverage of BSCs on plant interactions were modified by water regime when the target species were C. virgata and S. viridis; 3) plant interactions were species-specific. In conclusion, the percent coverage of BSCs affected plant interactions, and the effects were species-specific and could be modified by water regimes. Further studies should focus on effects of the coverage of BSCs on plant-soil hydrological processes

Genetic divergence and gene flow among Mesorhizobium strains nodulating the shrub legume Caragana

Although the biogeography of rhizobia has been investigated extensively, little is known about the adaptive molecular evolution of rhizobia influenced by soil environments and selected by legumes. In this study, microevolution of Mesorhizobium strains nodulating Caragana in a semi-fixing desert belt in northern China was investigated. Five core genes-atpD, glnII, gyrB, recA, and rpoB, six heat-shock factor genes-clpA, clpB, dnaK, dnaf, grpE, and hlsU, and five nodulation genes-nodA, nodC, nodD, nodG, and nodP, of 72 representative mesorhizobia were studied in order to determine their genetic variations. A total of 21 genospecies were defined based on the average nucleotide identity (ANI) of concatenated core genes using a threshold of 96% similarity, and by the phylogenetic analyses of the core/heat-shock factor genes. Significant genetic divergence was observed among the genospecies in the semi-fixing desert belt (areas A-E) and Yunnan province (area F), which was closely related to the environmental conditions and geographic distance. Gene flow occurred more frequently among the genospecies in areas A-E, and three sites in area B, than between area F and the other five areas. Recombination occurred among strains more frequently for heat-shock factor genes than the other genes. The results conclusively showed that the Caragana-associated mesorhizobia had divergently evolved according to their geographic distribution, and have been selected not only by the environmental conditions but also by the host plants. (C) 2015 Elsevier GmbH. All rights reserved

New field wind manipulation methodology reveals adaptive responses of steppe plants to increased and reduced wind speed

Background: Wind strongly impacts plant growth, leaf traits, biomass allocation, and stem mechanical properties. However, whether there are common whole-plant wind responses among different plant species is still unclear. We tested this null hypothesis by exposing four eudicot steppe species to three different wind treatments in a field experiment: reduced wind velocity using windbreaks, ambient wind velocity, and enhanced wind velocity through a novel methodology using wind-funneling baffles. Results: Across the four species, wind generally decreased plant height, projected crown area, and stepwise bifurcation ratio, and increased root length and stem base diameter. In contrast, the response patterns of shoot traits, especially mechanical properties, to wind velocity were idiosyncratic among species. There was no significant difference in total biomass among different treatments; this might be because the negative effects on heat dissipation and photosynthesis of low wind speed during hot periods, could counteract positive effects during favorable cooler periods. Conclusions: There are common wind response patterns in plant-size-related traits across different steppe species, while the response patterns in shoot traits vary among species. This indicates the species-specific ways by which plants balance growth and mechanical support facing wind stress. Our new field wind manipulation methodology was effective in altering wind speed with the intended magnitude. Especially, our field wind-funneling baffle system showed a great potential for use in future field wind velocity enhancement. Further experiments are needed to reveal how negative and positive effects play out on whole-plant performance in response to different wind regimes, which is important as ongoing global climatic changes involve big changes in wind regimes