Grazing weakens temporal stabilizing effects of diversity in the Eurasian steppe

Many biodiversity experiments have demonstrated that plant diversity can stabilize productivity in experimental grasslands. However, less is known about how diversity–stability relationships are mediated by grazing. Grazing is known for causing species losses, but its effects on plant functional groups (PFGs) composition and species asynchrony, which are closely correlated with ecosystem stability, remain unclear. We conducted a six‐year grazing experiment in a semi‐arid steppe, using seven levels of grazing intensity (0, 1.5, 3.0, 4.5, 6.0, 7.5, and 9.0 sheep per hectare) and two grazing systems (i.e., a traditional, continuous grazing system during the growing period (TGS), and a mixed one rotating grazing and mowing annually (MGS)), to examine the effects of grazing system and grazing intensity on the abundance and composition of PFGs and diversity–stability relationships. Ecosystem stability was similar between mixed and continuous grazing treatments. However, within the two grazing systems, stability was maintained through different pathways, that is, along with grazing intensity, persistence biomass variations in MGS, and compensatory interactions of PFGs in their biomass variations in TGS. Ecosystem temporal stability was not decreased by species loss but rather remain unchanged by the strong compensatory effects between PFGs, or a higher grazing‐induced decrease in species asynchrony at higher diversity, and a higher grazing‐induced increase in the temporal variation of productivity in diverse communities. Ecosystem stability of aboveground net primary production was not related to species richness in both grazing systems. High grazing intensity weakened the temporal stabilizing effects of diversity in this semi‐arid grassland. Our results demonstrate that the productivity of dominant PFGs is more important than species richness for maximizing stability in this system. This study distinguishes grazing intensity and grazing system from diversity effects on the temporal stability, highlighting the need to better understand how grazing regulates ecosystem stability, plant diversity, and their synergic relationships.     

Redescription of Rigidohymena inquieta (Stokes, 1887) Berger, 2011 as Metahymena inquieta gen. nov., comb. nov. (Ciliophora,Hypotricha) Based on Morphology,Morphogenesis, and Molecular Phylogeny

The morphology and morphogenesis of Rigidohymena inquieta (Stokes, 1887) Berger, 2011, isolated from a lawn soil in the campus of the University of Ulsan, Korea, was studied, using live observation and protargol impregnation. The molecular phylogeny was studied based on the SSU rRNA gene sequences. The morphology of the Korean population of R. inquieta matches the previously known populations; however, the morphogenetic pattern shows differences to the species R. candens in the involvement of cirrus V/3 in the anlagen formation. A novel genus namely Metahymena gen. nov. has been erected for the present species based on the ontogenetic difference, and the new combination Metahymena inquieta gen. nov., comb. nov. is proposed. The morphology, morphogenesis, distribution, and phylogeny of M. inquieta are presented. The morphologic and morphogenetic data corroborate the phylogenetic analyses as M. inquieta clusters among the stylonychid ciliates in a clade distant from Rigidohymena candens.     

植物保护剂防治害虫效果的评价方法

在以作用因子组建的生命表和干扰作用控制指数(IIPC)的基础上建立植物保护剂的研究方法和综合评价指标,以表示驱避成虫选择寄主,干扰成虫的产卵行为,对卵孵化的影响,以及干扰幼虫的行为,包括逃避、拒食、幼虫特别是初孵幼虫中毒死亡的作用.采用所建立的研究方法和评价指标的试验结果表明,菜田附近大多数非寄主植物的乙醇抽提物(干重1g·100ml-1)如大叶桉(Eucalytusrubusta)、蟛蜞菊(Wedeliachinensis)等对保护十字花科蔬菜免受小菜蛾为害起着明显的作用.印楝油对小菜蛾幼虫的防治效果相当显著.机油乳剂(CALTEX产品)对桔全爪螨具有明显的控制效果     

Disturbance Winners or Losers? Plants Bearing Extrafloral Nectaries in Brazilian Caatinga

Plants bearing extrafloral nectaries (EFNs) often have traits typical of pioneer species, and may be expected to proliferate in disturbed habitats. However, a negative effect of disturbance on visitation by attendant ants could prevent EFN‐bearing plants from acting as disturbance winners. Here, we address the effects of chronic anthropogenic disturbance on the abundance of EFN‐bearing plants and their interactions with attendant ants in Caatinga vegetation of northeastern Brazil. We recorded the abundance of EFN‐bearing plants, proportion of plants visited by ants and composition of ant attendant species at 24 sites varying in levels of disturbance. EFN‐bearing plants as a whole did not behave as a disturbance winner group. The responses of the 13 species to increasing disturbance were highly variable, with three species declining in abundance (loser species). The richness of ant species attending EFNs did not vary with disturbance, but species composition did. The overall proportion of EFN‐bearing plants attended by ants per 5‐min period was not affected by disturbance. However, for the three loser species, attendance decreased from about 50 percent with low and moderate disturbance to half that with very high disturbance. We hypothesize that disturbed sites are more stressful for loser species compared with other EFN‐bearing plants, with physiological stress resulting in lower production of EFN secretions and reduced attraction of ants. This would make such species double losers, with physiological stress at disturbed sites not only directly influencing their performance but also indirectly affecting it through the disruption of a key mutualism.     

Mammal Browsers and Rainfall Affect Acacia Leaf Nutrient Content,Defense, and Growth in South African Savannas

Five sets of herbivore exclosures situated in mesic and semi‐arid savannas in Hluhluwe‐iMfolozi Park, South Africa were used to investigate the effects of mammal browsers and savanna type on plant traits relating to leaf nutrient content, defense, and growth in seven Acacia species. Mostly, browsing did not significantly affect leaf nutrient content but for a few species (i.e., increasing foliar N and P, decreasing C/N, and total polyphenols). Browser effects on structural defenses tended to be more pronounced than for leaf nutrient content and chemical defenses, particularly for semi‐arid species, resulting in longer, thicker, and denser spines, and a lower bite size index on browsed plants for most semi‐arid species. Browsing had no significant effect on growth rates for all species. Secondly, we investigated the effect of savanna type (mesic vs. semi‐arid) on the same set of plant traits and growth rates. A trade‐off in defense strategy was evident where mesic species had lower quality leaves and invested more heavily in growth and chemical defenses, while semi‐arid species generally had higher nutrient content leaves and invested more in structural defenses and higher levels of ramification. These findings suggest that the previously documented trade‐off in plant growth, resprouting ability and architecture between herbivore versus fire‐adapted savanna woody species can possibly be extended to include browse quality and defense type.     

The crystal structure of Z‐Gly‐Aib‐Gly‐Aib‐OtBu

The synthetic peptide Z‐Gly‐Aib‐Gly‐Aib‐OtBu was dissolved in methanol and crystallized in a mixture of ethyl acetate and petroleum ether. The crystals belong to the centrosymmetric space group P4/n that is observed less than 0.3% in the Cambridge Structural Database. The first Gly residue assumes a semi‐extended conformation (φ ±62°, ψ ?131°). The right‐handed peptide folds in two consecutive β‐turns of type II' and type I or an incipient 3₁₀‐helix, and the left‐handed counterpart folds accordingly in the opposite configuration. In the crystal lattice, one molecule is linked to four neighbors in the ab‐plane via hydrogen bonds. These bonds form a continuous network of left‐ and right‐handed molecules. The successive ab‐planes stack via apolar contacts in the c‐direction. An ethyl acetate molecule is situated on and close to the fourfold axis. Copyright © 2015 European Peptide Society and John Wiley & Sons, Ltd.     

Impacts of altered precipitation regimes on soil communities and biogeochemistry in arid and semi‐arid ecosystems

Altered precipitation patterns resulting from climate change will have particularly significant consequences in water‐limited ecosystems, such as arid to semi‐arid ecosystems, where discontinuous inputs of water control biological processes. Given that these ecosystems cover more than a third of Earth's terrestrial surface, it is important to understand how they respond to such alterations. Altered water availability may impact both aboveground and belowground communities and the interactions between these, with potential impacts on ecosystem functioning; however, most studies to date have focused exclusively on vegetation responses to altered precipitation regimes. To synthesize our understanding of potential climate change impacts on dryland ecosystems, we present here a review of current literature that reports the effects of precipitation events and altered precipitation regimes on belowground biota and biogeochemical cycling. Increased precipitation generally increases microbial biomass and fungal:bacterial ratio. Few studies report responses to reduced precipitation but the effects likely counter those of increased precipitation. Altered precipitation regimes have also been found to alter microbial community composition but broader generalizations are difficult to make. Changes in event size and frequency influences invertebrate activity and density with cascading impacts on the soil food web, which will likely impact carbon and nutrient pools. The long‐term implications for biogeochemical cycling are inconclusive but several studies suggest that increased aridity may cause decoupling of carbon and nutrient cycling. We propose a new conceptual framework that incorporates hierarchical biotic responses to individual precipitation events more explicitly, including moderation of microbial activity and biomass by invertebrate grazing, and use this framework to make some predictions on impacts of altered precipitation regimes in terms of event size and frequency as well as mean annual precipitation. While our understanding of dryland ecosystems is improving, there is still a great need for longer term in situ manipulations of precipitation regime to test our model.     

陇中黄土高原半干旱区苜蓿地土壤干燥化特征及适宜种植年限

研究了陇中黄土高原半干旱区不同种植年限紫花苜蓿地土壤水分特征及适宜种植年限.结果表明： 3、8、12和14年生苜蓿地0～300 cm土层土壤平均含水量均明显低于当地土壤稳定湿度值.12和14年生苜蓿地0～300 cm土层土壤含水量仅为9.2%和7.1%,甚至低于作物有效水分下限.1、3、8、12和14年生紫花苜蓿地0～300 cm土层干燥化指数分别为125.4%、30.5%、18.4%、-34.2%和-83.3%,除1年生苜蓿地土壤无干燥化现象之外,其余种植年限苜蓿地土壤均呈不同程度的干燥化.随苜蓿种植年限的延长,土壤干燥化程度加剧,但干燥化速率呈减缓趋势.综合苜蓿生产力动态和土壤水分状况,该区紫花苜蓿适宜的种植年限为8～10 年.     

Remotely‐sensed foliage cover and ground‐measured stand attributes are complimentary when estimating tree hollow abundances across relictual woodlands in agricultural landscapes

Hollows, also known as tree cavities, are critical to the survival of many animal species but are too poorly mapped across landscapes to allow for their adequate consideration in regional planning. Managing cost is important, so we tested whether freely available satellite‐derived foliage projective cover and field‐measured stand attributes could be used separately or combined to predict tree hollow abundance in relictual Australian temperate woodlands. Satellite‐derived foliage projective cover revealed variation in woody vegetation densities both within mapped woodland remnants and cleared areas of the agricultural matrix. Plot‐based field assessment of the actual number of hollows in each one‐hectare site (n = 110 sites) revealed a relationship with foliage cover. Improvement of the model was achieved if site‐based estimates of the proportion of the canopy due to Eucalyptus species and the number of mature trees per hectare were included. Remotely sensed foliage cover can improve on traditional vegetation mapping for predicting hollow‐bearing tree and hollow abundances at landscape scales when managing hollow‐dependent fauna habitat across relictual woodlands in temperate Australian agricultural landscapes. At finer scales, the addition of other predictors is necessary to raise the accuracy of the predicted hollow densities.