The role of experience in plant foraging by the aphid parasitoidDiaeretiella rapae (Hymenoptera: Aphidiidae)

Experiments were conducted to test the hypothesis that plant learning by a relative plant-specialist parasitoid wasp should influence the probability of orienting to plant odors (plant finding) and the duration of searching on a plant after landing (plant examining). The insect tested was Diaeretiella rapaeM'Intosh (Hymenoptera: Aphidiidae), a parasitoid wasp that usually attacks aphids on cruciferous plants, but occasionally on other plants. Laboratory experiments using collard as the cruciferous plant and potato as the novel plant demonstrated that postemergence (adult) plant experience affected plant examining only on the less preferred plant, potato, and was reversible and relatively long-term (that is, lasted >2 days). Postemergence experience with potato did not increase orientation to potato odor in a wind tunnel, but postemergence experience with collard resulted in a trend of increased likelihood of flying to collard odor. Preemergence treatments affected plant finding but not plant examining.     

Linking species performance to community structure as affected by UV-B radiation: an attenuation experiment

Aims UV-B radiation is known to affect plant physiology and growth rate in ways that can influence community species composition and structure. Nevertheless, comparatively little is known about how UV-B radiation induced changes in the performance of individual species cascades to affect overall community properties. Because foliage leaves are primarily responsible for photosynthesis and carbon gain and are the major organ that senses and responds to UV-B radiation, we hypothesized that, under reduced UV-B radiation, species with larger leaf areas per plant would manifest higher growth rates and hence tend to improve their community status compared to species with smaller leaf areas per plant in herbaceous plant communities.Methods We tested this hypothesis by examining plant traits (leaf area per plant and plant height), plant growth rate (aboveground biomass per plant and plant biomass per area) and community status (species within-community relative biomass) for 19 common species in a two-year field experiment in an alpine meadow on Tibetan Plateau.Important findings Aboveground biomass per plant, as well as per area, progressively increased in a 39% reduced (relative to ambient) UV-B treatment during the experimental period. At the second year, 11 out of 19 species significantly or marginally significantly increased their plant height, leaf area per plant and aboveground biomass per plant. No species was negatively affected by reducing UV-B. As hypothesized, the increase in aboveground biomass per plant increased with increasing leaf area per plant, as indicated by cross-species regression analysis. Moreover, the change in species within-community status increased with increasing leaf area per plant. Our study demonstrates that UV-B radiation has differential effects on plant growth rate across species and hence significantly affects species composition and plant community structure. We suggest that UV-B radiation is an ecological factor structuring plant communities particularly in alpine and polar areas.     

Profiling the secretomes of plant pathogenic Proteobacteria

Secreted proteins are central to the success of plant pathogenic bacteria. They are used by plant pathogens to adhere to and degrade plant cell walls, to suppress plant defence responses, and to deliver bacterial DNA and proteins into the cytoplasm of plant cells. However, experimental investigations into the identity and role of secreted proteins in plant pathogenesis have been hindered by the fact that many of these proteins are only expressed or secreted in planta, that knockout mutations of individual proteins frequently have little or no obvious phenotype, and that some obligate and fastidious plant pathogens remain recalcitrant to genetic manipulation. The availability of genome sequence data for a large number of agriculturally and scientifically important plant pathogens enables us to predict and compare the complete secretomes of these bacteria. In this paper we outline strategies that are currently being used to identify secretion systems and secreted proteins in Proteobacterial plant pathogens and discuss the implications of these analyses for future investigations into the molecular mechanisms of plant pathogenesis.     

Increased compensatory ability of an invasive plant to above- and below-ground enemies in monocultures

Above- and below-ground enemies have prominent influence on plant invasions, and increasing evidence has shown that plant invasions are also affected by inter- or intraspecific interactions between individual plants. However, how these two factors interactively affect plant invasions has rarely been tested. Here, we examined the response of the invasive plant Alternanthera philoxeroides (Mart.) Griseb. to above- and below-ground enemies at varying plant densities in a greenhouse experiment in Wuhan, China. We found that both above- and below-ground enemies decreased the plant total and root mass at individual and population levels, but that of the two, below-ground enemies had a greater effect than above-ground enemies, and that the two guilds of enemies acted additively on the plant. However, their impacts decreased as the plant density increased, due to enhanced plant tolerance to both guilds of enemies. The increased plant tolerance may result from changes in plant resource allocation patterns, corresponding to a positive linear relationship between the ratio of fine root mass to total root mass and plant density. Given that forming dense monocultures in their new ranges is one of the most important characteristics of invasive plants, we propose that the high compensatory ability at dense monocultures may be an important mechanism underlying exotic species invasion.     

Distribution patterns and changes of aquatic plant communities in Napahai Wetland in northwestern Yunnan Plateau,China

Using GPS technology and community research methods for plant communities,we investigated the distribution patterns of aquatic plant communities in the high plateaus of the Napahai Wetlands,Yunnan,China,as well as the species changes of plant communities compared with that of 24 years ago since 2005.We found that the types and numbers of aquatic plant communities have changed.Some pollution-tolerant,nutrient-loving plant communities such as Scirpus tabernaemontani,Zizania caduciflora,Myriophyllum spicatum,and Azolla imbricata flourished,while the primary aquatic plant com-munities were reduced or even disappeared.The number of aquatic plant communities were increased from nine to 12 with the addition of two new emergent plant com-munities and one new floating-leaved plant community.The increase in emergent plant communities was signifi-cant.From east to west and from south to north,various types of plant communities were continuously distributed,including floating-leaved plant communities,emergent plant communities and submerged plant communities.The composition of the communities became more com-plicated and the number of accompanying species increased,while the percentage ratio of dominant plant species declined.In 2005,the coverage of emergent plant communities was the largest (528.42 hm2) followed by submerged plant communities (362.50 hm2) and the float-ing-leaf plant communities was the smallest (70.23 hm2).The variations in the distribution of aquatic plant com-munities in the Napahai Wetlands reflect the natural responses to the change of the wetland ecological envir-onment.This study indicates that human disturbances have led to an inward movement of the wetland shoreline,a decrease in water quality and a reduction in wetland habitat.     

Can we use plant traits and soil characteristics to predict leaf damage in savanna woody species?

Although several hypotheses aim to explain insect herbivory on plants, the relative importance of plant traits, environment, and organizational scale (i.e., individual or community) to herbivory damage level is not well understood. We used an approach based on a local scale, divided into individual and community levels, to test if plant traits, soil characteristics, and plant density explain leaf damage. We sampled 983 individuals in 49 plots distributed over dense and open savanna formations in Emas National Park. In order to explain plant damage, we performed a multi-model inference analysis of four plant traits associated with plant damage, five soil characteristics, and plant density. We did not find any support to plant vigor or plant stress hypotheses at individual plant level. However, the resource concentration hypothesis and plant stress hypothesis explained leaf damage at the community level. We found that increased availability of calcium (Ca) in soils reduced plant damage at the community level. Because soil Ca concentration is a major constraint to plant development in the Brazilian savanna, we postulated that its increasing availability permits plants to invest more in defense strategies. We demonstrate that plant density, Ca soil concentration, and leaf size can be used to predict the plant damage suffered by woody species in savannas at community level.     

The "sensational" power of movement in plants: A Darwinian system for studying the evolution of behavior

Darwin's research on botany and plant physiology was a landmark attempt to integrate plant movements into a biological perspective of behavior. Since antiquity, people have sought to explain plant movements via mechanical or physiological forces, and yet they also constructed analogies between plant and animal behavior. During the Renaissance and Enlightenment, thinkers began to see that physiochemical explanations of plant movements could equally apply to animal behavior and even human thought. Darwin saw his research on plant movements as a strategic front against those who argued that his theory of evolution could not account for the acquisition of new behavioral traits. He believed that his research explained how the different forms of plant movement evolved as modified habits of circumnutation, and he presented evidence that plants might have a brain-like organ, which could have acquired various types of plant sensitivity during evolution. Upon publication of The Power of Movement in Plants, his ideas were overwhelmingly rejected by plant physiologists. Subsequently, plant biologists came to view the work as an important contribution to plant physiology and biology, but its intended contribution to the field of evolution and behavior has been largely overlooked.     

刺槐叶片可塑生长的密度依赖性

为了探明刺槐叶片性状对种植密度的依赖性,通过刺槐田间栽培试验,研究了刺槐叶片可塑生长的密度依赖性以及主要叶片性状因子之间的关系.结果表明,不同种植密度条件下刺槐叶片厚度均无显著差异,但叶面积、叶绿素含蜃、叶片干重、比叶面积、叶干物质含量和叶片N含量差异显著,表明不同种植密度条件下刺槐叶性因子参数的变异较大,刺槐叶片性状对密度的依赖性较强.叶干重、叶厚度和叶片干物质含量均随种植密度的降低而呈增加趋势,叶片干物质含量与种植密度的相关性达到显著水平(P<0.01),而叶干重、叶厚度与种植密度的相关性不显著(P>0.05).比叶而积和叶片N含鼍均随种植密度的降低而降低,表明刺槐各叶性因子之间对种植密度的依赖性差异明显.对刺槐各叶性因子的相关分析表明,不同种植密度条件下各叶性因子之间的相关性及其强弱均存在差别,表明种植密度是影响刺槐叶性因子变异及叶性因子之间关系的因素之一.叶性特征对种植密度响应存在差异的主要原因是叶性因子之间的协同变化、刺槐生长微环境的差异和刺槐间竞争强度的差异,刺槐不同叶性因子之间的协调平衡和对种植密度响应程度与方向的差异表明了刺槐对其生长环境的适应.     

Plant species identity and diversity effects on different trophic levels of nematodes in the soil food web

Previous studies on biodiversity and soil food web composition have mentioned plant species identity, as well as plant species diversity as the main factors affecting the abundance and diversity of soil organisms. However, most studies have been carried out under limitations of time, space, or appropriate controls. In order to further examine the relation between plant species diversity and the soil food web, we conducted a three-year semi-field experiment in which eight plant species (4 forb and 4 grass species) were grown in monocultures and mixtures of two, four and eight plant species. In addition there were communities with 16 plant species. We analyzed the abundance and identity of the nematodes in soil and roots, including feeding groups from various trophic levels (primary and secondary consumers, carnivores, and omnivores) in the soil food web.
Plant species diversity and plant identity affected the diversity of nematodes. The effect of plant diversity was attributed to the complementarity in resource quality of the component plant species rather than to an increase in total resource quantity. The nematode diversity varied more between the different plant species than between different levels of plant species diversity, so that plant identity is more important than plant diversity. Nevertheless the nematode diversity in plant mixtures was higher than in any of the plant monocultures, due to the reduced dominance of the most abundant nematode taxa in the mixed plant communities. Plant species identity affected the abundances of the lower trophic consumer levels more than the higher trophic levels of nematodes. Plant species diversity and plant biomass did not affect nematode abundance. Our results, therefore, support the hypothesis that resource quality is more important than resource quantity for the diversity of soil food web components and that plant species identity is more important than plant diversity per se.     

Incorporating biotic factors in species distribution modeling: are interactions with soil microbes important?

It is increasingly recognized that species distributions are driven by both abiotic factors and biotic interactions. Despite much recent work incorporating competition, predation, and mutualism into species distribution models (SDMs), the focus has been confined to aboveground macroscopic interactions. Biotic interactions between plants and soil microbial communities are understudied as potentially important drivers of plant distributions. Some soil bacteria promote plant growth by cycling nutrients, while others are pathogenic; thus they have a high potential for influencing plant occurrence. We investigated the influence of soil bacterial clades on the distributions of bryophytes and 12 vascular plant species in a high elevation talus‐field ecosystem in the Rocky Mountain Front Range, Colorado, USA. We used an information‐theoretic criterion (AICc) modeling approach to compare SDMs with the following different sets of predictors: abiotic variables, abiotic variables and other plant abundances, abiotic variables and soil bacteria clade relative abundances, and a full model with abiotic factors, plant abundances, and bacteria relative abundances. We predicted that bacteria would influence plant distributions both positively and negatively, and that these interactions would improve prediction of plant species distributions. We found that inclusion of either plant or bacteria biotic predictors generally improved the fit, deviance explained, and predictive power of the SDMs, and for the majority of the species, adding information on both other plants and bacteria yielded the best model. Interactions between the modeled species and biotic predictors were both positive and negative, suggesting the presence of competition, parasitism, and facilitation. While our results indicate that plant–plant co‐occurrences are a stronger driver of plant distributions than plant–bacteria co‐occurrences, they also show that bacteria can explain parts of plant distributions that remain unexplained by abiotic and plant predictors. Our results provide further support for including biotic factors in SDMs, and suggest that belowground factors be considered as well.     

水稻不同基因型耐低氮能力差异评价

以水稻单株谷重及其氮素反应指数作为耐低氮能力指标,分析不同施氮水平下水稻种质资源的耐低氮能力以及单株谷重及其氮素反应指数与其他农艺性状的相关关系。结果表明,水稻种质资源的耐低氮能力在不同施氮水平间均有较大差异,多数农艺性状的表型差异顺序为未施氮〉施低氮〉普通施氮;不同施氮水平间单株谷重、单株草重和穗数的差异大于其他农艺性状。在不同施氮水平下,单株谷重与单株草重均呈极显著正相关;单株谷重的氮素反应指数与单株谷重、单株草重和谷草比均呈极显著正相关。在未施氮水平下,单株谷重与株高、穗数、穗粒数和单株草重的相关性以及单株谷重的氮素反应指数与穗数、单株谷重、单株草重和谷草比的相关性比施低氮或普通施氮水平更为密切。花峰稻、中作9059、旱稻9号、旱稻502和IRAT359等种质资源表现较迟钝的氮素反应,具有较强的耐低氮能力。     

Silicon alleviates the deleterious salt effect on tomato plant growth by improving plant water status

In order to investigate the role of Si in alleviating the deleterious effects of salinity on tomato plant growth, the tomato cultivar Moneymaker was grown with 0 or 80mM NaCl combined with 0 and 2.5mM Si. Plant growth parameters, salt accumulation in plant tissues and plant water relations were analysed. Si treatment did not alter salt input into the plant or salt distribution between plant organs. There were non-significant differences in plant water uptake, but plant water content in salinised plants supplied with Si was 40% higher than in salinised plants that were not supplied with Si. Plants treated with NaCl alone showed a reduction in plant dry weight and total plant leaf area of 55% and 58%, respectively, while the reduction in plants treated with NaCl plus Si was only 31% and 22%, respectively. Leaf turgor potential and net photosynthesis rates were 42% and 20% higher in salinised plants supplied with Si than in salinised plants that were not supplied with Si. Water use efficiency calculated from instantaneous gas exchange parameters and as the ratio between plant dry matter and plant water uptake were, respectively, 17% and 16% higher in salinised plants supplied with Si. It can be concluded that Si improves the water storage within plant tissues, which allows a higher growth rate that, in turn, contributes to salt dilution into the plant, mitigating salt toxicity effects.     

Structure and ecological function of the soil microbiome affecting plant–soil feedbacks in the presence of a soil-borne pathogen

Interactions between plants and soil microbes are important for plant growth and resistance. Through plant–soil-feedbacks, growth of a plant is influenced by the previous plant that was growing in the same soil. We performed a plant–soil feedback study with 37 grass, forb and legume species, to condition the soil and then tested the effects of plant-induced changes in soil microbiomes on the growth of the commercially important cut-flower Chrysanthemum in presence and absence of a pathogen. We analysed the fungal and bacterial communities in these soils using next-generation sequencing and examined their relationship with plant growth in inoculated soils with or without the root pathogen, Pythium ultimum. We show that a large part of the soil microbiome is plant species-specific while a smaller part is conserved at the plant family level. We further identified clusters of plant species creating plant growth promoting microbiomes that suppress concomitantly plant pathogens. Especially soil inocula with higher relative abundances of arbuscular mycorrhizal fungi caused positive effects on the Chrysanthemum growth when exposed to the pathogen. We conclude that plants differ greatly in how they influence the soil microbiome and that plant growth and protection against pathogens is associated with a complex soil microbial community.     

The influence of arbuscular mycorrhizae on the relationship between plant diversity and productivity

Ecological theory predicts a positive and asymptotic relationship between plant diversity and ecosystem productivity based on the ability of more diverse plant communities to use limiting resources more fully. This is supported by recent empirical evidence. Additionally, in natural ecosystems, plant productivity is often a function of the presence and composition of mycorrhizal associations. Yet, the effect of mycorrhizal fungi on the relationship between plant diversity and productivity has not been investigated. We predict that in the presence of AMF, productivity will saturate at lower levels of species richness because AMF increase the ability of plant species to utilize nutrient resources. In this study we manipulated old-field plant species richness in the presence and absence of two species of AMF. We found that in the absence of AMF, the relationship between plant species richness and productivity is positive and linear. However, in the presence of AMF, the relationship is positive but asymptotic, even though the maximum plant biomass was significantly different between the two AMF treatments. This is consistent with the hypothesis that AMF increase the redundancy of plant species in the productivity of plant communities, and indicates that these symbionts must be considered in future investigations of plant biodiversity and ecosystem function.     

Ploidy level interacts with population size and habitat conditions to determine the degree of herbivory damage in plant populations

Recently it has been suggested that ploidy level of a plant population may have important effects on plant‐animal interactions. Plant‐animal interactions can also be strongly altered by factors such as plant population size and habitat conditions. It is, however, not known how these factors interact to shape the overall pattern of plant‐animal interactions. I studied the interaction between a perennial plant, Aster amellus, and a monophagous herbivorous moth, Coleophora obscenella, and investigated the effect of ploidy level of the plant population, plant population size, isolation and habitat conditions on density of the insect, damage by the insect, and plant performance. Ploidy level, plant population size and habitat conditions, but not isolation, strongly influence plant‐herbivore interactions. Furthermore, there are significant interactions between effects of ploidy level and plant population size and between ploidy level and isolation. Hexaploid plants suffer higher seed damage by the herbivore, but their seed production is still higher than that of diploids. Herbivores thus partly limit the evolutionary success of the hexaploid plants. Plant‐animal interactions are also strongly determined by plant population size. Small populations of A. amellus (below forty flowering ramets) host no C. obscenella larvae, indicating a minimum A. amellus population size that can sustain a viable C. obscenella population. Negative and positive effects of plant population size balance and result in no relationship between plant population size and number of developed seeds per flower head. The results also show a significant interaction between ploidy level and plant population size, indicating that the increase in density of C. obscenella larvae with plant population size is greater in hexaploid than in diploid populations. The results also indicate that the effect of ploidy level on plant‐herbivore interactions can be altered by plant population size, which suggests that plant‐herbivore interactions are driven by a complex of interactions among different factors. Studying each factor separately could thus lead to biased conclusions about patterns of interactions in such systems.     

Is a physiological perspective relevant in a 'genocentric' age?

Currently, the major thrust of plant physiology research is to identify and understand the regulation of genes that might be relevant in plant development and growth. The dominance of a genocentric view of plant behaviour has, unfortunately, resulted in the development of major disconnects in the classical view of plant physiology as a partnership between fundamental and practical research contributing to improved plant production. One disconnect is that much of the genocentric research appears to be organized and executed without regard to the practical needs of enhancing plant performance under applied conditions. Although practical benefits from genocentric research are often claimed, basic assumptions guiding much research and the experimental protocols used are commonly not relevant for real-world plant production. A second disconnect is a failure fully to appreciate the lessons learned in 40 years of classical plant physiology research concerning the role of physiological processes in altering whole plant performance. Regulation of plant systems has proved to be complex and redundant. Alteration of a single physiological process is compensated or dampened so that commonly very little change in plant growth and yield results from modification of a single physiological process. Based on a few successful projects employing classical plant physiology to achieve crop yield increase, key characteristics for research projects that truly seek to increase plant performance in production systems are identified. Basically, the partnership between the fundamental and practical research long espoused for plant physiology needs to be re-established in an intimate and meaningful way.     

Response of pest control by generalist predators to local‐scale plant diversity: a meta‐analysis

Disentangling the effects of plant diversity on the control of herbivores is important for understanding agricultural sustainability. Recent studies have investigated the relationships between plant diversity and arthropod communities at the landscape scale, but few have done so at the local scale. We conducted a meta‐analysis of 32 papers containing 175 independent measures of the relationship between plant diversity and arthropod communities. We found that generalist predators had a strong positive response to plant diversity, that is, their abundance increased as plant diversity increased. Herbivores, in contrast, had an overall weak and negative response to plant diversity. However, specialist and generalist herbivores differed in their response to plant diversity, that is, the response was negative for specialists and not significant for generalists. While the effects of scale remain unclear, the response to plant diversity tended to increase for specialist herbivores, but decrease for generalist herbivores as the scale increased. There was no clear effect of scale on the response of generalist predators to plant diversity. Our results suggest that the response of herbivores to plant diversity at the local scale is a balance between habitat and trophic effects that vary according to arthropod specialization and habitat type. Synthesis and applications. Positive effects of plant diversity on generalist predators confirm that, at the local scale, plant diversification of agroecosystems is a credible and promising option for increasing pest regulation. Results from our meta‐analysis suggest that natural control in plant‐diversified systems is more likely to occur for specialist than for generalist herbivores. In terms of pest management, our results indicate that small‐scale plant diversification (via the planting of cover crops or intercrops and reduced weed management) is likely to increase the control of specialist herbivores by generalist predators.     

Predicting the effect of competition on secondary plant extinctions in plant–pollinator networks

What are the limitations of models that predict the behavior of an ecological community based on a single type of species interaction? Using plant–pollinator network models as an example, we contrast the predicted vulnerability of a community to secondary extinctions under the assumption of purely mutualistic interactions versus mutualistic and competitive interactions. We find that competition among plant species increases the risk of secondary extinctions and extinction cascades. Simulations over a number of different network structures indicate that this effect is stronger in larger networks, more strongly connected networks and networks with higher plant:pollinator ratios. We conclude that efforts to model plant–pollinator communities will systematically over‐estimate community robustness to species loss if plant competition is ignored. However, because the effect of plant competition depends on network architecture, and because characterization of plant competition is work intensive, we suggest that efforts to account for plant competition in plant–pollinator network models should be focused on large, strongly connected networks with high plant:pollinator ratios.     

植物凝集素的分子生物学研究

植物凝集素是一类具有高度特异性糖结合活性的蛋白,含有一个或多个可与单糖或寡聚糖特异可逆结合的非催化结构域。它的糖结合特异性主要针对外源寡糖,主要生理功能是介异植物的防御反应。到目前为止已克隆了２２２个植物凝集素基因。作者就植物凝集素的分类、性质、功能、凝集素基因的克隆和凝集素的翻译后加工过程作一综述。     

Most soil trophic guilds increase plant growth: a meta‐analytical review

Trophic cascades are important drivers of plant and animal abundances in aquatic and aboveground systems, but in soils trophic cascades have been thought to be of limited importance due to omnivory and other factors. Here we use a meta‐analysis of 215 studies with 1526 experiments that measured plant growth responses to additions or removals of soil organisms to test how different soil trophic levels affect plant growth. Consistent with the trophic cascade hypothesis, we found that herbivores and plant pathogens (henceforth pests) decreased plant growth and that predators of pests increased plant growth. The magnitude of this trophic cascade was similar to that reported for aboveground systems. In contrast, we did not find evidence for trophic cascades in decomposer‐ and symbiont‐based (henceforth mutualist) food chains. In these food chains, mutualists increased plant growth and predators of mutualists also increased plant growth, presumably by increasing nutrient cycling rates. Therefore, mutualists, predators of mutualists and predators of pests all increased plant growth. Further, experiments that added multiple organisms from different trophic levels also increased plant growth. As a result, across the dataset, soil organisms increased plant growth 29% and non‐pest soil organisms increased plant growth 46%. Omnivory has traditionally been thought to confound soil trophic dynamics, but here we suggest that omnivory allows for a simplified perspective of soil food webs – one in which most soil organisms increase plant growth by preying on pests or increasing nutrient cycling rates. An implication of this perspective is that processes that decrease soil organism abundance (e.g. soil tillage) are likely to decrease aboveground productivity. Synthesis Soil foodwebs have resisted generalizations due to their diversity and interconnectedness. Here we use results from a meta‐analysis to inform a simplified perspective of soil foodwebs: one in which most soil trophic guilds increase plant growth. Our review also includes the first widespread support for the presence of trophic cascades in soils.