Impact of rhizobacterial inoculants on plant growth and enzyme activities in soil treated with contaminated bottom sediments

The impact of contaminated bottom sediments on plant growth and soil enzyme activities was evaluated in a greenhouse pot study. The sediments were moderately contaminated with zinc and heavily contaminated with polycyclic aromatic hydrocarbons and polychlorinated dibenzo-p-dioxins and furans. The sediments were mixed with soil and planted with either Festuca arundinacea or Tagetes patula. The capacity of two rhizobacterial strains (Massilia niastensis P87 and Streptomyces costaricanus RP92), previously isolated from contaminated soils, to improve plant growth under the chemical stress was tested. Application of sediments to soil was severely phytotoxic to T. patula and mildly to F. arundinacea. On the other hand, the addition of sediments enhanced the soil enzymatic activity. Inoculation with both bacterial strains significantly increased shoot (up to 2.4-fold) and root (up to 3.4-fold) biomass of T. patula. The study revealed that the selected plant growth-promoting bacterial strains were able to alleviate phytotoxicity of bottom sediments to T. patula resulting from the complex character of the contamination.     

Natural soil microbes alter flowering phenology and the intensity of selection on flowering time in a wild Arabidopsis relative

Plant phenology is known to depend on many different environmental variables, but soil microbial communities have rarely been acknowledged as possible drivers of flowering time. Here, we tested separately the effects of four naturally occurring soil microbiomes and their constituent soil chemistries on flowering phenology and reproductive fitness of Boechera stricta, a wild relative of Arabidopsis. Flowering time was sensitive to both microbes and the abiotic properties of different soils; varying soil microbiota also altered patterns of selection on flowering time. Thus, soil microbes potentially contribute to phenotypic plasticity of flowering time and to differential selection observed between habitats. We also describe a method to dissect the microbiome into single axes of variation that can help identify candidate organisms whose abundance in soil correlates with flowering time. This approach is broadly applicable to search for microbial community members that alter biological characteristics of interest.     

Smells from the desert: Microbial volatiles that affect plant growth and development of native and non‐native plant species

The plant microbiota can affect host fitness via the emission of microbial volatile organic compounds (mVOCs) that influence growth and development. However, evidence of these molecules and their effects in plants from arid ecosystems is limited. We screened the mVOCs produced by 40 core and representative members of the microbiome of agaves and cacti in their interaction with Arabidopsis thaliana and Nicotiana benthamiana. We used SPME‐GC‐MS to characterize the chemical diversity of mVOCs and tested the effects of selected compounds on growth and development of model and host plants. Our study revealed that approximately 90% of the bacterial strains promoted plant growth both in A. thaliana and N. benthamiana. Bacterial VOCs were mainly composed of esters, alcohols, and S‐containing compounds with 25% of them not previously characterized. Remarkably, ethyl isovalerate, isoamyl acetate, 3‐methyl‐1‐butanol, benzyl alcohol, 2‐phenylethyl alcohol, and 3‐(methylthio)‐1‐propanol, and some of their mixtures, displayed beneficial effects in A. thaliana and also improved growth and development of Agave tequilana and Agave salmiana in just 60 days. Volatiles produced by bacteria isolated from agaves and cacti are promising molecules for the sustainable production of crops in arid and semi‐arid regions.     

Warming, plant phenology and the spatial dimension of trophic mismatch for large herbivores

Temporal advancement of resource availability by warming in seasonal environments can reduce reproductive success of vertebrates if their own reproductive phenology does not also advance with warming. Indirect evidence from large-scale analyses suggests, however, that migratory vertebrates might compensate for this by tracking phenological variation across landscapes. Results from our two-year warming experiment combined with seven years of observations of plant phenology and offspring production by caribou (Rangifer tarandus) in Greenland, however, contradict evidence from large-scale analyses. At spatial scales relevant to the foraging horizon of individual herbivores, spatial variability in plant phenology was reduced--not increased--by both experimental and observed warming. Concurrently, offspring production by female caribou declined with reductions in spatial variability in plant phenology. By highlighting the spatial dimension of trophic mismatch, these results reveal heretofore unexpected adverse consequences of climatic warming for herbivore population ecology.     

Contrasting effects of warming and increased snowfall on Arctic tundra plant phenology over the past two decades

Recent changes in climate have led to significant shifts in phenology, with many studies demonstrating advanced phenology in response to warming temperatures. The rate of temperature change is especially high in the Arctic, but this is also where we have relatively little data on phenological changes and the processes driving these changes. In order to understand how Arctic plant species are likely to respond to future changes in climate, we monitored flowering phenology in response to both experimental and ambient warming for four widespread species in two habitat types over 21 years. We additionally used long‐term environmental records to disentangle the effects of temperature increase and changes in snowmelt date on phenological patterns. While flowering occurred earlier in response to experimental warming, plants in unmanipulated plots showed no change or a delay in flowering over the 21‐year period, despite more than 1 °C of ambient warming during that time. This counterintuitive result was likely due to significantly delayed snowmelt over the study period (0.05–0.2 days/yr) due to increased winter snowfall. The timing of snowmelt was a strong driver of flowering phenology for all species – especially for early‐flowering species – while spring temperature was significantly related to flowering time only for later‐flowering species. Despite significantly delayed flowering phenology, the timing of seed maturation showed no significant change over time, suggesting that warmer temperatures may promote more rapid seed development. The results of this study highlight the importance of understanding the specific environmental cues that drive species’ phenological responses as well as the complex interactions between temperature and precipitation when forecasting phenology over the coming decades. As demonstrated here, the effects of altered snowmelt patterns can counter the effects of warmer temperatures, even to the point of generating phenological responses opposite to those predicted by warming alone.     

Putative biotic drivers of plant phenology: With special reference to pathogens and deciduousness

Plant phenology is not only manifested in the seasonal timing of vegetative and reproductive processes but also has ontogenetic aspects. The adaptive basis of seasonal phenology has been considered mainly in terms of climatic drivers. However, some biotic factors as likely evolutionary influences on plants’ phenology appear to have been under‐researched. Several specific cases of putative biotic factors driving plant phenology are outlined, involving both herbivores and pathogens. These illustrate the diversity of likely interactions rather than any systematic coverage or review. Emphasis is on woody perennials, in which phenology is often most multifaceted and complicated by the ontogenetic aspect. The complete seasonal leaf fall that characterizes deciduous plants may be a very important defense against some pathogens. Whether biotic influences drive acquisition or long‐term persistence of deciduousness is considered. In one case, of leaf rusts in poplars, countervailing influences of the rusts and climate suggest persistence. Often, however, biotic and environmental influences likely reinforce each other. The timing and duration of shoot flushing may in at least some cases contribute to defenses against herbivores, largely through brief periods of “predator satiation” when plant tissues have highest food value. Wide re‐examination of plant phenology, accommodating the roles of biotic factors and their interplays with environments as additional adaptive drivers, is advocated toward developing and applying hypotheses that are observationally or experimentally testable.     

Evaluating vegetation effects on animal demographics: the role of plant phenology and sampling bias

Plant phenological processes produce temporal variation in the height and cover of vegetation. Key aspects of animal life cycles, such as reproduction, often coincide with the growing season and therefore may inherently covary with plant growth. When evaluating the influence of vegetation variables on demographic rates, the decision about when to measure vegetation relative to the timing of demographic events is important to avoid confounding between the demographic rate of interest and vegetation covariates. Such confounding could bias estimated effect sizes or produce results that are entirely spurious. We investigated how the timing of vegetation sampling affected the modeled relationship between vegetation structure and nest survival of greater sage‐grouse (Centrocercus urophasianus), using both simulated and observational data. We used the height of live grasses surrounding nests as an explanatory covariate, and analyzed its effect on daily nest survival. We compared results between models that included grass height measured at the time of nest fate (hatch or failure) with models where grass height was measured on a standardized date – that of predicted hatch date. Parameters linking grass height to nest survival based on measurements at nest fate produced more competitive models, but slope coefficients of grass height effects were biased high relative to truth in simulated scenarios. In contrast, measurements taken at predicted hatch date accurately predicted the influence of grass height on nest survival. Observational data produced similar results. Our results demonstrate the importance of properly considering confounding between demographic traits and plant phenology. Not doing so can produce results that are plausible, but ultimately inaccurate.     

Genetic variation in flowering phenology and avoidance of seed predation in native populations of Ulex europaeus

The genetic variation in flowering phenology may be an important component of a species’ capacity to colonize new environments. In native populations of the invasive species Ulex europaeus, flowering phenology has been shown to be bimodal and related to seed predation. The aim of the present study was to determine if this bimodality has a genetic basis, and to investigate whether the polymorphism in flowering phenology is genetically linked to seed predation, pod production and growth patterns. We set up an experiment raising maternal families in a common garden. Based on mixed analyses of variance and correlations among maternal family means, we found genetic differences between the two main flowering types and confirmed that they reduced seed predation in two different ways: escape in time or predator satiation. We suggest that this polymorphism in strategy may facilitate maintain high genetic diversity for flowering phenology and related life‐history traits in native populations of this species, hence providing high evolutionary potential for these traits in invaded areas.     

Direct and indirect effects of episodic frost on plant growth and reproduction in subalpine wildflowers

Frost is an important episodic event that damages plant tissues through the formation of ice crystals at or below freezing temperatures. In montane regions, where climate change is expected to cause earlier snow melt but may not change the last frost‐free day of the year, plants that bud earlier might be directly impacted by frost through damage to flower buds and reproductive structures. However, the indirect effects of frost mediated through changes in plant–pollinator interactions have rarely been explored. We examined the direct and pollinator‐mediated indirect effects of frost on three wildflower species in southwestern Colorado, USA, Delphinium barbeyi (Ranunculaceae), Erigeron speciosus (Asteraceae), and Polemonium foliosissimum (Polemoniaceae), by simulating moderate (?1 to ?5°C) frost events in early spring in plants in situ. Subsequently, we measured plant growth, and upon flowering measured flower morphology and phenology. Throughout the flowering season, we monitored pollinator visitation and collected seeds to measure plant reproduction. We found that frost had species‐specific direct and indirect effects. Frost had direct effects on two of the three species. Frost significantly reduced flower size, total flowers produced, and seed production of Erigeron. Furthermore, frost reduced aboveground plant survival and seed production for Polemonium. However, we found no direct effects of frost on Delphinium. When we considered the indirect impacts of frost mediated through changes in pollinator visitation, one species, Erigeron, incurred indirect, negative effects of frost on plant reproduction through changes in floral traits and pollinator visitation, along with direct effects. Overall, we found that flowering plants exhibited species‐specific direct and pollinator‐mediated indirect responses to frost, thus suggesting that frost may play an important role in affecting plant communities under climate change.     

An extended root phenotype: the rhizosphere,its formation and impacts on plant fitness

Plants forage soil for water and nutrients, whose distribution is patchy and often dynamic. To improve their foraging activities, plants have evolved mechanisms to modify the physicochemical properties and microbial communities of the rhizosphere, i.e. the soil compartment under the influence of the roots. This dynamic interplay in root?soil?microbiome interactions creates emerging properties that impact plant nutrition and health. As a consequence, the rhizosphere can be considered an extended root phenotype, a manifestation of the effects of plant genes on their environment inside and/or outside of the organism. Here, we review current understanding of how plants shape the rhizosphere and the benefits it confers to plant fitness. We discuss future research challenges and how applying their solutions in crops will enable us to harvest the benefits of the extended root phenotype.     

武夷山不同龄级香果树开花物候及其生殖特性

该研究采用固定样地观测研究了不同龄级香果树的开花物候和生殖特性,分析了物候指数与生殖构件之间的相关性。结果表明：香果树单花花期一般为5~9 d,平均为6.79 d,随着树龄增大,其单花花期呈幂函数增长趋势;不同树龄香果树的始花期不同,但终花期基本一致;随着树龄的增大,始花期逐渐提前,花期持续时间延长。20~50 a树龄的香果树始花期约为8月9日,花期持续时间最短,仅为36 d。110~140 a树龄的香果树始花期约为7月15日,花期持续时间为61 d;对于单株母树来讲,香果树的花枝数,花朵总数以及果实总数随着树龄的增大均显著增加;单花枝产花量随着树龄的增加呈上升趋势,单花枝产果实数量呈先上升后下降的趋势;香果树花枝和单花枝产花量在树冠方位上的分布由大到小依次为南>东/西>北、上>中>下,但单花枝果实数量则表现出不同规律,即东>南>西>北、中>下>上。香果树具有花多果少现象,开花物候指数与生殖构件数量间的相关性分析表明,其花期持续时间与花枝数、花数和果实数均存在极显著正相关关系,始花期与生殖构件数量呈极显著负相关关系,而物候指数与香果树树龄亦存在显著相关关系。     

Extreme copy number variation at a tRNA ligase gene affecting phenology and fitness in yellow monkeyflowers

Copy number variation (CNV) is a major part of the genetic diversity segregating within populations, but remains poorly understood relative to single nucleotide variation. Here, we report on a tRNA ligase gene (Migut.N02091; RLG1a) exhibiting unprecedented, and fitness‐relevant, CNV within an annual population of the yellow monkeyflower Mimulus guttatus. RLG1a variation was associated with multiple traits in pooled population sequencing (PoolSeq) scans of phenotypic and phenological cohorts. Resequencing of inbred lines revealed intermediate‐frequency three‐copy variants of RLG1a (trip+; 5/35 = 14%), and trip+ lines exhibited elevated RLG1a expression under multiple conditions. trip+ carriers, in addition to being over‐represented in late‐flowering and large‐flowered PoolSeq populations, flowered later under stressful conditions in a greenhouse experiment (p < 0.05). In wild population samples, we discovered an additional rare RLG1a variant (high+) that carries 250–300 copies of RLG1a totalling ~5.7 Mb (20–40% of a chromosome). In the progeny of a high+ carrier, Mendelian segregation of diagnostic alleles and qPCR‐based copy counts indicate that high+ is a single tandem array unlinked to the single‐copy RLG1a locus. In the wild, high+ carriers had highest fitness in two particularly dry and/or hot years (2015 and 2017; both p < 0.01), while single‐copy individuals were twice as fecund as either CNV type in a lush year (2016: p < 0.005). Our results demonstrate fluctuating selection on CNVs affecting phenological traits in a wild population, suggest that plant tRNA ligases mediate stress‐responsive life‐history traits, and introduce a novel system for investigating the molecular mechanisms of gene amplification.     

Phenotypic selection on flowering phenology and size in two dioecious plant species with different pollen vectors

Dioecious plants may be pollinated biotically by animals or abiotically via wind or water currents. It has been hypothesized that these two types of pollen vectors might impose contrasting selective pressures on plant flowering phenology. In the present study we describe the flowering phenology of two sympatric dioecious species with contrasting pollination modes: Mercurialis perennis (wind‐pollinated) and Tamus communis (insect‐pollinated). We estimated selection differentials and gradients for flowering time and flowering synchrony. As flowering time might depend on the accumulation of enough internal resources, we also estimated direct and indirect selection on plant size. Both species have male‐biased sexual ratios, and males are bigger and produce larger flower displays than females, but only in T. communis do males bloom earlier and for longer than females. Selection gradients suggest that selection tends to favor early‐flowering females of T. communis. There is no evidence of direct current selection on the flowering phenology of M. perennis. Intersexual differences in phenology fit with sex allocation and sexual selection theories. As we hypothesized, phenology of the animal‐pollinated species is under stronger selection than that of the wind‐pollinated species and we discuss the potential role of pollen vectors in shaping the flowering phenologies of the study species.     

The negative effects of soil microorganisms on plant growth only extend to the first weeks

土壤微生物对植物生长的负面影响只延续到最初几周 土壤微生物群落可以显著影响植物的生长表现。在本文中,我们提出一个问题：土壤微生物群落对植物生长的影响可以持续多久。我们监测了早期、中期和晚期3个阶段的植物生长速率,在无菌土壤或活土壤中对一种菊科植物疆千里光(Jacobaea vulgaris)进行了两次分别为49天和63天的生长实验。在第3个实验中,我们用4种不同的时间处理方法研究了种植前土壤接种时间对该植物相对生长速率的影响。研究结果表明,3个实验中,在无菌土壤和活土壤中生长的植物的生物量差异都增加了。此外,在前2–3周,灭菌土壤中植物的相对生长速率仅显著高于活土壤中植物的相对生长速率。在第3个实验中,植物生物量随着接种和种植之间时间的增加而减少。总体而言,这些结果表明,疆千里光在无菌土壤中的生长优于在活土壤中。土壤接种对植物生物量的负面影响似乎可以延伸到整个生长期,但源于最初几周发生的对相对生长速率的负面影响。     

The causes of selection on flowering time through male fitness in a hermaphroditic annual plant

Flowering is a key life‐history event whose timing almost certainly affects both male and female fitness, but tests of selection on flowering time through male fitness are few. Such selection may arise from direct effects of flowering time, and indirect effects through covariance between flowering time and the environment experienced during reproduction. To isolate these intrinsically correlated associations, we staggered planting dates of Brassica rapa families with known flowering times, creating populations in which age at flowering (i.e., flowering time genotype) and Julian date of flowering (i.e., flowering time environment) were positively, negatively, or uncorrelated. Genetic paternity analysis revealed that male fitness was not strongly influenced by seasonal environmental changes. Instead, when age and date were uncorrelated, selection through male fitness strongly favored young age at flowering. Strategic sampling offspring for paternity analysis rejected covariance between sire age at flowering and dam quality as the cause of this selection. Results instead suggest a negative association between age at flowering and pollen competitive ability. The manipulation also revealed that, at least in B. rapa, the often‐observed correlation between flowering time and flowering duration is environmental, not genetic, in origin.     

Bacterial siderophores promote plant growth: Screening of catechol and hydroxamate siderophores

The aim of the study was to determine the quality and quantity of siderophores produced by bacteria isolated from plants' roots. The second aim was to determine the effect of siderophores on plants growth (Festuca rubra L. and Brassica napus L.). The study was carried out using bacteria isolated from roots of: Arabidopsis thaliana L., F. rubra, and Agrostis capillaris L., growing on the heavy metals contaminated area. The chrome azurol sulfonate (CAS) test, Arnow's test for catechol siderophores, and Csaksy's test for hydroxamate siderophores were performed. Among the bacteria, 42 isolates (39%) had a positive result in the CAS. Endophytic bacteria were mostly producing the catechol siderophores. It was found that F. rubra is the plant which is linked with the highest number of siderophores producing bacteria. The highest concentration of siderophores was noted for ectorhizospheric bacteria associated with A. thaliana, hyperaccumulating plant. It was found that hydroxamate siderophores are mainly produced by ectorhizosphere and rhizoplane bacteria. The siderophores producing bacteria reduced the toxicity of metals and improved the phytoremediation. Siderophores treatment increased the growth of plants in the biological assay, growing on two different soils: one highly contaminated with heavy metals and the second strongly alkaline soil.     

Geographical variation in insect developmental period: effect of host plant phenology on the life cycle of the bruchid seed feeder shape Kytorhinus sharpianus

The voltinism of the bruchid Kytorhinus sharpianus Bridwell (Coleoptera: Bruchidae) and the phenology of its host plant Sophora flavescens Aiton (Leguminosae) were observed at four latitudes: Aomori (40°46' N), Obanazawa (38°37' N), Kujiranami (37°21' N) and Mitsuma (36°05' N) in northeastern Honshu (Japan). Kytorhinus sharpianus life cycle ranged from bivoltine and partially trivoltine in the south to univoltine and partially bivoltine in the north. Sophora flavescens started growing later in spring at higher latitudes. However, the relative growth rate was higher in the north (Aomori) than in the south (Mitsuma). In parallel with this, the first-generation of adult K. sharpianus appeared later at higher latitudes. When the four local populations were reared at 24 °C, L16:D8 and 65% r.h., males developed faster than females. The mean developmental time showed a saw-toothed latitudinal cline. The reversion in the latitudinal trend of variation corresponded to the change in the major type of life cycles from univoltine to bivoltine. Two heat units throughout the year and post-fruiting period were calculated as the sums of degree-days above the developmental threshold (12 °C) of K. sharpianus. Both heat units decreased in parallel with each other with increasing latitude. The greater growth rate of hosts in the northern population compensated for the smaller heat units. In addition, when the heat units were divided by the degree-days needed to complete development, the numerical value was the approximate number of generations observed in each locality.