Low Competitive Ability Research Articles

Morpho-physiological responses of potato cultivars under weed competition

Morpho-physiological responses of potato cultivars under weed competition

Rhizosphere microbial community changes due to weed-weed competition

Many species of weeds are present in agricultural areas, but weeds with greater competitive ability normally become dominant in the field. Rhizosphere soil microbiota can influence weed-weed interactions. However, the role of rhizosphere soil microorganisms in weed-weed interactions remains largely unexplored. In this study, we investigated the ecological relationships and microbial taxa present in the rhizosphere of weeds in monoculture and coexistence systems. The weed species Ageratum conyzoides, Ipomoea ramosissima, and Bidens pilosa were grown in monoculture and coexistence pairs under greenhouse conditions for 80 days. The ecological relationships between weeds were analyzed by calculating the Relative Interaction Index (RII) based on the total dry mass of the plants. The rhizosphere microbiome was analyzed after extracting the metagenomic DNA from rhizosphere microbial populations, followed by PCR amplification and sequencing of the 16S rDNA gene and ITS region, using the Illumina MiSeq platform. Competitive interactions were observed for all combinations of weed species. Ageratum conyzoides showed the greatest decrease in dry matter production due to competition. Weed-weed competition changed rhizosphere microbial community composition and bacterial diversity. The abundance of different bacterial genera in rhizosphere soil varied according to the treatments. When comparing the competition between A. conyzoides and B. pilosa and their respective monocultures, the abundances of Opitutus, Diplorickettisiales uncultured and Bdellovibrio increased in B. pilosa monoculture. When comparing the competition between A. conyzoides and I. ramosissima and their respective monocultures, the abundance of Pseudonocardia increased while the abundance of Fimbriiglobus decreased in A. conyzoides monoculture. Already the abundances of Actinospica, Chitinophaga, Gemmatirosa, 1921-2 and Hymenobacter decreased I. ramosissima monoculture. When comparing the competition between B. pilosa and I. ramosissima, and their respective monocultures, the abundances of Flexibacter and Candidatus Xiphinematobacter decreased I. ramosissima monoculture. The abundances of Clostridium and Rhodobacter increased in competition while the abundance of Pajaroellobacter increased in B. pilosa monoculture. The fungal genera that had their abundances significantly altered were Scytalidium, whose abundance decreased in competition of A. conyzoides and B. pilosa when compared to the respective monocultures, while the abundance of Robillarda increased in B. pilosa monoculture. Already the abundance of Myriodontium increased in B. pilosa monoculture when compared with I. ramosissima monoculture and competition between both plants. Weeds can recruit specific taxa depending on the competition situation in which they are involved. Such changes in the rhizobiome are possibly related to the lower competitive ability and dry matter production of A. conyzoides. B. pilosa have a greater capacity to determine the structure of the rhizobiome when in competition with A. conyzoides. I. ramosissima seem to be less affected by rhizobiome taxon-specific changes.

Expression of Sailx suchowensis SsIRT9 enhances cadmium accumulation and alters metal homeostasis in tobacco

Cadmium (Cd) contamination in soils is of great concern for plant growth and human health. Willow (Salix spp.) is a promising phytoextractor because of its high biomass production. However, as a non-hyperaccumulator, willow has a low competitive ability in extraction of Cd. Thus, improving Cd concentrations in developing tissues is one of the primary tasks. Here, our study uncovers a novel SsIRT9 gene from Sailx suchowensis which manipulates plant Cd accumulation. SsIRT9 was more highly expressed in willow roots than other SsIRT genes. As a plasma membrane-localized protein, when expressed in yeast, SsIRT9 retarded cell growth more severely than other SsIRT proteins in the presence of Cd. Furthermore, SsIRT9 was cloned and expressed in tobacco and SsIRT9 did not affect plant growth. In hydroponic experiments, SsIRT9 lines displayed higher Cd in the shoots than the wild type. When grown in Cd-contaminated soils, Cd levels in transgenic tobacco increased by 152–364% in roots and by 135–444% in shoots, demonstrating significant superiority in Cd accumulation over other functional IRT/ZIP transporters. Moreover, expressing SsIRT9 in tobacco altered metal homeostasis, especially manganese and zinc. Taken together, we envision that SsIRT9 expression in plants is a promising strategy for upgrading extraction of Cd from soils.

Tolerance to aerial exposure influences distributional patterns in multi-species intertidal seagrass meadows

Multi-specific seagrass meadow assemblages dominate most tropical intertidal regions but the relative role of environmental stress in determining distribution patterns is still uncertain. Here we combine observational and experimental approaches to examine aerial exposure as a factor driving species occurrence patterns in intertidal meadows of the Andaman archipelago, where up to 6 seagrass species co-occur. In the studied meadow, patterns of exposure did not map onto distance from the coast, instead creating a patchy matrix of exposure, based on fine-scale bathymetric differences. Distributional surveys showed that seagrass species were similarly patchy, often tracking the degree of aerial exposure during low tide. While some species (Halophila ovalis, Halophila minor, and Thalassia hemprichii) frequently occurred in submerged or subtidal areas and were rarely found in completely exposed areas, other species (Cymodocea rotundata, Halophila beccarii, and Halodule uninervis) also occupied areas that were subject to partial or complete aerial exposure during low tide. To confirm this pattern, we used field-based transplant experiments, employing a natural gradient of tidal exposure to subject six seagrass species to different desiccation exposure times. After a month, H. beccarii and H. uninervis transplants survived in areas that sustained more than 3 h of aerial tidal exposure without significant mortality, compared with other species (H. ovalis, H. minor, T. hemprichii, C. rotundata) that showed dramatic shoot mortality at the same exposure regimes. For all species, 4 h represented the upper limit of exposure, in both experimental and distributional studies. However, despite their wider tolerance of exposure to air, H. beccarii and H. uninervis did not dominate the entire meadow. This could be a result either of their poor tolerance to other environmental factors or their lower competitive abilities among other mechanisms. This suggests that in tropical multi-specific meadows, strong environmental filters could override clear intertidal zonation to create patchy matrices based on species tolerances.

Effects of organic and inorganic mulching, nettle extract, and manual weeding on weed management under direct-seeded lentil in Meknes region, Morocco

Weeds represent a major problem for the production of food legumes in Morocco. In order to cover its legume needs, the country currently imports this commodity, particularly lentils (Lens culinaris Medik.). The present study was conducted to investigate the effects of some agroecological strategies, such as manual weeding, fermented nettle extract (Urtica dioica L.), black plastic, and wheat straw mulching, on weed management, yield and yield components of lentil. The experiment was carried out at the Agroecology and Environment platform of the National School of Agriculture in Meknes, Morocco, in 2020–21 and 2021–22. Five treatments were tested in a complete randomized block design with four replications. The data analysis revealed that crop competition with weeds can result in a yield loss of over 60%. The weed flora identified was very diverse, with 27 different species. All treatments resulted in effective weed management compared to the control (untreated), significant economic gains and a difference in protein content, and a significant decrease in weed density and dry biomass by more than 50% at the flowering and maturity stages. The nettle extract treatment was less effective than the other treatments, but did not show phytotoxic effects on the crop, and it inhibited the germination of more than 50% of Glebionis coronaria (L.) seeds and more than 80% of Avena stirilis (L.) seeds compared to the control under laboratory conditions, which was confirmed in the field. The agroecological practices tested in this study resulted in the highest yield and yield components of the lentil crop compared to the control, leading us to conclude that reducing weed infestation is useful in cropping systems where chemical or mechanical weed control is not feasible, and for crops with low weed competitive ability.

КОМПЛЕКСНАЯ СИСТЕМА ЗАЩИТЫ КАРТОФЕЛЯ ОТ СОРНЯКОВ, БОЛЕЗНЕЙ И ВРЕДИТЕЛЕЙ

Potatoes are among the crops that are heavily affected by diseases. To a large extent, this is due to the peculiarities of the biology of the potato plant. In the conditions of the North Caucasus region, the probability of the spread of late blight and various viral diseases is high. In addition, potatoes, like other crops, high-yielding varieties are most sensitive to climatic factors, their potential yield cannot be realized if they are not resistant to extreme conditions. In the southern regions of Russia, including in the Republic of Alania, such limiting factors should include, first of all, high summer temperatures and rather long dry or long rainy periods during the growing season of potatoes. Under the influence of high temperatures during the formation and growth of tubers, prolonged hot weather causes metabolic disorders, a decrease in yield; weakened plants are more affected by viral, viroid and mycoplasma diseases. In this regard, the most urgent issue is the identification of drought-resistant varieties and hybrids. In recent years, along with the immunological characteristics of varieties, more and more attention has been paid to their qualitative consumer properties, therefore, resistance to diseases, pests and weeds should be combined with the main economically useful qualities - yield, starchiness and others. The weed control system in landscape farming should be considered as an integral part of the management of the entire agricultural system. To build a weed control system, it is necessary, first of all, to know the actual and potential contamination of the object under examination (plot, field, crop rotation). The analysis of factors shows that one of the main reasons is a strong contamination of potato plantings with the floral composition of perennial, annual cereal and broad-leaved weeds, infestation with pests and diseases. Weeds, pests and diseases, having complex biological features, are characterized by strong adaptability to potato cultivation conditions, high competitive ability, harmfulness and on this basis reduce the yield of tubers, their quality in the absence of a scientifically-based comprehensive system for protecting plantings from them. In this regard, potato plants are characterized by low competitive ability compared to weeds, pests and diseases, and vulnerability to them, which necessitates the integrated use of protection methods at all stages of crop cultivation technology. At the same time, it is advisable to direct the agricultural technology of culture cultivation to create favorable conditions for the growth and development of potato plants, the dominant component of agrophytocenosis, increasing its competitive ability against harmful objects and reducing their harmfulness. Agroecological assessment of the conditions affecting the clogging of potato plantings, their infestation with pests and diseases allows us to note that this is facilitated by a decrease in the material and technical base and financial capabilities of agriculture, violation of farming systems, crop rotations, established technologies, lack of monitoring of the species composition of weeds, weak implementation of the results of scientific developments

О распространении и состоянии ценопопуляций редких видов лишайников в Ростовской области

The paper summarizes the accumulated data on the distribution and status of coenopopulations of 5 lichen species listed in the Red Data Book of the Rostov Region: Cetraria steppae, Cladonia foliacea, C. magyarica, Xanthoparmelia pulla, Thalloidima sedifolium. Thalloidima physaroides detected for the first time for the territory of the Rostov Region. In the region under study, 32 new localities of Cetraria steppae, 20 of Cladonia foliacea, 20 of C. magyarica, 15 of Xanthoparmelia pulla, 7 of Thalloidima sedifolium, and 11 of Th. physaroides were identified. The limiting factors for the listed species are both natural factors (low competitive ability, narrow ecological amplitude, low density, and number of coenopopulations) and anthropogenic factors.

The long-term persistence of transgenic volunteers in wild mustard and rice populations

The undesired presence of GM plants outside of cultivation is one of main concerns for the ecological risk assessment and regulation of GM plants, and how long transgenic volunteers can persist in the nature remains unknown. We conducted two long-term coexistence experiments of Bt-transgenic insect-resistant crops in populations of their wild relatives, using Bt-transgenic oilseed rape (Brassica napus) in wild mustard (B. juncea) populations from 2012 to 2019, and Bt-transgenic rice (Oryza sativa) in wild rice (O. rufipogon and O. minuta) populations from 2013 to 2019. Transgenic oilseed rape volunteers survived only in the 2012 winter, because it is a spring variety and not be resistant to cold climate and competition from weeds. Transgenic rice was not survived because of its low competitive ability compared to wild rice, but survived five years in one population of wild rice O. minuta who could not tolerant to cold temperature. Our results indicated that transgenic volunteers can persist in the wild populations under natural conditions, but the fate of transgenic volunteers in the nature depends on whether the growth environment is favorable, and they could not disperse over its niche or “tolerance zone”.

Does a Widespread Species Have a Higher Competitive Ability Than an Endemic Species? A Case Study From the Dongting Lake Wetlands.

The distribution range of plants is usually related to their competitiveness. The competitive ability between common widespread, which are generally considered to be invasive, and common endemic species, is still not very clear. Five plant communities were monitored in the field to compare the competitive abilities of widespread species, Phragmites australis, and endemic species, Triarrhena lutarioriparia, in the Dongting Lake wetlands. The ratios of individual numbers of T. lutarioriparia to P. australis per square meter were found to be 9:0, 14:1, 10:5, 7:6, and 0:11 in the five respective communities. A manipulation experiment was then performed with five planting modes (T. lutarioriparia: P. australis was 4:0, 3:1, 2:2, 1:3, and 0:4, respectively). Results from field monitoring showed that the two plant species exhibited similar decreased survival percentages during flooding. P. australis had higher aboveground biomass before the flooding and a higher relative elongation rate, whereas T. lutarioriparia had higher aboveground biomass after flooding and a higher relative growth rate (RGR). P. australis had a higher competitive ability than T. lutarioriparia before and after the flooding. The manipulation experiment revealed that P. australis had a higher survival percentage than T. lutarioriparia, with no differences in plant biomass, RGR, and the relative elongation rate between the two species. P. australis was found to have a higher competitive ability than T. lutarioriparia in the early growing stage and a lower competitive ability in the middle and later stages. The relative yield total in the field monitoring and manipulation experiment was 1, indicating that T. lutarioriparia and P. australis occupied different niches in the experimental conditions. It was concluded that, compared with T. lutarioriparia, P. australis has a higher competitive ability in submerged habitats and a lower competitive ability in the non-submerged habitat. The niche differences between the two species enabled their coexistence in the Dongting Lake wetlands with seasonal flooding.

Trait divergence between endemic plants of Aegean islands and their widespread congeners

Evolutionary processes on islands, and the attributes of rare plant species restricted to islands have received increasing attention in the last decade, but most of the evidence comes from oceanic archipelagos while continental islands have been much less studied. We test if narrow endemic species of Aegean islands (E Mediterranean region) have evolved particular trait values and ecological attributes. In 64 pairs of congeneric species i.e., an island endemic and a congeneric widespread species, we compared morphological traits (both vegetative and reproductive), and altitudinal range using a phylogenetically constrained multilevel model. Island endemics had larger propagules, larger petals, shorter stems, shorter flowering duration, and they occupied a narrower altitudinal range. The results are interpreted in terms of lower competitive ability and lower dispersal capacity in Aegean endemics. Larger corolla could be accounted for by competition for pollinators in insect-rich ecosystems. Field observations are needed to test if island endemics and their widespread congeners occupy distinct niches when in sympatry on the same island.

Maternal food restriction during pregnancy affects offspring development and swimming performance in a placental live-bearing fish.

ABSTRACTHow pregnant mothers allocate limited resources to different biological functions such as maintenance, somatic growth, and reproduction can have profound implications for early life development and survival of offspring. Here, we examined the effects of maternal food restriction during pregnancy on offspring in the matrotrophic (i.e. mother-nourishment throughout gestation) live-bearing fish species Phalloptychus januarius (Poeciliidae). We fed pregnant females with either low or high food levels for 6 weeks and quantified the consequences for offspring size and body fat at birth and 1 week after birth. We further measured fast-start escape performance of offspring at birth, as well as swimming kinematics during prey capture at 0, 2 and 7 days after birth. We found that the length of maternal food restriction during pregnancy negatively affected offspring dry mass and lean dry mass at birth, as well as body fat gain during the first week after birth. Moreover, it impacted the locomotor performance of offspring during prey capture at birth and during the first week after birth. We did not observe an effect of food restriction on fast-start escape performance of offspring. Our study suggests that matrotrophic poeciliid fish are maladapted to unpredictably fluctuating resource environments, because sudden reductions in maternal food availability during pregnancy result in smaller offspring with slower postnatal body fat gain and an inhibition of postnatal improving swimming skills during feeding, potentially leading to lower competitive abilities after birth.

Люцерна — высокобелковая кормовая культура

The results of selection studies conducted at the Central Experimental Base of the V.R. Williams in the Non-Chernozem Zone of the Russian Federation are presented. Brief data on promising varieties of alfalfa created in the department of alfalfa breeding for the yield of green and dry mass, crude protein and other indicators are presented. Alfalfa varieties of a new generation adapted to local soil and climatic conditions have been created. Alfalfa is one of the best legume grasses for the preparation of high-protein feed. Alfalfa is a culture that is characterized by ecological plasticity, longevity, capable in many regions of Russia to solve the problem of eliminating the deficiency of vegetable protein in the diets of farm animals. It can be used as a legume component of grass mixtures on pastures and hayfields of the Non-Chernozem zone of Russia. The level of productivity and sustainability of fodder agrophytocenoses is determined by the competitiveness of species and varieties. Alfalfa varieties have a low competitive ability, do not withstand three or four times mowing, quickly fall out of the grass stand. It is known that the use of mineral nitrogen in meadow and field feed production is limited due to high energy costs in the production of nitrogen fertilizers. Therefore, the need for nitrogen in meadows and pastures should be met by legume-cereal grass mixtures, for which it is necessary to create new varieties of legumes, in particular alfalfa variable or hybrid.

Evaluation of Chemical Seed Treatment to Reduce Injury Caused by Preemergent Herbicides on Direct-seeded Turnips and Collard Greens

Poor competitive ability and limited herbicide options make weed management of Brassica crops difficult. Growers often adopt the use of transplants, which is less efficient in terms of time, material, and labor when compared with direct seeding, resulting in higher prices per unit. Seed treatment with protective compounds could decrease crop injury from preemergent (PRE) herbicides making it profitable to direct-seed Brassica plants for production. Research was conducted to evaluate the ability of three candidate safeners [24-epibrassinolide, melatonin, and ascorbic acid (AsA)] to reduce injury caused by four herbicides (S-metolachlor, pyroxasulfone, halosulfuron, and mesotrione) applied PRE on the collard green cultivar Top Bunch and turnip cultivar Purple Top White Globe. Two independent greenhouse trials were conducted at the Clemson University Coastal Research and Education Center in Charleston, SC. Visual injury of the treated plants was evaluated weekly and dry mass was collected 21 days after treatment. Seed treatment did not reduce injury efficiently caused by pyroxasulfone, halosulfuron, and mesotrione; all doses were lethal for both crops. However, collard seeds treated using melatonin and AsA had 66% and 54% less injury caused by S-metolachlor at 514 g⋅ha–1 a.i., respectively. On turnips, melatonin was the only treatment that reduced the S-metolachlor damage on seedlings, with 43% less injury than untreated seedlings. Plant injury and plant weight correlated significantly for both Brassica crops. The reduction in injury caused by S-metolachlor when seeds were treated with melatonin and AsA validated those compounds’ protective ability. Seed treatment with melatonin could be combined with PRE applications of S-metolachlor to overcome the low weed competitive ability of these species early in the season.

Condition- and context-dependent alternative reproductive tactic in Drosophila prolongata

Abstract Species with intense male–male competition for access to females often show alternative reproductive tactics (ARTs) where males of lower competitive ability adopt a sneaky behavior to gain access to mates. These ARTs are usually associated with intrasexual dimorphisms, in that males with distinct morphologies show different tactics. In some cases, however, males adopt different tactics without being dimorphic. Male Drosophila prolongata exhibit continuous variation in body size and shape, with enlarged forelegs that they use in male-male contests and in courtship, including stimulation of the female’s abdomen. During this “leg vibration,” however, nearby males can intercept the courted female and mate without their own courtship. Here, we studied the causes and consequences of these different mating tactics in competitive mating trials between males varying in their size and shape. We found that male mating tactics were condition-dependent. Whereas large, high-condition males were more likely to show leg vibration in their courtship, smaller, lower-condition males were more likely to intercept. However, the number of offspring produced was independent of male condition and reproductive tactic. We discuss possible scenarios for the evolution and maintenance of the ARTs and some future directions for the study of ARTs in this species and in general.

Эколого-фитоценотическая приуроченность и сезонный ритм развития Paeonia anomala L. в Восточном Казахстане

В статье приведено описание эколого-биологических особенностей, фитоценотической структуры и сезонного ритма развития популяций Paeonia anomala L. на территории Казахстанского Алтая в Восточно-Казахстанской области. По результатам исследований выявлены закономерности приуроченности вида к экологическим и геоморфологическим условиям среды обитания, выявлены лимитирующие факторы, обусловливающие редкость вида, и даны рекомендации по сохранению естественных популяций вида. Установлено, что P. anomala в исследуемом регионе растет по крутым лесным икустарниковым склонам северной экспозиции, зарастающим курумам, днищам межгорных логов, долинам рек в высотном диапазоне700–1850 м над ур. м. Наиболее оптимальные условия обитания для P. anomala— кедрово-лиственничные разреженные леса. Возрастной спектр популяций пиона уклоняющегося характеризуется абсолютным максимумом генеративных особей. Популяции в загущенных лесных и кустарниковых местах обитания на юго-западных микросклонах находятся в неблагоприятных для вида экологических условиях. Лимитирующими факторами, обусловливающими редкость вида, являются сбор букетов, заготовка лекарственного сырья, выпас скота и низкая конкурентная способность сеянцев на ранних этапах развития, а также массовое уничтожение семян грызунами. Для сохранения естественных популяций пиона уклоняющегося на Западном Алтае необходимы строгая охрана вида от обрывания на букеты, запрет на заготовки лекарственного сырья, а также разработка промышленных технологий выращивания вида в культуре.

Evolutionary and ecological perspectives on the wheat phenotype

Technologies, from molecular genetics to precision agriculture, are outpacing theory, which is becoming a bottleneck for crop improvement. Here, we outline theoretical insights on the wheat phenotype from the perspective of three evolutionary and ecologically important relations—mother–offspring, plant–insect and plant–plant. The correlation between yield and grain number has been misinterpreted as cause-and-effect; an evolutionary perspective shows a striking similarity between crop and fishes. Both respond to environmental variation through offspring number; seed and egg size are conserved. The offspring of annual plants and semelparous fishes, lacking parental care, are subject to mother–offspring conflict and stabilizing selection. Labile reserve carbohydrates do not fit the current model of wheat yield; they can stabilize grain size, but involve trade-offs with root growth and grain number, and are at best neutral for yield. Shifting the focus from the carbon balance to an ecological role, we suggest that labile carbohydrates may disrupt aphid osmoregulation, and thus contribute to wheat agronomic adaptation. The tight association between high yield and low competitive ability justifies the view of crop yield as a population attribute whereby the behaviour of the plant becomes subordinated within that of the population, with implications for genotyping, phenotyping and plant breeding.

Native and alien species suffer from late arrival, while negative effects of multiple alien species on natives vary

Ongoing globalisation and climate change are causing plant species to invade new habitats and thereby alter biodiversity and ecosystem functioning. Since numbers of plant invasions continue to increase globally, it is crucial to investigate the effects of multiple co-occurring alien species on native communities. Furthermore, priority effects due to the earlier emergence of certain species affecting fitness of later arriving species can shape community structure and affect native species performance. We investigate in a common garden pot experiment the interactions among five alien-native species pairs. First we focus on the effect of growing with either one or two alien neighbour species on a native plant, second we alter the arrival time of the alien or native neighbour by 3 weeks. Generally, native species performance decreased when surrounded by two alien species compared to only one, although the magnitude of this effect varied depending on species, with one species even performing better with alien neighbours than in monoculture. Species performance greatly decreased when arriving second in the pot, for both native and alien species. In contrast, alien species tended to benefit more from arriving early. Given that we studied annual ruderal species, their potentially lower competitive ability might explain why we detected negative effects of late arrival. We highlight the need to further elucidate underlying mechanisms of small-scale invasion dynamics to achieve generalisations concerning the response of multiple alien and native plants given their species-specific differences in response to neighbour species and arrival time.

Symmetric response to competition in binary mixtures of cultivars associates with genetic gain in wheat yield.

The evolution in the definition of crop yield—from the ratio of seed harvested to seed sown to the contemporary measure of mass of seed per unit land area―has favoured less competitive phenotypes. Here we use binary mixtures of cultivars spanning five decades of selection for yield and agronomic adaptation to ask three questions. First, what is the degree of symmetry in the response of yield to neighbour; this is, if an older, more competitive cultivar increases yield by 10% with a less competitive neighbour in comparison to pure stands, would the newer, less competitive cultivar reduce yield by 10% when grown with older neighbour. Lack of symmetry would indicate factors other than competitive ability underly yield improvement. Second, what are the yield components underlying competitive interactions. Third, to what extent are the responses to neighbour mediated by radiation, water and nitrogen. A focus on yield components and resources can help the interpretation of shifts in the crop phenotype in response to selection for yield. The rate of genetic gain in yield over five decades was 24 kg ha−1 year−1 or 0.61% year−1. A strongly symmetrical yield response to neighbour indicates that yield improvement closely associates with a reduction in competitive ability. Response to neighbour was larger for grain number and biomass than for grain weight and allocation of biomass to grain. Under our experimental conditions, competition for radiation was dominant compared to competition of water and nitrogen. High‐yielding phenotypes had lower competitive ability for radiation but compensated with higher radiation use efficiency, a measure of canopy photosynthetic efficiency. Genetic and agronomic manipulation of the crop phenotype to reduce competitive ability could further improve wheat yield to meet the challenge of global food security.

Alternative States in Plant Communities Driven by a Life-History Trade-Off and Demographic Stochasticity.

AbstractLife-history trade-offs among species are major drivers of community assembly. Most studies investigate how trade-offs promote deterministic coexistence of species. It remains unclear how trade-offs may instead promote historically contingent exclusion of species, where species dominance is affected by initial abundances, causing alternative community states via priority effects. Focusing on the establishment-longevity trade-off, in which high longevity is associated with low competitive ability during establishment, we study the transient dynamics and equilibrium outcomes of competitive interactions in a simulation model of plant community assembly. We show that in this model, the establishment-longevity trade-off is a necessary but not sufficient condition for alternative stable equilibria, which also require low fecundity for both species. An analytical approximation of our simulation model demonstrates that alternative stable equilibria are driven by demographic stochasticity in the number of seeds arriving at each establishment site. This site-scale stochasticity is affected only by fecundity and therefore occurs even in infinitely large communities. In many cases where the establishment-longevity trade-off does not cause alternative stable equilibria, the trade-off still decreases the rate of convergence toward the single equilibrium, resulting in decades of transient dynamics that can appear indistinguishable from alternative stable equilibria in empirical studies.

Invasion Success of Bunias orientalis (Warty Cabbage) in Grasslands: A Mesocosm Experiment on the Role of Hydrological Stress and Disturbance

Climate change is altering precipitation patterns, with higher frequency and magnitude of extreme events. Specifically, longer and more pronounced waterlogged conditions are predicted after rain spells as well as more frequent droughts, especially in Central Europe. Such hydrological changes can severely affect species performance and alter the function of ecosystems, as well as favor plant invasions. Competition with native communities may change depending on water stress. Bunias orientalis is an invasive plant that may benefit from disturbance or precipitation changes. We conducted a 3-year mesocosm experiment in a common garden to investigate how invasion success of B. orientalis in native German grassland communities is affected by varying hydrological conditions (from very dry to waterlogged). We measured the establishment and growth of B. orientalis in varying water table depths in bare soil (simulating disturbance) vs. in the community. Establishment and biomass of B. orientalis was generally highest under non-stress conditions. The species was also highly tolerant to dry conditions, but only when growing in bare soil. However, performance of B. orientalis was generally low, whereby interspecific competition in communities greatly limited invasion success. This might be due to the low competitive ability of the species in conditions of hydrological stress and the near-natural grassland communities with an extensive mowing regime used in our experiment. Our results suggest that invasion success of B. orientalis in grasslands will not increase if precipitation patterns change toward more extreme events. However, disturbance that creates bare soil patches might favor B. orientalis under drought conditions.