Differential responses to cadmium stress and competition in Alternanthera philoxeroides and Trifolium repens: stress resistance and adaptive strategies

I investigated the interactions of intra— and interspecific competition with parasitism for populations of two terrestrial isopods, Porcellio scaber and Porcellio laevis, infected with a lethal virus. In field experiments, I varied densities of one or both isopod species in enclosures in which food and virus presence were also manipulated. I estimated the effects of intra— and interspecific competition, additional food, and virus infection on both the survival of P. scaber and the prevalence of the virus. In uninfected populations, intraspecific and interspecific competition negatively affected isopod survival, although food resources had no effect. In infected treatments, interspecific competition produced higher levels of virus prevalence than did intraspecific competition. Virus infection and reduced food interacted to produce higher overall mortality in interspecific competition treatments than in intraspecific competition treatments. The lack of significant effect of food on competition suggests that interference interactions rather than resource competition predominated. This mechanism is supported by a laboratory study in which total food availability was controlled. These results indicate that competition and parasitism interacted to produce the observed mortality patterns, and that ignoring mortality due to the virus would produce apparent interspecific competition. The data suggest that the impact of P. laevis on P. scaber involves both direct and indirect effects.

While the recognised influence of resource competition on the structure of aquatic ecosystems is well‐established, its effects on allochthonous matter dynamics in streams, particularly regarding interspecific and intraspecific indirect competition, remain understudied and inadequately understood. In this investigation, we explored the impacts of interspecific and intraspecific indirect competition on leaf litter consumption by the shredder organisms Phylloicus spp. and Aegla spp. The effects of indirect competition were evaluated through a microcosm experimental setup, comprised of two controls and three treatments: (i) Phylloicus control competition‐free; (ii) Aegla control competition‐free; (iii) intraspecific competition within Aegla ; (iv) intraspecific competition within Phylloicus ; and (v) interspecific competition. In the competition‐free controls, a single organism occupied a 2 L microcosm, whereas in indirect competitive pressure treatments, two organisms were introduced into a 4 L microcosm with a 0.05‐mm mesh partition. Our findings revealed that interspecific indirect competition had a disproportionately higher impact on Phylloicus , whereas intraspecific indirect competition had a more pronounced effect on Aegla . Phylloicus demonstrated superior shredding efficiency compared to Aegla , possibly due to Aegla 's broader feeding range and distinctive leaf litter utilisation strategies. The presence of potential competitors led to reduced consumption rates in Phylloicus , highlighting its sensitivity to competition. Furthermore, Aegla 's predatory behaviour and cannibalism likely intensified intraspecific indirect competition within the species. These results underscore the pivotal role of indirect competition in shaping the feeding behaviour of shredder organisms in leaf litter banks, ultimately influencing plant matter fragmentation in aquatic ecosystems.

Heavy metal accumulation in soils has been one of the environmental and ecological issues, as it caused life and biodiversity problems. However, many invasive plants can survive in heavy metal polluted areas, but little is known about the invasiveness while under different densities either with native species or themselves. In this study, a greenhouse experiment was performed to examine how cadmium contamination with different concentrations (0, 100, and 200 mg/kg) may influence the interspecific competition between invasive plant Alternanthera philoxeroides and the landscape grass T. regens, as well as the intraspecific competition of A. philoxeroides with different densities. The results showed that stronger interspecific competition would alleviate cadmium damage to both A. philoxeroides and T. regens, but the two species adopted different allocation strategies. A. philoxeroides allocated more biomass to belowground and less to aboveground, while T. regens showed exactly the opposite allocation strategy. There was a significant density effect of intraspecific competition on A. philoxeroides. That is to say, with the increase of A. philoxeroides density, the cadmium stress on the growth of A. philoxeroides decreased. Our findings provide a theoretical basis and technical support for the effective control of A. philoxeroides invasion, as well as the restoration and reconstruction of green vegetation.

PDF HTML阅读 XML下载 导出引用 引用提醒 施氮对空心莲子草(Alternanthera philoxeroides)和莲子草(Alternanthera sessilis)种间关系的影响 DOI: 10.5846/stxb201405281098 作者: 作者单位: 北京林业大学自然保护区学院,北京林业大学自然保护区学院,北京林业大学自然保护区学院,北京林业大学自然保护区学院,北京林业大学自然保护区学院 作者简介: 通讯作者: 中图分类号: 基金项目: 中央高校基本科研业务费专项资金资助(TD-JC-2013-1);高等学校博士学科点专项科研基金新教师类资助课题(20120014120001);国家自然科学基金项目(31200313,31200314) Effects of nitrogen addition on interspecific competition between Alternanthera philoxeroides and Alternanthera sessilis Author: Affiliation: School of Nature Conservation, Beijing Forestry University,,School of Nature Conservation, Beijing Forestry University,, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:自然界的氮素释放总是呈现出空间和时间上的异质性,但关于异质性氮释放对于入侵植物和本地植物种间关系影响的研究相对较少。将入侵植物空心莲子草(Alternanthera philoxeroides)和同属本地植物莲子草(Alternanthera sessilis)分别进行单种种植(12株,无种间竞争)和混种种植(每种6株,有种间竞争),模拟大气氮湿沉降设置由两种不同施氮总量(15g N m-2 a-1和30g N m-2 a-1)和两种不同施氮频率(每5天1次和每15天1次)交叉组成的4种施氮处理,并以不施氮为对照。施氮总量的增加显著促进了两种植物的生长,但对两种植物的种间竞争关系没有显著影响。施氮频率对两种植物的生长以及种间竞争关系都没有显著影响。两种植物在面对竞争时表现出不同的生物量分配策略,空心莲子草将更多的生物量分配到茎,而莲子草将更多的生物量分配到根。在全球变化的背景下,大气氮湿沉降可能会改变两种植物的种群结构和动态,但可能对这两种植物的种间关系影响较小。 Abstract:Nitrogen (N) is one of the most important soil nutrients for plants, and the amount and frequency of N release in soils is heterogeneous. Many studies have focused on the effects of heterogeneous N addition on a single plant species, but little is known about the effects of N amount and short-term N pulse on interspecific competition between invasive and native plant species. A replacement series experiment was conducted under greenhouse conditions to examine the effects of N amount and frequency release on the growth and interspecific competition between an invasive wetland clonal plant, Alternanthera philoxeroides (alligator weed), which is native in South America but highly invasive in China, and its native congener Alternanthera sessilis (sessile joyweed). Plant materials of A. philoxeroides and A. sessilis were collected from five locations in Xixi Wetland Park in Hangzhou, Zhejiang Province, China. Stem fragments of similar length (20 cm), with a stem tip for each species, were grown in monoculture (12 ramets in one container, no interspecific competition) and in mixture (six invasive plants with six native plants, with interspecific competition) in five different N treatments: control (no N added), low amount and high frequency (a total of 15 g N m-2 a-1 added every 5 days), low amount and low frequency (a total of 15 g N m-2 a-1 added every 15 days), high amount and high frequency (a total of 30 g N m-2 a-1 added every 5 days), and high amount and low frequency (a total of 30 g N m-2 a-1 added every 15 days). The results showed that N addition significantly increased the growth of both A. philoxeroides and A. sessilis. No significant difference was observed between the control and treatments for the relative yield (yield of each species in mixture divided by yield in its monoculture) for both species, indicating that N addition did not significantly affect the interspecific competition between the two species. The probable reason is that both species are from the same functional group and may have comparable capacities to compete and utilize the soil nutrients. The N pulse did not significantly modify growth or interspecific competition for either species. The sufficient soil water content and availability of nutrients other than N may explain why there were no effects of a N pulse on competition between the two species. Alternatively, high tolerance of both species to low soil nutrients and water content may lead to weaker responsiveness to a N pulse. With interspecific competition, the invasive species, A. philoxeroides, invested more biomass to stems, i.e., the stem biomass increased by 60%, which significantly decreased the root to shoot ratio. The native species, A. sessilis, allocated more biomass to roots, i.e., the root biomass increased by 250%, which significantly increased the root to shoot ratio. The results indicate that increasing atmospheric N deposition in the context of climate change may change population structure and dynamics of both species, but may not affect the interspecific competition of these plants. 参考文献 相似文献 引证文献

Aims Arbuscular mycorrhizal fungi can have a substantial effect on the water and nutrient uptake by plants and the competition between plants in harsh environments where resource availability comes in pulses. In this study we focus on interspecific competition between Acaia etbaica and Boswellia papyrifera that have distinctive resource acquisition strategies. We compared the extent of interspecific competition with that of intraspecific competition. Methods In a greenhouse study we examined the influence of Arbuscular Mycorrhiza (AM) and pulsed water availability on competitive interactions between seedlings of the rapidly growing species A. etbaica and the slowly growing species B. papyrifera. A factorial experimental design was used. The factors were AM, two water levels and five species combinations Important Findings Seedlings of both species benefitted from AM when grown alone, and the positive growth response to pulsed water availability in B. papyrifera seedlings was in contrast with the negative growth response for A. etbaica seedlings. AM also affected the competitive performance of both species. B. papyrifera was not affected by intraspecific competition, whereas A. etbaica was negatively affected compared to the seedlings grown alone. This effect was stronger in the presence of AM. In interspecific competition, A. etbaica outcompeted B. papyrifera. Mycorrhiza and pulsed water availability did not affect the outcome of interspecific competition, and the aggressivity index of A. etbaica remained unchanged. The extent to which AM influences plant competition in a drought-stressed environment may depend on belowground functional traits of the species. AM and pulsed water availability could modify the balance between intraspecific and interspecific competition. By affecting the balance between intraspecific and interspecific competition, both factors could impact the establishment and survival of seedlings.

The effects of long-term carbon dioxide enrichment on competition for nutrients and light in a ryegrass/clover association were determined for simulated swards of perennial ryegrass (Lolium perenne L. cv. Parcour) and white clover (Trifolium repens L. cv. Karina), which were grown as monocultures and in three mixtures (25/75, 50/50, 75/25), according to the replacement design, at two levels of nitrogen (N) supply (no additional N and 200 kg N ha-1 ) and at season-long ambient (380 ppm) and elevated (670 ppm) CO2 concentrations, in open-top chambers. Stands were cut four times, at about monthly intervals, to a height of 5 cm. Plant material was separated into different species, fresh and dry weights were determined and the content of macroelements (N, P, K, S, Mg) in both species was measured. In addition, plant height of both species at harvest dates and during several regrowth periods was monitored. Results indicate that both species made demand on different resources and profited from growth in a mixed sward. Co2 related yield increase amounted to 16-4-2 % for white clover whereas the effect of high CO2 on ryegrass yield ranged between -33% and +9% depending on N supply, mixture and year. As a result the contribution of white clover to total yield in mixed swards was significantly enhanced by CO2 enrichment at many harvests in both N supply treatments. Without additional N supply, shoot competition for light was intensified by CO2 enrichment to the disadvantage of ryegrass, since clover petioles grew longer and ryegrass was shorter at elevated CO2 With N fertilization, no marked effect of CO2 enrichment on interspecific competition could be observed. Since clover and total yield were increased by CO2 enrichment, nutrient requirements were also increased and potassium deficiency and increased intraspecific competition of clover for K was observed in the mixtures under elevated CO2 which had the highest nutrient withdrawal. Although white clover profited much more from CO2 enrichment in both N fertilization treatments, the suppression of ryegrass in mixed swards could only be observed under low N conditions. Generally, the effect of N fertilization on competitive interference between both species was much greater than the effect of CO2 enrichment and it is suggested that the effect of elevated CO2 on the balance of species and the outcome of competition in a grass/clover sward is mainly dependent on the N status.

There have been very few studies on the effects of plant competition on the rhizosphere bacterial community. To investigate the impacts of intra- and interspecific plant competition, we analyzed the responses of rhizosphere bacterial communities to plant density as determined by 16S rRNA gene targeted sequencing. We included five weedy plant species growing in field soil in monocultures and mixed cultures at three densities in a greenhouse experiment. The rhizosphere bacterial community of each species changed more with density in a mixture of all five plant species than in monocultures, so intra- and interspecific plant competition had different effects on the bacterial community. For the dominant plant competitor, Centaurea cyanus, neither intra- nor interspecific competition had major effects on the composition of its rhizosphere bacterial communities. In contrast, the bacterial communities of the weakest competitor, Trifolium repens, were affected differently by intra- and interspecific competition. During increasing intraspecific competition T. repens maintained a highly specialized bacterial community dominated by Rhizobium; while during interspecific competition, the relative abundance of Rhizobium declined while other nitrogen fixing and potentially plant growth promoting taxa became more abundant. Contrary to previous observations made for soil microbial communities, the bacterial rhizosphere community of the weakest competitor did not become more similar to that of the dominant species. Thus, the process of competition, as well as the plant species themselves, determined the rhizosphere bacterial community. Our results emphasize the role of plant-plant interactions for rhizosphere bacterial communities. These effects may feedback to affect plant-plant interactions, and this is an important hypothesis for future research.

Positive responses of soil nutrients and enzyme activities to AM fungus under interspecific and intraspecific competitions when associated with litter addition

Arbuscular mycorrhizal (AM) fungi can affect plant growth by regulating competition. Nutrient-deficient karst habitats contain abundant plants that compete for nutrients through interspecific or intraspecific competition, involving the nutritional transformation of litter decomposition. However, how plant competition in the presence of AM fungi and litter affects root development and nutrition remains unclear. A potted experiment was conducted, including AM fungus treatment with or without Glomus etunicatum, the competition treatment concerning intraspecific or interspecific competition through planting Broussonetia papyrifera and Carpinus pubescens seedlings, and the litter treatment with or without the mixture of B. papyrifera and C. pubescens litter leaves. The root morphological traits were analyzed, and nitrogen (N), phosphorus (P), and potassium (K) were measured. The results showed that AM fungus differently affected the root morphological development and nutrition of both competitive plants, significantly promoting B. papyrifera roots in the increase of dry weight, length, volume, surface area, tips, and branches as well as N, P, and K acquisitions regardless of litter addition. However, there was no apparent influence for C. pubescens roots, except for the diameter in the interspecific competition with litter. The root dry weight, length, volume, surface area, and tips of B. papyrifera under two competitive styles were significantly greater than C. pubescens regulated by AM fungus, presenting significant species differences. The responses of the relative competition intensity (RCI) on root morphological and nutritional traits indicated that AM fungus and litter both asymmetrically alleviated more competitive pressure for B. papyrifera than C. pubescens, and the interspecific competition facilitated more root morphological development and nutrition utilization by endowing B. papyrifera root superiority relative to C. pubescens compared with the intraspecific competition. In conclusion, interspecific competition is more beneficial for plant root development and nutrition than intraspecific competition in the presence of AM fungus and litter via asymmetrically alleviating competitive pressure for different plants.

AimsPopulus deltoides and P. euramericana are widely used in China as major forestry species. At present, little is known about their responses to nitrogen (N) deficiency when grown in monocultures or mixed plantations. The aim of this investigation was to analyze the growth, and morphological and physiological responses of P. deltoides and P. euramericana to different N levels under competition conditions.MethodsWe employed two Populus species (P. deltoides and P. euramericana) to discover how N deficiency affects plant traits under different competition types (P. deltoides × P. deltoides, intraspecific competition; P. euramericana × P. euramericana, intraspecific competition; P. deltoides × P. euramericana, interspecific competition). Potted seedlings were exposed to two N levels (normal N, N deficiency), and nitrogen- and competition-driven differences in growth, morphology and physiology were examined.Important FindingsUnder normal N conditions, interspecific competition significantly decreased the total root weight, root mass fraction (RMF), root–shoot ratio (R/S) and carbon/nitrogen ratio (C/N), and increased the leaf dry weight, leaf mass fraction and total leaf area of P. euramericana compared with intraspecific competition. The same conditions significantly affected the growth and morphological variables of P. deltoides, except for the dry weight of fine roots, R/S, specific leaf area, RMF, total nitrogen content and C/N compared with intraspecific competition. In addition, chlorophyll a (Chla), total chlorophyll (Tchl), carotenoid contents (Caro) and the carbon isotope composition (δ 13C) of P. deltoides were significantly lower in interspecific competition than in intraspecific competition, but no difference was detected in P. euramericana. The effects of N deficiency on P. deltoides under intraspecific competition were stronger than under interspecific competition. In contrast, the effects of N deficiency on P. euramericana between intraspecific and interspecific competition were not significantly different. These results suggest that under normal N condition, P. deltoides is expected to gain an advantage in monocultures rather than in mixtures with P. euramericana. Under N deficiency, the growth performance of P. euramericana was more stable than that of P. deltoides under both cultivation modes.

Plant–plant interactions change in response to environmental conditions, and riparian species are commonly influenced by flooding. This study tested whether flooding affects the intraspecific and interspecific competition of two riparian species and whether such effects depend on the topographic positions where plants have established. Seeds of the riparian species Polygonum hydropiper were collected from both low and high positions within the shoreline of the Three Gorges Reservoir. Groups of P. hydropiper seedlings from each position were either grown alone (i.e., without competition), with another group of P. hydropiper seedlings (i.e., intraspecific competition), or with a group of seedlings of the companion species Xanthium sibiricum (i.e., interspecific competition). Each group comprised six replicates. In total, 288 plants of P. hydropiper and 84 plants of X. sibiricum were selected for the experiment. Seedlings were subjected to control and flooding treatments for 60 days. Irrespective of competition type (i.e., intra- or interspecific), both flooding and competition negatively affected the growth and/or photosynthetic capacities of P. hydropiper. Flooding only interacted with competition to explain total biomass. Flooding reduced total biomass in a larger proportion in the absence of competition, and, to a lesser extent, with intraspecific competition, compared to interspecific competition. However, such interaction effects were independent of the positions where the seeds that originated from the plants were collected from. Interspecific competition significantly decreased the chlorophyll content and photosynthetic efficiency of plants, while intraspecific competition did not. In general, plants from lower positions had higher total chlorophyll content than plants from higher positions. These results suggest that flooding may regulate the population dynamics of P. hydropiper by altering its competitive interactions.

Field Competition Between Tall Morningglory and Soybean. II. Development and Distribution of Root Systems

QuestionSeed‐transmitted fungal endophytes of grasses can influence competitive interactions via direct effects of infection on host plant performance or via indirect effects, such as plant–soil feedback effects that operate through changes to soil properties. To date, however, these direct and feedback effects have been evaluated separately. What is the relative importance of endophyte infection vs endophyte‐mediated plant–soil feedback effects on competition between seedlings of the grass tall fescue (Schedonorus phoenix) and common species of American Midwestern old‐field successional grasslands?LocationLong‐term field experimental plots at the Indiana University Research and Teaching Preserve and greenhouse of Indiana University (Bloomington, IN, USA).MethodsEndophyte‐free (E‐) and endophyte‐infected (E+) tall fescue seedlings were grown individually and in intraspecific competition and pair‐wise interspecific competition. Endophyte‐mediated plant–soil feedback effects were incorporated by growing seedlings in soil conditioned by either E– or E+ tall fescue.ResultsWe found that E– and E+ tall fescue experienced stronger intra‐ and interspecific competition when competing in self‐conditioned soils. This pattern was consistent regardless of competitor identity.ConclusionsOur findings suggest that the direct benefits of endophyte infection do not drive competitive responses of tall fescue at the early stages of plant development, at least under the conditions examined in our study. Rather, negative plant–soil feedbacks may be more important in moderating plant responses to competitive interactions during seedling establishment of this species. Explicit manipulation of factors such as herbivory and abiotic stress is an important future direction for studies evaluating the relative importance of endophyte infection vs soil‐mediated endophyte effects on host plant performance.

Competitive interactions between two species of intertidal herbivorous gastropods from Victoria, Australia

Coexistence of species requires equalizing mechanisms that minimize fitness differences, which are balanced by stabilizing mechanisms that enhance negative intraspecific interactions versus interspecific ones. Here, we develop a simple theoretical framework that allows measuring the relative strength of intraspecific versus interspecific competition in dominance hierarchies. We use it to evaluate mechanisms promoting coexistence between two congeneric charr that compete for foraging positions, which strongly influence density-dependent growth and survival. Agonistic interactions (n=761) among 71 Dolly Varden Salvelinus malma and whitespotted charr Salvelinus leucomaenis were measured by snorkelling in two pools in the sympatric zone of a Hokkaido stream during two summers. Interspecific dominance hierarchies, analysed using three methods, were closely correlated with fish length but the species treated each other equally. Ranks for the most dominant fish in each pool, determined directly by knockout experiments, were also virtually identical to ranks by length. Similarly, exponential random graph modelling of the social networks provided no evidence that either species was dominant over the other. Instead, larger fish were more likely to win contests, especially over fish of the next lower ranks. These results demonstrated that the two species were nearly ecological equivalents in accessing key resources in this sympatric zone. Nearly identical growth and stable densities over 4years further supported this inference, although Dolly Varden were a minority (29% of the assemblage), a sign of some fitness difference. Detailed foraging observations coupled with two concurrent studies revealed an effective stabilizing mechanism. Dolly Varden shifted to feeding directly from the benthos when drifting invertebrates declined, a behaviour enhanced by morphological character displacement, thereby partitioning food resources and enhancing intraspecific competition while avoiding agonistic encounters with whitespotted charr. The plurality of evidence indicates that fitness differences between these ecologically equivalent species are small in this local assemblage, and balanced by resource partitioning, a modest stabilizing mechanism that promotes coexistence. The theoretical framework presented here is a useful tool to evaluate the strength of interspecific versus intraspecific competition, which combined with information on trade-offs in ecological performance can contribute to a mechanistic understanding of species coexistence.