Competition along a nutrient gradient: A case study with Daucus carota and Chenopodium album

A binary competition experiment between carrot (Daucus carota L.) and Chenopodium album L. was conducted in a greenhouse at seven population densities and eight nutrient concentrations to investigate the effects of a nutrient gradient on plant competition in both monocultures and mixtures. The patterns of carrot biomass allocation (measured as root : shoot ratio) in monocultures and mixtures with C. album were affected by both nutrient availability and population density. Chenopodium album had a broader response to nutrient concentrations than carrot. The maximum yield of carrot in both monocultures and mixtures occurred at fourfold the standard concentration of nutrients, while C. album in both monocultures and mixtures had the maximum yield at 16-fold the standard nutrient concentration. The yield–density relationship of carrot tended to be increasing or asymptotic at lower nutrient concentrations but parabolic at higher concentrations, whereas that of C. album was little affected by nutrient availability. Nutrient availability had a profound influence on the competitive relationships between the two species: at both low and high nutrient concentrations, C. album tended to be more competitive than carrot, while at intermediate levels of nutrients, carrot was more competitive than C. album. Our results suggest that in relation to competitive performance, the weed has a greater ability to adapt itself to varying environments than does the crop. Additionally, the relative merits of the quantitative measures of competitive ability are briefly discussed.     

Comparative performance of invasive alien Eichhornia crassipes and native Ludwigia stolonifera under non-limiting nutrient conditions in Lake Naivasha, Kenya

The ability of Ludwigia stolonifera to thrive in the presence of Eichhornia crassipes was investigated in Lake Naivasha, Kenya. L. stolonifera (indigenous) and E. crassipes (invasive alien) were grown in outdoor experimental boxes in monocultures and mixtures under non-limiting nutrient conditions. An additive series design with eight combinations of planting densities and four replicates was used. Competitive interactions between the two species were determined by assessing the final total biomass and above–below-ground biomass allocation after 98 days of growth. Biomass accumulation and allocation were significantly affected by competition in relation to species, with L. stolonifera accumulating more biomass than E. crassipes. ANOVA analysis indicated that there was no significant difference in Relative Growth Rate (RGR) and root/shoot ratio between monocultures and mixtures with E. crassipes. However, significant differences in RGRs were observed between monocultures and mixtures of L. stolonifera. Multiple regressions on species RGRs revealed that increasing initial biomass of a con-specific neighbour resulted to a greater reduction in species RGR in relation to increasing initial biomass of a hetero-specific neighbour. Thus, a stronger intra- than inter-specific competition coupled with the significantly higher RGR of L. stolonifera relative to that of E. crassipes enabled L. stolonifera to outperform E. crassipes.     

Effects of plant species richness on stand structure and productivity

Aims Aboveground biomass production commonly increases with species richness in plant biodiversity experiments. Little is known about the direct mechanisms that cause this result. We tested if by occupying different heights and depths above and below ground, and by optimizing the vertical distribution of leaf nitrogen, species in mixtures can contribute to increased resource uptake and, thus, increased productivity of the community in comparison with monocultures.Methods We grew 24 grassland plant species, grouped into four nonoverlapping species pools, in monoculture and 3- and 6-species mixture in spatially heterogeneous and uniform soil nutrient conditions. Layered harvests of above- and belowground biomass, as well as leaf nitrogen and light measurements, were taken to assess vertical canopy and root space structure.Important findings The distribution of leaf mass was shifted toward greater heights and light absorption was correspondingly enhanced in mixtures. However, only some mixtures had leaf nitrogen concentration profiles predicted to optimize whole-community carbon gain, whereas in other mixtures species seemed to behave more 'selfish'. Nevertheless, even in these communities, biomass production increased with species richness. The distribution of root biomass below ground did not change from monocultures to three- and six-species mixtures and there was also no indication that mixtures were better than monocultures at extracting heterogeneously as compared to homogeneously distributed soil resources. We conclude that positive biodiversity effect on aboveground biomass production cannot easily be explained by a single or few common mechanisms of differential space use. Rather, it seems that mechanisms vary with the particular set of species combined in a community.     

A comparison between two models for plant competition

The differential equation of de Wit (1970) which predicts the growth of plant species in mixtures from their yield–density response in monocultures is compared with a simpler equation. This model is also based on the yield–density response of species grown in monocultures, but is static and predicts only the net result of plant competition during discrete time periods. Data from successive harvests in yield–density experiments in monocultures of one grass and two legume species were fitted to both models and the relative reproductive rate and the relative replacement rate were calculated from model predictions. Predictions from our model agreed more closely with observations than predictions from the de Wit model. It is concluded that our model deserves further attention in the studies of population dynamics in mixtures when the final outcome of competition is the main interest.     

Interspecific interactions and biomass allocation among grassland plant species

Although a handful of studies have shown how interspecific interactions may influence plant shoot to root ratios, the issue of how these interactions influence biomass partitioning among coexisting plant species remains largely unexplored. In this study, we determined whether a given plant species could induce other plant species to allocate relative biomass to each of four zones (aboveground, and three soil depth layers) in a different manner to what they would otherwise, and whether this may influence the nature of competitive or facilitative interactions amongst coexisting plant species. We used a glasshouse study in which mixtures and monocultures of ten grassland plant species were grown in cylindrical pots to determine the effects of plant species mixtures versus monocultures on the production of shoots and of roots of other species for each of three soil depths. Across all experiments, stimulation of production in mixtures was far less common than suppression of production. Different plant species shifted their allocation to shoots or roots at different depths, suggesting that interspecific interactions can either: (1) increase the ratio of deep to shallow roots, perhaps because competition reduces root growth in the uppermost part of the soil profile; or (2) decrease this ratio by reducing plant vigour to such an extent that the plant cannot produce roots that can reach deep enough to exploit resources at lower depths. Further, these results suggest that there are instances in which competition may have the potential to enforce resource partitioning between coexisting plant species by inducing different species to root at different depths to each other.     

Exotic tree seedlings are much more competitive than natives but show underyielding when growing together

Aims Invasive species continue to be a worldwide threat to ecosystems mainly as a cause for biodiversity loss. Forest ecosystems, for example, are subject to a change in species composition due to the invasion of exotic species. Specifying the attributes that cause the strong competitiveness of several exotic species may improve the ability to understand and effectively manage plant invasions in the future. In this study the following hypotheses were tested: (1) biomass production of below- and aboveground plant components of the exotic tree species is higher than that of the natives, resulting in a higher competitiveness of the exotics; (2) the exclusion of root competition has a positive effect on the biomass production of the inferior native species; and (3) mixtures of native and exotic species yield a higher biomass production than the respective monocultures.Methods A pot experiment, containing about 2000 tree seedlings, was established. We investigated the biomass productivity and growth reactions of two native (Quercus robur L., Carpinus betulus L.) and two exotic tree species (Prunus serotina Ehrh., Robinia pseudoacacia L.) in different intra- and interspecific, competitive situations with and without the influence of root competition.Important findings The biomass production of both exotic species was significantly higher and led to a strong competitive advantage, resulting in a biomass decrease of the less competitive native species. The high belowground biomass of both exotic species had a negative effect on the biomass production. The competitive pressure of exotic tree seedlings on the native ones was largely driven by root competition. Furthermore, mixtures of native and exotic tree species had a higher productivity than their growth in monocultures would have predicted. Competition was lower for exotic species in mixtures with the less productive native species compared to the competition in monocultures or in mixture with the other highly productive exotic species. Accordingly, both highly competitive exotic species produced less biomass in mixture with each other compared to monocultures. Despite the significantly higher biomass of P. serotina in all mixtures and in monoculture, R. pseudoacacia seemed to be the dominating species. Due to its strong root competition, R. pseudoacacia significantly reduced the biomass production of P. serotina .     

Combined effects between temporal heterogeneity of water supply,nutrient level,and population density on biomass of four broadly distributed herbaceous species

Temporal heterogeneity of water supply affects grassland community productivity and it can interact with nutrient level and intraspecific competition. To understand community responses, the responses of individual species to water heterogeneity must be evaluated while considering the interactions of this heterogeneity with nutrient levels and population density. We compared responses of four herbaceous species grown in monocultures to various combinations of water heterogeneity, nutrient level, and population density: two grasses (Cynodon dactylon and Lolium perenne), a forb (Artemisia princeps), and a legume (Trifolium repens). Treatment effects on shoot and root biomass were analyzed. In all four species, shoot biomass was larger under homogeneous than under heterogeneous water supply. Shoot responses of L. perenne tended to be greater at high nutrient levels. Although root biomass was also larger under homogeneous water supply, effects of water heterogeneity on root biomass were not significant in the grasses. Trifolium repens showed marked root responses, particularly at high population density. Although greater shoot and root growth under homogeneous water supply appears to be a general trend among herbaceous species, our results suggested differences among species could be found in the degree of response to water heterogeneity and its interactions with nutrient level and intraspecific competition.     

Response of cowpea to variations in planting density and nutrient level

A greenhouse study was carried out using cowpea (Vigna unguiculata (L.) Walp.) grown in Perlite^® and inoculated with Nitragin^® to investigate the concentration of plant nutrients and planting density required for optimum biomass production. Five concentrations (full, 0.5, 0.2, 0.1 and 0.05 strength) of Bisseling's nutrient solution and five planting densities (one to five plants per pot) were tested in a factorial randomized Graeco-Latin square design. Growth was determined as fresh and dry weights of leaves, stems, petioles, roots, flowers and pods, and whole plant.Optimum biomass production was found at 0.5 strength nutrient solution and a density of one plant per pot. Plants were more sensitive to higher planting density than to alterations of nutrient level. Over a twenty-fold range of nutrient supply, whole plant biomass yield varied at most by 44%, whereas increasing planting density from one to five plants per pot decreased biomass production by as much as 77%. There is a decrease in the shoot/root ratio as nutrient level decreases. The data suggests a potential for higher seed production at the higher densities and lowest nutrient levels, but this data was inconclusive.     

Soil nutrient heterogeneity and competitive ability of three grass species (<Emphasis Type="Italic">Festuca ovina,Arrhenatherum elatius</Emphasis> and <Emphasis Type="Italic">Calamagrostis epigejos</Emphasis>) in experimental conditions

We studied the effects of differences in root growth and nutrient pool on the competitive ability of Festuca ovina (short grass), Arrhenatherum elatius and Calamagrostis epigejos (tall grasses) grown in monocultures and in mixtures of homogeneous and heterogeneous environments during two growing seasons. Analysis of variance revealed a significant effect of plant species on nutrient concentrations in above-ground biomass and of substrate type on contents of N, K, Ca, Mg in biomass. The ANOVA also confirmed the significant effect of competitive environment on the concentration of N, K in above-ground biomass. In heterogeneous environments, both tall grasses (in competition with F. ovina) were able to produce more roots in the nutrient-rich patches and to accumulate more nitrogen in plant tissues, which was associated with higher yield of their above-ground biomass. Thus, the relative competitive ability for nutrients of both tall grasses was higher than that of F. ovina. This competitive ability of A. elatius to C. epigejos increased in heterogeneous treatments.     

Host responses to AMF from plots differing in plant diversity

Increased plant species richness in a plant community leads to changes in the composition of the associated arbuscular-mycorrhizal fungal (AMF) community. We tested whether AMF from plots with increased plant diversity cause significant differences in the growth of Lespedeza capitata, Schizachyrium scoparium or Liatris aspera. Seedlings of each were transplanted into pasteurized soil inoculated with soil from their own monocultures, or from plots with one, seven, or 15 additional plant species. In addition, inocula from S. scoparium and L. capitata monocultures were tested for reciprocal growth effects. Inocula from plots containing the native tallgrass prairie species Lespedeza capitata showed increasing AMF species richness and spore density with increasing plant diversity; this was not true with plots containing Schizachyrium scopariumor Liatris aspera. All three species responded to AMF inoculation with increased growth and Cu concentrations, and lowered Mn concentrations compared to non-inoculated control plants. Increasing the plant diversity of the inoculum source-plots significantly affected plant weights of L. capitata, but not of the other two host plants. Both S. scoparium and L. capitata showed increases in growth with inoculum from S. scoparium monocultures compared to that from L. capitata monocultures. Spore density of inoculum source plots was associated with subsequent plant growth or nutrient content only in Lespedeza plots, which contained considerably fewer spores, plant cover, and root biomass in plots with lower plant diversity.     

Dwarf shrubs are stronger competitors than graminoid species at high nutrient supply in peat bogs

Climate warming is likely to increase nutrient mineralization rates in bog ecosystems which may change the plant species composition. We examined the competitive relationships between two graminoid species, Eriophorum vaginatum and Rhynchospora alba, and two ericoid species, Calluna vulgaris and Vaccinium oxycoccus, at different nutrient supply rates. In a greenhouse, the plants were grown in monocultures and mixtures at four nutrient treatments: control, high N, high P, and high N + P. The results show that the ericoids responded more strongly to the nutrient treatments than the graminoids. The dwarf shrubs showed higher growth rates and reduced root:shoot ratio at high N + P supply. When grown in mixture the ericoids increased their growth, while graminoids decreased in biomass or showed signs of nutrient limitation compared to their monoculture plants. This suggests that under increased nutrient availability, bogs are more likely to turn into dwarf shrub dominated ecosystems and not grassland.     

Cascading effects of belowground predators on plant communities are density‐dependent

Soil food webs comprise a multitude of trophic interactions that can affect the composition and productivity of plant communities. Belowground predators feeding on microbial grazers like Collembola could decelerate nutrient mineralization by reducing microbial turnover in the soil, which in turn could negatively influence plant growth. However, empirical evidences for the ecological significance of belowground predators on nutrient cycling and plant communities are scarce. Here, we manipulated predator density (Hypoaspis aculeifer: predatory mite) with equal densities of three Collembola species as a prey in four functionally dissimilar plant communities in experimental microcosms: grass monoculture (Poa pratensis), herb monoculture (Rumex acetosa), legume monoculture (Trifolium pratense), and all three species as a mixed plant community. Density manipulation of predators allowed us to test for density‐mediated effects of belowground predators on Collembola and lower trophic groups. We hypothesized that predator density will reduce Collembola population causing a decrease in nutrient mineralization and hence detrimentally affect plant growth. First, we found a density‐dependent population change in predators, that is, an increase in low‐density treatments, but a decrease in high‐density treatments. Second, prey suppression was lower at high predator density, which caused a shift in the soil microbial community by increasing the fungal: bacterial biomass ratio, and an increase of nitrification rates, particularly in legume monocultures. Despite the increase in nutrient mineralization, legume monocultures performed worse at high predator density. Further, individual grass shoot biomass decreased in monocultures, while it increased in mixed plant communities with increasing predator density, which coincided with elevated soil N uptake by grasses. As a consequence, high predator density significantly increased plant complementarity effects indicating a decrease in interspecific plant competition. These results highlight that belowground predators can relax interspecific plant competition by increasing nutrient mineralization through their density‐dependent cascading effects on detritivore and soil microbial communities.     

A problem for biodiversity-productivity studies: how to compare the productivity of multispecific plant mixtures to that of monocultures?

The study of the relationship between species richness of a plant community and its productivity has received much attention, recently renewed by the concern on the loss of biological diversity at a global scale. Here, we briefly review some indices widely used in agronomic and competition experiments to compare monocultures and mixtures, and compare them to other, more recently designed ones. These various indices are then calculated for two experiments. In the first experiment, two grass and two legume species were grown at six levels of nitrogen availability, either in monocultures or in mixtures of the four species in a substitutive design; in the second experiment, five grass species were grown at 16 levels of total nutrient availability, either in monocultures or in mixtures of the five species in an additive design. These data clearly show that the conclusions drawn from the experiments depend on the index used to compare the experimental communities. We argue that a clear test of whether the productivity of communities increases with species richness requires that: (1) all species present in the multispecies assemblages also be grown in monocultures under the same environmental conditions, and (2) the productivity of these assemblages be compared to the most productive monoculture. We conclude that there are as yet very few cases where superior productivity of multispecies assemblages as compared to monocultures has been clearly shown.     

Intra-plant versus Inter-plant Root Competition in Beans: avoidance,resource matching or tragedy of the commons

Root competition inhibits root proliferation. All else equal, a plant should invest roots in a nutrient patch devoid of roots rather than one already occupied by roots. Less clear is how a plant should respond to intra-plant versus inter-plant root competition. We consider three responses for how a plant may select habitats based on intra-versus inter-plant root competition: inter-plant avoidance, resource matching, or intra-plant avoidance. The first assumes that plants prefer to have their own space and preferentially proliferate roots away from neighboring plants. The second response, based on the ideal free distribution, assumes that plants invest so as to equalize average returns from roots, regardless of the identity of the neighboring roots. The third, based on game theory, assumes that the plant proliferates roots so as to maximize whole-plant fitness, in which case it is better to proliferate plants among a neighbor's roots than to continue proliferating amongst one's own roots. To test among these models we grew beans (Phaseolus varigaris, var. Kenya) in a greenhouse under two planting scenarios. Both scenario were tested under 0.5 and 0.1 strength of nutrient solution. Under scenario A (fence-sitters), two split-root plants each shared two patches by virtue of having roots in each. Under scenario B (owners) two plants each had their own patch. The results supported the game theory model of intra-plant avoidance (whole plant habitat selection). Fence-sitters produced 150% more root mass per individual than owners. Owners produced 90% more yield (dry mass of pods) than fence-sitters. Furthermore, owners had significantly higher shoot-root ratios than fence-sitters. These effects did not vary with high or low nutrient levels. The over-proliferation of roots under inter-plant competition (fence-sitters) was manifest by the tenth day after planting. In short, the fence-sitters engaged in a tragedy of the commons in which they competed with each other through root proliferation. At the ESS, the fitness maximizing strategy of the individual is to sacrifice collective yield in a quest to `steal' nutrients from its neighbor. The research has three implications. First, plants may be able to assess and respond to local opportunities in a manner that maximizes the good of the whole plant. Second, nutrient foraging as a game may provide a fresh perceptive for viewing root competition either intra-specifically or inter-specifically. Third, it may be possible to increase the yield of certain crop species by breeding more `docile' cultivars that do not overproduce roots in response to inter-plant competition.     

异质养分环境下邻株竞争对3个木荷种源干物质积累及氮磷效率的影响

为了探究不同木荷种源混交林和纯林生产力差异原因,采用盆栽试验,模拟异质和同质性森林土壤环境,并设计木荷单植、双株纯植和与杉木混植3种栽植模式,重点研究了异质养分环境下邻株竞争对3个木荷种源(福建建瓯、江西信丰和浙江龙泉种源)干物质积累及氮磷效率的影响。结果表明:与同质养分环境相比,木荷种源在异质养分环境中具有干物质量大,氮、磷吸收效率高的特点,尤以福建建瓯种源优势最大。邻株竞争对木荷种源的干物质量和氮、磷吸收效率影响显著。在异质养分环境中,与杉木邻株竞争时,木荷福建建瓯种源干物质积累量优于单植和双株纯植模式。这与其根冠比和生理可塑性较强有关,混植时,其根冠比明显降低,将更多的干物质分配至叶片,增强了光合能力;同时氮、磷吸收效率也显著提高,进而积累了较高的干物质量,提高了竞争力。相反,混植时江西信丰和浙江龙泉种源氮和磷吸收效率却不同程度地低于其单植或与之相近,根冠比较高,结果影响了干物质积累。同种邻株竞争虽促进了浙江龙泉和江西信丰种源的氮、磷吸收,但抑制了两元素的利用效率,而福建建瓯种源氮、磷效率受影响较小,且明显高于其他种源,从而形成较高的干物质量。以上研究结果表明,福建建瓯种源较高的生物量分配和生理可塑性是其生产力高和生长竞争优势明显主要原因。     

Neighborhood effects on soil properties,mycorrhizal attributes,tree growth,and nutrient status in afforested zones

A harmonious interspecies relationship is the key to the success of mixed afforestation. This study was conducted to assess the responses of afforestation species to their neighboring trees. We examined five types of stands—monocultures of Chinese pine (Pinus tabuliformis), black locust (Robinia pseudoacacia), sea‐buckthorn (Hippophae rhamnoides), and two mixtures (Chinese pine × black locust mixture and Chinese pine × sea‐buckthorn mixture)—in the Loess Plateau, northwestern China. The height and diameter at breast height of each tree species were measured, and rhizosphere soil, shoot, and root were sampled. In monocultures, black locust was taller than Chinese pine and sea‐buckthorn, while the height of Chinese pine and sea‐buckthorn was similar. In mixtures, Chinese pine grew better with sea‐buckthorn than alone as a result of modified soil properties and plant nutrition, but not with black locust. When Chinese pine was used as neighbors, it affected the level of arbuscular mycorrhizal (AM) colonization of black locust, soil properties and AM fungal spore density of black locust and sea‐buckthorn, but did not significantly affect their growth. Our results suggest that the reciprocal effects between tree species in mixture are not symmetric, and thus planning for efficient mixed afforestation requires knowledge of species‐specific growth rate, nutrient requirements, and species interactions.     

Competitive ability of two Brassica varieties in relation to biomass allocation and morphological plasticity under varying nutrient availability

Green cabbage (Brassica campestris, leafy variety) and turnip (Brassica campestris var. rapifera, rooty variety) were grown in both monocultures and mixtures at three nutrient levels to investigate their responses to nutrient availability with respect to biomass allocation, morphological plasticity and competitive ability. Their allocation parameters and leaf morphological traits were affected by both nutrient availability and developmental stage. Both of the varieties had a smaller biomass allocation to leaf blades, but a greater allocation to petioles at high nutrient levels. Root:shoot ratio (RSR) of green cabbage decreased with increasing nutrient availability, whereas that of turnip increased. Turnip had a smaller leaf blade weight ratio (LBWR) than cabbage, being compensated for by larger leaf area ratio (LAR) and specific leaf area (SLA). Leaf area ratio and SLA of both the varieties increased with increasing nutrient availability as did their mean dry weights. The mean dry weight of turnip was slightly greater than that of green cabbage in their respective monocultures, while that of green cabbage was greater than that of turnip in their 1:1 mixture. Therefore, green cabbage, having inherently greater biomass allocation to leaves, was generally more competitive than turnip with more biomass allocation to roots, especially at higher nutrient levels. However, within a variety, morphological plasticity (variation in LAR and SLA) was more important than the plasticity in biomass allocation (e.g. variation in RSR and LBWR) in determining competitive ability. The implication of our results is that competition models based on biomass allocation pattern alone may fail to predict competitive outcomes and that such models should also take morphological plasticity into full account.     

The relation between above- and belowground biomass allocation patterns and competitive ability

Summary In a 2-year experiment, the evergreen shrubsErica tetralix andCalluna vulgaris (dominant on nutrient-poor heathland soils) and the perennial deciduous grassMolinia caerulea (dominant on nutrient-rich heathland soils) were grown in replacement series in a factorial combination of four competition types (no competition, only aboveground competition, only belowground competition, full competition) and two levels of nutrient supply (no nutrients and 10 g N+2 g P+10 g K m⁻² yr⁻¹). Both in the unfertilized and in the fertilized treatmentsMolinia allocated about twice as much biomass to its root system than didErica andCalluna. In all three species the relative amount of biomass allocated to the roots was lower at high than at low nutrient supply. The relative decrease was larger forMolinia than forErica andCalluna. In the fertilized monocultures biomass of all three species exceeded that in the unfertilized series.Molinia showed the greatest biomass increase. In the unfertilized series no effects of interspecific competition on the biomass of each species were observed in either of the competition treatments. In the fertilized mixtures where only belowground competition was possibleMolinia increased its biomass at the expense of bothErica andCalluna. When only aboveground competition was possible no effects of interspecific competition on the biomass of the competing species were observed. However, in contrast with the evergreens,Molinia responded by positioning its leaf layers relatively higher in the canopy. The effects of full competition were similar to those of only belowground competition, so in the fertilized series belowground competition determined the outcome of competition. The high competitive ability ofMolinia at high nutrient supply can be attributed to the combination of (1) a high potential productivity, (2) a high percentage biomass allocation to the roots, (3) an extensive root system exploiting a large soil volume, and (4) plasticity in the spatial arrangement of leaf layers over its tall canopy. In the species under study the allocation patterns entailed no apparent trade-off between the abilities to compete for above- and belowground resources. This study suggests that this trade-off can be overcome by: (1) plasticity in the spatial arrangement of leaf layers and roots, and (2) compensatory phenotypic and species-specific differences in specific leaf area and specific root length.     

Competition between Australian native and introduced grasses along a nutrient gradient

Abstract Seven grass species were grown in monocultures and in multispecies mixtures along a gradient of total nutrient levels that ranged from 1/64 to 16× the normal level of nutrient solution. The seven grasses represented three ecological groups: (i) three perennial species native to Australia (Themeda triandra, Poa labillardieri and Danthonia carphoides); (ii) two introduced annuals (Vulpia bromoides and Hordeum leporinum); and (iii) two introduced perennials (Lolium perenne and Dactylis glomerata). We hypothesized that the native grasses would prove less competitive when grown at increased nutrient levels than those introduced from Europe. Results supported the hypothesis. The native species were unable to compete in mixtures even at the lowest nutrient level, where T. triandra was the most productive species in monoculture. Lolium perenne and Dactylis glomerata dominated mixtures at intermediate nutrient levels. The responses of the annual introduced grasses differed in that Vulpia bromoides showed an optimum at intermediate nutrient levels in both monoculture and in mixtures, whereas Hordeum leporinum dominated at the highest nutrient levels in mixture but was suppressed by V. bromoides, L. perenne and D. glomerata at intermediate levels. The results are discussed in terms of predicting species responses in mixtures from their performance in monocultures as well as in terms of previous observations on the sequential changes in botanical composition of south‐eastern Australian grasslands after 150 years of continuous grazing by sheep.     

Species ecological strategy and soil phosphorus supply interactively affect plant biomass and phosphorus concentration

Excess soil phosphorus often constrains ecological restoration of degraded semi-natural grasslands in Western-Europe. Slow-growing species, often target of restoration (measures), are at a disadvantage because they are outcompeted by fast-growing species. Gaining insight into the responses of plant species and communities to soil phosphorus availability will help understanding restoration trajectories of grassland ecosystems. We set up two pot experiments using twenty grassland species with contrasting growth forms (i.e. grasses versus forbs) and nutrient use strategies (i.e. acquisitive versus conservative nutrient use). We quantified the nutrient use strategy of a species based on the stress-tolerance value of the CSR framework (StrateFy et al. 2017). We grew these species (1) as monocultures and (2) in mixtures along a soil phosphorus gradient and measured the aboveground biomass and plant phosphorus concentrations. Plant phosphorus concentration generally increased with soil phosphorus supply and biomass increased with soil phosphorus supply only in conservative communities. Forbs had higher plant phosphorus concentrations compared to grasses both in monocultures and mixtures. The species’ nutrient use strategy had contrasting effects on plant tissue phosphorus concentrations, depending on soil phosphorus supply (interaction effect) and vegetation biomass (dilution effect). Our findings contribute to the knowledge required for successful ecological restoration of species-rich grasslands. Our results suggest that under specific conditions (i.e. nitrogen limitation, no dispersal limitation, no light limitation), slow-growing species can survive and even thrive under excess soil phosphorus availability. In the field, competition by fast-growing species may be reduced by increased mowing or grazing management.