The impact of plant community composition on plant interactions in grasslands

The impact of plant community composition on

plant interactions in grasslands

Bachelor Future Planet studies

Institute for Biodiversity and Ecosystem dynamics

Author:Y.C. (Yse Coco) Tuynman (11299592)

Supervisors: Mrs. E. (Eileen) Enderle, Ms. prof. dr. ir. F.T. (Franciska) de Vries & Mrs A (Anne).G. Uilhoorn

Date: 31-05-2021 Place: Amsterdam

Inhoudsopgave

Relative competition intensity ... 10

Average aboveground biomass per species and community ... 12

Total average biomass per mesocosm ... 13

Discussion ... 14

Conclusions ... 16

Acknowledgement

In this section I would want to express my gratitude to everyone who have supported me during the writing of this BSc thesis. I would like to thank my supervisor Eileen Enderle for her hard work, her time, effort, and patience while helping me with the whole process of writing this BSc thesis! I also would like to thank Franciska de Vries for making this project possible and being my supervisor, Anne Uilhoorn for helping me with the data-analysis and Leonardo Hinojosa, Tom Scheltema, Abbe Hekkert and Emma Schermerhorn for helping me during fieldwork.

Abstract

Ecosystem functioning is threatened increasingly by anthropogenic activity since community compositions in grasslands are changing. These changes in community compositions influence plant interactions such as competition respectively. This research aims to get more insights into how plant community composition influences plant interactions to understand how grasslands need to be treated to maintain and improve the stability, productivity, and sustainability of the ecosystem. Intra-and interspecific competition, growth strategy Intra-and plant functional type will be considered. Relative competition intensities are calculated for 4 different grassland species with different growth strategies and plant functional types: The slow-growing resource-conservative grass Anthoxanthum odoratum (Ao), the fast-growing, acquisitive grass Dactylis glomerata (Dg), the slow-growing resource-conservative forb Leontodon hispidus (Lh), and the fast-growing, resource-acquisitive forb Rumex acetosa (Ra). Twenty experimental grassland mesocosms with five different plant community compositions have been set up at the University of Amsterdam at Science Park to simulate a natural grassland community. This research gave new insights into how plants affect each other’s growth in grassland ecosystems. The question of whether intraspecific competition is higher than interspecific competition is species-dependent and could be explained by growth strategy. Fast-growing species experience higher intra-specific competition than slow-growing species. In general, there is a pattern that the fast-growing species, have the highest biomass in the communities of the slow-growing species. The fact that the slower-growing species experience higher interspecific competition, may exert greater dominance over fast-growing species which needs to be considered while looking at the functioning of grassland ecosystems. This research concludes that the interplay of intra- and interspecific competition between species shapes plant community dynamics in grasslands.

Keywords

Intraspecific competition, interspecific competition, grasslands ecosystem, plant interactions, fast and slow growing species, community composition

Introduction

In ecological research, the observed worldwide loss in biodiversity and its consequences for ecosystem functioning is a frequently debated topic (Hector et al.,2000; Loreau et al.,2002). This worldwide loss in biodiversity has led to dramatic changes in grassland ecosystems and community composition concerning species richness and species evenness (Hillebrand et al., 2008). Species evenness is defined as the relative abundance of different species within a community, and species richness is defined as the number of different species in an area, these are the two main components of species diversity (Wilsey & Potvis, 2000). Species evenness responds often more rapidly to anthropogenic activity than species richness and is declining (Chapin et al.,2000). The changes in community composition can influence plant interactions such as competition and facilitation, which play a key role in the structure and functioning of grassland ecosystems, influencing the provision of ecosystem services (Cavieres & Badano, 2009; Chapin et al.,2000; Hillebrand et al., 2008). In a natural habitat, in this case, a grassland ecosystem, resources are often limited. Therefore, many species will have to compete (Silvertown, 2004). Competition is referred to the negative consequences of the presence of neighbors on plant growth and fitness (Asschehoug et al.,2016). Species could compete directly for limited resources like light, water, space, and nutrients (Silvertown, 2004). As well as indirectly, through feedback effects via pathogen transmission or the soil microbial community (Bardgett et al., 2006). When species compete for resources, they could compete with individuals of different species, which is called interspecific competition, and they could compete with individuals of the same species: intraspecific competition (Chesson, 2013). Next to competition, species can facilitate the coexistence, invasion, growth, or establishment of other species, by amelioration of the environment they live in through microbial communities and nutrient partitioning (Armas et al., 2008). In this research, the effects of plant community composition on plant interactions in grasslands are considered. There will be particularly looked at intra-and interspecific competition.

Community composition

Species evenness is strongly decreased in almost all ecosystems due to anthropogenic activity (Hillebrand et al., 2008). Chronic nitrogen enrichment of grassland ecosystems is an example of how anthropogenic activity can indirectly affect ecosystem functioning (Klumpp & Soussana, 2009). The effect of nitrogen enrichment on ecosystem functioning is that plant community diversity will be reduced, since highly productive fast-growing species will become dominant (Stevens et al., 2004; Hillebrand et al., 2008). Species differ in traits such as vulnerability to consumers, nitrogen fixation capacity, and growth form. If a certain trait is associated with a dominant species, this community interaction contributes more to aggregate processes in a community than that of rare species, since this trait is more represented in the community (Norberg, 2004). Consequently, the distribution of dominant species primarily determines the distribution of traits (Hillebrand et al., 2008). This can cause an imbalance of nutrient depletion and resistance/resilience against disturbances and environmental changes (Hillebrand et al., 2008; Chen et al., 2009). Furthermore, reduced evenness and increased dominance may have negative consequences for synergistic interaction, since one species dominates the other and the synergistic interaction fails (Hillebrand et al., 2008). When species evenness will be affected by anthropogenic activity, the magnitude of intra-and interspecific interaction will be influenced (Chesson 2000; Hillebrand et al., 2008).

Intra- and interspecific competition

The community composition in grassland ecosystems is next to diversity influenced by plant interactions such as competition (Chapin et al.,2000; Silvertown, 2004). To gain stable coexistence between competing species and optimal use of resources, different niches need to be occupied (Silvertown, 2004). This is possible since species differ in resource acquisition traits (Guiz et al., 2018) Different kinds of coexistence mechanisms, such as temporal and spatial environmental variation, species-specific natural enemies and resource partitioning can also lead to different niches (Adler et al., 2018). A core principle of the coexistence theory is that intraspecific competition is stronger than interspecific competition for stable coexisting species (Chesson, 2000). In other words, members of the same species are more competitive at using overlapping and limited resources, in comparison to individuals of different species. Therefore, the population growth of one species will be more limited than the population growth of its competitors (Chesson, 2013). When a community has a less even distribution, intraspecific interactions will become more important for dominant species, and interspecific interactions become more important for rare species. Differences in the relative strength of this intra and inter-specific interactions can significantly change the dynamics of a grassland community (Chesson 2000; Adler et al., 2007).

Growth strategy and plant functional type

Different growth strategies within a plant community can have a great impact on competition behavior and plant community dynamics (Reich,2014). Plants with a fast, resource-acquisitive growth strategy will generally have traits such as high metabolic rates and narrow- diameter, long roots. They have a minimal investment in root biomass and a fast resource acquisition strategy aboveground, with a short life cycle of their leaves (Elssenstat,1992; Ostonen et al., 2007). On the other hand, plants with a slow, resource-conservative growth strategy, are expected to construct thicker-diameter and denser roots with a longer life span (Elssenstat,1992; Ryser et al., 2000). Similarly, above ground tissues like leaves have a slower turnover rate (Elssenstat,1992). Under optimal conditions (No environmental stresses, high nutrients content) fast-growing species tend to dominate slow-growing species and are strong competitors. Under harsher conditions (Environmental stresses, low nutrient content) slow-growing plants often have an advantage, since they allocate more resources towards defense and stress tolerance mechanisms (Poorter & Garnier, 1999). Plant functional groups are a set of species who share similar morphology and phenology within the community ((Hooper & Dukes, 2004). Forbs usually have higher root diameters, a less explorative root system and faster exudation rates, and are known to have more positive plant-soil feedbacks than grasses what also influences their competition behavior (Williams et al., 2021). Next to root traits, the fungal community is strongly linked to the plant functional group (Sweeney et al., 2021). Legumes and forbs have a higher abundance of arbuscular mycorrhiza fungi (AMF), while grasses have the highest abundance of pathogens (Sweeney et al., 2021).

To conclude, ecosystem functioning is threatened increasingly by anthropogenic activity since community compositions are changing in grasslands ecosystems (Orwin et al., 2014; Hillebrand et al., 2008). This changes in community composition influences plant interactions respectively (Chapin et al.,2000). It is therefore of great importance to know how community composition influences plant interactions, and to look more specific at intra- and interspecific competition, growth strategy and plant functional type. This knowledge is essential to understand how grasslands can be managed to maintain and improve the stability, productivity, and sustainability of the ecosystem. To examine how plant community composition influences ecosystem functioning, biomass production is choses as a response variable, since it is one of the most important variables in an ecosystem (Siemann, 1998). An outdoor mesocosm study is used to simulate a grassland community of different composition. A grassland is used since grassland ecosystems is a quick-responding system with a naturally high diversity ((White et al.,2000). It covers 40% of the Earth’s surface area (excluding Antarctica and Greenland), and is therefore an important ecosystem (White et al., 2000). In order to maintain

ecosystem functioning under the increasing effects of human influence, this research aims to understand how plant community composition impacts plant interaction and tries to specifically find an answer how community composition, plant functional type and growth strategy affects intra-and interspecific competition in grasslands.

Objectives

1. Characterize the competition behavior within and between grassland plant species

2. To gain insight how growth strategy and plant functional type influences competition behavior in grassland ecosystems

3. To gain insight on how plant community composition influences biomass production in grassland ecosystems

This study aims to answer the research question:

· How does plant community composition impact plant interactions in grasslands?

the following sub questions are posed to create an integrated approach how community composition influences plant interactions:

1. Is intraspecific competition stronger than interspecific competition in grassland communities and does this differ between species?

2. How does growth strategy and plant functional type influence intra-and interspecific

competition in grassland communities?

3. How does plant community composition influence root and shoot biomass?

For the outcome of this research, I hypotize that:

1. Intraspecific competition is stronger than interspecific competition in grassland community compositions.

2. Fast-growing species are expected to experience higher intra-specific competition than slow-growing species and grasses suffer more from intraspecific competition than forbs.

3. Community compositions with even distributed species, will positively influence biomass production in grassland communities.

Methods

Experimental setup

To test the impact of community composition on plant interactions, 20 experimental grassland mesocosms with different plant community compositions have been set up at the University of Amsterdam at Science Park (52° 21′ NB, 4° 57′ OL) to simulate a natural grassland community in October 2020. In this research, four common Dutch types of grass are selected with different growth strategies: The slow-growing resource-conservative grass Anthoxanthum odoratum (Ao), the fast-growing, resource-acquisitive grass Dactylis glomerata (Dg), the slow-growing resource-conservative forb Leontodon hispidus (Lh) and the fast-growing, resource-acquisitive forb Rumex acetosa (Ra). In each mesocosm 36 seedlings were transplanted in equal abundance (EA): 9:9:9:9 or in dominance (DA) of one species: 30:2:2:2, resulting in five community types. All the pots have the same species richness since the four species are represented in each mesocosm. The soil used in this research is a local natural clay soil excavated in close proximity to Amsterdam. Each of the 20 pots has a volume of 43 liters. The seedlings are propagated in the greenhouse at Science Park in Amsterdam, from seeds obtained from Cruydt-Hoeck. The communities created in this experiment serve as a model of natural grasslands (Orwin et al., 2014), and can give a representation of the impact of intra-and interspecific competition, different growth strategies, and plant functional groups on biomass production.

To gain insight into the differences in biomass production between the individual plants and between different species, the aboveground vegetation is harvested at soil level at the end of April 2021. Each individual seedling is put in a paper bag. After the harvesting of the 720 seedlings, they are dried at 60-70 degrees Celsius for three days and are weighed afterwards.

Aboveground biomass is weighed per species and the average dry weight per seedling and species is determined. To estimate the belowground biomass per pot, 3 soil cores (3 cm diameter, 32 cm height) were taken per pot and stored at 4 degrees. The roots were washed to remove all the remaining soil particles. Afterward, the roots were stored in an EtOH solution. To measure the dry root weight, the roots were dried for 72 hours at 60-70 degrees.

To measure the effect of intra- and interspecific competition in these treatments, the relative competition intensity, RCI, is calculated for each species (Weigelt & Jolliffe, 2003). In order to say something about the intensity of competition, this formula will be used (Wilson& Keddy,1986):

RCI = (P¯dom−P¯mix)/ P¯dom

RCI is the relative competition intensity, Pmix [g]is the average biomass per seedling of a species in the even abundance community, Pdom [g] the average biomass of the same species in its own dominance community (Magla et al., 2011). This index controls for differences in growth rates for the 4 plant species, which can indicate the effects of competition when this species will differ in size (Connolly et al., 2001). A positive RCI indicates that the species experience stronger interspecific competition than intraspecific competition. While a negative RCI will indicate that the species experience a stronger intraspecific competition than interspecific competition (Hawkins & Crawford, 2018).

Statistical analysis

Statistical analyses are performed in R Studio to compare the means of the different species (Ao, Dg, Lh, Ra) and communities (AoDom, DgDom, even, LhDom, RaDom) via a Dunn’s test, an ART ANOVA and a Kruskal- Wallis tests. These non-parametric tests are used since all the data is not normally distributed and does not meet the assumptions for a parametric test. The Kruskal Wallis test followed by a Dunn’s test to test for significant differences between the RCI-value for the species. The ART ANOVA is used to compare the average biomass per species per community. The ART ANOVA analysis the interaction as well as the main effects. The Kruskal-Wallis test is used to compare the root and shoot biomass with the different communities. All the statistical tests are conducted with a 95-confidence interval.

Results

Relative competition intensity

Figure 1, Relative competition intensity.

The species in their own dominance community are represented in the legenda and on the x-axis. The light blue color represents the A. odoratum (Ao), the dark blue color represents D. glomerata (Dg), the light green color represent the L.hispidus (Lh), the dark green color represents the R.acetosa (Ra) The RCI value is represented on the y-axis. Error bars represent the standard deviation.

P-value

Ao Dg Lh

Dg 0.2070. - - Lh 0.0791 0.0129* - Ra 0.0374* 0.1672 0.0007*

Table 2, Results of Dunn’s test Kr

The relative competition intensity is species dependent. The slow-growing grass A. odoratum and the slow-growing forb L. hispidus have a positive RCI, meaning that the species experience stronger interspecific competition than intraspecific competition (Fig. 1). Both fast-growing species, the grass

D. glomerata and the forb R. acetosa, have a negative RCI, indicating that the species experience a

stronger intraspecific competition than interspecific competition (Hawkins & Crawford, 2018). The two forbs, L.hispidus and R.acetosa differ more in their competition intensity than the grasses A.

Odoratum and R. acetosa (Fig. 1), but the data RCI does not does not support a difference in

competition between grasses and forbs (Kruskal Wallis test, p= 0.753).

In community AoDom where the slow-growing resource- conservative grass A. odoratum is dominant, A positive RCI is visible, indicating that the species experience stronger interspecific competition than intraspecific competition (Hawkins & Crawford, 2018). Where the fast growing resource acquisitive grass D.glomerata is dominant, a negative RCI is present, which shows that the species experience a stronger intraspecific competition than interspecific competition (Hawkins & Crawford, 2018). In community LhDom, the slow-growing resource-conservative forb L. hispidus experience a positive RCI, meaning that this community experiences stronger interspecific competition than intraspecific competition (Hawkins & Crawford, 2018). The fast-growing, resource-acquisitive forb R. acetosa, in community RaDom has a negative RCI, what shows that the species experience a stronger intraspecific competition than interspecific competition (Hawkins & Crawford, 2018). The RCI values of the species Lh-Dg, Ra-Ao and Ra-Lh differ significantly from each other (Table 2). The RCI of L.hispidus is significantly higher than that of both fast-growing species, D. glomerata and R. acetosa, and the RCI of

Average aboveground biomass per species and community

Figure 2, Representation of the average aboveground biomass per seedling and species in the five different communities. The light blue color represents the A. odoratum (Ao), the dark blue color represents D. glomerata (Dg), the light green color represent the L.hispidus (Lh), the dark green color represents the R.acetosa (Ra). On the x-axis the 5 different communities are represented. The y-axis represents the average aboveground biomass (g/seedling). Error bars represent the standard deviation.

The average aboveground biomass production of the plants differed depending on the community they grew in. Only D. glomerata shows significant differences in biomass production in the different communities. D. glomerata is grows best in the communities where the slow-growing species, L.

hispidus and A. odoratum, are dominant (Table 3, Fig. 2). D. glomerata grows the worst in its own

dominance community. In general, there is a pattern that the fast-growing species, have the highest biomass in the communities of the slow-growing species. In communities where L.hispidus and A. odorata are dominant, R. acetosa and D.glomerata, both dominant species, have their highest biomass production. Dg p-value AoDom -DgDom 0.048 DgDom – LhDom 0.003 Even- LhDom 0.005 LhDom – RaDom 0.009

Total average biomass per mesocosm

There is a strong indication that community composition does affect above-and belowground biomass production, the p-values show almost significant results (Table 4). Community DgDom has the highest average biomass production per mesocosm. Community LhDom has the lowest average shoot biomass and the lowest average root biomass. In the community where R. acetosa is dominant, the root biomass per mesocosm is the highest.

Shoot biomass p-value Communities 0.071 Root biomass p-value Communities 0.075

Figure 3, Average biomass production per mesocosm

On the x-axis the 5 different communities are visible (AoDom = dominance A. odoratum, DgDom = dominance D.glomerata, even = even, LhDom = dominance L.hispidus, RaDom = dominance R.acetosa ), the y-axis represents the average biomass production per mesocosm. Brown bars represent the

estimated root dry weight per mesocosm, green bars represent shoot dry weight per mesocosm. Error bars represent the standard deviation.

Table 4, Results of Kruskal Wallis test

Discussion

In this research, the effects of plant community composition on plant interactions in grasslands are considered. From this research it becomes clear that plant interactions are influenced by community composition. What is important knowledge since community composition are changing due to anthropogenic activity (Chapin et al.,2000; Hillebrand et al., 2008). The most important findings are that the relative competition intensity is species dependent and could be explained by growth strategy. Also, there is a pattern visible that the fast-growing species, have the highest biomass in the communities of the slow-growing species.

No general pattern of intraspecific competition being stronger than interspecific competition could be found in this study. Species differed in the strength and direction of their relative competition intensities and therefore hypothesis 1 is not supported by this data. The reason that intraspecific competition is not stronger than interspecific competition in this grassland community composition, could be explained by the fact that the investigation is carried out at small spatial and temporal scales, omitting coexistence mechanisms that only operate in the presence of coarser scale environmental change (Adler et al., 2018). For example, negative plant-soil feedbacks, which are a likely source of intraspecific competition in mature communities, may not yet be established in short-term experimental treatments, like this experiment (Mangan et al. 2010). Therefore, it will be plausible that over a longer timeframe, the effects of intraspecific competition will be higher (Adler et al.,2018). On the other hand, slow-growing species, which already face higher interspecific competition than intraspecific competition, may exert greater dominance over fast-growing species since there could be more competition for resources as soil moisture, gradients of light, and partitioning of soil nutrients. This research concludes that the relative competition intensity is dependent on growth strategy (Fig. 1). The two fast-growing species, R. acetosa and D. glomerata experience stronger intra specific competition than slow-growing species, since their RCI value is positive (Table 2, Fig. 1), this supports the first halve of hypothesis 2. The two slow growing species A odoratum and L.hispidus, have both a negative RCI value indicating that interspecific competition is stronger than intraspecific competition. Slower-growing plant species appear to benefit more from mutualists that facilitate in nutrient acquisition, such as mycorrhiza fungi (positive plant-soil feedback), fast-growing plant species appear to be more prone to pathogens (negative plant-soil feedback), what could be the reason that the faster growing species have a higher intraspecific competition, and slow species a higher interspecific competition (Lekberg et al., 2018). The two forbs, L.hispidus and R.acetosa differ more in their competition intensity than the grasses A. Odoratum and R. acetosa (Fig.1), but the data does not support a difference in competition between grasses and forbs (Kruskal Wallis test, p= 0.753). This means that the second halve of hypothesis 2 is not supported by this data. Not only the relative competition intensity is species dependent, but the biomass production of the species also differed depending on the community they grew in. D. glomerata showed significant differences in biomass production in the different communities. D. glomerata grows the best in the communities where the slow-growing species, L. hispidus and A. odoratum, are dominant, and the worst in its own dominance community (Table 3, Fig. 2). In general, there is a pattern visible that the fast-growing species, have the highest biomass in the communities of the slow-growing dominant species. Thus, in this research, the highest biomass production of recessive fast- growing species, is found in the dominant communities of slow-growing species, where interspecific competition is higher than intraspecific competition. D. glomerata grows the worst in its own dominance community, because the competition for resources is stronger between members of the species D. glomerata than members of different species; given intraspecific competition is stronger than intraspecific competition, since the

RCI value of D.glomerata is negative. D.glomerata grows the best in the community where interspecific competition is the highest, the community where L. hispidus is dominant.

I hypothesized that communities with even distributed species, will positively influence aboveground and belowground biomass production in grassland communities. This is not supported by the findings of this research (Fig. 3). The even community has the second-lowest aboveground biomass per mesocosm. However, the root biomass of the even communities is the second highest. There is a strong indication that community composition does affect above-and belowground biomass, but these results are not significant (Kruskal-Wallis test, p = 0.07067; p = 0.07532). With a larger sample size, these differences might be statistically significant. In the community where D.glomerata is dominant, the highest average biomass production is found. The reason that the community with the fast-growing grass as dominant species has the highest total aboveground biomass production per mesocosm could be that D.glomerata is a fast growing species, and could generate more biomass faster than slow-growing species. In the community where L. hispidus is dominant, the belowground and aboveground biomass is the lowest. What makes that the community with the lowest total biomass. The slow-growing resource-conservative forbs L. hispidus experiences a positive RCI, meaning that this community experiences stronger interspecific competition than intraspecific competition. The fact that there is higher interspecific competition means that the dominant species (L.hispidus) are in competition with the recessive species and that this will consequently generate a low total biomass production. This interspecific competition can eventually lead to competitive exclusion and niche differentiation (Silvertown, 2004). In the community where the fast growing forb R.acetosa is dominant, the root biomass is the highest.

For further research concerning how community composition influences plant interactions, it would be interesting to grow species with different species richness. The species of all the pots in this experiment have the same species richness, namely four species. It would be interesting to grow the species in monoculture or a community with two or three species. Species richness is an important factor for intra- and interspecific competition since the distribution of traits is an essential for diversity and the stability of an ecosystem (Wilsey & Potvis, 2000; Hillebrand et al., 2008). The variable considered in this research is the shoot biomass and the root biomass. This is not the only variable that could affect plant interactions. The availability of nutrients could also be an interesting variable to study in future research. Next to the availability of nutrients, AMF and pathogens could also influence plant interactions (Zhang et al.,2021). Including these two variables could give further insight in the mechanisms of plant interactions. Besides that, for further research, it would be interesting to look at how species would behave under stress. Climate models expect that extreme drought events are increasing in many world regions (IPCC, 2014). There are differences in drought responses between species, that can consequently affect community compositions (Hoover et al., 2014). Fast-growing species, for instance, are expected to be favored by drought events at the expense of the forb abundance, which will consequently affect intra- and interspecific interactions (Hoover et al.,2014). Also, the effects of intraspecific competition will generally increase under drier conditions (Hawkins & Crawford, 2018). In the end, this research brought us to a better understanding of ecosystem

functioning, mainly how plant community compositions, plant functional, and growth strategy affect intra-and interspecific competition in grasslands.

Conclusions

This research gave new insights in how plants affect each other’s growth in grassland ecosystems. The question of whether intraspecific competition is higher than interspecific competition is species dependent and could be explained by growth strategy. Fast-growing species experience higher intra-specific competition than slow-growing species and the difference between intra- and interintra-specific competition of grasses is lower than that of forbs (values closer to 0). In general, there is a pattern that the fast-growing species, have the highest biomass in the communities of the slow-growing species. The even community does not have the highest biomass production as hypothesized. The fact that the slower growing species experience higher interspecific competition, may exert greater dominance over fast-growing species which needs to be considered while looking at the functioning of grassland ecosystems. This research concludes that the interplay of intra- and interspecific competition between species shapes plant community dynamics in grasslands and must be considered to maintain and improve the stability, productivity, and sustainability of the ecosystem.

References

Adler, P. B., J. HilleRisLambers, and J. M. Levine. 2007. A niche for neutrality. Ecology Letters 10:95– 104.

Adler, P. B., Smull, D., Beard, K. H., Choi, R. T., Furniss, T., Kulmatiski, A., ... & Veblen, K. E. (2018). Competition and coexistence in plant communities: intraspecific competition is stronger than interspecific competition. Ecology letters, 21(9), 1319-1329.

Armas C, Pugnaire FI, Sala OE (2008) Patch structure dynamics and mechanisms of cyclical succession in a Patagonian steppe (Argentina). J Arid Environ 72:1552–1561

Aschehoug, E. T., Brooker, R., Atwater, D. Z., Maron, J. L., & Callaway, R. M. (2016). The mechanisms and consequences of interspecific competition among plants. Annual Review of Ecology, Evolution, and

Systematics, 47, 263-281.

Bardgett, R. D., Smith, R. S., Shiel, R. S., Peacock, S., Simkin, J. M., Quirk, H., & Hobbs, P. J. (2006). Parasitic plants indirectly regulate below-ground properties in grassland ecosystems. Nature, 439(7079), 969-972.

Cavieres LA, Badano EI (2009) Do facilitative interactions increase species richness at the entire community level? J Ecol 97:1181–1191.

Chapin, F. S., E. S. Zavaleta, V. T. Eviner, R. L. Naylor, P. M. Vitousek, H. L. Reynolds, D. U. Hooper, S. Lavorel, O. E. Sala, S. E. Hobbie, M. C. Mack, and S. Diaz. 2000. Consequences of changing biodiversity. Nature 405:234–242.

Chen S-Y, Xu J, Maestre FT, Chu C-J, Wang G, Xiao S (2009) Beyond dual-lattice models: incorporating plant strategies when modeling the interplay between facilitation and competition along environmental severity gradients. J Theor Biol 258:266–273. Doi

Chesson, P. (2000). Mechanisms of maintenance of species diversity. Annual review of Ecology and

Systematics, 31(1), 343-366.

Chesson, P. (2013). Species competition and predation. In Ecological systems (pp. 223-256). Springer, New York, NY

Cortois, R., Schröder-Georgi, T., Weigelt, A., van der Putten, W. H., & De Deyn, G. B. (2016). Plant–soil feedbacks: role of plant functional group and plant traits. Journal of Ecology, 104(6), 1608–1617.

Guiz, J., Ebeling, A., Eisenhauer, N., Hacker, N., Hertzog, L., Oelmann, Y., ... & Hillebrand, H. (2018). Interspecific competition alters leaf stoichiometry in 20 grassland species. Oikos, 127(7), 903-914. Hawkins, A. P., & Crawford, K. M. (2018). Interactions between plants and soil microbes may alter the relative importance of intraspecific and interspecific plant competition in a changing climate. AoB

Hector A, et al. (2000) No consistent effect of plant diversity on productivity: response. Science 289:1255a

Hector, A., Schmid, B., Beierkuhnlein, C., Caldeira, M. C., Diemer, M., Dimitrakopoulos, P. G., ... & Lawton, J. H. (1999). Plant diversity and productivity experiments in European grasslands. science,

286(5442), 1123-1127.

Hillebrand, H., Bennett, D. M., & Cadotte, M. W. (2008). Consequences of dominance: a review of evenness effects on local and regional ecosystem processes. Ecology, 89(6), 1510-1520.

Hooper, D. U., & Dukes, J. S. (2004). Overyielding among plant functional groups in a long‐term experiment. Ecology Letters, 7(2), 95-105.

Hoover, D. L., Knapp, A. K., & Smith, M. D. (2014). Resistance and resilience of a grassland ecosystem to climate extremes. Ecology, 95(9), 2646–2656.

I. Ostonen, Ü. Püttsepp, C. Biel, O. Alberton, M. R. Bakker, K. Lõhmus, H. Majdi, D. Metcalfe,

Keddy, P.A., Twolan-Strutt, L. & Wisheu, I. (1994) Competitive effect and response rankings in 20 wetland plants: are they consistent across three environments?. Journal of Ecology, 635-643.

Lekberg, Y., Bever, J. D., Bunn, R. A., Callaway, R. M., Hart, M. M., Kivlin, S. N., ... & Van der Putten, W. H. (2018). Relative importance of competition and plant–soil feedback, their synergy, context dependency and implications for coexistence. Ecology Letters, 21(8), 1268-1281.

Loreau, M., Naeem, S., & Inchausti, P. (Eds.). (2002). Biodiversity and ecosystem functioning: synthesis

and perspectives. Oxford University Press on Demand.

Mangan, S.A., Schnitzer, S.A., Herre, E.A., Mack, K.M.L., Valencia, M.C., Sanchez, E.I. et al. (2010). Negative plant-soil feedback predicts tree-species relative abundance in a tropical forest. Nature, 466, 752– 755.

Mangla S, Sheley RL, James JJ, Radosevich SR. 2011. Intra and interspecific competition among invasive and native species during early stages of plant growth. Plant Ecology212:531–542.

Norberg, J. 2004. Biodiversity and ecosystem functioning: a complex adaptive systems approach. Limnology and Ocean- ography 49:1269–1277.

Orwin, K. H., Ostle, N., Wilby, A., & Bardgett, R. D. (2014). Effects of species evenness and dominant species identity on multiple ecosystem functions in model grassland communities. Oecologia, 174(3), 979-992.

P. B. Reich, The world-wide `fast-slow’ plant economics spectrum: A traits manifesto. J. Ecol. 102, 275– 301 (2014).

Poorter, H., & Garnier, E. (1999). Ecological significance of inherent variation in relative growth rate and its components. Handbook of functional plant ecology, 20, 81-120.

Siemann, E. 1998. Experimental tests of effects of plant productivity and diversity on grassland arthropod diversity. Ecology 79: 2057– 2070.

Stevens CJ, Dise NB, Mountford JO, Gowing DJ. 2004. Impact of nitrogen deposition on the species richness of grasslands. Science 303: 1876–1879.

Sweeney, C. J., Vries, F. T., Dongen, B. E., & Bardgett, R. D. (2021). Root traits explain rhizosphere fungal community composition among temperate grassland plant species. New Phytologist, 229(3), 1492–1507.

Weigelt, A., & Jolliffe, P. (2003). Indices of plant competition. Journal of ecology, 91(5), 707-720.

White rP, murray rohweder m (2000) Pilot analysis of global ecosystems: grassland ecosystems. World resources Institute, Washington, DC

Williams, A., Langridge, H., Straathof, A. L., Muhamadali, H., Hollywood, K. A., Goodacre, R., & de Vries, F. T. (2021). Root functional traits explain root exudation rate and composition across a range of grassland species. Journal of Ecology.

Wilsey, B. J., & Potvin, C. (2000). Biodiversity and ecosystem functioning: importance of species evenness in an old field. Ecology, 81(4), 887-892

Wilson, S. D., & Keddy, P. A. (1986). Measuring diffuse competition along an environmental gradient: results from a shoreline plant community. The American Naturalist, 127(6), 862-869.

Yang, Y., Tilman, D., Lehman, C., & Trost, J. J. (2018). Sustainable intensification of high-diversity biomass production for optimal biofuel benefits. Nature sustainability, 1(11), 686-692.