Nitrogen enrichment affects and changes the community structure of terrestrial ecosystems. Recently, intransitivity competition networks have been widely considered to in maintaining coexistence and biodiversity. However, whether the structure and function of the species competition network changes under nitrogen enrichment remains unclear. In this paper, we applied the Apriori algorithm to find dominant species assemblies to simulate competition matrices. We found that (1) intransitive competition networks derived by a species-dominant assembly accounted for a relatively large proportion of the derived networks, and the species acting as mediators constituted a nested pattern; (2)Under N enrichment, the complexity of the networks varied from an intransitive network to a sub-competition structure, and transitive networks was a transition structure between these two structures; (3) the negative effect of N-enrichment on species network was counteracted by mowing and rainfall; and (4) increasing the number of loops enhances the diversity in a community, while high competition among species is a representation of an intransitive competition network.

Tall clonal grasses commonly display competitive advantages with nitrogen (N) enrichment. However, it is currently unknown whether their height is derived from the vegetative or reproductive module. Moreover, it is unclear whether the height of the vegetative or reproductive system regulates the probability of extinction and colonization, and determines species richness (frequency). In this study, the impacts on clonal grasses were studied in a field experiment employing two frequencies (twice a year or monthly) crossed with nine N addition rates in a temperate grassland. We found that the N addition decreased species frequency and increased extinction probability, but did not change the species colonization probability. A low frequency of N addition decreased species frequency and colonization probability, but increased extinction probability. Species reproductive height is the best index to predict the extinction probability of clonal grasses in N-enriched conditions relative to the vegetative height, average height, and species biomass. No significant relationships were detected between plant height and species colonization probability. The low frequency of N addition may overestimate the negative effect from N deposition on clonal grass diversity, suggesting that a higher frequency of N addition is more suitable in assessing the ecological effects of N deposition. Moreover, this study illustrates that reproductive height, not the vegetative height, was associated with the clonal species extinction probability under N-enriched environment.

Atmospheric nitrogen (N) deposition is a potential danger factor for grassland ecology, and will cause unpredictable consequences to plant communities. However, how plant species interactions response to N enrichment and then affect ecological functions are not fully known. We investigated how intransitive competition network was related to the functional attributes of plant community under a 13-years N-deposition experiment. Results showed that intransitive competition network was not a single structure, but a complexly interwoven structure of various simple structures. Nested work was more common, accounting for 76.96%, and gained new species at a higher colonization rate than short network did. The network had a long-term mechanism to maintain the small-scale Alpha diversity, and a significant lag effect on the large-scale Gamma diversity. Under the conditions of N ≥ 2 g N·m-2·year-1, without mowing and under high fertilization frequency, the increase of network complexity significantly decreased plot biomass gradually. The relationship between biomass and network complexity is quadratic curves, also between abundancy and the complexity, but with the opposite bending directions, which indicated that biomass and abundance were complementary to each other, which may be a mechanism of maintaining the relative balance of species competition. In addition, the decrease of species asynchronism changing with the increase of N-enrichment gradually destroyed ecosystem stability. However, at medium N enrichment, intransitive network counteracted the negative effects of N enrichment and maintained or even improved the biomass ecosystem stability. Our results suggested that intransitive competition network is an internal mechanism of self-restoration of a grassland ecosystem. Under nitrogen enrichment conditions, competitive networks complexity is reduced, leading to a reduction in species diversity. These analyses emphasize the important role of intransitive network structure to stabilize grassland ecosystem. In order to achieve sustainable development of grassland, it is indispensable to control nitrogen addition rate.

Elucidating mechanisms underlying community assembly and biodiversity patterns is central to ecology and evolution. Genome size (GS, i.e. nuclear DNA content) determines species’ capacity to tolerate environmental stress and therefore potentially drives community assembly. However, its role in driving β-diversity (i.e., spatial variability in species composition) remains unclear. We measured GS for 161 plant species and investigated their occurrences within plant communities across 52 sites spanning a 3200-km transect in the temperate grasslands of China. Using species distribution modelling, we found that environmental factors showed larger effects on β-diversity of large-GS than that of small-GS species and that communities with abundant resources had a greater representation of large-GS species. The latter finding was confirmed following analysis of data from a 10-yr resource (water, nitrogen, and phosphorus) manipulation experiment in which resource addition resulted in increased community weighted GS based on plant biomass estimates, suggesting that large-GS species are more sensitive to environmental resource limitation and explaining the greater environmental selection on β-diversity of large-GS species. These findings highlight the roles of GS in driving community assembly and predicting species responses to global change.

Elucidating mechanisms underlying community assembly and biodiversity patterns is central to ecology and evolution. Genome size (GS, i.e. nuclear DNA content) determines species’ capacity to tolerate environmental stress or to exploit new environments and therefore potentially drive community assembly. However, its role in driving β-diversity (i.e., the site-to-site variability in species composition) remains unclear. We measured GS for 169 plant species and investigated their occurrences within plant communities across 52 sites spanning a 3200-km transect in the temperate grasslands of China. We found environmental factors showed larger effects on β-diversity of large-GS than that of small-GS species. Community weighted mean GS increased with mean annual precipitation, soil total nitrogen and phosphorus concentrations, but decreased with mean annual temperature, suggesting a negative selection against species with large GS in resources-limited or warmer climates. These findings highlight the roles for GS in driving community assembly and predicting species responses to climate change.

Mutualistic associations between plants and arbuscular mycorrhizal (AM) fungi may have profound influences on their response to climate changes. Existing theories evaluate the effects of interdependency and environmental filtering on plant-AM fungal community dynamics separately; however, abrupt environmental changes such as climate extremes can provoke duo-impacts on the metacommunity simultaneously. Here, we experimentally tested the relevance of plant and AM fungal community responses to extreme drought (chronic or intense) in a cold temperate grassland. Irrespective of drought intensities, plant species richness and productivity responses were significantly and positively correlated with AM fungal richness and also served as best predictors of AM fungal community shifts. Notably, the robustness of this community synergism increased with drought intensity, likely reflecting increased community interdependence. Network analysis showed a key role of Glomerales in AM fungal interaction with plants, suggesting specific plant-AM fungal pairing. Thus, community interdependence may underpin climate change impact on plant-AM fungal diversity patterns in grasslands.

Extreme drought impacts ecosystem function and processes dramatically. However, a comprehensive understanding of how extreme drought affects root biomass at regional scales remains elusive. Here, we investigated the effects across six grasslands with extreme drought treatment replicated across a precipitation gradient in Inner Mongolia, China. We found the root biomass and belowground net primary productivity (BNPP) were significantly positively correlated with precipitation at the reginal scale. Extreme drought decreased the slope of this correlation in 0-10 cm and increased in 10-20 cm. Root biomass and BNPP increased by extreme drought in the four relatively arid sites and decreased in the two relatively mesic sites in 0-10 cm, and the reverse pattern showed in 10-20 cm. These shifts were driven by the response of soil moisture. Our findings suggest that including vertical responses of belowground primary productivity to extreme drought should improve models predictions of plant roots to future climate change.

Plant biochemical reactions are dependent on the combined action of multiple elements. However, it remains unclear how these elements co-vary to adapt to environmental change. Here, we propose a novel concept of the multi-element network (MEN) including the mutual effects between elements to more effectively explore the alterations in response to long-term nitrogen (N) deposition simulations. MENs were constructed with 18 elements and were species specific. Macroelements were more stable, but microelements were more susceptible to N deposition. Interestingly, higher MEN plasticity determined increased relative aboveground biomass (species importance) for different species in one functional group under simulated N deposition. Furthermore, the association between MEN plasticity and species importance was consistently verified along a dry–wet transect. In summary, MENs provide a novel approach for exploring the adaptation strategies of plants and to better predict community composition under altering nutrient availability or environmental stress associated with future global climate change.