Shifts in plant community composition weaken the negative effect of nitrogen addition on community-level arbuscular mycorrhizal fungi colonization

Wild species rice OsCERK1DY-mediated arbuscular mycorrhiza symbiosis boosts yield and nutrient use efficiency in rice breeding

Meeting the ever-increasing food demands of a growing global population while ensuring resource and environmental sustainability presents significant challenges for agriculture worldwide. Arbuscular mycorrhizal symbiosis (AMS) has emerged as a potential solution by increasing the surface area of a plant's root system and enhancing the absorption of phosphorus, nitrogen nutrients, and water. Consequently, there is a longstanding hypothesis that rice varieties exhibiting more efficient AMS could yield higher outputs at reduced input costs, paving the way for the development of Green Super Rice (GSR). Our prior research study identified a variant, OsCERK1DY, derived from Dongxiang wild-type rice, which notably enhanced AMS efficiency in the rice cultivar "ZZ35." This variant represents a promising gene for enhancing yield and nutrient use efficiency in rice breeding. In this study, we conducted a comparative analysis of biomass, crop growth characteristics, yield attributes, and nutrient absorption at varying soil nitrogen levels in the rice cultivar "ZZ35" and its chromosome single-segment substitution line, "GJDN1." In the field, GJDN1 exhibited a higher AM colonization level in its roots compared with ZZ35. Notably, GJDN1 displayed significantly higher effective panicle numbers and seed-setting rates than ZZ35. Moreover, the yield of GJDN1 with 75% nitrogen was 14.27% greater than the maximum yield achieved using ZZ35. At equivalent nitrogen levels, GJDN1 consistently outperformed ZZ35 in chlorophyll (Chl) content, dry matter accumulation, major nutrient element accumulation, N agronomic efficiency (NAE), N recovery efficiency (NRE), and N partial factor productivity (NPFP). The performance of OsCERK1DY overexpression lines corroborated these findings. These results support a model wherein the heightened level of AMS mediated by OsCERK1DY contributes to increased nitrogen, phosphorus, and potassium accumulation. This enhancement in nutrient utilization promotes higher fertilizer efficiency, dry matter accumulation, and ultimately, rice yield. Consequently, the OsCERK1DY gene emerges as a robust candidate for improving yield, reducing fertilizer usage, and facilitating a transition towards greener, lower-carbon agriculture.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-024-01459-8.

Host plant height explains the effect of nitrogen enrichment on arbuscular mycorrhizal fungal communities

Nitrogen (N) enrichment is widely known to affect the root-associated arbuscular mycorrhizal fungal (AMF) community in different ways, for example, via altering soil properties and/or shifting host plant functional structure. However, empirical knowledge of their relative importance is still lacking. Using a long-term N addition experiment, we measured the AMF community taxonomic and phylogenetic diversity at the single plant species (roots of 15 plant species) and plant community (mixed roots) levels. We also measured four functional traits of 35 common plant species along the N addition gradient. We found divergent responses of AMF diversity to N addition for host plants with different innate heights (i.e. plant natural height under unfertilized treatment). Furthermore, our data showed that species-specific responses of AMF diversity to N addition were negatively related to the change in maximum plant height. When scaling up to the community level, N addition affected AMF diversity mainly through increasing the maximum plant height, rather than altering soil properties. Our results highlight the importance of plant height in driving AMF community dynamics under N enrichment at both species and community levels, thus providing important implications for understanding the response of AMF diversity to anthropogenic N deposition.

Identifying thresholds of nitrogen enrichment for substantial shifts in arbuscular mycorrhizal fungal community metrics in a temperate grassland of northern China

Nitrogen (N) enrichment poses threats to biodiversity and ecosystem stability, while arbuscular mycorrhizal (AM) fungi play important roles in ecosystem stability and functioning. However, the ecological impacts, especially thresholds of N enrichment potentially causing AM fungal community shifts have not been adequately characterized. Based on a long-term field experiment with nine N addition levels ranging from 0 to 50 g N m^-2  yr^-1 in a temperate grassland, we characterized the community response patterns of AM fungi to N enrichment. Arbuscular mycorrhizal fungal biomass continuously decreased with increasing N addition levels. However, AM fungal diversity did not significantly change below 20 g N m^-2  yr^-1 , but dramatically decreased at higher N levels, which drove the AM fungal community to a potentially unstable state. Structural equation modeling showed that the decline in AM fungal biomass could be well explained by soil acidification, whereas key driving factors for AM fungal diversity shifted from soil nitrogen : phosphorus (N : P) ratio to soil pH with increasing N levels. Different aspects of AM fungal communities (biomass, diversity and community composition) respond differently to increasing N addition levels. Thresholds for substantial community shifts in response to N enrichment in this grassland ecosystem are identified.

Mixed conifer-broadleaf trees on arbuscular mycorrhizal and ectomycorrhizal communities in rhizosphere soil of different plantation stands in the temperate zone, Northeast China

In comparison with ectomycorrhizal (EM) tree species, arbuscular mycorrhizal (AM) trees have different litter quality and nitrogen cycle modes, which may affect mycorrhizal colonization and the community composition and diversity. However, available studies addressing the mycorrhizal fungal colonization rate, diversity and community composition in mixed forest stands composed of AM and EM trees are rare. In the present study, we assessed litter quality, soil physicochemical properties and correlated them with mycorrhizal community characteristics in rhizosphere soils of monoculture and mixture plantation stands of AM tree species (Fraxinus mandschurica Rupr.) and EM tree species (Larix gmelinii Rupr., Picea koraiensis Nakai) in Northeast China. We hypothesized that (1) the effect of mixture pattern on mycorrhizal colonization rate and diversity would change with tree species, (2) the effect of mixture pattern on mycorrhizal community composition would be less pronounced in comparison with that of tree species. We found that mixture did not change AMF colonization rate regardless of mixture identity, whereas mixture and tree species exerted significant effects on EMF colonization rate. For AMF community, both M-AS (Fraxinus mandschurica Rupr. and Picea koraiensis Nakai) and M-AL (Fraxinus mandschurica Rupr. and Larix gmelinii Rupr.) mixtures significantly increased Pielou index and Simpson index, whereas only M-AS significantly increased Sobs. For EMF community, mixture significantly affected examined diversity indices except for Chao1. Mixture significantly shifted AMF and EMF community, and the magnitude was tree species dependent. The dominant genera in AMF and EMF communities in plantation stands were Glomus and Tomentella, respectively. The EnvFit analysis showed that the determinant factors of EMF community are soil moisture, pH, nitrate nitrogen content, dissolved organic nitrogen content, soil organic matter content, soil organic carbon/total nitrogen and litter carbon/total nitrogen. In conclusion, mixed conifer-broadleaf trees significantly changed soil physicochemical properties, litter quality as well as mycorrhizal fungi community diversity and composition.

Host diversity positively affects the temporal stability of foliar fungal diseases in a Tibetan alpine meadow

BACKGROUND AND AIMS

Plant disease can dramatically affect population dynamics, community composition and ecosystem functions. However, most empirical studies focus on diseases at a certain time point and largely ignore their temporal stability, which directly affects our ability to predict when and where disease outbreaks will occur.

METHODS

Using a removal experiment that manipulates plant diversity (i.e. a plant biodiversity and ecosystem function experiment) and a fertilization experiment in a Tibetan alpine meadow, we investigated how different plant biodiversity indices and nitrogen fertilization affect the temporal stability of foliar fungal diseases (measured as the mean value of community pathogen load divided by its standard deviation) over seven consecutive years.

KEY RESULTS

We found that the temporal stability of foliar fungal diseases increased with plant diversity indices in the plant biodiversity and ecosystem function experiment. Meanwhile, we observed a weakly positive relationship between host diversity and temporal stability in the fertilization experiment. However, the nitrogen treatment did not affect temporal stability, given that fertilization increased both the mean and standard deviation of pathogen load by roughly the same magnitude.

CONCLUSIONS

We conclude that host diversity regulates the temporal stability of pathogen load, but we note that this effect may be attenuated under rapid biodiversity loss in the Anthropocene.

Shifts in plant community composition weaken the negative effect of nitrogen addition on community-level arbuscular mycorrhizal fungi colonization

Nitrogen addition affects plant-arbuscular mycorrhizal fungi (AMF) association greatly. However, although the direct effect of nitrogen addition on AMF colonization has received investigation, its indirect effect through shifts in plant community composition has never been quantified. Based on a 7-year nitrogen addition experiment in an alpine meadow of Qinghai-Tibet Plateau, we investigated the effects of nitrogen addition on plant community, AMF diversity and colonization, and disentangled the direct and indirect effects of nitrogen addition on community AMF colonization. At plant species level, nitrogen addition significantly decreased root colonization rate and altered AMF community composition, but with no significant effect on AMF richness. At plant community level, plant species richness and AMF colonization rate decreased with nitrogen addition. Plant species increasing in abundance after nitrogen addition were those with higher AMF colonization rates in natural conditions, resulting in an increased indirect effect induced by alternation in plant community composition with nitrogen addition, whereas the direct effect was negative and decreased with nitrogen addition. Overall, we illustrate the effect of nitrogen addition and plant species in influencing the AMF diversity, demonstrate how shifts in plant community composition (indirect effect) weaken the negative direct effect of nitrogen addition on community-level AMF colonization rate, and emphasize the importance of plant community-mediated mechanisms in regulating ecosystem functions.