Unraveling the diversity of hyphal explorative traits among Rhizophagus irregularis genotypes.

Differences in functioning among various genotypes of arbuscular mycorrhizal (AM) fungi can determine their fitness under specific environmental conditions, although knowledge of the underlying mechanisms still is very fragmented. Here we compared seven homokaryotic isolates (genotypes) of Rhizophagus irregularis, aiming to characterize the range of intraspecific variability with respect to hyphal exploration of organic nitrogen (N) resources, and N supply to plants. To this end we established two experiments (one in vitro and one in open pots) and used 15N-chitin as the isotopically labeled organic N source. In Experiment 1 (in vitro), mycelium of all AM fungal genotypes transferred a higher amount of 15N to the plants than the passive transfer of 15N measured in the non-mycorrhizal (NM) controls. Noticeably, certain genotypes (e.g., LPA9) showed higher extraradical mycelium biomass production but not necessarily greater 15N acquisition than the others. Experiment 2 (in pots) highlighted that some of the AM fungal genotypes (e.g., MA2, STSI) exhibited higher rates of targeted hyphal exploration of chitin-enriched zones, indicative of distinct N exploration patterns from the other genotypes. Importantly, there was a high congruence of hyphal exploration patterns between the two experiments (isolate STSI always showing highest efficiency of hyphal exploration and isolate L23/1 being consistently the lowest), despite very different (micro) environmental conditions in the two experiments. This study suggests possible strategies that AM fungal genotypes employ for efficient N acquisition, and how to measure them. Implications of such traits for local mycorrhizal community assembly still need to be understood.

Grazing Intensity Rather than Host Plant's Palatability Shapes the Community of Arbuscular Mycorrhizal Fungi in a Steppe Grassland.

Arbuscular mycorrhizal fungi (AMF) are the predominant type of mycorrhizal fungi in roots and rhizosphere soil of grass species worldwide. Grasslands are currently experiencing increasing grazing pressure, but it is not yet clear how grazing intensity and host plant grazing preference by large herbivores interact with soil- and root-associated AMF communities. Here, we tested whether the diversity and community composition of AMF in the roots and rhizosphere soil of two dominant perennial grasses, grazed differently by livestock, change in response to grazing intensity. We conducted a study in a long-term field experiment in which seven levels of field-manipulated grazing intensities were maintained for 13 years in a typical steppe grassland in northern China. We extracted DNA from the roots and rhizosphere soil of two dominant grasses, Leymus chinense (Trin.) Tzvel. and Stipa grandis P. Smirn, with contrasting grazing preference by sheep. AMF DNA from root and soil samples was then subjected to molecular analysis. Our results showed that AMF α-diversity (richness) at the virtual taxa (VT) level varied as a function of grazing intensity. Different VT showed completely different responses along the gradient, one increasing, one decreasing, and others showing no response. Glomeraceae was the most abundant AMF family along the grazing gradient, which fits well with the theory of disturbance tolerance of this group. In addition, sheep-grazing preference for host plants did not explain much of the variation in AMF α-diversity. However, the two grass species exhibited different AMF community composition in their roots and rhizosphere soils. Roots exhibited a lower α-diversity and higher ß-diversity within the AMF community than soils. Overall, our results suggest that long-term grazing intensity might have changed the abundance of functionally diverse AMF taxa in favor of those with disturbance-tolerant traits. We suggest our results would be useful in informing the choice of mycorrhizal fungi indicator variables when assessing the impacts of grassland management choices on grassland ecosystem functioning.

Seasonal variation in the response of arbuscular mycorrhizal fungi to grazing intensity.

Despite existing evidence of pronounced seasonality in arbuscular mycorrhizal (AM) fungal communities, little is known about the ecology of AM fungi in response to grazing intensity in different seasons. Here, we assessed AM fungal abundance, represented by soil hyphal length density (HLD), mycorrhizal root colonization intensity (MI), and arbuscule intensity (AI) throughout three seasons (spring, summer, autumn) in a farm-scale field experiment in typical, grazed steppe vegetation in northern China. Seven levels of field-manipulated, grazing intensities had been maintained for over 13 years within two topographies, flat and slope. We also measured soil nutrients and carbon content throughout the growing season to investigate whether seasonal variation in AM fungal abundance was related to seasonal shifts in soil resource availability along the grazing gradient. We further examined the association between AM fungal metrics in the different grazing treatments through the growing season. Our results showed a pronounced seasonal shift in HLD but there was no clear seasonality in MI and AI. HLD was significantly negatively related to grazing intensity over the course of the growing season from spring to autumn. However, MI and AI were related negatively to grazing intensity only in spring. In addition, differential responses of AM fungal abundance to grazing intensity at the two topographical sites were detected. No strong evidence was found for associations between AM fungal abundance and soil resource availability. Moreover, AM fungal internal and external abundance were correlated positively under the different grazing intensities throughout the growing season. Overall, our study suggests that external AM fungal structures in soil were more responsive to seasonal variation and grazing than internal structures in roots. The findings also suggest that early grazing may be detrimental to AM fungal root colonization of newly emerged plants.

Nutrient-dependent cross-kingdom interactions in the hyphosphere of an arbuscular mycorrhizal fungus.

Introduction: The hyphosphere of arbuscular mycorrhizal (AM) fungi is teeming with microbial life. Yet, the influence of nutrient availability or nutrient forms on the hyphosphere microbiomes is still poorly understood. Methods: Here, we examined how the microbial community (prokaryotic, fungal, protistan) was affected by the presence of the AM fungus Rhizophagus irregularis in the rhizosphere and the root-free zone, and how different nitrogen (N) and phosphorus (P) supplements into the root-free compartment influenced the communities. Results: The presence of AM fungus greatly affected microbial communities both in the rhizosphere and the root-free zone, with prokaryotic communities being affected the most. Protists were the only group of microbes whose richness and diversity were significantly reduced by the presence of the AM fungus. Our results showed that the type of nutrients AM fungi encounter in localized patches modulate the structure of hyphosphere microbial communities. In contrast we did not observe any effects of the AM fungus on (non-mycorrhizal) fungal community composition. Compared to the non-mycorrhizal control, the root-free zone with the AM fungus (i.e., the AM fungal hyphosphere) was enriched with Alphaproteobacteria, some micropredatory and copiotroph bacterial taxa (e.g., Xanthomonadaceae and Bacteroidota), and the poorly characterized and not yet cultured Acidobacteriota subgroup GP17, especially when phytate was added. Ammonia-oxidizing Nitrosomonas and nitrite-oxidizing Nitrospira were significantly suppressed in the presence of the AM fungus in the root-free compartment, especially upon addition of inorganic N. Co-occurrence network analyses revealed that microbial communities in the root-free compartment were complex and interconnected with more keystone species when AM fungus was present, especially when the root-free compartment was amended with phytate. Conclusion: Our study showed that the form of nutrients is an important driver of prokaryotic and eukaryotic community assembly in the AM fungal hyphosphere, despite the assumed presence of a stable and specific AM fungal hyphoplane microbiome. Predictable responses of specific microbial taxa will open the possibility of using them as co-inoculants with AM fungi, e.g., to improve crop performance.

Mycorrhiza governs plant-plant interactions through preferential allocation of shared nutritional resources: A triple (13C, 15N and 33P) labeling study.

Plant-plant interactions and coexistence can be directly mediated by symbiotic arbuscular mycorrhizal (AM) fungi through asymmetric resource exchange between the plant and fungal partners. However, little is known about the effects of AM fungal presence on resource allocation in mixed plant stands. Here, we examined how phosphorus (P), nitrogen (N) and carbon (C) resources were distributed between coexisting con- and heterospecific plant individuals in the presence or absence of AM fungus, using radio- and stable isotopes. Congeneric plant species, Panicum bisulcatum and P. maximum, inoculated or not with Rhizophagus irregularis, were grown in two different culture systems, mono- and mixed-species stands. Pots were subjected to different shading regimes to manipulate C sink-source strengths. In monocultures, P. maximum gained more mycorrhizal phosphorus uptake benefits than P.bisulcatum. However, in the mixed culture, the AM fungus appeared to preferentially transfer nutrients (33P and 15N) to P.bisulcatum compared to P. maximum. Further, we observed higher 13C allocation to mycorrhiza by P.bisulcatum in mixed- compared to the mono-systems, which likely contributed to improved competitiveness in the mixed cultures of P.bisulcatum vs. P. maximum regardless of the shading regime. Our results suggest that the presence of mycorrhiza influenced competitiveness of the two Panicum species in mixed stands in favor of those with high quality partner, P. bisulcatum, which provided more C to the mycorrhizal networks. However, in mono-species systems where the AM fungus had no partner choice, even the lower quality partner (i.e., P.maximum) could also have benefitted from the symbiosis. Future research should separate the various contributors (roots vs. common mycorrhizal network) and mechanisms of resource exchange in such a multifaceted interaction.

Evolving framework of studies on global gulf ecosystems with Sustainable Development Goals.

Gulf ecosystems provide many beneficial services to humanity and play a key role in achieving the Sustainable Development Goals (SDGs). However, the sustainability of gulf ecosystems has been severely threatened by climatic and anthropogenic stresses. Using network analysis of article records downloaded from Web of Science, we summarize the current research framework of gulf ecosystems via the perspectives of research themes, interdisciplinarity, and international collaborations. Research themes involve nutrient and eutrophication, biodiversity, mangrove and sediment pollution, and ecosystem service and climate change. Nevertheless, these themes usually focus on gulf ecosystems themselves with little consideration of their connectivity with other ecosystems. Interdisciplinarity has remained mostly within natural sciences while international collaborations exist mainly between developed and developing countries and among developed countries. Combined with the SDGs, we propose the future research framework where research themes should consider the impacts of terrestrial and freshwater ecosystems on gulf ecosystems at the watershed scale. Interdisciplinarity between natural and social and management sciences needs to be promoted by utilizing the advantages of data sciences. Collaborations with developing countries led by China, Mexico, Brazil, and India need to be strengthened. The evolved research framework could offer decision support for stakeholders to manage gulf ecosystems and achieve the SDGs.

Revisiting seasonal dynamics of total nitrogen in reservoirs with a systematic framework for mining data from existing publications.

Investigation of seasonal variations of water quality parameters is essential for understanding the mechanisms of structural changes in aquatic ecosystems and their pollution control. Despite the ongoing rise in scientific production on spatiotemporal distribution characteristics of water quality parameters, such as total nitrogen (TN) in reservoirs, attempts to use published data and incorporate them into a large-scale comparison and trends analyses are lacking. Here, we propose a framework of Data extraction, Data grouping and Statistical analysis (DDS) and illustrate application of this DDS framework with the example of TN in reservoirs. Among 1722 publications related to TN in reservoirs, 58 TN time-series data from 19 reservoirs met the analysis requirements and were extracted using the DDS framework. We performed statistical analysis on these time-series data using Dynamic Time Warping (DTW) combined with agglomerative hierarchical clustering as well as Generalized Additive Models for Location, Scale, and Shape (GAMLSS). Three patterns of seasonal TN dynamics were identified. In Pattern V-Sum, TN concentrations change in a "V" shape, dropping to its lowest value in summer; in Pattern P-Sum, TN increases in late summer/early fall before decreasing again; and in Pattern P-Spr, TN peaks in spring. Identified patterns were driven by phytoplankton growth and precipitation (Pattern V-Sum), nitrate wet deposition and agricultural runoff (Pattern P-Sum), and anthropogenic discharges (Pattern P-Spr). Application of the DDS framework has identified a key bottleneck in assessing the dynamics of TN - low data accessibility and availability. Providing an easily accessible data sharing platform and increasing the accessibility and availability of raw data for research will facilitate improvements and expand the applicability of the DDS framework. Identification of additional spatiotemporal patterns of water quality parameters can provide new insights for more comprehensive pollution control and management of aquatic ecosystems.