Stable C and N isotope natural abundances of intraradical hyphae of arbuscular mycorrhizal fungi

Integration of Horse Manure Vermicompost Doses and Arbuscular Mycorrhizal Fungi to Improve Fruit Quality, and Soil Fertility in Tomato Field Facing Drought Stress

Climate change poses major challenges for agriculture in arid and semi-arid regions, with drought conditions severely affecting water-intensive crops such as tomatoes. This study evaluates the efficacy of organic amendments, derived from horse manure, and arbuscular mycorrhizal fungi (AMF) on enhancing tomato (Solanum lycopersicum L.) fruit quality and soil health under semi-arid field conditions. The experimental design included two irrigation regimes (well-watered and drought stress) and two levels of vermicompost application (C1 5 t ha-1 and C2 10 t ha-1), applied individually or in combination with AMF. The results indicate that drought stress reduced tomato fruit growth and yield, while osmoprotectant accumulation, antioxidant enzyme activity, and bioactive compound levels increased, and the 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity of tomato fruit also increased. Notably, the biostimulants application, especially (C1+AMF), counteracted the adverse effects of drought, compared to the control, by significantly enhancing fruit yields (60%), as well as increasing ascorbic acid levels (59%) and free amino acids content (90%). These treatments also improved the activity of bioactive compounds and nutrient uptake in the fruit. Furthermore, biostimulant application positively affected the physicochemical properties of soil. The results obtained confirm that the application of biostimulants can be suitable for improving crop sustainability and adaptability under conditions of water stress in semi-arid field regions.

Ecological stoichiometry and fungal community turnover reveal variation among mycorrhizal partners in their responses to warming and drought

Symbiotic fungi mediate important energy and nutrient transfers in terrestrial ecosystems. Environmental change can lead to shifts in communities of symbiotic fungi, but the consequences of these shifts for nutrient dynamics among symbiotic partners are poorly understood. Here, we assessed variation in carbon (C), nitrogen (N) and phosphorus (P) in tissues of arbuscular mycorrhizal (AM) fungi and a host plant (Medicago sativa) in response to experimental warming and drought. We linked compositional shifts in AM fungal communities in roots and soil to variation in hyphal chemistry by using high-throughput DNA sequencing and joint species distribution modelling. Compared to plants, AM hyphae was 43% lower in (C) and 24% lower in (N) but more than nine times higher in (P), with significantly lower C:N, C:P and N:P ratios. Warming and drought resulted in increases in (P) and reduced C:P and N:P ratios in all tissues, indicating fungal P accumulation was exacerbated by climate-associated stress. Warming and drought modified the composition of AM fungal communities, and many of the AM fungal genera that were linked to shifts in mycelial chemistry were also negatively impacted by climate variation. Our study offers a unified framework to link climate change, fungal community composition, and community-level functional traits. Thus, our study provides insight into how environmental change can alter ecosystem functions via the promotion or reduction of fungal taxa with different stoichiometric characteristics and responses.

Rhizosphere effect of nanoscale zero-valent iron on mycorrhiza-dependent maize assimilation

Rhizosphere effect of nanoscale zero-valent iron (nZVI) is crucial but little reported. Maize seeds were dressed with four nZVI concentrations (0, 1.0, 1.5, 2 g kg^-1 ) and inoculated with arbuscular mycorrhizal fungus (AMF) (Funneliformis mosseae). The SEM images illuminated that excessive nZVI particles (2 g kg^-1 ) were agglomerated on the surface of hyphae and spore, causing severe deformation and inactivation of AMF symbionts and thereafter inhibiting water uptake in maize seedlings. This restrained the scavenging effects of enzymatic (superoxide dismutase, peroxidase) and non-enzymatic compounds (proline & malondialdehyde) on ROS, and leaf photoreduction activity and gas exchange ability (p < 0.05). Interestingly, the inoculation with AMF effectively alleviated above negative effects. In contrast, appropriate dose of nZVI, that is, ≤1.5 g kg^-1 , can be evenly distributed on the hyphae surface and form the ordered symbionts with AMF. This help massively to enhance hyphae growth and water and nutrient uptake. The enhanced mycorrhizal infection turned to promote rhizosphere symbiont activity and leaf Rubisco and Rubisco activase activity. Light compensation point was massively lowered, which increased photosynthetic carbon supply for AMF symbionts. Particularly, such priming effects were evidently enhanced by drought stress. Our findings provided a novel insight into functional role of nZVI in agriculture and AMF-led green production.

An Ecological Profile of Hydropsyche alternans (Trichoptera: Hydropsychidae) in Lake Superior, the Last Stronghold of a Once-Dominant Great Lakes Surf Zone Caddisfly

Simple Summary

Prior to the invasion and spread of Dreissena mussels in the late 1980s, the nearshore waters of the Laurentian Great Lakes were home to diverse assemblages of native aquatic insects, including the net-spinning caddisfly Hydropsyche alternans, which occurred in rocky surf-exposed habitat throughout the system from Lake Superior downstream to Lake Ontario. These surf zone caddisflies are still abundant in the largely Dreissena-free waters of Lake Superior where the present study was conducted. They have not been reported in the lakes below Lake Superior for decades, and are presumed to have been extirpated from Dreissena-infested habitats. The ecological profile presented here documents the life history of H. alternans in Lake Superior, and reveals details of its feeding biology that shed light on the roles that surf zone net-spinners play in the native nearshore food webs of the Great Lakes. The H. alternans life history in Lake Superior begins in mid-summer shortly after oviposition, which features females swimming to surf-exposed lake bottom substrates. Larval development takes approximately 10 months, but most of it occurs during their first 100 days. Adult emergence is broadly synchronous, with large numbers present from the summer solstice through mid-July. Gut content analyses showed that larvae opportunistically feed on algal, animal, and detrital material of aquatic and terrestrial origin. δ¹³C and δ¹⁵N stable isotope data indicate that they function as omnivores that link coastal, nearshore, and pelagic food webs. These energetic links, and the very existence of surf zone insect assemblages in the Great Lakes, depend on the Dreissena populations in Lake Superior remaining relatively small and isolated.

Abstract

We studied the life history, diet, and trophic ecology of Hydropsyche alternans in four rocky sites located along the south-central coast of Lake Superior. The H. alternans life history and broad trophic niche space were similar to those of its riverine relatives. Quantitative sampling over the course of one ice-free season revealed that most individuals lived univoltine life histories that featured early to mid-summer mating, and oviposition and rapid growth and development through summer into fall. Most individuals overwintered as ultimate or penultimate larval instars. Pupation followed ice-out in the spring. Gut content sampling and δ¹³C and δ¹⁵N stable isotope analyses indicated that the typical larval diet is a mix of benthic, pelagic, and terrestrial food resources, including diatoms, small arthropods, sloughed periphyton, and in one site, fugal hyphae apparently of foredune origin. As a suspension-feeding omnivore that relies on waves and currents to deliver food to its nets, H. alternans larvae form energetic links between coastal, nearshore, and offshore food webs. These connections have been lost throughout the lower Laurentian Great Lakes as a consequence of the invasion and spread of Dreissena mussels.

Addition of high C:N crop residues to a P-limited substrate constrains the benefits of arbuscular mycorrhizal symbiosis for wheat P and N nutrition

Many aspects concerning the role of arbuscular mycorrhizal (AM) fungi in plant nutrient uptake from organic sources remain unclear. Here, we investigated the contribution of AM symbiosis to N and P uptake by durum wheat after the addition of a high C:N biomass to a P-limited soil. Plants were grown in pots in the presence or absence of a multispecies AM inoculum, with (Org) or without (Ctr) the addition of 15N-labelled organic matter (OM). A further treatment, in which 15N was applied in mineral form (Ctr+N) in the same amount as that supplied in the Org treatment, was also included. Inoculation with AM had positive effects on plant growth in both control treatments (Ctr and Ctr+N), mainly linked to an increase in plant P uptake. The addition of OM, increasing the P available in the soil for the plants, resulted in a marked decrease in the contribution of AM symbiosis to plant growth and nutrient uptake, although the percentage of mycorrhization was higher in the Org treatment than in the controls. In addition, mycorrhization drastically reduced the recovery of 15N from the OM added to the soil whereas it slightly increased the N recovery from the mineral fertiliser. This suggests that plants and AM fungi probably exert a differential competition for different sources of N available in the soil. On the whole, our results provide a contribution to a better understanding of the conditions under which AM fungi can play an effective role in mitigating the negative effects of nutritional stresses in plants.