Abstract
Common mycorrhizal networks (CMNs) allow the transfer of nutrients between plants, influencing the growth of the neighboring plants and soil properties. Cleistogene squarrosa (C. squarrosa) is one of the most common grass species in the steppe ecosystem of Inner Mongolia, where nitrogen (N) is often a key limiting nutrient for plant growth, but little is known about whether CMNs exist between neighboring individuals of C. squarrosa or play any roles in the N acquisition of the C. squarrosa population. In this study, two C. squarrosa individuals, one as a donor plant and the other as a recipient plant, were planted in separate compartments in a partitioned root-box. Adjacent compartments were separated by 37 µm nylon mesh, in which mycorrhizal hyphae can go through but not roots. The donor plant was inoculated with arbuscular mycorrhizal (AM) fungi, and their hyphae potentially passed through nylon mesh to colonize the roots of the recipient plant, resulting in the establishment of CMNs. The formation of CMNs was verified by microscopic examination and 15N tracer techniques. Moreover, different levels of N fertilization (N0 = 0, N1 = 7.06, N2 = 14.15, N3 = 21.19 mg/kg) were applied to evaluate the CMNs’ functioning under different soil nutrient conditions. Our results showed that when C. squarrosa–C. squarrosa was the association, the extraradical mycelium transferred the 15N in the range of 45–55% at different N levels. Moreover, AM fungal colonization of the recipient plant by the extraradical hyphae from the donor plant significantly increased the plant biomass and the chlorophyll content in the recipient plant. The extraradical hyphae released the highest content of glomalin-related soil protein into the rhizosphere upon N2 treatment, and a significant positive correlation was found between hyphal length and glomalin-related soil proteins (GRSPs). GRSPs and soil organic carbon (SOC) were significantly correlated with mean weight diameter (MWD) and helped in the aggregation of soil particles, resulting in improved soil structure. In short, the formation of CMNs in this root-box experiment supposes the existence of CMNs in the typical steppe plants, and CMNs-mediated N transfer and root colonization increased the plant growth and soil properties of the recipient plant.
Highlights
Arbuscular mycorrhizal (AM) symbiosis between higher plant roots and the fungi belonging to the phylum Glomeromycota is one of the most common mutualistic associations in terrestrial ecosystems [1,2]
Microscopic examination revealed the presence of AM fungal extraradical hyphae extending from the donor to the recipient compartment through the 37 μm mesh (Figure S1a) and the recipient plant roots were colonized by the AM fungi (Figure S1b)
In mycorrhizal treatment where the donor plant was inoculated with AM fungi, the average dry shoot weight (DSW) (Figure S2a) and average dry root weight (DRW) (Figure S2b) of the donor and recipient plants was increased as compared to non-mycorrhizal treatment
Summary
Arbuscular mycorrhizal (AM) symbiosis between higher plant roots and the fungi belonging to the phylum Glomeromycota is one of the most common mutualistic associations in terrestrial ecosystems [1,2]. Extensively branched extraradical mycelia can interconnect neighboring plants to form common mycorrhizal networks (CMNs) [4,5,6]. These CMNs can affect the distribution of mineral nutrients like carbon [7,8], N [9], and phosphorus [10] among the connected plants. This could influence the plant’s establishment [11,12], survival [13,14], growth [15] and physiology [16,17]. The underground network is very complex, and a deep understanding of CMN’s formation, existence and functioning requires microscopic or tracer element techniques
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