Mycorrhiza-released glomalin-related soil protein fractions contribute to soil total nitrogen in trifoliate orange

Glomalin released from arbuscular mycorrhizal fungi (AMF) has important roles in soil nutrient cycles, whereas contributing to glomalin-related soil protein (GRSP) fractions to soil nitrogen (N) is unknown. In this study, a two-chambered root-box that was divided into root chamber (root and mycorrhizal fungi hypha) and hypha chamber (free of the root) was used, and three AMF species including Diversispora epigaea, Paraglomus occultum, and Rhizoglomus intraradices were separately inoculated into the root chamber. Plant growth, soil total N, N content of purified GRSP fractions, and its contribution to soil total N, and leaf and root N contents were analysed. After four months, total biomass and root total length, surface area, and volume were improved by all AMF inoculations. AMF inoculations dramatically increased soil total N content in two chambers. The N content of purified easily extractable GRSP (EE-GRSP) and difficultly extractable GRSP (DE-GRSP) was 0.10 ± 0.01 mg/g and 0.16 ± 0.02 mg/g, respectively, accounted for 15.6 ± 1.6% and 18.1 ± 1.8% of soil total N, respectively. AMF inoculations stimulated the N accumulation in EE-GRSP and DE-GRSP, especially in the hypha chamber. It concluded that GRSP, especially DE-GRSP, acts as a soil N pool accounting for 33.8 ± 1.9% of soil total N in orchards.

Formation of Common Mycorrhizal Networks Significantly Affects Plant Biomass and Soil Properties of the Neighboring Plants under Various Nitrogen Levels

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.

ROOT CHARACTERISTICS IN COWPEA RELATED TO DROUGHT TOLERANCE AT THE SEEDLING STAGE

Cowpea (Vigna unguiculata) has relatively higher drought tolerance than other legume crops. It is widely grown in semi-arid regions, particularly in West Africa. One objective of the present study was to determine the effects of soil moisture stress on the length, dry matter and distribution of the roots of two cowpea varieties with different drought tolerances. Another objective was to evaluate the pin-board root-box as a method for identifying the role of root characteristics in drought tolerance. Two cowpea varieties, IT96D-604 (drought tolerant) and TVu7778 (drought susceptible), were used in this study. There were three watering treatments, T1 (well-watered), T2 (mild water stress) and T3 (severe water stress). Between varieties, there were no significant differences in shoot and root characteristics except for leaf area in T1. Under T2, the shoot:root ratio (S:R ratio) of IT96D-604 was significantly decreased compared with that under T1 as a result of the increase in root dry matter and decrease in leaf area without significant differences in total dry matter. In addition, the root dry matter per leaf area, which indicates the capacity to absorb water, of IT96D-604 was significantly higher than that of TVu7778. Under T3, the total dry matter of TVu7778 was about one third of those of the other treatments for the same variety, whereas that of IT96D-604 was more than half. Regarding root distribution, the centres of root dry matter and root length density of both varieties moved downwards significantly under water-stress conditions compared with those of the well-watered condition. This tendency was more pronounced in IT96D-604 than in TVu7778. Drought tolerance in IT96D-604 was associated with the increase in root dry matter per leaf area under mild water-stress conditions, and downward movement of roots (increasing access and use of soil moisture in deep soil layers) under mild and severe water stress conditions. In addition, the root-box method was versatile and can be used for studying root responses to edaphic factors relevant to root growth.