Bede Mickan

Arbuscular mycorrhizal fungi improved plant growth and nutrient acquisition of desert ephemeral Plantago minuta under variable soil water conditions

Desert ephemeral plants play an important role in desert ecosystem. Soil water availability is considered as the major restrictive factor limiting the growth of ephemeral plants. Moreover, arbuscular mycorrhizal fungi (AM fungi) are widely reported to improve the growth of desert ephemerals. The present study aimed to test the hypothesis of that AM fungi could alleviate drought stress of desert ephemeral Plantago minuta, and AM fungal functions reduced with the improvement of soil water content. A pot experiment was carried out with three levels of soil water contents (4.5%, 9.0%, and 15.8% (w/w)), and three AM inoculation treatments (Glomus mosseae, Glomus etunicatum and non-inoculation). The results indicate that mycorrhizal colonization rate decreased with the increase of soil water availability. Inoculation improved plant growth and N, P and K acquisition in both shoots and roots regardless water treatments. When comparing the two fungi, plants inoculated with G. mosseae performed better than those inoculated with G. etunicatum in terms of plant growth and nutrient acquisition. These results showed that ameliorative soil water did not suppress arbuscular mycorrhizal fungal functions in improving growth and nutrient acquisition of desert ephemeral Plantago minuta.

Application of compost and clay under water-stressed conditions influences functional diversity of rhizosphere bacteria

Applications of compost and clay to ameliorate soil constraints such as water stress are potential management strategies for sandy agricultural soils. Water repellent sandy soils in rain-fed agricultural systems limit production and have negative environmental effects associated with leaching and soil erosion. The aim was to determine whether compost and clay amendments in a sandy agricultural soil influenced the rhizosphere microbiome of Trifolium subterraneum under differing water regimes. Soil was amended with compost (2% w/w), clay (5% w/w) and a combination of both, in a glasshouse experiment with well-watered and water-stressed (70 and 35% field capacity) treatments. Ion Torrent 16S rRNA sequencing and Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) analysis of functional gene prediction were used to characterise the rhizosphere bacterial community and its functional component involved in nitrogen (N) cycling and soil carbon (C) degradation. Compost soil treatments increased the relative abundance of copiotrophic bacteria, decreased labile C and increased the abundance of recalcitrant C degrading genes. Predicted N cycling genes increased with the addition of clay (N2 fixation, nitrification, denitrification) and compost + clay (N2 fixation, denitrification) and decreased with compost (for denitrification) amendment. Water stress did not alter the relative abundance of phylum level taxa in the presence of compost, although copiotrophic Actinobacteria increased in relative abundance with addition of clay and with compost + clay. A significant role of compost and clay under water stress in influencing the composition of rhizosphere bacteria and their implications for N cycling and C degradation was demonstrated.

Mechanisms for Alleviation of Plant Water Stress Involving Arbuscular Mycorrhizas

Arbuscular mycorrhizal (AM) fungi can aid in the alleviation of host plant water stress under soil water-deficit conditions. AM fungi are likely to alleviate water stress through a combination of processes. The mechanisms involved may operate directly through enhancing plant water uptake or indirectly through modification of the rhizosphere-soil environment. Direct mechanisms of water alleviation to the host plant have been reported through the ultra-narrow hyphal network, which is the external phase of AM fungi ability to scavenge water/nutrients within soil pores and also extend beyond the root depletion zone. Additionally, AM fungi are reported to increase beneficial plant biochemical compounds that alleviate oxidative stress (antioxidants) and enhance osmoregulation (proline) caused by soil water deficit. Indirect enhancement of soil structure to enhance soil water relations through AM fungi hyphae is through a combination of physical, biochemical, and biological soil interactions which altogether has the capacity to increase soil aggregation.

Use of Mycorrhiza in Sustainable Agriculture and Land Restoration

Arbuscular mycorrhizal (AM) fungi belong to the phylum Glomeromycota and form symbioses with more than 80 % of terrestrial plants. They have a range of roles related to soil functions. AM fungi and ectomycorrhizal (ECM) fungi are the most abundant and common symbionts in agricultural and forest ecosystems, respectively. The functions of mycorrhizas in sustainable agriculture and forestry ecosystems are well demonstrated. In this review, we highlight functions of AM and ECM fungi in native forest ecosystems and the function of AM fungi in agricultural ecosystems.