Date Published: April 20, 2018
Publisher: Springer Berlin Heidelberg
Author(s): Xiaohui Wang, Changdong Wang, Junkang Sui, Zhaoyang Liu, Qian Li, Chao Ji, Xin Song, Yurong Hu, Changqian Wang, Rongbo Sa, Jiamiao Zhang, Jianfeng Du, Xunli Liu.
Rhizospheric microorganisms can increase phosphorus availability in the soil. In this regard, the ability of phosphofungi to dissolve insoluble phosphorus compounds is greater than that of phosphate-solubilizing bacteria. The aim of the current study was to identify efficient phosphofungi that could be developed as commercial microbial agents. Among several phosphate-solubilizing fungal isolates screened, strain CS-1 showed the highest phosphorus-solubilization ability. Based on phylogenetic analysis of the internal transcribed spacer region sequence, it was identified as Aspergillus niger. High-performance liquid chromatography analysis revealed that the mechanism of phosphorus solubilization by CS-1 involved the synthesis and secretion of organic acids, mainly oxalic, tartaric, and citric acids. Furthermore, strain CS-1 exhibited other growth-promoting abilities, including efficient potassium release and degradation of crop straw cellulose. These properties help to returning crop residues to the soil, thereby increasing nutrient availability and sustaining organic matter concentration therein. A pot experiment revealed that CS-1 apparently increased the assessed biometric parameters of wheat seedlings, implying the potential of this strain to be developed as a commercial microbial agent. We used Illumina MiSeq sequencing to investigate the microbial community composition in the rhizosphere of uninoculated wheat plants and wheat plants inoculated with the CS-1 strain to obtain insight into the effect of the CS-1 strain inoculation. The data clearly demonstrated that CS-1 significantly reduced the content of pathogenic fungi, including Gibberella, Fusarium, Monographella, Bipolaris, and Volutella, which cause soil-borne diseases in various crops. Strain CS-1 may hence be developed into a microbial agent for plant growth improvement.
Phosphorus is the second most important limiting element required for plant growth (Chai et al. 2011; Li et al. 2015a; Ram et al. 2015), and it cannot be substituted by any other nutrient. However, even though soils may contain a substantial reserve of total phosphorus (Collavino et al. 2010), most natural soils are typically deficient in this element. This is particularly true for highly weathered soils, in which phosphorus forms insoluble complexes with aluminum, iron, and hydroxides (in acidic soils), and with calcium (in alkaline soils) (Mendez 2014). To sustain crop production, the traditional method of rectifying phosphorus deficiency involved applying large amounts of phosphate fertilizers to the soil. However, only a small fraction of this added phosphate is available to plants, whereas a considerable proportion becomes immobilized after application (Singh 2011). This not only increases production costs but also leads to environmental pollution.
Phosphate is a nutrient that is limiting for the growth of crops, with only 0.1% of total phosphorous in the soil available to plants (Vessey and Heisinger 2001). Although in China, the soil may harbor a total phosphorus reserve, it cannot be efficiently used by the plants because of low soil quality (Wu 2004). PSMs able to release phosphorus from the soil minerals play a key role in soil fertility (Wakelin et al. 2012) when P availability is low or P demand is high. Most relevant literature pertains to PSB and their potential use for the enhancement of soil fertility (Collavino et al. 2010; Ghosh et al. 2012). However, a few filamentous nonmycorrhizal fungi are also involved in phosphate solubilization, especially Aspergillus spp. and Penicillium spp. (Altomare et al. 1999; Singh 2011). The beneficial effects for various crops of such phosphate-solubilizing fungi (PSF) as Aspergillus (Mittal et al. 2008), Trichoderma (Zayed and Abdelmotaal 2005), Penicillium (Reyes et al. 2002), and vesicular arbuscular mycorrhizae (Omar 1997) have been demonstrated.