Variations in rhizosphere soil total phosphorus and bioavailable phosphorus with respect to the stand age in Pinus massoniana Lamb

Synergistic variation of rhizosphere soil phosphorus availability and microbial diversity with stand age in plantations of the endangered tree species Parashorea chinensis

Introduction

Soil physicochemical properties and nutrient composition play a significant role in shaping microbial communities, and facilitating soil phosphorus (P) transformation. However, studies on the mechanisms of interactions between P transformation characteristics and rhizosphere microbial diversity in P-deficient soils on longer time scales are still limited.

Methods

In this study, rhizosphere soils were collected from a pure plantation of Parashorea chinensis (P. chinensis) at six stand ages in the subtropical China, and the dynamic transformation characteristics of microbial diversity and P fractions were analyzed to reveal the variation of their interactions with age.

Results

Our findings revealed that the rhizosphere soils across stand ages were in a strongly acidic and P-deficient state, with pH values ranging from 3.4 to 4.6, and available P contents ranging from 2.6 to 7.9 mg·kg-1. The adsorption of P by Fe3+ and presence of high levels of steady-state organic P highly restricted the availability of P in soil. On long time scales, acid phosphatase activity and microbial biomass P were the main drivers of P activation. Moreover, pH, available P, and ammonium nitrogen were identified as key factors driving microbial community diversity. As stand age increased, most of the nutrient content indicators firstly increased and then decreased, the conversion of other forms of P to bio-available P became difficult, P availability and soil fertility began to decline. However, bacteria were still able to maintain stable species abundance and diversity. In contrast, stand age had a greater effect on the diversity of the fungal community than on the bacteria. The Shannon and Simpson indices varied by 4.81 and 0.70 for the fungi, respectively, compared to only 1.91 and 0.06 for the bacteria. Microorganisms play a dominant role in the development of their relationship with soil P.

Discussion

In conclusion, rhizosphere microorganisms in P. chinensis plantations gradually adapt to the acidic, low P environment over time. This adaptation is conducive to maintaining P bioeffectiveness and alleviating P limitation.

Characterization of 35 Masson pine (Pinus massoniana) half-sib families from two provinces based on metabolite properties

Plant metabolism is an important functional trait, and its metabolites have physiological and ecological functions to adapt to the growth environment. However, the physiological and ecological functions of metabolites from different provinces of the same plant species are still unclear. Therefore, this study aimed to determine whether metabolites from different provinces of Masson pine (Pinus massoniana Lamb.) have the corresponding metabolic traits. The gas chromatography–mass spectrometry technique and metabonomic analysis methods were used to characterize 35 Masson pine half-sib families from two provinces. A total of 116 metabolites were putatively identified in 35 families of Masson pine, among which the average content of organic acids was the highest, followed by saccharides and alcohols, and phosphoric acids. Comparative analysis of metabolite groups showed that organic acids, amines, and others were significantly different between the Masson pine families from Guangxi and Guizhou provinces. Six differential metabolites were found between the provinces from Guizhou and Guangxi, namely caffeic acid, L-ascorbic acid, gentiobiose, xylitol, d-pinitol, and β-sitosterol. The most significantly enriched pathways among differentially expressed metabolites between the two provinces were steroid biosynthesis, phenylpropanoid biosynthesis, glutathione metabolism, pentose and glucuronate interconversions. Overall, the results showed that Masson pine half-sib families from different geographical provinces have different metabolite profiles and their metabolites are affected by geographical provenance and growth environment adaptability. This study revealed that the breeding of Masson pine families from different provinces changed the metabolite profiles, providing a reference for the multipurpose breeding of Masson pine.

Long-term fertilization has different impacts on bacterial communities and phosphorus forms in sugarcane rhizosphere and bulk soils under low-P stress

The application of phosphorus (P) fertilizer effectively improves soil P availability, but it also affects soil microbial communities. However, the responses of soil bacterial communities and P forms to long-term P fertilization, and the relationships of bacterial communities with soil P forms remain unclear in P-deficient field. In this study, the impacts of different P fertilization treatments (chemical nitrogen and potassium (NK); chemical N, P and K (NPK); and NPK plus straw (NPKS)) on the bacterial communities and P forms in sugarcane rhizosphere (RS) and bulk soils (BS) were evaluated. Compared with the NK, the NPK and NPKS treatments significantly (P<0.05) increased the yield and quality characters of sugarcane, especially under NPKS. Additionally, P fertilization significantly increased the available P (AP), soluble inorganic P (Pi) and retained Pi in both the RS and BS, but they significantly increased the Chao1 and Shannon index only in the BS; and almost all these indices were significantly higher in the RS than in the BS. The bacterial community compositions were also significantly altered by P fertilization, with major changes in the RS and minor changes in the BS. The bacterial genera that were enriched in the sugarcane rhizosphere mainly included Bradyrhizobium, Rhodanobacter, Pseudolabrys, Conexibacter, and Burkholderia-Caballeronia-Paraburkholderia, some of which potentially promote the plant growth. Compared to NK, functional groups involved in the cycling of carbon, N, and sulfur significantly increased or decreased with fertilizer P application. Moreover, the relative abundances of many bacterial species were significantly correlated with the soil P forms. In conclusion, long-term P fertilization altered bacterial structure and functions in P-deficient sugarcane soil, which could help the soil P cycling and suppling. The results provide useful information to stimulate the power of the microbes by fertilization measures to improve soil nutrients and crop production.