Effects of H2SO4, GA3, and cold stratification on the water content, coat composition, and dormancy release of Tilia miqueliana seeds.

Introduction: Tilia miqueliana is an endemic species whose population is declining. The permeability barrier and mechanical constraint of the pericarp (seed coat) are important causes of its seed dormancy. Although there has been considerable research on this subject, questions remain regarding how the permeability barrier and mechanical constraint of the seed coat are eliminated during dormancy release and how water enters the seed. Therefore, protecting the species by improving its germination/dormancy breaking in the laboratory is urgent. Methods: In this study, the changes in the cellular structure, mechanical properties, and components of the Tilia miqueliana seed coat after an H2SO4-gibberellic acid (GA3) treatment were analyzed during dormancy release. Various analyses (e.g., magnetic resonance imaging, scanning electron microscopy, and paraffin section detection) revealed the water gap and water channel. Results: The H2SO4 treatment eliminated the blockage at the micropyle and hilum of the seeds. Water entered the seeds through the water gap (micropyle) rather than through the hilum or seed coat, after which it dispersed along the radicle, hypocotyl, and cotyledon to the endosperm. During the cold stratification period, the cellular structure was damaged and an increasing number of holes appeared on the inner and outer surfaces of the seed coat. Vickers hardness tests showed that GA3 decreased the seed coat hardness. Additionally, the seed coat lignin and total phenol contents continuously decreased during the cold stratification period. Notably, the Liquid chromatography-mass spectrometry (LC-MS) analysis of the seed coat detected polyethylene glycol (osmoregulator), which may have destabilized the water potential balance inside and outside the seed and increased the water content to levels required for germination, ultimately accelerating seed dormancy release. Discussion: This sophisticated and multi-level study reveals how H2SO4 and GA3 eliminate the permeability barrier and mechanical constraints of the seed coat during dormancy release of Tilia miqueliana seeds. This will be beneficial to artificially assist the natural regeneration and population expansion of Tilia miqueliana.

Cryo-attenuated properties of Tilia miqueliana pericarps and seeds.

Introduction: Cryo treatment of dry seeds is known to attenuate the structure of fruit and seed coats, but little is known about the microstructural impacts of such treatment. The seeds of Tilia miqueliana are dispersed within a hard pericarp, the manual removal (hulling) of which is time-consuming and inefficient. Rapid hulling technology is urgently needed for sustainable production and convenience of edible nuts. Methods: We explored the mechanistic basis of liquid nitrogen (N)-treatment weakening of the pericarp of T. miqueliana fruits using a range of microscopical, biophysical and chemical approaches. Results: Liquid N treatment (40 s) resulted in lower pericarp contents of cellulose and hemicellulose, and increased amounts of lignin. Profound changes in cell structure and mechanical properties included the emergence of large holes and gaps between the mesocarp and endocarp cells. Also, the toughness of the pericarp decreased, whilst the hardness and brittleness increased, thereby changing the fracture type from ductile to brittle. Liquid N treatment of dry fruits followed by tapping with a hammer, reduced the number of damaged seeds three-fold and pericarp peeling time four-fold compared with manual hulling, whilst seed viability was not negatively affected. Discussion: Comparable findings for the efficient and economical removal of hard covering structures from dispersal units of five more species from three other families following liquid N treatment indicates the potential application of our findings to large-scale production of seeds and seedlings for breeding, forestry and conservation/restoration purposes. Furthermore, it introduces a novel concept for postharvest treatment and pre-treatment of deep processing in nuts.

The metagenomics of soil bacteria and fungi and the release of mechanical dormancy in hard seeds.

Persistence in the soil is a function of seed physiology, particularly non-germination and inherent lifespan. However, for seeds with mechanical dormancy, non-germination is also a function of the composition and activity of the soil microbiota. We attempted to screen out microorganisms in the soil that can specifically and rapidly decompose the hard fruit pericarps of Tilia miqueliana Maxim., a unique native tree species in China. Using the classical replica plating method, more than 100 different culturable microorganisms that could rapidly erode the pericarp were collected from the surface of pericarps under different culture conditions. At the same time, we successfully extended the concept of metagenomics and applied it to the identification of mixed artificial cultures. The decomposition process of the pericarps in soil was also simulated artificially. The physical and chemical data suggested a potential mechanism of microbial scarification and cracking in pericarp, whilst the embryos inside the eroded fruits retained good viability. Our discoveries could pave the way for the removal of physical and mechanical obstacles that prevent hard coat seeds from germinating. We anticipate that the use of this technology will improve the germination of other hard coat seeds. More research is needed to investigate the impacts on other seeds. The findings of this research can inform the design of experiments on the seed ecology of persistence.

Metagenomic analysis reveals the different characteristics of microbial communities inside and outside the karst tiankeng.

BACKGROUND: Karst tiankengs serve as a reservoir of biodiversity in the degraded karst landscape areas. However, the microbial diversity of karst tiankengs is poorly understood. Here, we investigated the composition and function of the microbial community in a karst tiankeng. RESULTS: We found that habitat differences inside and outside the karst tiankeng changed the composition and structure of the soil microbial communities, and the dominant phyla were Proteobacteria, Actinobacteria, Chloroflexi and Acidobacteria. The Shannon-Wiener diversity of microbial communities inside and outside the tiankeng was significantly different, and it was higher inside the tiankeng (IT). Venn and LEfSe analysis found that the soil microbial communities inside the tiankeng had 640 more endemic species and 39 more biomarker microbial clades than those identified outside of the tiankeng (OT)..Functional prediction indicated that soil microorganisms in outside the tiankeng had a high potential for carbohydrate metabolism, translation and amino acid metabolism. There were biomarker pathways associated with several of human diseases at both IT and OT sites. Except for auxiliary activities (AA), other CAZy classes had higher abundance at IT sites, which can readily convert litter and fix carbon and nitrogen, thereby supporting the development of underground forests. The differences in microbial communities were mainly related to the soil water content and soil total nitrogen. CONCLUSIONS: Our results provide a metagenomic overview of the karst tiankeng system and provide new insights into habitat conservation and biodiversity restoration in the area.

Fine Identification and Classification of a Novel Beneficial Talaromyces Fungal Species from Masson Pine Rhizosphere Soil.

Rhizosphere fungi have the beneficial functions of promoting plant growth and protecting plants from pests and pathogens. In our preliminary study, rhizosphere fungus JP-NJ4 was obtained from the soil rhizosphere of Pinus massoniana and selected for further analyses to confirm its functions of phosphate solubilization and plant growth promotion. In order to comprehensively investigate the function of this strain, it is necessary to ascertain its taxonomic position. With the help of genealogical concordance phylogenetic species recognition (GCPSR) using five genes/regions (ITS, BenA, CaM, RPB1, and RPB2) as well as macro-morphological and micro-morphological characters, we accurately determined the classification status of strain JP-NJ4. The concatenated phylogenies of five (or four) gene regions and single gene phylogenetic trees (ITS, BenA, CaM, RPB1, and RPB2 genes) all show that strain JP-NJ4 clustered together with Talaromyces brevis and Talaromyces liani, but differ markedly in the genetic distance (in BenA gene) from type strain and multiple collections of T. brevis and T. liani. The morphology of JP-NJ4 largely matches the characteristics of genes Talaromyces, and the rich and specific morphological information provided by its colonies was different from that of T. brevis and T. liani. In addition, strain JP-NJ4 could produce reduced conidiophores consisting of solitary phialides. From molecular and phenotypic data, strain JP-NJ4 was identified as a putative novel Talaromyces fungal species, designated T. nanjingensis.

Identification of Two Fungal Pathogens Responsible for Liriodendron chinense × tulipifera Black Spot and Screening of Trichoderma sp. for Disease Control.

Liriodendron chinense × tulipifera black spot is a newly discovered disease that causes yellowing and early shedding of leaves, affecting the growth of Liriodendron trees, and significantly reducing their ornamental value as a garden species. The pathogen responsible for this disease, and how it can be prevented and controlled, are not clear. In this study, the occurrence of this disease was first investigated according to Koch's postulates, and the primary pathogens causing Liriodendron black spot were determined to be Colletotrichum gloeosporioides and Alternaria alternata. Biocontrol strains antagonistic to these two pathogens were then screened from the leaf microorganisms of L. chinense × tulipifera, and a preliminary investigation of the biological control of Liriodendron black spot was performed. Through the screening of antagonistic microorganisms on the leaf surface of L. chinense × tulipifera, the strain Trichoderma koningiopsis T2, which displayed strong antagonism against C. gloeosporioides and A. alternata, was obtained. The T2 strain could inhibit the growth of the two pathogens via three mechanisms: hyperparasitism, volatile and nonvolatile metabolite production, and environmental acidification. The biocontrol experiments in the greenhouse and field showed that initial spraying with a T. koningiopsis T2 spore suspension followed by the two pathogens resulted in the lowest disease incidence. These results confirmed the black spot pathogens of L. chinense × tulipifera, clarified the antagonistic mechanism of T. koningiopsis T2 against the two pathogens, and provided a theoretical basis and technical support for the biological control of the disease.

Forest Tree Associated Bacterial Diffusible and Volatile Organic Compounds against Various Phytopathogenic Fungi.

Plant growth-promoting rhizobacteria (PGPR) can potentially be used as an alternative strategy to control plant diseases. In this study, strain ST-TJ4 isolated from the rhizosphere soil of a healthy poplar was found to have a strong antifungal activity against 11 phytopathogenic fungi in agriculture and forestry. Strain ST-TJ4 was identified as Pseudomonas sp. based on 16S rRNA-encoding gene sequences. The bacterium can produce siderophores, cellulase, and protease, and has genes involved in the synthesis of phenazine, 1-phenazinecarboxylic acid, pyrrolnitrin, and hydrogen cyanide. Additionally, the volatile compounds released by strain ST-TJ4 can inhibit the mycelial growth of plant pathogenic fungi more than diffusible substances can. Based on volatile compound profiles of strain ST-TJ4 obtained from headspace collection and GC-MS/MS analysis, 1-undecene was identified. In summary, the results suggested that Pseudomonas sp. ST-TJ4 can be used as a biocontrol agent for various plant diseases caused by phytopathogenic fungi.

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Bay cities have abundant land-sea resources and higher environmental carrying capacity. The high density of population and industry surrounding the bay makes bay cities a type of ecologically fragile areas. With Quanzhou, a typical bay city, as an example, we simulated the land use and landscape pattern change in 2030 based on multiple data sources (land use data, meteorological site data, topographic data and statistical data) using Logistic-CA-Markov coupling model to set natural scenarios, planning scenarios and protection scenarios. Four key ecosystem service (ES) including water retention, soil conservation, carbon sequestration (NPP), food supply and their trade-offs were calculated and predicted. Under the three scenarios, the area of cultivated land and construction land in Quanzhou City would increase in 2030. Forest land, grassland and water area would be reduced in varying degrees. The fragmentation of land use would be serious. In comparison with 2015, except for soil conservation service, water retention, carbon sequestrtion and food supply of Quanzhou City would decline to varying degrees in 2030. Ecosystem service function in natural scenario would be more decreased, with the decline under the protection scenario being lower than the planning scenario. In the protection and planning scenarios, the synergy between water conservation and soil conservation, water conservation and carbon sequestrtion, soil conservation and carbon sequestrtion in 2030 would be enhanced and the trade-offs would be weakened.

The phosphate-solubilizing ability of Penicillium guanacastense and its effects on the growth of Pinus massoniana in phosphate-limiting conditions.

Microbes in soil can degrade insoluble inorganic and organic phosphorus, which are components of the soil phosphorus cycle and play an important role in plant growth. Pinus massoniana is a pioneer tree species used for afforestation in southern China and grows in poor, acidic soil. A shortage of available phosphorus in soil limits the growth of P massoniana To alleviate this situation, it is necessary to improve soil fertility. A fungal strain (JP-NJ2) with the ability to solubilize phosphate was isolated from the P massoniana rhizosphere. The ability of JP-NJ2 to solubilize inorganic and organic phosphorus and promote the growth of P massoniana was evaluated. It showed that JP-NJ2 could grow in NBRIP inorganic phosphate (AlPO4, FePO4·4H2O, and Ca3[PO4]2) fermentation broths, with the highest phosphorus concentration (1.93 mg/ml) and phosphate-solubilizing rate (43.7%) for AlPO4 and in Monkina organic phosphate fermentation broth with a phosphorus concentration of 0.153 mg/ml. The phosphate-solubilizing capability in inorganic and organic fermentation broths was negatively correlated with pH. JP-NJ2-produced acids at a total concentration of 4.7 g/l, which included gluconic (2.3 g/l), oxalic (1.1 g/l), lactic (0.7 g/l) and malonic (0.5 g/l) acids. It prioritized extracellular acidic phosphatase and combined with phytase to solubilize organic phosphates. The fungal suspension and extracellular metabolites from phosphate-solubilizing fungi promoted the shoot length of P massoniana seedlings by 97.7% and 59.5%, respectively, while increasing the root crown diameter by 46.8% and 27.7%. JP-NJ2 was identified as Penicillium guanacastense based on its morphology and phylogenetic analyses of five genes/regions (ITS, ben A, cmd, cox1 and tef). This is the first report on P guanacastense isolated from pine tree rhizosphere soil in China and its high phosphate-solubilizing capability, which promoted the growth of P massoniana P guanacastense JP-NJ2 has potential use as a biological fertilizer in forestry and farming.