Isaria farinosa is an important entomopathogenic fungus. By using ISSR, this paper studied the genetic heterogeneity of six I. farinosa populations at different localities of Anhui Province, East China. A total of 98.5% polymorphic loci were amplified with ten polymorphic primers, but the polymorphism at population level varied greatly, within the range of 59.6%-93.2%. The genetic differentiation index (G(st)) between the populations based on Nei's genetic heterogenesis analysis was 0.3365, and the gene flow (N(m)) was 0.4931. The genetic differentiation between the populations was lower than that within the populations, suggesting that the genetic variation of I. farinosa mainly come from the interior of the populations. The UPGMA clustering based on the genetic similarities between the isolates revealed that the Xishan population was monophylectic, while the other five populations were polyphylectic, with the Yaoluoping population being the most heterogenic and the Langyashan population being the least heterogenic. No correlations were observed between the geographic distance and the genetic distance of the populations. According to the UPGMA clustering based on the genetic distance between the populations, the six populations were classified into three groups, and this classification was accorded with the clustering based on geographic environment, suggesting the effects of environmental heterogeneity on the population heterogeneity.
Silicon (Si) pools and fluxes are affected by plant community shifts in forest ecosystems. Moso bamboo (Phyllostachys pubescens) is a Si accumulating plant, and its expansion exerts various ecological effects in colonized forest ecosystems. However, it is unclear how bamboo expansion might alter the biogeochemical Si cycle. To estimate the consequences of bamboo expansion on Si availability and biochemical cycling in subtropical areas, we selected bamboo-pure forest (BPF), bamboo-broadleaved mixed forest (BMF), and adjacent secondary evergreen broadleaved forest (EBF) stands in an area of bamboo expansion and compared Si pools and fluxes of plants in each forest type. We found that the content of the soluble and exchangeable Si in soils of BPF was lower than EBF (0.18 g kg−1 versus 0.25 g kg−1), that is, bamboo expansion decreased the soluble and exchangeable Si fraction, whereas there was no significant difference among BPF, BMF and EBF. In addition, the plant Si pool in BPF (285 g Si m−2) was 32.6 % lower than EBF (428 g Si m−2), and there was a shift in Si allocation from aboveground to belowground with conversion from EBF to BPF, largely attributed to abundant roots in BPF. We found that bamboo expansion accelerated the biogeochemical Si cycle to some extent, with higher production of phytoliths and quicker turnover of fine roots in BPF than EBF. We also highlight that bamboo expansion accelerated the uptake and return of Si, and promoted the release and dissolution of phytoliths. These results have implications for assessing the impacts of vegetation shifts on the biogeochemical Si cycle.
Phosphate-solubilizing fungi (PSF) generally enhance available phosphorus (P) released from soil, which contributes to plants' P requirement, especially in P-limiting regions. In this study, two PSF, TalA-JX04 and AspN-JX16, were isolated from the rhizosphere soil of moso bamboo (Phyllostachys edulis) widely distributed in P-deficient areas in China and identified as Talaromyces aurantiacus and Aspergillus neoniger, respectively. The two PSF were cultured in potato dextrose liquid medium with six types of initial pH values ranging from 6.5 to 1.5 to assess acid resistance. Both PSF were incubated in Pikovskaya's liquid media with different pH values containing five recalcitrant P sources, including Ca3(PO4)2, FePO4, CaHPO4, AlPO4, and C6H6Ca6O24P6, to estimate their P-solubilizing capacity. No significant differences were found in the biomass of both fungi grown in media with different initial pH, indicating that these fungi could grow well under acid stress. The P-solubilizing capacity of TalA-JX04 was highest in medium containing CaHPO4, followed by Ca3(PO4)2, FePO4, C6H6Ca6O24P6, and AlPO4 in six types of initial pH treatments, while the recalcitrant P-solubilizing capacity of AspN-JX16 varied with initial pH. Meanwhile, the P-solubilizing capacity of AspN-JX16 was much higher than TalA-JX04. The pH of fermentation broth was negatively correlated with P-solubilizing capacity (p<0.01), suggesting that the fungi promote the dissolution of P sources by secreting organic acids. Our results showed that TalA-JX04 and AspN-JX16 could survive in acidic environments and both fungi had a considerable ability to release soluble P by decomposing recalcitrant P-bearing compounds. The two fungi had potential for application as environment-friendly biofertilizers in subtropical bamboo ecosystem.
In September 2019, approximately 75 to 90% of camphor trees (Cinnamomum camphora) were observed with cankers and branch dieback symptoms in Anyi (N28°32'54'', E115°37'52'') and Xinyu (N27°37'38'', E114°50'25'') county (Jiangxi Province, China). The symptoms included dark brown to dark, oval-shaped canker lesions, sunken and cracked longitudinally, cracked and evenly swelling, or reddish brown (Figure 1 A-D). Samples were collected from symptomatic branches and were cut into small pieces (ca. 0.5 cm × 0.5 cm × 0.5 cm). Sections were surface sterilized as described by Zhang et al. (2020), then placed on potato dextrose agar amended with 0.01% penicillin and 0.015% streptomycin sulfate and incubated in the laboratory at 25℃ with darkness. After 3 to 5 days, mycelium growing out from tissues were transferred onto PDA medium. In total, 68 fungal isolates including 22 isolates of Diaporthe sp. were obtained from cankers and then were classified into five categories based on morphological characteristics and sequencing of the ITS for morphological representative strains. Pathogenicity tests were conducted in the greenhouse (Figure 1 E-M) and field (Figure 1 N-Q). Branches were surface sterilized and inoculated as described by Prencipe et al. (2017). In the greenhouse, a total of 13 representative isolates (including 6 isolates of Diaporthe sp., 2 isolates of Neofusicoccum sp., 2 isolates of Botryosphaeria sp. and 3 isolates of Colletotrichum sp.) were selected and evaluated using 2-year-old seedlings of camphor tree in pots with 5 replicates per isolate, in which 3 isolates of Collectotrichum sp. had no pathogenicity. Then, two isolates of Diaporthe sp. (Z4 and Z7) were selected for field experiment. In field tests, the same method was used as in the greenhouse. The inoculated and control branches were collected 40 days after inoculation and the fungi were isolated and placed on PDA plates to recover the inoculated fungi and complete Koch's postulates. Both isolates of Diaporthe sp. produced canker symptoms on the branches. Isolate Z4 caused discoloration also on the branch without wounding. Both isolates produced pycnidia scattered in PDA plates supplemented with stems of alfalfa, were dark brown to black, globose to subglobose (Figure 1 T). Alpha conidia were cylindrical, 5.72-9.98 µm (mean 7.64 µm) × 2.15-3.13 µm (mean 2.69 µm) (n = 30) (Figure 1 S, red arrow), while beta conidia were biguttulate, one-celled, hyaline, non-septate, and 16.21-25.52 µm (mean 21.60 µm) × 0.76~1.65 µm (mean 1.14 µm) (n = 30, green arrow) (Figure 1 S). Five isolates (Z4, S-Z4, P-Z4, Z7 and S-Z7) including those used for pathogenicity test were selected for multi-locus phylogenetic analyses of ITS (White et al., 1990), TEF1-α and TUB2 (Glass et al. 1995) gene sequences, which the accession number was MW036358- MW036362 for ITS, MW052267- MW052271 for TEF1- α, MW052276-MW052280 for TUB2. Based on the phylogenetic tree analysis using IQ-TREE 2, all five isolates were identified as D. eres (Figure 2). D. eres has been reported to cause canker on many different woody plants, such as almond (Holland et al. 2020), peach (Prencipe et al. 2017), hazelnut (Wiman et al. 2019), and so on. However, this is the first report worldwide of D. eres causing disease on Cinnamomum camphora in China.
Si can be important for the growth, functioning, and stoichiometric regulation of nutrients for high-Si-accumulating bamboo. However, other trees do not actively take up dissolved silicic acid [Si(OH)4] from the soil, likely because they have fewer or no specific Si transporters in their roots. It is unclear what causes differential growth and C:N:P stoichiometry between bamboo and other trees across levels of Si supply.Si supply increased the relative growth rate of height and basal diameter of bamboo saplings, likely by increasing its net photosynthetic rate and ratios of N:P. Moreover, a high concentration of Si supply decreased the ratio of C:Si in bamboo leaves due to a partial substitution of C with Si in organic compounds. We also found that there was a positive correlation between leaf Si concentration and its transpiration rate in tree saplings.We demonstrated that Si supply can decrease the ratio of C:Si in bamboo leaves and increase the ratio of N:P without altering nutrient status or the N:P ratio of tree saplings. Our findings provide experimental data to assess the different responses between bamboo and other trees in terms of growth, photosynthesis, and C:N:P stoichiometry. These results have implications for assessing the growth and competition between high-Si-accumulating bamboo and other plants when Si availability is altered in ecosystems during bamboo expansion.
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