Yang Fengjian

Characteristics of the microbial community in rhizosphere of Camptotheca acuminata cultured with exotic invasive plant Eupatorium adenophorum

The traditional culture-dependent plate counting and culture-independent small-subunit-ribosomal RNA gene-targeted molecular techniques, Single-Strand Conformation Polymorphism (SSCP) and terminal Restriction Fragment Length Polymorphism (tRFLP) combined with 16S rDNA clone library were adopted to investigate the impacts of secretion from Camptotheca acuminata (abbreviated to Ca) roots on the quantities and structure of eukaryotic microbes and bacteria in the rhizosphere, and the possibility that Ca controls exotic invasive plant Eupatorium adenophorum (Ea). The counting results indicated that the number of bacteria increased in turn in rhizospheres of Ea, Ca-Ea mixed culture and Ca, while that of eukaryotic microbes decreased. PCR-SSCP profiles showed eukaryotic microbial bands (corresponding to biodiversity) in rhizosphere of Ea were more complex than those of Ca and CE. Meristolohmannia sp., Termitomyces sp. and Rhodophyllus sp. were the dominant populations in the rhizosphere of Ca. Bacterial terminal restriction fragments (TRFs) profiles showed no difference among three kinds of rhizospheres, and the sequences of the 16S rDNA clone library from Ca rhizospheres were distributed in 10 known phyla, in which phylum Proteobacteria were the absolute dominant group and accounted for 24.71% of the cloned sequences (δ-Proteobacteria accounted for up to 17.65%), and phyla Acidobacteria and Bacteroidetes accounted for 16.47% and 10.59% of the cloned sequences, respectively. In addition, high performance liquid chromatography detected a trace amount of camptothecin and hydroxycamptothecin in the rhizospheric soil of Ca and CE, but examined neither camptothecin nor hydroxycamptothecin in rhizospheric soil of Ea. Therefore, invasion and diffusion of Ea evidently depended on distinguishing the eukaryotic community structure, but not on that of the bacterial pattern. Ca was able to alter the eukaryotic community structure of invasive Ea by secreting camptothecin and hydroxycamptothecin into rhizospheres, and may benefit the control of overspread of Ea. This study provided theoretical evidence for rhizospheric microbial aspects on substituting Ca for Ea.

Effects of closed forest on diameter class structure ofQuercus mongolica forest in eastern area of Xiaoxing’an Mountains

In eastern area of Xiaoxing’an Mountains, Heilongjiang Province (44o4′–47o26 N′, 126o33′–131o41 E′) the diameter-class structure ofQuercus mongolica forest after different closed time was studied in the plots with different slope direction. Six repetitive plots within 5-year, 16-year and 24-year closedQ. mongolica forests were selected in sunny slope and shade slope, respectively. The area of each plot was 20m×20m. Diameter at breast height (DBH), tree height and canopy diameter of all the trees were measured. Six classes of diameter were determined as 2, 4, 6, 8, 10, and 12 depending on the range of DBH (0–3, 3–5, 5–7, 7–9, 9–11, and 11–13 cm). The results showed that: 1) After 5-year closed treatment, the population quantitiesQ. mongolica, Tilia mandshurica andUlmsis laciniata decreased with the increase in diameter class, which indicated they were healthy populations; 2) After 16-year closed treatment the tree number ofTilia mandshurica andUlmsis laciniata decreased because of canopy coverage increasing and became the associated species inQ. mongolica population; 3)Q. mongolica, after 24-year closed treatment, became dominant species; 4) Canopy coverage increased more rapidly in sunny slope than that in shade slope. Recession ofTilia mandshurica andUlmsis laciniata populations in sunny slope was more obviously than that in shade slope.