Yanli Xu

Leaf dew contributes nutrients to paddies and improves rice growth

Abstract Leaf dew is an important input in farmland ecosystems, but information regarding the nutrients from leaf dew deposition in paddy fields is scarce. Leaf dew samples were monitored and collected in situ from the Sanjiang Plain paddy experimental station during the rice growing periods in 2008, 2009, and 2010. The pH and essential nutrients [ammonium nitrogen ( ), nitrate nitrogen ( ), and phosphorus (P)] in paddy leaf dew were investigated, the nutrients in guttation and condensed dew were distinguished. In addition, the nutrient contributions of foliar fertilizer to Oryza sativa L (rice) were compared with those of leaf dew. The results indicate that the mean pH of leaf dew on rice is 6.3 (n=56), lower than the pH of rain and surface water. Condensed dew contributes about 97.7% of the nitrogen (N) and 95.7% of the phosphorus (P) in paddy leaf dew. Guttation provides a minor part of the N and P in leaf dew. The amount of leaf dewfall is much larger than the volume of foliar fertilization, with the amount of , , and P deposition from leaf dew almost 100 higher than from foliar fertilization. Compared with foliar fertilizer, leaf dew is a natural and potential fertilizer. Leaf dew is an important pathway for nutrient transfer within paddies.

Developing suppressive soil for root diseases of soybean with continuous long-term cropping of soybean in black soil of Northeast China

Field experiments were set up in 1991 to test if suppressive soil to soybean root diseases could be developed with continuous long-term soybean cropping in black soil of Northeast China. Based on the field observation in 2007, 2009, and 2011, soybean root growth was promoted, and the severities of root disease were reduced in a field with continuous long-term cropping with soybean. Population densities of the pathogens (Fusarium spp. and Heterodera glycines) in the soybean cropping field were significantly (P < 0.05) lower than rotation of soybean with wheat or corn. Higher levels of biological control agents (Trichoderma harzianum, Pochonia chlamydosporia, or Paecilomyces lilacinus) also were found in the long-term soybean cropping field. Therefore, continuous long-term cropping of soybean in black soil of Northeast China could develop suppressive soil to soybean root diseases.

Effect of long-term fertilization on free-living nematode community structure in Mollisols

The influence of long-term application of pig manure combined with chemical fertilizer (MCF) or chemical fertilizer (CF) on free-living nematodes was evaluated in this study. The application model of fertilizers lasted 14 years in Mollisols, and treatments included MCF, CF and no fertilizer (NF). A total of 26 free-living nematode genera belonging to seven functional guilds were found in maize fields, and the community structure of free-living nematodes was different in MCF, CF and NF. Pig manure increased the abundance of bacterivores, especially those belonging to c-p1 (Ba1) and c-p2 (Ba2) guilds. Channel index (CI) was higher in NF than in MCF and CF, but enrichment index (EI) was higher in MCF and CF compared to NF. The structure index (SI) was highest in NF among three treatments. Total bacterivores, Ba1 and Ba2 guilds were positively correlated to organic C, total N, available N, total P and available P, but fungivores only had correlation with organic C and soil moisture. The SI index was negatively related to organic C, total N, available N, total P and available P. Collectively, these results indicate that the pig manure or chemical fertilizer normally applied to increase soil nutrition also induce negative influence on soil food web structure as reflected from biological aspect, and that soil nematodes can enhance agroecological assessments of changes induced by long-term fertilizer application in maize field in Mollisols.

Soil fauna community in the black soil of Northeast China under different tillage systems

Soil fauna is an important component in soil ecosystems. This study tested whether conservation tillage or conventional tillage of a black soil (Udic Mollisol) field in Northeast China could affect its soil fauna communities. Two different conservation tillage systems, no-tillage (NT) and reduced tillage (RT), as well as a conventional rotary tillage system (CT), were chosen for this study. There were 4562 individuals isolated from this study, which included two orders and 35 families. Acariformes was the most abundant family and represented 91.56% of the total faunal abundance. The abundance and the number of faunal families were higher in conservation tillage systems than in the CT. The RT system had the highest individual number of soil fauna among three tillage methods. The faunal accumulation in the soil surface also was significantly higher in the two conservation tillage systems than in the CT. Our results indicate that the conservation tillage systems could protect the soil fauna in the soil ecosystem better than the CT.

Diversity of parasitic fungi from soybean cyst nematode associated with long-term continuous cropping of soybean in black soil

ABSTRACT The soybean cyst nematode (SCN) is a major yield-limiting pest of soybean. In this study, experiments were conducted to examine the diversity of parasitic fungi from SCN associated with disease-suppressive soil fields in Northeast China. Soil samples were collected from three fields under different rotation systems that were established in 1991: (1) a continuous long-term cropping field with soybean (SSSS) that had been shown to be SCN-suppressive, (2) cycles of three-year rotation with corn, soybean, and wheat (WCS), and (3) continuous cropping field with three-year cycles of two years soybean and one-year corn (SSC). In the traditional method result, cyst densities of SCN declined as increase of parasitic fungi, and the percentage of parasitic fungi associated with cyst of SCN was higher in SSSS field than other two fields. Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) also showed that parasitic fungi of SCN were also increased in SSSS field, compared with the other two fields. Principal component analysis based on PCR-DGGE data revealed that fungal communities on cysts could be divided into three groups: one group occurred in SSSS, and the other two groups were in WCS and SSC fields, respectively. Long-term cropping with soybean monoculture in the black soil field might increase parasitic fungi of SCN. These fungal communities may play an important role in the ecological suppression of SCN in disease-suppressive soil.

Colonization of Clonostachys rosea on soybean root grown in media inoculated with Fusarium graminearum

Soybean root rot, caused by Fusarium graminearum, is an important disease in Canada. Clonostachys rosea has been reported to provide protection against plant pathogens in different crops. The objectives of this study were to determine if a strain of C. rosea, ACM 941, can colonize soybean root that were grown in media inoculated with F. graminearum, and to determine if the distribution of C. rosea was different at different root depths. There were three treatments in this study, which included a control (CK) using normal seed without any fungal treatments; seed inoculated with ACM 941 (ACM); and seed inoculated ACM 941 and growing media inoculated with F. graminearum (ACM +Fg). Results showed that the colony forming unit (CFU) of ACM 941 was lower on the tap roots and secondary roots growing 8–13 cm below ground level than sections of roots growing 0–3 cm or 3–8 cm below ground level. ACM 941 was found in roots at the third day after soybean seed was planted, and maintained high CFU most of the time during soybean growth. Inoculation with F. graminearum had no effect on CFU of ACM 941. The ACM 941 strain colonized soybean root rapidly and was not affected by the existence of F. graminearum, suggesting that ACM 941 can successfully compete with F. graminearum, may have potential as an effective biocontrol agent for protecting soybean from the Fusarium root rot.

Assessment of parasitic fungi for reducing soybean cyst nematode with suppressive soil in soybean fields of northeast China

ABSTRACT Experiments were conducted to study the inhibitor factors present in suppressive soil that suppressed the soybean cyst nematode (SCN) in the black soil fields with 21 years continuous cropping of soybean (SSSS) and 3 years continuous cropping of soybean followed by 1 year corn (SSSC). Compared with the SSSC field, the densities of SCN significantly (P < 0.05) declined in SSSS field. In a soil microcosm with suppressive soil, the population of SCN decreased after the addition of pimaricin (fungal inhibitor) and streptomycin (bacterial inhibitor), but the population of SCN declined more significantly by adding streptomycin to the suppressive soil than adding pimaricin. Fusarium equiseti, Pochonia chlamydosporia and Purpureocillium lilacinum were isolated from cysts, eggs and J2 of SCN and soil in SSSS and SSC field. The population density of these parasitic fungi was significantly (P < 0.05) higher in SSSS field than in SSSC field. The density of P. chlamydosporia was higher than other fungi. Real-time PCR was used to test genomic DNA of P. chlamydosporia in SSSS and SSC field soil. The mass of genomic DNA and the population density of P. chlamydosporia were significantly (P < 0.05) higher in SSSS field than in SSSC field. This study has revealed that fungi, especially P. chlamydosporia, may play an important role in the suppression of SCN population in the suppressive soil.