Effects of Soil Texture on the Growth of Young Apple Trees and Soil Microbial Community Structure Under Replanted Conditions

A two-year field experiment was carried out in order to study the occurrence degree and mechanism of apple replant disease(ARD)in the apple orchards with different soil textures.So we can adopt appropriate controlmeasures according to the severity of ARD.Healthy two-year-old seedlings with consistent growth were selected,of which the root stock was T337 and the scion was Yanfu 3.There were significant differences in biomass between methyl bromide fumigation and replanted treatments,and the difference was the largest in clay loam,followed by sandy loam,and loam,which verified ARD in clay loam was most serious,followed by sandy loam and loam.Based on high-throughput sequencing of fungi in soil samples,fungal richness and diversity were the highest in clay loam,followed by sandy loam,and loam.The relative abundance of Fusarium in SX,SL,FX,FL,WX and WL was 7.33%,19.32%,2.70%,4.24%,10.71%and 23.87%,respectively.Based on Real-time quantitative analysis,there were significant differences in the number of Fusarium oxysporum and Fusarium solani between methyl bromide fumigation and replanted treatments,i.e.,clay loam>sandy loam>loam.Fusarium was the main pathogen causing ARD.This shows that ARD is the most serious under replanted clay loam condition.High-throughput sequencing technology was used to prove the difference in Fusarium was one of the important reasons for ARD under different soil textures.This technology provides a new idea for the prevention and control of ARD.

A conserved arbuscular mycorrhizal fungal core-species community colonizes potato roots in the Andes

Plant-symbiotic arbuscular mycorrhizal fungi(AMF)are of high global ecological and economic importance,but describing environmental communities of AMF at the species level remains a challenge,despite the need to understand AMF-plant preferences and to apply AMF in sustainable agriculture.Here,the potato-associated AMF species community composition was assessed for three Andean countries along an altitudinal gradient and at different plant stages,by using 454 GS-FLX+sequencing of a 760 bp LSU rRNA gene PCR amplicon.Two methods were compared:defining OTUs based on a simple sequence similarity threshold,or affiliating reference sequences to species based on a high throughput phylogenetic annotation approach using an evolutionary placement algorithm(EPA).The EPA-based approach was not only more precise,but also fundamental to robustly unveil the AMF species community composition.The principal advantage of this approach was also demonstrated by using artificially constructed datasets based on validated public database sequences.The affiliation of sequence reads to species using phylogenetic annotation revealed a surprisingly conserved AMF core-species community structure in Andean potatoes,regardless of different plant stages and environmental factors.In total,41 species were detected and in some cases more than 25 species were found colonizing an individual root system.Acaulospora species were identified as dominant colonizers,co-occurring with Cetraspora nodosa and certain Claroideoglomus and Rhizophagus species in most potato root samples.

Temperature and Straw Quality Regulate the Microbial Phospholipid Fatty Acid Composition Associated with Straw Decomposition

Variations in temperature and moisture play an important role in soil organic matter(SOM) decomposition. However, relationships between changes in microbial community composition induced by increasing temperature and SOM decomposition are still unclear.The present study was conducted to investigate the effects of temperature and moisture levels on soil respiration and microbial communities involved in straw decomposition and elucidate the impact of microbial communities on straw mass loss. A 120-d litterbag experiment was conducted using wheat and maize straw at three levels of soil moisture(40%, 70%, and 90% of water-holding capacity)and temperature(15, 25, and 35?C). The microbial communities were then assessed by phospholipid fatty acid(PLFA) analysis.With the exception of fungal PLFAs in maize straw at day 120, the PLFAs indicative of Gram-negative bacteria and fungi decreased with increasing temperatures. Temperature and straw C/N ratio significantly affected the microbial PLFA composition at the early stage, while soil microbial biomass carbon(C) had a stronger effect than straw C/N ratio at the later stage. Soil moisture levels exhibited no significant effect on microbial PLFA composition. Total PLFAs significantly influenced straw mass loss at the early stage of decomposition, but not at the later stage. In addition, the ratio of Gram-negative and Gram-positive bacterial PLFAs was negatively correlated with the straw mass loss. These results indicated that shifts in microbial PLFA composition induced by temperature, straw quality, and microbial C sources could lead to changes in straw decomposition.