Soil fumigation and compost amendment alter soil microbial community composition but do not improve tree growth or yield in an apple replant site

Apple replant disease (ARD) is a disease complex that reduces survival, growth and yield of replanted trees, and is often encountered in establishing new orchards on old sites. Methyl bromide (MB) has been the fumigant used most widely to control ARD, but alternatives to MB and cultural methods of control are needed. In this experiment, we evaluated the response of soil microbial communities and tree growth and yield to three pre-plant soil treatments (compost amendment, soil treatment with a broad-spectrum fumigant, and untreated controls), and use of five clonal rootstock genotypes (M.7, M.26, CG.6210, G.30 and G.16), in an apple replant site in Ithaca, New York. Polymerase chain reaction (PCR)—denaturing gradient gel electrophoresis (DGGE) analysis was used to assess changes in the community composition of bacteria and fungi in the bulk soil 8, 10, 18 and 22 months after trees were replanted. PCR-DGGE was also used to compare the community composition of bacteria, fungi and pseudomonads in untreated rhizosphere soil of the five rootstock genotypes 31 months after planting. Tree caliper and extension growth were measured annually in November from 2002 to 2004. Apple yield data were recorded in 2004, the first fruiting year after planting. Trees on CG.6210 rootstocks had the most growth and highest yield, while trees on M.26 rootstocks had the least growth and lowest yield. Tree growth and yield were not affected by pre-plant soil treatment except for lateral extension growth, which was longer in trees growing in compost-treated soil in 2003 as compared to those in the fumigation treatment. Bulk soil bacterial PCR-DGGE fingerprints differed strongly among the different soil treatments 1 year after their application, with the fingerprints derived from each pre-plant soil treatment clustering separately in a hierarchical cluster analysis. However, the differences in bacterial communities between the soil treatments diminished during the second year after planting. Soil fungal communities converged more rapidly than bacterial communities, with no discernable pattern related to pre-plant soil treatments 10 months after replanting. Changes in bulk soil bacterial and fungal communities in response to soil treatments had no obvious correlation with tree performance. On the other hand, rootstock genotypes modified their rhizosphere environments which differed significantly in their bacterial, pseudomonad, fungal and oomycete communities. Cluster analysis of PCR-DGGE fingerprints of fungal and pseudomonad rhizosphere community DNA revealed two distinct clusters. For both analyses, soil sampled from the rhizosphere of the two higher yielding rootstock genotypes clustered together, while the lower yielding rootstock genotypes also clustered together. These results suggest that the fungal and pseudomonad communities that have developed in the rhizosphere of the different rootstock genotypes may be one factor influencing tree growth and yield at this apple replant site.     

Incorporation of tracers and dazomet by rotary tillers and a spading machine

Soil fumigant efficacy in forest-tree and ornamental nurseries depends on the tillage tool used for incorporation. Maximum depth and uniformity of incorporation of surface applied materials by three rotary tillers and a spading machine were compared in a loamy sand nursery using ceramic-sphere tracers (1–3 mm diameter) and dazomet (tetrahydro-3,5,dimethyl-2H-1,3,5-thiadiazone-2-thione) micro-granules. Depth of incorporation in the top 30 cm of soil was evaluated by (1) recovery of incorporated spheres in 2 cm increments, (2) biocidal activity in 6 cm increments, and (3) cone resistance by 1.5 cm increments to 45 cm. Uniformity of incorporation was evaluated by sphere recovery and biocidal activity. Depths above which more than 95% of the spheres were recovered for the four implements were: 12.5 cm, Kuhn and Fobro rotary tillers; 17 cm, Northwest rotary tiller; 21 cm, Gramegna spading machine. The spading machine produced a distribution of spheres through the soil profile closest to a uniform distribution compared with that produced by the three rotary tillers. Lettuce seed (Lactuca sativa L.) germination was inhibited in the upper 12 cm in low and high dazomet rate treatments, indicating that all four implements effectively incorporated dazomet into that zone. Maximum depth (24 cm) for total inhibition of germination was observed for the spading machine regardless of chemical rate. Cone index values showed the following maximum penetration: 14 cm, Fobro rotary tiller; 22 cm, Kuhn and Northwest rotary tillers; 27 cm, spading machine. All three measures of depth show a distinct superiority of the spading machine when the chemical fumigant must reach depths greater than 18 cm. Within transects across the width of the implement, variations of sphere counts among 5 cm³ volumes were much larger for the rotary tillers than for the spade machine.     

Seasonal fluctuations in soil microbial biomass carbon,phosphorus, and activity in no-till and reduced-chemical-input maize agroecosystems

Summary The soil microbial biomass contains important labile pools of C, N, P, and S, and fluctuations in its size and activity can significantly influence crop productivity. In cropping systems where fertilizer use is reduced or eliminated and green-manure legumes are used, nutrient availability is more directly linked to C-cycle dynamics. We observed the fluctuations in microbial biomass C and P, and in microbial biomass activity over three cropping seasons in continuous maize and 2-year maize-wheat-soybean rotation agroecosystems under no-till and reduced-chemical-input management. We estimated the concentrations of microbial C and P using fumigation-incubation and fumigation-extraction techniques for the surface 20 cm of Cecil and Appling series soils (clayey, kaolinitic, thermic, Typic Kanhapludults). There were significant seasonal fluctuations in microbial C and P under all cropping systems. Generally, the magnitude of fluxes and the quantity of microbial C and P tended to be higher in reduced-chemical-input systems due to tillage and incorporation of crop, weed, and legume residues. Over 3 years, the means for microbial C were 435 under reduced-input maize; 289 under no-till maize; 374 und the reduced-input crop rotation; and 288 mg kg^-1 soil under the no-till rotation. The means for microbial P were 5.2 under reduced-input maize; 3.5 under no-till maize; 5.0 under the reduced-input rotation; and 3.5 mg kg^-1 soil under the no-till rotation. Estimates of microbial activity, derived from CO₂–C evolution and specific respiratory activity (mg CO₂–C per mg biomass C), suggest that reduced-chemical-input management may cause a larger fraction of the biomass to be relatively inactive but may also increase the activity of the remaining fraction over that in no-till. Thus in these specific systems, the turnover of C and P through the microbial biomass with a reduced chemical input to the soil may be higher than under a no-till system.     

不同载体对DDVP熏蒸田间防治大豆食心虫效果的影响

以海绵、粉笔、玉米芯3种材料为载体,进行了DDVP熏蒸防治大豆食心虫成虫效果的比较研究,结果表明,在3种载体中,以海绵效果最好,玉米芯次之,粉笔最差。同时,针对DDVP熏蒸防治大豆食心虫成虫的有效距离进行了测定,结果显示,DDVP熏蒸防治大豆食心虫成虫的有效距离为2.6m(36h内靶标死亡率100%),田间有效防治的载体单元投放量不能少于25个/667m2。风对DDVP熏蒸效果有影响,但在大面积应用时,风的影响可被多点的传递效应所抵消。     

蒌蒿杀虫成分的微波辅助提取及生物活性测定

[目的]研究蒌蒿杀虫成分对菜粉蝶的生物学活性。[方法]在微波辅助加热条件下,以乙醇、乙醚、水、甲苯为溶剂对蒌蒿进行浸提,测定各溶剂提取物对菜粉蝶幼虫的拒食、胃毒、触杀和熏蒸活性。[结果]各溶剂提取物对菜粉蝶幼虫均表现出一定的拒食、胃毒、触杀和熏蒸活性,其中,以乙醇提取物的生物活性最强。[结论]该研究结果可为开发利用蒌蒿植物源杀虫剂提供参考。     

1-MCP对鹤望兰切花贮运期间生理代谢的影响

在常温(25℃)与冷藏(12℃)下用1-MCP熏蒸鹤望兰鲜切花,对其贮运期间生理代谢的影响进行研究。结果表明,在两种温度下,1-MCP各浓度处理切花的失水率均随着贮运时间的延长而递增,并呈极显著的相关性;中等浓度处理(1.0~4.0μl/L)均极显著地抑制切花乙烯的释放、降低花瓣相对膜透性、提高次花开放率和保鲜率,显著地抑制切花失水,从而延长鹤望兰的贮运期,并以2.0μl/L的处理效果最好;低浓度(0.2μl/L)处理的各项生理代谢指标也受到不同程度的抑制,但强度较弱;高浓度(8.0μl/L)处理反而促使切花提前衰败,缩短贮运期。除高浓度处理外,冷藏贮运的保鲜效果均好于常温贮运。但无论是冷藏还是常温下,1-MCP对鹤望兰贮运保鲜的最佳处理浓度均为2.0μl/L。     

肉桂精油防控玉米霉变的研究

[目的]拟利用内桂精油的挥发性、天然安全性和广谱抑菌特性,对玉米颗粒进行防霉研究.[方法]采用精油熏蒸的方法,将玉米颗粒置于自制的密闭容器中,人工模拟高温高湿条件对其进行肉桂精油熏蒸.[结果]研究表明,玉米颗粒的含水量对其霉变的影响很大.空气湿度为75％时,空间浓度分别为175和100 μl/L的肉桂精油对玉米颗粒霉菌的熏杀抑制效果随着熏蒸时间的延长而逐渐提高,熏蒸时间为8d时达到了最高的抑菌率.高湿高温条件下,肉桂精油空间浓度为1 000～2000 μl/L是最适抑菌浓度区间,其中精油浓度2000 μl/L为最佳抑菌浓度.[结论]研究可为玉米储藏的防霉工作提供理论依据.     

熏蒸直接提取法测定土壤MB－S中几个因素的研究

就影响薰蒸直接提取法测定土壤ＭＢ－Ｓ的一些因素（预培养时间和土壤湿度，氯仿消杀时间，浸提剂与土壤比例和振荡时间）进行了研究，提出了适用于一般实验室测定土壤ＭＢ－Ｓ的较好程序。     

青海高寒草甸不同植被土壤微生物生物量的测定

以青海高寒草甸不同植被类型土壤为研究对象,采用氯仿熏蒸浸提法对土壤微生物生物量碳进行了测定分析。结果表明:不同植被类型土壤中微生物生物量的大小依次为:沼泽草甸>小嵩草草甸>金露梅灌从草甸>禾草草甸>矮嵩草草甸>金露梅灌丛间草地>杂类草草甸,随着土壤深度的增加,生物量呈下降趋势。相关分析表明:微生物生物量碳与土壤水分含量、真菌数量呈显著的正相关;细菌数量、放线菌数量与微生物量碳的相关性不显著。结论:土壤真菌是土壤微生物生物量的主要贡献者,土壤水分含量对土壤微生物代谢、繁殖有着直接的作用。     

Ergosterol and microbial biomass relationship in soil

Ergosterol and microbial biomass C were measured in 26 arable, 16 grassland and 30 forest soils. The ergosterol content ranged from 0.75 to 12.94 g g^-1 soil. The geometric mean ergosterol content of grassland and forest soils was around 5.5 g g^-1, that of the arable soils 2.14 g g^-1. The ergosterol was significantly correlated with biomass C in the entire group of soils, but not in the subgroups of grassland and forest soils. The geometric mean of the ergosterol: microbial biomass C ratio was 6.0 mg g^-1, increasing in the order grassland (5.1), arable land (5.4) and woodland (7.2). The ergosterol:microbial biomass C ratio had a strong negative relationship with the decreasing cation exchange capacity and soil pH, indicating that the fungal part of the total microbial biomass in soils increased when the buffer capacity decreased. The average ergosterol concentration calculated from literature data was 5.1 mg g^-1 fungal dry weight. Assuming that fungi contain 46% C, the conversion factor from micrograms ergosterol to micrograms fungal biomass C is 90. For soil samples, neither saponification of the extract nor the more effective direct saponification during extraction seems to be really necessary.