Distribution of phosphatase activity and various bacterial phyla in the rhizosphere of Hordeum vulgare L. depending on P availability

Despite the importance of the rhizosphere for nutrient turnover, little is known about the spatial patterns of organic phosphorus mineralization by plants and by microorganisms in the rhizosphere. Therefore, the distribution of acid and alkaline phosphatase activity and the abundance of bacteria belonging to various bacterial phyla were investigated in the rhizosphere of barley (Hordeum vulgare L.) as dependent on the availability of inorganic P. For this purpose, we conducted a greenhouse experiment with barley growing in inclined boxes that can be opened to the bottom side (rhizoboxes), and applied soil zymography and fluorescence-in situ-hybridization (FISH). Acid phosphatase activity was strongly associated with the root and was highest at the root tips. Due to P fertilization, acid phosphatase activity decreased in the bulk soil, and less strongly in the rhizosphere. Alkaline phosphatase activity, i.e., microbial phosphatase activity was high throughout the soil in the control treatment and was reduced due to inorganic P fertilization especially in the rhizosphere and less strongly in the bulk soil. P-fertilization slightly increased the total number of bacteria in the rhizosphere. Moreover, P-fertilization decreased the abundance of Firmicutes and increased the abundances of Beta- and Gamma-Proteobacteria. The total number of bacterial cells was significantly higher at the root surface than at the root tip and at a distance of 30 μm from the root surface. Our results show that alkaline phosphatase activity decreased more strongly in the rhizosphere than in the bulk soil due to P fertilization, which might be because of greater C deficiency in the bulk soil compared to the rhizosphere. Furthermore, the results indicate a spatial separation between hotspots of acid phosphatase activity and hotspots of bacteria in the rhizosphere of H. vulgare. Taken together, our study shows that bacteria and phosphatase activity were very heterogeneously distributed in soil, and that the effects of P fertilization on phosphatase activity differed strongly between bulk soil and rhizosphere as well as between various zones of the rhizosphere.     

Forest biomass and root–shoot allocation in northeast China

Temperate and boreal forests act as major sinks for atmospheric CO₂. To assess the magnitude and distribution of the sinks more precisely, an accurate estimation of forest biomass is required. However, the determinants of large-scale biomass pattern (especially root biomass) are still poorly understood for these forests in China. In this study, we used 515 field measurements of biomass across the northeast part of China, to examine factors affecting large-scale biomass pattern and root–shoot biomass allocation. Our results showed that, Picea & Abies forest and coniferous & broadleaf mixed forest had the highest mean biomass (178–202 Mg/ha), while Pinus sylvestris forest the lowest (78 Mg/ha). The root:shoot (R/S) biomass ratio ranged between 0.09 and 0.67 in northeast China, with an average of 0.27. Forest origin (primary/secondary/planted forest) explained 31–37% of variation in biomass (total, shoot and root), while climate explained only 8–15%, reflecting the strong effect of disturbance on forest biomass. Compared with shoot biomass, root biomass was less limited by precipitation as a result of biomass allocation change. R/S ratio was negatively related to water availability, shoot biomass, stand age, height and volume, suggesting significant effects of climate and ontogeny on biomass allocation. Root–shoot biomass relationships also differed significantly between natural and planted forests, and between broadleaf and coniferous forests. Shoot biomass, climate and forest origin were the most important predictors for root biomass, and together explained 83% of the variation. This model provided a better way for estimating root biomass than the R/S ratio method, which predicted root biomass with a R² of 0.71.     

Soil sterilization effects on root growth and formation of rhizosheaths in wheat seedlings

Sterilized soils are frequently used in experiments related to soil biology. Soil sterilization is known to alter physicochemical characteristics of soil, plant growth and community structure of the newly developed bacterial population. However, little information exists regarding soil sterilization effects on belowground processes mediated through root–microbe–soil interactions, e.g., development of rhizosheaths which significantly promote the plant growth under stress environments. The present study was conducted to elucidate effects of soil sterilization on wheat root growth and formation of rhizosheaths in relation to chemical changes caused by soil sterilization and the proportion of expolysaccharide (EPS)-producers in bacterial population recolonizing the sterilized soils. Wheat plants were grown for two weeks under greenhouse conditions either in the unsterilized soil or in soils sterilized by autoclaving (121 °C, 1 h) or by gamma (γ)-irradiation (50 kGy). While soil sterilization had no effect on the release of macronutrients, both sterilization procedures significantly increased the electrical conductivity, water-soluble carbon and DTPA-extractable Mn. Seedlings grown in sterilized soils produced higher root biomass and the rhizosheath soil (RS) mass as compared to those grown in the unsterilized soil. Soil sterilization also increased the root length, surface area, volume and number of tips. In bulk soil, RS and on roots, the proportion of EPS-producers in the total bacterial population was higher in sterilized treatments than in the unsterilized. Amending the unsterilized soil with glucose-C increased the root biomass, whereas adding Mn II increased the RS mass. The results showed that soil sterilization by autoclaving or γ-irradiation increases the root growth and RS mass of wheat seedlings. The water-soluble C and DTPA-extractable Mn released upon sterilization, and the increased proportion of EPS-producers in the bacterial population recolonizing the sterilized soils were involved in the observed effects. The results may have implications in studies using autoclaved or γ-irradiated soils to investigate soil–plant–microbe interactions and signify the need to account for intrinsic stimulatory effects of soil sterilization.     

The effect of short day treatments on containerized Douglas-fir morphology,physiology and phenology

The effect of short day treatments (blackout) on Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) container seedlings at the time of lift and following cold storage was investigated. Variables measured included height, root collar diameter (RCD), root growth capacity (RGC), photosynthetic efficiency after –18 °C freezing (PEF), and days to terminal bud break (DBB). From one to four blackout dormancy induction treatments were started on three dates (July 12, July 26, and August 10) with 10 or 20 d between multiple blackouts. Increasing the number of blackout treatments resulted in lower RCD, lower DBB in the late winter/early spring, and higher PEF in the early fall. Later blackout start dates decreased PEF in the early fall, and increased overall height and late fall RGC as compared to earlier blackout start dates. Nurseries growing Douglas-fir seedlings from coastal Pacific Northwest provenances should be aware that blackout regimes can decrease RGC in the late fall, and cause quicker dormancy release in the early spring. Coastal Douglas-fir can be lifted and planted in the early fall, when RGC and DBB are relatively high. If planting between February and April is necessary, seedlings given blackout should be cold stored in January to maintain an adequate level of dormancy, RGC and PEF.     

Compatibility of root growth and tuber production of potato cultivars with dynamic and static water‐saving irrigation managements

The important root characteristics of root length density (RLD) and root mass density (RMD) generally differ among irrigation managements and potato cultivars. The objective of this study was to investigate the RLD and RMD variations and their functional relationships with gross potato tuber yield for two commercial potato cultivars, Agria and Sante, under different irrigation strategies. Full irrigation and water‐saving irrigation strategies, deficit and partial root drying irrigations, were applied statically (S) and dynamically (D) based on daily crop evapotranspiration. Results showed that SPRD had significantly greater RLD (3.64 cm/cm³) and RMD (132.7 μg/cm³) than other irrigation treatments. Between the potato cultivars, Agria had significantly larger values of RLD (3.50 cm/cm³) and RMD (138.7 μg/cm³) than Sante. The functional relationship between the root growth characteristics and tuber yield showed that under water‐saving irrigations, Agria increased root mass at the expense of gross tuber yield but Sante increased root mass to maintain larger gross tuber yields. However, Agria produced more roots and gross tuber yield than Sante, and it is concluded that Agria is a more drought‐tolerant potato cultivar, which is recommended for tuber production in regions where water might be scarce. It was shown that larger root production in potatoes was associated with improved tolerance to water stress.     

鸡痘病毒282E4株Bam HI部分片段的重组载体质粒构建与序列分析

在中国鸡痘病毒２８２Ｅ４弱毒株基因组部分ＢａｍＨＩ片段的质粒ｐＵＢ、ｐＵＣ、ｐＵＤ、ｐＵＤ２、ｐＵＥ和ｐＵＦ酶切分析的基础上,对ｐＵＦ进行了亚克隆获得ｐＵＦ－Ｅ和ｐＫＳ－Ｘ,对最可能存在非必需区的ｐＵＥ质粒进行了序列分析,改造了含Ｐ１１Ｐ７．５－ＬａｃＺ报告基因盒,并在上述质粒的相应单一酶切位点插入Ｐ１１Ｐ７．５－ＬａｃＺ报告基因盒,构建成ｐＵＢ１、ｐＵＦＣ１、ｐＵＦＥ１、ｐＵＦ－Ｅ１和ｐＫＳＦ－Ｘ１５个重组载体质粒。体内重组等工作正在进行中。     

Comparison of the Value of Pulsed-field Gel Electrophoresis,Random Amplified Polymorphic DNA and Amplified rDNA Restriction Analysis for Subtyping Taylorella equigenitalis

Eight strains of Taylorella equigenitalis were identified by a polymerase chain reaction using a primer pair specific to the 16S rDNA of T equigenitalis. These eight strains were chosen because they had previously been shown to represent eight distinct genotypes by pulsed-field gel electrophoresis analysis after separate digestion of the genomic DNA with ApaI or NotI. The eight strains could be classified into six or seven types by random amplified polymorphic DNA analysis using different kinds of primers. Amplified rDNA restriction analysis after separate digestion with five restriction enzymes, including AluI and MboI, of the 1,500 bp fragments of rDNA amplified by polymerase chain reaction did not discriminate the genomic variations among the eight strains of T equigenitalis. Thus, pulsed-field gel electrophoresis was shown to discriminate these eight organisms better than random amplified polymorphic DNA analysis, while amplified rDNA restriction analysis was found to be unsuitable for subtyping T equigenitalis.     

杂交苜蓿(Medicago varia Martyn)根系特性的研究

杂交苜蓿是野苜蓿 (M .falcata)和紫苜蓿 (M .sativaL .)的杂交后代 ,兼具亲本的许多优良性状 ,适于广泛栽培。对其在根系特性上所表现出的优势进行研究发现 :根颈处的劈裂将植株分为母株与子株 ,实现营养繁殖 ;位于茎基部的当年芽数量明显大于亲本 ,是地上生物量增长的基础 ;明显的缩根现象有利于茎基部和根颈顶部芽的产生和越冬 ;明显优于亲本的侧根与不定根 ,为根劈裂分株繁殖的植株提高地上生物量奠定了基础     

科尔沁沙地苜蓿根系和根颈特性

播种当年,苜蓿根重和根深因品种、播种期和耕深的不同而变化明显。结果表明,草原2号苜蓿总根量较高,入土较深,而敖汉苜蓿则较低较浅。播期越早根量越高,根系也越深,反之则较差。深耕能促进苜蓿根系的生长发育,增加根量和根深。播期越早根颈越粗,根重越高,分枝也越多,而晚播则下降。随着苜蓿生长年限的增加,根颈随之增粗,但根颈分枝数则以5年生苜蓿居多,尔后呈下降趋势。     

3种圭亚那柱花草根系分泌物对杂草幼苗生长的影响

为明确3种圭亚那柱花草(Stylosanthes guianensis Sw.)(‘热研2号’、‘热研5号’和热研21号)的根系分泌物对杂草生长的化感效应,采用营养液培法分别收集其根系分泌物,研究其对5种外来入侵杂草幼苗形态特征及生物量分配的影响。结果表明,除对含羞草(Mimosa pudica L.)幼苗无显著影响外,3种圭亚那柱花草对其余4种杂草的总化感综合效应均为抑制作用。‘热研5号’柱花草对杂草幼苗生长的化感抑制效应强于其他二者,对蒺藜草(Cenchrus echinatus L.)幼苗的根长、株高、地下生物量、地上生物量、总生物量和根冠比均有显著抑制效应(P<0.05),对羽芒菊(Tridax procumbens L.)幼苗的侧根数、地下生物量和根冠比有显著抑制效应(P<0.05),也显著抑制假臭草(Eupatorium catarium V.)幼苗的生物量向地下分配(P<0.05),仅对鬼针草(Bidens pilosa L.)幼苗的抑制效应相对较弱。灰色关联分析表明,进行圭亚那柱花草的化感效应研究中应重点关注总生物量、地上生物量和株高。由此推测,3种圭...