Biological soil crusts promote N accumulation in response to dew events in dryland soils

Dew is an important source of water in drylands, particularly for biological soil crusts (BSCs), which are soil communities dominated by lichens, mosses and cyanobacteria that are prevalent in these environments and play important roles in nutrient cycling. While BSCs can retain and use water from dew, the effects of dew events on the cycling of nitrogen (N) and carbon (C) in BSC-dominated ecosystems are largely unknown. We conducted an experiment to evaluate the effects of BSCs and dew on N and C cycling; intact soil cores from either bare ground or BSC-dominated microsites were incubated over 14 days under control and artificial dew addition treatments. A positive increment in the amount of total available N and phenols was observed in response to dew events under BSCs. We also found an increase in the concentration of dissolved organic N, as well as in the pentoses:hexoses ratio, under BSCs, suggesting that dew promoted an increase in the decomposition of organic matter at this microsite. The increase in the amount of available N commonly observed under BSCs has been traditionally associated with the fixation of atmospheric N₂ by BSC-forming cyanobacteria and cyanolichens. Our results provide a complementary explanation for such an increase: the stimulation of microbial activity of the microorganisms associated with BSCs by dew inputs. These effects of dew may have important implications for nutrient cycling in drylands, where dew events are common and BSCs cover large areas.     

Trichothecene production is detrimental to early root colonization by Fusarium culmorum and F. graminearum in fusarium crown and root rot of wheat

Fusarium culmorum (Fc) and F. graminearum (Fg) belong to the predominant causal agents of fusarium crown and root rot (FCR) in wheat. While many studies have been done to investigate crown rot, including stem base infection, root colonization and mycotoxin production associated with root rot is not well understood. In this study the impact of mycotoxins on the colonization of wheat roots and stem bases was analysed by using Fc and Fg isolates that varied in both quantity and types of trichothecenes they produce. Seedling inoculations in growth chambers with a high deoxynivalenol (DON)- and 3-acetyldeoxynivalenol (3ADON)-producing isolate led to more severe symptoms and 20-times greater colonization of the stem base, as measured by Fc DNA accumulation, than isolates that produced less DON/3ADON. In contrast to stem base colonization, in vitro inoculations of roots with a Tri5 deletion mutant deficient in Fg trichothecene production led to three-times higher colonization than the wildtype. Furthermore, an Fc isolate that produced low levels of zearalenone resulted in twice the level of colonization of a high DON/3ADON-producing isolate included in the study. When root inoculation with a low DON/3ADON-producing Fc isolate was supplemented with exogenous DON, DON production decreased by more than half per unit weight of Fc DNA, and root colonization doubled compared to the untreated control. Therefore, in contrast to its potential role as an aggressiveness factor in stem base infection, trichothecene production by Fc and Fg is detrimental to the early stages of wheat root colonization in FCR.     

粮食中DON-免疫亲和层析净化高效液相色谱法的回收率方法比较

用免疫亲和层析净化高效液相色谱法测定粮食中的脱氧雪腐镰刀菌烯醇,且与GB/T 23503-2009《食品中脱氧雪腐镰刀菌烯醇的测定免疫亲和层析净化高效液相色谱法》、Romer labs实验室推荐方法、实验室优化方法进行比较。本实验方法在前两种方法的基础上优化后,在0.5mg/kg~5mg/kg的加标水平下,回收率在90.3%~100.2%,RSD在1.2%~2.0%之间,最低检出限则为44μg/kg,定量限为146μg/kg,能够很好的满足实验室分析要求。     

氰烯·戊唑醇不同用药时间和次数对小麦赤霉病及DON毒素的管控效果

扬花初期是防控小麦赤霉病的最佳时期,为了探索错过扬花初期用药补防对小麦赤霉病和毒素的管控效果,本试验选择姜堰地区存在的13个小麦品种,用48%氰烯·戊唑醇SC进行赤霉病防控,通过扬花初期漏防6天后补防1次和扬花初期用药1次、扬花初期用药2次3种方式,对各品种小麦赤霉病防效和DON毒素控减效果进行比较。结果表明：错过扬花初期6天后用48%氰烯·戊唑醇补防1次,对各品种赤霉病的平均病穗率和病指防效、DON毒素控减效果比扬花初期防治1次分别低15.87%、21.25%、35.48%,比扬花初期用药2次分别低39.79%、44.87%、66.84%。赤霉病最适首次防治时间是扬花初期,扬花初期漏防6天后补防1次,对赤霉病和DON毒素的管控效果较差,坚持扬花初期+6天后两次用药效果最好,在各个品种中该趋势表现一致。     

Soil- and enantiomer-specific metabolism of amino acids and their peptides by Antarctic soil microorganisms

Most nitrogen (N) enters many Arctic and Antarctic soil ecosystems as protein. Soils in these polar environments frequently contain large stocks of proteinaceous organic matter, which has decomposed slowly due to low temperatures. In addition to proteins, considerable quantities of d-amino acids and their peptides enter soil from bacteria and lengthy residence times can lead to racemisation of l-amino acids in stored proteins. It has been predicted that climate warming in polar environments will lead to increased rates of soil organic N turnover (i.e. amino acids and peptides of both enantiomers). However, our understanding of organic N breakdown in these soils is very limited. To address this, we tested the influence of chain length and enantiomeric composition on the rate of breakdown of amino acids and peptides in three contrasting tundra soils formed under the grass, moss or lichen-dominated primary producer communities of Signy Island in the South Orkney Islands. Both d- and l-enantiomers of the amino acid monomer were rapidly mineralized to CO₂ at rates in line with those found for l-amino acids in many other terrestrial ecosystems. In all three soils, l-peptides were decomposed faster than their amino acid monomer, suggesting a different route of microbial assimilation and catabolism. d-peptides followed the same mineralization pattern as l-peptides in the two contrasting soils under grass and lichens, but underwent relatively slow decomposition in the soil underneath moss, which was similar to the soil under the grass. We conclude that the decomposition of peptides of l-amino acids may be widely conserved amongst soil microorganisms, whereas the decomposition of peptides of d-amino acids may be altered by subtle differences between soils. We further conclude that intense competition exists in soil microbial communities for the capture of both peptides and amino acids produced from protein breakdown.     

Earthworms promote the reduction of Fusarium biomass and deoxynivalenol content in wheat straw under field conditions

A field experiment was conducted to elucidate ecosystem services provided by earthworms on the repression of phytopathogenic and toxinogenic fungi. The study focussed on decomposing Fusarium culmorum-infected and deoxynivalenol (DON)-contaminated wheat straw remaining on the soil surface as part in conservation tillage. Mesocosms were established in the topsoil of a winter wheat field located in Northern Germany, where conservation tillage has been practised for 20 years. Besides a non-earthworm treatment, two earthworm species were inoculated in the mesocosms either separately or combined: Lumbricus terrestris (anecic, detritivorous) and Aporrectodea caliginosa (endogeic, geophagous). The earthworms were exposed either to artificially Fusarium-infected wheat straw highly contaminated with DON or to non-infected straw serving as a control. The experiment was conducted during an eight week period after harvest from mid August to mid October. For both species, the artificially Fusarium-infected and DON-contaminated wheat straw was a more attractive food source than the non-infected control. In contrast to A. caliginosa, L. terrestris incorporated infected straw faster into the soil compared to control straw. Furthermore, the reduction of Fusarium biomass and DON concentration in wheat straw was significantly higher in the presence of L. terrestris than in treatments with A. caliginosa and without earthworms. Here, no significant differences could be measured between the Fusarium biomass and DON concentration in wheat straw. A. caliginosa seems not to be relevant for the reduction of Fusarium biomass and DON concentration. We concluded that amongst earthworms, anecic detritivorous species are the drivers to compensate possible negative consequences (like crop infection) of conservation tillage. They take an important role in the control of phytopathogenic and toxinogenic fungi surviving on plant residues and in the degradation of their mycotoxins.     

禾谷镰刀菌粗毒素的生物活性及其在小麦品种抗赤霉病性鉴定中的应用

 用小麦黄化芽鞘生物测定法探测禾谷镰刀菌粗毒素的生物活性，以及不同抗性小麦品种对粗毒素的反应。以纯脱氧雪腐镰刀菌烯醇（DON）作比较，证明了粗毒素具有与纯毒素DON相同的生物活性。对粗毒素在抗赤霉病性鉴定应用的初步探讨中，明确了小麦品种对粗毒素的敏感性与其在田间的抗赤霉病性呈负相关。     

禾谷镰刀菌组蛋白乙酰转移酶FgHat1在DON毒素生物合成中的功能

 由禾谷镰刀菌引起的小麦赤霉病是小麦最主要的真菌病害之一。禾谷镰刀菌侵染小麦时分泌脱氧雪腐镰刀菌烯醇(DON)真菌毒素,威胁人畜健康。本研究通过对组蛋白乙酰转移酶基因FgHAT1的功能研究,发现该基因编码的蛋白定位于细胞核并调控组蛋白H4的乙酰化。Fghat1敲除突变体在生长发育和致病过程中表现正常,但毒素合成存在显著缺陷。敲除FgHATI导致参与DON毒素合成的TRI基因转录水平降低,突变体产毒相关的细胞分化也表现异常。外源添加cAMP可以有效回复突变体的产毒缺陷,表明FgHat1对毒素的调控与cAMP信号通路有关。研究结果表明组蛋白表观修饰和胞内信号通路之间存在联系,这两者的交叉互作对DON毒素合成的精确调控至关重要。     

有机无机肥配施模式对氮素淋失的影响

为了探索农田氮素淋失低风险的有机无机肥配施模式,该研究收集了331个有效农田有机肥化肥配施数据对,分析了施肥总量、施肥结构（有机肥替代比）、施肥时间（基追施）、有机肥种类等因素对氮素淋失的总体影响。结果表明：与单施化肥相比,有机肥配施化肥中氮素总量较低时（N<200 kg/hm2）,农田总氮（Total Nitrogen,TN）、硝态氮（NO3--N）淋失分别减少36.77%、65.05%;有机肥替代比高于70%,虽然可减少TN淋失（39.64%）,但增加了溶解性有机氮（DON）淋失的风险（15.78%）,尤其是动物型有机肥替代化肥使DON淋失增加26.31%;氮肥基施可显著降低TN、NO3--N淋失（43.58%、70.51%,P<0.05）。碱性旱地土壤上有机肥配施化肥可有效抑制TN、NO3--N淋失,但增加了26.63%～42.95%的DON淋失。旱地氮素淋失以NO3--N为主,且淋失系数高于水田,提高有机肥替代比可以大幅降低旱地氮素淋失,但增强了DON淋失。因子重要性分析表明：有机肥替代比对TN淋失影响占主导作用,而施氮水平对NO3--N、DON淋失影响更为重要。因此,低施氮量、高替代比动物型有机肥可有效减少碱性旱地土壤氮素淋失,为有机肥配施化肥的农田应用提供依据。