Gas exchange, biomass partition, and water relationships of three grass seedlings under water stress

Three grass species, switchgrass ( Panicum virgatum ), foxtail millet ( Setaria italica ), and Old World bluestem ( Bothriochloa ischaemum ), referred to as introduced, traditional, and indigenous species, respectively, in the Loess hilly gully region on Loess Plateau in China, were grown in a growth chamber. Water was withheld to let the soil gravimetric moisture content (SGMC) decline gradually from 14.92% for 15 days. The gas exchange characteristics, leaf water conditions, root and shoot growth, and water use efficiency (WUE) of the three grasses were compared. The SGMC of foxtail millet declined faster than that of switchgrass and Old World bluestem, and it maintained higher leaf water potential at a lower soil water content, indicating that it might have greater drought tolerance. During the process of soil drying, the stomatal conductance (Gs), photosynthesis rate, and transpiration rate (Tr) of foxtail millet and Old World bluestem declined linearly, whereas those of switchgrass declined parabolically. The Gs of each grass was significantly different between the stressed and well-watered (WW) conditions. When the SGMC declined to ≈ 11.0%, 9.5%, and 8.6%, respectively, the leaf water potential was significantly different between the two growing conditions, showing the appearance of non-hydraulic and hydraulic signals. As a result of greater stomatal adjustment ability and a smaller Gs, foxtail millet had a high WUE. Among the three grasses, switchgrass had a high Tr and root/shoot (R/S) ratio under both WW and stressed conditions, and water stress significantly improved its R/S ratio. The results showed that foxtail millet seedlings have the best drought adaptability in the flexible soil–water environment, whereas switchgrass seedlings have the worst, but a high R/S ratio might be advantageous under drought conditions once the seedlings are established.     

Gross nitrogen transformations and N_2O emission sources in sandy loam and silt loam soils

The soil type is a key factor influencing N(nitrogen) cycling in soil; however, gross N transformations and N_2O emission sources are still poorly understood. In this study, a laboratory ~(15)N tracing experiment was carried out at 60% WHC(water holding capacity) and 25℃ to evaluate the gross N transformation rates and N_2O emission pathways in sandy loam and silt loam soils in a semi-arid region of Heilongjiang Province, China. The results showed that the gross rates of N mineralization, immobilization, and nitrification were 3.60, 1.90, and 5.63 mg N/(kg·d) in silt loam soil, respectively, which were 3.62, 4.26, and 3.13 times those in sandy loam soil, respectively. The ratios of the gross nitrification rate to the ammonium immobilization rate(n/ia) in sandy loam soil and silt loam soil were all higher than 1.00, whereas the n/ia in sandy loam soil(4.36) was significantly higher than that in silt loam soil(3.08). This result indicated that the ability of sandy loam soil to release and conserve the available N was relatively poor in comparison with silt loam soil, and the relatively strong nitrification rate compared to the immobilization rate may lead to N loss through NO_3~– leaching. Under aerobic conditions, both nitrification and denitrification made contributions to N_2O emissions. Nitrification was the dominant pathway leading to N_2O production in soils and was responsible for 82.0% of the total emitted N_2O in sandy loam soil, which was significantly higher than that in silt loam soil(71.7%). However, the average contribution of denitrification to total N_2O production in sandy loam soil was 17.9%, which was significantly lower than that in silt loam soil(28.3%). These results are valuable for developing reasonable fertilization management and proposing effective greenhouse gas mitigation strategies in different soil types in semiarid regions.     

Effects of three types of soil amendments on yield and soil nitrogen balance of maize-wheat rotation system in the Hetao Irrigation Area,China

Excessive fertilization combined with unreasonable irrigation in farmland of the Hetao Irrigation Area (HIR), China, has resulted in a large amount of nitrogen (N) losses and agricultural non-point source pollution. Application of soil amendments has become one of the important strategies for reducing N losses of farmland. However, there is still no systematic study on the effects of various soil amendments on N losses in the HIR. In this study, three types of soil amendments (biochar, bentonite and polyacrylamide) were applied in a maize-wheat rotation system in the HIR during 2015-2017. Yields of maize and wheat, soil NH₃ volatilization, N₂O emission and NO₃^- leaching were determined and soil N balance was estimated. The results showed that applications of biochar, bentonite and polyacrylamide significantly increased yields of maize by 9.2%, 14.3% and 13.3%, respectively, and wheat by 9.2%, 16.6% and 12.3%, respectively, compared with the control (fertilization alone). Applications of biochar, bentonite and polyacrylamide significantly reduced soil N leaching by 23.1%, 35.5% and 27.1%, soil NH₃-N volatilization by 34.8%, 52.7% and 37.8%, and soil N surplus by 23.9%, 37.4% and 30.6%, respectively. Applications of bentonite and polyacrylamide significantly reduced N₂O-N emissions from soil by 37.3% and 35.8%, respectively, compared with the control. Compared with application of biochar, applications of bentonite and polyacrylamide increased yields of maize and wheat by 5.1% and 3.5%, respectively. Our results suggest that soil amendments (bentonite and polyacrylamide) can play important roles in reducing N losses and increasing yield for the maize-wheat rotation system in the HIR, China.     

Elevated CO2 increases shoot growth but not root growth and C:N:P stoichiometry of Suaeda aralocaspica plants

The purpose of the current study was to investigate the eco-physiological responses, in terms of growth and C:N:P stoichiometry of plants cultured from dimorphic seeds of a single-cell C₄ annual Suaeda aralocaspica (Bunge) Freitag and Schütze under elevated CO₂. A climatic chamber experiment was conducted to examine the effects of ambient (720 μg/L) and CO₂-enriched (1440 μg/L) treatments on these responses in S. aralocaspica at vegetative and reproductive stages in 2012. Result showed that elevated CO₂ significantly increased shoot dry weight, but decreased N:P ratio at both growth stages. Plants grown from dimorphic seeds did not exhibit significant differences in growth and C:N:P stoichiometric characteristics. The transition from vegetation to reproductive stage significantly increased shoot:root ratio, N and P contents, but decreased C:N, C:P and N:P ratios, and did not affect shoot dry weight. Moreover, our results indicate that the changes in N:P and C:N ratios between ambient and elevated CO₂ are mainly caused by the decrease of N content under elevated CO₂. These results provide an insight into nutritional metabolism of single-cell C₄ plants under climate change.     

水钾耦合对花生根系形态及产量的影响

为优化花生生长发育的水钾耦合模式,以花育25为试验材料,采用盆栽试验,研究了花生根系形态及产量对水钾耦合效应的响应。结果表明,灌溉是关键因素,对根长具有显著影响,对根系生物量、根瘤数、根系平均直径、根系总体积、根系总表面积和荚果干产量均具有极显著影响。水分轻度胁迫W2(50%FC,FC为田间持水量)有利于根系的伸长,而湿润的土壤环境利于根系的增粗。各项指标水分效应平均值显示,W2处理根系总长最大,较水分适中W3(65%FC)提高了9.22%;根系直径W4(80%FC)W3(65%FC)W2(50%FC)W1(35%FC)。根系总表面积和总体积均随水分增多先增后减,最大值均在W3处理。增施钾肥利于根系生长发育,钾肥效应平均值显示,根系总体积、总表面积和总长均表现为K3(405 kg·hm~(-2))K2(270 kg·hm~(-2))K1(135 kg·hm~(-2))K0(0 kg·hm~(-2));根系生物量中钾(K2)和高钾(K3)处理分别较对照(K0)提高23.18%和9.27%。水钾耦合效应对根瘤数的影响达极显著水平,干旱情况下钾肥能促进根瘤的形成,在水分胁迫W1(35%FC)和轻度胁迫W2下,花生根瘤数随着施钾量的增加增大的趋势明显。适水中钾W3K2处理可以促进根系平均直径、总长、总表面积和总体积,该处理下的荚果产量最高,与同组不施钾处理(W3K0)相比增产12.7%。本试验条件下,水分控制在65%田间持水量,钾肥用量为270 kg·hm~(-2)时有利于促进根系的生长和根瘤的形成,提高产量,实现节水节肥。     

金合欢醇和烟碱对苹果黄蚜联合毒杀作用

以苹果黄蚜Aphis citricolavander Goot为试虫，对金合欢醇和烟碱的联合杀蚜活性进行了测定，以期为开发植物源杀蚜剂产品奠定基础。室内毒力测定采用微量点滴法；田间药效试验参照国家标准进行。金合欢醇和烟碱混用具有明显的杀蚜增效作用，在最佳质量配比（金合欢醇:烟碱=4.82:1）下，共毒系数（CTC）达151.63；经过对溶剂、表面活性剂等助剂的筛选，研制出6%烟碱·金合欢醇可溶液剂，配方为金合欢醇（5%）、烟碱（1%）、表面活性剂（10%）、溶剂（84%），质量检测符合可溶液剂国家质量标准；田间药效试验表明，以126.0 g a.i./hm²常量喷雾，药后7 d对小麦上的麦长管蚜Sitobion avenae Fabricius和麦二叉蚜Schizaphis graminum（Rondani）混合种群的防效达87.80%，以115.5 g a.i./hm²常量喷雾，药后7 d对苹果黄蚜的防效在81%以上。可见，金合欢醇和烟碱复配具有显著的杀蚜增效作用，具有进一步开发潜力。     

水氮耦合对郑麦9023结实期根系生理特性及产量的影响

以郑麦9023为材料,设置三个氮肥水平和两个水分处理来探讨水氮耦合下小麦根系生理特性差异及对产量的影响。结果表明:花后7~21 d,在同一水分条件下,随着施氮量的增加,根系活性、总吸收面积、活跃吸收面积及根系分泌的有机酸总量随着施氮量的增加呈先增加后降低的趋势,与200 kg·hm~(-2)(N2)相比,300 kg·hm~(-2)(N3)处理根系活性、总吸收面积、活跃吸收面积及有机酸总量分别降低了13.5%,9.0%,8.2%及20.9%;在同一氮肥水平下,与对照(-25 k Pa)相比较,水分胁迫(-60 k Pa)处理后根系总吸收面积、活跃吸收面积及有机酸总量有所增加,N3处理尤为明显。产量方面:在同一水分条件下,随施氮量的增加,小麦产量呈先增加后降低的趋势,与N1(0 kg·hm~(-2))处理相比,N2处理小麦产量平均提高72.1%,N3提高了61.4%,而N3处理比N2处理平均下降了6.6%;在同一氮肥处理下,水分胁迫后小麦产量有所增加。相关分析表明结实期根系活性、总吸收面积、活跃吸收面积及有机酸总量与产量呈显著及极显著正相关关系。说明灌浆期适度水分胁迫及N2条件下根系生理活性较强,更有利于产量的形成。     

局部根区滴灌与穴施尿素对土壤氮素空间分布的影响

为研究节水灌溉条件下穴施尿素、滴灌施肥对土壤铵态氮、硝态氮和碱解氮运移的影响，2019年在甘肃农业大学遮雨棚内开展施肥与灌溉试验，采用穴施尿素和滴灌施肥两种施肥方式，施纯氮量240 kg·hm^-2和180 kg·hm^-2，充分灌溉量和局部根区滴灌量分别是14 L和7 L。测定在距离滴头水平30 cm、垂直40 cm范围内土壤铵态氮、硝态氮和碱解氮含量，分析施肥与灌溉后土壤氮素转化及迁移特征。结果表明，土壤硝态氮更容易随灌水发生水平迁移，而土壤铵态氮更容易向土壤纵深迁移。土壤氮素含量的空间变异大小依次为：硝态氮>铵态氮>碱解氮；土壤硝态氮、铵态氮和碱解氮含量的平均变幅分别为32%~40%、26%~37%和6%~12%。局部根区滴灌土壤硝态氮含量的空间变幅比充分灌溉减小16%~20%。穴施尿素土壤铵态氮含量的空间变幅比滴灌施肥减小12%~28%。穴施尿素和局部根区滴灌调控土壤氮素转化速率，赋予肥料养分缓释性能，从而提高土壤氮素供应能力。因此，穴施尿素结合局部根区滴灌是较优的施肥与灌溉方式。     

减氮增密对西南丘陵区旱地直播油菜根系发育及水分利用的影响

以氮肥施用量N1(108 kg·hm~(-2))、N2(144 kg·hm~(-2))、N3(180 kg·hm~(-2))及种植密度D1(15×10~4株·hm~(-2))、D2(22.5×10~4株·hm~(-2))、D3(30×10~4株·hm~(-2))、D4(37.5×10~4株·hm~(-2))设置12个处理,以当地传统种植方式(N3D1)为对照,在生态脆弱、水土流失严重的西南丘陵区研究了油菜不同生育期根冠比(R/T)、根系形态、土壤蓄水量以及经济产量、水分利用效率、经济收益对不同氮肥施用量及种植密度的响应。结果表明:施氮量极显著影响油菜蕾薹期、角果期及成熟期的R/T与角果期的总根长和根系总表面积,同时显著影响蕾薹期的总根长和根系总体积;种植密度极显著影响蕾薹期R/T及角果期根系总体积,同时显著影响蕾薹期的根系总表面积和根系总根体积。角果期为地上部生物量积累速率最大时期,根冠比相较蕾薹期减小55.5%,而苗期的根冠比与经济产量呈显著负相关(r=-0.673~*)。氮肥减施可以有效增加土壤蓄水量和生育期总耗水量,且氮肥减施40%后更为显著,前者表现为N1N2N3,后者则为N3N2N1;相较N3,N1和N2下的各处理平均总耗水量分别减少5.03%和3.24%。在N2下,经济产量和水分利用效率则随着种植密度的增加而显著增加;经济收益与水分经济收益也表现出显著增长的变化趋势,其中,N2D3、N2D4处理较对照每公顷经济收益增加290.73元和503.37元,水分经济收益提高2.72%和9.93%。N2D3或N2D4处理能促进油菜产量、土壤蓄水量及经济收益的增长,并显著提升水分利用效率及水分经济收益,可作为西南丘陵区直播油菜减肥增效优化种植方式。     

Response of root traits of Reaumuria soongorica and Salsola passerina to facilitation

C3 plant Reaumuria soongorica and C4 plant Salsola passerina are super xerophytes and coexist in a mixed community in either isolated or associated growth, and interspecific facilitation occurs in associated growth. In the present study, the root traits including root distribution, root length(RL), root surface area(RSA), root weight(RW) and specific root length(SRL) of both species in two growth forms were investigated to clarify their response to facilitation in associated growth. Six isolated plants of each species, as well as six associated plants similar in size and development were selected during the plant growing season, and their roots were excavated at 0–10, 10–20, 20–30, 30–40 and 40–50 cm soil depths at the end of the growing season. All the roots of each plant were separated into the two categories of fine roots(2 mm diameter) and coarse roots(≥2 mm diameter). Root traits such as RL and RSA in the fine and coarse roots were obtained by the root analyzing system WinRHIZO. Most of the coarse roots in R. soongorica and S. passerina were distributed in the top 10 cm of the soil in both growth forms, whereas the fine roots of the two plant species were found mainly in the 10–20 and 20–30 cm soil depths in isolated growth, respectively. However, the fine roots of both species were mostly overlapped in 10–20 cm soil depth in associated growth. The root/canopy ratios of both species reduced, whereas the ratios of their fine roots to coarse roots in RL increased, and both species had an increased SRL in the fine roots in associated growth. In addition, there was the increase in RL of fine roots and content of root N for S. passerina in associated growth. Taken together, the root growth of S. passerina was facilitated for water and nutrient exploration under the interaction of the overlapped roots in both species in associated growth, and higher SRL allowed both species to more effectively adapt to the infertile soil in the desert ecosystem.     

局部施氮对玉米生理生化特性和产量的影响

采用大田试验,研究固定部分根区施氮、根系分区交替施氮及传统均匀施氮3种方式和高、中、低3个施氮水平对玉米叶片过氧化物酶(POD)活性、丙二醛(MDA)含量及百粒重和产量的影响。结果表明,与均匀施肥相比,固定施肥下玉米叶片的MDA含量显著增大,交替施肥明显减小。POD活性则表现为,交替施肥较之均匀施肥显著增大;固定施肥在高肥水平下明显增加,中、低肥水平下无显著差异。3种施氮方式下,MDA含量均随施氮量的增大而减小,POD活性随施氮量的增加显著增强。玉米百粒重表现为,与均匀施肥相比,交替施肥显著增大,固定施肥仅高肥水平下明显增加。两种局部施肥方式均明显提高了玉米的籽粒产量,其中,尤以交替施肥的增幅大。     

氮素形态配比对全膜双垄沟播玉米干物质积累及产量的影响

为优化陇中干旱、半干旱地区全膜双垄沟播玉米的氮肥运筹并最终提高子粒产量,通过大田试验,探索了硝态氮/铵态氮分别按1∶0(N1)、1∶1(N2)、1∶2(N3)、1∶3(N4)、2∶1(N5)、3∶1(N6)配比对旱地全膜双垄沟播玉米的光合特性、干物质积累、产量及其构成因素的影响。结果表明:硝态氮和铵态氮配施下玉米的叶面积、光合势相比单施硝态氮均有所提高,以硝铵比为3∶1(N6)最佳,较N1叶面积和光合势分别提高12.59%~39.85%、13.71%~25.00%。提高硝态氮的施用比例利于改善玉米的光合性能,进而促进干物质积累及产量形成。硝态氮和铵态氮两种氮素形态配施对玉米的生长发育具有明显的促进作用,较单施硝态氮的干物质量和产量分别提高了5.45%~52.74%和3.85%~9.93%。其中N6配比下玉米干物质的积累和产量最高,较其它配比分别平均提高了17.13%和4.73%,是最优配比。     

水氮供应对温室黄瓜叶绿素含量及光合速率的影响

利用温室小区试验,以黄瓜"博耐9-1"为供试品种,设置3个灌水水平:低水W1(60%ET0)、中水W2(80%ET0)和高水W3(100%ET0),全生育期灌水量分别为126、152 mm和177 mm;4个施氮水平:无氮N0(0)、低氮N1(180 kg·hm-2)、中氮N2(360 kg·hm-2)和高氮N3(540 kg·hm-2),共12个处理,研究了不同水氮供应对温室黄瓜叶绿素含量和光合速率的影响。结果表明:黄瓜叶绿素含量随着生育期的推进呈现先增加后降低的趋势,在盛果期取得最大值。在同一施氮水平条件下,灌水量的提高对叶绿素含量的提高均起到了促进作用。其中叶绿素总含量在W3N3处理下取得最大值,为12.32 mg·g-1,且与W2N2处理之间无显著差异。在各水氮供应条件下,黄瓜叶片的净光合速率日变化呈现单峰曲线,不施氮肥或严重亏水均会显著影响作物的净光合速率,而适量的节水节肥不仅能节约农业成本,且相比于充分灌水施肥,作物也能达到较好的净光合速率。在光照较强较稳定的情况下,W2处理下黄瓜叶片净光合速率达到最大值。从总体变化趋势看,W2N2处理(80%ET0,N 360 kg·hm-2)可认为是基于本试验条件下较适宜的水氮组合。     

水分对不同栽培年限日光温室土壤氮矿化的影响

采用室内短期（84 d）好气培养法评价了不同水分供应水平下（田间持水量的60%、80%及100%，分别用60FC、80FC和100FC表示）陕西杨凌地区不同栽培年限（种植前、种植第二年及种植第三年）日光温室土壤（0~20 cm及20~40 cm土层）氮素矿化特性。结果表明：随着日光温室栽培年限的延长，0~20 cm土层累积净矿化氮量显著增加，且随栽培年限的增加，20~40 cm 土层氮矿化势呈增加的趋势；土壤水分含量由60FC增加到80FC，土壤累积矿化氮量呈增加趋势，但当含水量达到100FC时，土壤累积矿化氮量降低。回归分析结果表明，土壤有机质含量每增加1 g·kg^-1, 60FC、80FC、100FC土壤含水量条件下土壤氮矿化势分别增加 1.62、1.88 mg·kg^-1和1.57 mg·kg^-1;土壤全氮含量每增加1 g·kg^-1，土壤氮矿化势分别增加28.93、33.42 mg·kg^-1和27.82 mg·kg^-1。因此，建议日光温室蔬菜栽培中应综合考虑温室年限及灌溉量对土壤氮素矿化过程的影响。     

西北干旱区土壤水力参数空间变异与模拟

为探明西北干旱区土壤水力参数的空间分布特征,在新疆地区布设107个样点,获取表层(0～5 cm)Ks(土壤饱和导水率)、FC(田间持水量)和PWP(永久萎蔫系数)数据,采用经典统计学和地统计学分析土壤水力参数的空间变异特征,并利用逐步回归和传递函数方程对Ks、FC和PWP进行模拟。结果表明:新疆地区Ks、FC和PWP平均值分别为10.999 mm·h~(-1)、0.162 g·g~(-1)和0.077 g·g~(-1),变异系数为39.88%～96.07%,均表现为中等程度变异。在区域尺度上Ks、FC和PWP具有强空间依赖性,变程为97～291 km。与经自变量数据转换构建的传递函数方程相比,多元逐步回归方程预测土壤水力参数精度更高,且方程使用更便利。基于土地利用、容重、土壤质地、有机碳含量和坡向的多元逐步回归方程,预测Ks、FC和PWP的决定系数R~2分别为0.290、0.494和0.491,均方根误差(RMSE)分别为2.540 mm·h~(-1),0.039 g·g~(-1)和0.023 g·g~(-1)。这些方程的建立,有利于西北干旱区土壤水力参数的快速估算,同时可为该地区的农业灌溉和生态水文模型提供关键参数。     

贝莱斯芽胞杆菌B006对不同水肥条件下娃娃菜生长及软腐病防效的影响

贝莱斯芽胞杆菌B006是一株高效生防菌株,但其在不同水肥条件下的防病促生效果尚不明确。本研究通过盆栽试验测定了不同土壤含水量和施肥条件下B006菌剂对娃娃菜生长及对软腐病防效的影响,结果表明：在土壤含水量为14%、施肥量为3.57 g/kg土的条件下,播种时沟施5 g B006菌剂（菌含量为1×10⁷ CFU/g）,出苗后浇灌B006菌悬液（3×10⁸ CFU/mL）可明显降低娃娃菜的发病率和病情指数,与相同条件下未施用B006菌剂处理相比,防效达77.4%。在日光温室开展土壤水势、施肥量及B006菌剂施用随机区组交互试验,结果表明：在土壤水势—50 kPa和追肥量1049.5 kg/hm²（N/P/K=18/5/13）条件下,施用B006菌剂可以促进植株生长,与土壤水势和追肥量分别为—50 kPa×1499.3 kg/hm²和—30 kPa×1499.3 kg/hm²的处理相比,娃娃菜产量分别提高了8.6%和11.2%。综上所述,适当少水、少肥并施用贝莱斯芽胞杆菌B006菌剂可以明显控制娃娃菜软腐病的发生,促进植物生长,并显著提高娃娃菜产量。     

生防菌解淀粉芽胞杆菌Lx-11悬乳剂研制及其对水稻白叶枯病的防治效果评价

目前已经登记的芽胞杆菌微生物杀菌剂剂型以悬浮剂和可湿性粉剂为主，剂型相对比较单一，为进一步提高货架期和利用效率，以解淀粉芽胞杆菌Lx-11作为研究对象，筛选出纳米材料作为载体，添加各种不同功能性助剂，在高速均质机的作用下剪切、均质，研制出解淀粉芽胞杆菌Lx-11悬乳剂。解淀粉芽胞杆菌Lx-11悬乳剂配方：发酵液70%～80%，吸附载体白炭黑10%～15%，大豆油30%～50%，乳化剂Span80和Tween80复配6%～10%，分散剂脂肪醇聚氧乙烯醚羧酸钠1%～3%，防冻剂乙二醇2%～4%，增效助剂SY-6535 1.5%～2.5%。该制剂的性能指标为：活菌体含量大于8×10⁸cfu/mL，悬浮率大于85%，粘度225 mPa·s，热贮稳定性合格；各项技术指标均符合产品标准要求。田间药效试验表明：解淀粉芽胞杆菌Lx-11悬乳剂对水稻白叶枯病的防治效果显著高于其发酵液。     

Competition Effects Among Isolates of Fusarium culmorum Differing in Aggressiveness and Mycotoxin Production on Heads of Winter Rye

Fusarium culmorum is a phytopathogenic, toxigenic fungus causing seedling diseases, foot rot and head blight of cereals. For estimating competition effects in mixtures of two single-spore isolates, two winter rye single crosses were tested with either four isolates individually or four 1 : 1 mixtures of the same isolates in six field environments. Two isolates (FC46, FC64) were highly aggressive deoxynivalenol (DON) and 3-acetyl DON-producers, the other two (FC30, FC71) were medium aggressive nivalenol-producers. Rye heads were inoculated during flowering with conidia of pairs of isolates expressing similar (FC46 + FC64, FC30 + FC71) or contrary (FC46 + FC71, FC30 + FC64) levels of aggressiveness and similar or different concentrations and chemotypes of mycotoxins, respectively. Head blight rating and yield components relative to the non-inoculated plots were recorded as aggressiveness traits. Additionally, mycotoxin concentrations were measured in the rye grain. Random pathogen samples were re-isolated from heads at the onset of symptom development and analysed by molecular markers (RAPD–PCR) in one environment. Aggressiveness of the isolate mixtures was significantly lower than that of the isolates applied individually on both rye genotypes. Similarly, mycotoxin concentrations were significantly lower in the mixtures in seven out of eleven comparisons. Among the re-isolates, the component genotypes of a mixture significantly deviated from the inoculated 1 : 1 ratio when a particular isolate (FC46) was present in the mixture. This isolate displayed a superior competitive ability irrespective of the aggressiveness or mycotoxin profile of the mixing partner illustrating that pathogenic fitness is caused by additional factors that have not, as yet, been identified.     

三唑酮对木霉根际竞争定殖的影响

 在粘壤土中施用4~12μg/g土三唑酮能提高耐药木霉菌株在西瓜根尖4~1cm处根际土中的种群密度。4μg三唑酮处理的木霉根际竞争定殖指数、以及在4~8cm和10~14cm根段的根际木霉种群密度均高于不施药对照。土壤接种量为1×10³cfu/g土时木霉菌在西瓜根际增殖的比例较接种量为1×10⁶cfu/g土时大,2种接种量下三唑酮处理的根际木霉种群密度分别高于相应的不加药对照。在质地较好、C/N比值较高的粘壤土中木霉菌在西瓜根际的种群密度较砂壤土和粘土大,三唑酮对木霉在西瓜根际的增殖作用也较明显。     

干旱地区灌溉农田化肥施用现状与环境影响分析

河西三地区氮、磷肥利用率较低 ,在整个作物生长期间 ,有 60～ 80 %的氮肥未被当季作物吸收利用而通过水、气进入环境。目前河西本地区仍有 97%的农田沿用大水漫灌方式进行灌溉 ,在春季灌水后和初冬灌冬水时 ,硝态氮大量随田间渗漏水排出 ,排出的氮、磷量占施肥量的 3 3 %和 58%以上。由此计算 ,通过农田排水和下渗损失的氮约 460 7.7t,磷约 4581 .7t,既污染了环境又加大了农业成本。所以加大有机肥施用量、发展绿色产品和采用节水灌溉、取缔大水漫灌方式是降低农业成本保护环境的有效途径。