种植密度对春玉米灌浆期光合特性及产量的影响

[目的]揭示玉米（Zea mays L.）光合生理指标和产量间的关系,以期为玉米高产、高效生产及合理密植提供理论依据和技术支持.[方法]研究了3个春玉米品种（紧凑型品种铁研124和郑单958,半紧凑型品种丹玉39）在4.5万、6.0万、7.5万株/hm2种植密度条件下灌浆期光合特性和产量的变化.[结果]种植密度对春玉米灌浆期光合速率、蒸腾速率和气孔导度有负影响;铁研124与郑单958在7.5万株/hm2种植密度下均获得了较高的产量,丹玉39在6.0万株/hm2种植密度下产量最高.相关分析表明,铁研124与郑单958的群体产量与单株光合速率、蒸腾速率和气孔导度均呈负相关;丹玉39的群体产量与单株光合速率、蒸腾速率和气孔导度均呈正相关.[结论]郑单958与铁研124的产量增加得宜于群体数量的增加,适宜密植.丹玉39主要来源于单株产量,不适宜密植.     

苏州主要园林树种的光合固碳能力对比分析

园林树种的光合固碳能够维持城市空气中CO2和O2的平衡。以苏州地区32个园林树种为材料,利用Li-6400便携式光合作用仪测定了其光合日变化,并利用测定结果计算其日净固碳能力,再以聚类分析法对其日净固碳量进行分类。结果如下:第1类[日净固碳量极高,17.55~18.76 g/(m2·d)]有紫荆、枫杨、垂柳,第2类[日净固碳量高,12.25~16.02 g/(m2·d)]有大叶女贞、乌桕、榉树、枫香树、垂丝海棠、樱花、夹竹桃,第3类[日净固碳量中等,8.57~11.97 g/(m2·d)]有银杏、红花檵木、朴树、乐昌含笑、红叶李、杜英、海桐、金边黄杨、杜鹃、重阳木、樟树、金丝桃、红叶石楠,第4类[日净固碳量低,3.81~7.64 g/(m2·d)]有红枫、洒金东瀛珊瑚、金叶女贞、八角金盘、五角枫、鹅掌楸、紫薇、木芙蓉、桂花。上述分析结果可对苏州的园林规划及树种选择提供一定的理论指导。     

A single application of Cu to field soil has long-term effects on bacterial community structure, diversity, and soil processes

Long-term diversity-disturbance responses of soil bacterial communities to copper were determined from field-soils (Spalding; South Australia) exposed to Cu in doses ranging from 0 through to 4012 mg Cu kg⁻¹ soil. Nearly 6 years after application of Cu, the structure of the total bacterial community showed change over the Cu gradient (PCR-DGGE profiling). 16S rRNA clone libraries, generated from unexposed and exposed (1003 mg Cu added kg⁻¹ soil) treatments, had significantly different taxa composition. In particular, Acidobacteria were abundant in unexposed soil but were nearly absent from the Cu-exposed sample (P<0.05), which was dominated by Firmicute bacteria (P<0.05). Analysis of community profiles of Acidobacteria, Bacillus, Pseudomonas and Sphingomonas showed significant changes in structural composition with increasing soil Cu. The diversity (Simpsons index) of the Acidobacteria community was more sensitive to increasing concentrations of CaCl-extractable soil Cu (Cu_Ext) than other groups, with decline in diversity occurring at 0.13 Cu_Ext mg kg⁻¹ soil. In contrast, diversity in the Bacillus community increased until 10.4 Cu_Ext mg kg⁻¹ soil, showing that this group was 2 orders of magnitude more resistant to Cu than Acidobacteria. Sphingomonas was the most resistant to Cu; however, this group along with Pseudomonas represented only a small percentage of total soil bacteria. Changes in bacterial community structure, but not diversity, were concomitant with a decrease in catabolic function (BioLog). Reduction in function followed a dose-response pattern with Cu_Ext levels (R²=0.86). The EC₅₀ for functional loss was 0.21 Cu_Ext mg kg⁻¹ soil, which coincided with loss of Acidobacteria diversity. The microbial responses were confirmed as being due to Cu and not shifts in soil pH (from use of CuSO₄) as parallel Zn-based field plots (ZnSO₄) were dissimilar. Changes in the diversity of most bacterial groups with soil Cu followed a unimodal response - i.e. diversity initially increased with Cu addition until a critical value was reached, whereupon it sharply decreased. These responses are indicative of the intermediate-disturbance-hypothesis, a macroecological theory that has not been widely tested in environmental microbial ecosystems.     

Short-term competition between crop plants and soil microbes for inorganic N fertilizer

Agricultural systems that receive high amounts of inorganic nitrogen (N) fertilizer in the form of either ammonium (NH₄⁺), nitrate (NO₃⁻) or a combination thereof are expected to differ in soil N transformation rates and fates of NH₄⁺ and NO₃⁻. Using ¹⁵N tracer techniques this study examines how crop plants and soil microbes vary in their ability to take up and compete for fertilizer N on a short time scale (hours to days). Single plants of barley (Hordeum vulgare L. cv. Morex) were grown on two agricultural soils in microcosms which received either NH₄⁺, NO₃⁻ or NH₄NO₃. Within each fertilizer treatment traces of ¹⁵NH₄⁺ and ¹⁵NO₃⁻ were added separately. During 8 days of fertilization the fate of fertilizer ¹⁵N into plants, microbial biomass and inorganic soil N pools as well as changes in gross N transformation rates were investigated. One week after fertilization 45-80% of initially applied ¹⁵N was recovered in crop plants compared to only 1-10% in soil microbes, proving that plants were the strongest competitors for fertilizer N. In terms of N uptake soil microbes out-competed plants only during the first 4 h of N application independent of soil and fertilizer N form. Within one day microbial N uptake declined substantially, probably due to carbon limitation. In both soils, plants and soil microbes took up more NO₃⁻ than NH₄⁺ independent of initially applied N form. Surprisingly, no inhibitory effect of NH₄⁺ on the uptake and assimilation of nitrate in both, plants and microbes, was observed, probably because fast nitrification rates led to a swift depletion of the ammonium pool. Compared to plant and microbial NH₄⁺ uptake rates, gross nitrification rates were 3-75-fold higher, indicating that nitrifiers were the strongest competitors for NH₄⁺ in both soils. The rapid conversion of NH₄⁺ to NO₃⁻ and preferential use of NO₃⁻ by soil microbes suggest that in agricultural systems with high inorganic N fertilizer inputs the soil microbial community could adapt to high concentrations of NO₃⁻ and shift towards enhanced reliance on NO₃⁻ for their N supply.     

Bacterial diversity in cucumber (Cucumis sativus) rhizosphere in response to salinity, soil pH, and boron

Soil salinity is a major factor relating microbial communities to environmental stress in the microbial selection process as stress can reduce bacterial diversity. In the San Joaquin Valley (SJV) of California, the problem of increasing salinity and consequently, decreasing crop productivity, due to reuse of saline drainage water are major concerns. An experiment was conducted in a closed, recirculating volumetric lysimeter system (VLS) consisting of 24 experimental plant growth units to determine the interactive effects of salinity, boron and pH on rhizosphere and non-rhizosphere microbial composition of cucumber (Cucumis sativus L. cv. Seminis Turbo hybrid). Plants in the VLS were irrigated from individual reservoirs containing a modified half-strength Hoagland's nutrient solution combined with salinity, boron (B), and pH treatments. The results indicated that salinity and pH were the most influential factors affecting the growth of plants and the effect of boron on the plant was more severe under slightly acidic conditions. Total bacterial DNA was extracted from rhizosphere and non-rhizosphere samples, and a 236-bp DNA fragment in the V3 region of the small subunit ribosomal RNA genes of eubacteria was amplified. The 16S rRNA and the products were subjected to denaturing gradient gel electrophoresis (DGGE) and sequencing. Analyses of bacterial diversity showed that the effects of salinity, boron, and pH were more severe on the rhizosphere bacterial population during the first week of growing cucumber, with decreasing impacts with plant growth. However, there was no salinity-B-pH interaction effects on plant biomass, but the effects were seen in the number of heterotrophic bacteria in the rhizosphere and on species richness and diversity during week seven of the study. These suggest that the effects of salinity-B-pH interactions may influence microorganisms first before plants and may pose long term effects on soil quality.     

Fate of prions in soil: Degradation of recombinant prion in aqueous extracts from soil and casts of two earthworm species

Prions represent the active agent in transmissible spongiform encephalopathy (TSE) diseases and can remain infective to mammals even after prolonged periods in soil. The influence of mesofauna on prion dispersal and degradation in soil, however, remains unknown. In this study the effect of earthworms on the retention/dissemination of TSEs in soil was evaluated using a model recombinant prion protein (recPrP) and aqueous extracts from soil and fresh casts of two earthworm species, Lumbricus terrestris and Aporrectodea caliginosa. Our results showed that earthworm gut-derived enzymes did not enhance the degradation of recPrP in comparison to soil, even though non-prion related proteolytic activity was higher in fresh worm excrements than in soil samples. Complete degradation of recPrP occurred in the aqueous extracts from all samples within up to 6 days at +15 °C. The proteolytic enzymes responsible for degrading recPrP were inhibited by aprotinin and leupeptin and studies in pure cultures suggested these were most probably of soil microbial origin.     

不同基质配比对黄瓜幼苗生长的影响

为提高农业废弃物利用率,减少环境污染,以黄瓜品种津绿3号为试验材料,研究牛粪、花生壳、草炭、蛭石、珍珠岩等不同基质成分配比对黄瓜幼苗生长及光合作用的影响。结果表明:不同基质配比对黄瓜的生长有显著影响。其中C处理(花生壳︰蛭石︰珍珠岩体积比7︰3︰3)效果最好,育苗40 d后,黄瓜幼苗叶片大而肥厚,叶色浓绿,株高、茎粗、地上和地下部分鲜质量均达到了最大值,分别为17.21 cm、5.4 mm、6.82 g和2.26 g,分别是对照的2.1倍、1.5倍、2.7倍和1.1倍;光合速率为13.95μmol/(m2·s),比A处理稍低,但无显著差异,且显著高于其他处理。综合各项指标,C处理成本低,原料来源方便,建议在黄瓜育苗中应用。     

银杏光合特性的研究

银杏的光饱和点为１０６２．２μｍｏｌ．ｍ＾－２．ｓ＾－１，光补偿点为３３．８μｍｏｌ．ｍ＾－２，ｓ＾－１。银杏光合作用受叶片内部气孔调节和外部空气相对湿度，光量子通量密度等因子影响，净光合速率的日变化在强光，高温，干燥的晴天呈双峰曲线型，在多云天气呈单峰曲线型。净光合速率的年变化呈双峰曲线型，主峰出现在６月上旬，次峰在９有旬，５月下旬和７月中旬叶片光合能力最强。     

梨不同砧穗组合光合特性

 用CIRAS-1 便携式光合作用测定系统研究了豆梨(Pyrus betulaefolia Bunge) 、杜梨(P.calleryana Dcen.) 幼树以及豆梨、杜梨与砂梨(P. pyrifolia Nakai) 品种丰水、新高4 种砧穗组合幼树叶片的光合作用。结果表明, 砧木显著影响栽培品种的光合作用, 杜梨比豆梨以及以杜梨为砧木的丰水、新高幼树比以豆梨为砧木的两品种幼树叶片净光合速率(Pn) 、表观量子产量(Φi) 、羧化效率(CE) 、水分利用效率(WUE) 高。新高的Pn、Φi 、CE 和WUE 值较丰水高, 且在两种砧木上均表现出同样的结果。     

起身期断根对冬小麦后期光合和生长的影响

通过盆栽小麦起身期断根试验,研究了断初生根和部分次生根对小麦后期光合和生长的影响。结果表明:断初生根和部分次生根,均降低了断根初期小麦光合速率,而促进后期光合速率;同时,断根降低了成熟期小麦根系干质量、地上部干质量以及产量;断初生根比断部分次生根对小麦的影响更明显。