Variations of SOC and MBC observed in an incubated brown loam soil managed under different tillage systems for 12 years

To assess changes in organic carbon pools, an incubation experiment was conducted under different temperatures and field moisture capacity (FMC) on a brown loam soil from three tillage practices used for 12 years: no‐till (NT), subsoiling (ST) and conventional tillage (CT). Total microbial respiration was measured for incubated soil with and without the input of straw. Results indicated that soil organic carbon (SOC) and microbial biomass carbon (MBC) under ST, NT and CT was higher in soil with straw input than that without, while the microbial quotient (MQ or MBC: SOC) and metabolic quotient (qCO₂) content under CT followed the opposite trend. Lower temperature, lower moisture and with straw input contributed to the increases in SOC concentration, especially under NT and ST systems. The SOC concentrations under ST, with temperatures of 30 and 35°C after incubation at 55% FMC, were greater than those under CT by 28.4% and 30.6%, respectively. The increase in MBC was highest at 35°C for 55%, 65% and 75% FMC; in soil under ST, MBC was greater than that under CT by 199.3%, 50.7% and 23.8%, respectively. At 30°C, the lower qCO₂ was obtained in soil incubated under NT and ST. The highest MQ among three tillage practices was measured under ST at 55% FMC, NT at 65% FMC and CT at 75% FMC with straw input. These data indicate the benefits of enhancing the MQ; the low FMC was beneficial to ST treatment. Under higher temperature and drought stress conditions, the adaptive capacity of ST and NT is better than that of CT.     

Interactions between crop biomass and development of foliar diseases in winter wheat and the potential to graduate the fungicide dose according to crop biomass

Foliar pathogens such as Zymoseptoria tritici and Puccinia striiformis causing septoria leaf blotch and yellow rust respectively can cause serious yield reduction in winter wheat production, and control of the diseases often requires several fungicide applications during the growing season. Control is typically carried out using a constant fungicide dose in the entire field although there may be large differences in crop development and biomass across the field. The objective of the study reported in this paper was to test whether the fungicide dose response curve controlling septoria leaf blotch and other foliar diseases in winter wheat was dependent on crop development and biomass level. If such a biomass dependent dose response was found it was further the purpose to evaluate the potential to optimize fungicide inputs in winter wheat crops applying a site-specific crop density dependent fungicide dose. The study was carried out investigating fungicide dose response controlling foliar diseases in winter wheat at three biomass densities obtained growing the crop at three nitrogen levels and using variable seed rates. Further the field experiments included three fungicide dose rates at each biomass level, an untreated control, and 75%, 50% and 33% of the recommended fungicide dose rate and the experiments were replicated for three years. Crop biomass had a significant influence on occurrence of septoria and yellow rust with greater disease severity at increasing crop biomass. In two of three years, the interaction of crop biomass and fungicide dose rate had a significant influence on disease severity indicating a biomass-dependent dose response. The interaction occurred in the two years with high yield potential in combination with severe disease attack. If the variation in crop density and biomass level obtained in the study is representative of the variation found cultivating winter wheat in heterogeneous fields, then there seems to be scope for optimizing fungicide input against foliar diseases site-specific adapting the dose according to crop density/biomass.     

Effects of Different Nitrogen Treatments on N use Efficiency and Grain Yield of Mechanically-transplanted Hybrid Rice

In order to investigate effects of topdressing on grain yield and N use efficiency of mechanically-transplanted hybrid rice,this experiment was conducted with 2-line hybrid rice cultivars,Quanliangyou 1 and Quanliangyou 681 with 3 application levels of N fertilizer,No,N1,N2,respectively.The results showed that there were no significant differences in grain yields of the 2 varieties between treatments N1 and N2.It was indicated that N is not the factor which could limit grain yield within limited application levels of N fertilizer.High N fertilizer treatment could contribute to the formation of effective panicles and spikelets per panicle,but it could also lead to the decline in grain filling rate.It was suggested that lowering the amount of Nfertilizer could facilitate improvement of N-use efficiency.     

Summer drought decreases Leymus chinensis productivity through constraining the bud,tiller and shoot production

Extreme drought events can directly decrease productivity in perennial grasslands. However, for rhizomatous perennial grasses it remains unknown how drought events influence the belowground bud bank which determines future productivity. Ninety‐day‐long drought events imposed on Leymus chinensis, a rhizomatous perennial grass, caused a 41% decrease in the aboveground biomass and a 28% decrease in belowground biomass. Aboveground biomass decreased due to decrease in both the parent and the daughter shoot biomass. The decreases in daughter shoot biomass were due to reductions in both the shoot number and each individual shoot weight. Most importantly, drought decreased the bud bank density by 56%. In addition, drought induced a bud allocation change that decreased by 41% the proportion of buds that developed into shoots and a 41% increase in the buds that developed into rhizomes. Above results were supported by our field experiment with watering treatments. Thus, a 90‐day‐long summer drought event decreases not only current productivity but also future productivity, because the drought reduces the absolute bud number. However, plasticity in plant development does partly compensate for this reduction in bud number by increasing bud development into rhizomes, which increases the relative allocation of buds into future shoots, at the cost of a decrease in current shoots.     

甘蓝型油菜耐低温生长生理生化响应机制

为提高甘蓝型油菜耐寒育种过程中的筛选效率，研究甘蓝型油菜耐低温机理，以8个不同抗寒性的甘蓝型油菜为材料，对低温条件下各材料的生物量、叶绿素、脯氨酸和相对电导率进行测定，发现在室外平均气温2.75℃时，抗性材料的生物量、叶绿素和脯氨酸的累积量都显著高于敏感材料，相对电导率没有显著差异；当平均气温7.52℃回升至12.39℃，抗性材料和敏感材料生物量的累积量无显著差异；在恒定低温10℃/4℃处理下抗性材料和敏感材料在处理前3周生物量均持续累积，但从第4周开始敏感材料新叶出现白斑，生物量减少，抗性材料老叶出现白斑，生物量维持不变。结果表明，耐低温材料在低温条件下叶绿素含量受到的影响较小，脯氨酸的积累量持续上升，具有较强的快速适应能力，在低温下具有显著的持续生长优势。     

广西巨尾桉2年生人工幼林生物量及生产力研究

在对广西沙塘林场巨尾桉2年生人工林调查基础上，按标准木法测定巨尾桉人工幼林生物量，建立其估算模型，计算出巨尾桉人工林分的生物量和生产力，分析各器官生物量分配规律及林分生产力水平。结果表明，2年生巨尾桉人工林年生物量为16.57 t/hm^2，其中，干、根、叶、枝、皮各器官生物量所占比例依次为46.67％、16.85％、14.62％、12.16％、9.62％。应用建立的估算模型估测巨尾桉人工幼林生物量，其相关程度达显著水平。     

不同温度下TMV侵染枯斑三生烟的LncRNA差异表达

【目的】 筛选不同温度下烟草花叶病毒（Tobacco mosaic virus,TMV）侵染后枯斑三生烟（Nicotiana tabacum var. Samsun NN）差异表达的长链非编码RNA（long non-coding RNA,lncRNA）,研究lncRNA在枯斑三生烟抗性反应中的作用。【方法】 N基因的温度敏感性使枯斑三生烟在25℃时具备对TMV的抗性、在31℃抗性丧失,在这两个温度条件下对枯斑三生烟接种TMV和磷酸盐缓冲盐水（phosphate buffered saline,PBS）,48 h后提取系统叶总RNA,构建链特异性文库后进行深度测序。对测序结果进行过滤后利用HTSeq将有效数据与近缘品种TN90（N. tabacum var. TN90）基因组比对,筛选得到lncRNA后利用FPKM法估计lncRNA的表达水平。通过edgeR筛选差异表达lncRNA（differentially expressed lncRNA,DElncRNA）,并利用qRT-PCR技术对这一结果进行验证。通过共定位及共表达分析预测DElncRNA的靶基因,通过参考基因组注释、GO和KEGG富集分析研究靶基因的功能。【结果】 4个处理共12个样本经lncRNA-seq各测得约8 000万条clean reads,共获得4 737条已知lncRNA、40 169条新lncRNA。其中64个lncRNA在不同温度条件下TMV侵染后存在差异表达,qRT-PCR测定结果显示这些lncRNA的测序正确率在80%左右,表明本研究所得测序数据具备较高的可信度。对DElncRNA进行靶基因预测,发现一些基因同时被25℃下调和31℃上调的DElncRNA靶向。靶基因注释功能丰富,主要参与植物抗病、激素和代谢等生理过程。部分可能与激素通路相关的lncRNA,在25℃下TMV侵染时呈现下调趋势,而在31℃下TMV侵染则呈现上调趋势。GO富集分析显示靶基因主要参与构成膜、囊泡等组分,具备钙、钾离子通道抑制剂活性等分子功能,使相应离子得以转运引发随后的反应,同时也参与发病、抗原加工和呈现、细胞分裂素代谢等生理过程。KEGG分析发现靶基因显著富集在植物激素信号转导通路,25℃下调和31℃上调的DElncRNA靶基因同时富集在激素信号传导、ABC运输蛋白、苯丙烷类生物合成等通路。【结论】 不同温度（25℃和31℃）条件下TMV侵染枯斑三生烟后,长链非编码RNA差异表达,DElncRNA通过作用于激素信号传导、物质转运等过程参与寄主系统获得性抗性反应。研究结果可为揭示植物系统获得性抗性中lncRNA的调控功能以及新型抗病毒技术开发提供依据。     

Effect of the particle size on the ammonia removal rate and the bacterial community composition of bioflocs

The total ammonia nitrogen (TAN) removal efficiency and bacterial community composition of bioflocs with <50-μm particle size, > 50-μm particle size and un-sieved bioflocs were investigated in the current study. The initial ratio of dissolved organic carbon to TAN (DOC/TAN) in the three groups were about 14:1. No significant difference was found in the removal rate of TAN, average concentrations of TAN and nitrite nitrogen among the three groups (P > 0.05). The C/N (w/w) ratio of the > 50-μm bioflocs was significantly higher than those of the other groups. No significant differences were found in the crude protein content in the bioflocs among the three groups. The development of the bacterial community compositions of the bioflocs was analyzed by Illumina MiSeq sequencing analyses. Most OTUs were shared among the three groups at all the sampled time points. With the increase in the relative abundance of phylum Firmicutes, that of phylum Proteobacteria, Chorolexi, and Bacteroidetes decreased in all the three groups. The phylum Firmicutes and genus Bacillus were predominant in all the sampled time points. At the end of the experiment, genus Bacillus accounted for 81% in the < 50-μm group, 82% in the > 50-μm group, and 75% in the un-sieved group.     

Indicators and trade-offs of ecosystem services in agricultural soils along a landscape heterogeneity gradient

Soil functions can be classified as supporting (nutrient cycling) and provisioning (crop production) ecosystem services (ES). These services consist of multiple and dynamic functions and are typically assessed using indicators, e.g. microbial biomass as an indicator of supporting services. Agricultural intensification negatively affects indicators of soil functions and is therefore considered to deplete soil ES. It has been suggested that incorporating leys into crop rotations can enhance soil ES. We examined this by comparing indicators of supporting soil services – organic carbon, nitrogen, water holding capacity and available phosphorous (carbon storage and nutrient retention); net nitrogen mineralisation rate and microbial biomass (nutrient cycling and retention) – in barley fields, leys and permanent pastures along a landscape heterogeneity gradient (100, 500 and 1000 m radii). In addition, barley yields (provisioning service) were analysed against these indicators to identify trade-offs among soil services. Levels of most indicators did not differ between barley and ley fields and were consistently lower than in permanent pastures. Leys supported greater microbial biomass than barley fields. Landscape heterogeneity had no effect on the indicators or microbial community composition. However, landscape heterogeneity correlated negatively with yield and soil pH, suggesting that soils in heterogeneous landscapes are less fertile and therefore have lower yields. No trade-offs were found between increasing barley yield and the soil indicators. The results suggest that soil ES are determined at the field level, with little influence from the surrounding landscape, and that greater crop yields do not necessarily come at the expense of supporting soil services.     

Can differences in 15N natural abundance be used to quantify the transfer of nitrogen from legumes to neighbouring non-legume plant species?

Natural variations in the stable isotope ¹⁵N are often exploited in studies of N cycling in ecosystems. Lower ¹⁵N natural abundance in non-legume plants growing in association with legumes, compared with the non-legume grown alone in pure stands have been observed in cropping, forage, and agroforestry systems. Such observations have frequently been attributed to the transfer of biologically-fixed nitrogen (N) from the legume to the companion non-legume, and various methodologies have been employed to calculate the extent of the N transfer. While some of these ¹⁵N natural abundance-based estimates of N transfer were within the range previously reported using equivalent ¹⁵N-enriched techniques (<20% of non-legume plant N and <10 kg N ha⁻¹ derived from fixed N contributed by neighbouring legumes), many of the values obtained using natural abundance were much higher (30%–83% of the non-legume N derived from fixed N representing up to 30–40 kg N ha⁻¹) than generally measured by ¹⁵N-enriched methods; with even greater estimates being determined where data were available to allow N transfer to be re-calculated on the basis of total legume N rather than fixed N (42% to >100%, and up to 110 kg N ha⁻¹ per year). This review raises concerns about the assumptions behind the natural abundance approach, and provides some alternative interpretations for the observed differences in natural ¹⁵N abundance between plants grown in the presence and absence of legumes. It was concluded that simple comparative measures of non-legume δ¹⁵N alone cannot provide a quantitative estimate of N transfer between plant species if the dominant source and the isotopic identity of the transferred N cannot be validated, and if the extent of any isotopic fractionation associated with relevant N transformations occurring during transfer cannot be defined. To date this information is not forthcoming. There is a need to greatly improve our understanding of the transfer processes before the real value of the δ¹⁵N technology can be realized. In the first instance this will primarily be achieved by carefully executed experiments under controlled conditions, and in the field, employing both ¹⁵N natural abundance and enrichment approaches so estimates of transfer can be compared, and the data interrogated using modelling approaches to explore isotopic fractionation.