施肥与刈割对内蒙古草地生态化学计量特征的影响

为明确施肥和刈割对蒙古半干旱草地四种植物化学计量特征的影响,该文于2014年8月以内蒙古半干旱草地的四种植物冷蒿(Artimesia frigida)、菊叶委陵菜(Potentilla tanacetifolia)、羊草(Aneurotepidimu chinense)、扁蓿豆(Melissitus ruthenica)为研究对象,利用方差分析及多重比较分析对照、施氮肥、割草、割草和施氮肥处理下的植物碳、氮、磷含量的差异以及不同处理下碳氮比和氮磷比的变化。结果表明:施氮肥与割草均未影响植物碳含量。施氮肥显著提高了植物氮含量(P<0.05),进而降低了碳氮比(P<0.05),提高了氮磷比(P<0.05)。割草处理后扁蓿豆的氮含量显著提高了0.18%(P<0.05),羊草的氮含量显著降低了0.13%(P<0.05),冷蒿与菊叶委陵菜的氮含量无显著变化。割草显著提高了冷蒿和菊叶委陵菜的磷含量(P<0.05),但是未影响羊草和扁蓿豆的磷含量。该研究证实了氮添加或割草会影响部分草地物种的化学计量特征,但是氮添加或割草对植物化学计量特征的影响存在种间差异。     

茯苓碳氮磷化学计量学特征

为探明茯苓的碳、氮、磷生态化学计量学特征,采集了云南省11个州、市42个居群的茯苓样本,分析了其菌核与表皮中碳(C)、氮(N)、磷(P)的化学计量特征.结果 表明:茯苓菌核中C、N、P的含量分别为40.24％-43.58％、0.176％-0.532％和0.020％-0.077％;C∶N、C∶P和N∶P的范围分别为93....     

Nitrogen loss in chicken litter compost as affected by carbon to nitrogen ratio and turning frequency

The study was undertaken to investigate the effects of carbon to nitrogen (C:N) ratio and turning frequency (TF) on the loss of total nitrogen (TN) during composting of chicken litter (a mixture of chicken manure, waste feed, feathers and sawdust) with a view to producing good quality compost. Carbon to nitrogen ratios of 20:1, 25:1 and 30:1 and TF of 2, 4 and 6 days were experimented. The initial physico-chemical properties of the litter were determined. During the composting process, moisture level in the piles was periodically replenished to 55% and the temperature, pH and TN of the chicken litter were periodically monitored. Also, the dry matter (DM), total carbon (TC), total phosphorus (P) and total potassium (K) were examined at the end of composting. The results showed that both C:N ratio and TF had significant (p < or = 0.05) effect on pile temperature, pH changes, TN, TC, P and K losses while DM was only affected (p < or = 0.05) by C:N ratio. All treatments reached maturation at about 87 days as indicated by the decline of pile temperatures to near ambient temperature. Losses of TN, which were largely attributed to volatilization of ammonia (NH3), were highest within the first 28 days when the pile temperatures and pH values were above 33 degrees C and 7.7, respectively. Moisture loss increased as C:N ratio and TF increased. In conclusion, the treatment with a combination of 4 days TF and C:N ratio 25:1 (T4R25) had the minimum TN loss (70.73% of the initial TN) and this indicated the most efficient combination.     

Investigations on decomposition of foliage of woody species using a perfusion method

The time for half of the total oxidizable carbon to be converted into CO₂ and other gaseous products (t_1/2) was studied for five tree species used in agroforestry. The study was conducted in a perfusion system with continuous aeration, and moisture content maintained at field capacity. This method was found to be suitable for studies of the initial stages of tree foliage decomposition. The overall rate was in the decreasing order: Leucaena>Calliandra>Gliricidia>Prosopis>Cassia. Decomposition started rapidly and then decreased rapidly for 2 to 3 weeks followed by a gradual decrease which continued for the remainder of the time.The time for 50 per cent of total oxidizable carbon to decompose was about 19 days for Leucaena, 30 days for Calliandra and Gliricidia, while Prosopis and Cassia took more than 30 days. Leucaena released the largest quantity of total N into the perfusing solution while Cassia gave the lowest amount.     

Quantification of the Nitrogen Cycle in a Prairie Stream

Nitrogen (N) was added for 35 days in the form of ¹⁵NH₄Cl to Kings Creek on Konza Prairie, Kansas. Standing stocks of N in key compartments (that is, nutrients, detritus, organisms) were quantified, and the amount of labeled N entering the compartments was analyzed. These data were used to calculate turnover and flux rates of N cycling through the food web, as well as nutrient transformation rates. Inorganic N pools turned over much more rapidly in the water column of this stream than in pelagic systems where comparable measurements have been made. As with other systems, the mass of ammonium was low but it was the key compartment mediating nutrient flux through the ecosystem, whereas dissolved organic N, the primary component of N flux through the system, is not actively cycled. Nitrification was also a significant flux of N in the stream, with rates in the water column and surface of benthos accounting for approximately 10% of the total ammonium uptake. Primary consumers assimilated 67% of the inorganic N that entered benthic algae and microbes. Predators acquired 23% of the N that consumers obtained. Invertebrate collectors, omnivorous crayfish (Orconectes spp.), and invertebrate shredders dominated the N flux associated with primary consumers. Mass balance calculations indicated that at least 23% of the 309 mg of ¹⁵N added during the 35 days of release was retained within the 210-m stream reach during the release. Overall, the rates of turnover of N in organisms and organic substrata were significantly greater when C:N was low. This ratio may be a surrogate for biological activity with regard to N flux in streams. Received 2 August 1999; accepted 18 July 2000.     

Dissolved organic nitrogen budgets for upland, forested ecosystems in New England

Relatively high deposition ofnitrogen (N) in the northeastern United States hascaused concern because sites could become N saturated.In the past, mass-balance studies have been used tomonitor the N status of sites and to investigate theimpact of increased N deposition. Typically, theseefforts have focused on dissolved inorganic forms ofN (DIN = NH₄-N + NO₃-N) and have largelyignored dissolved organic nitrogen (DON) due todifficulties in its analysis. Recent advances in themeasurement of total dissolved nitrogen (TDN) havefacilitated measurement of DON as the residual of TDN– DIN. We calculated DON and DIN budgets using data onprecipitation and streamwater chemistry collected from9 forested watersheds at 4 sites in New England. TDNin precipitation was composed primarily of DIN. Netretention of TDN ranged from 62 to 89% (4.7 to 10 kgha^{minus 1} yr^{minus 1}) of annual inputs. DON made up themajority of TDN in stream exports, suggesting thatinclusion of DON is critical to assessing N dynamicseven in areas with large anthropogenic inputs of DIN.Despite the dominance of DON in streamwater,precipitation inputs of DON were approximately equalto outputs. DON concentrations in streamwater did notappear significantly influenced by seasonal biologicalcontrols, but did increase with discharge on somewatersheds. Streamwater NO₃-N was the onlyfraction of N that exhibited a seasonal pattern, withconcentrations increasing during the winter months andpeaking during snowmelt runoff. Concentrations ofNO₃-N varied considerably among watersheds andare related to DOC:DON ratios in streamwater. AnnualDIN exports were negatively correlated withstreamwater DOC:DON ratios, indicating that theseratios might be a useful index of N status of uplandforests.     

Assessment of the efficiency of different control programs to reduce Trioza apicalis Först. (Triozidae: Hemiptera) feeding damage and the spread of “Candidatus Liberibacter solanacearum” on carrots (Daucus carota ssp. sativus L.)

The control of carrot psyllid Trioza apicalis Förster largely relies on chemical measures, and the current integrated pest management (IPM) strategy is based on pest scouting. The number of active ingredients available for psyllid control will further decline in the coming years. The need for alternative control measures is therefore urgent. In this work the efficiency of different control programs including a kaolin particle film and plant-derived, crude saponin extract, chemical control, insect net and IPM (kaolin in combination with insecticides) programs to reduce psyllid feeding damage, reproduction and the spread of “Candidatus Liberibacter solanacearum” (CLso) in carrots was studied. Each year in 2016–2018, four replicates of each treatment were randomised in a row-column design on a commercial carrot farm. After the treatments were executed, the psyllid nymphs and eggs were counted. At the harvest, the carrot roots and shoots were weighed, damages assessed, and samples were taken for CLso detection from 50 plants at each replicate. Kaolin treatment alone and in combination with insecticides effectively reduced the number of psyllid nymphs and eggs in all the years studied. Saponin was applied only on the first year, since it significantly increased the number of T. apicalis eggs compared to other treatments. The insect net was superior to other treatments in all the studied aspects in all the years. Under normal weather conditions, the highest root weight was harvested under the insect net, followed by the chemical control program consisting of pyrethroids, kaolin treatment, untreated control and saponin treatment. During extreme weather conditions, chemical control programs were not effective at protecting the carrots from psyllid feeding, which was reflected as low root yield. In all years, the carrot leaf damage percent negatively correlated with the root weight. Similarly, the shoot:root ratio increased as the leaf-curling percentage rose, which was even pronounced under drought stress. The effect of climatic stress should be considered when developing IPM strategies.     

荒漠区地表凋落物分解对季节性降水增加的响应

为探讨季节性降水增加对荒漠生态系统凋落物分解的影响, 在古尔班通古特沙漠南缘, 选择粗柄独尾草(Eremurus inderiensis)叶、尖喙牻牛儿苗(Erodium oxyrrhynchum)叶、尖喙牻牛儿苗茎、沙漠绢蒿(Seriphidium santolinum)茎4种凋落物样品, 在2009-2011年研究了模拟季节降水增加(冬春增雪、夏季增水)和自然降水处理下凋落物的分解。持续2年的分解实验表明: (1)各组分凋落物的质量损失过程可以用负指数衰减方程较好地拟合(R²> 0.90); 经过637天的分解, 各组分凋落物质量残留率在自然降水、冬春增雪、夏季增水处理下均无显著性差异(p > 0.05)。粗柄独尾草叶、尖喙牻牛儿苗叶、尖喙牻牛儿苗茎、沙漠绢蒿茎在自然降水处理下的质量残留率分别为40.59%、35.50%、36.00%和63.96%; (2)各组分凋落物的质量残留率与N残留率显著正相关, 凋落物N的损失快于其质量损失, 且初始N含量与分解速率显著正相关(r = 0.60, p = 0.038), C/N解释了71%的地面凋落物分解速率。研究表明, 季节性的短暂降水增加对荒漠区地表凋落物分解没有显著影响, 凋落物初始化学组成是预测荒漠区地表凋落物分解的重要因素。     

The effects of insect–insect interactions on the performance of three biological control agents released against water hyacinth

Insect–insect interactions can have implications for biological control programmes when multiple agent species are released. In many cases there is an increase in the efficacy when more than one species is used; however, there is a possibility that releasing an additional species into a programme could have a negative effect. The interactions between three arthropod agents of water hyacinth Eichhornia crassipes (Martius) Solms-Laubach, Eccritotarsus catarinensis (Carvalho), Neochetina bruchi Hustache and Neochetina eichhorniae Warner were investigated in an experiment to measure the impact that pairwise combinations of the insects may have on their performance. There was a significant interaction between the mirid E. catarinensis and the weevil N. eichhorniae, with significantly fewer weevil feeding scars when in combination with the mirid (approximately 0.2 scars per cm²) than when alone (approximately 0.4 scars per cm²). There were also slightly fewer petioles mined by N. eichhorniae when in combination with the mirid. Interestingly there was a negative interaction between the two weevil species when in combination, with the number of feeding scars being significantly lower per individual when the two species were in combination. None of the insects performed significantly better when in combination with another insect, however, the mirid was never negatively affected by the presence of either weevil species. The interactions observed between the insects tested were identifiable but subtle and are unlikely to have implications on establishment or performance of the insects in the introduced range, South Africa.     

Determining the appropriate pretreatment procedures and the utility of liver tissue for bulk stable isotope (δ13C and δ15N) studies in sharks

Stable-isotope analysis (SIA) provides a valuable tool to address complex questions pertaining to elasmobranch ecology. Liver, a metabolically active, high turnover tissue (~166 days for 95% turnover), has the potential to reveal novel insights into recent feeding/movement behaviours of this diverse group. To date, limited work has used this tissue, but ecological application of SIA in liver requires consideration of tissue preparation techniques given the potential for high concentrations of urea and lipid that could bias δ¹³C and δ¹⁵N values (i.e., result in artificially lower δ¹³C and δ¹⁵N values). Here we investigated the effectiveness of (a) deionized water washing (WW) for urea removal from liver tissue and (b) chloroform-methanol for extraction of lipids from this lipid rich tissue. We then (a) established C:N thresholds for deriving ecologically relevant liver isotopic values given complications of removing all lipid and (b) undertook a preliminary comparison of δ¹³C values between tissue pairs (muscle and liver) to test if observed isotopic differences correlated with known movement behaviour. Tests were conducted on four large shark species: the dusky (DUS, Carcharhinus obscurus), sand tiger (RAG, Carcharias taurus), scalloped hammerhead (SCA, Sphyrna lewini) and white shark (GRE, Carcharodon carcharias). There was no significant difference in δ¹⁵N values between lipid-extracted (LE) liver and lipid-extracted/water washed (WW) treatments, however, WW resulted in significant increases in %N, δ¹³C and %C. Following lipid extraction (repeated three times), some samples were still biased by lipids. Our species-specific “C:N thresholds” provide a method to derive ecologically viable isotope data given the complexities of this lipid rich tissue (C:N thresholds of 4.0, 3.6, 4.7 and 3.9 for DUS, RAG, SCA and GRE liver_LEWW tissue, respectively). The preliminary comparison of C:N threshold corrected liver and muscle δ¹³C values corresponded with movement/habitat behaviours for each shark; minor differences in δ¹³C values were observed for known regional movements of DUS and RAG (δ¹³C_Diffs = 0.24 ± 0.99‰ and 0.57 ± 0.38‰, respectively), while SCA and GRE showed greater differences (1.24 ± 0.63‰ and 1.08 ± 0.71‰, respectively) correlated to large-scale movements between temperate/tropical and pelagic/coastal environments. These data provide an approach for the successful application of liver δ¹³C and δ¹⁵N values to examine elasmobranch ecology.     

Nitrogen input together with ecosystem nitrogen enrichment predict nitrate leaching from European forests

The IFEF database (Indicators of Forest Ecosystem Functioning), consisting of nitrogen deposition, nitrate leaching fluxes, and soil and ecosystem characteristics, is analysed to evaluate the C/N ratio in the organic horizon as an indicator of nitrate leaching. One hundred and eighty one forests are examined, from countries across Europe ranging from boreal to Mediterranean regions, encompassing broadleaf and coniferous sites and plot and catchment studies. N input in throughfall ranges from less than 1 kg N ha^?1 y^?1 in northern Norway and Finland to greater than 60 kg N ha^?1 y^?1 in the Netherlands and Czech Republic. The amount of NO₃^– leached covers a smaller range, between 1 and 40 kg N ha^?1 y^?1. Nitrate leaching is strongly dependent on the amount of nitrogen deposited in throughfall (N input) and simply adding the C/N ratio in the organic horizon to a regression equation does not improve this relationship. However, when the data are stratified based on C/N ratios less than or equal to 25 and greater than 25, highly significant relationships (P < 0.05) are observed between N input and NO₃^– leached. The slope of the relationship for those sites where C/N ratio is ≤ 25 (′nitrogen enriched′ sites) is twice that for those sites where C/N ratio is > 25. These empirical relationships may be used to identify which forested ecosystems are likely to show elevated rates of nitrate leaching under predicted future nitrogen deposition scenarios. Elevated NO₃^– leaching also shows a relationship with soil pH, with high rates of NO₃^– leaching only observed at sites with a pH < 4.5 and N inputs > 30 kg N ha^?1 y^?1. Tree age and species have no significant impact on the ecosystem response to N input at a regional scale.     

Synergistic effects of Trichoshield on enhancement of growth and resistance to downy mildew in pearl millet

Trichoshield, a talc formulation consisting of spores of Trichoderma harzianum, Trichoderma lignorum, Gliocladium virens and Bacillus subtilis was tested, following different application methods, for its ability to promote growth of pearl millet plants and to induce resistance to downy mildew of pearl millet. Under laboratory conditions, trichoshield seed treatment enhanced seed germination and seedling vigor of pearl millet significantly over the control; under greenhouse conditions vegetative growth parameters like height, fresh and dry weight, leaf area and number of tillers were significantly enhanced over the control: Trichoshield formulation offered greater protection against downy mildew in comparison with individual strains of T. harzianum, T. lignorum, G. virensand B. subtilis. Among the methods of application, foliar spray was found to be a more efficient delivery method than seed treatment or slurry treatment. Combinations of foliar spray with seed treatment and slurry treatment produced the same effect as foliar spray alone. Under field conditions, trichoshield treatment enhanced reproductive parameters like number of earheads, length and girth of earheads, 1000 seed weight and yield significantly over the control. Days required for 50% flowering was reduced by 4 days compared to the control. Yield enhancement of 28% over the control was highly significant. Trichoshield treatment offered protection ranging from 52 to 71% under field conditions, depending on the application method. However, the chemical fungicide metalaxyl Apron provided the highest protection against downy mildew, both under greenhouse and field conditions.