The potential of periphyton-based culture of two Indian major carps, rohu Labeo rohita (Hamilton) and gonia Labeo gonius (Linnaeus)

The effects of periphyton, grown on bamboo substrates, on growth and production of two Indian major carps, rohu, Labeo rohita (Hamilton) and gonia, Labeo gonius (Linnaeus), were studied at the Bangladesh Agricultural University, Mymensingh. For each species, five ponds were provided with bamboo substrates and five ponds without substrate (control). Ponds were stocked at a rate of 10 000 ha^?1 in both treatments. There was no discernible difference in water quality parameters between treatments. A large number of plankton (39 genera) showed periphytic nature and colonized the bamboo substrates. Rohu grew faster, resulting in a 77% higher net production (P < 0.05) in the ponds with bamboo substrates compared with the ponds without substrate. In contrast, the growth and production of gonia did not vary significantly (P > 0.05) between the substrate and control ponds. Rohu seems to be a more suitable candidate for periphyton‐based aquaculture systems than gonia.     

Impact of agricultural land use on distribution of microbial biomass and activity within soil aggregates

The presence of aggregates of various sizes in the soil is an important condition for soil carbon sequestration. In this system, microbial biomass is a key link. This work was devoted to the study of the influence of land use systems on the distribution of SOС, MB-SIR, microbial activity and eco-physiological indices (qCO₂, QR, MB-SIR/SOС and qCO₂/SOС) in relation to the size of soil aggregates. The distribution of SOС, MB-SIR and mineralization activity among the aggregates was heterogeneous. In the soil of crop rotation, high mineralization activity and MB-SIR were found in the aggregates 0.5–0.1 mm, in the monoculture soil in aggregates <0.1 mm and in the control soil in the aggregates 1–0.25 mm. There was a general trend towards a decrease in microbial activity, MB-SIR and SOС availability with an increase in aggregate size. In agricultural soils, microbial activity was determined by large aggregates (>5 mm), while in the control soil, by the aggregates 5–1 mm. Depending on the type of site and the size of aggregates, the differences in microbial metabolism were revealed. The qCO₂ and QR values decreased, and the MB-SIR/SOС and qCO₂/SOС increased in the series: control soil > crop rotation > monoculture. In the control soil, the values of the eco-physiological indices decreased with decreasing aggregate size. And vice versa, in agricultural soils, these parameters were the highest in the microaggregates (<0.25 mm). The monoculture soil, in contrast to the control soil and crop rotation soil, turned out to be more energy efficient.     

烟蒜轮作与套作对土壤微生物类群数量的影响

采取田间试验方式,以单作烤烟为对照,研究了不同年度和烤烟生育时期烟蒜轮作、烟蒜套作对根际和非根际土壤细菌、真菌、放线菌、解钾菌和解磷菌数量变化的影响。结果表明:随生育时期推进,烟蒜轮作和烟蒜套作处理根际土壤细菌含量高于单作烤烟的趋势越来越明显。2014年,上部叶成熟期烟蒜轮作、烟蒜套作根际土壤细菌数量是单作烤烟的1.41倍和1.24倍。中部叶成熟期和上部叶成熟期,烟蒜轮作处理根际土壤真菌数量最少,但2014年烟蒜轮作和烟蒜套作处理下非根际土壤真菌数量高于单作烤烟处理。烟蒜轮作、烟蒜套作处理根际土壤放线菌数量高于单作烤烟,上部叶成熟期分别是单作烤烟2.01倍和2.93倍(2013年)、1.12倍和1.28倍(2014年)。烟蒜轮作、烟蒜套作处理根际土壤解钾菌和解磷菌含量在烤烟生长发育的中后期显著高于单作烤烟,且非根际土壤的解磷菌含量也呈现相同的趋势。不同年度,烟蒜轮作与烟蒜套作处理烟叶产量和上中等烟率均显著高于单作烤烟处理。烟蒜轮作和烟蒜套作种植模式能改良土壤根际环境微生物结构,维持良好的土壤质量状态。     

干热河谷20年生2种人工恢复植被个体生长特性研究

以元谋干热河谷20年生赤桉纯林、新银合欢纯林以及赤桉×新银合欢混交林为研究对象,对其林木单株进行树干解析,研究不同造林模式下2个树种的生长特性。结果表明: 1）新银合欢的混植促进了赤桉的生长。2）赤桉、新银合欢树高平均生长量和连年生长量总体均呈下降趋势,胸径的平均生长量和连年生长量在5～10 年呈下降趋势,在10～15 年期间呈上升趋势（除混交林内赤桉）,之后又下降。3）根据Logistic生长曲线的变化率,可将赤桉、新银合欢5～10 年划分为生长初期,10～25 年为生长快速期,之后为生长稳定期;经模型预测:赤桉纯林在23 年时达到数量成熟,赤桉混交林在25 年时达到数量成熟,纯林以及混交林内新银合欢均在24 年时达到数量成熟。针对赤桉、新银合欢生长特点,提出在生长初期和生长快速期增加水肥供给并进行适当疏伐等措施以促进林木生长。      

中国南方红壤丘陵区大豆－柑橘间作系统植物磷的吸收特征

A field microplot experiment was conducted in the red soil hilly region of South China to evaluate plant phosphorus (P)uptake under soybean and citrus monoculture and the soybean-citrus intercropping system using the ³²P tracer technique. P fertilizer was applied at three depths (15, 35, and 55 cm). The experimental results showed that the planting pattern and ³²P application depth significantly affected the characteristics of P uptake by soybean and citrus. Under the soybean-citrus intercropping system, considerable competition was observed when the ³²P fertilizer was applied to the topsoil (15 cm); therefore, the 32P recovery rate declined by 41.5% and 14.7% for soybean and citrus, and 32P supplying amount of topsoil to soybean and citrus decreased by 346.8 and 148.1 mg plot^-1, respectively, compared to those under the monoculture. However, ³²P recovery of soybean was promoted when ³²P fertilizer was applied to the deeper soil layers (35 and 55 cm)under soybean-citrus intercropping. Under the soybean monoculture, 32P fertilizer could hardly be used by soybean when ³²P fertilizer was applied at the 55 cm depth or below, with the recovery rate being less than 0.1%; it was up to 0.253% by soybean under intercropping. The higher P recovery of soybean under soybean-citrus intercropping when P was applied in the deeper soil layers was because part of the P nutrient that the citrus absorbed from the deeper soil layers could be released into the topsoil and then it could be used by the soybean.     

石榴-绿豆间作系统土壤呼吸及其影响因子研究

土壤呼吸是陆地生态系统碳循环的重要环节,在维持全球碳平衡中发挥着重要作用。于2010年6—10月,在黄河小浪底森林生态系统研究站,利用Li-8100红外动态土壤呼吸自动观测系统、温湿度自动观测系统测定了石榴-绿豆间作系统（间作系统）和绿豆单作系统（单作系统）土壤呼吸速率(soil respiration rate, SRR)及土壤温度和湿度。结果表明:1) 间作系统和单作系统的SRR日波动在晴天-多云呈单峰变化趋势,在阴天日波动变化幅度较小。间作系统的SRR高于单作系统。整个观测时期内间作系统和单作系统的平均SRR分别为2.996 μmol ·m^-2· s^-1和2.378 μmol·m^-2·s^-1。2) 间作系统和单作系统SRR与15 cm处土壤温度存在显著的指数相关关系,在该深处的Q₁₀值分别为2.462和1.793 3) 间作系统和单作系统与20 cm处的土壤体积含水量与SRR的相关关系均不明显。     

马尾松与红椎纯林及混交林生态系统碳储量研究

为了解树种与造林模式对人工林生态系统碳储量的影响,在南亚热带相同立地上,采用样地调查方法,对33年生马尾松纯林(PCL)、红椎纯林(CCL)、马尾松×红椎同龄混交林(PCM)生态系统碳储量进行了研究。结果表明:PCM、PCL、CCL人工林生态系统碳储量分别为:235.38、196.40、144.59t/hm^2,处理间差异显著(P<0.05),混交林生态系统碳储量显著高于纯林,马尾松纯林显著高于红椎纯林。PCM、PCL、CCL人工林生态系统碳储量在不同层次的分配比例,乔木层分别为:53.70%、54.05%、33.02%;地被物层为:1.47%、2.06%、1.37%;土壤层为:44.83%、43.89%、65.61%。生态系统碳储量在不同层次分配比例排序,PCM、PCL都为乔木层>土壤层>地被物层;CCL为土壤层>乔木层>地被物层,乔木层和土壤层碳储量占生态系统碳储量的97.94%~98.63%,地被物层仅占1.37%~2.06%。     

不同种植模式核桃品质、产量的比较分析

为研究不同种植模式核桃品质、产量的差异,以单作（核桃纯林上坡B1、核桃纯林下坡B2）与间作（红枣/核桃上坡C1、红枣/核桃下坡C2）2种种植模式的核桃为研究对象,对其品质（单果质量、含水量、出仁率、脂肪含量、脂肪酸组分及其含量、蛋白质含量、氨基酸组分及其含量、还原糖含量）进行比较和产量分析。结果表明,不同种植模式的核桃品质、产量均有较大差异,纯林模式有利于核桃积累水解后还原性糖,而间作模式有利于核桃积累蛋白质。B2处理的核桃出仁率、脂肪含量、脂肪酸含量、氨基酸含量、还原糖含量均较高,而其蛋白质含量较低;同种种植模式,下坡处理的核桃产量显著高于上坡处理的核桃产量。综合考虑各项指标,B2处理的核桃的产量最高、品质较好。     

Long‐distance dispersal and its influence on adaptation to host resistance in a heterogeneous landscape

Small propagules like pollen or fungal spores may be dispersed by the wind over distances of hundreds or thousands of kilometres, even though the median dispersal may be only a few metres. Such long‐distance dispersal is a stochastic event which may be exceptionally important in shaping a population. It has been found repeatedly in field studies that subpopulations of wind‐dispersed fungal pathogens virulent on cultivars with newly introduced, effective resistance genes are dominated by one or very few genotypes. The role of propagule dispersal distributions with distinct behaviour at long distances in generating this characteristic population structure was studied by computer simulation of dispersal of clonal organisms in a heterogeneous environment with fields of unselective and selective hosts. Power‐law distributions generated founder events in which new, virulent genotypes rapidly colonized fields of resistant crop varieties and subsequently dominated the pathogen population on both selective and unselective varieties, in agreement with data on rust and powdery mildew fungi. An exponential dispersal function, with extremely rare dispersal over long distances, resulted in slower colonization of resistant varieties by virulent pathogens or even no colonization if the distance between susceptible source and resistant target fields was sufficiently large. The founder events resulting from long‐distance dispersal were highly stochastic and exact quantitative prediction of genotype frequencies will therefore always be difficult.