Soil organic matter, microbial biomass and enzyme activities in a tropical agroforestry system

 The effects of growing trees in combination with field crops on soil organic matter, microbial biomass C, basal respiration and dehydrogenase and alkaline phosphatase activities were studied in soils under a 12-year-old Dalbergia sissoo (a N₂-fixing tree) plantation intercropped with a wheat (Triticum aestivum) – cowpea (Vigna sinensis) cropping sequence. The inputs of organic matter through D. sissoo leaf litter increased and crop roots decreased with the increase in tree density. Higher organic C and total N, microbial biomass C, basal soil respiration and activities of dehydrogenase and alkaline phosphatase were observed in treatments with tree-crop combination than in the treatment without trees. Soil organic matter, microbial biomass C and soil enzyme activities increased with the decrease in the spacing of the D. sissoo plantation. The results indicate that adoption of the agroforestry practices led to an improved organic matter status of the soil, which is also reflected in the increased nutrient pool and microbial activities necessary for long-term productivity of the soil. However, tree spacing should be properly maintained to minimize the effects of shading on the intercrops. Received: 21 February 1997     

银中杨人工林抚育采伐技术研究

采用标准地调查方法,对初植密度为2 m×2m的银中杨人工林的抚育采伐开始期和采伐强度进行调查研究,确定抚育采伐开始期为8年生时,采伐强度为50%。研究确定了银中杨人工林的经营密度表,以期为生产经营提供依据。     

Quinone Binding Sites of Membrane Proteins as Targets for Inhibitors

Quinones are a central component of most photosynthetic and respiratory electron transfer chains. The proteins that reduce and oxidise these quinones have quinone binding sites—Q sites—that are good targets for pesticides. This paper reviews the diversity of these sites, their possible structure, and the types of compounds that act upon them.     

Basal internode elongation of rice as affected by light intensity and leaf area

Short basal internodes are important for lodging resistance of rice(Oryza sativa L.).Several canopy indices affect the elongation of basal internodes,but uncertainty as to the key factors determining elongation of basal internodes persists.The objectives of this study were(1)to identify key factors affecting the elongation of basal internodes and(2)to establish a quantitative relationship between basal internode length and canopy indices.An inbred rice cultivar,Yinjingruanzhan,was grown in two split-plot field experiments with three N rates(0,75,and 150 kg N ha−1 in early season and 0,90,and 180 kg N ha−1 in late season)as main plots,three seedling densities(16.7,75.0,and 187.5 seedlings m−2)as subplots,and three replications in the 2015 early and late seasons in Guangzhou,China.Light intensity at base of canopy(Lb),light quality as determined from red/far-red light ratio(R/FR),light transmission ratio(LTR),leaf area index(LAI),leaf N concentration(NLV)and final length of second internode(counted from soil surface upward)(FIL)were recorded.Higher N rate and seedling density resulted in significantly longer FIL.FIL was negatively correlated with Lb,LTR,and R/FR(P<0.01)and positively correlated with LAI(P<0.01),but not correlated with NLV(P>0.05).Stepwise linear regression analysis showed that FIL was strongly associated with Lb and LAI(R2=0.82).Heavy N application to pot-grown rice at the beginning of first internode elongation did not change FIL.We conclude that FIL is determined mainly by Lb and LAI at jointing stage.NLV has no direct effect on the elongation of basal internodes.N application indirectly affects FIL by changing LAI and light conditions in the rice canopy.Reducing LAI and improving canopy light transmission at jointing stage can shorten the basal internodes and increase the lodging resistance of rice.     

Influence of light intensity on biofilm formation and the performance of pink shrimp Farfantepenaeus paulensis juveniles reared in cages

A reduction in light intensity may increase shrimp activity, although it may also negatively affect the development of photoautotrophic organisms present in biofilm, an important natural food source for shrimp. This experiment evaluated the influence of light intensity on biofilm development and on the growth of cultured Farfantepenaeus paulensis juveniles. Six cages were deployed in a shrimp culture pond and stocked with 60 juveniles (0.72 ± 0.03 g). Three cages were randomly chosen and covered with five layers of polyamide net to reduce light incidence (shaded treatment), while the other three cages were not covered (control treatment). Biofilm chlorophyll a and microorganism abundance, as well as shrimp growth, were monitored during the experiment. Chlorophyll a concentration and the abundance of bacteria and flagellates were significantly lower in the shaded treatment (P<0.05). After 75 rearing days, shrimp stocked in control treatment achieved significantly higher (5.98 g) (P<0.05) mean weight than shrimp reared in shaded treatment cages (5.13 g). Similarly, the biomass produced was also significantly higher (P<0.05) in the control treatment (322.92 g) than in the shaded treatment (287.31 g). The results of this study demonstrate that light intensity has a huge influence on shrimp performance mainly due to the increase in natural food availability.     

电麻醉对西伯利亚鲟幼鱼行为特性与血清离子浓度的影响

研究了不同强度电麻醉对西伯利亚鲟幼鱼行为特性与血清离子浓度的影响。西伯利亚鲟电麻醉阶段包括部分失去平衡期、完全失去平衡期、完全麻醉期和鳃动停止期等4个时期。电麻醉时西伯利亚鲟呈现趋阳性;随着电压升高,到达各麻醉阶段时间与恢复时间逐渐缩短。西伯利亚鲟到达完全麻醉期时间在15 V、20 V、25 V、35 V组间均有显著差异,在30 V与35 V时分别仅为97.0 s和68.8 s,而恢复时间为0 s。各试验组西伯利亚鲟在电麻醉时鳃动频率均增加,而恢复阶段均降低。电麻醉对西伯利亚鲟摄食与活动状态均无显著影响。随着电压升高,钾离子与镁离子浓度先下降后上升,钙离子则先上升后下降。钠离子与氯离子浓度变化较大,均是15 V组时浓度最低,20 V时浓度最高。磷离子浓度呈现增高趋势。pH值在麻醉后降低,对照组与其余各组均有显著性差异。因此西伯利亚鲟幼鱼适宜电麻醉强度为25~30 V,电麻醉是种较好的麻醉方法,具有广泛的应用前景。     

Characteristics of phosphorus uptake kinetics of poinsettia and marigold

In a previous experiment it has been found that maximum uptake rate (I_max), Michaelis constant (K_m), and minimum nutrient concentration (C_min) as plant physiological characteristics may be important for phosphorus (P) uptake in peat-substrate. Thus, variation of P uptake parameters was evaluated with a series of depletion studies for poinsettia (Euphorbia pulcherrima) and marigold (Tagetes patula) under fluctuating climatic conditions and different developmental stages.     

农用柴油发动机噪声污染分析

柴油发动机广泛应用于各类农业机械中,由其带来的噪声污染也日益严重.为研究柴油机的整机噪声,利用声强测试技术中的p-p法,对某型农用六缸柴油发动机进行实测.通过对发动机各包络面上声强分布和声功率测试结果的分析,确定了其噪声源的位置、声功率的大小、主要噪声频率及整机辐射强度,为控制柴油发动机噪声污染提供了理论依据.     

Influence of light intensity on feeding, growth, and early survival of leopard coral grouper (Plectropomus leopardus) larvae under mass-scale rearing conditions

This study investigated the effect of different light intensities on feeding, growth and survival of early stage leopard coral grouper Plectropomus leopardus larvae. Four different light intensities (0, 500, 1000 and 3000 lx) were used and larvae were kept under constant light conditions from 0 day after hatching (DAH) to 5 DAH. The larvae were fed a small S-type of Thai strain rotifers at a density of 20 individuals/mL from 2 DAH. The number of rotifers in larval digestive organ and total length of larvae were examined at 3 h intervals between 04:00 and 22:00 h on 3 DAH, and thereafter at 6 h intervals until the end of the experiment (5 DAH). Four experimental trials of the larval rearing were repeated using by 60 kL mass-scale rearing tanks. The results indicate that coral grouper larvae are visual feeders and their food intake increases with increasing light intensity. Food intake of larvae reared at 3000 lx was significantly higher than those reared at 0–1000 lx on 3 DAH despite being the first-feeding day (P < 0.01). On 4 DAH, total length of larvae reared at 3000 lx was significantly larger than those reared at the lower light intensities (0, 500 and 1000 lx), and thereafter light intensity significantly influenced larval feeding and growth until the end of the experiment. Survival on 5 DAH did not show a significant difference between light intensities, but survival rate at 3000 lx and 1000 lx had a tendency to be higher than those reared at the lower light intensities (0 and 500 lx). In contrast, larvae reared at 0 lx exhibited stagnant and/or negative growth. These results indicate that light intensity is significantly the factor affecting larval feeding, growth, and survival in coral grouper larvae under the rearing conditions.     

四川盆地紫色土N,P损失载体及其影响因子

农业面源污染对环境的压力越来越大,已引起国内外广泛重视。利用人工降雨装置模拟3种不同强度的降雨,采用模拟径流小区研究了雨强及耕作措施对紫色土N,P损失量及载体的影响。结果表明:在耕作方式相同时,雨强越大,地表径流量越大,地下径流量减少,总径流量增加,不利于土壤保蓄雨水和含水量的提高。在相同雨强条件下,平作的地表径流量最大,土壤侵蚀也最剧烈。横坡垄作在中小雨强条件下控制地表径流和侵蚀的效果非常明显,但在大雨强条件下,控制径流和泥沙的效果减弱;横坡垄作有增加地下径流和N流失量的趋势。在本试验条件下,有约1%的化肥N(速效N)被雨水淋洗出土体并排放到环境中;而速效P的流失量只占化肥P的3/10000~10/10000,流失量很微小。紫色土坡耕地P流失载体是泥沙,流失量更易受雨强的影响,要控制P流失,首先应防止土壤侵蚀;横坡垄作能有效控制土壤侵蚀,因此,也能较好控制P流失。紫色土坡耕地N流失载体在雨强较小时是径流,径流中又以壤中流为主,要控制N流失,首先必须控制壤中流;传统横坡垄作会加大壤中流量,也就加大了N流失。全面控制紫色土的N,P损失,必须采用控蚀耕作、增厚土层、提升土壤有机质等措施。