杠柳ISSR引物的筛选及PCR反应体系的优化

为建立适用于杠柳ISSR分子标记研究的扩增体系,进一步利用ISSR标记研究杠柳遗传多样性,探讨了杠柳ISSR分子标记中的各影响因素,分别对河北11个不同地区杠柳基因组DNA进行PCR扩增,在Taq MasterMix(康为世纪)基础上对影响ISSR-PCR扩增结果的模板DNA浓度、循环次数、引物退火温度进行梯度筛选。结果表明:在100条通用引物中共筛选出34条扩增条带清晰、整齐的ISSR引物;确立了适合杠柳ISSR分子标记的反应体系:总反应体积25μL,其中Taq MasterMix(含DNA聚合酶、MgCl_2、dNTPs、反应缓冲液以及稳定剂)12.5μL,模板DNA 1μL(70ng/μL),正向引物和反向引物各1μL(10μmol/L)。该体系的确立为今后利用ISSR技术对杠柳种质资源的遗传多样性分析奠定了技术基础。     

Pesticidal Activity of the Leaf and Bark Extracts of Giliricidia sepium on Callosobrucus maculatus

Abstract

The effects of different concentrations of cold and hot aqueous extracts of G. sepium on C. maculatus, the storage pest of cow-pea were examined. The extracts had a killing effect on the weevils. The percentage mortality of the weevils increased with the increase in the extract concentrations. Statistical analyses at 5% level revealed that significant differences abound in the efficacies of the cold and hot aqueous extracts. The hot aqueous leaf and bark extracts tend to have more toxic effect than the cold aqueous extracts. Also, extracts from the bark tend to be more toxic to the weevils than those of the leaves.     

Temporal change in carbon stocks of cocoa–gliricidia agroforests in Central Sulawesi,Indonesia

In a false-time series, the temporal development of cocoa–gliricidia carbon (C) stocks and soil organic carbon (SOC) were investigated in Napu and Palolo Valleys of Central Sulawesi, Indonesia. As a first step, the Functional Branch Analysis (FBA) method was used to develop allometric equations for the above- and below-ground growth of cocoa and gliricidia. FBA resulted in shoot–root ratios of 2.54 and 2.05 for cocoa and gliricidia, respectively. In Napu and Palolo, the trunk diameter and carbon levels per gliricidia tree were always much greater than that of cocoa. The highest aerial carbon levels were attained at year four in Napu (aerial cocoa–gliricidia = 20,745.2 kg C ha⁻¹) and at year five in Palolo (aerial cocoa–gliricidia = 38,857.0 kg C ha⁻¹). After years four or five, however, the reduced stocking density of gliricidia attributed to a loss of aerial C. During the time spans in question, SOC remained fairly stable though slightly decreasing in Napu and slightly increasing in Palolo. The SOC harbored a vastly greater amount of system C (one-half and one-third of SOC in the 0–15 cm stratum in Napu and Palolo, respectively) relative to tree components. Eight years (Napu) or 15 years (Palolo) after conversion of a rainforest to cocoa–gliricidia agroforestry caused an 88% and 87% reduction of aerial C-stocks in Napu and Palolo, respectively.     

杠柳萃取物对小菜蛾幼虫的毒杀活性研究

以杠柳Periploca sepium Bunge的根为材料进行甲醇超声波提取,粗提物以水/氯仿(1:1,v/v)萃取获得杠柳根氯仿萃取物。测定了萃取物对小菜蛾Plutella xyllostellaL.3龄幼虫的胃毒和触杀活性。实验结果显示,在50μg/头剂量处理下24h和48h后,氯仿萃取物对小菜蛾3龄幼虫的胃毒死亡率分别为82.22%和92.59%,显著高于触杀死亡率58.89%和68.15%。这一结果表明,杠柳根中含有对小菜蛾幼虫具有较强胃毒作用的活性成分。     

Differential Phosphorus Uptake and Use Efficiency Among Selected Nitrogen‐Fixing Tree Legumes over Time

Abstract

A study was carried out on three nitrogen (N₂)‐fixing tree legumes, i.e., Gliricidia sepium cv. ILG50, Leucaena leucocephala cv. K28, and Albizia lebbeck to assess their differential phosphorus (P) nutrition capability over time. Dry‐matter (DM) yields, P concentration, P uptake and partitioning in plants, and P use efficiency were estimated at 4, 8, 12, and 16 months after planting (MAP). The trees showed a large interspecific variation both in DM yields and P uptake. Concentration of P ranged from 0.042 to 0.275% and varied both among parts in each tree and among tree species over time. Leaves P concentrations showed a greater reduction with tree age than either stems or roots. Phosphorus uptake correlated significantly with plant DM (r = 0.893–0.946) across tree species, and had a steady increasing pattern up to at least 12 MAP. Over ages, Gliricidia outperformed the other species in P uptake. However, Leucaena was the most efficient user of P followed by Albizia and Gliricidia, in that order. Further, Leucaena revealed an attractive feature for alley cropping in that it stored up to 37% of the P accumulated in its leaves in contrast to only 24.1% for Gliricidia and 19.2% for Albizia. Therefore, the low P supply by trees into alley cropping is in part due to its unbalanced partitioning into stems to the expenses of leaves. The study shows also that P concentration in perennials is lower than it is reported in annual crops.     

Transfer of N fixed by a legume tree to the associated grass in a tropical silvopastoral system

Below-ground transfer of nitrogen (N) fixed by legume trees to associated non-N₂-fixing crops has received little attention in agroforestry, although the importance of below-ground interactions is shown in other ecosystems. We used ¹⁵N natural abundance to estimate N transfer from the legume tree Gliricidia sepium (Jacq.) Kunth ex Walp. to C₄ grass Dichanthium aristatum (Poir.) C.E. Hubb. in a silvopastoral system, where N was recycled exclusively by below-ground processes and N₂ fixation by G. sepium was the sole N input to the system. Finding a suitable reference plant, a grass without contact with tree roots or litter, was problematic because tree roots invaded adjacent grass monocrop plots and soil isotopic signature in soil below distant grass monocrops differed significantly from the agroforestry plots. Thus, we used grass cultivated under greenhouse conditions in pots filled with agroforestry soil as the reference. A model of soil ¹⁵N fractionation during N mineralization was developed for testing the reliability of that estimate. Experimental and theoretical results indicated that 9 months after greenhouse transplanting, the percentage of fixed N in the grass decreased from 35% to <1%, due to N export in cut grass and dilution of fixed N with N taken up from the soil. The effect of soil ¹⁵N fractionation on the estimate of the reference value was negligible. This indicates that potted grass is a suitable reference N transfer studies using ¹⁵N natural abundance. About one third of N in field-grown grass was of atmospheric origin in agroforestry plots and in adjacent D. aristatum grassland invaded by G. sepium roots. The concentration of fixed N was correlated with fine root density of G. sepium but not with soil isotopic signature. This suggests a direct N transfer from trees to grass, e.g. via root exudates or common mycorrhizal networks.     

Tree phenology and water availability in semi-arid agroforestry systems

Four common agroforestry trees, including both exotic and native species, were used to provide a range of leafing phenologies to test the hypothesis that temporal complementarity between trees and crops reduces competition for water in agroforestry systems during the cropping period and improves utilisation of annual rainfall. Species examined included Melia volkensii, which sheds its leaves twice a year, Senna spectabilis and Gliricidia sepium, which shed their leaves once during the long dry season, and the evergreen Croton megalocarpus. Phenological patterns were examined in relation to climatic conditions in the bimodal rainfall regions of Kenya to identify factors which dictate the intensity of competition between trees and crops.

The main differences in leaf cover patterns were between indigenous and exotic tree species. The Central American species, S. spectabilis and G. sepium, shed their foliage during the dry season before the short rains, whereas the native species, M. volkensii and C. megalocarpus, exhibited reduced leaf cover during both dry seasons. C. megalocarpus was the only species to maintain leaf cover throughout the 2-year experimental period. M. volkensii and S. spectabilis exhibited similar leafing phenology, losing almost all leaf cover during the long dry season (July–October) and flushing before the onset of the ensuing rains. S. spectabilis lost few leaves during the short dry season, whereas M. volkensii shed a greater proportion of its foliage before flushing prior to the long rains (March–July). M. volkensii lost much of its leaf cover during the 1997/1998 short rains (October–February), when soil water content was unusually high. Although essentially evergreen, leaf cover in C. megalocarpus decreased during the dry season and increased rapidly during periods of high rainfall. G. sepium exhibited a period of low leaf cover during the long dry season and did not regain full leaf cover until mid-way through the short rains. The mechanisms responsible for these phenological changes and the implications of tree phenology for resource utilisation and competition with crops are discussed.     

Nitrogen contribution of five leguminous trees and shrubs to alley cropped maize in Ibadan, Nigeria

There are abundant local legume trees and shrubs potentially suitable for alley cropping systems in the sub-Saharan Africa, which are yet to be studied. The nitrogen contribution of two years old Albizia lebbeck and S. corymbosato yield of maize grown in alley cropping was compared to that of Senna siamea, Gliricidia sepium and Leucaena leucocephala in four seasons at Ibadan. Maize shoot biomass and maize grain yield in A. lebbeck alley compared favourably with that in G. sepium and L. leucocephala. Maize biomass and grain yield in S. corymbosa alleys were the lowest. Within A. lebbeck, L. leucocpehala, and G. sepium alleys there were no significant differences in the maize yield in the alleys that received 0, 40 or 80 kg N/ha. Application of more than 40 kg N/ha in S. corymbosa alleys was not necessary as there was no significant increase in maize yield at the higher level of nitrogen. Maize yield and N uptake in A. lebbeck alleys were not significantly different from yield and N uptake in G. sepium, and L. leucocephala at the same fertilizer level. There was a significant correlation between hedgerow tree biomass and maize grain yield. At the end of twelve weeks after pruning application, the organic residues of the pruning applied in the alleys ranged from 5% in G. sepium and 44% in A. lebbeck in the first year compared with the original pruning applied which showed that the slow rate of A. lebbeck decomposition could have a beneficial effect on the soil. The maize N recovery from applied N fertilizer was low (10–22%). Percentage N recovery from the prunings was low in the non-N fixing trees (12–22%), while the recovery was high (49–59%) in A. lebbeck as well as in the other nitrogen fixing tree prunings. Thus A. lebbeck, apart from enhancing maize growth and grain yield like in L. leucocephala and G. sepium, had an added advantage because it remained longer as mulching material on the soil because of its slow rate of decomposition. It was able to survive pruning frequencies with no die-back. This indicates that A. lebbeck is a good potential candidate for alley cropping system in West Africa. S. corymbosa performed poorly compared with the other legume trees. Though it responded to N fertilizer showing a positive interaction between the hedgerow and fertilizer application, it had a high die back rate following pruning periods and termite attack.This revised version was published online in November 2005 with corrections to the Cover Date.     

Decomposition and nutrient release from leaves,twigs and roots of three alley-cropped tree legumes in central Togo

The decomposition of leaves, twigs and roots of two diameter classes (<1.5 mm, 1.5–5 mm) were examined in an alley cropping experiment withGliricidia sepium, Calliandra calothyrsus andSenna sianea in the subhumid savanna of Central Togo using the litterbag technique. The effect of the application of leaves and twigs as mulch or green manure was examined. Gliricidia showed the most rapid mass loss. For all species, leaves decomposed faster than roots. Twigs had the lowest decomposition rate except forCalliandra. The two diameter classes of roots decomposed differently in the three species:Gliricidia fine roots decomposed faster than its coarser root fraction, the coarse roots ofSenna decomposed faster than the fine roots.Termites influenced the mass loss of twigs and roots to varying extents for the different species. In the case of twigs this was markedly influenced by the mode of application: green manure showed more termite frass than mulch.Nutrient release resembled the mass loss patterns of the prunings except for K, which was leached independently from mass loss. The release of the different nutrients was in the order CaGliricidia andSenna seemed to be best for mulch and green manure production at our site.