Tree-grass coexistence in a flood-disturbed, semi-arid savanna system

The coexistence of trees and grasses in savanna ecosystems is a contentious phenomenon. Fire and herbivory disturbances are often cited as major structuring forces that create a sustainable tree–grass relationship. However, periodic flooding of savanna patches may also enable coexistence. The aim of this study was to investigate the effects of flood-disturbance on the recruitment patterns of Acacia karroo trees in a semi-arid savanna system in South Africa. We analysed the spatial coincidence of A. karroo seedlings with tussocks of the tall spiny grass Stipagrostis namaquensis in the riverbed and related herbivory intensity to spatial position. The data showed that A. karroo seedlings were significantly positively associated with S. namaquensis (Chi-square test, $ \chi_{1}^{2} = 4 5. 20 $ , n = 118, P < 0.001); A. karroo seedlings growing inside of tussocks experienced less browsing pressure than those growing in the floodplain (Kruskal–Wallis test, H = 11.90, n = 118, P < 0.01); and recruitment success of A. karroo trees was spatially discrete (K–S test, D = 0.78, n = 196, P < 0.01). We suggest that floods create an enemy-free zone, which S. namaquensis colonises and then facilitates successful A. karroo establishment. High levels of A. karroo recruitment in the riverbed may replenish the woodlands fringing the river, which appear to be sink areas for A. karroo seedlings. Thus, the interaction between disturbances at different spatial and temporal scales (flooding versus herbivory) seems to maintain the inherently unstable coexistence of tree and grass species in this ecosystem. These findings also suggested that flood disturbances alter the tree–grass relationship.     

Effect of Cold Hardening on Growth and Essential Oil Content of Mentha piperita L.

Divisions of running rhizomes of peppermint plants were planted in loamy clay soil in the experimental farm of National Research Centre, Dokki, Cairo, Egypt. After 21 days, the plants were exposed to low temperature 4, 7°C for 6, 9 and 12 days in controlled chamber before transplanting to large pots in winter season. Three cuttings were taken from the plants of different treatments during the season after 4, 7 and 10 months from transplanting. Representative samples of 6 replicates from each treatment were taken for the determination of vegetative growth and oil content in the leaves and branches.
The results obtained indicated that the highest fresh and dry weight of leaves and branches was recorded in the second cutting, however, it markedly decreased in the third one. The highest favourable effect of cold hardening on vegetative growth was observed at 4°C for 12 days exposure in the second cutting. The percentage of volatile oil in the leaves recorded the highest values in treatment of 7°C for 6 days in the second sampling date. Cold hardening either at 4°C or 7°C resulted in pronounced increase in the essential oil yield produced by the plant with the superiority of 4°C for 12 days which recorded the highest value.
It can be concluded from the obtained results that hardening peppermint plants with low temperature, particularly 4°C for 12 days before transplanting improved plant growth and considerably increased the volatile oil content in plant leaves and branches.     

Relay Cropping of Sorghum and Legume Shrubs for Crop Yield Improvement and Striga Control in the Subsistence Agriculture Region of Tigray (Northern Ethiopia)

Striga hermonthica is a major constraint in the subsistence agriculture regions of northern Ethiopia. Low soil fertility and overall environmental degradation has contributed to the build up of the parasitic weed infestation. Improved cropping systems have to be introduced to address the interrelated problems of Striga and soil fertility decline. Thus, relay cropping of sorghum with legume shrubs was investigated at two locations representing different environments. Results showed that the output of the improved cropping system was dependent on ecological endowments. Relay cropping led to significant improvement in yield at Sheraro, at the site with relatively better weather and soil conditions. The legume shrubs resulted in significantly lower sorghum yield in a dryland location (Adibakel). Overall Striga infestation declined over the 3‐year period; however, treatment differences were not apparent. Among the two legume shrubs, Sesbania sesban was better adapted to the dryland areas. Relay cropping could provide a viable option for farmers in both types of environments that are characterized by accelerated decline in natural resource base. However, it could mean compromising the yield of non‐fertilized sorghum in the interest of long‐term benefits of low incidence of Striga and more rewarding crop enterprise in dry areas.     

Intercropping for the Improvement of Sorghum Yield, Soil Fertility and Striga Control in the Subsistence Agriculture Region of Tigray (Northern Ethiopia)

Striga hermonthica is a major biotic constraint in the dry and less fertile areas of northern Ethiopia. Emphasis is being placed on improved cropping systems to address the interrelated problems of Striga and soil fertility decline. The potential benefits of intercropping were investigated at two sites representing different environments for crop yield improvement, soil fertility maintenance and Striga control. Ten food legume and oilseed crop species were compared in inter‐row arrangement with sorghum under non‐fertilized conditions. In most cases, there was no significant negative impact of intercropping on sorghum growth and development. Among the intercrops, two cowpea varieties – cv. TVU 1977 OD and cv. Blackeye bean – produced the highest supplemental yield of up to 329 and 623 kg ha^?1 grain and 608 and 1173 kg ha^?1 biomass at Adibakel and Sheraro respectively. Treatment differences on Striga infestation and measured soil fertility indicators were not significant. Nevertheless, valuable grain and biomass obtained from the legume intercrops, without seriously compromising sorghum yield, could offer multiple benefits as a source of protein, additional income, feeds for animals and manure in the subsistence agriculture regions of northern Ethiopia.     

Zinc Diffusion and Self-Diffusion Coefficient in Alkaline Soils as Affected by Soil Properties and Zinc Carrier

The apparent diffusion coefficients, D_p/b+ø, of Zn and ZnEDTA were linear functions of added Zn, and were related to the adsorption and fixation capacities of soils rather than their pH. Lower apparent diffusion coefficient values were found in an Haplustoll soil that had higher clay and humus contents inspite of its lower pH. At comparable rates of added Zn, the apparent diffusion of ZnEDTA was 930–1010 (Bakyria), 700–1330 (Dirab), and 730–1880 (Baha) times that of Zn in the soils. The adsorbed Zn per cm³ of soil/Zn per cm³ of the equilibrium solution at the water content existing in the diffusion experiment approximated the capacity factor and was determined by extrapolation. The self-diffusion coefficient of Zn in Baha soil (5 × 10^?7 cm²sec^?1) of higher clay and water content was higher than in Bakyria or Dirab soil (2 × 10^?7 cm²sec^?1). These values were similar to the self-diffusion coefficient of P in soils of similar texture at similar water content.     

Dietary supplementation of potassium sorbate,hydrated sodium calcium almuniosilicate and methionine enhances growth,antioxidant status and immunity in growing rabbits exposed to aflatoxin B1 in the diet

The present experiment was conducted to evaluate the effect of dietary supplementation with some feed additives (potassium sorbate; Sor, hydrated sodium calcium almuniosilicate; Hsc and L-methionine; L-M) against aflatoxin B1 (AF) toxicity in rabbits. A total of 72 growing rabbits (5-week-old) were distributed into six equal groups (4 replicates with 3 rabbits each). The experimental groups are as follows: control group, AF group (supplemented with AF 0.3 mg/kg diet), AF + Sor group (AF 0.3 mg/kg diet + Sor 2 g/kg diet), AF + Hsc group (AF 0.3 mg/kg diet + Hsc 5 g/kg diet), AF + L-M group (AF 0.3 mg/kg diet + L-M 8 g/kg diet) and AF + Mix group (AF 0.3 mg/kg diet + 2 Sor + 5 Hsc + 8 L-M g/kg diet). Live body weight and weight gain at 13 weeks of age were significantly reduced by AF. Feed intake at 13 weeks of age was decreased in AF, AF + Hsc and AF + Mix compared to the control. AF, AF + Hsc and AF + Mix showed the lowest total antioxidant capacity compared to the control. The highest level of reactive oxygen species and 8-Hydroxy-2-desoxyguanosine was observed in AF group. Using of other supplements with AF increased immunoglobulinM than AF alone. In conclusion, dietary supplementation of Sor, L-M, Hsc or their mixture was effective in reducing the adverse effects of AF on performance, antioxidant and immune status of rabbits with more better improvement obtained by Sor or L-M separately.     

Protective role of propolis against reproductive toxicity of chlorpyrifos in male rats

Chlorpyrifos (CPF) is causing different toxicity and propolis has been reported to be an effective antioxidant. Therefore, the present study is aimed to elucidate the possible protective effects of propolis in alleviating the toxicity of chlorpyrifos on reproductive performance, testosterone levels, enzyme activities and lipids profile in serum of male rats. Animals were divided into four groups; one orally administered (o.d.) CPF at a dose of 9 mg/kg b.w. for consecutive 70-days, propolis group (50 mg/kg b.w.), propolis and chlorpyrifos group and a control group. Results showed that there was a correlation between CPF administration and the significant decrease of the sperm counts, spermatozoon survival and testosterone level as well as increase of sperm aberrations. CPF increased significantly the lipid profile and the levels of various serum liver marker enzymes. In contrast, co-administration of propolis to CPF-treated rats restored almost most of these biochemical parameters to normal levels. On the other hand, CPF resulted in histopathological alterations in testes of male rats. However, pre-administration of propolis to CPF-treated animals improved the testicular damage and alleviates the toxic effects of CPF on reproductive functions in male rats.     

Plant regeneration from hypocotyl and cotyledon explant of tomato (Lycopersicon esculentum Mill.)

Three tomato cultivars were used to examine the influence of the genetic background on the regeneration efficiency. White embryonic calli were formed within two weeks of culture. Shoots emerged either directly from the explant or indirectly from the embryonic callus. Multiple adventitious shoots were formed by clonal propagation of somatic embryos in the presence of 2 mg zeatin L^-1. The meristematic end of the hypocotyl of the cultivar Pontaroza showed a high regeneration frequency (70.2%) compared with the cotyledonary leaf explant (35.3%). The plants grown in the green house and the regenerants obtained showed a similar peroxidase banding pattern. The combined analysis of variance indicated that the difference in shoot induction between cultivars was highly significant. Shoot induction frequency was 57.2%, 43.5%, and 35.5% for the cultivars UC-97, Pontaroza, and Zuishi, respectively. The regeneration frequency was 50%, 28%, and 20% for the cultivars UC-97, Pontaroza, and Zuishi, respectively. The observed differences in shoot induction between cultivars were due to the genetic difference between them.     

Impact of plasma irradiation on Tribolium castaneum

Radio frequency plasma (RFP) could provide reliable, compact, cost-effective irradiation applications against insect pests of stored food and feed products. Sensitivity of red flour beetle Tribolium castaneum to RFP has been investigated using an irradiation applicator system with the two types of inert gases, argon (Ar) and helium (He), at 100 W for five exposure time levels of 0, 20, 40, 60 and 90 s, respectively. We demonstrated that He RFP was more efficient against T. castaneum than Ar RFP. In addition, a positive correlation was observed between mortality percentages of treated insect stages and exposure times for both He and Ar RFP. The adult stage showed the highest tolerance to RFP irradiation followed by larvae and pupae; however, it was more susceptible than larvae within 24 h after He RFP treatments. The optimum exposure time was 90 s with He RFP, where a full mortality at all tested stages was accomplished, while mortalities of 71.4, 65.3 and 36.7% were recorded for pupae, larvae and adult stage, respectively, after an Ar RFP treatment of 90 s. In case of treated adults, the reproduction rate was higher than treated larvae and pupae. Our findings indicated that He RFP was an effective method for inhibiting T. castaneum development and impacting the insect life cycle and could be considered a promising tool for pest control of stored food.