Source of mycorrhizal inoculum influences growth of Faidherbia albida seedlings

Poor land use management and practice inhibit the growth and establishment of tree seedlings in dryland areas.We assessed arbuscular mycorrhizal fungi(AM)status of Faidherbia albida(Del.)A.Chev.trees grown on different land uses.We quantified the growth and nutrient uptake of F.albida seedlings inoculated with AM from different sources.These efforts were based on soil and fine root samples from the rhizosphere soils of F.albida trees.AM root colonization was determined using the gridline intersect method.Spores were extracted by the wet sieving and decanting method and identified to genus level.The seedling experiment had a completely randomized onefactorial design with four treatments and five replications.Faidherbida albida seedlings were grown in a greenhouse.All in situ F.albida trees were colonized by AM fungi.AM root colonization of F.albida trees was significantly higher(P<0.0086)in area exclosures than on lands used for grazing or cultivation.Spore abundance was significantly higher(P<0.0014)in area exclosures followed by cultivated land and grazing land.Glomus was the dominant genus in all land-uses.AM-inoculated F.albida seedlings grew better(P<0.05)than non-inoculated controls.Seedlings inoculated with AM from area exclosure had significantly(P<0.05)higher growth and nutrient uptake than those inoculated with AM from grazing and cultivated land.This emphasizes the importance of the native soil AM potential for better establishment of seedlings to achieve optimum plant growth improvement and assist in rehabilitation of degraded arid lands.     

Geographic Pattern of Genetic Diversity Among 43 Ethiopian Mustard(Brassica carinata A. Braun) Accessions as Revealed by RAPD Analysis

As an oilseed crop, the cultivation of Ethiopian mustard (Brassica carinata) is restricted only to Ethiopia. Even though geographic diversity is a potent source of allelic diversity, the extent of genetic diversity among germplasm material of Ethiopian mustard from different countries has not been assessed. Forty-three accessions, comprising 29 accessions from eight different geographic regions of Ethiopia and 14 exotic accessions from Australia, Pakistan, Spain, and Zambia were analysed for their genetic diversity using random amplified polymorphic DNA (RAPD) technique. A set of 50 primers yielded a total of 275 polymorphic bands allowing an unequivocal separation of every Ethiopian mustard accession. The usefulness of the 50 RAPD primers in measuring heterozygousity and distinguishing accessions was variable such that polymorphic information content (PIC) varied from 0.05 to 0.40, band informativeness (BI) from 0.05 to 0.65 and primer resolving power (RP) from 0.15 to 6.83. Jaccard's similarity coefficients ranged from 0.44 to 0.87 indicating the presence of a high level of genetic diversity. On the average, Australian and Ethiopian accessions were the most similar while, Spanish and Zambian accessions were the most distant ones. Cluster analysis grouped the 43 accessions into four groups, which has quite a high fit (r = 0.80) to the original similarity matrix. With no prior molecular information, the RAPD technique detected large genetic diversity among the 43 accessions from five different countries and their grouping by dendrogram and principal coordinate analysis (PCoA) was inclined towards geographic differentiation of RAPD markers. Conversely, RAPD differentiation along geographic origin was not apparent within the Ethiopian accessions.     

Arbuscular mycorrhizal association of indigenous agroforestry tree species and their infective potential with maize in the rift valley, Ethiopia

Tree species in agroforestry are important source of inoculum for companion agricultural crops. Agroforestry trees can serve as a source of Arbuscular mycorrhiza (AM) inoculants to intercropped annuals. We studied spore abundance, root colonization of Albizia gummifera (J.F. Gmel.) and Croton macrostachyus (Hochst Ex Del.) trees and their effect on colonization of maize. Soil and root samples were collected from field standing trees from under and outside the canopy of trees and maize crops in the main rainy season. The number of spore count was significantly higher under the canopy of A. gummifera (791/100 g of dry soil) and C. macrostachyus (877/100 g of dry soil) trees than outside the canopy (547 and 588/100 g of dry soil, respectively). The level of root colonization of C. macrostachyus (45 %) was higher than A. gummifera (41 %). Root colonization of maize crops grown under the canopy of A. gummifera and C. macrostachyus trees was significantly higher than outside the canopy (P < 0.001). Maize seedlings grown on non-sterilized soils collected under and outside the canopy of A. gummifera and C. macrostachyus trees recorded higher root colonization, plant height, shoot and root dry weight than grown on sterilized soils (P < 0.001). The percentage of AM colonized roots of Zea mays seedlings was significantly positively correlated with the number of spore counts for field soils. The rhizospheres of indigenous agroforestry perennial species are important source of inoculum for annuals. The integration of perennials and annuals in an agroforestry system enhances the maintenance of soil quality in the tropics.     

Agronomic and Economic Efficiency of Manure and Urea Fertilizers Use on Vertisols in Ethiopian Highlands

Soil fertility depletion is among the major impediments to sustained agricultural productivity especially in the less developed countries because of limited application of fertilizers. Soil fertility maintenance requires a balanced application of inorganic and organic nutrient sources. This study was conducted on a Vertisol in Ethiopia to determine the optimum farm yard manure （M） and nitrogen （N） application rates for maximum return under cereal-pulse-cereal rotation system. The main and interaction effects of M and N significantly affected biomass, grain and straw yields of wheat （Triticum durum） and tef （Eragrostis tear）, but the residual effect on chickpea （Cicer arietinum） was not significant. Application of 6 t M ha^-1 and 30 kg N ha^-1, gave the largest grain yield of both crops but a comparable result was obtained due to 3 t M ha^-1 and 30 kg N ha^-1. The economic analysis revealed that 6.85 t M ha^-1 and 44 kg N ha^-1 for wheat, and 4.53 t M ha^-1 and 37 kg N ha^-1 for tef were the economic optimum rates. The additional benefit obtained due to these rates was about 450 USD ha^-1. Therefore, application of the economic optimum combination of both organic and inorganic sources of nitrogen is recommended for use on cereals in the cereal-legume-cereal rotation system.     

Forest observational studies-an essential infrastructure for sustainable use of natural resources

This contribution complements Forest Ecosystems＇ Thematic Series on ＂Forest Observational Studies＂. We provide essential clarification regarding the definition and purpose of long-term field studies, review some of the extensive literature and discuss different approaches to collecting field data. We also describe two newly established forest observational networks that serve to illustrate the scope and diversity of forest field studies. The first is a large-scale network of forest observational studies in prominent natural forest ecosystems in China. The second example demonstrates observational studies in mixed and uneven-aged pine-oak forests which are selectively managed by local communities in Mexico. We summarize the potential for analysing and modeling forest ecosystems within interdisciplinary projects and provide argumentation in favour of long-term institutional commitment to maintaining forest observational field studies.     

Sources of within- and between-stand variability in specific leaf area of three ecologically distinct conifer species

Specific leaf area (SLA) is an important ecophysiological variable, but its variability within and between stands has rarely been simultaneously examined and modeled across multiple species. Extensive datasets on SLA in coastal Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco), hybrid spruce (Picea engelmannii Parry × Picea glauca (Moench) Voss × Picea sitchensis (Bong.) Carr.), and ponderosa pine (Pinus ponderosa Dougl. ex P. & C. Laws.) were used to estimate variability of SLA within a canopy and its relationship to tree- and stand-level covariates, and to predict SLA at various locations in tree crowns. Also, in the case of hybrid spruce, variation in SLA due to different relative horizontal lengths from the bole was examined. In all species, SLA systematically increased from tree tip to crown base and decreased with foliage age class. Cardinal direction did not have a highly significant influence in either Douglas-fir or hybrid spruce, but SLA did significantly decrease from branch tip to bole in hybrid spruce. Tree- and stand-level (e.g. density, site index) factors had relatively little influence on SLA, but stand age did have a significant positive influence. For ponderosa pine, a significant relationship between canopy mean current-year SLA and carbon isotope discrimination was also found, suggesting the importance of water stress in this species. An equation was fitted to estimate SLA at various points in the canopy for each species and foliage age class using absolute height in the canopy, relative vertical height in the tree, and stand age.     

Accuracy and suitability of selected sampling methods within conifer dominated riparian zones

Sixteen sampling alternatives were examined for their performance to quantify selected attributes of overstory conifers in riparian areas of western Oregon. Each alternative was examined at eight headwater forest locations based on a 0.52 ha square stem maps. The alternatives were evaluated for selected stand attributes (trees per hectare, basal area per hectare and height to diameter ratio), using root mean square error, absolute percent bias, and mean absolute deviation as criteria. In general, rectangular strip designs outperformed fixed area circular or radial plots and variable area plots. Sampling 3.6 m wide strips perpendicular to the stream outperformed all other alternatives.     

Analysis of potential impacts of climate change on forests of the United States Pacific Northwest

As global climate changes over the next century, forest productivity is expected to change as well. Using PRISM climate and productivity data measured on a grid of 3356 plots, we developed a simultaneous autoregressive (SAR) model to estimate the impacts of climate change on potential productivity of Pacific Northwest (PNW) forests of the United States. Productivity, measured by projected potential mean annual increment (PMAI) at culmination, is explained by the interaction of annual temperature, precipitation, and precipitation in excess of evapotranspiration through the growing season. By utilizing information regarding spatial error in the SAR model, the resulting spatial bias is reduced thereby improving the accuracy of the resulting maps. The model, coupled with climate change output from four generalized circulation models, was used to predict the productivity impacts of four different scenarios derived from the fourth IPCC special report on emissions, representing different future economic and environmental states of the world, viz., scenario A1B, A2, B1 (low growth, high economic development and low energy usage), and COMMIT. In these scenarios, regional average temperature is expected to increase from 0.5 to 4.5 °C, while precipitation shows no clear trend over time. For the west and east side of the Cascade Mountains, respectively, PMAI increases: 7% and 20% under A1B scenario; 8% and 23% under scenario A2; 5% and 15% under scenario B1, and 2% and 5% under the COMMIT scenario. These projections should be viewed as potential changes in productivity, since they do not reflect the mitigating effects of any shifts in management or public policy. For managers and policy makers, the results suggest the relative magnitude of effects and the potential variability of impacts across a range of climate scenarios.