Roots are hidden by soil, making their excavation and measurement of their size very laborious (Gregory, 2006) and difficult to analyze (Rood et al., 2011). However, the study of their spatial distributions allows the discovery of their main sources of water and minerals (Lynch, 1995). Given the quantitative and qualitative heterogeneity in Abstract: Despite xeric conditions, Pistacia atlantica Desf. subsp. atlantica (Atlas pistachio) succeeds in developing impressive dendrometric dimensions (25-m high, 2-m trunk diameter). It is among the rare spontaneous phanerophytes of the North African steppe. With access to water being the primary condition for survival, we focused on its root system. According to a gradient of increasing climatic and edaphic aridity in Algeria, we recorded different root architectures set up by this tree. We sampled its underlying soil and determined its main physico-chemical characteristics. Root architecture is mainly of the superficial type with more than 60% of roots located in the top 50 cm of soil along the north-south transect. With the decrease in precipitation and the rising of temperatures, length of the dry season, and the content of sand in soil, the number of superficial roots and their ramifications decrease, while their average circumferences, and the length and average circumference of the deep roots increase. These deep and thick roots allow access and storage of moisture present in the deep levels and protected there from evaporation, and, on the other hand, provide an important anchor in these soft soils. The Atlas pistachio adapts to increasing climatic and edaphic aridity by adopting a phreatophytic strategy.

Short term changes that occur in soil properties of an ultisol under different pigeon pea hedgerow alley populations and inter-hedgerow alley spacing and the effect of such changes on ginger rhizome yield response were evaluated in a two-year (2010 and 2011) field study in South Eastern Nigeria. Treatments comprised pigeon pea hedgerow alley populations of 20,000, 33, 333 and 66, 667 plants/ha in factorial combinations with three inter-hedgerow alley width spacing of 1, 2 and 3 m in a randomized complete block design with three replications. A plot having no pigeon pea component but planted to sole ginger constituted the control. Relative to the control, growing ginger in-between pigeon pea hedgerow alleys resulted in significant improvement in soil exchangeable Ca, Mg, and K, base saturation, organic carbon and available P in addition to reducing soil dry bulk density. Highest response in soil available P, organic carbon, dry bulk density, exchangeable Ca and Na and pH was achieved using pigeon pea population of 66, 667 plants/ha, while highest response for soil total N, base saturation and exchangeable K was achieved with 20,000 pigeon pea plants/ha. Optimum ginger rhizome yield response comparable with the control was achieved using pigeon pea hedgerow alley population of 20,000 plants/ha spaced 3 m apart. Increasing pigeon pea hedgerow alley population beyond 20,000 plants/ha and decreasing pigeon pea inter-hedgerow alley width below 3 m resulted in rhizome yield reduction due to probable nutrient competition. Apart from its capacity to continuously maintain the fertility of the fragile and infertile soils of South Eastern Nigeria, planting ginger in-between pigeon pea hedgerow alley will also serve as additional source of revenue to smallholder resource-poor ginger farmers in Nigeria.

Because of the global warming threat, multidisciplinary studies of arid environment ecology are highly expected. In four populations of Atlas pistachio (Pistacia atlantica Desf.) located in Algeria along an aridity gradient, both the taxonomic diversity and the morphological types of communities of arbuscular mycorrhizal fungi (AMF) in rhizospheric soil were assessed. AMF taxonomic richness was low in all sampled populations, with a dominance of the Glomeraceae family. The AMF morphological Arum type was identified in fine roots of all sampled individuals, and the Paris type only in those sampled in the two less arid sites. Along the increasing aridity gradient, climatic conditions would be a determining factor in the decrease of the AMF taxonomic richness within Atlas pistachio rhizospheric soils; it could also indirectly influence the expression of both morphological types (Arum and/or Paris) within Atlas pistachio fine roots.