Effect of rain enrichment on soil respiration of Nitraria sphaerocarpa community in a hyperarid area

In order to analyze the effect of rain enrichment on soil respiration rate of a Nitraria sphaerocarpa community, we measured soil respiration rate in bare and vegetated areas in a hyperarid area （Dunhuang） during the growing season. Results show that rain enrichment can increase bare and vegetated soil respiration rates. The more rainfall enrichment, the greater the increment and the longer duration time effect for soil respiration rate. 200% （16 mm） and 300% （24 mm） of rain enrichment can significantly increase bare soil respiration rates by 90% and 106% （P〈0.01）, respectively. By contrast, areas with 100% （8 mm）, 200% （16 mm） and 300% （24 mm） of rain enrichment can significantly increase shrub area respiration rates by 68%, 157% and 205% （P〈0.01）, respectively. The response time of bare and vegetated soil respiration to rainfall enrichment is asynchronous. Response variable of soil respiration in vegetated soil is higher （118%） than in bare soil. There was significant positive correlation between soil respiration rate and soil water content during the growing season （P〈0.01）. For every 1 mm increment of precipitation, soil respiration rate increased by 0.01 and 0.04 pmol/（m2.s）, respectively in vegetated and bare soils.     

Effect of vegetation with different evolution degree on soil organic matter in a semi-arid environment (Cabo de Gata-Níjar Natural Park, SE Spain)

The organic matter of the surface horizons of soils developed below scrub vegetation in a Mediterranean semi-arid area of great environmental interest (Cabo de Gata-Níjar Natural Park, SE Spain) has been studied. The study mainly concentrates on examining the influence of two vegetation types, one evolved (according to its successional stage), and the other clearly degraded as a result of prior removal of vegetation. In spite of the homogeneity in the results obtained from the analysis of the organic matter from the soils studied, a relationship may be established between vegetation biotype and characteristics and evolution of the soil organic matter. The evolved vegetation results in the presence in the soil of a somewhat more evolved and stable organic matter (demonstrated by certain chemical and microbiological aspects), resulting in a greater degree of humification, thus favouring the protection of the soil and the ecosystem as a whole. Hence, the presence of degraded vegetation might lead to soil degradation, something that is unsustainable in semi-arid areas that are particularly fragile in nature.     

Short- and long-term effects of shrub management on vegetation in the Monte, Argentina

A comparison was made of plant cover, carrying capacity and diversity in areas of Monte vegetation at the Biosphere Reserve of Ñacuñán, Mendoza, Argentina, in 1982, 1984 and 1995. Treatments applied in 1981 were: control (untreated plots), selective hand-cutting, roller-chopping, and root-plowing. By 1995, woody cover was lower in root-plowed plots (27%) than in the others treatments (41–51%), and herbaceous cover was similar in treated (28–39%) and untreated areas (26%). Carrying capacity of treated areas (6–8 ha per Large Stock Unit (LSU)) was higher than in the control areas (12 ha LSU⁻¹). Woody species diversity, quantified by the Shannon index, for both areas was similar in the study period (0·62), except in root-plowed sites in 1982 (0·0) and 1995 (1·3). Herbaceous species diversity was similar on treated (0·81) and untreated sites (1·2) in 1995. We could recommend less drastic treatments to improve carrying capacity.     

The influence of elevation, shrub species, and biological soil crust on fertile islands in the Mojave Desert, USA

We quantified soil nutrients and biological crust cover (bryophytes and lichens) under the canopies of three species of Mojave Desert shrubs and in interspaces between shrubs at three elevations to determine the effects of shrub species, soil crust, and elevation on islands of soil fertility. Means of pH, organic matter, total Kjeldahl nitrogen, nitrogen mineralization, and gravimetric soil moisture are significantly greater in soils under Ambrosia dumosa (Gray) Payne, Larrea tridentata Cov., and Coleogyne ramosissima Torr. than soils from adjacent interspace microhabitats. Although soil moisture and soil organic matter increase by a factor of 1.5 from the low elevation to the high elevation site, the ratio of shrub to interspace concentrations, or the difference in mean soil variables between shrubs and interspaces, is effectively constant and independent of elevation. Total bryophyte and lichen cover is relatively low (24.5%), however, there are 11 species of bryophytes and two species of lichens distributed across three elevations with the highest species richness and cover at the low-elevation site. Bryophyte and lichen cover is correlated with silt but is not related, consistently, to soil nutrients. Overall, the balance of processes controlling spatial aggregation of soil nutrients under shrubs is remarkably insensitive to potential differences in organic inputs among elevations, shrub species, and soil crust surfaces.     

Distribution and Characteristics of Nitraria sphaerocarpa nebkhas in a Gobi habitat outside an oasis in Hexi Corridor region, China

Nitraria sphaerocarpa Maxim., a typical desert plant which often appears in nebkha form, is widely distributed along the periphery of oasis in arid regions of Northwest China, and plays an important role in desertification control around oases. In this paper, the characteristics and distribution patterns of N. sphaerocarpa nebkhas were investigated in a Gobi environment outside an oasis. Results shows that about 200 N. sphaerocarpa nebkhas per hectare was recorded and total sand sediments was 25 m³/ha. Nebkhas vary in size, and the mean height (H) and horizontal composition (L) were 15 cm and 80 cm, respectively. There exists a significant linear relationship between H and L, suggesting that the investigated nebkhas are mostly in the growth stage. The numbers, height and sand deposit of nebkhas decreased with increasing distance away from the oasis. Grain-size analysis indicates that the mean grain size of sediments at the crests of nebkhas increased with increasing nebkha height. Organic C and total N concentrations were related to the mean grain size. It was concluded that N. sphaerocarpa shrubs are efficient horizontal sand traps for wind-driven sediments. A better understanding of the development of nebkha can provide information for the design of biological sand control measures around oases in arid regions.     

Influence of shrubs on soil characteristics and their function in Sahelian agro-ecosystems in semi-arid Niger

Soil beneath shrubs form ‘fertile islands’ in fallow sites and millet fields in semi-arid Niger. To gain more information about this phenomena different shrub species in fallow sites following a gradient from 350–650 mm precipitation were examined. For each shrub two different areas were distinguished: an area under the canopy of the shrubs and an area in the nearby open land. Soil samples were taken from a depth of 0–10 cm and analysed for C_org, N_total, P_Bray, pH(H₂O), exchangeable cations, effective cation exchange capacity (ECEC) and soil texture. Significantly higher concentrations between 38–51% for C, N, P and 22% on ECEC for K⁺were found in the soil under the shrubs. The pH showed only slight but significant differences, whereas Al³⁺and H⁺rates on ECEC under the shrubs were increased by 44–55%. For Guiera senegalensis, the most common shrub of the studied area, enrichment ratios of most soil properties increased relatively more with increasing aridity. In general, enrichment ratios decreased with the age of the fallows, whereas concentrations showed no clear evolution. The chemical composition of the shrub litter seems to influence the degree of soil enrichment. The main step of fertile island formation takes place during the cultivation period by trapping wind-blown sediment. This work shows that shrubs are of vital importance for the accumulation of nutrients and maintenance of soil fertility within agro-ecosystems of Niger.     

Comparison of soil bacterial communities associated with actinorhizal, non-actinorhizal plants and the interspaces in the sclerophyllous matorral from Central Chile in two different seasons

The spatial heterogeneity of resources in desert and semi-arid shrubland appears to be important in determining higher soil bacteria abundance around plants than in soil without plant cover. Thus, these bacterial communities could be important contributors to nutrient cycling in arid ecosystems. Bacterial diversity from Chilean sclerophyllous matorral was determined by Terminal Restriction Fragment Length Polymorphism (T-RFLP). Soil samples associated with the actinorhizal plant Colletia hystrix, non-actinorhizal plants and interspace soil without plant cover, were collected in May and October. The non-actinorhizal and interspace soil differed significantly in their potassium content in May and pH in October. The T-RFLP analysis revealed differences in the bacterial community structure from the different habitats. The soil bacterial communities associated with plants were the most similar, whereas the interspace soil community differed in both sampling times. The factors that best explained the groupings were potassium and pH. The greatest diversity was observed in the interspace soil. The Microbial Community Analysis showed a significant proportion of T-RFs identified as Firmicutes and Proteobacteria. Likewise, spatial and temporal differences were observed in the main groups' abundance. The dominance of Firmicutes suggests that the sclerophyllous matorral could be a different ecosystem to other arid and semi-arid soils with respect to the bacterial community structure.     

Studies on the effect of salinity, drought stress and soil type on nodule activities of Lablab purpureus (L.) sweet (Kashrangeeg)

Lablab purpureus(50 cultivars throughout the world) is a drought-tolerant legume widely grown as a high-protein grain food and forage legume within a wide range of neotropical regions with extensive production in India and similar climatic areas of Asia, Africa, Central and South America. The objective of this work was to study the nitrogen-fixing potentialities of L. purpureus under the effects of the extreme environmental conditions prevailing in the southern part of Egypt aiming at the recommendation of its propagation in areas of the National giant projects.L. purpureusinoculated with Rhizobium sp. Strain I₄ (21 days after planting) grown on Nile valley and Wadi Allaqi soils was relatively tolerant to mild levels of salinity, but the nodule number was reduced to about 35% of the control plants when subjected to a high salt level (120mM NaCl). Lablab plants were similarly affected by different rates of water deficits. This legume was tolerant to moderate levels of drought. The nodule number and weight at 50% of field capacity was about 70% of the control. These values were reduced to 45–55% at a field capacity of 16·5%.Absolute nitrogenase activity, leghaemoglobin content of nodules and protein content of bacteroids and cytosol were moderately affected by mild levels of NaCl and drought but significantly reduced to about 25–35% of the control treatments.The results also indicate that plants grown on the soil of Nile Valley exhibited slightly higher values (nitrogenase, protein, etc.) than those grown on Wadi Allaqi soil. This would encourage the possibility of propagating L. purpureus in the newly reclaimed areas of southern Egypt.     

Influence of environmental, root, and stand parameters on soil surface CO2 efflux in a Populus euphratica of desert forest in extreme arid region

Spatial variation in soil surface CO2 efflux was measured in a stand of Populus euphratica in the Ejina Oasis of desert riparian forest in the extreme arid region in northwestern China from April 2007 through October 2007.Measurements were taken with a gas-exchange analyzer linked to a soil-respiration chamber.The mean soil CO2 efflux in the stand was 2.71 μmol/(m2·s) during the growing season and 1.38 μmol/(m2·s) in the nongrowing season.The seasonal maximum (end of May through early June) andminimum (October) CO2 efflux were 3.38 and 0.69 μmol/(m2·s),respectively.The diurnal fluctuation of CO2 efflux was relatively small (< 20 percent),with theminimum appearing around 05:00 and the maximum around 15:00.Linear regression analysis showed soil-surface CO2 efflux to be most highly correlated with soil temperature (R2=0.435) and soil moisture (R2=0.213).When all variables were considered simultaneously,only soil temperature (R2=0.378),soil moisture (R2=0.147),and root volume density (R2=0.021) explained a significant amount of variance in soil surface CO2 efflux.Stand volumes were not correlated with soil CO2 efflux on our sites.     

Crop water relationships and thermal adaptation of kathika beans (Phaseolus vulgaris L.) and green grams (Vigna radiata L. Wilczek) with special reference to temporal patterns of potential growth in the drylands of SE-Kenya

High soil temperatures influence seedling emergence as well as the performance of plant organs and yields. Temperatures of above 40°C were recorded in the topsoil of the Ferralsols of the semi-arid areas of SE-Kenya during the rainy season. Experiments were conducted in the climatological laboratory of the University of Trier, Germany, on two legumes (green grams and common beans var. kathika), grown by smallholder farmers in the study area under varying soil temperature conditions. The main objective was to examine the effect of soil temperature on various parameters: seedling emergence, crop water requirements, leaf area index and phenology of the two legumes. The simulated climatological laboratory conditions were similar to those at Kiboko, SE-Kenya. This study confirmed that under high soil temperature conditions, green grams are well adapted to semi-arid and hot tropical lowlands as well as lower midlands due to low water requirements, high seedling emergence rates and good yield performance. However, kathika beans were very susceptible to the simulated extreme climatic environment. By means of crop simulation modelling, a temporal differentiation for potential growth of green grams is presented for the long and short rains according to different rainfall conditions (ENSO, antiENSO, normal) over a period of 31 years.