Profiling soil free-living nematodes in the Namib Desert,Namibia

Functional structure and diversity of soil free-living nematodes in a desert environment depend on plant gender and sampling site.The objective of this study was to compare the composition,abundance and tropic group of soil free-living nematodes in the upper 0–10 cm soil layer under the male and female Acanthosicyos horridus Welw.ex Hook.f.plants and in the inter-shrub open areas(control)in the Namib Desert,Namibia in April 2015.Soil moisture,organic matter(OM)and pH was also analyzed.Free-living nematodes were extracted from 100 g soil using the Baermann funnel procedure,and total number of nematodes was counted under a microscope.Community composition and diversity of soil free-living nematodes were analyzed using 18S rDNA sequences.Results indicated that a total of 67 groups,including 64 species,2 genera and 1 family were identified.Feeding behavior of 58 species were identified as follows:15 bacteria-feeding species,12 fungi-feeding species,10 plant-parasite species,5 omnivorous-predator species,8 animal-parasite species,5 invertebrate-parasite species and 3 non-free-living nematodes,known as marine species.Moreover,soil free-living nematodes were found to be affected by sampling locations and plant gender,and community composition and density of these nematodes were strongly influenced by soil OM content.Result confirmed that spatial location and plant cover were main factors influencing the diversity of soil free-living nematodes.Moreover,molecular tools were found to be very useful in defining the richness of soil non-free-living nematodes.In conclusion,the results elucidated the importance of biotic variables in determining the composition and abundance of soil free-living nematodes in the Namib Desert,Namibia.     

Simulating the effect of potassium fertilization on carbon sequestration in soil

The impact of horticultural management on carbon sequestration in soils has been limited so far to tillage and nitrogen fertilization. Our objective was to evaluate by mathematical modeling the effect of potassium fertilization on CO₂ binding in cropland soils. The developed model integrates three subunits: (1) A published simulator of crop dry‐matter (DM) production in response to N, P, K fertilization, but not DM partitioning; (2) a published soil–crop–atmosphere model predicting crop yield and DM partitioning as a function of N but not K fertilization; (3) an original model computing the organic‐inorganic carbon transformations, inorganic‐carbon reactions and transport in soil, CO₂ diffusion, and soil carbon sequestration. The model described the K‐fertilization effect on C binding in soil as a function of the soil pH, the Ca²⁺ concentration in the soil solution, hydraulic properties, air temperature, and crop DM production, and partitioning characteristics. In scenarios of corn (Zea mays L.) growth in clayey soil and wheat (Triticum aestivum L.) in loam soil, the computed K‐induced CO₂ sequestration amounted to ≈ 14.5 and 24 kg CO₂ (kg K)^–1, respectively (0 vs. 100 kg ha^–1 K application). The soil CO₂ sequestration declined by 8% when corn grew in sandy instead of clayey soil and by 20% when the temperature was 10°C higher than the temperature prevailing in mild semiarid zones. All predicted CO₂‐sequestration results were approximately 30‐fold higher than the 0.6 kg CO₂ emitted per kg of K manufactured in industry.     

Road-kills affect avian population quality

Owing to the extensive development of road networks, millions of animals are killed annually. This impact on the natural environment has been questioned: is there a selection of victims in the car collisions? and do road-kills, as do predators, influence a population by eliminating individuals in poor condition? We compared road-killed individuals to those killed by predators in SE Poland in three bird species: Yellowhammer Emberiza citrinella, Barn Swallow Hirundo rustica, and Chaffinch Fringilla coelebs. We applied ptilochronology, in which the width of feather growth bars represents an individual’s relative nutritional condition. Our results show that the analyzed species were in significantly better body condition than those killed by raptors. Our study does not concur with previous studies which concluded that weaker individuals are more vulnerable on the road. Raptors select prey in poor condition, but road-killed individuals are in significantly better condition, so apparently road-kill results in the random elimination of healthy individuals. The conservation implications of this study are far-reaching; future road construction and safety regulations must take wildlife into consideration. If these human-created habitats are killing a significant proportion of the healthier part of natural populations in a non-selective manner, this could result in situations where fragmented populations could be driven to a critical stage, and/or the situation of declining or endangered populations worsened further.     

Do long-lived ants affect soil microbial communities?

This study was designed to test the hypothesis that desert ant species that build nests that remain viable at a particular point in space for more than a decade produce soil conditions that enhance microbial biomass and functional diversity. We studied the effects of a seed-harvester ant, Pogonomyrmex rugosus, and two generalist ant species, Aphaenogaster cockerelli and Myrmecocystus depilis, on soil microbial communities. Microbial biomass was higher in P. rugosus-modified soils than in reference soils when soil water content was higher than 3%. Microbial biomass was either higher in reference soils or exhibited no difference in reference soils and nest-modified soils of A. cockerelli and M. depilis. There were differences in microbial functional diversity and microbial community level physiological profiles (MicroResp method) between ant-nest-modified and reference soils of the three ant species on some sampling dates. Temporal patterns of soil microbial communities associated with the ant species resulted from differences in soil moisture, density, and species composition of the annual plant communities associated with the ant nests and in reference areas. Differences in annual plant communities associated with ant nests and surrounding areas resulted in different chemical inputs into the soil organic-matter pools. This study shows that generalizations about the effects of long-lived ant nests on soil biota in arid regions must consider feeding behaviors of the ant species and temporal patterns of rainfall.     

Soil Microbial Biomass Under the Canopy of Coastal Sand Dune Shrubs

Coastal sand dunes are affected by seasonal fluctuations in salinity due to seawater spray and precipitation. Salinity was found to be very high in summer soil samples and was about 15-20 times lower in the preceding rainy winter. High microbial biomass values of 234.6 and 173.1 mugC g-1 dry soil were found under Artemisia monosperma and Retama raetam, respectively, even at elevated salinity. The metabolic quotient for CO2, which may serve as an indicator for changes in microbial diversity or environmental stress, was unexpectedly high (58.5 and 48.8 mug mg-1 d-1 under A. monosperma and R. raetam, respectively) in low-saline samples from the winter when compared to the summer (a maximal value of 20 mug mg-1 d-1), probably indicating a shift in community structure. It may be concluded that even under hostile conditions in poor sandy soils and with high salinity the presence of perennial shrubs creates favorable niches for microorganisms and affects their activity.     

Glycolytic and chitinolytic activities of Phlebotomus papatasi (Diptera: Psychodidae) from diverse ecological habitats

The sand fly Phlebotomus papatasi Scopoli, 1786, the vector of Leishmania major Yakimoff et Schokhor, 1914, is found in desert areas where sugars are scarce but also in habitats that abound in sugar sources. The sand flies require sugar meals from plant sources for their energy requirements and to hydrolyze these complex sugars, they need a repertoire of glycosidases. We presumed that there are differences in the levels of glycosidase activities in flies from such habitats and also assumed that they may be instrumental in modulating the flies' susceptibility to L. major infections. Phlebotomus papatasi originating from diverse ecological habitats ranging from an oasis to desert sites were colonized. They were analyzed for weight changes and glycosidase activities before and after feeding on 1M sucrose solution. Oasis flies were smaller than desert flies but took larger sugar meals. Homogenates of these flies hydrolyzed 16 synthetic and 2 natural glycoside substrates to varying degrees. The arid-region flies tended to produce more glycosidase activity than those originating in sugar-rich environments, especially sucrase, alpha- and beta-glucosidase, aalpha-fucosidase, alpha-mannosidase, and alpha- and beta-N-acetylgalactosaminidase. However, chitinolytic enzyme activities and particularly the beta-N-acetylhexosaminidase activity of oasis flies were higher than other flies tested. In comparing the desert flies, there were also significant differences in glycolytic enzyme activities between the spring-line (flowering season) of flies and the autumn-line (end of dry season) flies. A range of saccharide inhibitors was tested to demonstrate the specificity of the enzymes.     

Temporal and shrub adaptation effect on soil microbial functional diversity in a desert system

The Negev Desert is characterized by spatial and temporal patterns of resource distribution, in which soil biota are considered to be among the most sensitive biological characteristics, easily influenced by changes related to soil and abiotic factors. Soil water availability and organic matter are among the most important factors, acting as triggers that determine the length of the period of activity. The main source of organic matter in this xeric environment is input from annual and perennial shrubs. In order to persist and propagate in this xeric environment, the plants have developed different ecophysiological adaptations (e.g. the excretion of salt (Reaumuria negevensis) and chemical compounds (Artemisia sieberi) via the leaves). We found that the values of soil moisture obtained for soil samples collected in the vicinity of R. negevensis were larger than for samples collected in the vicinity of Noaea mucronata and A. sieberi and in the open area. The maximum values of CO₂ evolution, microbial biomass and Shannon index (H′) were obtained for the samples collected from the vicinity of N. mucronata. Therefore, we assume that the vicinity of N. mucronata afforded the best conditions for the soil bacterial community. In the Negev Desert, we also found that water availability and pulses of rain compared with frequent rainfall influenced CO₂ evolution, microbial biomass, qCO₂ and the Shannon index (H′). The differences in water amount and availability between the two rainy seasons caused larger values in most of the properties during the first four seasons (December 2005–November 2006) compared with the last four seasons (December 2006–November 2007) for most of the samples.     

Substrate utilization patterns of desert soil microbial communities in response to xeric and mesic conditions

The Negev Desert is characterized by low soil moisture and organic matter content and an unpredictable rainfall amount, dispersion, and intensity. Water and nutrient availability are, therefore, the major limiting factors of biological activity in arid and semi-arid ecosystems. Plants have developed different ecophysiological adaptations in order to cope with the harsh conditions in this xeric environment, e.g., excretion of salt (Reaumuria negevensis) and chemical compounds (Artemisia sieberi) through the leaves. Microorganisms constitute a major part of these ecosystems' total biomass, and are diverse members of the soil food web, being primarily responsible for breaking down complex organic compounds, which are then recycled. They are also known to be very sensitive to abiotic changes and can time their activity to the environmental conditions.Soil samples were collected monthly from a 0 to 10 cm depth, under the canopies of A. sieberi, Noaea mucronata, and R. negevensis. Samples collected from inter-shrub spaces served as control. CO₂ evolution, microbial biomass, microbial functional diversity, and the physiological profile of the community, were determined by MicroResp™ analysis. A significant difference was found between the two dry periods in most of the examined parameters. The values of water, organic matter content, and total soluble nitrogen were higher in soil samples collected in the vicinity of R. negevensis than in samples collected in the vicinity of N. mucronata, A. sieberi, and the open area. A similar trend was found in CO₂ evolution, microbial biomass, and H' values, in which soil samples collected beneath the canopies of N. mucronata and R. negevensis and from open area had higher values during the wet periods (which were characterized by a mesic environment) and in samples collected beneath the A. sieberi in the wet 2006 and dry 2007 periods.     

Carbon stock potentials of woodlands in north western lowlands of Ethiopia

ABSTRACT

This paper examined the potential of dry north western woodlands of Ethiopia (Adi Goshu, Lemlem Terara, and Gemed) for carbon stocks. Allometry equations were used to determine the aboveground, belowground, and dead woods biomasses; litter and herbaceous biomasses were determined using direct harvesting method. The result showed the estimated mean carbon stocks of the aboveground, belowground, and the dead wood biomass for the Untapped Boswellia Papyrifera Woodland (UW) in Lemlem Terara site were significantly higher (P < 0.05) than that of the Adi Goshu site. In the Gemed site, the mean Herb Biomass Carbon (HBC) stock was 1.2 Mg ha^?1, which is significantly highest (P < 0.05) than the other two study sites (Lemlem Terara, 0.42 Mg ha^?1 and Adi Goshu, 0.45 Mg ha^?1) for the Tapped Boswellia Papyrifera Woodland (TW). In UW, the mean soil carbon stock of the Lemlem Terara site (58.19 Mg ha^?1) was significantly (P < 0.05) higher than that of Adi Goshu (33.61 Mg ha^?1). In the case of the total carbon stocks in UW stratum, for the Adi Goshu site, the carbon stock was estimated to be about 55.26 Mg ha^?1 while 96.74 Mg ha^?1 for Lemlem Terara. Therefore, Carbon stock in different carbon pools (aboveground and belowground biomass, dead wood, litter, herbaceous biomass, and soil) has a potential to decrease the rate of enrichment of atmospheric concentration of carbon dioxide.     

Effect of elevated CO2 on vegetative and reproductive growth characteristics of the CAM plants Hylocereus undatus and Selenicereus megalanthus

This study examined the vegetative and reproductive growth responses of the crassulacean acid metabolism (CAM) vine-cactus fruit crop species Hylocereus undatus and Selenicereus megalanthus to CO₂ enrichment (1000 μmol mol⁻¹ vs. control of 380 μmol mol⁻¹). H. undatus plants enriched with CO₂ demonstrated 52%, 22%, 18%, and 175% increases, relative to plants measured in ambient CO₂, in total daily net CO₂ uptake, shoot elongation, shoot dry mass, and number of reproductive buds, respectively. The responses of S. megalanthus plants exposed to elevated CO₂ were greater than those of H. undatus under the same conditions. Compared to plant responses in ambient CO₂, under conditions of CO₂ enrichment, S. megalanthus showed 129%, 73%, 68%, and 233% increases in total daily net CO₂ uptake, shoot elongation, shoot dry mass, and number of reproductive buds, respectively. Moreover, for H. undatus, there was no significant change in fruit fresh mass although it showed a slight (7%) upward trend. On the other hand, fruit fresh mass of S. megalanthus significantly increased by 63% in response to elevated CO₂. These results indicate the high potential of CAM plants to respond to CO₂ enrichment. It is thus apparent that S. megalanthus grown under CO₂ enrichment may benefit from elevated CO₂ to a greater extent than H. undatus grown under sub-optimal growth conditions.