Carbon stock and its responses to climate change in Central Asia

Central Asia has a land area of 5.6 × 10⁶ km² and contains 80–90% of the world's temperate deserts. Yet it is one of the least characterized areas in the estimation of the global carbon (C) stock/balance. This study assessed the sizes and spatiotemporal patterns of C pools in Central Asia using both inventory (based on 353 biomass and 284 soil samples) and process‐based modeling approaches. The results showed that the C stock in Central Asia was 31.34–34.16 Pg in the top 1‐m soil with another 10.42–11.43 Pg stored in deep soil (1–3 m) of the temperate deserts. They amounted to 18–24% of the global C stock in deserts and dry shrublands. The C stock was comparable to that of the neighboring regions in Eurasia or major drylands around the world (e.g. Australia). However, 90% of Central Asia C pool was stored in soil, and the fraction was much higher than in other regions. Compared to hot deserts of the world, the temperate deserts in Central Asia had relatively high soil organic carbon density. The C stock in Central Asia is under threat from dramatic climate change. During a decadal drought between 1998 and 2008, which was possibly related to protracted La Niña episodes, the dryland lost approximately 0.46 Pg C from 1979 to 2011. The largest C losses were found in northern Kazakhstan, where annual precipitation declined at a rate of 90 mm decade^?1. The regional C dynamics were mainly determined by changes in the vegetation C pool, and the SOC pool was stable due to the balance between reduced plant‐derived C influx and inhibited respiration.     

The effect of lichen‐dominated biological soil crusts on growth and physiological characteristics of three plant species in a temperate desert of northwest China

Biocrusts (biological soil crusts) cover open spaces between vascular plants in most arid and semi‐arid areas. Information on effects of biocrusts on seedling growth is controversial, and there is little information on their effects on plant growth and physiology. We examined impacts of biocrusts on growth and physiological characteristics of three habitat‐typical plants, Erodium oxyrhynchum, Alyssum linifolium and Hyalea pulchella, growing in the Gurbantunggut Desert, northwest China. The influence of biocrusts on plant biomass, leaf area, leaf relative water content, photosynthesis, maximum quantum efficiency of PSII (F_v/F_m), chlorophyll, osmotic solutes (soluble sugars, protein, proline) and antioxidant enzymes (superoxide dismutase, catalase, peroxidase) was investigated on sites with or without biocrust cover. Biomass, leaf area, leaf water content, photosynthesis, F_v/F_m and chlorophyll content in crusted soils were higher than in uncrusted soils during early growth and lower later in the growth period. Soluble sugars, proline and antioxidant enzyme activity were always higher in crusted than in uncrusted soils, while soluble protein content was always lower. These findings indicate that biocrusts have different effects on these three ephemeral species during growth in this desert, primarily via effects on soil moisture, and possibly on soil nutrients. The influence of biocrusts changes during plant development: in early plant growth, biocrusts had either positive or no effect on growth and physiological parameters. However, biocrusts tended to negatively influence plants during later growth. Our results provide insights to explain why previous studies have found different effects of biocrusts on vascular plant growth.     

Effect of precipitation variability on net primary production and soil respiration in a Chihuahuan Desert grassland

Precipitation regimes are predicted to become more variable with more extreme rainfall events punctuated by longer intervening dry periods. Water‐limited ecosystems are likely to be highly responsive to altered precipitation regimes. The bucket model predicts that increased precipitation variability will reduce soil moisture stress and increase primary productivity and soil respiration in aridland ecosystems. To test this hypothesis, we experimentally altered the size and frequency of precipitation events during the summer monsoon (July through September) in 2007 and 2008 in a northern Chihuahuan Desert grassland in central New Mexico, USA. Treatments included (1) ambient rain, (2) ambient rain plus one 20 mm rain event each month, and (3) ambient rain plus four 5 mm rain events each month. Throughout two monsoon seasons, we measured soil temperature, soil moisture content (θ), soil respiration (R_s), along with leaf‐level photosynthesis (A_net), predawn leaf water potential (Ψ_pd), and seasonal aboveground net primary productivity (ANPP) of the dominant C₄ grass, Bouteloua eriopoda. Treatment plots receiving a single large rainfall event each month maintained significantly higher seasonal soil θ which corresponded with a significant increase in R_s and ANPP of B. eriopoda when compared with plots receiving multiple small events. Because the strength of these patterns differed between years, we propose a modification of the bucket model in which both the mean and variance of soil water change as a consequence of interannual variability from 1 year to the next. Our results demonstrate that aridland ecosystems are highly sensitive to increased precipitation variability, and that more extreme precipitation events will likely have a positive impact on some aridland ecosystem processes important for the carbon cycle.     

The dazed and confused identity of Agassiz's land tortoise, Gopherus agassizii (Testudines, Testudinidae) with the description of a new species, and its consequences for conservation

We investigate a cornucopia of problems associated with the identity of the desert tortoise, Gopherus agassizii (Cooper). The date of publication is found to be 1861, rather than 1863. Only one of the three original cotypes exists, and it is designated as the lectotype of the species. Another cotype is found to have been destroyed in the 1906 San Francisco earthquake and subsequent fire. The third is lost. The lectotype is genetically confirmed to be from California, and not Arizona, USA as sometimes reported. Maternally, the holotype of Gopherus lepidocephalus (Ottley & Velázques Solis. 1989) from the Cape Region of Baja California Sur, Mexico is also from the Mojavian population of the desert tortoise, and not from Tiburon Island, Sonora, Mexico as previously proposed. A suite of characters serve to diagnose tortoises west and north of the Colorado River, the Mojavian population, from those east and south of the river in Arizona, USA, and Sonora and Sinaloa, Mexico, the Sonoran population. Species recognition is warranted and because Gopherus lepidocephalus is from the Mojavian population, no names are available for the Sonoran species. Thus, a new species, Gopherus morafkaisp. n., is named and this action reduces the distribution of Gopherus agassizii to only 30% of its former range. This reduction has important implications for the conservation and protection of Gopherus agassizii, which may deserve a higher level of protection.     

Influence of temporal fluctuations in seed abundance on the foraging behaviour of harvester ants (Pogonomyrmex spp.) in the central Monte desert,Argentina

The simultaneous study of the temporal dynamics of foraging behaviour, diet and seed abundance is essential to assess the way in which resources affect the behaviour and ecology of harvester ants. Here, we evaluate how fluctuations in grass seed abundance during three consecutive growing seasons influenced the foraging behaviour and diet of the harvester ants Pogonomyrmex rastratus, P. mendozanus and P. inermis in the central Monte desert, Argentina. Seed abundance of the most consumed grasses varied greatly through ant activity season, and ants altered their foraging behaviour in response to those changes. Foragers spent more time travelling and searching for food, and their foraging trips took longer during the low seed availability season. Foraging distance was very similar among species and, contrary to our expectations, did not vary between seasons. Foraging success of P. rastratus and P. inermis increased during the high availability season. This matched the seasonal pattern of foraging activity, suggesting that colonies may detect seed abundance and regulate their foraging effort with the rate of forager success. Although grass seeds were the main item in the diet of the three species, P. mendozanus, and to a lesser extent P. rastratus, turned more generalist when grass seeds were scarce. In contrast, P. inermis showed a very narrow diet breadth, only harvesting grass seeds in both seasons. Our results indicate the relevance of seed availability on foraging behaviour of harvester ants, which should be taken into account when predicting and evaluating the effect of ants on seed resources as well as numerical responses of harvester ant populations to the temporal and spatial variations in grass seed abundance.     

Interactions between granivorous and omnivorous ants in a desert grassland: results from a long-term experiment

Abstract.  1. There is growing evidence that granivorous ants compete for seeds in desert ecosystems. But ants that diverge in diet may still interact strongly if existing colonies deter foundress queens. Granivores (seed eaters) and omnivores (ants that scavenge and feed on plant exudates) are common components of desert ecosystems.
2. The results of a 15-year granivore reduction experiment to explore the responses of two common omnivorous ants, Forelius cf pruinosus and Dorymyrmex insana , in a desert grassland were analysed. The food competition hypothesis predicts that granivore removal will have no net effect on omnivores. The spatial competition hypothesis predicts compensatory increases in omnivores on granivore removal plots.
3. A grain-based gut poison significantly reduced the densities of three of the four common granivorous ants. Densities of the large-colony (10⁵-worker) omnivore Forelius did not increase with granivore removal. In contrast, and consistent with the hypothesis of competition for space, densities of the small-colony omnivore (10²−10³ worker) Dorymyrmex increased on granivore removal plots; however, this effect was only observed in years of high Dorymyrmex abundance.     

Temperate Utah chub form valid otolith annuli in the absence of fluctuating water temperature

Utah chub Gila atraria , a temperate freshwater minnow, formed valid otolith annuli (annual growth rings), even when raised in a constant‐temperature desert spring environment. This suggests that factors other than seasonal variation in water temperature control annual otolith marking.     

Arthropod communities on creosote bush (<Emphasis Type="Italic">Larrea tridentata</Emphasis>) in desert patches of varying degrees of urbanization

The goal of the present study was to investigate the influence of urbanization on the richness, abundance and composition of arthropod communities associated with creosote bush, Larrea tridentata [DC] Cov., in Phoenix, Arizona. Arthropod communities were sampled in two desert types varying in degree of urbanization including fringe deserts (relatively undisturbed expanses of desert outside of Phoenix) and urban deserts (patches of desert within the urban core of Phoenix). Two studies were conducted including (1) a seasonal study (conducted at two fringe desert and two urban desert sites over a nine-month period), and (2) a snapshot study (conducted at multiple fringe desert and urban desert sites over an eight-day period). Results from both studies demonstrated that overall richness and abundance of creosote bush arthropod communities were lower in urban deserts than in fringe deserts. Additionally, creosote bush arthropod community composition varied greatly, both temporally and spatially. These differences in richness and abundance between fringe deserts and urban deserts suggest that the creosote bush arthropod community may be a useful focal biotic community to monitor when assaying for environmental change due to urbanization in arid habitats.