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Shrubs are important plant species in grassland ecosystems worldwide, and their density and cover have been gradually increasing globally. However, the interaction effect of grazing and aridity on population recruitment and population growth of shrub species in grasslands has not been examined explicitly. We examined sapling establishment, sexual recruitment, population mortality, and population growth of Caragana stenophylla along a climatic aridity gradient and a grazing intensity gradient in the Inner Mongolia Steppe, using manipulative field experiments. Sapling establishment, sapling height, and sexual recruitment of C. stenophylla decreased as climatic aridity and grazing intensity increased. The negative effects of grazing on sapling establishment and sexual recruitment gradually increased as climatic aridity increased. The effect of climatic aridity and grazing on population mortality was influenced by sexual recruitment. In the combined treatments of climatic aridity and grazing, population mortality was relatively high when sexual recruitment was relatively high, while population mortality increased as climatic aridity and grazing increased when sexual recruitment was relatively low. C. stenophylla population increased under relatively low drought stress and mild grazing but declined under strong drought stress and/or severe grazing. Our results suggested that to maintain viable Caragana populations, appropriate grazing policies must be made according to climate aridity gradient. [ABSTRACT FROM AUTHOR]

Abstract: In this study, we examined the alterations in canopy size and reproduction of Caragana stenophylla along the climatic drought gradient on the Inner Mongolia Plateau, China. We found that the canopy area and height of C. stenophylla increased gradually with increase of drought stress from the semi-arid zone to the strongly arid zone. The proportions of sexual reproduction decreased and the asexual reproduction increased with increase of the climatic drought stress. The majority of C. stenophylla offspring grew (separately) outside shrubs in the semi-arid (63.9%) and the arid zones (45.8%). But in the strongly arid zone, C. stenophylla offspring only grew inside shrubs. With the increase of climatic drought stress the ramet radius increased, while the spacer length decreased. In both the semi-arid and arid zones, the spacer length was more than 2 times of the ramet radius. Thus, some spaces were kept between the crowns of ramets. On the other hand, the spacer length was less than 2 times of the ramet radius in the strongly arid zone, so that the crowns were closely intertwined. Our results demonstrate that with the increase of climatic drought stress and associated desertification, the reproduction of C. stenophylla changes from more sexual reproduction to more clonal propagation; offspring establishment strategy changes from having more outside-shrub offspring to having only inside-shrub offspring; the clonal architecture changes from guerrilla type to phalanx type. Alterations in the reproduction of C. stenophylla along the climatic drought gradient result due to an increase of its canopy size from the northeast to the southwest on the Inner Mongolia Plateau. [Copyright &y& Elsevier]

Accumulation and potential health risks of toxic elements are associated with excessive fertilizer and manure applications in vegetable production systems. The goal of the present study was to explore the effects of potential toxic elements on the function of a cohort of beneficial organisms, specifically, the insect parasitic nematodes known as entomopathogenic nematodes. We assessed the impact of heavy metal accumulation on entomopathogenic nematodes ( Steinernema carpocapsae and Heterorhabditis bacteriophora ) and plant parasitic nematodes ( Meloidogyne incognita ). Genearlly, pretreatment with 1.5 mg Cu/L, 50 mg Zn/L or 7.5 mg Cr/L solution for 24 h caused direct mortality of infective juvenile S. carpocapsae and H . bacteriophora nematodes, and lowered virulence of H . bacteriophora against Galleria mellonella . Interestingly, we found that 24 h exposure to 4.5 mg Cu/L, 50 mg Zn/L or 7.5 mg Cr/L solution already caused higher mortality in H. bacteriophora than M. incognita in a laboratory assay. Moreover, in a potted plant experiment, pretreatment of H. bacteriophora with Cu, Zn or Cr salts resulted in increased penetration of M. incognita into cucumber roots compared with H. bacteriophora that were not treated (thus reducing biocontrol efficacy). Pretreatment of S. carpocapsae with Cu also caused increased penetration of M. incognita into cucumber roots; however, none of the Zn and Cr pretreatment concentrations exposed to S. carpocapsae resulted in increased M. incognita root penetration, and lower concentrations of these elements caused decreased penetration (enhancing biocontrol efficacy). Our results indicate that heavy metals can have a direct negative effect on entomopathogenic nematodes (via direct mortality) and also an indirect effect by disrupting biocontrol efficacy against plant parasitic nematodes, but in some cases low concentration may stimulate biocontrol activity. High levels of heavy metal accumulation in greenhouse vegetable production systems could substantially influence nematode community structure and impact other soil biota as well. [ABSTRACT FROM AUTHOR]