Effects of benomyl and drought on the mycorrhizal development and daily net CO2 uptake of a wild platyopuntia in a rocky semi-arid environment

The effects of drought and the fungicide benomyl on a wild platyopuntia, Opuntia robusta Wendl., growing in a rocky semi-arid environment were assessed. Cladode phosphorus content, cladode water potential and daily net CO2 uptake were measured monthly in 2000 and 2001 before, during and after the summer rainy period. During 2000, the formation of new roots and new cladodes was severely suppressed in response to a prolonged drought, impairing the development of the symbiotic relationship between the arbuscular mycorrhizal (AM) fungi and the roots. Hence no effect of benomyl application was observed on daily carbon assimilation by this Crassulacean acid metabolism plant. During 2001, drought was interrupted, and new cladodes and roots were formed in response to rainfall. Benomyl was highly effective in suppressing root colonization by AM-fungi; however, daily C assimilation was reduced by benomyl application only in October. Thus, the inhibition of AM-fungal colonization by benomyl did not affect photosynthesis, water uptake and P uptake under prolonged drought.     

Arabinan-cellulose composite in Opuntia ficus-indica prickly pear spines

The ultrastructure of the spines decorating the cladodes of the cactus Opuntia ficus-indica was investigated by optical microscopy, scanning and transmission electron microscopy, wide angle X-ray, and solid state 13C NMR analyses. Each spine consisted of a compact parallel arrangement of slender cellulosic fibers (0.4 mm in length and 6-10 microm in diameter) with small lumens. The fibers were disencrusted by alkali and sodium chlorite bleaching, yielding a remarkable arabinan-cellulose (1:1) product. X-ray fiber diagrams of the spines before and after purification confirmed the presence of crystalline cellulose domains with molecular axis parallel to the spine axis. CP-MAS 13C T1 NMR data showed a strong interaction at a nanometric level of a fraction of the arabinan and the cellulose crystalline domains. By sequential hydrothermal extractions, followed by a trifluoroacetic acid treatment, a relatively pure cellulose was isolated while the extracted fibers became fibrillated into slender microfibrils having no more than 4-6 nm diameter. The hydrothermal extract yielded the alpha-L-arabinofuranan consisting of a chain of (1-->5)-linked L-arabinosyl residues with branching either at C-2 or C-3 or at both C-2 and C-3. Taken together, these observations suggest that the bulk of the spine fibers consists of an intimate composite of cellulose microfibrils embedded in an arabinan matrix.     

Polyamine levels during the onset of “CAM” inOpuntia F. indica (Miller)

Summary Polyamines have been related to the Crassulacean Acid Metabolism (CAM) in higher plants. Such relationship was however observed in plants where CAM activity is inducible by external factors. Results presented here indicate that, inOpuntia F. indica, cladodes where onset of CAM is dependent on internal conditions, i.e. leaf age, the concentration of putrescine increases in parallel to the acidity of the cytoplasm. The parallel increase of putrescine concentration and acidity (malic acid concentration) can be best evaluated during the onset of CAM (young cladodes), while such correlation is not observed in mature cladodes where CAM is already in it's full function. Spermidine and spermine show no correlation with CAM activity neither during the onset of CAM nor during it's full function. However, spermidine levels correlate negatively to CAM activity when cladodes attain > 30 days of age. The results suggest that putrescine in free form could possibly counteract the increase of cellular acidity during onset of CAM inOpuntia F. indica; the possible roles of spermidine are discussed.Abbreviations PA polyamines - put putrescine - spd spermidine - spm spermine - HPLC high performance liquid chromatography This work was supported by grants from Italian Ministry of University and Scientific Research (60%).     

Competition between three Chihuahuan desert species: evidence from plant size-distance relations and root distribution

Abstract. Using size-distance data we tested the intensity and importance of competition between Hilaria mutica (a tussock grass), Larrea tridentata (a microphyllous shrub) and Opuntia rastrera (a succulent) in the Chihuahuan desert. We also compared the vertical and horizontal distribution of roots to assess the potential degree of overlap in the use of soil resources. The relationships between sizes and distances of nearest-neighbour plants suggested that intraspecific competition is generally more important than interspecific competition. However, evidence of stronger inter than intraspecific competition was found in some cases. Species combinations showing significant interspecific competition involved always Opuntia, whereas Larrea and Hilaria did not influence each other. The analysis of the symmetry of competition showed that Opuntia was adversely affected by the presence of Hilaria or Larrea. Although differences were found in the distribution of roots, the results of the size-distance study support the idea that, (particularly) Opuntia, below-ground niche differentiation is not sufficiently important to totally avoid the negative effects of plant competition.     

Landscape partitioning by nocturnal rodent assemblages in the Llanos de Ojuelos,in Mexico’s Central High Plateau

Aim The Llanos de Ojuelos in Mexico’s Central High Plateau supports unique Opuntia scrublands and the southernmost Chihuahuan grasslands. Although human activities have modified strongly its landscape and impacted its biodiversity at an unknown scale, such impacts are poorly known. We aimed at understanding how nocturnal rodent species distributed across the landscape and formed assemblages and on the role and integration of the different habitats at the landscape level. Location The study was carried out at 43 sites in a study area of approximately 3350 km² in the Llanos de Ojuelos. Methods During the Spring of 2008, we surveyed nocturnal rodents, through live‐trapping. We redefined habitat classes based on log‐linear multinomial regressions of rodent captures. Species rarefaction curves and true alpha, beta and gamma diversities were calculated for the different habitat classes. A map of the different habitats was constructed based on Landsat imagery. Results We captured 458 individuals of 20 rodent species. Multinomial regressions caused the merger of 11 a priori defined habitat classes into 7. Leguminous scrub and mixed nopaleras, both secondary habitats, had the highest alpha and gamma diversity values. Closed arboreal nopaleras and grasslands had the highest within‐habitat variability (¹D_β) and the lowest area coverage. Within‐habitat ¹D_β was larger than landscape ¹D_β, because of the great overlap in rodent assemblage composition between the habitats. Main conclusions There are no ‘typical’ rodent assemblages per habitat class, but they are organized loosely and have fuzzy borders. Rodent community organization was highly species‐centred. At the landscape level, secondary habitats have a profound effect on rodent diversity and should be included in management schemes for biological conservation. The most endangered habitats seem to be the closed arboreal nopaleras and grasslands. Any conservation efforts must consider their conservation and an increase in the size of remaining patches.     

中国仙人掌科一新归化种——匍地仙人掌

在进行多肉植物资源调查时,在我国山东省发现一仙人掌科仙人掌属新记录种——匍地仙人掌[Opuntia humifusa(Raf.) Raf.]。该种具有独特的匍匐生长习性,叶状茎深绿色,无白霜,无针状刺,花黄色,与国内分布的仙人掌属其他物种区别明显。匍地仙人掌原产于北美洲,是仙人掌科为数不多的耐寒种类之一,现归化于中国山东省日照市五莲县,系目前发现的在我国野外分布最北的仙人掌科植物。该种可能于20世纪50年代在国家推广中药材时期引入种植,人类活动致使其种群逐渐扩散。同时,对匍地仙人掌与江苏报道的二色仙人掌之间的分类学问题进行了论述,并对将来匍地仙人掌在我国暖温带地区合理的开发利用进行了展望。     

Assessing the Effects of Invasive Alien Species on Rural Livelihoods: Case Examples and a Framework from South Africa

The detrimental impacts of invasive alien species (IAS) on ecosystem goods and services and local and regional economies are well documented. However, the use of IAS by rural communities is little understood, and rarely factored into IAS control programmes. Understanding the use of IAS by rural communities and factoring these into cost-benefit models is complex, depending upon a range of local-level attributes such as the time since invasion, abundance, and local-level costs and benefits. This paper reports on two case studies examining the role of IAS in rural livelihoods in the Eastern Cape, South Africa. In both cases, rural communities made widespread consumptive use of the IAS and generally would prefer higher densities, except in certain key localities. Several households traded in IAS products to generate supplementary income. We present a conceptual framework to guide interpretation of these and future case studies, considering attributes such as time since invasion, the competitiveness of the species, and the relative costs and benefits.     

Dactylopius opuntiae,a new prickly pear cactus pest in the Mediterranean: an overview

The Opuntia cochineal scale or false carmine cochineal scale, Dactylopius opuntiae (Cockerell) (Hemiptera: Dactylopiidae), is spreading rapidly in many countries, especially in the Mediterranean basin, where it has become a serious pest of prickly pear crops, Opuntia ficus‐indica (L.) Miller (Cactaceae). This crop is an important food resource both for humans and livestock. The cochineal was originally used as a biological agent to control cactaceous weeds in many countries where Opuntiaceae had been introduced. Currently, in some countries where the prickly pear is no longer considered a weed but a productive crop, as in the Mediterranean area, D. opuntiae has changed its role from a highly prized biological control agent to the status of serious pest. This paper provides an overview of the current knowledge on D. opuntiae for farmers and stakeholders in order to indicate the most appropriate way to limit or counteract the spread of this pest especially in new cultivated areas.