Nonrandom processes maintain diversity in tropical forests     

Wills C  Harms KE  Condit R  King D  Thompson J  He F  Muller-Landau HC  Ashton P  Losos E  Comita L  Hubbell S  Lafrankie J  Bunyavejchewin S  Dattaraja HS  Davies S  Esufali S  Foster R  Gunatilleke N  Gunatilleke S  Hall P  Itoh A  John R  Kiratiprayoon S  de Lao SL  Massa M  Nath C  Noor MN  Kassim AR  Sukumar R  Suresh HS  Sun IF  Tan S  Yamakura T  Zimmerman J 《Science (New York, N.Y.)》2006,311(5760):527-531

An ecological community's species diversity tends to erode through time as a result of stochastic extinction, competitive exclusion, and unstable host-enemy dynamics. This erosion of diversity can be prevented over the short term if recruits are highly diverse as a result of preferential recruitment of rare species or, alternatively, if rare species survive preferentially, which increases diversity as the ages of the individuals increase. Here, we present census data from seven New and Old World tropical forest dynamics plots that all show the latter pattern. Within local areas, the trees that survived were as a group more diverse than those that were recruited or those that died. The larger (and therefore on average older) survivors were more diverse within local areas than the smaller survivors. When species were rare in a local area, they had a higher survival rate than when they were common, resulting in enrichment for rare species and increasing diversity with age and size class in these complex ecosystems.  相似文献   

Characterization of free-living cyanobacterial strains and their competence to colonize rice roots     

Chingkheihunba Akoijam  Arvind Kumar Singh  Amar Nath Rai 《Biology and Fertility of Soils》2012,48(6):679-687

A total of 45 cyanobacterial strains isolated from rice fields near Loktak Lake in Manipur, India were tested for their rice root colonization capacity under light and under darkness. Twenty-one of these strains showed significant colonization of rice roots. The average colonization values were 637 and 381?μg chl a g^?1 root dry wt in N₂ medium and 792 and 451?μg chl a g^?1 root dry wt in NO ₃ ^? medium under light and darkness, respectively. Thus, while the colonization was higher under light and in NO ₃ ^? medium, there was significant level of colonization under darkness in N₂ medium (381?μg chl a g^?1 root dry wt). A 16S rRNA gene fragment-based denaturing gradient gel electrophoresis analysis revealed difference in the competence of individual strains to colonize rice roots exposed to individual or mixed population. The colonization pattern of seven strains used in competition experiments was found to be biphasic. A 16S rRNA gene-based phylogenetic analysis revealed high level of molecular similarity among strains of Nostoc and Anabaena.  相似文献   

Hydrochemistry of Arsenic-Enriched Aquifer from Rural West Bengal, India: A Study of the Arsenic Exposure and Mitigation Option     

Bibhash Nath  Sudip J. Sahu  Joydev Jana  Aishwarya Mukherjee-Goswami  Sharmi Roy  Madhav J. Sarkar  Debashis Chatterjee 《Water, air, and soil pollution》2008,190(1-4):95-113

The present study aims to understand the hydrochemistry vis-à-vis As-exposure from drinking groundwater in rural Bengal. The characteristic feature of the groundwaters are low Eh (range, ?151 to ?37 mV; mean, ?68 mV) and nitrate (range, 0.01–1.7 mg/l; mean, 0.14 mg/l) followed by high alkalinity (range, 100–630 mg/l; mean, 301 mg/l), Fe (range, 0.99–38 mg/l; mean, 8.1 mg/l), phosphate (range, 0.01–15 mg/l; mean, 0.54 mg/l), hardness (range, 46–600 mg/l; mean, 245 mg/l) and sulphate (range, 0.19–88 mg/l; mean, 7.2 mg/l), indicating reducing nature of the aquifer. The land use pattern (sanitation, surface water bodies, sanitation coupled with surface water bodies and agricultural lands) demonstrates local enrichment factor for As/Fe in groundwater. Among these, sanitation is the most prevailing where groundwater is generally enriched with As (mean, 269 μg/l) and Fe (mean, 9.8 mg/l). Questionnaire survey highlights that ～70% of the villagers in the study area do not have proper sanitation. This demonstrating the local unsewered sanitation (organic waste, anthropogenic in origin) could also cause As toxicity in rural Bengal. In the agricultural lands, higher mean values of alkalinity, phosphate, sulphate, hardness and electrical conductivity was observed, and could be linked with the excessive use of fertilizers for agricultural production. Bio-markers study indicates that the accumulation of As in hair and nail is related with the construction of exposure scenario with time dimension. The strength and weakness of the on-going West Bengal and Bangladesh drinking water supply scenario and achievability towards alternative options are also evaluated.  相似文献   

Foliar fertilization of nickel affects growth,yield component and micronutrient status of barley (Hordeum vulgare L.) grown on low nickel soil     

Omkar Kumar  Ashish Maroatrao Latare  Shobha Nath Yadav 《Archives of Agronomy and Soil Science》2018,64(10):1407-1418

Foliar application of nickel (Ni) has higher use efficiencies and is preferred over soil application in view of its very low requirement. Pot experiments were conducted during winter season of 2012-2013 and repeated during 2013-2014. Treatments consisted of twelve Ni levels applied as nickel sulphate (NiSO4.7H₂O) spray (T₁-Ni_0%, T₂-Ni_0.05%, T₃-Ni_0.1%, T₄-Ni_0.2%, T₅-Ni_0.3%, T₆-Ni_0.4%, T₇-Ni_0.5%, T₈-Ni_0.6%, T₉-Ni_0.7%, T₁₀-Ni_0.8%, T₁₁-Ni_0.9%,and T₁₂-Ni_1.0%,) with recommended doses of fertilizers (RDF) applied in all pots. The result showed that growth and yield attributes viz. plant height, leaf greenness index, number of tillers, number of ears pot^-1, number of grains ear^-1, straw yield, grain yield and weight of 1000 grains of barley was the maximum with three foliar application of 0.2% of NiSO4.7H₂O (T₄-Ni_0.2%) at 20, 40, and 60 days after sowing (DAS) during both the years. The concentration of Fe, Mn and Zn in grain increased significantly up to T₄-Ni_0.2% and after this level, a significant decline was recorded during both the years. As regards to the concentration of Ni is concerned, it increased significantly both in grain and straw with increasing levels of Ni spray and the maximum concentration was at T₁₂-Ni_1.0%, during both the years. The uptake of Fe, Mn, Cu and Zn in grain of barley increased significantly during both the years up to T₄-Ni_0.2%,thereafter, it declined significantly with successive increase in dose of Ni spray. Thus 0.2% foliar spray of NiSO4.7H₂O significantly increased growth, yield and Fe, Cu, Mn, Zn (micronutrients) status in barley.  相似文献   

Littered Cans—Death Trap of Snakes     

Subhendu Mallik  Sudipta Ranjan Singh  Indramani Nath 《The Forestry Chronicle》2017,28(1):56-57

  相似文献   

Expression and Characterization of Constitutive Heat Shock Protein 70.1 (HSPA‐1A) Gene in In Vitro Produced and In Vivo‐Derived Buffalo (Bubalus bubalis) Embryos     

GT Sharma  A Nath  S Prasad  S Singhal  N Singh  NE Gade  PK Dubey  G Saikumar 《Reproduction in domestic animals》2012,47(6):975-983

Cells are blessed with a group of stress protector molecules known as heat shock proteins (HSPs), amongst them HSP70, encoded by HSPA‐1A gene, is most abundant and highly conserved protein. Variety of stresses hampers the developmental competence of embryos under in vivo and in vitro conditions. Present work was designed to study the quantitative expression of HSPA‐1A mRNA in immature oocytes (IMO), matured oocytes (MO), in vitro produced (IVP) and in vivo‐derived (IVD) buffalo embryos to assess the level of stress to which embryos are exposed under in vivo and in vitro culture conditions. Further, HSPA‐1A gene sequence was analysed to determine its homology with other mammalian sequences. The mRNA expression analysis was carried out on 72 oocytes (40 IMO; 32 MO), 76 IVP and 55 IVD buffalo embryos. Expression of HSPA‐1A was found in oocytes and throughout the developmental stages of embryos examined irrespective of the embryo source; however, higher (p < 0.05) expression was observed in 8–16 cell, morula and blastocyst stages of IVP embryos as compared to IVD embryos. Phylogenetic analysis of bubaline HSPA‐1A revealed that it shares 91–98% identity with other mammalian sequences. It can be concluded that higher level of HSPA‐1A mRNA in IVP embryos in comparison with in vivo‐derived embryos is an indicator of cellular stress in IVP system. This study suggests need for further optimization of in vitro culture system in which HSPA‐1A gene could be used as a stress biomarker during pre‐implantation development.  相似文献   

Purification, characterization and evaluation of insecticidal activity of trypsin inhibitor from Albizia lebbeck seeds     

Pratima Sharma  Amarjit K Nath  Reena Kumari  SV Bhardwaj 《林业研究》2012,23(1):131-137

A Bowman-Birk inhibitor with activity against gut proteases of Helicoverpa armigera was extracted in 0.1 M sodium phosphate buffer from defatted seed flour of Albizia lebbeck. It was purified to 29.62 folds with 51.43% recovery using ammonium sulfate precipitation, gel filtration chromatography on Sephadex G-100 column and ion exchange chromatography on DEAE-Sephadex A50. The purified protein had a molecular weight of 12,303 daltons as determined by SDS-PAGE. It was found to be heat stable up to 60°C and had two pH optima of 7.5 and 9.0. The inhibitor exhibited non-competitive pattern of inhibition with a low Ki value of 0.2 μM. The inhibitor was found to be susceptible to varying concentrations of reducing agents like DTT and 2-mercaptoethanol, thereby indicating the role of disulphide bridges in maintaining its three dimensional structure and stability. The purified inhibitor caused mortality and suppressed larval growth of Pieris brassicae larvae. It was also found to be effective against gut trypsin extracted from Spodoptera littoralis. The sequence of the genes encoding for such inhibitors can be determined and the genes expressing protease inhibitors can be used in vegetable crops to confer resistance against insect pests and other plant pathogens.  相似文献   

Deep Gluteal Abscess in a Zebra (Equus burchelli boehmi)     

Indramani Nath  Subharaj Samantara  Susen K. Panda 《Journal of Equine Veterinary Science》2012

A male zebra aged about 7 years, weighing approximately 250 kg showed signs of lameness on its hindquarter. It was treated by the zoo veterinarians symptomatically, and it recovered. However, there was recurrence of the symptoms after 1 month. The animal was treated with fluid, electrolyte, antibiotic, and analgesic therapy. The hematology and serum biochemistry profiles were tested and found within the normal range. The animal was tranquilized, and physical and external examinations were conducted. Radiological examination of hoof ruled out any chances of laminitis or any other hoof deformities. Per-rectal examination along with flexion and extension of the hind limbs could not reveal any abnormalities. However, there was no improvement, and finally it died. Postmortem examination revealed an internal deep gluteal abscess. This is a rare report of deep gluteal abscess in a zebra. The difficulties encountered in diagnosing the case and its serious possible complications and possible methods of diagnosing have been described, which may help future equine and wildlife vets in diagnosing such cases successfully and may help in saving the precious lives of the patients suffering from such conditions.  相似文献   

A survey of the trichostrongylid nematode species present on UK sheep farms and associated anthelmintic control practices     

Burgess CG  Bartley Y  Redman E  Skuce PJ  Nath M  Whitelaw F  Tait A  Gilleard JS  Jackson F 《Veterinary parasitology》2012,189(2-4):299-307

A survey of sheep farms from across the UK was conducted to establish information on farming practices, the trichostrongylid nematode species present and anthelmintic usage. Questionnaires and faecal samples were returned from 118 farms. First stage larvae (L(1)) were cultured from faecal samples and used for PCR analysis to determine the presence/absence of selected trichostrongylid species. Teladorsagia circumcincta was the only species present on 100% of farms. Haemonchus contortus was found on ～50% of farms and was widespread throughout the UK. The most common Trichostrongylus spp. was T. vitrinus, found on 95% of farms. Determining the anthelmintic dose rate based on the weight of the heaviest animal in the flock to avoid under dosing was carried out on 58% of farms and was associated with a significantly lower mean epg (p<0.001) in lambs. However, the weight of animals was only estimated (as opposed to animals weighed) on 32% of farms. Macrocyclic lactones (ML) were the most commonly used anthelmintic class for ewes, whilst benzimidazoles (BZ) were the most widely used in lambs. Twenty-two of the surveyed farms had confirmed anthelmintic resistance, of these, 18 had BZ resistance, one had levamisole (LEV) resistance and 3 had resistance to both BZ and LEV. No farms in this survey reported resistance to ML. Location had a significant effect on the incidence of anthelmintic resistance on the farms in this survey (p=0.002). There was evidence of a lower risk of anthelmintic resistance occurring on farms from Scotland compared to those in England (p(f)=0.047) and Wales (p(f)=0.012). Farm type, flock type and open or closed status did not have any significant effect on the incidence of anthelmintic resistance when all other factors were taken into consideration.  相似文献   

Surface Treated Jute Fiber Induced Foam Microstructure Development in Poly(lactic acid)/Jute Fiber Biocomposites and their Biodegradation Behavior     

Mohammad Tahir Zafar  Sanjeev Kumar  Rajendra Kumar Singla  Saurindra Nath Maiti  Anup Kumar Ghosh 《Fibers and Polymers》2018,19(3):648-659

Poly(lactic acid) (PLA)/jute fiber biocomposites with: i) untreated jute fiber, ii) NaOH treated jute fiber, and iii) (NaOH+silane) treated jute fibers were prepared by melt extrusion process. Microcellular foaming of the injection molded samples was carried out by using single stage batch process. The effects of jute fiber content as well as that of matrix-fiber phase adhesion, in composites with surface treated jute fibers, on the foam microstructure were studied. Further, water absorption, thickness swelling, and biodegradation behavior of the foamed biocomposites were studied and correlated with their foam microstructures. It was observed that on increasing jute fiber content in PLA/JFU biocomposites, cell density increased from 6.5×10⁷ to 8.1×10⁷, while the cell size and expansion ratio decreased from 40 to 23 μm and 2.41 to 1.45, respectively. Again, on increasing the extent of the jute fiber surface treatment in the biocomposites, cell size and expansion ratio increased from 40 to 78 μm and 2.41 to 2.80 respectively. This study also revealed that the rate of biodegradation accelerated with increase in the jute fiber content in the biocomposites while the same retarded with increase in the extent of jute fiber surface treatment.  相似文献