Phytoplankton community of Reis lake in the Brazilian Amazon

<p id="para1">Reis Lake is located in the municipality of Caracara&#237;, state of Roraima (Brazil) and is subject to fluctuations in water level. The aim of this study was to analyze the structure of the phytoplankton community on the nictemeral and seasonal scales and determined the influence of limnological variables. Sampling was performed in the rainy season (June/2006) and dry season (November/2006), considering two nictemeral cycles. The phytoplankton community was assessed with regard to composition and density, abiotic variables were analyzed simultaneously. The lake had low concentrations of oxygen, clinograde profile and water stratified during the day and homogenous at night, with low concentrations of nutrients and waters ranging from slightly acidic to alkaline. The phytoplankton was represented by 43 taxa, 35 species in the dry season and 29 species in the rainy season. Low densities of phytoplankton occurred in both nictemeral cycles, with accentuated vertical gradient. The highest densities were recorded in the dry season. Reis Lake exhibits characteristics that classify it as a polymythic and oligotrophic environment. The variability in the data was more important seasonally than on the nictemeral scale, supporting the hypothesis of the influence of the hydrological cycle on the dynamics of phytoplankton communities in floodplain lakes.</p><br><p id="para2">O lago dos Reis est&#225; localizado no munic&#237;pio de Caracara&#237;, no estado de Roraima (Brasil) e est&#225; sujeito a flutua&#231;&#245;es no n&#237;vel da &#225;gua. O objetivo do estudo foi analisar a estrutura da comunidade fitoplanct&#244;nica nas escalas nictemeral e sazonal e determinar a influ&#234;ncia de vari&#225;veis limnol&#243;gicas nesta comunidade. As amostragens foram realizadas nos periodos chuvoso e seco, considerando dois ciclos nictemeral. A comunidade fitoplanct&#244;nica foi avaliada no que diz respeito &#224; composi&#231;&#227;o e densidade, simultaneamente, vari&#225;veis abi&#243;ticas foram analisadas. O lago apresentou baixas concentra&#231;&#245;es de oxig&#234;nio, perfil clinogrado, coluna d' &#225;gua estratificada durante o dia e homog&#234;nea &#224; noite, com baixas concentra&#231;&#245;es de nutrientes e pH variarando de levemente &#225;cido a alcalino. Baixas densidades fitoplanct&#244;nicas ocorreram em ambos os ciclos nictemeral, com um gradiente vertical acentuado. As maiores densidades foram registradas durante a esta&#231;&#227;o seca e a menor foi registrada durante a esta&#231;&#227;o chuvosa. Lago dos Reis apresenta caracter&#237;sticas que o classificam como um ambiente polim&#237;tico e oligotr&#243;fico. A variabilidade dos dados foi mais importante sazonalmente do que na escala nictemeral, refor&#231;ando a hip&#243;tese da influ&#234;ncia do ciclo hidrol&#243;gico sobre a din&#226;mica das comunidades fitoplanct&#244;nicas em lagos de v&#225;rzea.</p

Targeted Genomic Disruption of H-ras and N-ras, Individually or in Combination, Reveals the Dispensability of Both Loci for Mouse Growth and Development

Mammalian cells harbor three highly homologous and widely expressed members of the ras family (H-ras, N-ras, and K-ras), but it remains unclear whether they play specific or overlapping cellular roles. To gain insight into such functional roles, here we generated and analyzed H-ras null mutant mice, which were then also bred with N-ras knockout animals to ascertain the viability and properties of potential double null mutations in both loci. Mating among heterozygous H-ras(+/−) mice produced H-ras(−/−) offspring with a normal Mendelian pattern of inheritance, indicating that the loss of H-ras did not interfere with embryonic and fetal viability in the uterus. Homozygous mutant H-ras(−/−) mice reached sexual maturity at the same age as their littermates, and both males and females were fertile. Characterization of lymphocyte subsets in the spleen and thymus showed no significant differences between wild-type and H-ras(−/−) mice. Analysis of neuronal markers in the brains of knockout and wild-type H-ras mice showed that disruption of this locus did not impair or alter neuronal development. Breeding between our H-ras mutant animals and previously available N-ras null mutants gave rise to viable double knockout (H-ras(−/−)/N-ras(−/−)) offspring expressing only K-ras genes which grew normally, were fertile, and did not show any obvious phenotype. Interestingly, however, lower-than-expected numbers of adult, double knockout animals were consistently obtained in Mendelian crosses between heterozygous N-ras/H-ras mice. Our results indicate that, as for N-ras, H-ras gene function is dispensable for normal mouse development, growth, fertility, and neuronal development. Additionally, of the three ras genes, K-ras appears to be not only essential but also sufficient for normal mouse development

Iron-mediated soil carbon response to water-table decline in an alpine wetland

The tremendous reservoir of soil organic carbon (SOC) in wetlands is being threatened by water-table decline (WTD) globally. However, the SOC response to WTD remains highly uncertain. Here we examine the under-investigated role of iron (Fe) in mediating soil enzyme activity and lignin stabilization in a mesocosm WTD experiment in an alpine wetland. In contrast to the classic &apos;enzyme latch&apos; theory, phenol oxidative activity is mainly controlled by ferrous iron [Fe(II)] and declines with WTD, leading to an accumulation of dissolvable aromatics and a reduced activity of hydrolytic enzyme. Furthermore, using dithionite to remove Fe oxides, we observe a significant increase of Fe-protected lignin phenols in the air-exposed soils. Fe oxidation hence acts as an &apos;iron gate&apos; against the &apos;enzyme latch&apos; in regulating wetland SOC dynamics under oxygen exposure. This newly recognized mechanism may be key to predicting wetland soil carbon storage with intensified WTD in a changing climate.Chinese National Key Development Program for Basic Research [2015CB954201, 2014CB954003]; National Natural Science Foundation of China [41422304, 31370491]; National Thousand Young Talents recruiting plan of ChinaSCI(E)ARTICLE