Coastal oceanographic conditions in the Prydz Bay region (East Antarctica) during the Holocene recorded in an isolation basin

Information on East Antarctic coastal environments during the Holocene is relatively sparse. This is surprising as sedimentary records from the interface between land and sea can provide chronologies of climatic change, isostatic uplift, relative sea level and the colonization of newly formed biomes. Here we examine a sediment core from Pup Lagoon, a coastal lake in the Larsemann Hills, East Antarctica. Sediment stratigraphy, fossil pigments and diatoms were used to infer the sequence of Holocene environmental and climatic change. Results show that between 5800 and 5500 cal. yr BP the marine coast of Prydz Bay was characterized by stratified, open-water conditions during spring and summer and seasonally warm conditions. From 5500 to 2750 cal. yr BP sea-ice duration in Prydz Bay increased with the coast being ice-free for 2-3 months each year, conditions which are similar to the present day. A return to stratified, open-water conditions and a reduction in winter sea-ice extent between 2750 and 2200 cal. yr BP is signalled by enhanced biogenic production and more open-water diatom taxa. This is consistent with evidence for the mid-Holocene Hypsithermal detected in other records in East Antarctica. Isostatic isolation of the Pup Lagoon basin from the sea between 2200 and 2000 cal. yr BP slightly precedes the emergence of lakes with comparable sill heights from the nearby Vestfold Hills. The colonization of Pup Lagoon after its isolation as a freshwater lake was initiated by a siliceous flora dominated by stomatocysts with microbial mat development being prevented by mechanical or physical stress. A brief period of marine incursion following the mid-Holocene Hypsithermal may be related to local events such as iceberg calving or to minor sea-level change. Weighted averaging regression, used to infer salinity in the lacustrine zone, shows that from 1500 cal. yr BP Pup Lagoon is a freshwater lake, where the flora is dominated by stratified cyanobacterial mats, with green algae and diatoms as co-dominants, comparable to modem Pup Lagoon and other lakes in the Larsemann Hills

Variability of soybean germplasm in relation to phosphorus uptake and use efficiency Variabilidade em germoplasma de soja para eficiência na absorção e utilização de fósforo

Plant efficiency for phosphorus uptake and utilization may contribute to improve crop yield potential in situations of low P availability. Twenty nine soybean [Glycine max (L.) Merr.] cultivars were evaluated and classified in relation to the response to phosphorus (P) levels in nutrient solution. P uptake and use efficiency were estimated by the variables: shoot and root dry matter (DM) yield, P-concentrations and contents in plant parts and P-efficiency index (EI). The experiment was conducted in a greenhouse, during 1999, at Campinas, State of São Paulo, Brazil. The experimental design consisted of randomized complete blocks, arranged in split-plots, with three replications. The main plots were the P levels in the nutrient solution (64.5; 129; 258 and 516 mmol L-1), and the subplots were the twenty-nine soybean cultivars, grouped according days to maturity. The plants were harvested at flowering, separated in shoots and roots for dry matter determination and chemical analysis. The analyses of variance indicated differences in plant responses to P-levels and cultivars. Multivariate analysis showed high correlation among the variables shoot-DM, total-DM and shoot P-concentration and P-efficiency index (EI). Cultivars were classified in efficient-responsive (ER)-- 'IAC-1', 'IAC-2', 'IAC-4', 'IAC-5', 'IAC-6', 'IAC-9', 'Sta. Rosa' and 'UFV-1'; efficient-non-responsive (ENR) -- 'IAC-7', 'IAC-11', 'IAC-15', 'S. Carlos' and 'Cristalina'; inefficient-responsive (IR) -- 'IAC-8', 'IAC-10', 'IAC-14', 'Bossier' and 'Foscarin'; and inefficient-non-responsive (INR) -- 'IAC-12', 'IAC-13', 'IAC-16', 'IAC-17', 'IAC-18', 'IAC-19', 'IAC-20', 'IAC-22', 'Paraná', 'IAS-5' and 'BR-4'. The efficient-responsive soybean cultivars showed the highest values for shoot and total DM and EI, and the lowest shoot P-concentrations.<br>A eficiência da planta na absorção e utilização de fósforo em situação de baixa disponibilidade do nutriente pode contribuir para aumentar o potencial produtivo da cultura. Vinte e nove cultivares de soja [Glycine max (L.) Merr.] foram avaliados e classificados quanto à resposta a concentrações de fósforo (P) em solução nutritiva. Determinaram-se as variáveis relacionadas com a eficiência na absorção e utilização de P: produção de matéria seca (MS) da parte aérea e das raízes, teores de P nas partes das plantas e os índices de eficiência de utilização de P (IE). O experimento foi instalado em casa de vegetação em Campinas, em 1999. Foi utilizado o delineamento em blocos ao acaso, em parcelas subdivididas com três repetições. As parcelas principais constituíram-se das concentrações de P na solução nutritiva (64,5; 129; 258 e 516 mmol L-1) e as subparcelas, dos vinte e nove cultivares de soja, agrupados de acordo com o ciclo. As plantas foram colhidas no florescimento, separadas em parte aérea e raízes para determinação da matéria seca e análise química de nutrientes. A análise de variância indicou diferenças nas respostas das plantas para concentrações de P e cultivares. A análise multivariada mostrou alta correlação entre a MS de parte aérea e MS-total com os teores de P na parte aérea e índices de eficiência de utilização de P (IE). Os cultivares foram classificados em eficientes e responsivos (ER) -- 'IAC-1', 'IAC-2', 'IAC-4', 'IAC-5', 'IAC-6', 'IAC-9', 'Sta. Rosa' e 'UFV-1'; eficientes não responsivos (ENR) -- 'IAC-7', 'IAC-11', 'IAC-15', 'S. Carlos' e 'Cristalina'; ineficientes responsivos (IR) -- 'IAC-8', 'IAC-10', 'IAC-14', 'Bossier' e 'Foscarin'; e ineficientes não responsivos (INR) -- 'IAC-12', 'IAC-13', 'IAC-16', 'IAC-17', 'IAC-18', 'IAC-19', 'IAC-20', 'IAC-22', 'Paraná', 'IAS-5' e 'BR-4'. Os cultivares eficientes e responsivos mostraram os maiores valores para MS de parte aérea, MS total e IE, e os menores teores de P na parte aérea