Singular spectrum analysis (SSA) is considered from a linear invariant systems perspective. In this terminology, the extracted components are considered as outputs of a linear invariant system which corresponds to finite impulse response (FIR) filters. The number of filters is determined by the embedding dimension.We propose to explicitly define the frequency response of each filter responsible for the selection of informative components. We also introduce a subspace distance measure for clustering subspace models. We illustrate the methodology by analyzing Electroencephalograms (EEG).

O arroz, é essencialmente produzido como monocultura, em canteiros alagados, nas regiões do centro e sul do País (Vales do Mondego, Tejo e Sado). O ião NH4 + é a forma de N mineral mais abundante e preferencialmente absorvida pelo arroz, em condições de alagamento. O alagamento potencia a mineralização, por acção dos microrganismos aeróbios facultativos, aumentando a sua concentração na solução do solo. No solo, este catião pode ser adsorvido nos colóides ou "fixado" nos minerais argilosos do tipo 2:1, tornando-se temporariamente indisponível para a cultura. A taxa de "fixação" e posterior libertação para a solução depende da textura do solo, do teor e mineralogia da argila, pH, potencial redox, temperatura e presença de outros catiões. Não se conhecem os efeitos do aumento simultâneo da concentração de CO2 na atmosfera e da temperatura na "fixação" do NH4 + , sabendo-se que, isoladamente, o aumento da temperatura potencia a "fixação". Neste estudo, avaliou-se o teor de NH4 + em dois solos (areno-franco e argilo-limoso) alagados e cultivados com arroz, em 2012, como resposta à fertilização mineral e ao alagamento. Compararam-se esses teores com os medidos no solo argilo-limoso, em condições controladas de aumento da [CO2] e temperatura. O teor de NH4 + "fixado" em ambos os solos (ar livre) foi superior ao da concentração de NH4 + disponível no respectivo solo. A concentração de NH4 + "fixada" no solo argilo-limoso manteve-se superior à do solo arenofranco, variando com os tratamentos (ar livre > CO2+temperatura = temperatura), com as datas de amostragem e com a fertilização azotada.

Data on the movements of available N and non-exchangeable NH4 + in the soil are of crucial importance in designing an efficient plant N nutrition management scheme in paddy rice fields. To investigate the processes affecting the dynamics of N and pH under Mediterranean conditions, rice (Oryza sativa L. cv. Ariete) was cultivated in 2011 and 2012 in Salvaterra de Magos (central Portugal) under the following climate scenarios: (i) ambienttemperature and ambient [CO2] in the open-field, (ii) elevated temperature (+3 C) and ambient [CO2] in open-top chambers, and (iii) elevated temperature (+3 C) and elevated [CO2] (+175mmol mol1 ) in open-top chambers. Plants were grown under an intermittent flooding regime. Soil and water samples were taken at eight different stages of plant growth, including before and after N basal and topdressing. Our study indicated that the processes underlying N changes in response to the timing of N fertilization were different depending on the N form. After basal dressing under aerobic conditions, both available and non-exchangeable NH4 + contents were increased. Following the topdressing under flooded conditions, the available content of soil N increased, whereas the non-exchangeable NH4 + content decreased. A negative relationship was found between soil pH and NH4 + “fixation” when roots were active, and vice-versa. Elevated temperature alone or in combination with elevated [CO2] had no effect on the total available N content in the soil and floodwater. Under elevated temperature, however, the non-exchangeable NH4 + content was significantly reduced (11%), with the same magnitude of change (10%) observed under co-elevation of temperature and [CO2]. These results suggested that non-exchangeable NH4 + in paddy fields might be insensitive to [CO2] elevation under Mediterranean conditions, while reductions observed under co-elevation of [CO2] and temperature might be associated with temperature alone. This information could be used to alter rice management practices and to adjust N application under climate change.

Abstract The present field experiment was conducted during two consecutive cropping seasons in central Portugal to study the effects of simultaneous elevation of carbon dioxide concentration ([CO2]) (550 lmol mol-1 ) and air temperature (?2–3 C) on japonica rice (Oryza sativa L. ‘‘Ariete’’) yield, crop duration, and SPAD-values across the seasons compared with the open-field condition. Open-top chambers were used in the field to assess the effect of elevated air temperature alone or the combined effect of elevated air temperature and atmospheric [CO2]. Open-field condition was assessed with randomized plots under ambient air temperature and actual atmospheric [CO2] (average 382 lmol mol-1 ). Results obtained showed that the rice ‘‘Ariete’’ had a moderate high yielding under open- field condition, but was susceptible to air temperature rise of ?2–3 C under controlled conditions resulting in reduction of grain yield. The combined increase of atmospheric [CO2] with elevated air temperature compensated for the negative effect of temperature rise alone and crop yield was higher than in the open-field. SPAD-readings at reproductive stage explained by more than 60 % variation the straw dry matter, but this finding requires further studies for consolidation. It can be concluded that potential increase in air temperature may limit rice yield in the near future under Mediterranean areas where climate change scenario poses a serious threat, but long term field experiments are required.

Rice is one of the most important food crops in the world and the staple for more than half of the global population. Portugal is the first rice consumer, per capita, in Europe and the fourth producer (6 t ha-1), contributing to the 5.3% of the total European production. Rice cultivation in Portugal is intensive and is mostly located in the central and southern regions (Mondego, Tagus and Sado Valleys). The cultivation in Europe is mainly by flooding to control soil temperature, weeds and pests. The water content of soils can vary considerably, depending on climatic conditions, soil type and agricultural practices. In Portugal, rice straw is returned to the field after harvest, partially is burnt and partly is incorporated preceding the rice cultivation. Straw incorporation in soil in the non-rice-growing season can result in lower methane emission in the following rice-growing season than does the incorporation just before rice cultivation. The anaerobic conditions in flooded soils influence nitrogen (N) fertilizers dynamics, particularly the redox potential and soil pH. Rice roots absorb nitrate (NO3 –) or ammonium (NH4 +) from soil using a variety of transporters, but NH4 + is the preferential form in waterlogged soils. Nitrogen use efficiency is generally low (20-35%). In 2011, we evaluated the soil and floodwater N and pH dynamics, and the rice response to the actual agricultural practices in an open field at Salvaterra de Magos (central Portugal), and in open top chambers with increased atmospheric carbon dioxide concentration [CO2] and temperature.

The “newly fixed” NH4 + in clay minerals should be considered for an efficient management of plant nutrition. In a clayloam soil cultivated in 2012 with rice under intermittent flooding and conventional agronomic practices, the dynamics of pH, N-inorganic and non-exchangeable NH4 + was evaluated i) under field conditions, air temperature and atmospheric [CO2 ] (375 µmol mol-1 air) in Salvaterra de Magos (Portugal), and ii) under elevated temperature and temperature+[CO2 ] in controlled microclimate. For that, open-top chambers were used to simulate the conditions of an increased mean air temperature (2-3 °C), alone or combined with increased [CO2 ] (550 µmol mol-1 air). Non-exchangeable NH4 was significantly higher under open-field conditions compared with the temperature elevation, with or without elevated atmospheric [CO2 ]. Temperature elevation reduced the “fixation” rate of the cation, while the CO2 concentration rise did not affect particularly the non-exchangeable form. Further studies are required for consolidation of these findings together with microbial communities and dynamics of C and N in soil.

A cultivar de arroz Ariete apresentou uma eficiência máxima de uso do N de 64% e uma produção de 8,5 t ha-1, após aplicação de 120 kg N ha-1, metade em fundo e metade ao afilhamento. Os fatores de emissão de GEEs medidos no campo foram de 136 kg CH4 ha-1 e 1,5% para o N2O. As emissões de COVs (especialmente na forma de terpenos) e NH3 foram reduzidas, mas atingiram 8 kg N-NH3 ha-1 dia-1 após a adubação de cobertura.