Plants are constantly subjected to variations in their surrounding environment, which affect their functioning in different ways. The influence of environmental factors on the physiology of plants depends on several factors including the intensity, duration and frequency of the variation of the external stimulus. Water deficit is one of the main limiting factors for agricultural production worldwide and affects many physiological processes in plants. The aim of this study was to analyse the effects of different rates of induced water deficit on the leaf photosynthetic responses of soybean (Glycine max L.) and cowpea (Vigna unguiculata L.). The plants were subjected to two types of water deficit induction: a rapid induction (RD) by which detached leaves were dehydrated by the exposure to air under controlled conditions and a slow induction (SD) by suspending irrigation under greenhouse conditions. The leaf gas exchange, chlorophyll (Chl) a fluorescence, and relative water content (RWC) were analysed throughout the water-deficit induction. V. unguiculata and G. max demonstrated similar dehydration as the soil water percentage declined under SD, with V. unguiculata showing a greater stomatal sensitivity to reductions in the RWC. V. unguiculata plants were more sensitive to water deficit, as determined by all of the physiological parameters when subjected to RD, and the net photosynthetic rate (P N ) was sharply reduced in the early stages of dehydration. After the plants exposed to the SD treatment were rehydrated, V. unguiculata recovered 65% of the P N in relation to the values measured under the control conditions (initial watering state), whereas G. max recovered only 10% of the P N . Thus, the better stomatal control of V. unguiculata could enable the maintenance of the RWC and a more efficient recovery of the P N than G. max.

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Because of the complexity of plant responses to water deficit, researchers have attempted to identify simplified models to understand critical aspects of the problem by searching for single indicators that would enable evaluations of the effects of environmental changes on the entire plant. However, this reductionist approach, which is often used in plant sciences, makes it difficult to distinguish systemic emergent behaviours. Currently, a new class of models and epistemology have called attention to the fundamental properties of complex systems. These properties, termed 'emergent', are observed at a large scale of the system (top hierarchical level) but cannot be observed or inferred from smaller scales of observation in the same system. We propose that multivariate statistical analysis can provide a suitable tool to quantify global responses to water deficit, allowing a specific and partially quantitative assessment of emergent properties. Based on an experimental study, our results showed that the classical approach of the individual analysis of different data sets might provide different interpretations for the observed effects of water deficit. These results support the hypothesis that a cross-scale multivariate analysis is an appropriate method to establish models for systemic understanding of the interactions between plants and their changing environment.

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RESUMO -A manutenção do status hídrico de uma planta é essencial para seu desenvolvimento adequado em ambientes com limitação da disponibilidade de água. Diferentes espécies possuem diversos mecanismos que conferem maior habilidade de sobrevivência em condições de seca. O objetivo deste estudo foi avaliar as alterações de parâmetros fisiológicos da espécie isohídrica Beaucarnea recurvata Lem. O estudo envolveu experimentos com desidratação lenta (DL) realizado por meio da suspensão da irrigação seguida por reidratação, e com desidratação rápida (DR), onde folhas individuais foram destacadas e colocadas para desidratar em bancada de laboratório. Os resultados mostraram que apesar da porcentagem de água no solo atingir valores críticos (12%) logo nos primeiros dias de DL as plantas apresentaram manutenção do conteúdo relativo de água (≅80%) ao longo de 54 dias de DL, quando a fotossíntese líquida (P N ) atingiu valores nulos. Ao longo de DL foi observado que a P N , a condutância estomática (gs), a eficiência instantânea de carboxilação, a eficiência fotoquímica e o conteúdo de clorofila foram reduzidos. No experimento de DR foi observada alta correlação entre P N e gs. Os resultados sugerem que a redução da fotossíntese foi inicialmente causada por um ajuste estomático, culminando com um desequilíbrio entre a produção de energia fotoquímica e o seu consumo pelo aparato bioquímico da fotossíntese. Entretanto, após a reidratação, os parâmetros de trocas gasosas foram recuperados, indicando que o comportamento isohídrico dessa espécie contribuiu para que as plantas não sofressem danos extensivos durante um período prolongado de suspensão da irrigação. Palavras-chave:Beaucarnea recurvata Lem. Desidratação. Regulação hídrica. Trocas gasosas. PHOTOSYNTHETIC CHARACTERIZATION OF THE ISOHIDRIC SPECIES PONYTAIL PALM UNDER WATER DEFICITABSTRACT -The maintenance of a plant water status is essential for keeping of its development in environments with limited water availability. Different species have different mechanisms that provide greater ability to survive under drought conditions. The objective of this study was to evaluate physiological parameters changes of the isohydric species Beaucarnea recurvate Lem. under irrigation suspension. The study involved experiments with slow dehydration (SD) performed by withholding water followed by plants rehydration, and with rapid dehydration (RD), where individual leaves were detached and placed to dehydrate in the laboratory bench. The results showed that although of the soil water content (% H 2 O) reach critical values (12%) in the first days of the irrigation suspension, the plants showed maintenance of the relative water content (≅80%) over the 54-day SD period, when the net photosynthesis (P N ) reached null values. Throughout SD, it was observed that the P N , stomatal conductance (g s ), instantaneous carboxylation efficiency, the electrons transport rate, the potential quantum efficiency of PSII and chlorophyll content were reduced. In RD, experiment was observed a high cor...

Plants in natural environments are subjected to a multitude of environmental cues. However, studies addressing physiological analyzes are usually focused on the isolation of a stress factor, making it difficult to understand plants behavior in their extremely complex natural environments. Herein, we analyzed how environmental variability (noise) may influence physiological processes of Glycine max under water deficit conditions. The plants were kept in a greenhouse (semi-controlled environment -E SC ) and in a growth chamber (controlled environment -E C ) under two water regime conditions (100 and 30% of replacement of the water lost by evapotranspiration) for 30 days. The environmental variability was daily monitored with automatic sensors to record temperature, humidity, and irradiance. The physiological responses were analyzed by leaf gas exchanges, chlorophyll fluorescence, biomembrane integrity, and growth parameters. The results showed that water deficiency caused significant reductions in the physiological parameters evaluated. However, the environment with high variability (E SC ) caused more extensive damages to biomembranes, regardless the water regime likely compromising physiological efficiency. The lower variability of E C promoted higher efficiency of total biomass production in both water regimes compared to the E SC . Therefore, our results support the hypothesis that more variable environmental conditions can limit the growth of Glycine max in response to the fluctuation of resources, therefore amplifying the effect of water deficit.

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