The influence of light on the growth of watercress (Nasturtium officinale R. Br.)

Abstract

In stream ecosystems, the growth of aquatic primary producers is affected by spatial and temporal variations in the riparian canopy, which can influence the availability of light resources. Aquatic plants can acclimate to low light environments by employing a suite of morphological or physiological mechanisms to increase light capture or photosynthetic efficiency. Some species may also use alternate types of propagules to colonize environments with heterogeneous light environments. In a greenhouse experiment we examined the morphological and physiological response of watercress (Nasturtium officinale R. Br.) to a gradient of increasing light levels, which ranged from 7% ambient light to full sunlight. We also determined if watercress seedlings and vegetative fragments differed in their growth response to increasing light levels. Total biomass and root biomass of seedlings and vegetative fragments decreased with decreasing light levels. The difference in plant biomass across treatments was due to morphological changes in total canopy area and leaf area, both of which increased with decreasing light levels. Seedlings and vegetative fragments did not differ in their response to light availability, but vegetative fragments had higher final biomass as a result of higher initial biomass. Physiological acclimation to low light levels appears to be of secondary importance for watercress as the concentrations of total chlorophyll, chlorophyll a, chlorophyll b, and chlorophyll a:b did not differ among light levels or between seedlings and vegetative fragments. Seedlings and vegetative fragments grown under high light levels had a greater percentage of carbon and a lower percentage of nitrogen than plants grown under low light conditions. The results of this study indicate that watercress displays considerable morphological plasticity and acclimates to low light conditions primarily by increasing leaf area and canopy surface area. There is no evidence that the type of watercress propagule (seedling vs. vegetative fragment) imparts any growth advantage in low light environments and watercress grown from either type of propagule showed no differences in their morphological or physiological responses to varying light regimes.

The effect of different nutrient concentrations on the growth rate and nitrogen storage of watercress (Nasturtium officinale R. Br.)

“…Previous work has shown that watercress biomass increases with photoperiod and light availability (Engelen-Eigles et al, 2006;Going et al, 2008). The discrepancy in growth rates reported for Grime and Hunt's (1975) laboratory experiments and our mesocosm experiment may be attributable to a longer day length in the laboratory study (18 h), compared to our study in which natural day length ranged from 10 to 12 h over the duration of the experiment.…”

Desempenho produtivo do agrião d'água cultivado em solo sob telas de sombreamento

“…O tratamento a pleno sol promoveu menor capacidade de rebrota, o que é atribuído ao baixo desempenho produtivo do primeiro ciclo de cultivo, que, associado às altas temperaturas, resultou em impacto negativo no acúmulo das massas fresca e seca. De acordo com Going et al (2008), plantas de agrião d'água provenientes de fragmentos vegetativos com maior massa inicial apresentam maior incremento na massa final. Isso confirma os resultados obtidos no presente trabalho, em que os tratamentos com elevada produção de massa de matéria fresca apresentaram Tabela 2.…”

“…Going et al (2008) verificaram que o agrião d'água apresenta elevada plasticidade morfológica e aclimatação a condições de baixa luminosidade, em razão do aumento de área foliar, o que é importante para o uso de telas de sombreamento. Cabe destacar, no entanto, que nem todas as espécies apresentam resposta positiva ao sombreamento: em algumas plantas, há redução da produtividade com o sombreamento proporcionado pelas telas (Chagas et al, 2010;Costa et al, 2014).…”

“…A média dos tratamentos no primeiro e no segundo ciclo de cultivo foi de 44,9 e 42,2, respectivamente. Going et al (2008) não observaram diferenças na concentração de clorofila do agrião d'água Tabela 3. Largura e comprimento das folhas, bem como altura do dossel de plantas de agrião d'água (Rorippa nasturtiumaquaticum) produzido em solo sob diferentes telas de sombreamento e a pleno sol (1) .…”

“…Going et al (2008) relatam que o agrião d'água apresenta boa aclimatação fisiológica à ambiente com baixa intensidade luminosa.…”