Effects of light and temperature on seed germination of cacti of Brazilian ecosystems
MARCOS VINICIUS MEIADO,*† MARIANA ROJAS-ARÉCHIGA,‡ JOSÉ ALVES de SIQUEIRA-FILHO§ and
INARA ROBERTA LEAL¶ *Departament of Bioscience, Federal University of Sergipe, Itabaiana, Sergipe, †Postgraduate Program in Plant Biology, ¶Department of Botany, Federal University of Pernambuco, Recife, §Reference Centre for the Restoration of Degraded Areas of
Caatinga, Federal University of São Francisco Valley, Petrolina, Pernambuco, Brazil; and ‡Department of Biodiversity, Ecology
Institute, National Autonomous University of Mexico, Ciudad de Mexico, Mexico
Environmental factors are used by plants as spatio-temporal indicators of favorable conditions for seed germination. Thus, the objective of this study was to determine the effect of light and temperature on seed germination of 30 taxa of Cactaceae occurring in northeastern Brazil and to evaluate whether fluctuations in temperature are capable of altering light sensitivity. The seeds were tested for germination under two light conditions (12 h photoperiod and continuous darkness) and 10 temperature treatments: eight constant temperatures (10, 15, 20, 25, 30, 35, 40 and 45°C) and two alternating temperatures (30/20°C and 35/25°C). The species studied showed two photoblastic responses. All cacti from the Cactoideae subfamily (22 taxa) were classified as positive photoblastic (i.e., no germination in darkness), regardless of the temperature treatment used. Likewise, temperature fluctuation did not alter the seed sensitivity to light. On the other hand, the species of the Opuntioideae (five taxa) and Pereskioideae (three taxa) subfamilies are indifferent to light (i.e., germinated both in the presence and absence of light). The cacti from the areas of Caatinga and Cerrado showed an optimal germination temperature of 30°C, while the species from Atlantic Forest and Restinga areas showed an optimal germination temperature of 25°C.
Keywords: Caatinga, Cactaceae, germinability, photoblastism, semi-arid.
Received 16 August 2014; revision received 30 October 2014; accepted 10 December 2014
Establishment success of plant species is often related to the time required for seed germination, which may be affected by several environmental factors (Vázquez-Yanes & Orozco-Segovia 1996). Seeds present in the soil respond to specific combinations of light, humidity, and favorable temperatures for seed germination and seedling establishment, maximizing their reproductive success (Baskin &
Baskin 2014). Thus, environmental factors such as light and temperature are simultaneously used by plants as indicators of favorable site and timing for seedling establishment, since after germination, the seed looses its tolerance to desiccation and needs to remain constantly hydrated, under favorable conditions for its development (Castro et al. 2004).
For several years researchers have been trying to understand germinative response patterns of seeds exposed to different intensities and qualities of light. Initially, it was believed that light sensitivity was related only to seed size, since large seeds with many resources would be able to germinate in darkness, simulating the low light intensity observed in deeper soil layers. On the other hand, small seeds with only a few resources stored in their tissue would need to germinate in the presence of light, in more superficial soil layers, establishing themselves and producing leaves rapidly to assume their autotrophic function (Milberg et al. 2000; Baskin & Baskin 2014). Recently, several studies have tried to relate light sensitivity to other plant attributes, such as plant growth-form
Correspondence: Marcos Vinicius Meiado
Plant Species Biology (2015) ••, ••–•• doi: 10.1111/1442-1984.12087 bs_bs_banner © 2015 The Society for the Study of Species Biology (Ortega-Baes et al. 2010), plant height (Flores et al. 2011), perenniality (De Villiers et al. 2002), seed size (Milberg et al. 2000; Pearson et al. 2003; Rojas-Aréchiga et al. 2013), and phylogeny (Moles et al. 2005; Wang et al. 2009;
Rojas-Aréchiga et al. 2013). However, as these studies are still in development, the photoblastic response patterns of many plant families are still undetermined.
Some environmental factors such as extreme and/or alternating temperatures may replace the light requirement for seed germination of many species that occur in arid and semi-arid environments, since extreme temperatures and temperature fluctuations interfere with the active production of phytochrome and may induce seed germination in darkness (Pons 2000; Probert 2000). Alterations in the patterns of light response associated with other environmental factors have been determined for several families throughout the years, such as the plants of the Cactaceae family, where the effect of light on seed germination is relatively well known for native species of
North America (Flores et al. 2011). According to RojasAréchiga et al. (1997), the light requirement for seed germination of cacti may be related to the cactus’ growth form, due to the maternal effects induced by temperature during seed production. Globose cacti are positive photoblastic and columnar cacti may be positive or neutral photoblastic (Rojas-Aréchiga et al. 1997). Several studies with globose cacti (Benítez-Rodríguez et al. 2004;
Flores et al. 2006; Rebouças & Santos 2007; Gurvich et al. 2008; Rojas-Aréchiga et al. 2008, 2013), as well as with columnar cacti (Rojas-Aréchiga et al. 2001; De la Barrera &
Nobel 2003; Ortega-Baes & Rojas-Aréchiga 2007; Meiado et al. 2008, 2010), corroborate the germination behavior pattern proposed by Rojas-Aréchiga et al. (1997).
However, some works have demonstrated that columnar cacti showed two types of responses to light and that globose cacti may also germinate when submitted to continuous darkness (Flores-Martínez et al. 2002; JiménezAguilar & Flores 2010), though the methodology used to determine the photoblastic response of these globose cacti is not clear. This fact could be related to the geographical distribution of the species or their phylogenetic origin (Flores et al. 2011; Rojas-Aréchiga et al. 2013).