Light and nitrate effects on seed germination of Mediterranean plant species of several functional groups

Abstract

Post-fire conditions are characterized by enhanced light and the availability of nitrogenous compounds in the soil. It is not known, however, to what extent light or nitrogenous compounds control the germination response of species growing in burned areas and, in particular, whether functional groups of plants differ in their response. The germination response to light and nitrate was tested for 53 species representative of the flora of a Mediterranean recently burned area in Central-Eastern Spain. Differences in germination among species, with and without taking into account their phylogeny, were studied by classifying them according to their life-form (chamaephytes, hemicryptophytes), regeneration strategy (non-sprouters, sprouters) and geographical distribution range (Iberian Peninsula endemics, Mediterranean, widely distributed species). The overall germination mean was not affected by any of the two treatments. There were statistically significant interactions between species and the two treatments. That is, not all species were equally affected, and about 30% of the species were significantly affected by light (half of them positively and the other half negatively) and 25% by nitrate (most of them positively). Species response was related to functional groups. Light response (stimulation vs. non-stimulation) was associated to life-form, regeneration strategy and distribution range. Hemicryptophytes, sprouters and widely distributed species were positively affected by light. No evidence of such an association for nitrate was found. No statistically significant effects of light and nitrate on the mean germination of the various groups (life-form, regeneration strategy, distribution range) were found. Moreover, significant interactions emerged between light and nitrate for all three groups. In summary, the studied set of plants appears to be nondependent on factors that may change with fire, such as increased light and soil nitrate, for germination. Nonetheless, some species and groups will be affected by such changes. That means that fire will modify the relative balance of germination among species and functional groups. Due to the particular sensitivity of Iberian Peninsula endemics to light, a factor that significantly changes with fire, these species may be at risk under the current fire regime.

The assessment of influence of different nitrogen compounds and time on germination of Lupinus angustifolius seeds and chemical composition of final products

“…Concentrated, non-selective substances have a negative effect as their cause sprout deformation. The group of well-known germination stimulators used in research includes thiourea, urea, potassium nitrate as well as glutathione, glutamine and vitamins [15,19]. According to Pérez-Fernández et al [14], the germination reaction of plants to the medium composition may vary; however, the quantity and form of nitrogen in the medium have the greatest influence on the process, which is confirmed by this research.…”

“…According to Pérez-Fernández et al [14], the germination reaction of plants to the medium composition may vary; however, the quantity and form of nitrogen in the medium have the greatest influence on the process, which is confirmed by this research. Out of 52 plants examined by Luna and Moreno [15], potassium nitrate had a (positive or negative) influence (in the amount of 20 mM) on only approx. 25% of species.…”

“…It has been shown that salts added during the germination process at appropriate small concentrations (fractions or a few %) may have a stimulatory effect on the seeds, while these compounds can be toxic in large doses [10][11][12][13][14][15][16]. It is also possible to enrich sprouts with minerals (e.g.…”

Effects of nutrient addition and soil drainage on germination of N-fixing and non-N-fixing tropical dry forest tree species

“…Signal effects are instances when nutrient availability acts as a cue for germination. These can either be stimulatory, as proposed for both nitrate (Luna and Moreno 2009) and phosphate (Bell et al 1993), whose availability increases in the soil after fires and may signal favourable germination conditions, or inhibitory cues, as observed for ammonium and phosphate in clover broomrape seeds (Yoneyama et al 2001). By far, reductions in germination with nutrient addition have largely been attributed to toxicity, especially with respect to added N in the form of ammonia or urea (Bremner 1995), which itself dissociates to release ammonium.…”

“…Therefore, assessing the effects of nutrient deposition on the early post-reproductive stages of plants, such as germination, is important in quantifying the mid-to long-term impacts of N and P deposition on ecosystems (Ackerly and Bazzaz 1995;Callahan et al 2008). Although water availability (Khurana and Singh 2004;Renzhong and Qiong 2004;Ronnenberg et al 2008), temperature (Ronnenberg et al 2008;Milbau et al 2009), soil properties (Roem et al 2002) and the intensity, as well as quality of available light (Metcalfe 1996;Broncano et al 1998;Holl et al 2000;Ceccon et al 2003;Luna and Moreno 2009), are all well recognised as important determinants of germination success, the role of nutrient availability remains poorly quantified. As a considerable fraction of a seed's mass is made up of stored carbohydrate and nutrient reserves (Fenner and Thompson 2005), it can be argued that the availability of nutrients in the germination media or environment may have only a minimal effect, if any on germination success (e.g.…”