Effects of simulated acid rain on germination, seedling growth and oxidative metabolism of recalcitrant‐seeded Trichilia dregeana grown in its natural seed bank

Abstract

Increased air pollution in a number of developing African countries, together with the reports of vegetation damage typically associated with acid precipitation in commercial forests in South Africa, has raised concerns over the potential impacts of acid rain on natural vegetation in these countries. Recalcitrant (i.e. desiccation sensitive) seeds of many indigenous African species, e.g. must germinate shortly after shedding and hence, may not be able to avoid exposure to acid rain in polluted areas. This study investigated the effects of simulated acid rain (rainwater with pH adjusted to pH 3.0 and 4.5 with 70:30, H2 SO4 :HNO3 ) on germination, seedling growth and oxidative metabolism in a recalcitrant-seeded African tree species Trichilia dregeana Sond., growing in its natural seed bank. The results suggest that acid rain did not compromise T. dregeana seed germination and seedling establishment significantly, relative to the control (non-acidified rainwater). However, pH 3.0 treated seedlings exhibited signs of stress typically associated with acid rain: leaf tip necrosis, abnormal bilobed leaf tips, leaf necrotic spots and chlorosis, reduced leaf chlorophyll concentration, increased stomatal density and indications of oxidative stress. This may explain why total and root biomass of pH 3.0 treated seedlings were significantly lower than the control. Acid rain also induced changes in the species composition and relative abundance of the different life forms emerging from T. dregeana's natural seed bank and in this way could indirectly impact on T. dregeana seedling establishment success.

A new approach towards the so-called recalcitrant seeds

“…Among the groups that persist in the area, the panel that was demonstrated up to two decades ago did not change much afterward (Figure 1). The majority of the studies are basically focused on desiccation tolerance Corsato et al, 2012;Chapell et al, 2015;Amoedo and Ferraz, 2017;Gasparin et al, 2017;Subbiah et al, 2017;Chandra and Keshavkant, 2018;Plitta-Michalak et al, 2018), identification of storage behavior (Comin et al, 2014;Joshi et al, 2015;Vicente et al, 2016; 2017; Plitta-Michalak et al, 2018), analysis of deterioration and evaluation of techniques to extend the storage period (Barbedo and Cicero, 2000;Andréo et al, 2006;Bonjovani and Barbedo, 2008;Ballesteros et al, 2014;Lan et al, 2014;Parkhey et al, 2014;Garcia et al, 2015;Ming-Yue et al, 2015;Umarani et al, 2015;Araldi et al, 2016;Hossel et al, 2016;Félix et al, 2017), and rare studying other aspects such as seed maturation (Avila et al, 2009;Lamarca et al, 2013b;Mata et al, 2013;Schultz et al, 2014;Araldi and Coelho, 2015;Shibata and Coelho, 2016;Souza et al, 2018a, b), whose importance will be discussed later, and ecological (Ramlall et al, 2015;Vaz et al, 2016;Porto et al, 2018) or germinative aspects (Moothoo-Padayachie et al, 2016). An analysis, albeit superficial, of studies developed in Brazil and in the world shows small differences.…”

“…The first important characteristic of seeds of these species of Eugenia, apparently rare in nature, is the ability to germinate and produce seedlings even when more than half of their reserve tissue is removed (Silva et al, 2003;Delgado et al, 2010;Prataviera et al, 2015). This ability may be related to a co-evolution with predatory insects since seeds with more than half of the cotyledons consumed by insect larvae are frequently found (Côrtes et al, 2009;Silva and Pinheiro, 2009;Teixeira and Barbedo, 2012;Gaggeti et al, 2016).…”

Quality of Roof-Harvested Rainwater as a Function of Environmental and Air Pollution Factors in a Coastal Mediterranean City (Haifa, Israel)

“…SO 2 affected both alkalinity and hardness. A reaction between SO 2 , O 3 , and water produces H + , which decreases the alkalinity [19]. However, Taffere et al [6], described a positive correlation between Mg 2+ and SO 4 2− (created by SO 2 and water), resulting in an increased roof runoff hardness.…”

“…These compounds undergo oxidation in the atmosphere in combination with ozone, forming strong acids (sulphuric and nitric acids), which, when dissolved in rainwater, decrease its pH [19]. In addition, the station provided daily averages of wind direction (WDD) and speed (WDS), and daily average concentrations of particulate matter (PM).…”

The Impact of Criteria Air Pollutants on Soil and Water: A Review

“…Acid rain is an ongoing issue which involves a great number of effects on the environment. Reactions between nitrogen oxide, sulphur oxide and some amount of ozone are the reason for causing acid rain [23]. Fig.…”