Abstract
A higher photosynthesis and lower energetic cost are recognized as important characteristics for invasive species, but whether these traits are also important for the ability of alien mangrove species to become invasive has seldom been reported. A microcosm study was conducted to compare the photosynthetic characteristics, energetic cost indices and other growth traits between two alien species (Sonneratia apetala and S. caseolaris) and four native mangrove species over four seasons in a subtropical mangrove nature reserve in Shenzhen, South China. The aim of the study was to evaluate the invasive potential of Sonneratia based on these physiological responses. The annual average net photosynthetic rate (Pn), stomatal conductance (Gs) and total carbon assimilation per unit leaf area (Atotal) of the two alien Sonneratia species were significantly higher than the values of the native mangroves. In contrast, the opposite results were obtained for the leaf construction cost (CC) per unit dry mass (CCM) and CC per unit area (CCA) values. The higher Atotal and lower CC values resulted in a 72% higher photosynthetic energy-use efficiency (PEUE) for Sonneratia compared to native mangroves, leading to a higher relative growth rate (RGR) of the biomass and height of Sonneratia with the respective values being 51% and 119% higher than those of the native species. Higher photosynthetic indices for Sonneratia compared to native species were found in all seasons except winter, whereas lower CC values were found in all four seasons. The present findings reveal that alien Sonneratia species may adapt well and become invasive in subtropical mangrove wetlands in Shenzhen due to their higher photosynthetic characteristics coupled with lower costs in energy use, leading to a higher PEUE. The comparison of these physiological responses between S. apetala and S. caseolaris reveal that the former species is more invasive than the latter one, thus requiring more attention in future.
Highlights
Biological invasions are one of the most important threats affecting biodiversity, species composition, and the structure and function of ecosystems, and have caused significant global economic losses [1,2]
The annual averages of photosynthetic rate (Pn) and Gs of the alien Sonneratia were significantly higher than those of the native mangrove species according to the independent samples T-test (S1 Table), with increases of 32% and 34%, respectively (Fig 1A and 1B)
The higher Pn of the Sonneratia species resulted in a 32% higher Atotal compared to the native mangroves (S1 Table); the Atotal values of the alien and native species were 49.33 and 37.39 mol CO2 m-2, respectively
Summary
Biological invasions are one of the most important threats affecting biodiversity, species composition, and the structure and function of ecosystems, and have caused significant global economic losses [1,2]. Previous studies have shown that successful invasive species have other morphological and physiological traits that increase their light capture and utilization efficiency [5]. Invasive plants can be successful by maximizing photosynthesis and growth [6,7], and the success of many rapidly growing, often invasive species has been attributed to higher photosynthetic nitrogen-use efficiency (PNUE) compared to slower growing native species [9,10,11,12,13,14,15,16]. Song et al [21] compared the photosynthetic ability, energetic cost index and other growth traits between alien and native species and found that these physiological factors influencing invasions were important measures for better prediction and control of potentially invasive alien species
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