CSAWAC 44 (11) 1429-1598 (2016) · Vol. 44 · No. 11 · November 2016 CLEAN Soil Air Water Renewables Sustainability Environmental Monitoring 11 | 2016 www.clean-journal.com 1591 Congyan Wang1,2 Research Article Jun Liu1 Hongguang Xiao1 Jiawei Zhou1 Differences in Leaf Functional Traits Between Rhus typhina and Native Species 1School of the Environment and Safety Engineering, Jiangsu University, Zhenjiang, P. R. China The differences in leaf functional traits between invasive and native species are 2State Key Laboratory of Soil and considered to be closely linked to the mechanisms underlying successful plant invasion Sustainable Agriculture, Institute of because co-occurring invasive and native species experience similar or even identical Soil Science, Chinese Academy of environmental selective pressures. This study aims to determine the differences in leaf Sciences, Nanjing, P. R. China functional traits and resource-use strategy between the invader Rhus typhina and the native species Sapindus mukorossi. Leaf chlorophyll and nitrogen concentrations, specific leaf area (SLA), and leaf moisture of R. typhina were significantly higher than those of S. mukorossi, but leaf length, leaf width, and single-leaf wet and dry weights of R. typhina were significantly lower than those of S. mukorossi. Plasticity indices of leaf shape index and SLA of R. typhina were obviously higher than those of S. mukorossi, while plasticity indices of single-leaf wet and dry weights, and leaf moisture of R. typhina were obviously lower than those of S. mukorossi. The higher leaf chlorophyll and nitrogen concentrations, SLA, and leaf moisture as well as the high range of phenotypic plasticity of leaf shape index and SLA for R. typhina may confer it a competitive advantage and thus play an important role in its successful invasion. Keywords: Environmental changes; Invasive species; Leaf functional traits; Phenotypic plasticity; Specific leaf area Received: February 22, 2016; revised: May 31, 2016; accepted: June 20, 2016 DOI: 10.1002/clen.201600144 1 Introduction Invasive plants have triggered serious threats to native ecosys- tems, changing the structure and function of the ecosystems in Leaves play an important role in plant development, growth, and which those invasions occur [11–13]. Numerous studies have survival [1, 2]. Leaves influence the acquisition of sunlight, which is revealed that certain plants successfully invade certain environ- perhaps one of the most important environmental factors that ments because leaf functional traits (such as higher SLA) of those influence plant growth [1, 2]. Thus, the response of leaf functional invaders can enable them to acquire more resources and grow at a traits to changes in environmental factors can improve the high growth rate than co-occurring native species [14–17]. The adaptability of plants in a wide variety of habitats and then expand differences in leaf functional traits between invasive and native their ecological niche because leaves are exposed to a multivariate species are believed to be closely linked to the mechanisms environment and are sensitive to environmental changes [3–7]. As underlying the success of plant invasions because co-occurring one of the most crucial leaf functional traits, specific leaf area (SLA) invasive and native species in the same ecosystem experience similar can indicate the resource-use strategy of plants [3, 8, 9]. SLA is or even identical environmental selective pressures [14, 18]. defined as the investment of sunlight capture surface per unit area This study aims to determine the differences in leaf functional of leaf [3, 8, 9]. Normally, high SLA indicates high resource traits of the controversial invader Rhus typhina and the native species acquisition and use efficiency with low investment in leaf Sapindus mukorossi. The two species can coexist in the same construction and protective tissues [3, 8, 9]. Leaf size, leaf thickness, ecosystem. Both are members of the Sapindales order. R. typhina is leaf shape index, single-leaf wet and dry weights, and leaf moisture a deciduous tree native to Canada and the United States and was are also important indices of leaf functional traits as they can introduced to China in 1959 as a common forestry species by the indicate the resource-use strategy of plants [3, 5–7, 10]. Hence, Botanical Garden of the Institute of Botany in the Chinese Academy determining the leaf functional traits of plants is an important part of Sciences [19, 20]. This species also has some ornamental value of enucleating the mechanism underlying their successful ecologi- because of its fruit clusters, which look like burning torches in late cal strategy. summer and early autumn, and because of its brilliant red foliage in mid-autumn [19]. Meanwhile, the species can demonstrate vigorous growth even in poor soils [19, 21]. For this reason, it is frequently used for rehabilitation of degraded lands in most mountain areas of Correspondence: Dr. Congyan Wang, School of the Environment and north China [19, 21]. However, the species possesses somewhat Safety Engineering, Jiangsu University, No. 301, Xuefu Road, Zhenjiang invasive characteristics such as vigorous growth and rapid 212013, P. R. ChinaE-mail: [email protected] reproduction [19, 21]. To date, the species has spread into almost Abbreviations: SLA, specific leaf are. all habitats from urban to montane, including roadsides, farmlands, © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.clean-journal.com Clean – Soil, Air, Water 2016, 44 (11), 1591–1597 1592 C. Wang et al. and protected areas [19]. Thus, R. typhina has been identified as a SLAwas computed using the ratio of theleaf areato thecorresponding destructive invader by many botanists [19, 22]. leaf dry weight (cm2 gÀ1), following previous studies [5–8, 28]. In this study, leaf functional traits (i.e., leaf size [indicated by Leaf moisture was calculated by subtracting the leaf dry weight leaf length and leaf width], leaf shape index, leaf chlorophyll and from the leaf wet weight; the difference was then divided by the leaf nitrogen concentrations, SLA, single-leaf wet and dry weights, wet weight [5, 6]. Single-leaf wet weight was determined using an leaf moisture, and leaf thickness) of R. typhina and S. mukorossi electronic balance. Single-leaf dry weight was obtained by initially were assessed to gain insight into their ecological strategies. subjecting the samples to oven-drying at 60°C for 24 h to achieve The results of this study can provide a platform for better a constant weight; the final single-leaf dry weight was then understanding the mechanisms underlying the successful inva- determined using an electronic balance with an accuracy of sion of R. typhina, and may establish an important theoretical 0.001 g [5, 6]. foundation and carry practical significance for effective invasion Leaf thickness was calculated by overlaying five leaves and prevention and control. This study presents the following measuring their combined thickness using a Vernier caliper with an hypotheses. First, the SLA of R. typhina maybehigherthanthat accuracy of 0.01 mm [5–7]. of S. mukorossi because invasive species invest more biomass in Plasticity indices (the index ranged from zero (no plasticity) to one leaf growth rather than leaf structures per unit area to achieve a [maximum plasticity]) of plant characteristics were calculated with higher growth rate than native species [14–17]. In particular, a the following equation [29]: higher SLA is often correlated with a growth advantage for invasive species over native species [23, 24]. Second, the plasticity Maximum À minimum Plasticity index ¼ mean mean ð1Þ index of R. typhina may be higher than that of S. mukorossi because Maximummean higher phenotypic plasticity can allow plants to enhance their adaptability via the higher phenotypic plasticity in response to the changes in environmental factors [14, 15]. More importantly, 2.3 Statistical analysis the phenotypic plasticity of invasive species is known to be positively correlated with their invasiveness [14, 25]. Third, leaf One-way ANOVA was performed to evaluate the differences in leaf thickness, and single-leaf wet and dry weights are likely to be functional traits of the two species. Correlation analysis was negatively correlated with SLA; by contrast, leaf size, leaf performed using Pearson product-moment correlation coefficient to chlorophyll and nitrogen concentrations, and leaf moisture are determine the patterns among various dependent variables. All likely to be positively correlated with SLA because leaves with low statistical analyses were performed using SPSS Statistics (version SLAslikelyinvestgreatbiomassinleafstructures,butleaveswith 22.0; IBM, Armonk, NY). Then, a Mantel test [30] was conducted using high SLAs require low structural investment [3, 9, 10]. TFPGA (version 1.3) to quantify the relationships given in the correlation matrix between leaf functional traits of R. typhina and those of S. mukorossi. Statistical significance was set at p-values equal 2 Materials and methods to or <0.05. 2.1 Experimental design In mid-August 2015, plant samples were collected in Jinan, P. R. 3 Results China (36.63°N, 117.03°E) which has a warm temperate climate. Leaf chlorophyll and nitrogen concentrations, SLA, and leaf The annual mean temperature of the area is approximately moisture of R. typhina were significantly higher than those of 13.8°C, and the monthly mean temperature reaches a maximum S. mukorossi (Tabs. 1 and 2, p < 0.01). By contrast, leaf length, leaf of 27.2°C in July and decreases to a minimum of À3.2°C in width, and single-leaf wet and dry weights of R. typhina were January. Annual precipitation is approximately 614 mm and the significantly lower than those of S. mukorossi (Tabs. 1 and 2, monthly mean precipitation reaches a maximum of 196 mm in p < 0.0001). No significant difference was observed in leaf shape July and decreases to a minimum of 7 mm in January. Fifteen index and leaf thickness between R. typhina and S. mukorossi (Tabs. 1 plant individuals for each species were collected randomly.