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ecosystem. Global warming induced by climate change increases risks of floods in Central and Western Europe (Alfieri et al., 2018). The biodiversity of flooding tolerant plants along river systems is very important in riparian ecosystems. The management of water resources and climate changes may have severe effects on species distributions and interactions. It also altere natural flow regimes and flooding patterns in the river system, reducing frequency, extent and duration of many European floodplains (Tonkin et al., 2018). The ecosystems of the Danube River Basin (Europe’s second largest river basin) are under pressure due to pollution from agriculture, industry and cities (
In the process of evolution, the leaves as plants organs are sensitive to environmental changes and may exhibit phenotypic plasticity in their physiology, morphology and development as response to abiotic and biotic stress, which has been revealed in many studies (Xu et al., 2009; Miljković et al., 2018; Miljković et al., 2019). The fluctuating asymmetry of bilaterally symmetrical organs, as one of the aspects of morphological variability, is used as an assessment indicator for developmental instability in natural suboptimal environmental conditions. Random deviation from phenotypic symmetry is an indicator of the development instability, depending on the type of stressor and the length of its effect (Hagen et al., 2008; Miljković et al., 2018; Miljković et al., 2019). The flooding dramatically reduced leaf size and shape (Zhuang et al., 2011; Rood et al., 2003) and also it impacted the developmental stability process in the seasonal or perennial flooding areas. In the last decade the geometric morphometric analysis were employed instead of traditional morphometric analyses in numerous studies (Klingenberg, 2016). The geometric morphometry as a type of quantitative morphometric analysis allows statistical and visual defining of differences in the analyzed leaf shapes in complex of environmental surroundings (Rohlf and Corti 2000; Bookstein et al., 2003).
Vojvodina is a province in northern Serbia and it is well known for numerous protected wetlands such as swamps and marshes (Basarin et al., 2014). This research focused on the area of Special Nature Reserve “Gornje Podunavlje” which represents complex of peculiar marshland, originating from former vast inundated parts of the Danube basin. It covers an alluvial plain area of 19.648 ha on the left bank of the upper Danube Basin in Vojvodina, from the 1367th to 1433rd km of its course. The research area is located in the middle part of the Danube basin, which extends from the Gate of Devin (Bratislava) to the Iron Gate (between Serbia and Romania). This reserve covers aquatic and semi aquatic vegetation, wet meadows and riparian forests, without significant exposure at 82 - 87 m a.s.l. Forest vegetation is primarily dependent on floodwater or groundwater impacts related to the Danube water level (Bobinac et al., 2010).
As a result of work on the embankment and drainage systems, dating back to 1890’s (Bobinac et al., 2010), the hydrological regime has changed considerably, considering the fact that a large quantity of water remained in a narrow area next to the riverbed and stagnated for a long time. This directed changes in the distribution and composition of riparian ecosystem, where fragmentation processes were dominated by ash, oak and elm forests, and willow and poplar forests started to dominate, while the situation was opposite on other side of embankment.
European black poplar (Populus nigra L.), an ecologically and economically significant species, is a key pioneer tree species colonizing alluvial sediments along large rivers in temperate climate zones of Europe, northern Africa and western Asia (Dickmann and Kuzovkina, 2008; DeWoody et al., 2015; Čortan and Tubić, 2017). The dynamics of P. nigra populations and the different phases of colonization are directly related to the dynamics of the rivers (details in Herpka 1986). In the last century, modifications of European river systems imposed significant threats to large riparian ecosystems. As a prominent early successional species on European floodplains, the absence of P. nigra populations indicates reduced geomorphological activity following river control (Hughes et al., 2000).
Considering the fact that the morphological traits of P. nigra have high phenotypic plasticity which allows adaptation and resistance to the fluctuating and prolonged floods (Čortan et al., 2019), the main aims of this exploratory study address the questions: i) Does flooding effect on leaf morphology? and ii) If it does, which of leaf morphological traits (centroid size, shape, developmental instability, specific leaf area or petiole length) could be considered an indicator of suboptimal environmental conditions for riparian tree Populus nigra L.
Material and methods
Materijali i metode
2.1. Study locations
For this research we have selected samples located on both sides of embankment (Fig. 1), in defended area (localities A1, B1, C1 and E1) and in the flooded area (localities A2, C2, D2 and E2). Ten adult trees (over 30 years old) from each locality were used for the analysis; in total 80 trees. Ten full developed and undamaged leaves were sampled from each tree in July 2016, from the south/south west side of the crown, at the height between 3-6 m (about 800 leaves were analysed).
The water level was measured and analysed at two hydrologic stations (Bezdan and Apatin) in the period of 2013 to 2016, covering all selected localities. The highest water level was recorded in 2013, and the lowest in 2015. The maximum water level in this period is recorded in May and June (Fig. 2).