Behavior and Impact of Zirconium in the Soil–Plant System: Plant Uptake and Phytotoxicity

Because of the large number of sites they pollute, toxic metals that contaminate terrestrial ecosystems are increasingly of environmental and sanitary concern (Uzu et al. 2010, 2011; Shahid et al. 2011a, b, 2012a). Among such metals is zirconium (Zr), which has the atomic number 40 and is a transition metal that resembles titanium in physical and chemical properties (Zaccone et al. 2008). Zr is widely used in many chemical industry processes and in nuclear reactors (Sandoval et al. 2011; Kamal et al. 2011), owing to its useful properties like hardness, corrosion-resistance and permeable to neutrons (Mushtaq 2012). Hence, the recent increased use of Zr by industry, and the occurrence of the Chernobyl and Fukashima catastrophe have enhanced environmental levels in soil and waters (Yirchenko and Agapkina 1993; Mosulishvili et al. 1994 ; Kruglov et al. 1996)

Sunlight and Soil-Litter Mixing: Drivers of Litter Decomposition in Drylands

Decomposition of leaf litter is a key component of biogeochemical cycles but the mechanisms driving it in arid and semiarid ecosystems (drylands) remain unresolved. Here, we review recent findings that demonstrate dual roles of solar radiation (ultraviolet and photosynthetically active radiation) and soil–litter mixing as drivers of decomposition in drylands. We focus on the known and potential mechanisms by which these factors influence leaf litter decomposition, explore how the importance of these two drivers may shift over time, and propose possible avenues by which these factors may interact. Special attention is given to UV in sunlight, as this radiation is known to have multiple roles in influencing decomposition and has received considerable recent research attention. We also identify important uncertainties and challenges and offer a generalized conceptual model to guide future research aimed at enhancing our mechanistic understanding and quantitative modeling of the processes by which soil deposition and solar radiation together influence leaf litter decomposition rates in globally extensive dryland ecosystems

Ecohydrological implications of aeolian processes in drylands

Aeolian processes, the erosion transport and deposition of soil particles by wind, are dominant geomorphological processes in many drylands, and important feedbacks are known to exist among aeolian, hydrological, and vegetation dynamics (Field et al. 2010; Ravi et al. 2011). The wind, a natural geomorphic agent, has been active as an erosive agent throughout geological times in many parts of the world. Outstanding examples are the extensive loess deposits along the Huanghe River (Yellow River) in China and along the Missouri and Mississippi rivers in the United States. Climatic changes and anthropogenic activities can greatly accelerate soil erosion by wind with implications for soil and vegetation degradation (Kok et al. 2012; Webb and Pierre 2018; Nauman et al. 2018). For instance, in the 1930s, a decreased precipitation coupled with intensive agricultural activities caused a dramatic increase in wind erosion in the Great Plains of the United States, resulting in the so-called Dust Bowl. Wind erosion can be activated also by land-use change. An example is provided by the Mu Us region in North China with an annual precipitation of 400 mm, which was once a grassland partially covered with forest, yet now is one of the major sources of dust in the world as a result of overgrazing and agricultural practices (Wang et al. 2005; Miao et al. 2016)