Update on the Role of Plants in the Effects of Global Change The Role of Plants in the Effects of Global Change on Nutrient Availability and Stoichiometry in the Plant-Soil System1[W]

The impact on nitrogen (N) and phosphorus (P) cycles of human activity is a growing concern and has several causes and consequences (MacDonald et al., 2011; Peñuelas et al., 2012; Sardans et al., 2012b). Carbon (C) inputs by human CO2 emissions and N inputs from diverse human-driven sources are continuously increasing (Peters et al., 2011; Peñuelas et al., 2012). On the other hand, anthropogenic biospheric inputs of P are increasing much less than emissions of N and P (Peñuelas et al., 2012). These changes impact all ecosystems, including cropland (MacDonald et al., 2011), and seem to lead to shifts in C-N-P ratios and balances (Mackenzie et al., 2002; Peñuelas et al., 2012), with significant impacts on the structures and functions of ecosystems through effects on growth rates and on the competitive abilities of different species (Sterner and Elser, 2002; Peñuelas et al., 2012). Furthermore, increased warming, drought, and concentrations of atmospheric CO2 also change the N and P contents and stoichiometry of plants (Reich et al., 2006; Funk and Vitousek, 2007; Elser et al., 2010; RivasUbach et al., 2012) and, therefore, can indirectly impact soil processes and nutrient availability and stoichiometry. These increases also influence ecosystemic structures and functions and the capacity of Earth to balance its levels of CO2, given the importance of nutrients in the efficiency of plants to take up CO2 (Vicca et al., 2012). Invasion by plant species, another driver of global change, is also strongly related to the availability and stoichiometry of soil nutrients in most cases (Davis et al., 2000; Chun et al., 2007; Dassonville et al., 2007, 2008; González et al., 2010) and exerts an additional effect on the availability and stoichiometry of N and P in ecosystems and frequently interacts significantly with other drivers of global change, such as N deposition (Huebner et al., 2009; He et al., 2011). Plants respond to drivers of global change by several metabolic and physiological shifts that frequently alter, among several other functions, a plant’s capacity to take up and reallocate nutrients and, consequently, the elemental composition and stoichiometry of plants. Plants are thus the main factor underlying the links between global change and the status of N and P in ecosystems. This role of plants is critical to Earth’s N and P biogeochemical cycles and to the changes occurring in these cycles. We urgently need to review our knowledge of the role that plant responses to global change plays in changing and/or buffering the availability and stoichiometry of nutrients in ecosystems. In this Update, we discuss (1) the effects of plants on the availability and stoichiometry of nutrients in ecosystems through their responses to drivers of global change at the individual, population, and community levels, (2) the consequences and feedback mechanisms occurring from changes in the availability and stoichiometry of nutrients in terrestrial ecosystems, and (3) the key aspects we need to investigate to reach a global understanding of the links among drivers of global change, plant responses, and the availability and stoichiometry of nutrients.