Effects of plant species traits on ecosystem processes: Experiments in the Patagonian steppe

Centro de Investigaciones del Mar y la Atmósfera, Departamento de Ciencias de la Atmósfera y los Océanos, CONICET/FCEN-UBA/UMI, Pabellón II Piso 2, Ciudad Universitaria, C1428EGA Buenos Aires, Argentina.
Ecology (Impact Factor: 4.66). 02/2012; 93(2):227-34. DOI: 10.2307/23143902
Source: PubMed


Several experiments have shown that aboveground net primary productivity increases with plant species richness. The main mechanism proposed to explain this relationship is niche complementarity, which is determined by differences in plant traits that affect resource use. We combined field and laboratory experiments using the most abundant species of the Patagonian steppe to identify which are the traits that determine niche complementarity in this ecosystem. We estimated traits that affect carbon, water, microclimate, and nitrogen dynamics. The most important traits distinguishing among species, from the standpoint of their effects on ecosystem functioning, were potential soil nitrification, rooting depth, and soil thermal amplitude. Additionally, we explored the relationship between trait diversity and aboveground net primary production (ANPP) using a manipulative field experiment. ANPP and the fraction of ANPP accounted for by trait diversity increased with number of traits. The effect of trait diversity decreased as the number of traits increased. Here, the use of traits gave us a mechanistic understanding of niche complementarity in the Patagonian steppe.

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Available from: Pedro Flombaum, Jan 03, 2014
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    • "Using the simulation model, we estimated: (1) the biodiversity effect as the difference in modeled and expected anPP, and (2) the sampling effect using loreau and hector's method (2001). We focused on arid ecosystems because they are largely influenced by facilitation and resource partitioning (sala et al. 1989; Bertness and callaway 1994; Bruno et al. 2003; craine et al. 2003; Flombaum and sala 2012) and because their low diversity provides ideal models to study biodiversity and ecosystem functioning relationships (Flombaum and sala 2008). We parameterized our model to represent major ecological variables in an arid ecosystem, the Patagonian steppe. "
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    ABSTRACT: Resource partitioning, facilitation, and sampling effect are the three mechanisms behind the biodiversity effect, which is depicted usually as the effect of plant-species richness on aboveground net primary production. These mechanisms operate simultaneously but their relative importance and interactions are difficult to unravel experimentally. Thus, niche differentiation and facilitation have been lumped together and separated from the sampling effect. Here, we propose three hypotheses about interactions among the three mechanisms and test them using a simulation model. The model simulated water movement through soil and vegetation, and net primary production mimicking the Patagonian steppe. Using the model, we created grass and shrub monocultures and mixtures, controlled root overlap and grass water-use efficiency (WUE) to simulate gradients of biodiversity, resource partitioning and facilitation. The presence of shrubs facilitated grass growth by increasing its WUE and in turn increased the sampling effect, whereas root overlap (resource partitioning) had, on average, no effect on sampling effect. Interestingly, resource partitioning and facilitation interacted so the effect of facilitation on sampling effect decreased as resource partitioning increased. Sampling effect was enhanced by the difference between the two functional groups in their efficiency in using resources. Morphological and physiological differences make one group outperform the other; once these differences were established further differences did not enhance the sampling effect. In addition, grass WUE and root overlap positively influence the biodiversity effect but showed no interactions.
    Full-text · Article · Sep 2013 · Oecologia
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    • "This access to organic pools of nitrogen has been argued to increase plant access to nitrogen, especially in nitrogen limited habitats E.g. [1,2,6-8]. Additionally, ecologists have argued that plant access to a variety of different forms of nitrogen may also influence population and community processes by allowing increased dimensions of niche partitioning mediated through differences in nitrogen preference [7,9-13]. However, while ecologists have obtained large amounts of data investigating whether plants can or cannot capture specific amino acids, there is surprisingly little data that links this uptake to plant growth and performance. "
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    ABSTRACT: Ecologists recognize that plants capture nitrogen in many chemical forms that include amino acids. Access to multiple nitrogen types in plant communities has been argued to enhance plant performance, access to nitrogen and alter ecological interactions in ways that may promote species coexistence. However, data supporting these arguments have been limited. While it is known that plants uptake amino acids from soil, long term studies that link amino acid uptake to measures of plant performance and potential reproductive effort are not typically performed. Here, a series of experiments that link uptake of nitrate, glutamine or asparagine with lifetime reproductive effort in Arabidopsis thaliana are reported. Nitrogen was offered either singly or in mixture and at a variety of combinations. Traits related to reproductive output were measured, as was the preference for each type of nitrogen. When plants were supplied with a single nitrogen type at concentrations from 0.1-0.9 mM, the ranking of nitrogen types was nitrate > glutamine > asparagine in terms of the relative performance of plants. When plants were supplied with two types of nitrogen in mixture at ratios between 0.1:0.9-0.9:0.1 mM, again plants performed best when nitrate was present, and poorly when amino acids were mixed. Additionally, stable isotopes revealed that plants preferentially captured nitrogen types matching the hierarchy of nitrate > glutamine > asparagine. Comparing between the two experiments revealed that mixed nitrogen nutrition was a net cost to the plants. Plant performance on mixed nitrogen was less than half the performance on equal amounts of any single nitrogen type. We asked: why did A. thaliana capture amino acids when doing so resulted in a net cost? We argue that available data cannot yet answer this question, but hypothesize that access to lower quality forms of nitrogen may become important when plants compete.
    Full-text · Article · Jul 2013 · BMC Ecology
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    • "Given the correlation between response and effect traits, that is, the 'response–effect hypothesis' (Lavorel and Garnier, 2002), the complexity and (mutual) importance of such direct and indirect interactions among biodiversity, EF and the environment is challenging (Bradford et al., 2002; Lavorel et al., 2009; Zobel, 1997). A resulting niche complementarity is in fact the product of not only species interactions but also a direct consequence of combinations of traits (Flombaum and Sala, 2012). Hence, many of these phenomena are interwoven and are commonly merged together into 'services', like nutrient availability, soil structure, water regulation, biological pest control and resilience (Millennium Ecosystem Assessment, 2005). "

    Full-text · Dataset · Oct 2012
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