Abstract
Hypotheses on the existence of a universal “Root Economics Spectrum” (RES) have received arguably the least attention of all trait spectra, despite the key role root trait variation plays in resource acquisition potential. There is growing interest in quantifying intraspecific trait variation (ITV) in plants, but there are few studies evaluating (i) the existence of an intraspecific RES within a plant species, or (ii) how a RES may be coordinated with other trait spectra within species, such as a leaf economics spectrum (LES). Using Coffea arabica (Rubiaceae) as a model species, we measured seven morphological and chemical traits of intact lateral roots, which were paired with information on four key LES traits. Field collections were completed across four nested levels of biological organization. The intraspecific trait coefficient of variation (cv) ranged from 25 to 87% with root diameter and specific root tip density showing the lowest and highest cv, respectively. Between 27 and 68% of root ITV was explained by site identity alone for five of the seven traits measured. A single principal component explained 56.2% of root trait covariation, with plants falling along a RES from resource acquiring to conserving traits. Multiple factor analysis revealed significant orthogonal relationships between root and leaf spectra. RES traits were strongly orthogonal with respect to LES traits, suggesting these traits vary independently from one another in response to environmental cues. This study provides among the first evidence that plants from the same species differentiate from one another along an intraspecific RES. We find that in one of the world’s most widely cultivated crops, an intraspecific RES is orthogonal to an intraspecific LES, indicating that above and belowground responses of plants to managed (or natural) environmental gradients are likely to occur independently from one another.
Highlights
Elucidating the key dimensions of functional trait variation among plant species has been critical for understanding, predicting, and managing terrestrial ecological responses to environmental or land-use change
Observations that an intraspecific Root Economics Spectrum” (RES) in C. arabica is orthogonal to an intraspecific leaf economics spectrum (LES), contributes to our understanding of the causes of whole plant intraspecific trait variation (ITV) and will advance our predictive ability of C. arabica productive vigor and response to environmental change
Recent analyses point to a lack of root functional trait data as a major limitation when predicting the effects of climate change on yield or other agroecosystem functions (Rosenzweig et al, 2014)
Summary
Elucidating the key dimensions of functional trait variation among plant species has been critical for understanding, predicting, and managing terrestrial ecological responses to environmental or land-use change. Supporting the application of functional trait-based approaches to terrestrial ecology is arguably one unifying framework: evaluating how traits covary or trade-off to form distinct trait “spectra” (Grime, 1979; Lambers and Poorter, 1992; Reich et al, 1997; Westoby et al, 2002; Reich, 2014; Diaz et al, 2016). Hypotheses on the existence of a universal “Root Economics Spectrum” (RES) has received arguably the least attention (Reich, 2014), despite the key role root trait variation plays in resource acquisition potential (Lambers et al, 2008; Cahill et al, 2010; Bardgett et al, 2014), and other ecosystem functions such as soil stability (e.g., Rillig et al, 2015). Recent studies have found evidence for a RES in herbaceous species, but analyses suggest woody species show drastically different patterns (Larson and Funk, 2016; Roumet et al, 2016; Weemstra et al, 2016)
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