Abstract
Leaf Economics Spectrum (LES) trait variation underpins multiple agroecological processes and many prominent crop yield models. While there are numerous independent studies assessing trait variation in crops, to date there have been no comprehensive assessments of intraspecific trait variation (ITV) in LES traits for wheat and maize: the world's most widespread crops. Using trait databases and peer-reviewed literature, we compiled over 700 records of specific leaf area (SLA), maximum photosynthetic rates (Amax) and leaf nitrogen (N) concentrations, for wheat and maize. We evaluated intraspecific LES trait variation, and intraspecific trait-environment relationships. While wheat and maize occupy the upper 90th percentile of LES trait values observed across a global species pool, ITV ranged widely across the LES in wheat and maize. Fertilization treatments had strong impacts on leaf N, while plant developmental stage (here standardized as the number of days since planting) had strong impacts on Amax; days since planting, N fertilization and irrigation all influenced SLA. When controlling for these factors, intraspecific responses to temperature and precipitation explained 39.4 and 43.7 % of the variation in Amax and SLA, respectively, but only 5.4 % of the variation in leaf N. Despite a long history of domestication in these species, ITV in wheat and maize among and within cultivars remains large. Intraspecific trait variation is a critical consideration to refine regional to global models of agroecosystem structure, function and food security. Considerable opportunities and benefits exist for consolidating a crop trait database for a wider range of domesticated plant species.
Highlights
Functional traits refer to the structural, chemical, physiological or phenological properties of plants and plant parts, which mechanistically influence plant performance across environmental gradients (Violle et al 2007)
We focus on intraspecific trait variation (ITV) in Leaf Economics Spectrum (LES) traits in these crops, in order to address the following questions: (i) What is the extent of intraspecific variation in LES traits for the world’s most common crops? (ii) What climatic or management-related variables best account for ITV in crops? (iii) Have wheat and maize been shifted towards the extreme resource acquiring end of the LES?
Focusing on T. aestivum, T. durum and Z. mays is consistent with species-level taxonomy for the ‘Maize’ and ‘Wheat’ commodity groups recognized by the Food and Agricultural Organization of the United Nations (FAO). (Three additional wheat species, T. dicoccon, T. monococcum and T. spelta, were initially included in our search, but these species yielded prohibitively low returns (i.e. no data available in the TRY database, and less than three peer-reviewed publications with trait data for each species).) We initially sought to assess ITV at the within-cultivar level
Summary
Functional traits refer to the structural, chemical, physiological or phenological properties of plants and plant parts, which mechanistically influence plant performance (i.e. growth, survival and reproduction) across environmental gradients (Violle et al 2007). Westoby 1998; Díaz et al 2016) that individually or cumulatively contribute to ecologically important differences in functional biology among species. Of these groups of traits, leaf functional traits have arguably received the most attention by ecologists and plant ecophysiologists. The ‘Leaf Economics Spectrum’ (LES) has been hypothesized and tested, as a suite of covarying leaf traits that can be used to describe plant functional biology (Reich et al 1999; Wright et al 2004; Wright et al 2005a). LES traits factor heavily into applied research on multiple ecosystem functions including global net primary productivity (e.g. Van Bodegom et al 2012), plant decomposition (e.g. Cornwell et al 2008), disturbance recovery (e.g. SauraMas et al 2009), species invasions (e.g. Penuelas et al 2010) and species coexistence (e.g. Kraft et al 2008)
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