Archives mensuelles : mars 2018

Crop mixtures: does niche complementarity hold for belowground resources? An experimental test using rice genotypic pairs

Montazeaud G., Violle C., Fréville H., Luquet D., Ahmadi N., Courtois B., Bouhaba I., Fort F.

Agathe Roucou, Cyrille Violle, Florian Fort, Pierre Roumet, Martin Ecarnot, Denis Vile

1. Human selection, changes in environmental conditions and management practices drove the phenotypic trajectory of crops during domestication. The characterization of the crop domestication syndrome lies mostly on reproductive characters. However, biophysical and ecophysiological constraints during vegetative growth are also at play and can strongly impact crop phenotypes. It has been argued that a broadened examination of crop phenotypes through a functional trait‐based lens should improve our understanding of the domestication syndrome.
2. We used a collection of 39 genotypes representative of key steps during tetraploid wheat domestication and grew them in a common garden experiment. We quantified the vegetative phenotype of each genotype through the measurements of 13 functional traits related to root, leaf and whole‐plant dimensions.
3. In modern cultivars, compared to ancestral forms, leaf longevity was shorter, while net photosynthetic rate, leaf production rate and nitrogen content were higher. Modern cultivars had a shallower root system and exhibited a larger proportion of fine roots, preferring to invest biomass above‐rather than below‐ground. We found ancestral forms to be integrated phenotypes characterized by coordination between above‐ and below‐ground functioning. Conversely, in modern forms, human selection appeared to have broken this coordination and to have generated a new type of network of trait covariations.
4. Synthesis and applications. The examination of leaf, root and whole‐plant traits of wheat accessions indicated a strong shift in plant functional strategies over the course of domestication. Elite genotypes tended to better optimize resource‐use acquisition strategies than ancestral ones. The characterization of the crop phenotype based on vegetative traits thus suggests a much more complete domestication syndrome. Our findings highlight the benefits of using a functional trait‐based characterization of crop phenotypes to document the extent of domestication syndrome and to further advance the agroecological management of cereals.
   

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Grégoire T. Freschet, Oscar J. Valverde‐Barrantes, Caroline M. Tucker, Joseph M. Craine, M. Luke McCormack, Cyrille Violle, Florian Fort, Christopher B. Blackwood, Katherine R. Urban‐Mead, Colleen M. Iversen, Anne Bonis, Louise H. Comas, Johannes H. C. Cornelissen, Ming Dong, Dali Guo, Sarah E. Hobbie, Robert J. Holdaway, Steven W. Kembel, Naoki Makita, Vladimir G. Onipchenko, Catherine Picon‐Cochard, Peter B. Reich, Enrique G. de la Riva, Stuart W. Smith, Nadejda A. Soudzilovskaia, Mark G. Tjoelker, David A. Wardle, Catherine Roumet

1. Ecosystem functioning relies heavily on below‐ground processes, which are largely regulated by plant fine‐roots and their functional traits. However, our knowledge of fine‐root trait distribution relies to date on local‐ and regional‐scale studies with limited numbers of species, growth forms and environmental variation.
2. We compiled a world‐wide fine‐root trait dataset, featuring 1115 species from contrasting climatic areas, phylogeny and growth forms to test a series of hypotheses pertaining to the influence of plant functional types, soil and climate variables, and the degree of manipulation of plant growing conditions on species fine‐root trait variation. Most particularly, we tested the competing hypotheses that fine‐root traits typical of faster return on investment would be most strongly associated with conditions of limiting versus favourable soil resource availability. We accounted for both data source and species phylogenetic relatedness.
3. We demonstrate that: (i) Climate conditions promoting soil fertility relate negatively to fine‐root traits favouring fast soil resource acquisition, with a particularly strong positive effect of temperature on fine‐root diameter and negative effect on specific root length (SRL), and a negative effect of rainfall on root nitrogen concentration; (ii) Soil bulk density strongly influences species fine‐root morphology, by favouring thicker, denser fine‐roots; (iii) Fine‐roots from herbaceous species are on average finer and have higher SRL than those of woody species, and N₂‐fixing capacity positively relates to root nitrogen; and (iv) Plants growing in pots have higher SRL than those grown in the field.
4. Synthesis. This study reveals both the large variation in fine‐root traits encountered globally and the relevance of several key plant functional types and soil and climate variables for explaining a substantial part of this variation. Climate, particularly temperature, and plant functional types were the two strongest predictors of fine‐root trait variation. High trait variation occurred at local scales, suggesting that wide‐ranging below‐ground resource economics strategies are viable within most climatic areas and soil conditions.
   

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