Functional traits, productivity and effects on nitrogen cycling of 33 grassland species
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- 1Our goal was to determine the relationships among ecophysiological, whole-plant and ecosystem traits of a wide variety of grassland species grown under field conditions in the long term. We measured 87 traits for 33 species (32 perennial, one annual) grown in monoculture for 5 years on sandy soils, and determined the relationship among traits and their correspondence with current functional classifications.
- 2Among non-legumes, species that produced and maintained large amounts of biomass had tough, low-activity leaves and roots, high root : shoot ratios, and low extractable inorganic nitrogen and N mineralization in their soils. The set of correlations among the functional traits of fine roots for non-legumes parallels the set of correlations for leaf functional traits. Low-N species maintained greater biomass than high-N species, more by producing tissues with low N concentrations and greater longevity than by acquiring more N. Greater relative production below ground, and the production of long-lived below-ground structures, were both important in determining the high root : shoot ratio of species.
- 3For legumes, N2 fixation not only led to greater above-ground biomass production, but also was associated with low fine root production; greater relative production of stem biomass; and accelerated ecosystem N cycling compared to non-legumes.
- 4The measured traits, as condensed via principal components analysis, differentiated the 32 species into groups that corresponded with a common grassland functional classification scheme (C3 grasses, C4 grasses, forbs, legumes, woody species) as well as an alternative, continuous approach. For all traits, species can be arrayed well along two continuous axes. The first axis separates cool-season and warm-season legumes; the second low-N and high-N non-legumes.
- 5These continuous classifications show the generality of the two strategies for dealing with low nitrogen availability (N2 fixation and the low-N suite of traits) and extends the strategies to span organ-level traits to ecosystem processes including roots, whole-plant patterns of productivity, and nutrient cycling. The correlations of traits among species will also be useful in predicting a large number of important parameters associated with plant growth from the measurement of a few, key traits.