Shifts in trait-combinations along rainfall and phosphorus gradients

Cr. Fonseca et al., Shifts in trait-combinations along rainfall and phosphorus gradients, J ECOLOGY, 88(6), 2000, pp. 964-977
Citations number
Categorie Soggetti
Journal title
ISSN journal
0022-0477 → ACNP
Year of publication
964 - 977
SICI code
1 If different factors inhibiting plant growth, e.g. low rainfall or low so il nutrients, were to select for species that have similar constellations o f traits, then the unfavourable factors might usefully be grouped together as 'stress'. 2 We offer a method for assessing this issue. A species mixture at a site i s described by a point on a plane with two traits as axes. Change along an environmental gradient is then represented as a trajectory across the trait -plane. Trajectories along different environmental gradients are compared. 3 We measured leaf width, specific leaf area (SLA) and mature canopy height for the 386 perennial species found at 46 sites spread along rainfall and soil total phosphorus gradients in south-eastern Australia. Each trait was lognormally distributed across species within sites, hence the mean of log( 10)(trait) satisfactorily described the species mixture at each site. 4 Combinations of assemblage-mean leaf width with SLA followed similar traj ectories as rainfall and soil total P decreased. For these traits in this s etting, the method indicated that low rainfall and low soil P favour simila r trait-combinations. 5 Mature plant height also decreased along both rainfall and soil P gradien ts, and thus was positively correlated with leaf width and SLA at the level of assemblage means. The rainfall trajectories involving height behaved di fferently from the soil P trajectories, especially at rainfalls below c. 40 0 mm year(-1), where assemblage-mean height declined much further than at l ow soil P. 6 Across all species, traits were only very loosely correlated (r(2) from 0 .04 to 0.17). For leaf width and SLA, evolutionary divergences were positiv ely correlated, both before and after cross-correlation with divergence in rainfall and soil P was removed. This latter measures evolutionary divergen ce correlation. within habitat. For height the picture was more complicated . Considering these within-habitat divergence correlations, species that we re taller at maturity tended to have lower SLA and leaf width. This pattern is the reverse of the broad geographical correlation of assemblage means, showing that the patterns across assemblages result from species being sele ctively sifted from the regional flora into sites, not from evolutionary or cross-species correlations. 7 The trait-combination trajectory approach showed some commonalities betwe en low soil nutrient and low rainfall habitats with regard to traits favour ed in species occurring there, but also some differences. The approach has potential for clarifying which environmental factors can usefully be groupe d together as 'stress', and which trait combinations can usefully be regard ed as part of a syndrome favoured by stress.