Contribution of physiological and morphological plant traits to a species' competitive ability at high and low nitrogen supply

Abstract

Why do inherently fast-growing species from productive habitats generally have a higher rate of biomass production in short-term low-nitrogen experiments than slow-growing species from unproductive habitats, whereas the opposite is found in long-term experiments? Is this mainly due to inherent differences in biomass allocation, leaf characteristics or the plants' physiology? To analyse these questions we grew five monocotyledonous species from productive and unproductive habitats in a climate chamber at both high and low nitrogen supply. Nitrate was supplied exponentially, enabling us to compare inherent differences in morphological and physiological traits between the species, without any interference due to differences in the species' ability to take up nutrients. At high nitrogen supply, we found major inherent differences in specific leaf area and nitrogen productivity, i.e. daily biomass increment per unit plant nitrogen, where-as there were only small differences in net assimilation rate, i.e. daily biomass increment per unit leaf area, and biomass partitioning. We propose that the higher specific leaf area and nitrogen productivity of inherently fast-growing species are the key factors explaining their high abundance in productive habitats compared with inherently slow-growing ones. At low nitrogen supply, the net assimilation rate was decreased to a similar extent for all species, compared with that at high nitrogen supply. The nitrogen productivity of the inherentlyfast-growing species decreased with decreasing nitrogen supply, whereas that of the inherently slow-growing species remained constant. There were no inherent differences in nitrogen productivity in this treatment. At this low nitrogen supply, the inherently fast-growing species invested relatively more biomass in their roots that the slow-growing ones did. The inherently fast-growing species still had a higher specific leaf area at low nitrogen supply, but the difference between species was less than that at high nitrogen supply. Based on the present results and our optimization model for carbon and nitrogen allocation (Van der Werf et al. 1993a), we propose that the relatively large investment in root biomass of fast-growing species is the key factor explaining their higher biomass production in short-term experiments. We also propose that in the long run the competitive ability of the slow-growing species will increase due to a lower turnover rate of biomass. It is concluded that the plant's physiology (net assimilation rate and nitrogen productivity), only plays a minor role in the species' competitive ability in low-nitrogen environments.

Phosphorus allocation and utilization in three grass species with contrasting response to N and P supply

“…Dactylis glomerata, the species with the highest RGR^^^ and the highest NP of the species studied ( Van der W'erf et aL, 1993), is also the species with the highest biomass production per unit plant phosphorus. Phosphorus productivity seems to be positively related to RGRn;^^, in the same way as Np (Poorter, Remkes & Lambers, 1990;Van der Werf et al, 1993;Garnier & Vancaeyzeele, 1994). However, interspecific differences in pp increase with decreasing P supply, in contrast to decreasing differences in NP with decreasing N supply.…”

A comparison of specific leaf area, chemical composition and leaf construction costs of field plants from 15 habitats differing in productivity

“…This conclusion was corroborated in a survey of 111 published comparative growth experiments on herbaceous species, where again SLA was the predominant factor explaining variation in RGR (Poorter & Van der Werf, 1998). Based partly on these observations, it has been suggested that SLA, or more precisely factors pertaining to a complex of traits related to SLA, could have been the target of selection (Poorter, 1989 ;Van der Werf et al, 1993 ;Poorter & Garnier, 1999). Generally, high-SLA species are characterized by high concentrations of nitrogen ; high rates of CO # and N uptake per unit leaf and root mass, respectively ; and a high rate of photosynthesis per unit leaf N (Lambers & Poorter, 1992).…”

“…To enable a wider comparison between laboratory and field data, SLA values were also collected for the first eight of these species in other habitats, following the sampling scheme described above. Data were included from the literature on the SLA of Carex flacca and Galium aparine, obtained under exactly the same conditions in the same laboratory by Van der Werf et al (1993) and Den Dubbelden & Verburg (1996), respectively. All SLA values obtained in the laboratory are averages over all viable leaves of the plants.…”

Functional linkages between leaf traits and net photosynthetic rate: reconciling empirical and mechanistic models

“…Plant-level measurements in laboratory Atkin et al (1996) Grasses 6 (6) Den Dubbelden (1994) Herbaceous monocots and dicots 12 (12) Dijkstra & Lambers (1989) Plantago major 1 (2) Roumet et al (unpublished data) Grasses 11 (11) Poorter (1990) Herbaceous monocots and dicots, 285 µmol m −2 s −1 8 (8) Poorter & Remkes (1990) Herbaceous monocots and dicots 24 (24) Van den Boogaard et al (1996) Triticum aestivum 1 (4) Van der Werf et al (1993) Grasses 2 To compare our results with those reported by Reich et al (1999), we present Fig. 3 in which their data are superimposed on ours and our prediction equation for individual leaves.…”