Plasticity in response to phosphorus and light availability in four forest herbs

Abstract

The differential ability of forest herbs to colonize secondary forests on former agricultural land is generally attributed to different rates of dispersal. After propagule arrival, however, establishing individuals still have to cope with abiotic soil legacies from former agricultural land use. We focussed on the plastic responses of forest herbs to increased phosphorus availability, as phosphorus is commonly found to be persistently bioavailable in post-agricultural forest soils. In a pot experiment under field conditions, we applied three P levels to four forest herbs with contrasting colonization capacities: Anemone nemorosa, Primula elatior, Circaea lutetiana and Geum urbanum. To test interactions with light availability, half of the replicas were covered with shade cloths. After two growing seasons, we measured aboveground P uptake, vegetative and regenerative performance. We hypothesized that fast-colonizing species respond the most opportunistically to increased P availability and that a low light availability can mask the effects of P on performance. All species showed a significant increase in P uptake in the aboveground biomass. The P addition had a positive effect on the vegetative performance of two of the species, which was, however, unrelated to their colonization capacities. The regenerative performance was affected by light availability (not by P addition) and was related to the species' phenology. Forest herbs can obviously benefit from the increased P availabilities in post-agricultural forests, but not all species respond in the same way. Such differential patterns of plasticity may be important in community dynamics as they affect the interactions among species.

Former land use affects the nitrogen and phosphorus concentrations and biomass of forest herbs

“…Likewise, Baeten et al (2009a) showed that the contrasting land-use history of forest stands was reflected in the plant P concentrations of two forest herbs (P. elatior, G. urbanum). Furthermore, the plastic response of forest herbs to increased P availability we found here partly generalizes the results from pot experiments (Pigott and Taylor 1964;Hipps et al 2005;Baeten et al 2010) to field conditions and a larger set of species. The first hypothesis thus seems to hold regarding the plant P concentration.…”

“…If land-use history affects the composition and structure of the canopy, e.g. with higher light availability in post-agricultural sites, this might also account for the observed plasticity in biomass production for species such as U. dioica, A. podagraria and G. urbanum (Pigott and Taylor 1964;Elemans 2004;Baeten et al 2010). The relative importance of light availability was, however, not explicitly determined here.…”

“…The third hypothesis is thus not supported by the data. Baeten et al (2010) came to a similar conclusion for P in a pot experiment with four forest herbs: both slowly and fast colonizing species may exhibit high plasticity in response to P addition. In the present study, the variation in N and P concentration among species was also not related to differences in life form or phenology.…”

“…The observation that the species mainly responded in terms of P, and not N uptake, at least suggests that of the two nutrients P is the one that may be partly associated with the increased biomass in the post-agricultural stands, especially if we assume N to be a non-limiting nutrient at our sites (see above). In a pot experiment with four of the species we sampled here, Baeten et al (2010) found higher biomass production in response to P supply, but differences in light availability also had an effect. If land-use history affects the composition and structure of the canopy, e.g.…”

“…The past agriculture may have a persistent impact on the present-day soil N and P state: the soil P is generally higher in previously fertilized forest compared to ancient forest and the soil N may be lower, equal or higher (e.g., Koerner et al 1997;Verheyen et al 1999;De Keersmaeker et al 2004;Falkengren-Grerup et al 2006;Dambrine et al 2007). While pot experiments have demonstrated that some forest plants may increase their performance in response to increased N and P availability (Pigott and Taylor 1964;Elemans 2004;Hipps et al 2005;Baeten et al 2010), the results still need to be extended to field conditions (but see Falkengren-Grerup et al 2006;Fraterrigo et al 2009). …”