1. Global change drivers such as eutrophication and plant invasions will create novel environments for many plant species. Through adaptive trait plasticity plants may maintain their performance under these novel conditions and may outcompete those showing low adaptive trait plasticity. In a greenhouse study, we determined if plasticity in traits is adaptive or maladaptive in endangered, non-endangered and invasive plant species in response to variation of nitrogen (N) and phosphorus (P) availability (N:P ratios 1.7, 15 and 135) and whether plastic trait responses are adaptive and/or costly for fitness (i.e. biomass).
2. Species choice comprised 17 species from three functional groups (legumes, non-legume forbs and grasses), either classified as endangered, non-endangered or invasive. After two months plants were harvested and nine traits related to carbon assimilation and nutrient uptake were measured (leaf area, SLA, LDMC, SPAD, RMR, root length, SRL, root surface area and PME activity).
3. We found more traits responding plastically to variation in P than in N. Plasticity only created costs when P was varied. Plasticity in traits was mostly adaptively neutral towards fitness, with plasticity in three traits being similarly adaptive across all species groups: SPAD (as a measure of chlorophyll content, adaptive to N and P limitation), leaf area and root surface area (adaptive to P limitation). We found little differences in trait plasticity between endangered, non-endangered and invasive species.
4. Synthesis. Along a gradient from N limitation, balanced N:P supply and P limitation we found that the type of fluctuating nutrient (i.e. if N or P is varied) is decisive for the adaptive value of a trait. Variation in P availability (from balanced supply to P limitation) created both a stronger reduction in fitness as well as created plasticity costs in more traits than variation in N availability (from balanced supply to N limitation). However, the patterns observed in our study may change if nutrient availability is altered, either by nutrient inputs or by a shift in nutrient availabilities, e.g. by decreasing N input as foreseen by European Legislation, but without simultaneously decreasing P input.

The dataset contains plant trait information of 17 annual species (grasses, non-legume forbs, legumes). Plants were raised in a greenhouse and exposed to N (nitrogen) limitation, P (phosphorus) limitation, and a balanced supply of both N and P. After eight weeks, plants were harvested and traits were measured. 

General information: Family (Poaceae, Onagraceae, Fabaceae), Maturity (all plants mature at time of harvest), Status (plant species considered either invasive, endangered or non-endangered in central Europe), Plant Growth Form (grass, non-legume forb, forb), Life Span (annual), Start experiment (start date for each individual), End experiment (date of harvest for each individual), Treatment (N limitation, balanced nutrient supply, P limitation), total.supply.rate.N.mg (total amount of N supplied to each individual in the course of the experiment, i.e. 121.5mg, 40.5mg, 13.5mg) total.supply.rate.P.mg (total amount of P supplied to each individual in the course of the experiment, i.e. 0.9mg, 2.7mg, 8.1mg), repeats.per.trt (number of repetitions per trt and species, 1–10).

Plant species: Avena sterilis, Bromus hordeaceus, Bromus japonicus, Bromus secalinus, Bromus squarrosus, Epilobium anagallidifolium, Epilobium ciliatum, Epilobium fleischeri, Hordeum jubatum, Hordeum murinum, Lolium remotum, Lolium temulentum, Lupinus angustifolius, Medicago lupulina, Trifolium arvense, Trifolium dubium, Trifolium subterraneum

Plant traits include: Total Biomass (mg), Total leaf area (mm²), Specific leaf area (SLA, mm²/mg), Leaf dry matter content (LDMC, mg/g), SPAD (measure of chlorophyll content, dimensionless), Root mass ratio (RMR, mg/mg), Total root length (m), Specific root length (SRL, m/mg), Root surface area (cm²), root phosphomonoesterase activity (PME, µmol pNPP /g*h).

Measurement for most traits followed Pérez-Harguindeguy, N., et al. (2013). "New handbook for standardised measurement of plant functional traits worldwide." Australian Journal of Botany 61: 167-234.