The effect of nutrient availability on biomass allocation patterns in 27 species of herbaceous plants

We investigated allocation to roots, stems and leaves of 27 species of herbaceous clonal plants grown at two nutrient levels. Allocation was analyzed as biomass ratios and also allometrically. As in other studies, the fraction of biomass in stems and, to a lesser extent, in leaves, was usually higher in the high-nutrient treatment than in the low-nutrient treatment, and the fraction of biomass in roots was usually higher under low-nutrient conditions. The relationship between the biomass of plant structures fits the general allometric equation, with an exponent 1 in most of the species. The different biomass ratios under the two nutrient conditions represented points on simple allometric trajectories, indicating that natural selection has resulted in allometric strategies rather than plastic responses to nutrient level. In other words, in most of the species that changed allocation in response to the nutrient treatment, these changes were largely a consequence of plant size. Our data suggest that some allocation patterns that have been interpreted as plastic responses to different resource availabilities may be more parsimoniously explained as allometric strategies.     

Effect of Inorganic Nutrients on Relative Contributions of Fungi and Bacteria to Carbon Flow from Submerged Decomposing Leaf Litter

The relative contributions of fungi and bacteria to carbon flow from submerged decaying plant litter at different levels of inorganic nutrients (N and P) were studied. We estimated leaf mass loss, fungal and bacterial biomass and production, and microbial respiration and constructed partial carbon budgets for red maple leaf disks precolonized in a stream and then incubated in laboratory microcosms at two levels of nutrients. Patterns of carbon flow for leaf disks colonized with the full microbial assemblage were compared with those colonized by bacteria but in which fungi were greatly reduced by placing leaf disks in colonization chambers sealed with membrane filters to exclude aquatic hyphomycete conidia but not bacterial cells. On leaves colonized by the full microbial assemblage, elevated nutrient concentrations stimulated fungi and bacteria to a similar degree. Peak fungal and bacterial biomass increased by factors of 3.9 and 4.0; cumulative production was 3.9 and 5.1 times higher in the high nutrient in comparison with the low nutrient treatment, respectively. Fungi dominated the total microbial biomass (98.4 to 99.8%) and cumulative production (97.3 and 96.5%), and the fungal yield coefficient exceeded that of bacteria by a factor of 36 and 27 in low- and high-nutrient treatments, respectively. Consequently, the dominant role of fungi in leaf decomposition did not change as a result of nutrient manipulation. Carbon budgets indicated that 8% of leaf carbon loss in the low-nutrient treatment and 17% in the high-nutrient treatment were channeled to microbial (essentially fungal) production. Nutrient enrichment had a positive effect on rate of leaf decomposition only in microcosms with full microbial assemblages. In treatments where fungal colonization was reduced, cumulative bacterial production did not change significantly at either nutrient level and leaf decomposition rate was negatively affected (high nutrients), suggesting that bacterial participation in carbon flow from decaying leaf litter is low regardless of the presence of fungi and nutrient availability. Moreover, 1.5 and 2.3 times higher yield coefficients of bacteria in the reduced fungal treatments at low and high nutrients, respectively (percentage of leaf carbon loss channeled to bacterial production), suggest that bacteria are subjected to strong competition with fungi for resources available in leaf litter.     

Phosphorus addition increased carbon partitioning to autotrophic respiration but not to biomass production in an experiment with Zea mays

Plant carbon (C) partitioning—the relative use of photosynthates for biomass production, respiration, and other plant functions—is a key but poorly understood ecosystem process. In an experiment with Zea mays, with or without arbuscular mycorrhizal fungi (AMF), we investigated the effect of phosphorus (P) fertilization and AMF on plant C partitioning. Based on earlier studies, we expected C partitioning to biomass production (i.e., biomass production efficiency; BPE) to increase with increasing P addition due to reduced C partitioning to AMF. However, although plant growth was clearly stimulated by P addition, BPE did not increase. Instead, C partitioning to autotrophic respiration increased. These results contrasted with our expectations and with a previous experiment in the same set-up where P addition increased BPE while no effect on autotropic respiration was found. The comparison of both experiments suggests a key role for AMF in explaining these contrasts. Whereas in the previous experiment substantial C partitioning to AMF reduced BPE under low P, in the current experiment, C partitioning to AMF was too low to directly influence BPE. Our results illustrate the complex influence of nutrient availability and mycorrhizal symbiosis on plant C partitioning.     

Elevation effects on the carbon budget of tropical mountain forests (S Ecuador): the role of the belowground compartment

Carbon storage and sequestration in tropical mountain forests and their dependence on elevation and temperature are not well understood. In an altitudinal transect study in the South Ecuadorian Andes, we tested the hypotheses that (i) aboveground net primary production (ANPP) decreases continuously with elevation due to decreasing temperatures, whereas (ii) belowground productivity (BNPP) remains constant or even increases with elevation due to a shift from light to nutrient limitation of tree growth. In five tropical mountain forests between 1050 and 3060 m a.s.l., we investigated all major above‐ and belowground biomass and productivity components, and the stocks of soil organic carbon (SOC). Leaf biomass, stemwood mass and total aboveground biomass (AGB) decreased by 50% to 70%, ANPP by about 70% between 1050 and 3060 m, while stem wood production decreased 20‐fold. Coarse and large root biomass increased slightly, fine root biomass fourfold, while fine root production (minirhizotron study) roughly doubled between 1050 and 3060 m. The total tree biomass (above‐ and belowground) decreased from about 320 to 175 Mg dry mass ha^?1, total NPP from ca. 13.0 to 8.2 Mg ha^?1 yr^?1. The belowground/aboveground ratio of biomass and productivity increased with elevation indicating a shift from light to nutrient limitation of tree growth. We propose that, with increasing elevation, an increasing nitrogen limitation combined with decreasing temperatures causes a large reduction in stand leaf area resulting in a substantial reduction of canopy carbon gain toward the alpine tree line. We conclude that the marked decrease in tree height, AGB and ANPP with elevation in these mountain forests is caused by both a belowground shift of C allocation and a reduction in C source strength, while a temperature‐induced reduction in C sink strength (lowered meristematic activity) seems to be of secondary importance.     

Carbon-based Secondary Compounds at Elevated CO2

From literature sources we compiled the data on carbon-based-secondary compounds CBSC (phenolics and terpenoids) and biomass of 17 plant species grown at different CO₂ concentrations under low and high nutrient availabilities. With a low nutrient availability a possible inverse correlation was found between the biomass and CBSC changes. On the contrary, under a high nutrient availability, both the CBSC and biomass increased with elevated CO₂. The wide variation in the CBSC production among species and compounds (larger responses in phenolics than in terpenoids) indicates that the allocation to CBSC may not completely be governed by changes in CO₂ and nutrient availabilities per se. Yet the comparison shows that elevated CO₂ generally loads the carbon into CBSC [their leaf concentration increased an overall average of 14 % at 700 umol(CO₂) mol-r] which may improve our understanding of the carbon storage and cycling in ecosystems under the “global change” of climate. This revised version was published online in August 2006 with corrections to the Cover Date.     

Biotrophic transportome in mutualistic plant–fungal interactions

Understanding the mechanisms that underlie nutrient use efficiency and carbon allocation along with mycorrhizal interactions is critical for managing croplands and forests soundly. Indeed, nutrient availability, uptake and exchange in biotrophic interactions drive plant growth and modulate biomass allocation. These parameters are crucial for plant yield, a major issue in the context of high biomass production. Transport processes across the polarized membrane interfaces are of major importance in the functioning of the established mycorrhizal association as the symbiotic relationship is based on a ‘fair trade’ between the fungus and the host plant. Nutrient and/or metabolite uptake and exchanges, at biotrophic interfaces, are controlled by membrane transporters whose regulation patterns are essential for determining the outcome of plant–fungus interactions and adapting to changes in soil nutrient quantity and/or quality. In the present review, we summarize the current state of the art regarding transport systems in the two major forms of mycorrhiza, namely ecto- and arbuscular mycorrhiza.     

Global vegetation biomass production efficiency constrained by models and observations

Plants use only a fraction of their photosynthetically derived carbon for biomass production (BP). The biomass production efficiency (BPE), defined as the ratio of BP to photosynthesis, and its variation across and within vegetation types is poorly understood, which hinders our capacity to accurately estimate carbon turnover times and carbon sinks. Here, we present a new global estimation of BPE obtained by combining field measurements from 113 sites with 14 carbon cycle models. Our best estimate of global BPE is 0.41 ± 0.05, excluding cropland. The largest BPE is found in boreal forests (0.48 ± 0.06) and the lowest in tropical forests (0.40 ± 0.04). Carbon cycle models overestimate BPE, although models with carbon–nitrogen interactions tend to be more realistic. Using observation‐based estimates of global photosynthesis, we quantify the global BP of non‐cropland ecosystems of 41 ± 6 Pg C/year. This flux is less than net primary production as it does not contain carbon allocated to symbionts, used for exudates or volatile carbon compound emissions to the atmosphere. Our study reveals a positive bias of 24 ± 11% in the model‐estimated BP (10 of 14 models). When correcting models for this bias while leaving modeled carbon turnover times unchanged, we found that the global ecosystem carbon storage change during the last century is decreased by 67% (or 58 Pg C).     

Effect of Nutrients on Growth Rate and Carbohydrate Storage in Oxytropis sericea: A Test of the Carbon Accumulation Hypothesis

The pool of storage carbohydrates in plants may be formed in competition with allocation to growth ("true reserves") or, where growth is inhibited by external factors, with no cost to growth ("accumulated reserves"). The latter hypothesis was addressed using Oxytropis sericea, a perennial herb from the Rocky Mountains. To generate variation in growth rate, greenhouse-cultivated plants were assigned to low or high nutrient levels in 2 yr. Age of plants was also varied either by conducting consecutive harvests (1996) or using plants of different initial age (1997). In both years, plants from the high-nutrient group attained larger vegetative biomass than plants in the low-nutrient group and also displayed an overall lower carbon allocation to storage, consistent with the accumulation hypothesis.     

Aboveground Tree Growth Varies with Belowground Carbon Allocation in a Tropical Rainforest Environment

Young secondary forests and plantations in the moist tropics often have rapid rates of biomass accumulation and thus sequester large amounts of carbon. Here, we compare results from mature forest and nearby 15–20 year old tree plantations in lowland Costa Rica to evaluate differences in allocation of carbon to aboveground production and root systems. We found that the tree plantations, which had fully developed, closed canopies, allocated more carbon belowground - to their root systems - than did mature forest. This increase in belowground carbon allocation correlated significantly with aboveground tree growth but not with canopy production (i.e., leaf fall or fine litter production). In contrast, there were no correlations between canopy production and either tree growth or belowground carbon allocation. Enhanced allocation of carbon to root systems can enhance plant nutrient uptake, providing nutrients beyond those required for the production of short-lived tissues such as leaves and fine roots, and thus enabling biomass accumulation. Our analyses support this deduction at our site, showing that enhanced allocation of carbon to root systems can be an important mechanism promoting biomass accumulation during forest growth in the moist tropics. Identifying factors that control when, where and for how long this occurs would help us to improve models of forest growth and nutrient cycling, and to ascertain the role that young forests play in mitigating increased atmospheric carbon dioxide.     

Competitive ability of two Brassica varieties in relation to biomass allocation and morphological plasticity under varying nutrient availability

Green cabbage (Brassica campestris, leafy variety) and turnip (Brassica campestris var. rapifera, rooty variety) were grown in both monocultures and mixtures at three nutrient levels to investigate their responses to nutrient availability with respect to biomass allocation, morphological plasticity and competitive ability. Their allocation parameters and leaf morphological traits were affected by both nutrient availability and developmental stage. Both of the varieties had a smaller biomass allocation to leaf blades, but a greater allocation to petioles at high nutrient levels. Root:shoot ratio (RSR) of green cabbage decreased with increasing nutrient availability, whereas that of turnip increased. Turnip had a smaller leaf blade weight ratio (LBWR) than cabbage, being compensated for by larger leaf area ratio (LAR) and specific leaf area (SLA). Leaf area ratio and SLA of both the varieties increased with increasing nutrient availability as did their mean dry weights. The mean dry weight of turnip was slightly greater than that of green cabbage in their respective monocultures, while that of green cabbage was greater than that of turnip in their 1:1 mixture. Therefore, green cabbage, having inherently greater biomass allocation to leaves, was generally more competitive than turnip with more biomass allocation to roots, especially at higher nutrient levels. However, within a variety, morphological plasticity (variation in LAR and SLA) was more important than the plasticity in biomass allocation (e.g. variation in RSR and LBWR) in determining competitive ability. The implication of our results is that competition models based on biomass allocation pattern alone may fail to predict competitive outcomes and that such models should also take morphological plasticity into full account.     

Estimating carbon stock in lowland Papua New Guinean forest: Low density of large trees results in lower than global average carbon stock

Papua New Guinean forests (PNG), sequestering up to 3% of global forest carbon, are a focus of climate change mitigation initiatives, yet few field‐based studies have quantified forest biomass and carbon for lowland PNG forest. We provide an estimate for the 10 770 ha Wanang Conservation Area (WCA) to investigate the effect of calculation methodology and choice of allometric equation on estimates of above‐ground live biomass (AGLB) and carbon. We estimated AGLB and carbon from 43 nested plots at the WCA. Our biomass estimate of 292.2 Mg AGLB ha^?1 (95% CI 233.4–350.6) and carbon at 137.3 Mg C ha^?1 (95% CI 109.8–164.8) is higher than most estimates for PNG but lower than mean global estimates for tropical forest. Calculation method and choice of allometric model do not significantly influence mean biomass estimates; however, the most recently calibrated allometric equation generates estimates 13% higher for lower 95% confidence intervals of mean biomass than previous allometric models – a value often used as a conservative estimate of biomass. Although large trees at WCA (>70 cm diameter at breast height) accounted for 1/5 total biomass, their density was lower than that seen in SE Asian and Australia forests. Lower density of large trees accounts for lower AGLB than in neighbouring forests – as large trees contribute disproportionately to forest biomass. Reduced frequency of larger trees at WCA is explained by the lack of diversity of large dipterocarp species common to neighbouring SE Asian forests and, potentially, higher rates of local disturbance dynamics. PNG is susceptible to the El Niño Southern Oscillation (ENSO) extreme drought events to which large trees are particularly sensitive and, with still over 20% carbon in large trees, differential mortality under increasing ENSO drought stress raises the risk of PNG forest switching from carbon sink to source with reduced long‐term carbon storage capacity.     

Nitrogen addition promotes terrestrial plants to allocate more biomass to aboveground organs: A global meta-analysis

A significant increase in reactive nitrogen (N) added to terrestrial ecosystems through agricultural fertilization or atmospheric deposition is considered to be one of the most widespread drivers of global change. Modifying biomass allocation is one primary strategy for maximizing plant growth rate, survival, and adaptability to various biotic and abiotic stresses. However, there is much uncertainty as to whether and how plant biomass allocation strategies change in response to increased N inputs in terrestrial ecosystems. Here, we synthesized 3516 paired observations of plant biomass and their components related to N additions across terrestrial ecosystems worldwide. Our meta-analysis reveals that N addition (ranging from 1.08 to 113.81 g m⁻² year⁻¹) increased terrestrial plant biomass by 55.6% on average. N addition has increased plant stem mass fraction, shoot mass fraction, and leaf mass fraction by 13.8%, 12.9%, and 13.4%, respectively, but with an associated decrease in plant reproductive mass (including flower and fruit biomass) fraction by 3.4%. We further documented a reduction in plant root-shoot ratio and root mass fraction by 27% (21.8%–32.1%) and 14.7% (11.6%–17.8%), respectively, in response to N addition. Meta-regression results showed that N addition effects on plant biomass were positively correlated with mean annual temperature, soil available phosphorus, soil total potassium, specific leaf area, and leaf area per plant. Nevertheless, they were negatively correlated with soil total N, leaf carbon/N ratio, leaf carbon and N content per leaf area, as well as the amount and duration of N addition. In summary, our meta-analysis suggests that N addition may alter terrestrial plant biomass allocation strategies, leading to more biomass being allocated to aboveground organs than belowground organs and growth versus reproductive trade-offs. At the global scale, leaf functional traits may dictate how plant species change their biomass allocation pattern in response to N addition.     

三种高寒植物幼苗生物量分配及性状特征对光照和养分的响应

为了解高寒植物幼苗对生境资源异质性的适应策略,以高寒草甸中常见的3种草本植物大耳叶风毛菊(Saussurea macrota)、甘西鼠尾草(Salvia przewalskii)和千里光(Senecio scandens)为材料,比较研究了这3种植物幼苗对不同光照和养分资源的响应。结果表明:光照和养分异质性显著影响了3种植物幼苗的性状特征和生物量分配,并存在一定的交互影响。随着光照的降低,3个物种的幼苗的生物量和根分配呈现降低趋势,但是其株高、比叶面积、叶分配、茎分配却逐渐升高。在低养分条件下,3个物种幼苗的总生物量、株高、比叶面积和叶分配均降低,而根分配均却显著增加。对于光照和养分资源异质性而言,光照异质性对高寒植物生物量分配和性状特征的改变具有更大的影响。喜阴物种大耳叶风毛菊和喜光物种甘西鼠尾草比中性生境物种千里光表现出了较大的性状特征和生物量分配的可塑性指数。     

Growth schedule of Xanthium canadense: Does it optimize the timing of reproduction?

Summary The effects of nutrition on the timing of reproductive initiation of a short-day annual plant Xanthium canadense (cocklebur) were examined with the following hypotheses in mind: If the plant always follows an optimal growth schedule, low-nutrient plants will initiate reproductive growth earlier than high-nutrient plants. On the other hand, if the plant flowers in response to photoperiodic stimuli, both plants will initiate reproductive growth on the same day. The sand-culture experiment showed that high-nutrient plants flowered earlier than the low-nutrient plants, leading to rejection of the first hypothesis. The predicted optimal flowering time is 2 days later than the actual flowering time in high-nutrient plants and 10 days earlier in low-nutrient plants. These deviations from the optimal times reduced the reproductive yield by 0.1% and 2.3%, respectively. The ratio of the final reproductive yield to the vegetative mass at flower initiation was 1.10 in high-nutrient plants and 0.63 in low-nutrient plants. Since the expected ratio for the optimal growth schedule is 1.0, high-nutrient plants followed the opitmal growth schedule more closely than the low-nutrient plants. Cocklebur is a fast-growing annual which is common in relatively nutrient-rich environments. This study suggests that cocklebur adapts itself to such environments through its photoperiodic response.     

Nutrient use efficiency in evergreen and deciduous species from heathlands

Summary The nutrient (N, P) use efficiency (NUE: g g^–1 nutrient), measured for the entire plant, of field populations of the evergreen shrubs Erica tetralix (in a wet heathland) and Calluna vulgaris (in a dry heathland) and the deciduous grass Molinia caerulea (both in a wet and a dry heathland) was compared. Erica and Calluna are crowded out by Molinia when nutrient availability increases. NUE was measured as the product of the mean residence time of a unit of nutrient in the population (MRT: yr) and nutrient productivity (A: annual productivity per unit of nutrient in the population, g g^–1 nutrient yr^–1. It was hypothesized that 1) in low-nutrient habitats selection is on features leading to a high MRT, whereas in high-nutrient habitats selection is on features leading to a high A; and that 2) due to evolutionary trade-offs plants cannot combine genotypically determined features which maximize both components of NUE.Both total productivity and litter production of the Molinia populations exceeded that of both evergreens about three-fold. Nitrogen and phosphorus resorption from senescing shoots was much lower in the evergreens compared with Molinia. In a split-root experiment no nutrient resorption from senescing roots was observed. Nutrient concentrations in the litter were equal for all species, except for litter P-concentration of Molinia at the wet site. Both Erica and Calluna had a long mean residence time of both nitrogen and phosphorus and a low nitrogen and phosphorus productivity. The Molinia populations showed a shorter mean residence time of N and P and a higher N- and P-productivity. These patterns resulted in an equal nitrogen use efficiency and an almost equal phosphorus use efficiency for the species under study. However, when only aboveground NUE was considered the Molinia populations had a much higher NUE than the evergreens.The results are consistent with the hypotheses. Thus, the low potential growth rate of species from low-nutrient habitats is probably the consequence of their nutrient conserving strategy rather than a feature on which direct selection takes place in these habitats.     

Light, nutrients and the growth of herbaceous forest species

The herb layer of forests planted on former agricultural land often differs from that of old-growth forest. This study investigates if the expected increased nutrient availability in the shaded conditions of newly planted forests and the plasticity of the species to adjust their biomass allocation to different levels of light and nutrients help to explain these differences in the herb layers of the two forest types. In a greenhouse experiment biomass distribution and production of two species characteristic for the highly shaded forest floor, Circaea lutetiana and Mercurialis perennis, and two species more common in the forest-edge, Aegopodium podagraria and Impatiens parviflora were studied at different levels of light (2%, 8% and 66% of the full light level) and nutrients (30 and 300 kg N ha^–1 per year). The main factor affecting allocation and biomass production was light availability. Nutrient supply only had a significant effect at the higher light levels. Species were mainly plastic to changes in light and the two species from the forest floor showed to be more rigid in allocation pattern than the species from the forest-edge. So, although the species from the forest-edge were more plastic, they did not profit from the increased nutrient supply because the main factor affecting biomass distribution and production was light availability.     

Invasive clonal plant species have a greater root-foraging plasticity than non-invasive ones

Clonality is frequently positively correlated with plant invasiveness, but which aspects of clonality make some clonal species more invasive than others is not known. Due to their spreading growth form, clonal plants are likely to experience spatial heterogeneity in nutrient availability. Plasticity in allocation of biomass to clonal growth organs and roots may allow these plants to forage for high-nutrient patches. We investigated whether this foraging response is stronger in species that have become invasive than in species that have not. We used six confamilial pairs of native European clonal plant species differing in invasion success in the USA. We grew all species in large pots under homogeneous or heterogeneous nutrient conditions in a greenhouse, and compared their nutrient-foraging response and performance. Neither invasive nor non-invasive species showed significant foraging responses to heterogeneity in clonal growth organ biomass or in aboveground biomass of clonal offspring. Invasive species had, however, a greater positive foraging response in terms of root and belowground biomass than non-invasive species. Invasive species also produced more total biomass. Our results suggest that the ability for strong root foraging is among the characteristics promoting invasiveness in clonal plants.     

Plant respiration: Controlled by photosynthesis or biomass?

Two simplifying hypotheses have been proposed for whole‐plant respiration. One links respiration to photosynthesis; the other to biomass. Using a first‐principles carbon balance model with a prescribed live woody biomass turnover, applied at a forest research site where multidecadal measurements are available for comparison, we show that if turnover is fast the accumulation of respiring biomass is low and respiration depends primarily on photosynthesis; while if turnover is slow the accumulation of respiring biomass is high and respiration depends primarily on biomass. But the first scenario is inconsistent with evidence for substantial carry‐over of fixed carbon between years, while the second implies far too great an increase in respiration during stand development—leading to depleted carbohydrate reserves and an unrealistically high mortality risk. These two mutually incompatible hypotheses are thus both incorrect. Respiration is not linearly related either to photosynthesis or to biomass, but it is more strongly controlled by recent photosynthates (and reserve availability) than by total biomass.     

Long- and short-term effects of fire on nitrogen cycling in tallgrass prairie

Fires in the tallgrass prairie are frequent and significantly alter nutrient cycling processes. We evaluated the short-term changes in plant production and microbial activity due to fire and the long-term consequences of annual burning on soil organic matter (SOM), plant production, and nutrient cycling using a combination of field, laboratory, and modeling studies. In the short-term, fire in the tallgrass prairie enhances microbial activity, increases both above-and belowground plant production, and increases nitrogen use efficiency (NUE). However, repeated annual burning results in greater inputs of lower quality plant residues causing a significant reduction in soil organic N, lower microbial biomass, lower N availability, and higher C:N ratios in SOM. Changes in amount and quality of below-ground inputs increased N immobilization and resulted in no net increases in N availability with burning. This response occurred rapidly (e.g., within two years) and persisted during 50 years of annual burning. Plant production at a long-term burned site was not adversely affected due to shifts in plant NUE and carbon allocation. Modeling results indicate that the tallgrass ecosystem responds to the combined changes in plant resource allocation and NUE. No single factor dominates the impact of fire on tallgrass plant production.     

Trait convergence and plasticity among native and invasive species in resource-poor environments

? Premise of study: Functional trait comparisons provide a framework with which to assess invasion and invasion resistance. However, recent studies have found evidence for both trait convergence and divergence among coexisting dominant native and invasive species. Few studies have assessed how multiple stresses constrain trait values and plasticity, and no study has included direct measurements of nutrient conservation traits, which are critical to plants growing in low-resource environments. ? Methods: We evaluated how nutrient and water stresses affect growth and allocation, water potential and gas exchange, and nitrogen (N) allocation and use traits among a suite of six codominant species from the Intermountain West to determine trait values and plasticity. In the greenhouse, we grew our species under a full factorial combination of high and low N and water availability. We measured relative growth rate (RGR) and its components, total biomass, biomass allocation, midday water potential, photosynthetic rate, water-use efficiency (WUE), green leaf N, senesced leaf N, total N pools, N productivity, and photosynthetic N use efficiency. ? Key results: Overall, soil water availability constrained plant responses to N availability and was the major driver of plant trait variation in our analysis. Drought decreased plant biomass and RGR, limited N conservation, and led to increased WUE. For most traits, native and nonnative species were similarly plastic. ? Conclusions: Our data suggest native and invasive biomass dominants may converge on functionally similar traits and demonstrate comparable ability to respond to changes in resource availability.