Tali D. Lee

Plant traits—the morphological, anatomical, physiological, biochemical and phenological characteristics of plants—determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of trait‐based plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traits—almost complete coverage for ‘plant growth form’. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and trait–environmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects. We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives.

Wolf and Ziska suggest that soil and species attributes can explain an unexpected 20-year reversal of C ₃ -C ₄ grass responses to elevated CO ₂ . This is consistent with our original interpretation; however, we disagree with the assertion that such explanations somehow render our results irrelevant for questioning a long-standing paradigm of plant response to CO ₂ based on C ₃ -C ₄ differences in photosynthetic pathway.

A short-term trend reversed: Theory and empirical data both support the paradigm that C ₄ plant species (in which the first product of carbon fixation is a four-carbon molecule) benefit less from rising carbon dioxide (CO ₂ ) concentrations than C ₃ species (in which the first product is a three-carbon molecule). This is because their different photosynthetic physiologies respond differently to atmospheric CO ₂ concentrations. Reich et al. document a reversal of this pattern in a 20-year CO ₂ enrichment experiment using grassland plots with each type of plant (see the Perspective by Hovenden and Newton). Over the first 12 years, biomass increased with elevated CO ₂ in C ₃ plots but not C ₄ plots, as expected. But over the next 8 years, the pattern reversed: Biomass increased in C ₄ plots but not C ₃ plots. Thus, even the best-supported short-term drivers of plant response to global change might not predict long-term results. Science , this issue p. 317 ; see also p. 263

Most plant communities support a diverse assemblage of arbuscular mycorrhizal fungi (AMF). AMF communities have the potential to affect plant community structure and vice versa. We examined AMF sporulation in a 4.5‐ha reconstructed prairie in Eau Claire County, Wisconsin. In fall 2003, the site was planted with varied numbers and combinations of native prairie species from four functional guilds: C₃ grasses/sedges, C₄ grasses, legume, and nonleguminous forbs. We hypothesized that more diverse plant seeding mixtures would promote AMF diversity. To examine the interaction between plant and fungal communities, plots were divided and subplots treated with the fungicide chlorothalonil to suppress AMF, enriched with ammonium nitrate fertilizer, treated with both fungicide and nitrogen, or remained untreated (control). Soil samples were collected during the summers of 2004, 2006, and 2007 from each subplot. Spores of AMF were extracted, identified to species, and enumerated. Initial plant seeding diversity did not significantly influence spore abundance, fungal diversity, plant productivity, or plant richness 4 years after establishment. Fungal species richness was positively, but weakly, correlated with plant productivity (r² = 0.11) and plant richness (r² = 0.09). Fungal community composition changed significantly over time; nitrogen addition, fungicide application, and site characteristics also shaped community composition. After 4 years of treatment, nitrogen and fungicide reduced AMF richness, changed sporulation patterns among AMF taxa, and reduced diversity and productivity in plant communities. Divergence in AMF community is being mirrored by changes in the plant community independent of initial seeding treatments, though causation could not be determined.

Plant fitness is typically correlated with total seed biomass or the number of seeds produced per plant, but the connection from seed production to seedlings the following year is seldom made. Seedling production in grasses, including wild rice ( Zizania palustris L.) is determined by the number of inflorescences produced, the number of seeds per inflorescence, the mean mass per seed, proportion of seeds that are filled, predation on seeds, and germination rates. Previous studies have shown that wild rice biomass production is limited primarily by nitrogen and secondarily by phosphorus and light. To test how nitrogen, phosphorus, and light modulate plant fitness, we evaluated the effects of nitrogen, phosphorus, and light on the above parameters. Nitrogen addition increased number of inflorescences, seeds per inflorescence, and mean seed mass, resulting in more seedlings produced, hence greater fitness, despite increased rice worm predation and lower germination rates of seeds compared to seeds from plants grown without nitrogen addition. Phosphorus additions and full sunlight also increased the number of seedlings per plant, mainly after nitrogen was added. Therefore, the maternal environment not only affects seed production but the number of seedlings that emerge the following year, especially with respect to nitrogen.

Separating plastic from ontogenetic and growth-limiting responses of plants to changes in resource availability can be challenging because there are a total of eight combinations of these three types of responses. These can, however, be uniquely distinguished on plots of root:shoot ratios against total biomass through time. We used this approach to separate ontogenetic, plastic, and growth-limiting responses of wild rice (Zizania palustris L.) to changes in nitrogen, phosphorus, and light availabilities. Relative growth rate was limited primarily by nitrogen but responded to increased light and phosphorus after nitrogen limitations were alleviated. Nitrogen addition increased relative growth rate because it simultaneously increased unit leaf rate, specific leaf area, and leaf weight ratio. Increased light did not change relative growth rate because decreased specific leaf area and leaf weight ratio compensated the increased unit leaf rate. Phosphorus did not change either relative growth rate or its underlying components. Plants responded ontogenetically to increased nitrogen and light availabilities by accelerating their developmental rate, and plastically by decreasing or increasing their root:shoot ratios, respectively. Plants did not respond either ontogenetically or plastically to increased phosphorus availability. Ontogenetic changes in growth can be separated from plastic and growth-limiting responses by plotting root:shoot ratio against total biomass in the context of the eight possible responses identified above, and also by examining how the underlying components of relative growth rate respond.

Summary: Co‐occurring species often differ in their leaf lifespan (LL) and it remains unclear how such variation is maintained in a competitive context. Here we test the hypothesis that leaves of long‐LL species yield a greater return in carbon (C) fixed per unit C or nutrient invested by the plant than those of short‐LL species. For 10 sympatric woodland species, we assessed three‐dimensional shoot architecture, canopy openness, leaf photosynthetic light response, leaf dark respiration and leaf construction costs across leaf age sequences. We then used the YPLANT model to estimate light interception and C revenue along the measured leaf age sequences. This was done under a series of simulations that incorporated the potential covariates of LL in an additive fashion. Lifetime return in C fixed per unit C, N or P invested increased with LL in all simulations. In contrast to other recent studies, our results show that extended LL confers a fundamental economic advantage by increasing a plant’s return on investment in leaves. This suggests that time‐discounting effects, that is, the compounding of income that arises from quick reinvestment of C revenue, are key in allowing short‐LL species to succeed in the face of this economic handicap.