SummaryVariation and tradeoffs within and among plant traits are increasingly being harnessed by empiricists and modelers to understand and predict ecosystem processes under changing environmental conditions. While fine roots play an important role in ecosystem functioning, fine-root traits are underrepresented in global trait databases. This has hindered efforts to analyze fine-root trait variation and link it with plant function and environmental conditions at a global scale. This Viewpoint addresses the need for a centralized fine-root trait database, and introduces the Fine-Root Ecology Database (FRED, http://roots.ornl.gov) which so far includes > 70 000 observations encompassing a broad range of root traits and also includes associated environmental data. FRED represents a critical step toward improving our understanding of below-ground plant ecology. For example, FRED facilitates the quantification of variation in fine-root traits across root orders, species, biomes, and environmental gradients while also providing a platform for assessments of covariation among root, leaf, and wood traits, the role of fine roots in ecosystem functioning, and the representation of fine roots in terrestrial biosphere models. Continued input of observations into FRED to fill gaps in trait coverage will improve our understanding of changes in fine-root traits across space and time.

Growth and distribution of coarse roots in time and space represent a gap in our understanding of belowground ecology. Large roots may play a critical role in carbon sequestration belowground. Using ground-penetrating radar (GPR), we quantified coarse-root biomass from an open-top chamber experiment in a scrub-oak ecosystem at Kennedy Space Center, Florida, USA. GPR propagates electromagnetic waves directly into the soil and reflects a portion of the energy when a buried object is contacted. In our study, we utilized a 1500 MHz antenna to establish correlations between GPR signals and root biomass. A significant relationship was found between GPR signal reflectance and biomass (R2 = 0.68). This correlation was applied to multiple GPR scans taken from each open-top chamber (elevated and ambient CO2). Our results showed that plots receiving elevated CO2 had significantly (P = 0.049) greater coarse-root biomass compared to ambient plots, suggesting that coarse roots may play a large role in carbon sequestration in scrub-oak ecosystems. This nondestructive method holds much promise for rapid and repeatable quantification of coarse roots, which are currently the most elusive aspect of long-term belowground studies.

With an increasing focus on renewable fuels, it is vital to understand the environmental impacts from various alternative transportation fuel products and processes under development. This study analyzes greenhouse gas (GHG) emissions of renewable gasoline and diesel produced by the integrated hydropyrolysis and hydroconversion (IH2) process at an existing petroleum refinery in Memphis, TN, USA. In this study, we considered forest residues from the southeastern US and corn stover from the Midwest as the two feedstocks. H2 required for the process is either imported from a steam methane reformer using natural gas or produced from C1–C3 gas coproducts of the IH2 process. Life cycle GHG emission savings of 67–86% were calculated for IH2 gasoline and diesel compared to their fossil counterparts, depending on feedstock, transport and H2 sources. Monte Carlo simulations were conducted to assess the impact of input parameter uncertainty on the final GHG emission results. The impact of applying biochar coproduct as a soil amendment and soil carbon change due to residue harvest were also studied.

Elevated atmospheric carbon dioxide (CO 2 ) often stimulates the growth of fine roots, yet there are few reports of responses of intact root systems to long-term CO 2 exposure. We investigated the effects of elevated CO 2 on fine root growth using open top chambers in a scrub oak ecosystem at Kennedy Space Center, Florida for more than 7 years. CO 2 enrichment began immediately after a controlled burn, which simulated the natural disturbance that occurs in this system every 10-15 years. We hypothesized that (1) root abundance would increase in both treatments as the system recovered from fire; (2) elevated CO 2 would stimulate root growth; and (3) elevated CO 2 would alter root distribution. Minirhizotron tubes were used to measure fine root length density (mm cm À2 ) every three months. During the first 2 years after fire recovery, fine root abundance increased in all treatments and elevated CO 2 significantly enhanced root abundance, causing a maximum stimulation of 181% after 20 months. The CO 2 stimulation was initially more pronounced in the top 10 cm and 38-49 cm below the soil surface. However, these responses completely disappeared during the third year of experimental treatment: elevated CO 2 had no effect on root abundance or on the depth distribution of fine roots during years 3-7. The results suggest that, within a few years following fire, fine roots in this scrub oak ecosystem reach closure, defined here as a dynamic equilibrium between production and mortality. These results further suggest that elevated CO 2 hastens root closure but does not affect maximum root abundance. Limitation of fine root growth by belowground resources -particularly nutrients in this nutrient-poor soil -may explain the transient response to elevated CO 2 .

SummaryUncertainty surrounds belowground plant responses to rising atmospheric CO 2 because roots are difficult to measure, requiring frequent monitoring as a result of fine root dynamics and long-term monitoring as a result of sensitivity to resource availability.We report belowground plant responses of a scrub-oak ecosystem in Florida exposed to 11 yr of elevated atmospheric CO 2 using open-top chambers. We measured fine root production, turnover and biomass using minirhizotrons, coarse root biomass using groundpenetrating radar and total root biomass using soil cores.Total root biomass was greater in elevated than in ambient plots, and the absolute difference was larger than the difference aboveground. Fine root biomass fluctuated by more than a factor of two, with no unidirectional temporal trend, whereas leaf biomass accumulated monotonically. Strong increases in fine root biomass with elevated CO 2 occurred after fire and hurricane disturbance. Leaf biomass also exhibited stronger responses following hurricanes.Responses after fire and hurricanes suggest that disturbance promotes the growth responses of plants to elevated CO 2 . Increased resource availability associated with disturbance (nutrients, water, space) may facilitate greater responses of roots to elevated CO 2 . The disappearance of responses in fine roots suggests limits on the capacity of root systems to respond to CO 2 enrichment.