[1] We compiled new and published data on the natural abundance N isotope composition (d 15 N values) of soil and plant organic matter from around the world. Across a broad range of climate and ecosystem types, we found that soil and plant d ) with climate. Nitrogen isotopes reflect time integrated measures of the controls on N storage that are critical for predictions of how these ecosystems will respond to humanmediated disturbances of the global N cycle.

2005. Are you what you eat? Physiological constraints on organismal stoichiometry in an elementally imbalanced world. Á/ Oikos 109: 18 Á/28.The relative supply of energy and elements available to organisms in the environment has strong effects on their physiology, which, in turn, can alter important ecological processes. Here we consider how resource imbalances affect three basic physiological processes common to all organisms: elemental uptake, incorporation, and release. We review recent research that addresses these core issues (uptake, incorporation, and release) as they relate to elemental homeostasis in autotrophs and heterotrophs. Our review shows the importance that organism elemental homeostasis plays in determining the types of physiological processes used to acquire, assemble, store, and release biogenic elements, which are found in widely varying ratios in the environment. Future research should examine the degree to which organisms assess their internal nutritional composition and that of their food sources within a multiple elemental and biochemical context. Also, scientists should explore if and how the stoichiometry of cellular and molecular responses underlying nutrient (elemental and biochemical) acquisition, incorporation, and release depends on the nutritional composition of food resources. These types of queries will further improve our understanding of the physiological processing of primary elements involved in growth, reproduction, and maintenance of organisms.

The growth-rate hypothesis states that fast-growing organisms need relatively more phosphorus-rich RNA to support rapid rates of protein synthesis, and therefore predicts, within and among taxa, increases in RNA and phosphorus content (relative to protein and nitrogen content) with increased growth rate. Here, we present a test of this hypothesis in vascular plants. We determined nitrogen : phosphorus ratios and protein:RNA ratios in pines growing at different rates due to nutrient conditions. In general, when comparing leaves of the same species at low and high growth rates, the faster-growing plants had higher RNA content, higher %N and %P, and lower protein:RNA ratios, but not consistently lower N:P ratios. We found no link between growth rate and foliar N:P or protein:RNA when comparing multiple species of different inherent growth rates. We conclude that plants adjust the balance of protein and RNA to favour either speed or efficiency of protein synthesis, but this balance does not alone dictate leaf stoichiometry.

Like many conservation disciplines, invasion biology may suffer from a knowing-doing gap, where scientific research fails to inform management actions. We surveyed California resource managers to evaluate engagement with scientific research and to identify research priorities. We examined managers' access to information, judgment of the usefulness of existing research, ability to generate scientific information, and priorities for future research. We found that practitioners rely on their own experience, and largely do not read the peer-reviewed literature, which they regard as only moderately useful. Less than half of managers who do research carry out experiments conforming to the norms of hypothesis testing, and their results are not broadly disseminated. Managers' research needs are not restricted to applied science, or even basic ecology, but include social science questions. Scientists studying invasions can make their research more useful by crossing disciplinary boundaries, sourcing research questions from practitioners, and reporting results in accessible venues.

Climate change's impact on key ecosystem services E Nelson et al. 484www.frontiersinecology.org

Conversion of abandoned cattle pastures to secondary forests and plantations in the tropics has been proposed as a means to increase rates of carbon (C) sequestration from the atmosphere and enhance local biodiversity. We used a long‐term tropical reforestation project (55–61 yr) to estimate rates of above‐ and belowground C sequestration and to investigate the impact of planted species on overall plant community structure. Thirteen tree species (nine native and four nonnative species) were planted as part of the reforestation effort in the mid to late 1930s. In 1992, there were 75 tree species (>9.1 cm dbh) in the forest. Overall, planted species accounted for 40% of the importance value of the forest; planted nonnative species contributed only 5% of the importance value. In the reforested ecosystem, the total soil C pool (0–60 cm depth) was larger than the aboveground C pool, and there was more soil C in the forest (102 ± 10 Mg/ha [mean ± 1 se]) than in an adjacent pasture of similar age (69 ± 16 Mg/ha). Forest soil C (C3‐C) increased at a rate of ∼0.9 Mg·ha−1·yr−1, but residual pasture C (C4‐C) was lost at a rate of 0.4 Mg·ha−1·yr−1, yielding a net gain of 33 Mg/ha as a result of 61 years of forest regrowth. Aboveground C accumulated at a rate of 1.4 ± 0.05 Mg·ha−1·yr−1, to a total of 80 ± 3 Mg/ha. A survey of 426 merchantable trees in 1959 and 1992 showed that they grew faster in the second 33 years of forest development than in the first 22 years, indicating that later stages of forest development can play an important role in C sequestration. Few indices of C cycling were correlated with plant community composition or structure. Our results indicate that significant soil C can accumulate with reforestation and that there are strong legacies of pasture use and reforestation in plant community structure and rates of plant C sequestration.

We determined rates of acetylene reduction and estimated total nitrogen fixation associated with bryophytes, lichens, and decaying wood in Hawaiian montane rain forest sites with underlying substrate ranging in age from 300 to 4.1 million years. Potential N fixation ranged from ca 0.2 kg/ha annually in the 300‐year‐old site to ca 1 kg/ha annually in the 150,000‐year‐old site. Rates of acetylene reduction were surprisingly uniform along the soil‐age gradient, except for high rates in symbiotic/associative fixers at the 150,000‐year‐old site and in heterotrophic fixers at the 2100‐year‐old site. Low fixation at the youngest site, where plant production is known to be N‐limited, suggests that demand for N alone does not govern N fixation. Total N fixation was highest in sites with low N:P ratios in leaves and stem wood, perhaps because epiphytic bryophytes and lichens depend on canopy leachate for mineral nutrients and because heterotrophic fixation is partly controlled by nutrient supply in the decomposing substrate; however, differences in substrate cover, rather than in fixation rates, had the largest effect on the total N input from fixation at these sites.

Invasive plant species are often found to have advantages over native species in growth-related traits, such as photosynthetic rate, in disturbed or resource-rich environments. However, resource-use efficiency, rather than opportunistic resource capture, may confer more advantages when resources are scarce. In this study, performance and functional traits of invasive and non-invasive members of the genus Pinus were contrasted under the condition of nutrient limitations. Invasive species outperformed non-invasive congeners by growing 28% faster, on average. Invasives and non-invasives did not differ in biomass allocation traits (root-weight ratio, stem-weight ratio, leaf-weight ratio, leaf area ratio, root: shoot coefficient), but invaders had thinner and/or less dense leaves, as shown by a significantly lower leaf mass per area and leaf dry mass fraction. No differences between invasives and non-invasives were apparent in areabased leaf content of nitrogen, chlorophyll, or total protein, nor did the two groups differ in how efficiently they took up nutrients (specific absorption rate per unit root mass). The trait most strongly associated with invasives' superior performance was photosynthetic nitrogen-use efficiency. Non-invaders were more water-use efficient. The results suggests that the relative performance of invasive and non-invasive species is context-dependent. Invaders may allocate leaf nitrogen more efficiently to maximize photosynthesis and growth in nitrogen-poor soils, while noninvaders with more heavily defended leaves may have an advantage in drier areas. Rather than searching for a suite of traits that constitutes ''invasiveness'', it may be necessary to identify potential invaders by traits that are most adaptive to the local resource context.