Papers by Jennifer Powers
Nature ecology & evolution, Jan 28, 2018
The nutrient demands of regrowing tropical forests are partly satisfied by nitrogen-fixing legume... more The nutrient demands of regrowing tropical forests are partly satisfied by nitrogen-fixing legume trees, but our understanding of the abundance of those species is biased towards wet tropical regions. Here we show how the abundance of Leguminosae is affected by both recovery from disturbance and large-scale rainfall gradients through a synthesis of forest inventory plots from a network of 42 Neotropical forest chronosequences. During the first three decades of natural forest regeneration, legume basal area is twice as high in dry compared with wet secondary forests. The tremendous ecological success of legumes in recently disturbed, water-limited forests is likely to be related to both their reduced leaflet size and ability to fix N, which together enhance legume drought tolerance and water-use efficiency. Earth system models should incorporate these large-scale successional and climatic patterns of legume dominance to provide more accurate estimates of the maximum potential for nat...
Background/Question/Methods More than a decade ago, 106 estimates of biological nitrogen (BNF) fi... more Background/Question/Methods More than a decade ago, 106 estimates of biological nitrogen (BNF) fixation from terrestrial ecosystems around the world were compiled. Since then, our knowledge about the controls over BNF has advanced considerably, especially in the form of conceptual frameworks, but less so in terms of empirical evidence that validates them. The major natural sources of newly fixed N to forest ecosystems have rarely if ever been measured in tropical dry forests (TDF), where N2-fixing legume trees are ubiquitous. Our main goal was to determine the rates of and controls over BNF in a TDF in Costa Rica and compare this flux to other N inputs to these forests. We tested the hypothesis that legume trees employ a facultative strategy of N2-fixation and that this process is regulated by resource availability including light, soil moisture and nutrients. We estimated the quantities of N2 fixed annually by five common legume species, using the 15N natural abundance method, coun...
American journal of botany, 2017
The seedling stage is particularly vulnerable to resource limitation, with potential consequences... more The seedling stage is particularly vulnerable to resource limitation, with potential consequences for community composition. We investigated how light and soil variation affected early growth, biomass partitioning, morphology, and physiology of 22 tree species common in tropical dry forest, including eight legumes. Our hypothesis was that legume seedlings are better at taking advantage of increased resource availability, which contributes to their successful regeneration in tropical dry forests. We grew seedlings in a full-factorial design under two light levels in two soil types that differed in nutrient concentrations and soil moisture. We measured height biweekly and, at final harvest, biomass partitioning, internode segments, leaf carbon, nitrogen, δ(13)C, and δ(15)N. Legumes initially grew taller and maintained that height advantage over time under all experimental conditions. Legumes also had the highest final total biomass and water-use efficiency in the high-light and high-r...
PloS one, 2015
Lianas (woody vines) are particularly abundant in tropical forests, and their abundance is increa... more Lianas (woody vines) are particularly abundant in tropical forests, and their abundance is increasing in the neotropics. Lianas can compete intensely with trees for above- and belowground resources, including water. As tropical forests experience longer and more intense dry seasons, competition for water is likely to intensify. However, we lack an understanding of how liana abundance affects soil moisture and hence competition with trees for water in tropical forests. To address this critical knowledge gap, we conducted a large-scale liana removal experiment in a seasonal tropical moist forest in central Panama. We monitored shallow and deep soil moisture over the course of three years to assess the effects of lianas in eight 0.64 ha removal plots and eight control plots. Liana removal caused short-term effects in surface soils. Surface soils (10 cm depth) in removal plots dried more slowly during dry periods and accumulated water more slowly after rainfall events. These effects dis...
Proceedings of the National Academy of Sciences of the United States of America, Jan 27, 2015
Tropical forests store vast quantities of carbon, account for one-third of the carbon fixed by ph... more Tropical forests store vast quantities of carbon, account for one-third of the carbon fixed by photosynthesis, and are a major sink in the global carbon cycle. Recent evidence suggests that competition between lianas (woody vines) and trees may reduce forest-wide carbon uptake; however, estimates of the impact of lianas on carbon dynamics of tropical forests are crucially lacking. Here we used a large-scale liana removal experiment and found that, at 3 y after liana removal, lianas reduced net above-ground carbon uptake (growth and recruitment minus mortality) by ∼76% per year, mostly by reducing tree growth. The loss of carbon uptake due to liana-induced mortality was four times greater in the control plots in which lianas were present, but high variation among plots prevented a significant difference among the treatments. Lianas altered how aboveground carbon was stored. In forests where lianas were present, the partitioning of forest aboveground net primary production was dominat...
Changes in soil carbon storage that accompany land-cover change may have significant effects on t... more Changes in soil carbon storage that accompany land-cover change may have significant effects on the global carbon cycle. The objective of this work was to examine how assumptions about preconversion soil C storage and the effects of land-cover change influence estimates of regional soil C storage. We applied three models of land-cover change effects to two maps of preconversion soil C in a 140 000 ha area of northeastern Costa Rica. One preconversion soil C map was generated using values assigned to tropical wet forest from the literature, the second used values obtained from extensive field sampling. The first model of land-cover change effects used values that are typically applied in global assessments, the second and third models used field data but differed in how the data were aggregated (one was based on land-cover transitions and one was based on terrain attributes). Changes in regional soil C storage were estimated for each combination of model and preconversion soil C for three time periods defined by georeferenced land-cover maps. The estimated regional soil C under forest vegetation (to 0.3 m) was higher in the map based on field data (10.03 Tg C) than in the map based on literature data (8.90 Tg C), although the range of values derived from propagating estimation errors was large (7.67-12.40 Tg C). Regional soil C storage declined through time due to forest clearing for pasture and crops. Estimated CO 2 fluxes depended more on the model of land-cover change effects than on preconversion soil C. Cumulative soil C losses under the literature model of land-cover effects exceeded estimates based on field data by factors of 3.8-8.0. In order to better constrain regional and global-scale assessments of carbon fluxes from soils in the tropics, future research should focus on methods for extrapolating regional-scale constraints on soil C dynamics to larger spatial and temporal scales.
Document: JEN-3-34-60. Geographic variation in soil organic carbon dynamics following land-use ch... more Document: JEN-3-34-60. Geographic variation in soil organic carbon dynamics following land-use change in Costa Rica. POWERS, JS* Duke University, Durham, NC 27708 1. Abstract: Recent studies have suggested that the ...
New Phytologist, 2015
Rates of ecosystem nitrogen (N) cycling may be mediated by the presence of ectomycorrhizal fungi,... more Rates of ecosystem nitrogen (N) cycling may be mediated by the presence of ectomycorrhizal fungi, which compete directly with free-living microbes for N. In the regenerating tropical dry forests of Central America, the distribution of ectomycorrhizal trees is affected by succession and soil parent material, both of which may exert independent influence over soil N fluxes.
Global change biology, 2015
Ecosystems worldwide are increasingly impacted by multiple drivers of environmental change, inclu... more Ecosystems worldwide are increasingly impacted by multiple drivers of environmental change, including climate warming and loss of biodiversity. We show, using a long-term factorial experiment, that plant diversity loss alters the effects of warming on productivity. Aboveground primary productivity was increased by both high plant diversity and warming, and, in concert, warming (≈1.5°C average above and belowground warming over the growing season) and diversity caused a greater than additive increase in aboveground productivity. The aboveground biodiversity effects increased over time, particularly at higher levels of diversity, perhaps because of warming-induced increases in legume and C4 bunch grass abundances, and facilitative feedbacks of these species on productivity. Moreover, higher plant diversity was associated with the amelioration of warming-induced environmental conditions. This led to cooler temperatures, increased vapor pressure deficit, and increased surface soil moist...
How does land ownership affect biodiversity and biomass stocks in secondary tropical dry forests?... more How does land ownership affect biodiversity and biomass stocks in secondary tropical dry forests? Moana L. McClellan, Plant Biological Sciences, University of Minnesota, St. Paul, MN, Rebecca A. Montgomery, Forest Resources, University of Minnesota, St. ...
Background/Question/Methods: Antibiotic-producing soil bacteria are an underexplored microbial fu... more Background/Question/Methods: Antibiotic-producing soil bacteria are an underexplored microbial functional group with the potential to influence plant community composition. Actinobacteria in the genus Streptomyces produce diverse antibiotics and can influence plant fitness by inhibiting soil-borne pathogens and reducing disease. Streptomyces may moderate the effects of pathogens on plant communities, yet little is known about their distribution and ecology in nonmanaged ecosystems, especially tropical forests. Our objective is to characterize variation in pathogen inhibitory capacities among Streptomyces communities associated with five tree species in tropical dry forests of Costa Rica. Previous work demonstrated extensive variation in Streptomyces across the landscape and correlations between pathogen inhibition and soil nutrients at broad spatial scales. In the current study we sampled soil-borne Streptomyces communities from focal tree species in two sites (n = 5 trees/species/s...
Background/Question/Methods More than a decade ago, 106 estimates of biological nitrogen (BNF) fi... more Background/Question/Methods More than a decade ago, 106 estimates of biological nitrogen (BNF) fixation from terrestrial ecosystems around the world were compiled. Since then, our knowledge about the controls over BNF has advanced considerably, especially in the form of conceptual frameworks, but less so in terms of empirical evidence that validates them. The major natural sources of newly fixed N to forest ecosystems have rarely if ever been measured in tropical dry forests (TDF), where N2-fixing legume trees are ubiquitous. Our main goal was to determine the rates of and controls over BNF in a TDF in Costa Rica and compare this flux to other N inputs to these forests. We tested the hypothesis that legume trees employ a facultative strategy of N2-fixation and that this process is regulated by resource availability including light, soil moisture and nutrients. We estimated the quantities of N2 fixed annually by five common legume species, using the 15N natural abundance method, coun...
Background/Question/Methods Individual trees are known to influence soil chemical properties and p... more Background/Question/Methods Individual trees are known to influence soil chemical properties and processes, creating a sphere of influence that varies with distance from the tree trunk. The effects of particular species have been well documented in low-diversity systems such as temperate forests or tropical plantations. However these spatial patterns are less well studied in species-rich tropical forests. Legume tree species, which are abundant in tropical dry forest, may be a critical regulator of soil nutrient dynamics because of high foliar nitrogen and potential for symbiotic fixation. We investigated whether legumes have distinct soil chemistry under their crowns compared to nearby non-legume species when grown in both a diverse secondary forest or alone in 18-yr old plantations in northwestern Costa Rica. In each site, we collected samples from the top 10 cm of mineral soil beneath the canopy of trees of three legume species and three non-legume species that were at least two c...
Background/Question/Methods Recent theoretical models suggest that nitrogen (N) fixation is subje... more Background/Question/Methods Recent theoretical models suggest that nitrogen (N) fixation is subject to environmental variables beyond soil N availability, yet there are few empirical data that test this. Evidence suggests that tropical dry forests are not N deficient. Given the ubiquity of legume trees in this ecosystem, symbiotic fixation by individual trees should be down-regulated. We tested the hypothesis that symbiotic fixation in tropical legume trees responds to changes in light and nutrient availability. Seedlings of four dry forest N-fixing legume species and one non-N-fixing legume were grown in a shadehouse for 6 months in a mixture of forest soil and sand. After the third month, two treatments of light availability and fertilization (+NP, +N, +P, no nutrients) were applied (N=10 replicates per treatment and species). The response variables that we measured were: photosynthetic rates, growth rates, final biomass partitioning, nodule biomass, nodule activity via the acetyl...
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Papers by Jennifer Powers