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Earth system models predict large increases in global terrestrial net primary productivity (NPP) over the next century, largely reflecting positive effects of climate change and increasing atmospheric carbon dioxide concentrations on plant growth. However, while theory predicts that soil phosphorus (P) availability may keep pace with P demand as the climate warms, we lack experimental evidence to support this prediction. Here, using a set of laboratory experiments and incubations, we measured both the effect of temperature on the mechanism of biochemical P mineralization—phosphatase (Ptase) enzyme activities—and on rates of soil P mineralization in soils from a range of ecosystem types from the tropics to the Arctic. Consistent with temperature effects on soil nitrogen (N) mineralization, we found that both Ptase activities and P availability in soil increased with temperature following macromolecular rate theory (MMRT) based kinetics. However, across all sites and temperatures, there was no relationship between Ptase activity and mineralized P, indicating that the potential responses of P mineralization with warming vary among ecosystems. The lack of relationship between Ptase and P availability with increasing temperature is consistent with previous work showing that P mineralization rates are also strongly affected by other biotic and abiotic factors, including organic P substrate availability and the geochemical properties of soil. However, our results indicate that the use of Ptase temperature kinetics alone as a proxy for soil P mineralization in terrestrial ecosystems is insufficient to predict future P availability accurately, and modeling efforts that do so will likely overestimate the effects of temperature on soil P availability. [ABSTRACT FROM AUTHOR]

Though tropical forest ecosystems are among the largest natural sources of the potent greenhouse gas nitrous oxide (N2O), the spatial distribution of emissions across landscapes is often poorly resolved. Leaf cutter ants (LCA; Atta and Acromyrmex, Myrmicinae) are dominant herbivores throughout Central and SouthAmerica, and influencemultiple aspects of forest structure and function. In particular, their foraging creates spatial heterogeneity by concentrating large quantities of organic matter (including nitrogen,N) fromthe surrounding canopy into their colonies, and ultimately into colony refuse dumps. Here, we demonstrate that refuse piles created by LCA species Atta colombica in tropical rainforests of Costa Rica provide ideal conditions for extremely high rates of N2O production (high microbial biomass, potential denitrification enzyme activity, N content and anoxia) and may represent an unappreciated source of heterogeneity in tropical forest N2O emissions. Average instantaneous refuse pile N2O fluxes surpassed background emissions by more than three orders of magnitude (in some cases exceeding 80 000 mg N2O-N m22 h21) and generating fluxes comparable to or greater than those produced by engineered systems such as wastewater treatment tanks. Refuse-concentrating Atta species are ubiquitous in tropical forests, pastures and production ecosystems, and increase density strongly in response to disturbance. As such, LCA colonies may represent an unrecognized greenhouse gas point source throughout the Neotropics. [ABSTRACT FROM AUTHOR]

The genetics of native plants influence the success of ecological restoration, yet genetic variability of local seed collections and commercial seed releases remains unclear for most taxa. Poa secunda, a common native grass species in Intermountain West grasslands and a frequent component of restoration seed mixes, is one such species. Here, we evaluate the genetic variation of local Poa secunda collections in the context of wild populations and commercial seed releases. We evaluated AFLP markers for seven Poa secunda collections made over a 4000-hectare area and four commercial releases (High Plains, MT-1, Opportunity, and Sherman). We compare the genetic distance and distribution of genetic variation within and between local collections and commercial releases. The extent and patterns of genetic variation in our local collections indicate subtle site differences with most variation occurring within rather than between collections. Identical genetic matches were usually, but not always, found within 5 m2 collection sites. Our results suggest that the genetic variation in two Poa secunda releases (High Plains and MT-1) is similar to our local collections. Our results affirm that guidelines for Poa secunda seed collection should follow recommendations for selfing species, by collecting from many sites over large individual sites. [ABSTRACT FROM AUTHOR]

Abstract: The biogeochemical cycling of phosphorus (P) in temperate forest ecosystems is poorly understood relative to nitrogen (N) cycling because of the assumption that N is the main factor that limits plant growth. This dichotomous way of understanding nutrient regimes is likely an oversimplification of these dynamic, interacting cycles within the evermore-dynamic framework of soil development. In order to better understand P cycling in temperate deciduous forests, we sought to quantify labile (resin) P flux and determine if soil shows signs of P stress. Labile P flux was quantified in nine ambient and nine elevated P plots on unglaciated eastern deciduous forests in Eastern Ohio. Anion exchange membranes (AEMs) were deployed in situ for two weeks, in the fall and the winter. Flux values were contextualized by resin P pools, N and P mineralization, and phosphatase enzyme activities determined from soil samples collected both at the time of AEM deployment and harvest. Phosphorus flux was 0.64±0.23μgPd−1 (mean±SD) in ambient plots and 3.47±2.39μgPd−1 in amended P plots. Resin P pools were 4.16mgkg−1 and 10.26mgkg−1 in the control and elevated plots, respectively. Phosphorus turnover rate increased from one week in control plots, to 3 days in elevated P plots. Results indicate mild P stress relative to N, as N was mineralized (0.84±0.18mgNkg−1 d−1) while P was immobilized (−0.22±0.09mgPkg−1 d−1). The elevated P treatment did not increase P mineralization. Phosphatase enzyme activities were significantly suppressed by 34% with P amendment. Results suggest labile P is a shallow pool, but is rapidly cycling. [Copyright &y& Elsevier]

Summary: Phosphorus (P) for carbon (C) exchange is the pivotal function of arbuscular mycorrhiza (AM), but how this exchange varies with soil P availability and among co‐occurring plants in complex communities is still largely unknown.We collected intact plant communities in two regions differing c. 10‐fold in labile inorganic P. After a 2‐month glasshouse incubation, we measured 32P transfer from AM fungi (AMF) to shoots and 13C transfer from shoots to AMF using an AMF‐specific fatty acid. AMF communities were assessed using molecular methods.AMF delivered a larger proportion of total shoot P in communities from high‐P soils despite similar 13C allocation to AMF in roots and soil. Within communities, 13C concentration in AMF was consistently higher in grass than in blanketflower (Gaillardia aristata Pursh) roots, that is P appeared more costly for grasses. This coincided with differences in AMF taxa composition and a trend of more vesicles (storage structures) but fewer arbuscules (exchange structures) in grass roots. Additionally, 32P‐for‐13C exchange ratios increased with soil P for blanketflower but not grasses.Contrary to predictions, AMF transferred proportionally more P to plants in communities from high‐P soils. However, the 32P‐for‐13C exchange differed among co‐occurring plants, suggesting differential regulation of the AM symbiosis. [ABSTRACT FROM AUTHOR]

Ecosystem nutrient economies are commonly studied from the perspective of primary productivity in relation to nutrient availability, but a plant-specific view limits our ability to predict broader-scale patterns related to nutrient economics, such as ecosystem carbon turnover and storage controlled by soil microbial communities. Viewing nutrient economics from the heterotrophic decomposer community perspective can provide an additional perspective on ecosystem nutrient economics. We used microbial investment in extracellular enzyme production and ecoenzymatic stoichiometry theory as a conceptual framework to study nutrient economics in forest soils of the Northeast United States. Two years after experimentally increasing soil pH and phosphorus availability to offset the effects of chronic acid and nitrogen deposition, we found that belowground microbial communities were consistently investing more energy into phosphorus acquisition relative to nitrogen, in both space and time, suggesting that ecosystem demand for phosphorus might be high relative to nitrogen. Moreover, soil age and weathering, quantified by comparing glaciated vs non-glaciated regions, might not be useful predictors of nutrient economics in these forest systems. This study offers important insight into controls on ecosystem nutrient dynamics and soil microbial resource investment, information that can inform efforts to model soil microbial interactions and ecosystem carbon dynamics. [ABSTRACT FROM AUTHOR]

Many temperate forests of the Northeastern United States and Europe have received significant anthropogenic acid and nitrogen (N) deposition over the last century. Although temperate hardwood forests are generally thought to be N-limited, anthropogenic deposition increases the possibility of phosphorus (P) limiting productivity in these forest ecosystems. Moreover, inorganic P availability is largely controlled by soil pH and biogeochemical theory suggests that forests with acidic soils (i.e.,