Nitrogen has long been recognized as the most commonly limiting nutrient for plant production throughout the world. Yet, air pollution has created a modern chemical climate that has sometimes ...resulted in excess ecosystem N due to N deposition. In addition, climate warming could accelerate N cycling and N export from forested ecosystems. The result is increasing interest in understanding forest ecosystem N dynamics. This study used recently delineated climatic regions in Maine to investigate the possible influences of forest species composition, and energy and moisture gradients, on laboratory indices of forest floor N cycling. Concentrations of N and C, and potential net nitrification, potential net ammonification, and potential net N mineralization, were measured on forest floor samples from 20 sites distributed across Maine in both hardwood and softwood stands. Both forest types had nearly identical concentrations of N in the forest floor (∼1.6%), but the mean C/N ratio (28) under softwoods was significantly higher than that under hardwoods (24) due to higher concentrations of total C in soils under conifers. Forest floor N concentration was a better predictor of potential net N mineralization than was total C or C/N ratio. Although the most northerly region in this study was predictably the coldest, it was also the region with the highest values for total N and N cycling indices. Wet N deposition for the region indicates N deposition differences are not responsible for this spatial pattern, and further work is warranted to explain these results. Laboratory incubation measures of potential net N mineralization were significantly correlated with in situ annual net N mineralization, which supports the use of these techniques for forest soil N status evaluations. Most site measures of mean temperatures were negatively correlated with soil N indices indicating that warmer sites had lower rates of N cycling. Although differences existed in forest floor N characteristics between climate regions, they could not be predicted by simple relationships with temperature.
Measurements of tree tissue chemistry are influenced by the precision and accuracy of laboratory analyses, sampling position within the tree, variation among replicate trees of the same species, and ...variation from year to year. We characterized these sources of uncertainty for six northern hardwood species and compared them with observed rates of long-term change. Uncertainty associated with laboratory quality control was small (1%â5%) and differed among elements, with K concentrations exhibiting the lowest accuracy and precision. Sampling position within the tree was more important for branches (the coefficient of variation was 23%) and wood (37%) than for foliage or bark (12% for both) (p < 0.001). Foliar N and P concentrations in leaves were less variable than other elements or tissue types both from tree to tree (p = 0.02) and from year to year (p = 0.03), which means that more samples would be needed to detect differences over space or time for Ca, Mg, or K in branches or wood. Concentrations of foliar N increased over 25 years at the Huntington Forest (p ⤠0.03) by > 16%. Uncertainty analysis can be used to guide the allocation of sampling effort, depending on the elements and tissue types of interest and the objectives of the study.
Celotno besedilo
Dostopno za:
BF, DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Previous greenhouse gas (GHG) assessments for the shrub willow biomass crops (SWBC) production system lacked quantitative data on the soil CO.sub.2 efflux (F.sub.c). This study quantifies the mean ...annual cumulative F.sub.c, the C sequestration in the above- and belowground biomass, and the carbon balance of the production system. We utilized four SWBC fields, which have been in production for 5, 12, 14, and 19 years. Two treatments were applied: continuous production (CP)-shrub willows were harvested, and stools were allowed to regrow, and tear-out (TO) (crop removal)-shrub willows were harvested, and stools were sprayed with herbicide following spring, crushed, and mixed into the soil. Mean annual cumulative F.sub.c were measured using dynamic closed chambers (LI-8100A and LI-8150). Across different age classes, the mean cumulative F.sub.c ranged from 27.2 to 35.5 Mg CO.sub.2 ha.sup.-1 year.sup.-1 for CP and 26.5 to 29.3 Mg CO.sub.2 ha.sup.-1 year.sup.-1 for TO. The combined carbon (C) sequestration of the standing above- and belowground biomass, excluding stems, ranged from 50.6 to 94.8 Mg CO.sub.2 eqv. ha.sup.-1. In the CP treatment, the annual C sequestration in the fine roots and foliage offsets the annual cumulative F.sub.c. Across different age classes, C balances ranged from -21.5 to -59.3 Mg CO.sub.2 ha.sup.-1 for CP and 26.5 to 29.3 Mg CO.sub.2 ha.sup.-1 for TO. The GHG potential of SWBC is about -36.3 Mg CO.sub.2 eqv. ha.sup.-1 at the end of 19 years, suggesting that the SWBC system sequesters C until termination of the crop.
Previous greenhouse gas (GHG) assessments for the shrub willow biomass crops (SWBC) production system lacked quantitative data on the soil CO sub(2) efflux (F sub(c)). This study quantifies the mean ...annual cumulative F sub(c), the C sequestration in the above- and belowground biomass, and the carbon balance of the production system. We utilized four SWBC fields, which have been in production for 5, 12, 14, and 19 years. Two treatments were applied: continuous production (CP)-shrub willows were harvested, and stools were allowed to regrow, and tear-out (TO) (crop removal)-shrub willows were harvested, and stools were sprayed with herbicide following spring, crushed, and mixed into the soil. Mean annual cumulative F sub(c) were measured using dynamic closed chambers (LI-8100A and LI-8150). Across different age classes, the mean cumulative F sub(c) ranged from 27.2 to 35.5 Mg CO sub(2) ha super(-1) year super(-1) for CP and 26.5 to 29.3 Mg CO sub(2) ha super(-1) year super(-1) for TO. The combined carbon (C) sequestration of the standing above- and belowground biomass, excluding stems, ranged from 50.6 to 94.8 Mg CO sub(2) eqv. ha super(-1). In the CP treatment, the annual C sequestration in the fine roots and foliage offsets the annual cumulative F sub(c.) Across different age classes, C balances ranged from -21.5 to -59.3 Mg CO sub(2) ha super(-1) for CP and 26.5 to 29.3 Mg CO sub(2) ha super(-1) for TO. The GHG potential of SWBC is about -36.3 Mg CO sub(2) eqv. ha super(-1) at the end of 19 years, suggesting that the SWBC system sequesters C until termination of the crop.
The development of short-rotation intensive cultural (SRIC) willow systems as a source of bioenergy and bioproducts is growing in the northeastern and midwestern United States. Important data for ...sustainable management such as nutrient removal and nutrient use efficiency in willow bioenergy plantations is lacking. This study reports wood biomass production, annual removal of nutrients, and nutrient use efficiency in experimental plantings of SRIC willow and poplar at Tully, New York. Effects of clone, fertilization, irrigation, planting density, and harvest cycle were analyzed.
Annual biomass production of 15–22
dry
Mg/ha
removed 75–86, 10–11, 27–32, 52–79 and 4–
5
kg/ha/year
of N, P, K, Ca and Mg, respectively. For all the variables studied, the responses depended on clone. Fertilization and irrigation increased rates of nutrient removal by means of increased biomass production. Unlike planting density, harvest cycle significantly affected rates of nutrient removal and nutrient use efficiency. For clone SV1 (
Salix dasyclados), an irrigated and fertilized planting with a density of 36,960
trees/ha harvested on a 3-year rotation had the highest biomass production and nutrient use efficiency, and the lowest rates of nutrient removal. The annual harvest cycle had the lowest nutrient use efficiency and the highest annual removal of nutrients suggesting that this choice would be most appropriate for biomass crops that are to be used as buffer strips to manage nutrient runoff from agricultural fields. An appropriate choice of clone, planting density, and harvest cycle could tailor the rates of nutrient removal and nutrient use efficiency to match the objective of the planting.
Melanin is a ubiquitous biological pigment found in bacteria, fungi, plants, and animals. It has a diverse range of ecological and biochemical functions, including display, evasion, photoprotection, ...detoxification, and metal scavenging. To date, evidence of melanin in fossil organisms has relied entirely on indirect morphological and chemical analyses. Here, we apply direct chemical techniques to categorically demonstrate the preservation of eumelanin in two > 160 Ma Jurassic cephalopod ink sacs and to confirm its chemical similarity to the ink of the modern cephalopod, Sepia officinalis . Identification and characterization of degradation-resistant melanin may provide insights into its diverse roles in ancient organisms.
Objectives/Hypothesis Fistulae of the otic capsule occur in approximately 10% of cholesteatoma cases. Preoperative imaging of this complication is valuable in limiting intraoperative morbidity. ...Three‐dimensional virtual endoscopic imaging provides a new method for analysis of conventional computed tomography (CT) imaging data. The purpose of the study was to examine the feasibility and efficacy of this technique in detecting labyrinthine fistulae caused by cholesteatoma.
Study Design Retrospective case study.
Methods Fifteen patients with surgically confirmed lateral semicircular canal fistula and preoperative CT scan were included. Scans meeting inclusion criteria were imported into a software program for production of virtual endoscopic images. Dehiscent and normal lateral semicircular canals were navigated while varying threshold values for surrounding bone. Changes in threshold values produce the effect of thickening or thinning the bone enveloping the semicircular canal. Threshold parameters that produced easy circumnavigation (“open”) and intact inner surface of the lateral canal (“closed”) were recorded.
Results The fistula group demonstrated a significantly lower “closed” threshold level and, consequently, a greater range of navigation between “open” and “closed” thresholds. Intrasubject absolute differences in threshold values between normal and abnormal ears appeared to be the most accurate method for detecting a fistula. The suggested imaging parameters displayed an overall sensitivity for fistula detection of 67% with a specificity of 93%.
Conclusions The three‐dimensional virtual endoscopic algorithm shows promise as a method for confirmation of otic capsule dehiscences. Sensitivity for detection is suboptimal but can be improved by alterations in image acquisition parameters.
Nitrate (NO3−) leaching to ground water poses water quality concerns in some settings. Riparian buffers have been advocated to reduce excess ground water NO3− concentrations. We characterized ...inorganic N in soil solution and shallow ground water for 16 paired cropland‐riparian plots from 2003 to 2005. The sites were located at two private dairy farms in Central New York on silt and gravelly silt loam soils (Aeric Endoaqualfs, Fluvaquentic Endoaquepts, Fluvaquentic Eutrudepts, Glossaquic Hapludalfs, and Glossic Hapludalfs). It was hypothesized that cropland N inputs and soil‐landscape variability would jointly affect NO3− leaching and transformations in ground water. Results showed that well and moderately well drained fields had consistently higher ground water NO3− compared to more imperfectly drained fields receiving comparable N inputs. Average 50‐cm depth soil solution NO3− and ground water dissolved oxygen (DO) explained 64% of average cropland ground water NO3− variability. Cropland ground water with an average DO of <3 mg L−1 tended to have <4 mg L−1 of NO3− with a water table depth (WTD) of ≤1 m. Water table depth and DO explained 83% of ground water NO3− variability among buffers. More poorly drained buffers had low ground water NO3− and DO, a shallow WTD, and higher ground water ammonium and soil organic matter. Chloride patterns indicated that dilution was minor in most buffers, suggesting that denitrification losses were important. Soil‐landscape factors strongly influenced NO3− behavior and suggest the importance of accurately characterizing soil variability along cropland‐riparian zones.
The basic arrangement of limbs in euarthropods consists of a uniramous head appendage followed by a series of biramous appendages. The body is divided into functional units or tagmata which are ...usually distinguished by further differentiation of the limbs. The living horseshoe crabs are remnants of a much larger diversity of aquatic chelicerates. The limbs of the anterior and posterior divisions of the body of living horseshoe crabs differ in the loss of the outer and inner ramus, respectively, of an ancestral biramous limb. Here we report a new fossil horseshoe crab from the mid-Silurian Lagerstätte in Herefordshire, United Kingdom (approximately 425 Myr B.P.), a site that has yielded a remarkably preserved assemblage of soft-bodied fossils. The limbs of the new form can be homologized with those of living Limulus , but retain an ancestral biramous morphology. Remarkably, however, the two limb branches originate separately, providing fossil evidence to suggest that repression or loss of gene expression might have given rise to the appendage morphology of Limulus . Both branches of the prosomal limbs of this new fossil are robust and segmented in contrast to their morphology in Cambrian arthropods, revealing that a true biramous limb was once present in chelicerates as well as in the mandibulates.
In shrub willow biomass crop (SWBC) production systems, the soil CO sub(2) efflux (F sub(c)) component in the carbon cycle remains poorly understood. This study assesses (i) differences of F sub(c) ...rates among the 5-, 12-, 14-, and 19-year-old SWBCs with two treatments: continuous production (regrowth) willow fields that were harvested and allowed to regrow, and willow fields that were harvested, killed, and then stools and roots were ground into the soil (removal); (ii) temporal and spatial variations of F sub(c) rates; (iii) root respiration contributions to total F sub(c); and (iv) climatic variables affecting F sub(c). During the growing season (May to September), F sub(c) rates showed no statistically significant differences across different ages (P = 0.664), and between treatments (P = 0.351); however, there was an interaction between age and treatment (P = 0.001). Similarly, during the dormant season (October to April), F sub(c) rates revealed no statistically significant differences across different ages (P = 0.305) and treatment interaction with age (P = 0.097). F sub(c) rates differed significantly (P < 0.001) among different times of the day and times of the year. F sub(c) rates, between 00 and 1059 h, between 1100 and 1659 h, and between 1700 and 2400 h displayed consistency from May to November; however, F sub(c) rates in these three time intervals showed significant differences (P < 0.0001). In December, F sub(c) rates remained constant over 24 h. F sub(c) rates demonstrated higher temporal and spatial variations among willow age classes than between regrowth and removal treatments. Temporal and spatial variations of F sub(c) were higher during the dormant season than during the growing season. The proportion of root respiration to total F sub(c) ranged from 18 to 33% across age classes. F sub(c) rates showed strong association with soil and air temperatures, and relative humidity.
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