A method is described for the isolation of metabolically active heterocysts from Anabaena cylindrica. These isolated heterocysts accounted for up to 34% of the acetylene-reducing activity of whole filaments and had a specific activity of up to 1,560 nmol of C2H4 formed per mg of heterocyst chlorphyll per min. Activity of glutamine synthetase was coupled to activity of nitrogenase in isolated heterocysts as shown by acetylene-inhibitable formation of [13N]NH3 and of amidelabeled [13N]glutamine form [13N]N2. A method is also described for the production of 6-mCi amounts of [13N]NH3. Isolated heterocysts formed [13N]glutamine from [13N]NH3 and glutamate, and [14C]glutamine from NH3 and [14C]glutamate, in the presence of magnesium adenosine 5'-triphosphate. Methionine sulfoximine strongly inhibited these syntheses. Glutamate synthase is, after nitrogenase and glutamine synthetase, the third sequential enzyme involved in the assimilation of N2 by intact filaments. However, the kinetics of solubilization of the activity of glutamate synthase during cavitation of suspensions of A. cylindrica indicated that very little, if any, of the activity of that enzyme was located in heterocysts. Concordantly, isolated heterocysts failed to form substantial amounts of radioactive glutamate from either [13N]glutamine or alph-[14C]ketoglutarate in the presence of other substrates and cofactors of the glutamate synthase reaction. However, they formed [14C]glutamate rapidly from alpha-[14C]ketoglutarate by aminotransferase reactions, with various amino acids as the nitrogen donor. The implication of these findings with regard to the identities of the substances moving between heterocysts and vegetative cells are discussed.

Landscape profiles describing the pattern of the diversity of wetlands in a region can serve as a standard for characterizing the resource and quantifying the effects of management decisions. We used hydrogeomorphic (HGM) classification to generate landscape profiles to evaluate the effects of mitigation in the rapidly urbanizing area of Portland, Oregon, USA. The profiles were produced from information on the types, numbers, and relative abundances of wetlands by HGM class. Using field data, topographic maps, and National Wetland Inventory maps, we classified 45 naturally occurring wetlands (NOWs) into regional HGM classes (depression, riverine, slope, and lacustrine .fringe) and developed the corresponding landscape profile (the NOW-Profile). We then classified 51 mitigation wetlands (MWs) and added them to the profile (the All Site-Profile) to examine changes in the regional wetland resource. The classification of MWs required development of new, atypical HGM classes to describe the unique combinations of site morphology and landscape setting found in these wetlands : depression-in-riverine-setting, in-stream-depression, and depression-in-slope-setting. Comparison of the landscape profiles showed that the structure and settings of NOWs and MWs are very different. Most NOWs fell into the regional HGM classes (91%), but most MWs fit the atypical classes (75%). Most NOWs were riverine wetlands (56%), whereas most MWs were depressionsin-riverine-setting and in-stream-depressions (33% for each class). The All Site-Profile showed an increase in the proportion of wetlands with depressional morphology, comprised mostly of MWs. Results also showed that the majority (71%) of MWs were constructed, at least partially, within existing NOWs through an exchange of wetland types and that most of these MWs (86%) belonged to the atypical classes. The approach used shows that the cumulative effects of wetland management decisions can be discerned effectively through HGM classification and development of landscape profiles. Although our results are important in documenting the landscape changes taking place in a specific region through mitigation, our approach is generally applicable for evaluating wetland management decisions and helping resource managers to make betterinformed, broad-based decisions about the wetland resource.

Abstract:We measured soil organic matter (SOM) concentrations in a large sample ~n = 95) of freshwater emergent and open water weltands in the Portland, Oregon, USA, ,area as part of a study of the ecological development of mitigation wetlands. Mean SOM concentrations were higher in naturally occurring wetlands (NOWs) than in mitigation wetlands (MWs) at 0-5 cm (SOM = 9.75 and 5.83%, respectively, p = 0.0001) and at 15-20 cm (SOM = 6.85, 4.68%, p = 0.0551). If temporal accumulation of SOM is occurring, it is slow; we found no significant relationship between SOM and wetland age (p = 0.6003) and no signilicant change in SOM concentration in soils in MWs sampled in 1987 and 1993, Concentrations of SOM were not significantly related to land use but were related to soil series, texture class, and association, and to hydrogcomorphic class. For a subset of wetlands monitorcd for hydrology, we also found a significant negative relationship between SOM and the extent of inundation by standing water. Mitigation may be leading to direct loss of SOM, probably resulting from soil management practices during project construction. We also show that hydrologic regime significantly affects SOM. Because most projects in our study were built in pre-existing wetlands and have extensive areas of open water, our results suggest that low concentrations of SOM are likely to persist. For SOM and probably for SOM-supported wetland functions, fundament~d goals of mitigation and wetland management (in-kind wetland replacement, no-net-loss of structure and function) are not being achieved, at least in the short term. The success of mitigation, in terms of SOM, could be improved by better project design and better management of soils during project construction.

Hydrologic data are essential for understanding relationships between wetland morphology and function and for characterizing landscapeTscale patterns of wetland occurrence. We monitored water levels in 45 wetlands for three years to characterize the hydrology of wetlands in the vicinity of Portland, Oregon, USA and classified wetlands by hydrogeomorphic (HGM) class to determine whether hydrologic regimes differed in wetlands in different HGM classes. We also compared hydrologic regimes in naturally occurring wetlands (NOWs) and nutigation wetlands (MWs) and in wetlands with/without a human-made water-retention structure to determine whether and how human modifications are changing the hydrology of wetlands. We found no relationship between hydrologic attributes and land use, soil association, or wetland area. We did find significant differences related to presence of a water-retention structure and to wetland type (NOW or MW). Water levels were higher and had less temporal variability and more extensive inundation ~as % wetland area) in MWs and in wetlands modified to include a retention structure. HGM class was very effective for characterizing wetland hydrology, with significant differences among HGM classes for water level and for extent and duration of inundation. For three regional classes, we found the lowest water levels and lowest extent/duration of inundation in slope wetlands, intermediate conditions in riverine wetlands, and the highest water levels and greatest extent and duration of inundation in depressions. In "'atypical" classes tGwin et al. 1999), average water level and extent of inundation were similar to conditions in depressions, but the within-site variability in water levels in depressions-in-slope-setting and in-stream-depressions was significantly smaller than in the regional classes

The principal initial product of metabolism of ['3N]N2 and '3NH4' by five diverse cyanobacteria is glutamine. Methionine sulfoximine inhibits formation of [l:JN]glutamine except in the case of Gloeothece sp., an organism with a thick sheath through which the inhibitor may not penetrate. Thus, glutamine synthetase appears to catalyze the initial step in the assimilation of N2-derived or exogenous NH4' by these organisms. ['3N]Glutamate is, in all cases, the second major product of assimilation of "IN-labeled N2 and NH4+. In all of the N2-fixing cyanobacteria studied, the fraction of "N in glutamine declines and that in glutamate increases with increasing times of assimilation of ['3N]N2 and l NH4', and (Gloeothece again excepted) methionine sulfoximine reduces incorporation of`N into glutamate as well as into glutamine. Glutamate synthase therefore appears to catalyze the formation of glutamate in a wide range of N2-flxing cyanobacteria. However, the major fraction of [I:JN]glutamate formed by Anacystis nidulans incubated with "NH4' may be formed by glutamic acid dehydrogenase. The formation of ['3N]alanine from ":3NH4+ appears to be catalyzed principally either by alanine dehydrogenase (as in Cylindrospermum licheniforme) or by a transaminase (as in Anabaena variabilis). Experiments using the radioisotope '3N haveshown that in the heterocyst-forming cyanobacterium Anabaena cylindrica the major enzymatic pathway for the asimilation of NH4', whether derived from N2 or supplied exogenously, consists of glutamine synthetase (L-glutamate:ammonia ligase [ADP forming], EC 6.3.1.2) and glutamate synthase (L-glutamate:ferredoxin oxidoreductase [transaminating], EC 1.4.7.1) (11,19). Glutamic acid dehydrogenase and alanine dehydrogenase also function in the assimilation ofexogenously supplied NH41 in this cyanobacterium, but at a much lower rate even in the presence of relatively high levels of NH4+ (11). In this respect, A. cylindrica differs from some heterotrophic, dinitrogen-fixing bacteria in which N2-derived NH4+ is assimilated principally by the glutamine synthetase/ glutamate synthase pathway, whereas, during growth in the presence of high exogenous concentrations of NHEV, the NHE is assimilated via glutamic acid dehydrogenase (6).When A. cylindrica is grown aerobically, t Preent address: