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Striking spatial patterns in stable isotope ratios (isoscapes) and elemental ratios (stoichioscapes) of seagrass leaves and the water column nutrients indicate general P-limitation of both water column and benthic primary productivity on the Bermuda Platform, and they highlight the role of the Bermuda Islands as a source of N and P. We found consistent differences among the four seagrass species (Syringodium filiforme, Thalassia testudinum, Halodule sp. and Halophila decipiens) in the N, P, δ13C and δ15N of leaf tissues. The δ15N of seagrass leaves was especially variable, with values from −10.1 to 8.8 ‰, greatly expanding the reported range of values for all seagrass species globally. Spatial patterns from both the water column and the seagrass leaves indicated that P availability was higher near shore, and δ15N values suggest this was likely a result of human waste disposal. Spatially contiguous areas of extremely depleted seagrass 15N suggest unique N sources and cycling compared to other seagrass-dominated environments. Seagrass N : P values were not as far from the stoichiometric balance between N and P availability as in the water column, and there were no strong relationships between the water column N : P and the seagrass N : P. Such isoscapes and stoichioscapes provide valuable ecogeochemical tools to infer ecosystem processes as well as provide information that can inform food web and animal movement studies.

Using a calibrated bio-optical model we determined that the optical water quality conditions in several nitrogen-impaired embayments and in one unimpaired system were within the range of values known to support eelgrass growth. We also used the model to identify a range of light requirements for eelgrass (Zostera marina). Higher eelgrass light requirements, expressed as a percentage of surface-incident irradiance, corresponded with higher sediment organic matter content. These results corroborated findings by previous studies which indicate a generalized relationship: seagrasses growing in turbid conditions with poorer water and sediment quality have higher light requirements than those growing in less degraded conditions. The mechanistic reason for the variation in light requirements is still not completely explained and cannot be attributed to a single independent variable. Varying light requirement have important implications for eelgrass protection and should be considered when setting restoration targets for eelgrass in water quality and nitrogen remediation programs.

In 1994, 1995, and 1996, seagrasses in 46 of the 89 coastal embayments and portions of seven open-water near-shore areas in Massachusetts were mapped with a combination of aerial photography, digital imagery, and ground truth verification. In the open-water areas, 9,477.31 ha of seagrass were identified, slightly more than twice the 4,846.2 ha detected in the 46 coastal embayments. A subset of the 46 embayments, including all regions of the state were remapped in 2000, 2001, and 2002 and again in 2006 and 2007. We detected a wide range of changes from increases as high as 29% y−1 in Boston Harbor to declines as large as −33% y−1 in Salem Harbor. One embayment, Waquoit Bay, lost all of its seagrass during the mapping period. For the 12-year change analysis representing all geographic regions of the state, only three embayments exhibited increases in seagrass coverage while 30 of the original 46 embayments showed some indication of decline. For the decadal period, rates of decline in the individual embayments ranged from −0.06% y−1 to as high as −14.81% y−1. The median rate of decline by region ranged from −2.21% y−1 to −3.51% y−1 and was slightly less than the recently reported global rate of decline for seagrasses (−3.7% y−1). Accounting for the gains in three of the embayments, 755.16 ha (20.6%) of seagrass area originally detected was lost during the mapping interval. The results affirm that previously reported losses in a few embayments were symptomatic of more widespread seagrass declines in Massachusetts. State and Federal programs designed to improve environmental quality for conservation and restoration of seagrasses in Massachusetts should continue to be a priority for coastal managers.

Shallow seagrass beds worldwide are being negatively impacted by human activities. Damage by boats includes anchor scars, propeller scars, and hull groundings. In some Thalassia testudinum-dominated systems, vessel damage may persist for years or decades, and even small scars may leave seagrass habitat susceptible to severe erosion by wind and wave-driven currents and storms. Cost-effective techniques for restoration in these erosion-prone systems must include sedi- ment replacement and stabilization to best enhance seagrass recovery. We conducted 2 experiments to address the effects of excavation depth and sediment filling on seagrass and macroalgal recovery into small-scale disturbances such as propeller scars. Recovery in excavations ≥20 cm deep took 2 to 5 yr longer than recovery in shallower disturbances (10 cm). Seagrasses were able to grow in native limestone fill material (diameter 0.6 cm), although the compensatory response of Syringodium filiforme was dampened.

The endangered seagrass Halophila johnsonii Eiseman, exhibits high-light adapted photophysiology consistent with its distribution in intertidal and shallow subtidal (0–3 m) coastal-lagoon habitats along 200 km of southeastern Florida. To examine the short-term responses of this seagrass to three controlled-irradiance treatments (PAR + UVA + UVB [full spectrum], PAR + UVA, and PAR only), greenhouse-acclimated plants were transferred to outdoor mesocosms during July–August 2002. Chlorophyll fluorescence, UV fluorescence, and samples for pigment extraction were collected in the greenhouse, prior to moving the plants outside and on days 1, 2, 3, 4, 6, 10, and 21 of the 24-day experiment. Typical of sun-adapted plants, effective quantum yields measured by pulse-amplitude modulated (PAM) fluorometry were relatively low in all treatments, ranging from 0.46 ± 0.09 (PAR only) to 0.58 ± 0.08 (PAR + UVA + UVB). In the PAR only treatments, there were strong effects on days 1 and 4, presumably because the irradiance in the greenhouse not only lacked all λ

The threatened seagrass Halophila johnsonii Eiseman coexists subtidally with H. decipiens Ostenfeld in southeastern Florida, but only H. johnsonii also oc- curs intertidally. Pulse amplitude modulated fluorome- try and fiber-optic spectrometry were used to investigate the photobiology of two populations of H. johnsonii and H. decipiens in an attempt to explain these distribution patterns. Maximum photosynthetic quantum yields (Fv/ Fm) were measured in situ as a function of depth dis- tribution within, and between, these two species at two sites (Jupiter Sound, 26� 57¢N; 80� 04¢W, and northern Biscayne Bay, 25� 55¢N; 80� 07¢W) along the east coast of Florida, USA, during 6-10 March 2001. Reciprocal transplants at the northern site were used to evaluate the plasticity of photosynthetic patterns and pigment absorption spectra and to gain insights into the mecha- nisms responsible for variations in the observed depth- distribution patterns. Subtidal-population Fv/Fm values were generally higher for H. johnsonii than for H. deci- piens, at both sites. At the northern site, intertidal H. johnsonii had significantly lower Fv/Fm (0.494±0.138) than both subtidal H. johnsonii (0.696±0.045) and subtidal H. decipiens (0.668±0.048). In contrast, at the southern site intertidal H. johnsonii had the highest Fv/ Fm (0.663±0.047) and were the largest plants. Fv/Fm values of subtidal plants of both species decreased when they were transplanted into shallow, intertidal beds. Correspondingly, Fv/Fm increased for intertidal H. johnsonii transplanted into the subtidal, 2 m deep beds. Rapid light curves indicated that H. decipiens had lower maximum relative electron transport rates (RE- TRmax) than did H. johnsonii. In addition, the onset of photoinhibition occurred at lower irradiances for H. decipiens (537-820 lmol photons m )2 s )1 ) compared to H. johnsonii (1141-2670 lmol photons m )2 s )1 ). RETRmax values decreased for intertidal H. johnsonii transplanted into subtidal beds, but they increased for both species when transplanted from subtidal to inter- tidal beds. Absorption spectra for the acetone-soluble leaf pigments of intertidal H. johnsonii exhibited a dominant peak near 345 nm; this UV peak was 30% lower for subtidal plants. Pigment absorption spectra for H. decipiens lacked the 345 nm peak and absorbances, normalized to leaf pairs, were lower across the spectrum. Our results indicate that photosynthetic tolerance to higher irradiances and presence of UV-absorbing pig- ments (UVP) in H. johnsonii may allow this species to exploit the shallowest waters without competition from the closely related, but UVP-lacking H. decipiens.

Seagrass habitats exhibit high structural variability at local (

Unusually dense aggregations of the sea urchin Lytechinus variegatus overgrazed at least 0.81 km 2 of seagrass habitat in Outer Florida Bay (USA) between August 1997 and May 1998. Initially, sea-urchin densities were as high as 364 sea urchins m -2 , but they steadily declined to within a range of 20 to 50 sea urchins m -2 by December 1998. Prior to this event, sea-urchin densities were 95 % of the short-shoot apical meristems were removed by sea-urchin grazing in our study area. Such extensive loss may severely limit recovery of this seagrass community by vegetative reproduction. Effects of the removal of seagrass biomass have already resulted in the depletion of epifaunal-infaunal mollusk assemblages and resuspension of fine-grained (

Optimum or higher levels of soil potassium have been implicated with a decline in the incidence of disease and insect pests in several plant species. Light intensity is recognized as an important environmental factor that influences plant morphological and physiological processes. The objectives of this field-cage study were to determine the effects of soil potassium levels and reduced light intensities on the insect resistance and growth characteristics of a Mexican bean beetle, Epilachna varivestis Mulsant, resistant soybean, Glycine max (L.) Merr., line and to evaluate foliar concentrations of 12 nutrients in plants growth under the imposed physiological stresses. The soybean line MBB 85-116 was grown on a Matapeake silt loam soil during 1989, 1990, and 1991. Variables were three rates of soil K and three levels of light, obtained through the use of field cages (3.66 m2) and shade cloth. Field cages were infested with Mexican bean beetle adults at a rate of 5-8 beetles per 0.3 m of row. Soil K, Mg, Ca, and pH were significantly higher at the high K rate. Potassium was the only measured foliar nutrient significantly greater at the high K rate. Elevated levels of soil potassium had no effect on Mexican bean beetle feeding damage and little effect on seed yield. Reduced light and increased Mexican bean beetle feeding damage resulted in significant changes in concentrations of 10 foliar nutrients. However, none of the foliar nutrients was directly associated with Mexican bean beetle resistance. A 58% reduction in light resulted in a 6.3% increase in Mexican bean beetle feeding damage. These results indicated that the factors responsible for insect resistance in MBB 85-116 are altered by light intensity.

The objective of this study was to evaluate F 4 lines in both row- and hill-plots for agronomic traits in order to test the effectiveness of selecting high-yielding S 1 soyabean (Glycine max (L.) Merr.) lines selected in hill-plots after two cycles of recurrent selection. There was a cumulative seed yield loss of 197 kg/ha from cycle C 0 to C 2 when the selections were evaluated in row-plots but a cumulative gain in seed yield of 533 kg/ha from C 0 to C 2 was observed when the selections were evaluated in hill-plots. Ranking of seed yield between row- and hill-plots showed a non-significant association, but correlation coefficients between the two methods of testing were positive and highly significant for height, lodging and maturity. Thus, evaluation of height, lodging and maturity can be carried out effectively with either method of planting. There were increases in plant height, in lodging scores and in days to maturity with each cycle of selection. These changes were evident in both row and hill-plots. The lack of seed yield response to selection as measured in row-plots and a non-significant association between the two plot arrangements indicated that seed yield evaluation by S 1 testing in hill-plots was not a reliable procedure in the identification of productive genotypes

Seagrass transplanting experiments were conducted in Back Sound, Carteret County, North Carolina, and Tampa Bay, Pinellas County, Florida. In Florida, we compared three planting methods (cores, stapled bare root, and peat-pot plugs) for shoot addition rate coverage, and labor cost (harvest, fabrication, and deployment) using Halodule wrightii. Only planting methods and development rates were recorded for Syringodium filiforme. Fertilizer additions were made to peat-pot plantings of H. wrightii and Zostera marina in both North Carolina and Florida. Exclosure cages were tested to attempt to minimize bioturbation of H. wrightii and Z. marina in both North Carolina and Florida. Recovery from harvesting impacts to existing, natural beds of S. filiforme and H. wrightii were assessed in Florida. The peat-pot method was about 35% and 63% less expensive in work time than staples and core tubes, respectively. Response to fertilizer additions was masked by inconsistent release properties of the fertilizer, although some indication of positive response to phosphorus fertilizer in sediments with low carbonate content, and nitrogen in general, was detected. Complete loss of peat pots, largely ascribed to bioturbation, occurred in a large planting (Tampa Bay) but not in nearby smaller ones where exclosure cages were used. Cages did not affect planting unit survival in North Carolina but did improve number of shoots per planting unit in one of three experiments. No detrimental effects of cages were noted. Existing natura beds used to harvest transplanting stock in Tampa Bay recovered from excavations as large as 0.5 m2 in one year. Significant cost savings were found to be possible through methodological improvement, including planting techniques, bioturbation exclusion, and possibly fertilizer additions.

Differences in host plant quality to insect herbivores may be explained by variations in secondary plant compounds and plant nutrients. Soyban [Glycine max (L.) Merr.] germplasm resistant to foliar feeding insect pests have been identified and developed. Investigations into the chemical basis of this resistance have met with limited success [...]

(...) The objective of this study was to evaluate effects of stem termination, time of flowering, maturity, and various combinations of these characteristics on seed germination and infection of seed by P. longicolla. The cultivar Clark and seven of its near-isogenic lines differing in stem termination (indeterminate vs. determinate vs. semideterminate), time of flowering (normal vs. delayed vs. late), and maturity (normal vs. late) were evaluated for seed-borne disease in Maryland and two locations in 1984 and 1985 and one location in 1986. (...)

Race specificity may be involved in the reactions of certain soybean [ (L.) Merr.]cultivars previously characterized as tolerant to f. sp. Kuan & Erwin (). The objectives of this study were to determine if an inoculumlayer procedure could be used to differentiate race-specific reactions among soybean cultivars characterized as tolerant to Pmg and to distinguish root resistance reactions associated with tolerance from those conditioned by the gene. An inoculum-layer procedure was used in the greenhouse to determine the reactions of 21 soybean cultivars to Races 1 and 10 of . Some cultivars characterized as tolerant to Pmg and the cultivar CNS with the gene, which conditions race-specific root resistance to these races, were included to provide a comparison between various levels of seedling tolerance and root resistance. Seeds were planted 2.5 or 5.0 cm above an inoculum layer of lima bean agar cultures. Cultivar reaction to was recorded as percent survival of emerged seedlings 14 d after planting. Cultivars exhibited different levels of survival with Races 1 and 10, with variation also at the 2.5- and 5.0-cm inoculum layer depths. Seedling survival with Race 10 was significantly (P < 0.05) higher at the 5.0-cm compared with the 2.5-cm inoculum layer, whereas there was no consistent difference in survival with Race 1 among cultivars at the two depths. Nine cultivars exhibited high levels of seedling survival with Race 1 that were comparable with CNS. Only CNS and 'Emerald' survived both Races 1 and 10. Since the reactions of Emerald closely resemble those of CNS, they may be conditioned by the Rps2 gene. Results of the experiments indicate that it is difficult to distinguish between race-specific root resistance and high levels of tolerance when using the inoculum-layer test with certain cultivar/race/inoculum depth combinations. Limited information is available concerning differences in the expression of root infection between cultivars with race-specific root resistance and those with high levels of tolerance. The results emphasize the need for improved techniques to differentiate tolerance and root resistance, and to characterize precisely soybean lines or cultivars lacking major resistance genes.

Improved seed yield in the soybean [Glycine max (L.) Merr.] may result from selection to increase the N₂-fixing ability of the crop. To investigate that possibility, broad-sense heritabilities of total and fixed N in the seed were estimated for two F₂ soybean populations. One population was derived from a cross of high (‘Ware’) and low (D66-5566) N₂-fixing parents and was grown years. The second population, grown in 1 year only, was derived from a cross of intermediate N₂-fixing parents (‘Williams’ and ‘Calland’). Both populations and their parents were grown in ¹⁵N-labeled soil in the field along with ‘Clark’ rj₁rj₁ nonnodulating plants as controls. The amount of fixed N in the mature seed at harvest was determined by the ¹⁵N-dilution method for individual plants. Broad-sense heritability estimates of fixed N content of the seed ranged from 0.53 to 0.60. Estimates for percentage of fixed seed N varied from 0.12 to 0.43. Estimates for total seed N [as a weight (from 0.49 to 0.61) and as a percentage (from 0.20 to 0.87)], for seed yield (from 0.52 to 0.59), and for plant weights (from 0.57 to 0.62) are also reported. strong positive association was noted between seed dry weight and fixed N content of the seed (r = 0.99). These results suggest that improving N₂ fixation in the soybean is feasible through selection based on the mass of fixed N in the seed. Selection for high seed yield will probably likewise result in the identification of plants with a high rate of N₂ fixation.

Small-scale, on-farm oil production and extraction were evaluated for four oilseed crops produced in full-season or double cropping systems. Economic feasibility was determined by calculating the per-liter cost of vegetable oil based on total costs of production and processing as well as credits for feeding values of the oilseed residues. Per-liter costs ranged from a high of $1.76 for soybean oil (no-till, full-season soybeans) to a low of $0.97 for the conventionally tilled winter rape/soybeans cropping system (processing labor not included) for a 25% vegetable oil/diesel fuel mix for a typical 240-ha farm. When processing labor changes were included, all per-liter costs were increased accordingly. Total energy and fuel energy inputs and outputs were analyzed for winter rape, soybean, sunflower, and peanut oils. All four oilseeds yielded a positive energy balance (output greater than input). The total energy output-to-input ration range from 2.62 for conventional tillage sunflowers to 7.47 for no-till soybeans. The fuel energy output-to-input ratio ranged from 1.43 for conventionally tilled full-season soybeans to 13.52 for the no-till winter rape/sunflower cropping system.

Leaf tissue of 49 F5 soybean [Glycine max (L). Merr.] lines derived from a cross between an experimental line, MBB 80-115, and the cultivar ‘Ware’ were fed to Mexican bean beetle (MBB), Epilachna varivestis Mulsant, larvae in laboratory studies. The parents, Ware and MBB 80-115, and PI 171451 which was the original source of MBB resistance were included as checks in all studies. Laboratory tests suggested the presence of non-preference (antixenosis) and/or antibiosis in the resistant soybean genotypes and were efficient in identifying most resistant lines and mechanisms of resistance. The larvae reared on leaves of lines 119-2 and 119-11 took longer to pupate and reach the adult stage and had fewer numbers of emerging adults. Leaf tissue of selected lines was analyzed for the elements phosphorus, calcium, potassium, magnesium, and silicon to determine if any of these elements are associated with the feeding response and might serve as a quick index of selection for plant resistance. Calcium, phosphorus, and potassium content was each negatively correlated with pupal weight (r = −0.23**, −0.26**, −0.20*, respectively). No significant correlations were observed between silicon and magnesium content and pupal weight. The progeny line 119-2 which demonstrated a high level of antibiosis had a higher calcium, phosphorus, and magnesium content than either parent or the resistant PI 171451 and also had a potassium content that was similar to that of the resistant PI. PI 171451 had the lowest silicon content of all lines tested.

The difference method of measuring nitrogen fixation in soybeans ( Glycine max (L.) Merr.) relies on the assumption that nodulated and nonnodulated plants utilize equal amounts of soil nitrogen (N). The validity of this assumption has been challenged by reports of differences in root system size for nodulated and nondulated and nondulated genotypes. This field study, using a 15 N-tracer technique under conditions with reduced available soil N, was conducted to: (1) evaluate thee assumption that the nodulated and nonnodulated soybean genotypes utilize equal amounts of available soil N, (2) compare the root system mass in the nodulated and nonnodulated genotypes, and (3) determine the relationship between soil-N accumulation in the shoots and root dry-matter accumulation. In 1977 and 1978, one nonnodulated and six nodulated soybean genotypes were grown in replicated field plots labeled with 15 N on an Aqualfic Normudult (silt loam) soil. Plantts were sampled at 49, 70, and 91 days after planting and at full maturity in 1977, and at 62 and 112 days after planting in 1978. Shoot and root dry-matter accumulation, seed yield (in 1977 only), total-N concentration, total-N accumulation, soil-derived N accumulation, and fixed-N accumulation were measured. Significant differences were present among genotypes both years for all variables except soil-derived N accumulation in the shoots. Shoot and root weights for the nonnodulated genotype could not be distinguished statistically from the nodulated genotype either year, although the seed yield for the nonoddulated was only 37% of the mean of yields for the nodulating genotype in 1977. Root dry weight was positively correlated with shoot dry weight ( r e = 0.90 for, 1977, r w = 0.86 for 1978), seed yield ( r w = 0.79 for 1977), shoot total-N accumulation ( r w = 0.82 for 1977, r w = 0.68for 1978), soil-derived N accumulation in the shoots ( r w = 0.71 for 1977), and accumulation of fixed-N in the shoots ( r w = 0.84 for 1977, r w = 0.85 for 1978). Results of this study support the assumption of equal utilization of soil-derived N by nodulated and nonnodulated soybean genotypes. The use of the difference method under conditions of low N fertility is appropriate for preliminary studies and in areas where 15 N-tracer techniques are not available.

In an effort to obtain a greater understanding of the mechanisms of action for air pollutants on yield-limiting processes in crop plants, studies were conducted in the field and greenhouse in 1979 to investigate the effects of O₃ and SO₂ exposures on nodule activities in roots and chlorophylls a and b contents in leaves of soybeans [Glycine max (L.) Merr.]. Six cultivars of soybeans were exposed 4 h d⁻¹ for 5 successive days during flowering and pod development to the combination of 6.7 µmol m⁻³ O₃ and 11.1 µmol m⁻³ SO₂ in activated charcoal-filtered air. Acetylene reduction procedures were used to assay nodule activities. Significant differences (P < 0.1) were observed in total nodule activity (TNA) per plant for treatments and cultivars in combined analysis of variance (ANOVAs) for two greenhouse studies and two exposure dates in the field; however, treatment × cultivar interactions were nonsignificant in all cases. Compared with filtered air controls, the air pollution treatment reduced TNA by an average of 16.4 and 27.4% in the greenhouse and field studies, respectively. Specific nodule activities (SNA) were unaffected by the treatments in both studies. In the greenhouse studies, the O₄ and SO₂ treatment lowered the chlorophyll a content by 14.1%, but no significant differences were observed in the field study. Chlorophyll b contents were unaffected by treatments in both investigations. In these studies, the sensitivity of changes in chlorophyll contents in soybean leaves following exposures to O₃ and SO₂ at concentrations found in the atmosphere were found to be too low to be of practical value for screening plants for tolerance to air pollutants.

The effects of temperature on growth in broth and soil and on competition for nodule formation betweenRhizobium japonicum serotypes USDA 76 and 94 compared to 6 and 110 were studied. Increasing root temperatures of Lee soybean from 20 to 35°C increased the competitiveness of 76 and 94 relative to 6 and 110 for all inoculum ratios such that at 30 and 35°C symptoms ofRhizobium-induced chlorosis appeared. Tolerance to elevated temperatures was exhibited by 76 and 110, but not 94 and 6 in broth and soil which suggested that increased competitiveness of 76 and 94 at high soil temperatures was not dependent upon growth at elevated temperatures. Nodulation and vegetative growth of Lee soybeans were at a minimum at 20°C and optimum at 30°C. Differences in competitiveness of 6 to previous studies indicated the need to standardize temperatures of assays. Differences in growth responses of 76 and 94 to temperature from a previous study suggested a confounding effect on different carbon sources in growth media.

Twin seedlings were observed in the progeny of malesterile (msms) plants of (L.) Merrill from natural crossing blocks. Of the seedlings observed, more than 4% were embryonic twins. Triplets and conjoined individuals were also found. Cytological examinations of root-tip preparations revealed that most individual plants from twin sets were diploid (2n=40). However, diploid: haploid and diploid:triploid twin pairs were also identified. Genetic analysis of a marker trait in the twin seedlings and their selfed progeny indicated that diploid diploid sets originated primarily after cross-fertilization. Evidence suggests that the mechanism underlying the development of these twins involves a cleavage of the zygote or the development and fertilization of multiple embryo sacs within an ovule.

Seagrasses are a closely related group of 50 species of monocotyledonous angiosperms divided between two families and 12 genera which have evolved the characteristics required to colonize successfully the world’s shallow coastal zone (den Hartog, 1970). Seagrasses are the only vascular plants that can complete their entire life cycle fully submerged in a saline environment and are distinguished by their erect, linear grass-like leaves which extend from a rhizome that is usually anchored in unconsolidated sediments by an extensive root system (Figure 45.1). To obtain sufficient light energy for photosynthesis these plants grow in relatively shallow water.