Showing papers on "Growing season published in 1983"
TL;DR: The early emergence of most species, including three—fourths of the 35 species fruiting in the late rainy season, indicated that the early rainy season was the optimal time to emerge, and dormancy is the primary mechanism controlling time of germination.
Abstract: Seed germination in the seasonal tropical forest on Barro Colorado Island, Panama, was studied at the community level to (1) determine the seasonal timing of germination of the community, (2) identify primary selective factors controlling timing of germination, (3) determine the relative importance of dormancy vs. timing of seed dispersal as mechanisms controlling timing of germination, (4) examine inter— and intraspecific components of variance in length of dormancy, and (5) identify major seed germination syndromes. Three community—level measures of seedling emergence indicated that there was a unimodal community peak in germination within the first 2 mo of the 8—mo—long rainy season. Of the °185 dicot, mostly woody, species germinating each year, the median time of emergence of 75% of the species occurred within the 1st 3 mo. There was a unimodal peak in germination in pioneer tree species, lianas, canopy trees, wind— and animal—dispersed species, and seedlings with and without persistent seed reserves. In contrast, there was no distinct peak period of emergence in understory species and shade—tolerant tree species. Initial seedling height of species emerging sequentially throughout the rainy season did not increase. The early emergence of most species, including three—fourths of the 35 species fruiting in the late rainy season, indicated that the early rainy season was the optimal time to emerge. Maximizing the length of the first growing season was not an important factor selecting for early emergence, because later—emerging species did not compensate for the shorter growing season by being larger at germination or by having seed reserves for rapid growth. Seedling—seedling competition is a primary biotic factor selecting for early emergence in pioneer species growing in the intensely competitive light—gap habitat. In shaded understory habitats, where competition among seedlings is much less intense, understory and shade—tolerant tree species emerged throughout the rainy season. Mean length of dormancy (MLD),the time between sowing and germination, of 157 woody dicot species on Barro Colorado Island ranged from 2 to 370 d. In over half the species, MLD exceeded 4 wk; hence, delays in germination are common. The season in which seeds were dispersed and the dispersal mechanism explained small but significant portions of the variance in MLD among species; life form explained none; but differences among three germination syndromes explained two—thirds of this variance. In the delayed—rainy syndrome (18% of all species) seeds were dispersed in the rainy season but were dormant until the beginning of the next rainy season, 4—8 mo later. Dormancy is the primary mechanism controlling time of germination. In the delayed—rainy syndrome and the intermediate—dry syndrome which follows, the length of the dormant period decreased as the interval between seed dispersal and the beginning of the rainy season decreased. In the intermediate—dry syndrome (42% of all species) seeds were dispersed during the during the dry season and remained dormant until the beginning of the rainy season. Seeds are primarily dispersed 1—2 mo before the beginning of the rainy season, which reduces the number of false germination cues encountered and decreases the length of time seeds are exposed to postdispersal predation while dormancy prevents germination during dry season rains. In the rapid—rainy syndrome (40% of all species) seeds were dispersed in the rainy season and germinated during, but not early in, that season. Dormancy has been replaced entirely by timing of dispersal as a mechanism controlling time of germination. Half of these species germinated in <2 wk, the rest in 2—16 wk.
392 citations
TL;DR: S. juncea had a smaller minimum opening size for seedling establishment than S. canadensis, although both species grew and survived best in the largest openings made in the experiment, which was an abandoned field in southwestern Michigan, U.S.A.
Abstract: We investigated the effects of size of opening in the vegetation and litter cover on seedling establishment of two species of goldenrods (Solidago spp.) in an abandoned field in southwestern Michigan, U.S.A. Seeds of S. canadensis and S. juncea were sown into clipped plots, ranging from 0 cm (control, unclipped) to 100 cm in diameter, with and without litter. Seedling emergence, survival and growth were followed for one year. Soil moisture was not significantly different among the opening sizes, but, within a size, tended to be lower when litter was removed. Light intensity at the soil surface was positively related to opening size early in the growing season, but later in the growing season reached a maximum in intermediate-sized openings and then leveled off.
244 citations
TL;DR: It is concluded that N2-fixation is very important to Prosopis at six of seven sites in the Sonoran Desert and at the site where prosopis did not appear to be fixing N2, N2 -fixation was important only for legumes of the sub-family Papilionoideae.
Abstract: The 15N abundance of tissues of five Prosopis specimens at our primary study site (a Prosopis woodland at Harper's Well in the Sonoran desert of Southern California) was determined over two growing seasons 1980 and 1981. The 15N abundance of soil and of tissues of presumed non-N2-fixing (control) plants was also measured. Prosopis tissues were significantly lower in 15N than either soil N or corresponding tissues of presumed non-N2-fixing plants which derive their N entirely from soil. Soil N was also significantly higher in 15N than atmospheric N2. We conclude that it is feasible to use variations in the natural abundance of 15N as an index of N2-fixation in this kind of ecosystem, and that N2-fixation is of considerable importance to Prosopis growing at this site.We also determined the 15N abundance of leaf tissue of presumed N2-fixing and control plants growing at the same site at six additional sites (five in the Sonoran desert of southern California and one in Baja California, Mexico near the town of Catavina). Four of these additional sites were dominated by Prosopis and two were mixed communities. There were statistically significant differences between the 15N abundances of the pooled legume population and control plants at all sites, although not every legume specimen exhibited this difference. From 15N abundance data we estimated the fractional contribution of biologically fixed N to the N economy of desert legumes. We concluded that N2-fixation is very important to Prosopis at six of seven sites in the Sonoran Desert. At the site where Prosopis did not appear to be fixing N2, N2-fixation was important only for legumes of the sub-family Papilionoideae, Lupinus, Dalea, Astragalus and Lotus.
230 citations
TL;DR: In this paper, the authors measured methane emissions from a California rice paddy during the entire 1982 growing season and observed a very strong seasonal dependence was observed; daily emissions reached 5 g CH4/m2.
Abstract: To allow increased understanding of the global budget of atmospheric methane, individual methane sources require investigation. We have measured methane emissions from a California rice paddy during the entire 1982 growing season. A very strong seasonal dependence was observed. Methane emissions were highest in the last 2–3 weeks before harvest; daily emissions reached 5 g CH4/m2. Over the 100-day season, daily emissions averaged about 0.25 g CH4/m2, higher than our previously reported values. Attempts to estimate global rice paddy emissions must recognize the possibility of seasonal variations. Soil temperature at 10-cm depth correlated poorly with our measured fluxes; soil redox potential was a more reliable indicator.
221 citations
TL;DR: The differential patterns of temperature adaptation among the species further extend the proposal of Kemp and Williams (1980; Ecology 61:846–858) that seasonal temperature gradients in the shortgrass steppe have a regulatory role in maintaining offset patterns of resource utilization and decreasing interspecific competition.
Abstract: Several aspects of photosynthetic adaptation to temperature were examined in four graminoid species from the Colorado shortgrass steppe. The experimental species were chosen to provide examples of a variety of in situ seasonal phenology patterns. The cool season grass, Agropyron smithii (C3), exhibited higher photosynthesis rates when grown in a cool temperature regime (20/15°C), and compared to warm grown plants (35/15°C). The warm season species, Bouteloua gracilis (C4) and Buchloe dactyloides (C4), exhibited higher photosynthetic capacities when grown in the warmer temperature regime. The sedge, Carex eleocharis (C3), which exhibits seasonal growth potential during the cool and warm portions of the growing season, exhibited a marked capacity for photosynthetic temperature acclimation. Differential effects of growth temperature on the intracellular conductance to CO2 appeared to have a greater regulatory role in these responses for the two C3 species, relative to stomatal conductance or photorespiration (O2 inhibition of photosynthesis). In the two C4 species decreases in the intracellular conductance in cool grown plants were correlated with the decreased photosynthetic capacity in normal air for B. gracilis, but not for B. dactyloides. Analysis of the Arrhenius relationship for CO2 saturated net photosynthesis at low leaf temperatures (4.5-17°C) indicated sharp breaks in the apparent energy of activation at 5.8-9.0°C in the warm season species B. gracilis and B. dactyloides. Leaves of A. smithii and C. eleocharis exhibited no significant low temperature limitations according to this analysis. The low temperature limitations in the warm season species were partially reflected in an inhibition of the quantum yield for CO2 uptake after 2 h at 5-6°C in the presence of high photon flux densities. Temperature dependent increases in the chlorophyll fluorescence yield at high temperatures revealed the lowest breakpoint values for A. smithii, and the highest values for B. gracilis. The differential patterns of temperature adaptation among the species further extend the proposal of Kemp and Williams (1980; Ecology 61:846-858) that seasonal temperature gradients in the shortgrass steppe have a regulatory role in maintaining offset patterns of resource utilization and decreasing interspecific competition.
114 citations
TL;DR: Container and field experiments conducted to determine the physiological basis for reports that reports that the latter treatment was more effective as a control measure showed that oxygen could diffuse very readily to plant parts growing in an anoxic environment if there was a small amount of leaf or cut plant stem growing above the water level.
99 citations
TL;DR: Tidal cycle budgets for June, July, August, September, and November 1979 showed that inorganic N was imported to the wetland from the Delaware River early in the growing season and exported late in a growing season.
Abstract: Tidal cycle budgets for June, July, August, September, and November 1979 showed that inorganic N was imported to the wetland from the Delaware River early in the growing season and exported late in the growing season. Nitrate and organic nitrogen were imported following macrophyte dieback. Reactive P was never lost from the marsh, and was actually imported on three dates. Total P was imported in July, September, and November, but otherwise exported. The metal present in the lowest concentration, Cd, was always exported; Ni, Cu, Zn were imported on all but one date. Lead was imported late in the growing season and following macrophyte dieback. Nonpoint-source inputs of Pb exceeded inputs from tidal waters. The vegetation played a major role in the retention of N, P, Cu, Pb, and Ni entering the wetland through the growing season. The litter retained significant quantities of all heavy metals following macrophyte dieback, but it serves only as a temporary storage vehicle because rates of decomposition are high. The soil showed no definite seasonal pattern of nutrient or heavy metal retention. Elevated Pb levels occurred at sites near storm drains reflecting rapid sedimentation and retention of this metal as storm waters entered the wetland.more » It is concluded that freshwater tidal wetlands play an important seasonal role in reducing nutrient and heavy metal loading in the upper Delaware River estuary.« less
86 citations
TL;DR: Water resource partitioning among three co-occurring species of the California annual grassland was investigated and it was concluded that Hemizonia, the longest lived species, survives on water stored in decomposed rock below the soil layer.
Abstract: Water resource partitioning among three co-occurring species of the California annual grassland was investigated. Plantago erecta, Clarkia rubicunda and Hemizonia luzulifolia differ in lifespan. The lifespan of Plantago is coincident with the October–May rainy season, but the other two species reproduce during summer when no precipitation occurs, and thus depend on stored water. Field studies indicated differential access to stored water commensurate with the phenology of each species. Studies of artificial stands under controlled conditions showed no difference in the species' ability to exploit stored water in the soil. However there was a striking difference in root behavior between Plantago and Hemizonia when plants were grown in a soil layer above a non-nutritive, waterstoring substrate. We concluded that Hemizonia, the longest lived species, survives on water stored in decomposed rock below the soil layer. Clarkia is restricted to cooler slope faces where a slightly longer growing season appears just suficient to complete reproduction. Productivity is enhanced by addition of later blooming species to the community, but there is no indication that the mixture is the most productive system.
85 citations
TL;DR: The results strongly support the hypothesis invoking a gradient in soil water movement as the major general determinant of productivity by S. alterniflora and indicate factors in addition to salinity stress as possible specific regulators of salt marsh productivity.
Abstract: Increasing the subsurface drainage in a stand of intermediate-height smooth cordgrass Spartina alterniflora Loisel. caused significant increases in mean shoot height and above ground production in a single growing season, and continued through the second year of the experiment. The results 1) strongly support the hypothesis invoking a gradient in soil water movement as the major general determinant of productivity by S. alterniflora and 2) indicate factors in addition to salinity stress as possible specific regulators of salt marsh productivity.
85 citations
TL;DR: More vesicular–arbuscular mycorrhizal (VAM) fungal species and significantly more fungal spores were recovered from undisturbed prairie soils than four winter wheat field soils in Kansas through the 1980–1981 growing season.
Abstract: More vesicular–arbuscular mycorrhizal (VAM) fungal species and significantly more fungal spores were recovered from undisturbed prairie soils than four winter wheat field soils in Kansas through the 1980–1981 growing season. Two previously undescribed sporocarpic species of Endogonaceae were found in prairie samples but have not been successfully established in pot culture, leaving the genus to which they belong unclear. Though variable, 11–50% VAM root colonization was evident in all prairie grass roots sampled throughout the year. In contrast, no identifiable VAM root colonization was evident in wheat until May after flowering when 27% root colonization was observed. During the 1981–1982 growing season, roots of two other wheat fields were sampled with similar results. No colonization occurred until May when 8% root colonization was evident. The possible influence of such low levels of root colonization occurring quite late in the growing season of winter wheat is discussed.
80 citations
TL;DR: Results show that C3 grass cover is significantly correlated with increased post-disturbance vegetation age, low intensity grazing, high litter cover and cool, steep, poleward slopes, which contribute to lower growing season temperatures, favouring the competitive growth of C3 species.
Abstract: There are roughly equal numbers of C3 and C4 grass species in fynbos and allied shrublands of the warm temperate coastal regions of the south eastern Cape. Subtropical-tropical C4 species have the highest relative cover in all shrubland types, particularly in renosterveld communities on moderately fertile soils. Physiological characteristics of C3 and C4 grasses predict that C3 species will be most abundant in cool, shaded sites. This prediction, and the hypothesis that relative C3 grass cover would be highest on infertile soils, were tested by correlation and regression analyses. Results show that C3 grass cover is significantly correlated with increased post-disturbance vegetation age, low intensity grazing, high litter cover and cool, steep, poleward slopes. All these factors contribute to lower growing season temperatures, favouring the competitive growth of C3 species. Amongst the soil variables, high sand content and low levels of total nitrogen emerged as predictors of high relative C3 grass cover.
TL;DR: Salix species dispersing dormant seeds during the fall appear to have evolved, as an adaptation to short growing seasons in coldClimate, to develop dormancy while being held on the plant until the leaves senesce.
Abstract: Seeds of the 24 common Salix species of the Alaskan boreal forest and tundra were set to germinate in laboratory and field experiments, and seed dispersal times were observed. During the growing season, 16 species disperse short-lived, nondormant seeds. At the end of the growing season, eight other species, all tundra willows, disperse conditionally dormant seeds. These fall-dispersed seeds are fully developed in the same length of time as summer-dispersed seeds, but they develop dormancy while being held on the plant until the leaves senesce. At the time of dispersal, some seeds are capable of germinating at high temperatures, but no seeds can germinate at the low soil temperatures occurring then. Cold stratification gradually widens the range of temperatures at which seeds can germinate, and seeds germinate at low soil temperatures in the spring shortly after snowmelt. Salix species dispersing dormant seeds during the fall appear to have evolved, as an adaptation to short growing seasons in cold climate...
TL;DR: It appears that this changing growth pattern permitted Vallisneria plants to compensate for the presence of neighbors, and thereby attain similar biomass and sustain similar winter bud production in the presence and absence of neighbors.
Abstract: Biomass of the submersed macrophyte Vallisneria americana rose steadily from early June to 50 g dry wt·m-2 in ealry August. Leaves dominated the biomass of this perennial from mid-June through August, after which plants senesced to leave only winter buds as perennating organs. Only 24% of plants sampled flowered during the 1978 growing season, yielding a population mean of less than 0.6% of dry weight allocated to sexual reproduction, with a maximum value of 7.8% for one plant. In contrast, allocation to winter buds accounted for 11% of total dry weight at the close of the growing season.Total dry weight, leaf length, stolon length, rosette number, and winter bud production of Vallisneria americana at the close of the growing season had significantly higher mean values for individual plants in a monospecific stand of Vallisneria than at sites dominated by Potamogeton amplifolius or Chara vulgaris. The basis of site differences in growth by V. americana is unknown, although we demonstrate significantly higher interstitial soluble reactive phosphorus concentration and organic content of sediment at a Vallisneria site.Removal of neighbors of some Vallisneria plants at the Vallisneria, Potamogeton, and Chara sites resulted in longer leaves, but fewer rosettes for plants with neighbors than plants without neighbors. It appears that this changing growth pattern permitted Vallisneria plants to compensate for the presence of neighbors, and thereby attain similar biomass and sustain similar winter bud production in the presence and absence of neighbors.
TL;DR: The competitive survival of understory eastern redcedar under such environmental conditions was apparently due to it being an evergreen conifer in a deciduous forest, with maximum net photosynthetic rates occurring during periods when the overstory was leafless as discussed by the authors.
Abstract: Eastern redcedar (Juniperus virginiana) is a sun—adapted, drought—resistant pioneer species common to pastures, abandoned fields, fence rows, and calcareous rock outcrops throughout the eastern United States. However, it is also a frequent component of the understory in mature oak—hickory forests in central Missouri, where light levels are typically <10% of full sunlight during much of the growing season. This is below eastern redcedar's reported optimum for photosynthesis. The competitive survival of understory eastern redcedar under such environmental conditions was apparently due to it being an evergreen conifer in a deciduous forest. Hence, its foliage was able to maintain a positive carbon dioxide balance throughout much of the year, with maximum net photosynthetic rates occurring during periods when the overstory was leafless. The greatest daily average net photosynthetic rates (Phn) occurred during overstory leaf emergence when temperatures were moderate and light levels to the understory trees wer...
TL;DR: Eriophorum vaginatum, a tussock-forming member of the Cyperaceae, widespread in the arctic tundra, and a common food item for grazing herbivores on the Alaskan North Slope, is subjected to a variety of simulated grazing experiments to determine tiller responses to frequent and intensive defoliation.
Abstract: Eriophorum vaginatum is a tussock-forming member of the Cyperaceae, widespread in the arctic tundra, and a common food item for grazing herbivores on the Alaskan North Slope. Populations of this sedge at Atkasook, Alaska, were subjected to a variety of simulated grazing experiments to determine tiller responses to frequent and intensive defoliation.The intial, short-term response of Eriphorum to defoliation was an increase in leaf production at the expense of belowground structures. Multiple defoliations, however, resulted in proportionately greater reductions in leaf weight than leaf area. Leaf blades of defoliated plants weighed 0.71 mg/cm of length, compared to an average weight/length ratio of 0.91 mg/cm in control plants. Declines in leaf production were accompanied by weight losses in stem base and sheath components and a curtailment of root growth. Root initiation was reduced by 28 and 63%, respectively, after one and two seasons of multiple defoliations, and the depth of penetration of these annual roots was reduced substantially. Total root biomass was reduced 24% in the least severe defoliation treatment and 85% in the most severe treatment. The allocation of dry matter into new tillers on defoliated plants, relative to new tiller production of control plants, was reduced by 75% after two seasons of defoliation, although equivalent numbers of tillers were initiated. The reduced biomass of daughter tillers was restored to levels observed in control plants during the season of rest following the season of multiple defoliation. Sexual reproduction was significantly depressed in the most severe defoliation treatment and stimulated by the least severe treatment. Defoliation treatments of intermediate severity had no significant impact on flower initiation.Over 80% of the tillers subjected to complete defoliation at 10-day intervals for one entire growing season survived, overwintered and initiated growth the following season. Recovery from multiple defoliations was partially achieved by the stimulated growth and extended longevity of older leaves on the tiller, although one season of rest was not enough to fully replenish weight losses of storage organs. Tillers were capable of withstanding more defoliation events when clipping was initiated early in the growing season. Biomass of storage organs of tillers subjected to multiple defoliations imposed at 10-day intervals for two entire growing seasons was 34% above the estimated minimum biomass necessary for tiller survival. The data suggest that Eriophorum tillers can survive 100% leaf removal at 10-day intervals for 50 to 75% of their estimated three to four year lifespan.
TL;DR: In this paper, the authors used a portable radiometer to measure the reflectance from leaves of 16 oak trees, on a 4 X 4 grid, during the growing season, followed by analyzing the leaves for concentrations of trace metals and nutrients.
Abstract: Sixteen oak trees, on a 4 X 4 grid, were sampled monthly during the growing season. Reflectance from leaves using a portable radiometer, followed by analyzing the leaves for concentrations of trace metals and nutrients. Soil samples from the A horizon taken at the base of each tree were analyzed for similar elements. Mineralization detected in portions of the electromagnetic spectrum used for measuring chlorophyll content and leaf water absorption. Variation of trace metals in the soil found to be associated with leaf reflectance.--Modified journal abstract.
TL;DR: Four evergreen and four deciduous trees and shrubs were sampled from habitats with differing soil temperature regimes in interior Alaskan forests to examine the relative importance of habitat and species importance.
Abstract: Four evergreen and four deciduous trees and shrubs were sampled from habitats with differing soil temperature regimes in interior Alaskan forests to examine the relative importance of habitat and leaf habit in determining seasonal patterns of shoot growth, tissue nutrient concentration, respiration rate, and phosphate absorption rate. Leaf habit was the primary determinant of shoot growth, with deciduous species producing leaf area and leaf biomass earlier in the season than evergreens. Deciduous trees produced more biomass per shoot and per unit ground area than did evergreens. The seasonal pattern of leaf nitrogen and phosphorus concentration was correlated closely with patterns of leaf growth, declining through the growing season in deciduous species first as nutrient concentrations were diluted by increasing leaf biomass and later as nutrients were retranslocated from senescing leaves. In evergreens the seasonal decline in nutrient concentration was entirely due to dilution by increasing leaf biomass,...
TL;DR: In this article, the authors found that the geographic variation for seed and seedling traits of Douglas-fir from four elevations on west and east aspects of first and second ridges away from the ocean (latitude °42°30'N) were observed under two air-temperature regimes in a common garden.
Abstract: Patterns of geographic variation for seed and seedling traits of Douglas—fir from four elevations on west and east aspects of first and second ridges away from the ocean (latitude °42°30'N) were observed under two air—temperature regimes in a common garden Size and germination rate were recorded for seeds; phenological and size data were recorded on seedlings through two growing seasons The pattern of genetic variation appeared to be determined by adaptation to local moisture and temperature regimes In east—west comparisons (inland ridge vs coastal ridge or east aspect vs west aspect), seeds of east aspect or inland origin were larger and germinated more rapidly than seeds of more westerly origin Similarly, plants of inland origin or from east aspects tended to start and end elongation earlier and have smaller top : root ratios, compared to plants from the coastal ridge or west aspects Genetic differences were generally greater between the west and east aspects of the coastal ridge than between the two aspects of the inland ridge Variation in data of bud set and plant size was also related to elevation The change associated with elevation was greater on the coastal ridge than on the inland ridge Evidence is presented that indicates length of growing season and heat accumulation may change more with elevation and latitude near the ocean than inland in the Pacific Northwest This in turn may result in steeper elevational and latitudinal gradients of genetically based variability near the ocean than inland
TL;DR: A model predicting optimum growth initiation times for shoot buds of deciduous plants has been derived from simple assumptions based on maximizing average annual photosynthesis as a function of photosynthetic rates, length of growing season and the probability of late frost.
Abstract: A model predicting optimum growth initiation times for shoot buds of deciduous plants has been derived from simple assumptions based on maximizing average annual photosynthesis as a function of photosynthetic rates, length of growing season and the probability of late frost. This formulation predicts that optimum bud initiation time is sensitive to the variance in the frost probability but is independent of the average photosynthetic rate. Predicted optimal initiation times are only slightly affected by substantial changes in the length of the growing season (over a considerable change in latitude) except when the growing season is very short. The advantage of maximum frost resistance is also greatest in very short growing seasons. It is pointed out that the optimum time of leaf senescence at the end of the growing season must be based on more complex criteria than the time of growth initiation. Certain difficulties in interpreting bud break data from tree transplant experiments are discussed.
TL;DR: A realistic estimate of maximum vegetative productivity can be obtained by multiplying number of days of full light interception by a crop canopy, by acrop growth rate of 230 kg∙h−1∙day−1 and adding the weight of the crop at the onset of fullLight interception by the canopy.
Abstract: Duration of the growing season appears to be the single most important factor limiting vegetative productivity in Canada A theoretical estimate of annual vegetative productivity in the absence of limitations due to water, nutrients or soil structure, shows that potential productivity in the 5-mo growing season of Southern Canada is in the range of 25–55 tonne/ha Maximum productivity, however, lies considerably below the potential productivity estimate due to lower-than-expected photosynthetic efficiency during periods of high solar irradiance Crop growth rates appear to be rather independent of variation in radiant flux density during the growing season Consequently, a realistic estimate of maximum vegetative productivity can be obtained by multiplying number of days of full light interception by a crop canopy, by a crop growth rate of 230 kg∙h−1∙day−1 and adding the weight of the crop at the onset of full light interception by the canopy Maximum vegetative productivity could likely be improved by ex
TL;DR: Dung from irrigated perennial pastures never produced flies as large as that from annual pastures but generally high values were sustained during summer, apparently a result of the inverse relationship between digestibility of feed and length of growing season.
Abstract: The value of cattle dung as a food resource for the bush fly Musca vetustissima (Walker) in the winter rainfall agricultural region of southwestern Australia was assessed by bioassay in the laboratory. The size (headwidth) of adult females was measured from flies reared on different samples of dung. Variation in size correlated with seasonal patterns of pasture growth, larger flies being produced during the growing season from autumn to spring. Size declined with senescence of annual pastures in late spring and early summer, occurring later in southern areas where the growing season was longer. After pasture senescence, dung from shorter growing season areas usually produced larger flies, apparently a result of the inverse relationship between digestibility of feed and length of growing season. Dung from irrigated perennial pastures never produced flies as large as that from annual pastures but generally high values were sustained during summer. Grazing of cereal stubble and feeding of hay in annual pasture areas during summer usually caused some increase in fly size. A spontaneous resurgence in the size of flies often occurred several weeks after pasture senescence and was attributed to more thorough digestion as a result of reduced intake of less palatable dry pasture.
TL;DR: Overall, the ground-surface spider community in alfalfa appeared to be better established than that in soybean, probably due to the more constant environment resulting from the relatively dense vegetation cover and the formation of a thatch layer in the perennial habitat.
Abstract: Ground-surface spider communities were examined using pitfall traps during three consecutive growing seasons to determine whether a perennial crop (alfalfa) supported a more persistent community than an annual crop (soybean). Similarities were found between crops in species composition, seasonal patterns of evenness, and the relative abundances of guilds. However, differences were found in the seasonal trends of the number of individuals present, as well as species richness. Overall, the ground-surface spider community in alfalfa appeared to be better established than that in soybean. This was probably due to the more constant environment resulting from the relatively dense vegetation cover and the formation of a thatch layer in the perennial habitat.
TL;DR: Seedling densities, recruitment, and survival of Sedum lanceolatum during the growing season at seven populations between 2257 and 3726 m were studied to assess one aspect of successful sexual reproduction above and below timberline.
Abstract: Seedling densities, recruitment, and survival of Sedum lanceolatum during the growing season at seven populations between 2257 and 3726 m were studied to assess one aspect of successful sexual reproduction above and below timberline. Seedling densities declined drastically at timberline and above, even when corrections were made for differences in adult densities among populations. Seedlings can be so rare and patchily distributed in the alpine that they could not be detected using random sampling. However, above timberline there were microsites where seedling densities exceeded those at lower elevations and survivorship was homogeneous among most populations. Alpine seedlings can be just as successful as their below-timberline counterparts, depending upon the criteria selected for evaluation of
TL;DR: Spider communities were characterized using several ecological parameters to determine whether a more persistent community structure developed over a three-year period in a perennial crop (alfalfa) than in an annual crop (soybean).
Abstract: Spider communities were characterized using several ecological parameters to determine whether a more persistent community structure developed over a three-year period in a perennial crop (alfalfa) than in an annual crop (soybean). In alfalfa, seasonal trends in species richness, evenness, and guild structures were distinctly different during the initial growing season when compared to the two subsequent seasons. In soybean, seasonal patterns of species richness were similar among years, while those of evenness and guild structures varied. By the second year following planting, the alfalfa foliage spider community had become established. In soybean, the development of a stable community structure is impossible due to the transitory nature of the habitat, which results in a “new” assemblage of spiders in the soybean foliage during each growing season.
TL;DR: The decline in carbohydrates in roots of aspen (Populustremuloides Michx.) as a consequence of shoot production and the contribution of new shoots to root carbohydrate levels was investigated.
Abstract: The decline in carbohydrates in roots of aspen (Populustremuloides Michx.) as a consequence of shoot production and the contribution of new shoots to root carbohydrate levels was investigated as part of a study of the factors controlling aspen regrowth following top removal. The level of non structural carbohydrates in the roots of young aspen shoots which had been clipped during the growing season was estimated at the commencement of the dormant season. Segments of the roots were then placed in growth cabinets and kept either in darkness or in one of two light regimes having equal quantum flux densities, but with quality akin to either normal sunlight or shade. Shoot growth in darkness was greater from roots taken from plots where clipping had been conducted in midseason rather than later in the season, suggesting that some carbohydrate replenishment had taken place in those plots. Carbohydrate concentration in roots placed in the three light regimes declined to approximately the same extent over the 8 w...
TL;DR: In this article, the effects of pre-seeding, postseeding and split application of limited amounts of water on root growth, water use, dry matter accumulation and grain yield of wheat were investigated.
TL;DR: Fertility levels and pH of the soil of the study area where clipping frequency and fertilization was evaluated relatived to crude protein constants and herbage production of 4 grass species near Kingsville, Texas, during 1972-1973.' Nutrient availability
Abstract: Crude protein content of herbage produced by buffelgrass, blue panicgrass, and Bell rhodesgrass was improved with nitrogen and phosphorus fertilization and clipping every 4 orJ weeks, compared to harvests only at the end of the growing season. Within a fertilization level, the 8-week clipping frequency generally increased dry matter production of the grasses over the 4-week clipping frequency or the end-of-season single harvest. Kleberg bluestem herbage generally contained less protein at all phenological stages than that of buffelgrass, blue panicgrass, or Bell rhodesgrass, and dry matter production was not increased by fertilization. Crude protein content of Kleberg bluestenm herbage was only slightly increased with the highest level of fertilization, regardless of clipping frequency. The South Texas Plains occupies nearly 9 million hectares of level to rolling terrain with elevations ranging from sea level to 95 m. Annual rainfall ranges from 45 to 75 cm with peaks occurring in May and September. Because of the long growing season and rainfall patterns, this area has a high potential for forage production. However, primarily as a result of continued excessive grazing of domestic livestock and cessation of fires, undesirable woody species have increase to the detriment of naturally occurring desirable vegetation (Scifres 1980). Brush management as a part of overall sound range management has proven its merit in restoring forage production (Scifres et al. 1976, 1980; Polk et al. 1976). Generally, natural revegetation through secondary succession is too slow for economical returns following high-cost mechanical control of undesirable woody species. Artificial revegetation with commercially available, adapted species is often considered the most feasible alternative for rapid restoration of these grazing lands. Major species that have been seeded successfully include buffelgrass (Cenchrus ciliaris), Bell rhodesgrass (Chloris gayana), Kleberg bluestem (Dicanthium annulatum), and blue panicgrass (Panicum antidotale). Although these grasses have been utilized in the overall range improvement program in south Texas for the past 4 decades, little is known about specific post-seeding management practices which could improve forage yield and quality. Brief descriptions, planting dates, seeding rates, and responses to irrigation and fertilization are found in experiment station leaflets (Novosad and Pratt n.d., Lancaster n.d., Lancaster 1949, and Anon. 1968). Since most of the livestock in this area are raised in yearlong cow-calf operations, high protein forage is required throughout the year to meet demands of growing calves and lactating cows. Waite At the time of this research, authors were graduate research assistant and associate professor, College of Agriculture,Texas Al and April 15 and 582 JOURNAL OF RANGE MANAGEMENT 36(5), September 1983 This content downloaded from 157.55.39.127 on Mon, 27 Jun 2016 05:36:06 UTC All use subject to http://about.jstor.org/terms Table 1. Fertility levels and pH of the soil of the study area where clipping frequency and fertilization was evaluated relatived to crude protein constants and herbage production of 4 grass species near Kingsville, Texas, during 1972-1973.' Nutrient availability
TL;DR: The particulate phase of lake sediments showed a marked reduction in the concentration of N, P, K and C during late spring and summer as mentioned in this paper, and larger amounts of these elements were found towards the autumn, and these higher levels were maintained through winter until early spring.
Abstract: The particulate phase of lake sediments showed a marked reduction in the concentration of N, P, K and C during late spring and summer. Larger amounts of these elements were found towards the autumn, and these higher levels were maintained through winter until early spring. The reduction in the concentration of these mineral nutrients was greatest during the growing season of the macrophytes.
TL;DR: No relationship could be found between meteorological data and the length of the growing season from the 50% full-bloom stage until the recommended harvesting date, but good correlations were established between the number of days from 31 August to the recommended harvest date and meteorological variables which included temperature.
Abstract: SummaryThe relationship between the weather during the growing season and the UK Ministry’s recommended date for harvesting cv Cox’s Orange Pippin apples for long-term storage was investigated using data obtained between 1959 and 1980. No relationship could be found between meteorological data and the length of the growing season from the 50% full-bloom stage until the recommended harvesting date. However, good correlations were established between the number of days from 31 August to the recommended harvest date and meteorological variables which included temperature. July temperatures were particularly significant but the most significant were accumulated temperatures from June to September. Prediction of the Ministry’s recommended date was improved further by including the date of 50% full-bloom in a multiple regression which accounted for 72% of the variation. Using this regression the predicted and recommended dates differed by less than 3 days in all but one of the past 21 years. An equation was der...
TL;DR: The possibility of integrating crop and cultivar selection with appropriate irrigation management to improve production efficiency in southern Alberta is discussed and small changes in seed quality, tending towards higher protein and lower oil under wetter conditions, are corroborated in the literature.
Abstract: Field experiments were conducted from 1979 to 1982 in southern Alberta to determine the seasonal water use of soybeans. Soil moisture was determined every 5–6 days throughout the growing season and irrigation water was applied when soil moisture tension in the top 30 cm reached −40 kPa, with an additional treatment of −60 kPa for 1980 and 1981. Seasonal water use in a year of normal growth (1980) varied from 426 to 482 mm for the drier and wetter treatments, respectively. The drier treatments in 1980 and 1981 resulted in more efficient use of water. Low early-season water use with peak use after full pod development (R4) was defined. Water use peaked in late July to early August with a requirement of 7 mm/day. Small changes in seed quality, tending towards higher protein and lower oil under wetter conditions, are corroborated in the literature. The possibility of integrating crop and cultivar selection with appropriate irrigation management to improve production efficiency in southern Alberta is discussed...