Differences In Regrowth Research Articles

Diversity Effects on Canopy Structure Change throughout a Growing Season in Experimental Grassland Communities

Increasing plant diversity commonly enhances standing biomass and other ecosystem functions (i.e., carbon fluxes, water use efficiency, herbivory). The standing biomass is correlated with vegetation volume, which describes plant biomass allocation within a complex canopy structure. As the canopy structure of plant communities is not static throughout time, it is expected that its changes also control diversity effects on ecosystem functioning. Yet, most studies are based on one or two measures of ecosystem function per year. Here, we examine the temporal effects of diversity of grassland communities on canopy structural components in high temporal (bi-weekly throughout the growing season) and spatial resolutions as a proxy for ecosystem functioning. Using terrestrial laser scanning, we estimate metrics of vertical structure, such as biomass distribution (evenness) and highest biomass allocation (center of gravity) along height strata. For horizontal metrics, we calculated community stand gaps and canopy surface variation. Our findings show that species-rich communities start filling the vertical space (evenness) earlier in the growing season, suggesting a more extended period of resource use (i.e., light-harvesting). Moreover, more diverse communities raised their center of gravity only at the peak of biomass in spring, likely triggered by higher interspecific competition inducing higher biomass allocation at upper layers of the canopy. Furthermore, richer communities were clumpier only after mowing, revealing species-specific differences in regrowth. Lastly, species richness strongly affected canopy variation when the phenology status and height differences were maximal, suggesting differences in plant functional strategies (space to grow, resource use, and flowering phenology). Therefore, the effects of diversity on ecosystem functions depending on those structural components such as biomass production, decomposition, and herbivory, may also change throughout the season due to various mechanisms, such as niche differences, increased complementarity, and temporal and spatial variation in biological activity.

Frost hinders the establishment of trees in highland grasslands in the Atlantic Forest ecotone region of southern Brazil

AbstractQuestionsCold temperatures and freezing may hinder the process of forest expansion in moist climate regions, as predicted by the frost hypothesis. We examined the role of frost on the survival and regrowth of tree saplings under field conditions of open grasslands.LocationCambará do Sul, Rio Grande do Sul.MethodsWe established a field experiment protecting one of two groups of saplings of forest species from frost in grassland areas during the winter. We monitored 672 saplings from a total of seven species for 56 days. Saplings were brought back to the laboratory to evaluate regrowth rate and height. Survival curves of the two groups were compared using a Kaplan–Meier estimator. Correlation analysis was undertaken to estimate the relationship between survival and regrowth rate and a variance analysis was used to compare plant height between both groups.ResultsSpecies respond distinctly to frost incidence, with some not being affected by frost (two gymnosperms andMyrcianthes pungens). Most protected saplings had a higher above‐ground survival rate than unprotected ones (96.4% and 73.2%, respectively). Moreover, saplings that were damaged by frost showed differences in regrowth and height according to species identity, notwithstanding the fact that those from protected plots showed higher regrowth and height (88% and 25.65 cm compared to 68% and 17.15 cm).ConclusionsOur results showed clear negative effects of frost on the survival rate of aerial parts of saplings during the winter and the regeneration of damaged plants. Species‐specific traits can offer frost resistance; however, together with other disturbances, frost may hinder the establishment of forest trees over grassland areas where frost events are common during the winter.

Temporal trends in craniopharyngioma management and long-term endocrine outcomes: A multicentre cross-sectional study.

The optimal management of craniopharyngiomas remains controversial. To examine temporal trends in the management of craniopharyngioma with a focus on endocrine outcomes. This was a cross-sectional, multicentre study. Patients treated between 1951 and 2015 were identified and divided into four quartiles. Demographics, presentation, treatment and outcomes were collected. In total, 142 patients with childhood-onset craniopharyngioma (48/142; 34%) and adult-onset disease (94/142; 66%) were included. The median follow-up was 15years (IQR 5-23years). Across quartiles, there was a significant trend towards using transsphenoidal surgery (P<.0001). The overall use of radiotherapy was not different among the four quartiles (P=.33). At the latest clinical review, the incidence of GH, ACTH, gonadotrophin deficiencies and anterior panhypopituitarism fell significantly across the duration of the study. Anterior panhypopituitarism was not affected by treatment modality (surgery vs surgery and radiotherapy) (P=.23). There was no difference in the incidence of high BMI (≥25kg/m2 ) among the four quartiles (P=.14). BMI was higher in patients who treated with surgery and radiotherapy than those treated with surgery only (P=.006). Tumour regrowth occurred in 51 patients (51/142; 36%) with no difference in regrowth among quartiles over the time course of the study (P=.15). We demonstrate a significant reduction in panhypopituitarism in craniopharyngioma patients over time, most likely because of a trend towards more transsphenoidal surgery. However, long-term endocrine sequelae remain common and lifelong follow-up is required.

Hairy Vetch Varieties and Bi‐Cultures Influence Cover Crop Services in Strip‐Tilled Sweet Corn

Hairy vetch (Vicia villosa Roth) cover crops provide a wide array of ecosystem services including erosion protection, weed suppression, and N fixation. However, adoption has been hindered by risks including overwinter mortality and regrowth following mowing or crimping. Early‐flowering vetch varieties and mixed stands of vetch and cereal rye (Secale cereale L.) have the potential to reduce these risks, but little is known about their impact on N fixation. In field trials in Central Michigan, two early‐flowering hairy vetch varieties (Purple Bounty and Purple Prosperity) and one later‐flowering variety (‘Oregon’) were grown alone and in mixtures with cereal rye, prior to strip‐tilled sweet corn (Zea mays L. var. rugosa). Vetches grown in mixture with rye had equal or greater overwinter survival and earlier flowering than vetches grown in monoculture. Nitrogen fixation of early‐flowering varieties was not affected by mixture with rye. However, N fixation of Oregon was lower when grown in monoculture than when grown in mixture in 2009. Purple Bounty and Purple Prosperity flowered earlier than Oregon, exhibited comparable survival, and had equal or greater levels of N fixation. Despite differences in the timing of flowering, there were no differences in regrowth of hairy vetch following mowing. Nor were any differences in sweet corn yield or quality detected. These results demonstrate that rye–vetch mixtures can increase overwinter survival, accelerate flowering, and increase N fixation relative to vetch monocultures. Observed varietal differences in flowering time, N fixation, and response to bicultures may be exploited to optimize cover crop use in agroecosystems.

Probiotic Supplements (Lactobacillus reuteri DSM 17938 and ATCC PTA 5289) Do Not Affect Regrowth of Mutans Streptococci after Full-Mouth Disinfection with Chlorhexidine: A Randomized Controlled Multicenter Trial

The aim of this study was to investigate the effectiveness of tablets containing two probiotic Lactobacillus reuteri strains in inhibiting regrowth of salivary mutans streptococci (MS) after full-mouth disinfection (FMD) with chlorhexidine. The null hypothesis was that the levels of MS would not differ in comparison with a placebo protocol. The study population was comprised of 62 young adults (mean age 23 years) with moderate or high counts of salivary MS who volunteered after informed consent. The study was a double-blinded randomized controlled trial with two parallel groups. After a 3-day chlorhexidine regimen, the subjects were randomly assigned to a test group (n = 32) with probiotic lozenges (2/day) or a placebo group (n = 30). The intervention period was 6 weeks, and stimulated whole saliva was collected at baseline and after 1, 6, and 12 weeks. The samples were processed for MS by a chair-side test and DNA-DNA hybridization as an estimate of 19 bacterial strains associated with oral health and disease. There was no significant difference between the groups at inclusion, and FMD reduced the salivary MS levels significantly in both groups. The MS suppression lasted less than 6 weeks and there were no statistical differences in salivary MS regrowth between the test and control groups at any of the follow-ups. Likewise, there were no major differences in the regrowth patterns of the checkerboard panel between the two groups. We conclude that daily oral administration of L. reuteri did not seem to affect or delay the regrowth of salivary MS after FMD with chlorhexidine.

多種混在型草地の構成要素としてのセイヨウタンポポにおける刈取り後の再成長

Leaves size in longitudinal and transverse direction of dandelion (Taraxacum officinale Weber.) were measured in every two days after removal of whole above ground organs at natural day length and at dark conditions in pots culture. Area and dry weight of each leaf was estimated non-destructively by using allometric relations, which were made from sampling leaves. The light condition caused differences in re-growth of dandelions between at natural day length and at dark condition. Light-photosynthesis curve revealed that light saturated productivity of leaves was about 13.0 CO2 μmol/m&sup2/sec. and that respiration rate as 0.49 CO2 μmol/m&sup2/sec. Quantity balance of photosynthetic production was estimated for each leaf in every day. New leaf grew rapidly and reached the maximum size in 10 days after emergence. Surplus production kept nearly balanced zero throughout this period. The balance became surplus after leaf completed the growth. Production economy during the early stage in each leaf was a self-supporting process without depending source on other organs. A leaf got about 0.3g dry weight surplus production during the life span. It is considered that these characteristics of dandelion adapted to the grassland that disturbed frequently by mowing or trampling.

Regrowth in barley (Hordeum vulgare L.) and rye (Secale cereale L.)

Regrowth after cutting at four development stages, from heading to grain maturity, was investigated in a pot experiment containing three rye and four barley varieties. Regrowth in the barley varieties decreased strongly from heading to grain maturity. Rye generally showed stronger regrowth than barley after late cutting, but only the perennial variety ‘Soperta’ regenerated as many tillers at cutting as formed when harvested at the ripe grain stage. In both species, significant differences were found between varieties. The level of soluble carbohydrates reached a maximum between heading and maturity, but differences in regrowth could not be explained by such differences. Total N decreased from heading to maturity, except for perennial rye, where an increase was observed towards ripening. It is, however, uncertain whether this was an effect rather than a cause of the regrowth.

The effects of the spatial pattern of defoliation on regrowth of a tussock grass : I. Growth responses.

The effects of the spatial pattern of defoliation within a tussock grass, Agropyron desertorum, were investigated at a semiarid field site. In the middle of the spring growing season (mid-May), tussocks were clipped in repeatable defoliation patterns, and the regrowth of foliage was monitored. These clipping patterns involved removal of foliage from different locations within the tussock, but the total amount of foliage removed was held constant. Active meristems were left intact in all cases. The spatial pattern of defoliation affected both initial rates of tussock regrowth and total growing-season aboveground biomass production. When leaves were removed low in the tussock (older leaves), regrowth was greater than after removal of the same quantity of foliage high in the canopy (younger leaves). These differences in regrowth were due to differences in the rate of new tissue production rather than differences in the timing of senescence. The results were consistent over two years even though aboveground production differed considerably between years. The interaction of the spatial pattern and timing of defoliation was also studied by clipping additional plants in late May. The timing of defoliation affected the relative influence of different defoliation patterns on regrowth. In those defoliation patterns where active meristems were not removed in the late-May clipping, there were no differences in regrowth of tussocks which had either upper or lower foliage removed. However, because the grass culms had elongated by late May, active meristems were higher and were removed by one of the defoliation pattern treatments (a uniform clipping). This resulted in much less regrowth. Differences in the effects of clipping patterns applied in late May were associated with this removal of active meristems. Whereas, differences among clipping treatments following the earlier mid-May defoliation were probably a result of changes in factors which affected tussock carbon gain (e.g., light interception, foliage age structure). In either case, the spatial pattern of defoliation within a tussock grass clearly had significant effects on aboveground regrowth.

In vitro response to hyperthermia or X-irradiation of diploid and tetraploid RIF-1 cells separated by centrifugal elutriation.

The RIF-1 cell line at the University of Utah is comprised of approximately 65 per cent diploid and 35 per cent tetraploid cells. Because sensitivity to heat cell killing has been shown to be ploidy dependent (Lucke-Huhle 1978), the responses of these subpopulations were examined independently. Diploid and tetraploid cells were separated from stock in vitro cultures by centrifugal elutriation and maintained entirely in vitro. No influence of ploidy on Do or Dq of heat dose survival curves could be detected. Neither did ploidy affect sensitivity to X-irradiation. However, separation of the diploid and tetraploid subpopulations was imperfect. The ratio of diploid to tetraploid cells in the separated and parent (mixed ploidy) lines was therefore monitored at each passage. Tetraploid contamination of the diploid cell subline was undetectable at the time of separation but regrew to 35 per cent by 40 days after separation. Diploid contamination of the tetraploid subline was initially less than 5 per cent and remained quite low until it became undetectable at 74 days. Differences in regrowth of the contaminating subline could not be accounted for by differences in plating efficiency or doubling time, but might result from subpopulation interactions. If so, such phenomena should be considered when using ploidy-dependent cytotoxic treatments.

Soluble Carbohydrates, Concurrent Photosynthesis and Efficiency in Regrowth Following Defoliation: A Field Study with Agropyron Species

(1) The contribution of stored carbon to plant regrowth following defoliation is commonly thought to be large. This study quantitatively compared the amount of carbon supplied to regrowth from storage with photosynthesis of regrowth in the field. (2) Two bunchgrass species were selected for comparison because of markedly different abilities to regrow following defoliation despite very similar photosynthetic, morphologic and phonologic characteristics. (3) The more grazing-tolerant Agropyron desertorum (Fisch. ex Link) Schult. consistently produced more regrowth in the absence of photosynthesis than A. spicatum (Pursch) Scribn. & Smith, but a severe preclipping treatment (which has been shown to reduce carbohydrate reserves by more than 40%) did not significantly reduce etiolated regrowth in either species. (4) Differences in regrowth between and within species were not correlated with crown non-structural carbohydrate concentrations, total pools, or amounts utilized during regrowth. (5) The daily contribution of carbon from reserves exceeded measured daily photosynthetically-fixed carbon for only 2.5 days following defoliation when regrowth rate was maximal. However, when apical meristems were removed and regrowth was much slower, photosynthesis during regrowth immediately outweighed stored reserves as a source of carbon. The latter is the usual case when these grasses are subjected to managed grazing. (6) In both species, apical meristem removal was followed by sharply reduced regrowth efficiency due to a delay in and reduced rate of regrowth production. There was, however, no increase in respiration rate. (7) Meristematic limitations appear to be the dominant control on the amount of etiolated regrowth produced. These limitations also appear to be of prime importance in determining regrowth in the light and for grazing tolerance of plants.

Effect of Herbicides on the Production of Common Buffelgrass (Cenchrus ciliaris)

Dicamba (3,6-dichloro-o-anisic acid), 2,4-D [(2,4-dichlorophenoxy)acetic acid], 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid], 3,6-dichloropicolinic acid, picloram (4-amino-3,5,6-trichloropicolinic acid), triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid}, tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea}, and hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione] were applied at rates of 0.3, 0.6, 1.1, and 2.2 kg/ha pre- and postemergence to greenhouse-grown common buffelgrass (Cenchrus ciliarisL. ♯3PESCI). Buffelgrass tolerated preemergence sprays of 3,6-dichloropicolinic acid up to and including 1.1 kg/ha. All other treatments except picloram and 2,4,5-T at 0.3 kg/ha were phytotoxic to emerging buffelgrass. Buffelgrass tolerated early postemergence applications of 2,4-D, picloram, and tebuthiuron at 0.3 kg/ha; dicamba and 2,4,5-T at 0.6 kg/ha; and 3,6-dichloropicolinic acid at 2.2 kg/ha based on oven-dry shoot production 1 month after treatment. Regrowth of buffelgrass from stubble 1 month after original harvest of the early postemergence treatment occurred only with all rates of 3,6-dichloropicolinic acid and 2,4,5-T at 0.3 kg/ha. When treated at 45 days after planting, buffelgrass tolerated dicamba, 2,4-D, 2,4,5-T, 3,6-dichloropicolinic acid, and picloram at 2.2 kg/ha, but top growth production was significantly reduced by most rates of hexazinone and tebuthiuron. Relative differences in regrowth of buffelgrass 1 month after the original harvest were similar to those of the original harvest. Mature buffelgrass (90 or 150 days old) responded similarly to herbicides as the 45-day-old buffelgrass.

Regrowth, Nodulation, and Nitrogenase Activity of Strophostyles helvola with Rigorous Defoliation1

AbstractIndigenous legumes contribute toward increased N nutrition and enhanced grazing productivity of both native and improved pasture swards. However, quantitative assay of symbiotic dinitrogen fixation by pastured legumes is difficult. The objective of these studies was to determine defoliation effects on regrowth, nodulation, nitrogenase activity (C2H2 red.) and associated nodule enzymology of trailing field bean [Strophostyles helvola (L.) Ell.]. Plants were grown in a Psammentic Paleustalf (Eufaula) and inoculated with Rhizobium leguminosarum Frank, ATCC 10314. Characteristics of nondefoliated plants during 3 years of field experiments included near exponential growth with 10‐fold increase in dry weight from 1.49 to 17.45 g at 30 to 120 days after emergence (DAE). Number of stems tripled and stem length increased six‐fold. Average nodules per plant increased from 80.2 to 239.6. Nodule mass as fresh weight increased from 0.94 to 6.17 g, and mature nodules increased from 13% to 89%. Differences in regrowth after defoliation at 30‐day intervals was not significant averaging 4.21 g, CV 11 %. Nodules per plant after regrowth averaged 113 with fresh nodule wt. 2.06 g and 27 % were mature nodules. Nitrogenase (C2H2 red.) activity levels were highest at 90 DAE, 168.2 μmols. C2H4g−1h−1. Regrowing plants after defoliation averaged 156.3 μmol C2H4g−1h−1. Highest cytosol enzyme activity levels were for aspartic transaminase (AST) with 25.0 IU (nondefoliated) and 25.9 IU (defoliated) g−1 fresh nodule. Glutamine synthetase (GS) was 1.7 IU (nondefoliated) and 12.0 IU (defoliated). Multiple regression indicated significance for glutamate dehydrogenase (GDH) but not glutamine 2‐oxoglutarate aminotransferase (GOGAT) with interactions for the equation of best fit with P &lt; 0.05 level as nitrogenase (C2H2 red.) = 13.3 nodule wt. + 0.5 nodule no. + 4.5 nodule maturity % + 58.6 GDH, R2 = 80.9 and CV 11%. More knowledge of indigenous pastured legumes, as S. helvola, could have practical significance for improvement of symbiotic N fixation and grazing production for the extensive pastured regions with severe soil and climate limitations.

Further investigation into the utilization of summer spared sourveld

Abstract The effects of various methods of utilizing summer spared sourveld were investigated on two sites at the Döhne Agricultural Research Institute. A grazing trial was conducted where the utilization of veld of northern aspect was investigated when grazed in either early or late winter by sheep and cattle together, at different ratios and different stocking intensities. In the grazing trial very small differences in utilization resulted from the treatments, these differences being correlated mainly with botanical composition. Tuftiness occurred on camps with relatively large proportions of Elyonurus argenteus and Themeda triandra, while uniform utilization was achieved in the other camps. Grazing in autumn or early spring had a slight depressive effect on the herbage yield in the subsequent spring compared with grazing in mid‐winter. No differences in regrowth due to treatment were significant. Comparing mowing, burning and grazing, results showed that mowing had the least harmful effect on regrowth and seeding while spring burning depressed regrowth more than did grazing. Winter grazing depressed seeding slightly, but did not prevent the seeding of any of the species investigated.

EFFECT OF SOIL MOISTURE CONTENT AND STAGE OF DEVELOPMENT ON COLD-HARDINESS OF THE ALFALFA PLANT

Alfalfa plants were grown in the greenhouse to three developmental stages, (1) vegetative (48 days old), (2) early bud (62 days old), and (3) 50% bloom (78 days old), hardened and subjected to freezing temperatures in an environmental control chamber. Prior to hardening, the Tormentine sandy loam soil in which the plants were growing was brought to three moisture levels, (1) 25% of field capacity, (2) field capacity, (3) and saturation.Electrical conductivity of plant exudate from top growth of plants decreased during hardening and with freezing. Conductivity of root exudate increased during hardening but decreased during freezing.Plants were rated for freezing damage, immediately after freezing and 10 days later. Recovery was significantly higher for plants grown on soils at held capacity than at saturation. Differences in regrowth between 25% of field capacity and field capacity were not significant. Total available carbohydrate content and etiolated regrowth were also higher for plants grown in soil at field capacity.Saturated soil had an extremely adverse effect on development of cold-hardiness of alfalfa plants as compared with effect of field capacity and 25% of held capacity.Plants that were mature before hardening and freezing were more hardy under field capacity conditions than less mature stages of plants, as shown by weight of aerial and root portions of plants, carbohydrates, conductivity, growth without light, and rating of recovery after freezing.