Temporal variation in density of epiphytic bacteria on submerged vegetation in a calcareous stream

The density of epiphytic bacteria on (1) leaves, (2) stems and petioles, and (3) whole shoots of submerged Nasturtium officinale, Apium nodiflorum and Glyceria fluitans was determined from January to June 1984 in a calcareous stream in North Humberside. The density on leaves was less than on stems and petioles; reasons for this are suggested. The density on all three species decreased from late January to February-March and then increased to June. This temporal change was related to environmental variables (e. g. negative correlation with discharge and positive correlation with temperature), a situation which contrasts with Baker & Orr (1986) who found no such relationships in a Southern England chalk stream.     

Epilithic bacteria in an acid and a calcareous headstream

SUMMARY. 1. Environmental variables and epilithic bacteria on small stones were monitored during summer and winter in Burbage Brook and the River Lathkill, two headstreams in the Derbyshire Peak District.
2. Burbage Brook was usually near-neutral in summer, but acid in winter; the River Lathkill was circumneutral throughout the year.
3. In summer, epilithic bacteria showed few between-stream differences. In winter, however, total bacteria, colony-forming units, per cent chromogenic colony-forming units, per cent viable bacteria, V_max for glucose mineralization and V_max/bacterium were all significantly less in the acid Burbage Brook.
4. Inhibition of epilithic bacteria in Burbage Brook was also observed when pH fell to a low level during a summer spate.
5. Multiple-regression analysis confirmed that epilithic bacteria were less successful at low pH but also suggested that pH was not the only environmental variable to influence epilithic bacteria. Especially notable were positive relationships with density of epilithic chlorophyll a and temperature in Burbage Brook and with chlorophyll a in the River Lathkill.     

Downstream increase in the abundance and heterotrophic activity of suspended bacteria in an intermittent calcareous headstream

SUMMARY. 1. Concentration of total bacteria, and heterotrophic activity (as turnover rate for glucose assimilation), in the water of an intermittent spring-fed calcareous headstream, increased with distance from the source to 1600 m.
2. This increase was gradual rather than stepwise and might be due to release of bacteria from submerged vegetation and the stream bed, and to input of terrestrial bacteria with groundwater.
3. The increment per unit length of stream was greatest in summer when aquatic vegetation was most abundant and discharge was low.
4. When the stream was partly dry, isolated peaks of suspended bacteria occurred and there was no regular downstream increase.
5. A lesser spring which upwelled into a natural basin consistently contained more suspended bacteria than the principal source, which was an artificial culvert.     

A note on the attachment rate of suspended bacteria to submerged aquatic plants in a calcareous stream

The density of epiphytic bacteria on leaflets of laboratory-grown Apium nodiflorum , immersed in calcareous stream water, increased linearly with time over 10 h, both in the laboratory and in the field. This increase was probably due to attachment of suspended bacteria. The rate of attachment to leaflets of plants, immersed in a stream at different concentrations of suspended bacteria, was linearly related to the concentration of suspended bacteria. The attachment rate, relative to concentration, was 1.7 × 10⁴ bacteria/cm²/h for each 10⁵ bacteria/ml in the surrounding water.     

中国东部温带植被生长季节的空间外推估计

利用地面植物物候和遥感归一化差值植被指数（NDVI）数据,以及一种物候-遥感外推方法,实现植被生长季节从少数站点到较多站点的空间外推。结果表明：（1）在1982～1993年期间,中国东部温带地区植被生长季节多年平均起讫日期的空间格局与春季和秋季平均气温的空间格局相关显著;（2）在不同纬度带和整个研究区域,植被生长季节结束日期呈显著推迟的趋势,而开始日期则呈不显著提前的趋势,这与欧洲和北美地区植被生长季节开始日期显著提前而结束日期不显著推迟的变化趋势完全不同;（3）北部纬度带的植被生长季节平均每年延长1．4～3．6d,全区的植被生长季节平均每年延长1．4d,与同期北半球和欧亚大陆植被生长季节延长的趋势数值相近;（4）植被生长季节结束日期的显著推迟与晚春至夏季的区域性降温有关,而植被生长季节开始日期的不显著提前则与晚冬至春季气温趋势的不稳定变化有关;（5）在年际变化方面,植被生长季节开始和结束日期分别与2～4月份平均气温和5～6月份平均气温呈负相关关系。     

Long-term change in calcareous grassland vegetation and drivers over three time periods between 1970 and 2016

Plant Ecology - Analysis of long-term vegetation change is limited. Furthermore most studies evaluating change only examine two snapshots in time, which makes it difficult to define rates of change...     

Photosynthesis at ambient and elevated humidity over a growing season in soybean

Daytime rates of net photosynthesis of upper canopy leaflets of soybeans were compared on 17 days for leaflets exposed to air at the ambient humidity and at a higher humidity. Leaflets at the higher humidity had higher rates of net photosynthesis on 16 of the 17 days. The daily total of net photosynthesis of leaflets at the higher humidity was on average 1.32 times that for leaflets at ambient humidity. A strong limitation of net photosynthesis by ambient humidity was found throughout the growing season.     

Mn accumulation in a submerged plant Egeria densa (Hydrocharitaceae) is mediated by epiphytic bacteria

Many aquatic plants act as biosorbents, removing and recovering metals from the environment. To assess the biosorbent activity of Egeria densa, a submerged freshwater macrophyte, plants were collected monthly from a circular drainage area in Lake Biwa basin and the Mn concentrations of the plants were analysed. Mn concentrations in these plants were generally above those of terrestrial hyperaccumulators, and were markedly higher in spring and summer than in autumn. Mn concentrations were much lower in plants incubated in hydroponic medium at various pH levels with and without Mn supplementation than in field‐collected plants. The precipitation of Mn oxides on the leaves was determined by variable pressure scanning electron microscopy‐energy dispersive X‐ray analysis and Leucoberbelin blue staining. Several strains of epiphytic bacteria were isolated from the field‐collected E. densa plants, with many of these strains, including those of the genera Acidovorax, Comamonas, Pseudomonas and Rhizobium, found to have Mn‐oxidizing activity. High Mn concentrations in E. densa were mediated by the production of biogenic Mn oxide in biofilms on leaf surfaces. These findings provide new insights into plant epidermal bacterial flora that affect metal accumulation in plants and suggest that these aquatic plants may have use in Mn phytomining.     

Effects of seasonal snow on the growing season of temperate vegetation in China

Variations in seasonal snowfall regulate regional and global climatic systems and vegetation growth by changing energy budgets of the lower atmosphere and land surface. We investigated the effects of snow on the start of growing season (SGS) of temperate vegetation in China. Across the entire temperate region in China, the winter snow depth increased at a rate of 0.15 cm yr^?1 (P = 0.07) during the period 1982–1998, and decreased at a rate of 0.36 cm yr^?1 (P = 0.09) during the period 1998–2005. Correspondingly, the SGS advanced at a rate of 0.68 day yr^?1 (P < 0.01) during 1982–1998, and delayed at a rate of 2.13 day yr^?1 (P = 0.07) during 1998–2005, against a warming trend throughout the entire study period of 1982–2005. Spring air temperature strongly regulated the SGS of both deciduous broad‐leaf and coniferous forests, whereas the winter snow had a greater impact on the SGS of grassland and shrubs. Snow depth variation combined with air temperature contributed to the variability in the SGS of grassland and shrubs, as snow acted as an insulator and modulated the underground thermal conditions. In addition, differences were seen between the impacts of winter snow depth and spring snow depth on the SGS; as snow depths increased, the effect associated went from delaying SGS to advancing SGS. The observed thresholds for these effects were snow depths of 6.8 cm (winter) and 4.0 cm (spring). The results of this study suggest that the response of the vegetation's SGS to seasonal snow change may be attributed to the coupling effects of air temperature and snow depth associated with the underground thermal conditions.     

Quantitative observations on the ability of epiphytic bacteria to contribute to the populations of suspended bacteria in two dissimilar headstreams

SUMMARY. 1. Concentration of suspended bacteria in a calcareous headstream increased linearly from the source to 48 m; this indicated a diffuse origin of bacteria.
2. Drift loss of suspended bacteria and glucose-mineralization capacity from this length of stream were measured, and estimates were also made of the total number and glucose-mineralization capacity of epiphytic bacteria associated with the luxuriant submerged aquatic vegetation.
3. Mean drift loss per day represented 11–12% of total epiphytic bacteria and 8–18% of epiphyte glucose-mineralization capacity, hence the epiphytic population should be well able to sustain the observed downstream losses.
4. In a 90 m length of a contrasting acid, granitic, headstream, in which submerged vegetation was principally a leafy liverwort, there was no downstream change in concentration of suspended bacteria.
5. A substantial population of epiphytic bacteria was found in the acid stream, sufficient for only a 1–2% daily release to produce a doubling in concentration of suspended bacteria; reasons are suggested for the apparent non-release of epiphytes.     

Physiological state of epiphytic bacteria on submerged stems of the reed Phragmites australis compared with planktonic bacteria in gravel-pit ponds

Suspensions of epiphytic bacteria from submerged stems of Phragmites australis , collected from a gravel-pit pond, were prepared by treatment in a stomacher and by brushing. The two procedures were equally successful in dislodging bacteria. These epiphytic bacteria were compared with planktonic bacteria in water samples from within the reed bed. Colony-forming units (cfu) as a percentage of acridine-orange direct counts (AODCs), percentage of cells capable of intracellular reduction of 2-( p -iodophenyl)-3-( p -nitrophenyl)-5-phenyl tetrazolium chloride (INT) to INT-formazan, percentage of cells able to form microcolonies, and cell length were all greater for epiphytic bacteria. Epiphytic bacteria of P. australis from six further gravel-pit ponds were also compared with bacterioplankton; cfu as a percentage of AODCs, and percentage of cells capable of INT reduction were again greater for epiphytic bacteria. Because the epiphytic bacteria in these non-organically-enriched, gravel-pit ponds were physiologically different from the planktonic bacteria it is suggested that there was not continual casual exchange, by largely identical bacterial cells, between the epiphytic and planktonic mode. Instead, epiphytic and planktonic populations were independent of each other and/or if there was exchange then bacteria were more successful while in the attached mode, perhaps because of greater organic-nutrient availability at the stem surface.     

Landscape controls on the timing of spring,autumn, and growing season length in mid‐Atlantic forests

The timing of spring leaf development, trajectories of summer leaf area, and the timing of autumn senescence have profound impacts to the water, carbon, and energy balance of ecosystems, and are likely influenced by global climate change. Limited field‐based and remote‐sensing observations have suggested complex spatial patterns related to geographic features that influence climate. However, much of this variability occurs at spatial scales that inhibit a detailed understanding of even the dominant drivers. Recognizing these limitations, we used nonlinear inverse modeling of medium‐resolution remote sensing data, organized by day of year, to explore the influence of climate‐related landscape factors on the timing of spring and autumn leaf‐area trajectories in mid‐Atlantic, USA forests. We also examined the extent to which declining summer greenness (greendown) degrades the precision and accuracy of observations of autumn offset of greenness. Of the dominant drivers of landscape phenology, elevation was the strongest, explaining up to 70% of the spatial variation in the onset of greenness. Urban land cover was second in importance, influencing spring onset and autumn offset to a distance of 32 km from large cities. Distance to tidal water also influenced phenological timing, but only within ~5 km of shorelines. Additionally, we observed that (i) growing season length unexpectedly increases with increasing elevation at elevations below 275 m; (ii) along gradients in urban land cover, timing of autumn offset has a stronger effect on growing season length than does timing of spring onset; and (iii) summer greendown introduces bias and uncertainty into observations of the autumn offset of greenness. These results demonstrate the power of medium grain analyses of landscape‐scale phenology for understanding environmental controls on growing season length, and predicting how these might be affected by climate change.     

Circadian rhythms vary over the growing season and correlate with fitness components

Circadian clocks have evolved independently in all three domains of life, suggesting that internal mechanisms of time‐keeping are adaptive in contemporary populations. However, the performance consequences of either discrete or quantitative clock variation have rarely been tested in field settings. Clock sensitivity of diverse segregating lines to the environment remains uncharacterized as do the statistical genetic parameters that determine evolutionary potential. In field studies with Arabidopsis thaliana, we found that major perturbations to circadian cycle length (referred to as clock period) via mutation reduce both survival and fecundity. Subtler adjustments via genomic introgression of naturally occurring alleles indicated that clock periods slightly >24 hr were adaptive, consistent with prior models describing how well the timing of biological processes is adjusted within a diurnal cycle (referred to as phase). In segregating recombinant inbred lines (RILs), circadian phase varied up to 2 hr across months of the growing season, and both period and phase expressed significant genetic variances. Performance metrics including developmental rate, size and fruit set were described by principal components (PC) analyses and circadian parameters correlated with the first PC, such that period lengths slightly >24 hr were associated with improved performance in multiple RIL sets. These experiments translate functional analyses of clock behaviour performed in controlled settings to natural ones, demonstrating that quantitative variation in circadian phase is highly responsive to seasonally variable abiotic factors. The results expand upon prior studies in controlled settings, showing that discrete and quantitative variation in clock phenotypes correlates with performance in nature.     

Reduced snow cover changes nitrogen use in canopy and understory vegetation during the subsequent growing season

Plant and Soil - We examined how mechanical management of invasive macrophyte, Typha × glauca alters plant-soil interactions underlying carbon processes and nutrient cycling, which are...     

Character of short-term changes in the total number of soil bacteria, including ammonifiers, during the growing season

The total incidence of bacteria and the number of ammonificators were assayed to the direct count and plating techniques, respectively, several times within the vegetative period in the course of ten days under the field conditions. The incidence of the former and the latter varied though not in parallel, and the variations were temporal. The total bacterial incidence depended considerably on soil water content; in ammonificators, moisture determined only the level at which their number changed. The character of oscillations is suggestive of the rate of microbial growth at different periods of the vegetative stage. Daily determination of their number several times within the same period may result in contradictory conclusions.     

Carbon budget and methane and nitrous oxide emissions over the growing season in a Miscanthus sinensis grassland in Tomakomai,Hokkaido, Japan

Species in the Miscanthus genus have been proposed as biofuel crops that have potential to mitigate elevated atmospheric carbon dioxide (CO₂) levels and nitrous oxide (N₂O) and methane (CH₄) emissions. Miscanthus sinensis is widespread throughout Japan and has been used for biomass production for centuries. We assessed the carbon (C) budget and N₂O and CH₄ emissions over the growing season for 2 years in a M. sinensis‐dominated grassland that was naturally established around 1972 in Tomakomai, Hokkaido, Japan, which is near the northern limit for M. sinensis grassland establishment on Andisols. Average C budget was ?0.31 Mg C ha^?1, which indicates C was released from the grassland ecosystem to the atmosphere. Dominant components in the C budget appeared to be aboveground net primary production of plants (1.94–2.80 Mg C ha^?1) and heterotrophic respiration (2.27–3.11 Mg C ha^?1). The measurement of belowground net primary production (BNPP) of plants in the M. sinensis grassland was extremely variable, thus only an approximate value could be calculated. Mean C budget calculated with the approximated BNPP value was 1.47 and ?0.23 Mg C ha^?1 for 2008 and 2009, respectively. Given belowground biomass (9.46–9.86 Mg C ha^?1) was 3.1–6.5 times higher than that of aboveground biomass may provide additional evidence suggesting this grassland represents a C sink. Average CH₄ emissions across years of ?1.34 kg C ha^?1 would indicate this grassland acts as an atmospheric CH₄ sink. Furthermore, average N₂O emissions across years were 0.22 kg N ha^?1. While the site may contribute N₂O to the atmosphere, this value is lower compared with other grassland types. Global warming potential calculated with the approximated BNPP value was ?5.40 and 0.95 Mg CO₂ Eq ha^?1 for 2008 and 2009, respectively, and indicates this grassland could contribute to mitigation of global warming.     

Carbon dioxide exchange fluxes of a boreal peatland over a complete growing season, Komi Republic, NW Russia

The carbon pool of peatlands has been considered as potentially unstable in a changing climate. This study is the first presenting carbon dioxide (CO₂) net ecosystem exchange, CO₂ efflux due to ecosystem respiration and CO₂ uptake by gross primary production over a complete growing season for different microforms of a boreal peatland in Russia (61°56′N, 50°13′E). CO₂ fluxes were measured using the closed chamber technique from the 25th April in the period of snow melt until the end of the vegetation period and the first frost on the 20th October 2008 at seven different microform types: minerogenous and ombrogenous hollows, lawns and hummocks, respectively, and Carex lawns situated in a transition zone between minerogenous and ombrogenous mire parts. The total number of chamber flux measurements was 5,517. Ombrogenous hummocks and lawns were sources of CO₂ over the investigation period whereas hollows and minerogenous lawns were CO₂ sinks. Some plots of Carex lawns and minerogenous hummocks were sinks while other plots of these microform types were sources. The CO₂ fluxes were characterised by large variability not only between the microform types but also within the respective microform types. Of all microform types, the Carex, ombrogenous, and minerogenous lawns showed the highest variability in CO₂ fluxes, which is probably related to a stronger within-microform heterogeneity in vegetation composition and coverage as well as in the water table level. Air temperature was one of the dominant controls on the CO₂ flux dynamics. Water table and green area index were found to have strong influence on CO₂ fluxes both within different patches of the same microform type as well as between different microforms.     

Phenology shifts at start vs. end of growing season in temperate vegetation over the Northern Hemisphere for the period 1982–2008

Changes in vegetative growing seasons are dominant indicators of the dynamic response of ecosystems to climate change. Therefore, knowledge of growing seasons over the past decades is essential to predict ecosystem changes. In this study, the long‐term changes in the growing seasons of temperate vegetation over the Northern Hemisphere were examined by analyzing satellite‐measured normalized difference vegetation index and reanalysis temperature during 1982–2008. Results showed that the length of the growing season (LOS) increased over the analysis period; however, the role of changes at the start of the growing season (SOS) and at the end of the growing season (EOS) differed depending on the time period. On a hemispheric scale, SOS advanced by 5.2 days in the early period (1982–1999) but advanced by only 0.2 days in the later period (2000–2008). EOS was delayed by 4.3 days in the early period, and it was further delayed by another 2.3 days in the later period. The difference between SOS and EOS in the later period was due to less warming during the preseason (January–April) before SOS compared with the magnitude of warming in the preseason (June–September) before EOS. At a regional scale, delayed EOS in later periods was shown. In North America, EOS was delayed by 8.1 days in the early period and delayed by another 1.3 days in the later period. In Europe, the delayed EOS by 8.2 days was more significant than the advanced SOS by 3.2 days in the later period. However, in East Asia, the overall increase in LOS during the early period was weakened in the later period. Admitting regional heterogeneity, changes in hemispheric features suggest that the longer‐lasting vegetation growth in recent decades can be attributed to extended leaf senescence in autumn rather than earlier spring leaf‐out.