Nitrogen losses in puddled soils as affected by timing of water deficit and nitrogen fertilization

Erratic rainfall in rainfed lowlands and inadequate water supply in irrigated lowlands can results in alternate soil drying and flooding during a rice (Oryza sativa L.) cropping period. Effects of alternate soil drying and flooding on N loss by nitrification-denitrification have been inconsistent in previous field research. To determine the effects of water deficit and urea timing on soil NO₃ and NH₄, floodwater NO₃, and N loss from added ¹⁵N-labeled urea, a field experiment was conducted for 2 yr on an Andaqueptic Haplaquoll in the Philippines. Water regimes were continuously flooded, not irrigated from 15 to 35 d after transplanting (DT), or not irrigated from 41 to 63 DT. The nitrogen treatments in factorial combination with water regimes were no applied N and 80 kg urea-N ha^–1, either applied half basally and half at 37 DT or half at 11 DT and half at 65 DT. Water deficit at 15 to 35 DT and 41 to 63 DT, compared with continuous soil flooding, significantly reduced extractable NH₄ in the top 30-cm soil layer and resulted in significant but small (<1.0 kg N ha^–1) soil NO₃ accumulations. Soil NO₃, which accumulated during the water deficit, rapidly disappeared after reflooding. Water deficit at 15 to 35 DT, unlike that at 41 to 63 DT, increased the gaseous loss of added urea N as determined from unrecovered ¹⁵N in ¹⁵N balances. The results indicate that application of urea to young rice in saturated or flooded soil results in large, rapid losses of N (mean = 35% of applied N), presumably by NH₃ volatilization. Subsequent soil drying and flooding during the vegetative growth phase can result in additional N loss (mean = 14% of applied N), presumably by nitrification-denitrification. This additional N loss due to soil drying and flooding decreases with increasing crop age, apparently because of increased competition by rice with soil microorganisms for NH₄ and NO₃.     

Field investigations of ammonia exchange between barley plants and the atmosphere. I. Concentration profiles and flux densities of ammonia

The exchange of ammonia between the atmosphere and the canopy of spring barley crops growing at three levels of nitrogen application (medium N, high N and excessive N) was studied over two consecutive growing seasons by use of micrometeorological techniques. In most cases, ammonia was emitted from the canopy to the atmosphere. The emission started around 2 weeks before anthesis, and peaked about or shortly after anthesis. The volatilization of ammonia only took place in the daytime. During the night-time, atmospheric ammonia was frequently aborbed by the canopy. Occasionally, plants in the medium and high N treatments also absorbed ammonia from the atmosphere during the daytime. Daytime absorption of ammonia never occurred in the excessive N canopy. The loss of ammonia from the canopy amounted in both years to 0.5–1.5 kg NH₃-N ha^?1 and increased with the N status of the canopy. In agreement with the small losses of ammonia, the content of ¹⁵N-labelled nitrogen in the plants did not decline during the grain-filling period. The experimental years were characterized by very favourable conditions for grain dry matter formation, and for re-utilization of nitrogen mobilized from leaves and stems. Consequently, a very high part of the nitrogen in the mature plants was located in grain dry matter (80–84% in 1989; 74–80% in 1990). The efficient re-utilization of nitrogen may have reduced the volatilization of ammonia.     

The natural history of de Brazza's monkey in Kenya

Polygynous groups of de Brazzas monkeys (Cercopithecus neglectus) were observed in the Kisere Forest Reserve between December 1987 and March 1989. Total number of contact hours was 528. Three troops numbered 11, 13, and 16 monkeys. Three solitary adult males were seen. All troops had a single adult male, at least three adult females, and juveniles. Five births occurred in the course of the study. Home range varied from 4.1 to 6 ha, and flooded areas of the forest were heavily used. This species was only found near rivers and spent more than 50% of the time below 5 m. Daily path length ranged from 330 to 1001 m. The de Brazza's monkeys were mainly frugivorous, but leave and invertebrates also formed a substantial part of the diet. Other guenons avoided de Brazza's, which did not join polyspecific interactions.     

渍水对冬小麦生长的危害及其生理效应

小麦受渍后叶片的光合和蒸腾速率迅速下降,而后则显微弱的回升趋势。渍害不仅削弱小麦光合产物的积累,并且改变光合产物在地上部分和根系中的分配比例;植株根／冠比下降,而黄叶的发展与根／冠比的变化呈显著负相关;渍害改变小麦的发育进程,尤其是后期渍害明显促使小麦早衰。认为清水使叶片光合速率降低、光合有效面积损失和衰老加速,从而危害小麦的生长。     

Natal philopatry in passerine birds: genetic or ecological influences?

The degree of natal philopatry (the likelihood that individualsbreed at or near their place of origin) can influence the extentof inbreeding in animal populations. Passerine birds have beencited as typically showing high natal philopatry, and natalphilopatry has been proposed as an adaptation to promote optimalinbreeding. A review of published and unpublished studies ofpasserines showed that natal philopatry was typically low, somaintaining a high level of inbreeding appears relatively unimportantfor such birds. Rather, natal philopatry appeared to be morestrongly influenced by ecological factors. Migratory passerineexhibited low natal philopatry compared to resident passerines,as predicted if dispersal costs for young birds are an importantdeterminant of natal philopatry. The erroneous view that natalphilopatry for passerines is generally high has resulted froma reporting bias toward resident species that have sufficientnatal philopatry to study. Natal philopatry was found to beevolutionarily labile; populations of the same species and pairsof closely related species that differed in their degree ofisolation differed considerably in their degree of philopatry.Future studies of natal philopatry should consider both theecological factors that could affect dispersal costs and thereporting biases that influence which data on philopatry tendto be reported.     

On the ecology of Colurellidae (Rotifera)

A material consisting of 45 colurellid rotifers from diverse waters in south and central Sweden was analyzed to reveal their relationships to their substrate. Periphytic substrates were generally preferred. Most species are obviously mobile and more or less euryecious, but a few show a predilection for bog environments. Some colurellids are euryhaline, but when inhabiting fresh water they prefer rivers and other environments with a high oxygen concentration, probably because of problems with osmoregulation.     

Is there a threshold size regulating seaward migration of brown trout and Atlantic salmon?

We investigated the influence of variation in body size and growth rate on age of smolting in Atlantic salmon and brown trout in four different Norwegian rivers. In Atlantic salmon smolt ages varied between 2 and 6 years, and in brown trout between 2 and 7 years. Smolt age was negatively correlated with parr growth, and positively correlated with smolt size. Age at smolting was more variable in the two northern than the two southern rivers. Smolt sizes and ages were also more variable in brown trout than in Atlantic salmon. Based on the observed variation in smolt size and age, we reject the hypothesis that a threshold size alone regulates age at smolting. Within populations smolt age depends on growth rate so that fast-growing parr smolted younger and smaller than slow-growing parr. We hypothesize that smolt size and age is a trade-off between expected benefits and costs imposed by differences in individual growth rate.     

Variability in the distribution and abundance of stream salmonids, and the associated use of habitat models

The effective management of salmonid fisheries requires that the factors influencing variation in the abundance of stream populations are understood. The use of habitat models to explain the spatial component of population variance offers potential for management, but has not previously been set in the context of long term variation in population abundance because of the lack of suitable data sets. This paper examines contributions of spatial and temporal factors lo fish density variance using a 10-year data set from five tributaries of the River Conwy, North Wales. Recently developed habitat models were applied to the data to test their ability to explain nominal spatial variance. Spatial variance accounted for between 21 and 62% of the overall variance of salmonid abundance, and habitat models explained up to 95% of the spatial variance component. Synchrony in population variation amongst sites within and between tributaries is described, and some of the factors that may influence this are discussed.     

The consequences of habitat occupation and habitat overlap of the introduced tilapia Oreochromis mossambicus and indigenous fish species for fishery management in a Sri Lankan reservoir

Habitat occupation and habitat overlap of the introduced tilapia Oreochromis mossambicus and co-occurring indigenous fish species were studied in a shallow lowland reservoir in Sri Lanka. Results were used to discuss the possible existence of empty habitats in reservoirs and the position of the introduced O. mossambicus in the fish community. Predictions were made of the effects of a subsidiary small-meshed gillnet fishery for indigenous minor cyprinids on the yield of tilapia. The zooplanktivorous halfbeak Hyporamphus gaimardi, an indigenous invader from brackish water estuaries and lagoons, has successfully colonized the pelagic habitat in this reservoir. The habitat of the introduced O. mossambicus overlapped significantly with those of the indigenous minor cyprinids. Only the smallest size classes of O. mossambicus (below 45 mm) arc spatially segregated from these cyprinids. Spatial distribution patterns are influenced by the rainy seasons which trigger an inshore movement of O. mossambicus and several other species around November and May. Barbus spp, (Cyprinidae) need riverine habitats for spawning, but for all other species the available habitats within the reservoir are suitable to complete their full life cycle. Exploitation of Barbus spp. with gillnets with a mesh size of 30-mm stretched mesh is predicted to have considerable detrimental effects on the existing fishery for O. mossambicus. However, a gillnet fishery with 15-mm stretched mesh to exploit Amblypharyngodon melettinus, Rasbora daniconius and H. gaimardi in the open water zone is expected to be successful without harming the existing fishery for O, mossambicus or the populations of Barbus spp.     

PROROCENTRUM BELIZEANUM,PROROCENTRUM ELEGANS,AND PROROCENTRUM CARIBBAEUM,THREE NEW BENTHIC SPECIES (DINOPHYCEAE) FROM A MANGROVE ISLAND,TWIN CAYS,BELIZE1

Three new benthic dinoflagellate species, Prorocentrum belizeanum, Prorocentrum elegans, and Prorocentrum caribbaeum, from mangrove floating detritus are described from scanning electron micrographs. Species were identified based on shape, size, surface micromorphology, ornamentation of thecal plates, and architecture of the periflagellar area and intercalary band. Cells of P. belizeanum are round to slightly oval with a cell size of 55–60 μm long and 50–55 μm wide. Areolae are round and numerous (853–1024 per valve) and range from 0.66 to 0.83 μm in size. The periflagellar area of P. belizeanum is a broad V-shaped depression; it accommodates a flagellar and an auxiliary pore and a flared, curved apical collar. The intercalary band of P. belizeanum is horizontally striated. Prorocentrum elegans is a small species 15–20 μm long and 10–14 μm wide, with an ovate cell shape. The thecal surface is smooth. Two sizes of valve pores were recognized: large, round pores (20–22 per valve) arranged in a distinct pattern and smaller pores situated in an array along the intercalary band. The periflagellar area is V-shaped; it accommodates an uneven sized flagellar pore, an auxiliary pore, and an angled protuberant flagellar plate. The intercalary band is transversely striated. It is a bloom-forming species. Prorocentrum caribbaeum cells are heart-shaped with a rounded anterior end and a pointed posterior end. Cells range from 40 to 45 μm long and 30 to 35 μm wide. Thecal surface has two different-sized pores: large, round pores (145–203 per valve) arranged perpendicularly from the posterior margins, and small, round pores unevenly distributed on the thecal surface. The periflagellar area is ornate. It is V-shaped with a curved apical collar located next to the auxiliary pore; a smaller protuberant apical plate is adjacent to the flagellar pore. The intercalary band is transversely striated and sinuous. Cells are active swimmers.