Soils,a sink for N2O? A review

Soils are the main sources of the greenhouse gas nitrous oxide (N₂O). The N₂O emission at the soil surface is the result of production and consumption processes. So far, research has concentrated on net N₂O production. However, in the literature, there are numerous reports of net negative fluxes of N₂O, (i.e. fluxes from the atmosphere to the soil). Such fluxes are frequent and substantial and cannot simply be dismissed as experimental noise.
Net N₂O consumption has been measured under various conditions from the tropics to temperate areas, in natural and agricultural systems. Low mineral N and large moisture contents have sometimes been found to favour N₂O consumption. This fits in with denitrification as the responsible process, reducing N₂O to N₂. However, it has also been reported that nitrifiers consume N₂O in nitrifier denitrification. A contribution of various processes could explain the wide range of conditions found to allow N₂O consumption, ranging from low to high temperatures, wet to dry soils, and fertilized to unfertilized plots. Generally, conditions interfering with N₂O diffusion in the soil seem to enhance N₂O consumption. However, the factors regulating N₂O consumption are not yet well understood and merit further study.
Frequent literature reports of net N₂O consumption suggest that a soil sink could help account for the current imbalance in estimated global budgets of N₂O. Therefore, a systematic investigation into N₂O consumption is necessary. This should concentrate on the organisms, reactions, and environmental factors involved.     

Two‐step vegetation response to enhanced precipitation in Northeast Brazil during Heinrich event 1

High resolution palynological and geochemical data of sediment core GeoB 3910‐2 (located offshore Northeast Brazil) spanning the period between 19 600 and 14 500 calibrated year bp (19.6–14.5 ka) show a land‐cover change in the catchment area of local rivers in two steps related to changes in precipitation associated with Heinrich Event 1 (H1 stadial). At the end of the last glacial maximum, the landscape in semi‐arid Northeast Brazil was dominated by a very dry type of caatinga vegetation, mainly composed of grasslands with some herbs and shrubs. After 18 ka, considerably more humid conditions are suggested by changes in the vegetation and by C_org and C/N data indicative of fluvial erosion. The caatinga became wetter and along lakes and rivers, sedges and gallery forest expanded. The most humid period was recorded between 16.5 and 15 ka, when humid gallery (and floodplain) forest and even small patches of mountainous Atlantic rain forest occurred together with dry forest, the latter being considered as a rather lush type of caatinga vegetation. During this humid phase erosion decreased as less lithogenic material and more organic terrestrial material were deposited on the continental slope of northern Brazil. After 15 ka arid conditions returned. During the humid second phase of the H1 stadial, a rich variety of landscapes existed in Northeast Brazil and during the drier periods small pockets of forest could probably survive in favorable spots, which would have increased the resilience of the forest to climate change.     

VISUAL CHARACTERIZATION OF THE ESTHETIC QUALITY OF THE ROSEBUSH

Since its introduction into the analysis of foodstuffs, sensory analysis has been applied in several contexts. This work seeks to widen the field of sensory analysis to include ornamental plants and to characterize their esthetic quality. Using the rosebush as a plant model, an attribute generation protocol is proposed in order to develop a conventional profile of such products. Further to statistical treatments aiming to verify the unambiguity, discrimination and independence of these attributes, a reduced list of 18 attributes has been set up. These attributes make up the very core of the conventional profiling studies currently undertaken .

PRACTICAL APPLICATIONS

The generation of a list of attributes that is not too long, in order to describe plants as exhaustively as possible, is one of the first steps of extending sensory analysis methods to ornamental horticulture. This list will be used to train a panel of assessors to characterize the rosebush.
Two applications are in progress. The first application consists of evaluating the impact of nitrogen nutrition on the visual quality of the rosebush. The second has the objective of determining which characteristics influence consumer preferences.     

Heat Stress-induced Abortion of Buds and Flowers in Pea: Is Sensitivity Linked to Organ Age or to Relations between Reproductive Organs?

A short period of heat stress can cause a significant increasein abortion frequency of floral buds and flowers in pea, buta large variability in sensitivity exists among reproductiveorgans (ROs) within a plant or between plants. We have analysedspatial distribution of abortion frequency in plants subjectedor not subjected to heat stress in: (1) four controlled environmentexperiments in which apex temperature was increased to 31 °Cfor 6 h per day for 4 d (moderate stress); (2) one field experimentwith a similar level of stress; and (3) one experiment with2 d with 33/30 °C day/night (severe stress) in additionto treatment (1). Influence of neighbouring organs on sensitivityto heat stress was analysed by partial flower removal. Severeheat stress caused rapid interruption of RO development followedby abscission while, in moderate stress, at leat 4 d elapsedbetween cessation of stress and first symptoms of abortion.In both moderate stress and control treatments, abortion frequencyfollowed a consistent pattern along the stem with no abortionon the lowest reproductive phytomeres, a temperature-dependentabortion frequency on intermediate phytomeres and 100% abortionon apical phytomeres. Regardless of temperature, this patternwas shifted by four positions if ROs were removed on the lowestfour reproductive phytomeres, and no abortion was observed ifyoung pods were sequentially removed. Moderate heat stress increasedthe effect of developing ROs on abortion frequency of youngerROs located above them. We suggest that the effect of mild stressshould be viewed as the acceleration of a programme linked tothe normal termination of phytomere production during the plantcycle, rather than as an abrupt event linked to stress. Pisum sativum; heat stress; abortion; abscission; age; organ-to-organ relations