InGaN epilayer characterization by microfocused x-ray reciprocal space mapping

We report the use of microfocused three-dimensional x-ray reciprocal space mapping to study InGaN epilayers with average InN content 20%-22%. Analysis of the full volume of reciprocal space, while probing samples on the microscale with a focused x-ray beam, allowed us to gain valuable information about the nanostructure of InN-rich InGaN epilayers. It is found that “seed” InGaN mosaic nanocrystallites are twisted with respect to the ensemble average and strain-free. The initial stages of InGaN-on-GaN epitaxial growth, therefore, conform to the Volmer-Weber growth mechanism with “seeds” nucleated on strain fields generated by the a-type edge dislocations

Responses of germination and early growth of scorzonera (Scorzonera hispanica L.) to pH, mineral deficiencies and growth substrates

In order to identify early constraints to scorzonera cultivation, seed germination under a range of pH values, the response of plantlet growth to six different mineral deficiencies and to different growth substrates were investigated in laboratory and outdoor pot experiments. Total germination, time needed for germination to begin and to finish and asymmetry of germination distribution over time was insensitive to pH within the range 5−10. Generalized and clear symptoms of mineral deficiency in plantlets younger than two months were only found in the absence of iron. Significant reductions in shoot and total biomass were found in the absence of magnesium or iron and in the later also in root biomass. Very young scorzonera plantlets seem thus to be able to rapidly accumulate enough mineral reserves to sustain subsequent growth during a considerable period. After seven months growing outdoors, scorzonera plants especially the roots, grew significantly better in a very light texture mixture of sand and vermiculite than in a heavier commercial growth substrate. Altogether, these results suggest that scorzonera is a species able to grow in less favourable environments, thus offering good prospects for its cultivation as cash crop in marginal and less productive soils

Defensive role of allelopathic secondary compounds in plants I: testing two independent general hypotheses

This study tests two general and independent hypotheses with the basic assumption that phytoactive secondary compounds produced by plants evolved primarily as plant defences against competitor plant species. The first hypothesis is that the production and main way of release of phytoactive compounds reflect an adaptive response to climatic conditions. Thus, higher phytoactivity by volatile compounds prevails in plants of hot, dry environments, whereas higher phytoactivity by water-soluble compounds is preponderant in plants from wetter environments. The second hypothesis is that synergy between plant phytoactive compounds is widespread, due to the resulting higher energy efficiency and economy of resources. The first hypothesis was tested on germination and early growth of cucumber treated with either water extracts or volatiles from leaves or vegetative shoot tops of four Mediterranean-type shrubs. The second hypothesis was tested on germination of subterranean clover treated with either water extracts of leaves or vegetative shoot tops of one tree and of three Mediterranean-type shrubs or with each of the three fractions obtained from water extracts. Our data do not support either hypotheses. We found no evidence for higher phytoactivity in volatile compounds released by plants that thrive in hot, dry Mediterranean-type environments. We also found no evidence for the predominance of synergy among the constituents of fractions. To the contrary, we found either antagonism or no interaction of effects among allelopathic compounds

Defensive role of allelopathic secondary compounds in plants: a review of data on two independent general hypotheses

This review examines and whenever appropriate, reanalyses published literature related to two general and independent hypotheses having the underlying assumption that phytoactive secondary compounds produced by plants evolved primarily as plant defences against competitor plant species. The first hypothesis is that production and the main way of release of phytoactive compounds reflect an adaptive response to climate conditions. Thus, higher phytoactivity by volatile-compounds should prevail in plants of hot, dry environments whereas higher phytoactivity by water- solubles should be preponderant in plants from wetter environments. The second hypothesis is that the synergy between phytoactive compounds of plants should be widespread while antagonism or absence of interaction of effects should be rare because of the higher efficiency of energy and use of resources provided by synergy. Published literature does not support either hypotheses. We found no pattern of association between higher phytoactivity in volatile compounds in plants from drier environments or in water-soluble compounds in plants from wetter environments. Neither did we found evidences for the predominance of synergy. On the contrary, antagonism or no interaction of effects among allelopathic compounds largely prevailed

Ionic effects of NaCl counter osmotic inhibition of germination and seedling growth of Scorzonera hispanica and subsequent plantlet growth is not affected by salt

Scorzonera (Scorzonera hispanica) is experiencing range reduction in Portugal while its distribution in the Iberian Peninsula largely coincides with areas affected by salinization. Thus two experiments were conducted to evaluate the response of scorzonera to salinity. In the first experiment, seed germination and seedling growth were investigated under osmotic potentials down to −1.21 MPa using NaCl or iso-osmotic polyethylene glycol (PEG) solutions. Results of PEG treatments show that osmotic potential alone reduces germination and seedling growth while on NaCl reductions were much lower. Ionic effects of NaCl are stimulatory and clearly counteract osmotic effects. Most seeds completed germination after being transferred from PEG to distilled water. Conversely, on NaCl recovery results essentially from more time allowed for seeds to complete germination. In the second experiment, young plantlets were treated with NaCl solutions up to 250 mM. In general plantlets were insensitive to NaCl except for a concentration-dependent increase of relative chlorophyll content suggesting that scorzonera tolerance to NaCl might depend upon nitrogen availability. Altogether, results support the conclusion that scorzonera may be a naturally salt tolerant species able to accumulate and sequester NaCl, its tolerance increasing as plants grow older

Seed germination in Cistus ladanifer: heat shock, physical dormancy, soil temperatures and significance to natural regeneration

Seeds of Cistus ladanifer experience bursts of germination following fires. The effects of heat shock from 10 °C to 150 °C on seed germination were investigated by final germination plus the number of days required for germination to start and finish, and symmetry of cumulative germination. The occurrence of physical dormancy in C. ladanifer seeds was investigated by a variety of methods, including imbibition, scanning electron microscopy (SEM) and light microscopy, and use of dyes. The significance of responses of C. ladanifer seeds to fires was investigated essentially by abstracting existing literature and by using fire effects models and simulations. Parameters of germination were variously affected by heat treatments—positively in the range 80100 °C, negatively above 130 °C. Non-dormancy was consistently found in about 30% of seeds but no evidence was obtained to support the existence of physical dormancy in the dormant fraction of C. ladanifer seeds. Two complementary processes seem to be in place in seeds response to fire. A direct fire-driven increase in germination of virtually all seeds in response to the appropriate heat load produced by fire or, in the absence of such heat loads, the germination of the non-dormant fraction provided that above-ground vegetation burns

Ranking Mediterranean-type shrubs and trees by their allelopathic activity is not independent of how extract concentration is expressed

Water extracts from nineteen Mediterranean-type shrubs and trees were screened for phytoactivity on germination of lettuce. The existing model for the effects of pH and osmotic pressure on germination requires refitting. Extract concentrations were expressed as plant fresh weight, plant dry weight and extract dry weight and final ranking of the six phytoactive species was found to strongly depend on the way the concentrations are expressed. This methodological issue undoubtedly requires consideration when designing allelopathic bioassays. Extract dry weight is conceptually the most adequate way to express concentration and should be used despite the increase in time and labor it requires

Activity of water extracts of Cistus ladanifer and Lavandula stoechas in soil on germination and early growth of wheat and Phalaris minor

The phytoactivity of water extracts of C. ladanifer and L. stoechas on P. minor germination, as observed under controlled conditions, was lost in soil. Conversely, early growth of wheat and P. minor was sensitive to water extracts of C. ladanifer and L. stoechas. Nevertheless, because of differential effects on early growth of the weed and crop, L. stoechas unlike C. ladanifer, is worth searching for inhibitors of P. minor, among the ca. 80 compounds identified so far in its essential oil

Allelopathy, seed germination, weed control and bioassay methods

Even before its formal establishment as a scientific discipline, allelopathy has been intertwined with agriculture and the potential of allelopathy for weed control has been a permanent matter of interest. Therefore we investigate the importance of seeds and of permanent soil seed banks as a means for propagation of weed species as well as strategies for long-term weed control. Depleting seed banks is critical and encouraging weed seed germination prior to sowing crops is one of the most promising targets for weed control by allelopathins. The share of interest in weed control and in germination in Allelopathy Journal is also examined. Finally we present and discuss methodologic aspects to be taken into account in allelopathic studies for efficient weed control by either permanently inhibiting weed seed germination or by stimulating weed seed germination

Uso De água Residuária Da Piscicultura No Cultivo De Alface

Lettuce stands out as the main leafy vegetable consumed in Brazil, with divergence regarding adaptability to different environmental conditions, which include salinity. The objective of the work was to evaluate the response of lettuce cultivars to the use of saline wastewater from fish farming. The experiment was conducted in a completely randomized design with four replicates, in a factorial 7 × 4, corresponding to seven cultivars (Regiane, Vera, Isabela, Elisa, Amelia, Lavinia and Angelina) and four salt concentrations (1.2, 2.2, 3.2 and 4.2 dS m-1). The evaluated characteristics were: number of leaves, leaf area, crown diameter and shoot fresh and dry matter. Diluted wastewater from fish farming can be used in the preparation of solution for fertigation of lettuce. The cultivars Regiane and Elisa had higher production of leaves and leaf area, while Amélia and Angelina were the most productive in terms of biomass. The cultivars Vera, Isabela, Amélia and Angelina were more tolerant to the salinity of the fertigation solution. © 2016, Departamento de Engenharia Agricola - UFCG/Cnpq. All rights reserved.20872873