Response of collembolan assemblages to plant species successional gradient

It has been acknowledged that soil organisms play a significant role in nutrient cycling and thus may affect productivity and competition within plant assemblages with potential effects on vegetation trajectories. However, few studies have considered a single conceptual framework referring to both above–belowground linkages and plant succession. Consequently, we lack knowledge on the effects of plant successional processes on the dynamics of soil biota. Given this dearth of information, our study aimed to describe the dynamics of a major group of soil fauna, namely collembola, during the secondary succession on chalky slopes edging the Seine River. We selected five different plant assemblages as representative of a chronosequence: short grassland, tall grassland, encroached grassland, shrubland and forest. Our results clearly highlighted a strong response of collembolan assemblages to vegetation gradient. The changes in collembolan diversity were due to a high turnover rate in early successional stages and to nestedness in late successional stages. In addition, each collembolan life form had a specific response to vegetal succession. Euedaphic assemblages increased progressively during the succession while epedaphic did not follow a clear pattern. Our results also indicated a link between the dynamics of collembolan assemblages and plant life forms (e.g. trees and graminoids) rather than plant diversity. A focus on life forms, for plants and soil biota, seems to provide a good framework to study linkages between above and belowground biota.     

Evaluation of two methods of soil quality assessment as influenced by slash and burn in tropical rainforest ecology of Nigeria

The sustainability of slash-and-burn agriculture for sustainable crop production has been a subject of controversy. The objective of this study was to quantify the effect of slash and burn on soil quality. Two sites, Ibadan (7° 23′ N; 3° 51′ E) and Akure (7° 17′ N; 5° 14′ E), within the tropical rainforest of Nigeria were selected for the study. Burnt and unburnt soils were cropped with maize, melon, and cowpea (in sole and intercrops). Soil and earthworm cast samples were collected and analyzed for physical, chemical, and biological indicators. Integration into soil processes and quality indices involved the transformation of analyzed indicators using Soil Management Assessment Framework (SMAF) and Multiple Variable Indicator Transform (MVIT) techniques. Organic matter, water-stable aggregates, pH, cation exchange capacity, macroporosity, and water infiltration were reduced after burning in both sites. Active carbon and potentially mineralizable nitrogen increased after burning at Ibadan but decreased after burning at Akure. Soil quality decreased after burning by a range of 11.3–24.8% using SMAF and MVIT, respectively, although only MVIT showed significant differences (p ≤ 0.05). Test crops increased in yields on burnt soils due to prompt release of nutrients to the crops; the benefit was dwarfed by the adverse effects of burning on soil quality indices.     

Effect of the NH4/NO3 ratio on GS and PEPCase activities and on dry matter production in wheat

Previous experiments have indicated that under greenhouse and hydroponic conditions, spring wheat (Triticum aestivum L.) produces higher yields, more tillers and dry matter when supplied with mixtures of NH₄ and NO₃ than when supplied with only one of them. The goal of this study was to evaluate the effect of selected ammonium and nitrate mixtures on dry matter yield, content of soluble protein, and phosphoenolpyruvate carboxylase (PEPCase) and glutamine synthetase (GS) enzymatic activities. Cultivar ‘Salamanca’ wheat plants, 21 days old, were grown in one of five solutions containing one of the following: 7/0, 5/2, 3.5/3.5, 2/5 or 0/7 meq l^‐1 of NH₄NO₃.

After two weeks of treatment applications, the highest dry matter production in both roots and shoots of the 35‐day‐old plants was observed in plants receiving the 2/5 NH₄/NO₃ ratio. The same response was observed on the accumulation of soluble protein and the potential activity of PEPCase. The specific activity of PEPCase was related to the plant applications of ammonium.

Treatments 3.5/3.5 and 2/5 NH₄/NO₃ ratio enhanced leaf GS activity between 28 and 57 days, and it was consistently 300–500% higher than root activity during the same period. Dry weight of the leaves, stems and grain showed the highest yields with those treatments at the physiological maturity of grains (105 days).     

Canopy fuel characteristics in relation to crown fire potential in pine stands: analysis, modelling and classification

Crown fire occurrence and subsequent crown fire behaviour are strongly dependent on canopy fuel characteristics, especially canopy fuel load (CFL), canopy bulk density (CBD) and canopy base height (CBH). Therefore, quantification of such variables is required for the appropriate selection of silvicultural treatments aimed at reducing susceptibility to crown fire. Data from the IV Spanish National Forest Inventory and individual tree biomass dry weight equations were used to estimate the canopy fuel characteristics of four representative types of pine stands in north-western Spain. Probability of crown fire initiation and crown fire rate of spread were simulated by using the mean surface fuel load observed for each type of pine in this area and assuming different burning conditions. The results indicate that a 22.13 % of the sample plots analysed showed a rather high potential for active crown fire spread under moderate burning conditions, and this value increases to 69.27 % under extreme burning conditions. Equations relating the canopy fuel characteristics to common stand variables (stand density, basal area and dominant height) were fitted simultaneously for each pine, and weighting factors for heteroscedasticity were included. The models explained more than 93.90, 74.70 and 69.42 % of the observed variability in CFL, CBD and CBH, respectively. Basal area was the most important variable for estimating CFL and CBD while dominant height explained most of the observed variability in CBH. The use of the fitted equations together with existing dynamic growth models and fire management decision support systems will enable assessment of the crown fire potential associated with different silvicultural alternatives used in these types of pine stands.     

Plant species richness and ecosystem multifunctionality in global drylands

Experiments suggest that biodiversity enhances the ability of ecosystems to maintain multiple functions, such as carbon storage, productivity, and the buildup of nutrient pools (multifunctionality). However, the relationship between biodiversity and multifunctionality has never been assessed globally in natural ecosystems. We report here on a global empirical study relating plant species richness and abiotic factors to multifunctionality in drylands, which collectively cover 41% of Earth's land surface and support over 38% of the human population. Multifunctionality was positively and significantly related to species richness. The best-fitting models accounted for over 55% of the variation in multifunctionality and always included species richness as a predictor variable. Our results suggest that the preservation of plant biodiversity is crucial to buffer negative effects of climate change and desertification in drylands.     

Coupling quantum tunneling with cavity photons

Tunneling of electrons through a potential barrier is fundamental to chemical reactions, electronic transport in semiconductors and superconductors, magnetism, and devices such as terahertz oscillators. Whereas tunneling is typically controlled by electric fields, a completely different approach is to bind electrons into bosonic quasiparticles with a photonic component. Quasiparticles made of such light-matter microcavity polaritons have recently been demonstrated to Bose-condense into superfluids, whereas spatially separated Coulomb-bound electrons and holes possess strong dipole interactions. We use tunneling polaritons to connect these two realms, producing bosonic quasiparticles with static dipole moments. Our resulting three-state system yields dark polaritons analogous to those in atomic systems or optical waveguides, thereby offering new possibilities for electromagnetically induced transparency, room-temperature condensation, and adiabatic photon-to-electron transfer.     

Geostatistical analysis of fruit yield and detachment force in coffee

The aim of this study was to use geostatistical analysis to evaluate the spatial variation in the detachment force of coffee fruit and coffee yield by variograms and kriging for precision agriculture. This study was conducted at Brej?o farm, Três Pontas, Minas Gerais, Brazil. The detachment force of green and mature coffee fruit was measured with a prototype dynamometer and georeferenced. The yield data were obtained from manual harvesting and were georeferenced. The data were evaluated by variograms estimated by residual maximum likelihood (REML), which provided a satisfactory approach for modeling all the variables with a small sample size. Spherical and exponential models were fitted, the first provided the better fit to mature fruit detachment force and the latter provided the better fit to coffee yield and green fruit detachment force. They were used to describe the structure and magnitude of spatial variation in the variables studied. Kriged estimates were obtained with the best fitting variogram models and mapped. The statistical and geostatistical analyses enabled us to characterize the spatial variation of the detachment force of green and mature coffee fruit and coffee yield and to visualize the spatial relations among these variables. The precision agriculture techniques used in this paper to collect, map and analyze the variables studied will help coffee farmers to manage their fields. Maps of coffee yield will enable farmers to apply nutrients site-specifically and manage harvesting either manually or mechanically. In addition, maps of detachment force of coffee fruit can enable farmers to harvest coffee selectively by choosing the appropriate places and the right time to start. This will improve the quality of the final product and also increase profits.     

A trans-disciplinary study on the health risks of cryptosporidiosis from dairy systems in Dagoretti,Nairobi, Kenya: study background and farming system characteristics

This paper characterises the dairy farming system in Dagoretti, Nairobi. Characterisation was part of a broader ecohealth project to estimate the prevalence and risk of cryptosporidiosis and develop risk mitigation strategies. In the project a trans-disciplinary team addressed epidemiological, socioeconomic, environmental and policy aspects of cryptosporidiosis, an emerging zoonosis. This paper also provides background and describes sampling methods for the wider project. Three hundred dairy households were probabilistically sampled from a sampling frame of all dairy households in five of the six locations of Dagoretti, one of the eight districts of Nairobi Province. Randomly selected households identified 100 non-dairy-keeping households who also took part in the study. A household questionnaire was developed, pre-tested and administered in the dry and wet seasons of 2006. An additional study on livelihood and economic benefits of dairying took place with 100 dairy farmers randomly selected from the 300 farms (as well as 40 non-dairy neighbours as a control group), and a risk-targeted survey of environmental contamination with Cryptosporidium was conducted with 20 farmers randomly selected from the 29 farmers in the wider survey who were considered at high risk because of farming system. We found that around 1 in 80 urban households kept dairy cattle with an average of three cattle per household. Cross-breeds of exotic and local cattle predominate. Heads of dairy-keeping households were significantly less educated than the heads of non-dairy neighbours, had lived in Dagoretti for significantly longer and had significantly larger households. There was a high turnover of 10 % of the cattle population in the 3-month period of the study. Cattle were zero grazed, but productivity parameters were sub-optimal as were hygiene and husbandry practices. In conclusion, dairy keeping is a minor activity in urban Nairobi but important to households involved and their community. Ecohealth approaches are well suited to tackling the complex problem of assessing and managing emerging zoonoses in urban settings.