Nitrogen deposition in tropical forests from savanna and deforestation fires

We used satellite‐derived estimates of global fire emissions and a chemical transport model to estimate atmospheric nitrogen (N) fluxes from savanna and deforestation fires in tropical ecosystems. N emissions and reactive N deposition led to a net transport of N equatorward, from savannas and areas undergoing deforestation to tropical forests. Deposition of fire‐emitted N in savannas was only 26% of emissions – indicating a net export from this biome. On average, net N loss from fires (the sum of emissions and deposition) was equivalent to approximately 22% of biological N fixation (BNF) in savannas (4.0 kg N ha^?1 yr^?1) and 38% of BNF in ecosystems at the deforestation frontier (9.3 kg N ha^?1 yr^?1). Net N gains from fires occurred in interior tropical forests at a rate equivalent to 3% of their BNF (0.8 kg N ha^?1 yr^?1). This percentage was highest for African tropical forests in the Congo Basin (15%; 3.4 kg N ha^?1 yr^?1) owing to equatorward transport from frequently burning savannas north and south of the basin. These results provide evidence for cross‐biome atmospheric fluxes of N that may help to sustain productivity in some tropical forest ecosystems on millennial timescales. Anthropogenic fires associated with slash and burn agriculture and deforestation in the southern part of the Amazon Basin and across Southeast Asia have substantially increased N deposition in these regions in recent decades and may contribute to increased rates of carbon accumulation in secondary forests and other N‐limited ecosystems.     

Effects of Metabolic Inhibitors on the Calcification of a Freshwater Green Alga Gloeotaenium loitlesbergarianum Hansgirg. 2. Effects of Some Inhibitors of Protein Synthesis

The effects of five inhibitors of protein synthesis, viz. streptomycin,aurin tricarboxylic acid, tetracycline, chloramphenicol, andcycloheximide, on the calcification of Gloeotaenium loitlesbergarianumHansgirg, a freshwater green alga were studied. Streptomycinhad no effect while aurin tricarboxylic acid at 50 µgml^–1 and tetracyline, chloramphenicol and cycloheximideat 20 µg ml^–1 completely inhibited calcificationin the alga. High concentrations of chloramphenicol and cycloheximidewere not completely inhibitory when added 26 h and 32 h respectivelyafter the material was incubated in the induction medium. Itis concluded that the effects by these substrates are the resultsof inhibition of protein synthesis, which is directly or indirectlylinked to calcification. calcification, Gloeotaenium loitlesbergarianum Hansgirg, green alga, chlorophyceae, protein synthesis inhibitors     

Albedo estimates for land surface models and support for a new paradigm based on foliage nitrogen concentration

Vegetation albedo is a critical component of the Earth's climate system, yet efforts to evaluate and improve albedo parameterizations in climate models have lagged relative to other aspects of model development. Here, we calculated growing season albedos for deciduous and evergreen forests, crops, and grasslands based on over 40 site‐years of data from the AmeriFlux network and compared them with estimates presently used in the land surface formulations of a variety of climate models. Generally, the albedo estimates used in land surface models agreed well with this data compilation. However, a variety of models using fixed seasonal estimates of albedo overestimated the growing season albedo of northerly evergreen trees. In contrast, climate models that rely on a common two‐stream albedo submodel provided accurate predictions of boreal needle‐leaf evergreen albedo but overestimated grassland albedos. Inverse analysis showed that parameters of the two‐stream model were highly correlated. Consistent with recent observations based on remotely sensed albedo, the AmeriFlux dataset demonstrated a tight linear relationship between canopy albedo and foliage nitrogen concentration (for forest vegetation: albedo=0.01+0.071%N, r²=0.91; forests, grassland, and maize: albedo=0.02+0.067%N, r²=0.80). However, this relationship saturated at the higher nitrogen concentrations displayed by soybean foliage. We developed similar relationships between a foliar parameter used in the two‐stream albedo model and foliage nitrogen concentration. These nitrogen‐based relationships can serve as the basis for a new approach to land surface albedo modeling that simplifies albedo estimation while providing a link to other important ecosystem processes.     

Further evidence for the genetic basis of qualitative traits and their linkage relationships in dolichos bean (<Emphasis Type="Italic">Lablab purpureus</Emphasis> L.)

An investigation on inheritance of qualitative traits in dolichos bean revealed biallelic monogenic control of photoperiod-induced sensitivity to flowering time and flower colour in F ₂ and F ₃ generations. While, growth habit and pod curvature are each controlled by two genes that exhibit classical complementary epistasis, raceme emergence was controlled by two genes that displayed classical inhibitory epistasis. The dominant alleles, at two different unlinked pairs of genes are necessary for plants to exhibit indeterminate growth habit and bear straight pods. Any other combination of alleles at the two pairs of genes result in plants displaying determinate growth habit and bearing curved pods. While, the genes controlling growth habit, PSFT and raceme emergence are linked. Those controlling flower colour and pod curvature are segregated independent of each other. These results are discussed in relation to strategies for breeding dolichos bean.     

Studies in the Physiological Action of 2,2-Dichloropropionic Acid: II. THE EFFECTS OF LIGHT AND TEMPERATURE ON THE FACTORS RESPONSIBLE FOR THE INHIBITION OF GROWTH

When Lemna minor and Salvinia natans, grown in a constant environment,are subjected to sub-lethal concentrations of 2,2-dichioropropionicacid (DCPA), the relative growth-rates are progressively reduced.These cumulative reductions, which are greater for S. natans,are correlated with decreases in (1) the rate of leaf or frondformation, (2) the mean area per leaf or frond, and (3) thenet assimilation rate. Of these components, the first is themost important and the third is the least. The effects of light intensity (300, 600, 900 f.c.), temperature(20, 25, and 30°C), and concentration of DCPA on both therelative growth-rate and rate of leaf or frond multiplicationhave been examined in multi-factorial experiments. Over theconcentration range selected (100, 200, and 400 mg/l for S.natans and 100, 300, and 6oo mg/l for L. minor) there are positiveeffects of light intensity, temperature, and concentration.For each concentration the order of the depression is maximalunder a combination of the highest temperature and the greatestintensity. Using radioactive DCPA it has been established that uptake isalso a cumulative process, and that S. natans has a greatercapacity to absorb DCPA. The rate of uptake is independent ofthe light intensity but increases with temperature and concentration. DCPA brings about morphological and structural changes. In S.natans, many of the leaves become submerged and the proportionis positively dependent on light, temperature, and concentration.This failure to float is associated with a reduction in thedensity of epiderrnal hairs. It is concluded that the inhibitory effects of DCPA are maximalunder conditions which are optimal for both meristematic activityand accumulation.     

Studies in the Physiological Action of 2,2-Dichloropropionic Acid: III. FACTORS AFFECTING THE LEVEL OF ACCUMULATION AND MODE OF ACTION

The factors determining the pattern of uptake by Lemna minorof 2,2-dichloropropionic acid (DCPA), containing chlorine-36,have been examined. Entry takes place via both the roots andfrond and is largely in the ionic form. Initially, the net ratesare high and are replaced by slower but steady rates. It isconcluded that over the first 30 minutes, net uptake is dependenton the physico-chemical processes since (i) the rate is directlyproportional to the external concentration, (ii) on transferenceto buffer containing non-radioactive DCPA up to 90 per centof the radioactivity is exchangeable, (iii) the temperaturecoefficients for the rates of net influx and efflux range from1.2 to 1.4. During the second phase, the net rates of uptakeare curvilinearly related to concentration, the temperaturequotients are higher and the rates of efflux markedly lowerthan in the first phase. Phenylmercuric nitrate and cupric sulphateat 5x10^–6 M halve the net rate of uptake but higher concentrationsare demanded for dinitrophenol, arsenite, aside, and iodoacetate.The depression induced by phenylmercuric nitrate can to somedegree be reversed by the addition of either glutathione orcysteine. For pyruvic acid to halve the rate of uptake of DCPA,it requires more than a three hundredfold greater concentration.It is postulated that in the second phase, uptake is mediatedby metabolic processes involving thiol groups. The ability ofcalcium pantothenate and ß-alanine to reverse theinhibitory effects of DCPA on the growth of L. minor were investigatedin multifactorial experiments. Over a narrow range of concentrations,calcium pantothenate partially offset the inhibitions of growthbut the interactions for ß-alanine were not significant.These results do not support the view that the primary actionof DCPA is to interfere with the biosynthesis of Co-enzyme A.In a comparison of the maximal capacity of different speciesto accumulate DCPA in their roots, up to a six-fold differencewas recorded in the eight species examined. On the basis ofthese findings, the mechanisms determining selective actionand the inhibition of meristematic activity are discussed.     

Rhynchocephalians (Diapsida: Lepidosauria) from the Jurassic Kota Formation of India

Despite their rarity today, rhynchocephalians formed a diverse Early Mesozoic clade with a comparatively good fossil record. They had a Pangaean distribution in the Late Triassic and Early Jurassic, although the Gondwanan record remains more limited than the Laurasian one. We report here on new sphenodontian material from the Jurassic Kota Formation of peninsular India. Two taxa are represented, and both are attributed to new genera. One is a relatively derived sphenodontian with a premaxillary morphology similar to that of the Late Triassic/ Early Jurassic genus Clevosaurus. The other is somewhat more primitive in its morphology, although clearly a crown-group sphenodontian. In addition, three dentary fragments and a partial maxilla signal the presence of a primitive pleurodont lepidosauromorph similar to the basal rhynchocephalians Gephyrosaurus and Diphydonto-saurus from Britain.     

Disease assessment methods and their use in simulating growth and yield of peanut crops affected by leafspot disease

Peanut (Arachis hypogaea) crops in Benin often experience late leafspot (Cercosporidium personatum), which causes severe yield losses associated with leaf defoliation and necrosis. The objective of this research was to determine the best method of disease assessment and to test its utility in the CROPGRO‐peanut model to simulate growth and yield as affected by late leafspot in early and late maturing peanut cultivars grown at different sowing dates under rain‐fed conditions (without irrigation) in northern Benin. Two peanut cultivars TS 32‐1 and 69–101 were sown on three dates between May and August during 1998 and 1999. In both years there was severe occurrence of late leafspot and the progression of disease was earlier and faster with later sowing dates. Overall, the long duration cultivar 69–101 produced greater yield than the short duration cultivar TS 32‐1. The CROPGRO‐peanut model was able to predict and simulate the observed crop and pod dry matter over time when input on percent diseased leaf area and percent defoliation were provided. Of several disease assessments, the best approach was to input measured percent main‐stem defoliation above the fourth node and percent diseased leaf area estimated from visual leafspot score.