Projections of changes in grassland soil organic carbon under climate change are relatively insensitive to methods of model initialization

Model initialization in soil organic carbon (SOC) turnover models has often been described as a crucial step in making future projections. Model initialization by the spin‐up of pools of SOC (model equilibrium run) has been questioned, because equilibrium has to be assumed. Measured SOC pools are independent of model assumptions and are thought to reflect better real site conditions. It has been suggested that model initialization with measured SOC fractions could provide an advantage over model spin‐up of SOC pools. In this study we tested this suggestion in relatively undisturbed native grasslands in Australia. We tested the Rothamsted SOC turnover model (RothC) under climate change at 12 sites with three different initialization methods, viz. model initialization with (i) spin‐up of model pools with inert organic matter (IOM) pool size calculated from a regression equation, (ii) spin‐up of model pools with measured IOM and (iii) all pools estimated from measured fractions. Averaged over the sites and initialization methods, maximum absolute variations (absolute differences in projected SOC stocks expressed as a percentage of initial 2008 SOC stocks) as well as averaged absolute variations throughout the projection period were very small (2.2 and 1.6%, respectively). Averaged across the sites, there were no significant differences in projected grassland SOC stocks under climate change after 93 years of simulation with model initialization by different methods and averaged absolute variation was only 1.6% across initialization methods. These findings suggest that in a relatively undisturbed land‐use system such as native grassland, projections of SOC under climate change are relatively insensitive to the model initialization method.     

The modification of sex expression in papaya (Carica papaya L.)

Field trials with six times normal nitrogen supply produced a significant increase in the proportion of female papaya plants. The addition of nitrogen to the soil increased the leaf nitrogen content but had no effect on the amino acid content. Leaves of male plants contained more nitrogen than female plants but no difference could be detected in the contents of amino acids in the leaves and flower buds. Foliar application of 1-naphthalene acetic acid (NAA) and 2-chloroethyl-trimethyl ammonium chloride (CCC) resulted in a higher female : male ratio, but maleic hydrazide (MH) and gibberellic acid (GA₃) enhanced maleness. The animal sex hormone stilboesterol dipropionate had no apparent effect on sex expression but the application of testosterone propionate increased the proportion of male plants.     

Tree chitinases – stress‐ and developmental‐driven gene regulation

In recent years, a considerable number of studies have harnessed the power of genomics to decipher the role of pathogenesis‐related (PR) proteins in plant defence against various biotic and abiotic stresses. Chitinases are PR antifungal proteins expressed constitutively at low levels in plants and induced during biotic pressures and are demonstrated to be involved in the plant defence responses. Remarkable induction of chitinase enzymes by various abiotic agents (salicylic acid, jasmonic acid, ethylene and ozone) and biotic components (pathogens, insect pest, fungal cell wall components and oligosaccharides) is well demonstrated in plants. Several reviews on plant chitinase expression during host–pathogen interaction are available for annual species, whilst reports of their expression in tree species are limited to a few woody perennials: Populus, Pinus, Picea, Eucalyptus, Castanea and Pseudotsuga. The aim of this paper is to review the induction of chitinase during various stresses and developmental processes in forest tree species.     

Analysis of coat protein gene sequences of begomoviruses associated with different weed species in India

Sida cordifolia L., Croton bonplandianum L., Malachra capitata L., Eclipta prostrata L., Clerodendron inerme L., Acalypha indica L., and Urena lobata L. are common weeds found all over India. They are often infected by different begomovirus complexes and may act as reservoirs of crop-infecting begomoviruses. Cloning and sequencing were done to partially characterize the begomovirus complexes associated with these weed species from the eastern part of India and their genetic pattern was compared with respective geographical isolates throughout India. Coat protein (CP) genes were found to be amplified from all the infected samples tested in this study, whereas betasatellite molecules amplified only from four infected samples (Sida, Croton, Malachra and Urena). Sequence analysis using CP genes and betasatellites of the present begomovirus complexes showed significant variation among their geographical isolates and also exhibited closeness to different crop-infecting begomovirus complexes. The majority of the weed-infecting begomovirus complexes characterized in this paper are reported for the first time from India.     

Seaweed-based biostimulant improves photosynthesis and effectively enhances growth and biofuel potential of a green microalga Chlorella variabilis

Aquaculture International - The main aim of the present study was to determine the effects of a seaweed-based biostimulant’s supplementation on the growth of Chlorella variabilis. A liquid...     

Regulation of Correlative Senescence in Arachis hypogaea L. by Source-Sink Alteration through Physical and Hormonal Means

Amongst the plants ( Arachis hypogaea ) subjected to differential reproductive manipulations, the leaf levels of chlorophyll and sugar and the dry weight of the aerial plants increased more (except sugar level in defruited plant) in the deflorated plants than either in the defruited or control plants, and the order of senescence was: control > defruited > deflorated. Seed yield per plant increased in deflorated plants as a result of increase in the number of pods (sink size) and reduction in the sink strength (seed wt per pod). While 75 % defoliation caused a decrease in all the parameters relating to senescence (chlorophyll, protein, reduced nitrogen, sugar and dry wt), 25% defoliation caused a slight decrease of chlorophyll level of leaf and aerial plant weight. However, the level of protein and reduced nitrogen in the leaf and sugar in the stem increased by the latter (through 25% defoliation). Defoliation up to 25% reduced seed yield by only 2%. Whereas the level of chlorophyll and aerial plant dry weight were not significantly changed by either kinetin or ABA, the level of protein and reduced nitrogen in the leaf and sugar level in both leaf and stem increased by kinetin. GA₃ increased almost all the parameters studied. All the three phytohormones increased the yield, mainly by increasing the sink size rather than the sink strength. It is concluded that the aerial flowers are more lethal than the underground fruits in inducing whole plant senescence where the leaf senescence is uncoupled from fruit maturation in normal condition possibly due to sink limitation.     

Performance of Rapeseed-mustard Cultivars under Various Moisture Regimes on the Gangetic Alluvial Plain of West Bengal

A Field trial was conducted during 1988–89 and 1989–90 at Water Management Research Station, Memari. Bidhan Chandra Krishi Viswavidyalaya, Burdwan, to study the effect of three different irrigation regimes, namely rainfed (I₁) (No irrigation), one irrigation (I₂) at flowering and two irrigations (I₃ at flowering and at sihqua formation stages) on the grain yield and water expenses on four different rapeseed-mustard cultivars, namely Pusa Bold, Pusa Baroni, Varuna and DIR 247. The variety DIR 247 recorded maximum grain yield (12.1 qha') followed by Pusa Baroni (11.8 q ha⁻¹). The variety Varuna showed the lowest water use efficiency (48.1 kg ha⁻¹ cm⁻¹) while DIR 247 showed the maximum value of 57.0 kg ha⁻¹ cm⁻¹. The number of irrigations significantly increased the grain yield. Two irrigations, one at flowering and at siliqua formation stage increased grain yield by 28 % over the rainfed plots. During the crop growth period the actual water expenses among the cultivars in any moisture regime were more or less similar. The interaction between varieties and irrigation levels were, however, not significant.     

Weather-based prediction of anthracnose severity using artificial neural network models

Data were collected and analysed from seven field sites in Australia, Brazil and Colombia on weather conditions and the severity of anthracnose disease of the tropical pasture legume Stylosanthes scabra caused by Colletotrichum gloeosporioides . Disease severity and weather data were analysed using artificial neural network (ANN) models developed using data from some or all field sites in Australia and/or South America to predict severity at other sites. Three series of models were developed using different weather summaries. Of these, ANN models with weather for the day of disease assessment and the previous 24 h period had the highest prediction success, and models trained on data from all sites within one continent correctly predicted disease severity in the other continent on more than 75% of days; the overall prediction error was 21·9% for the Australian and 22·1% for the South American model. Of the six cross-continent ANN models trained on pooled data for five sites from two continents to predict severity for the remaining sixth site, the model developed without data from Planaltina in Brazil was the most accurate, with >85% prediction success, and the model without Carimagua in Colombia was the least accurate, with only 54% success. In common with multiple regression models, moisture-related variables such as rain, leaf surface wetness and variables that influence moisture availability such as radiation and wind on the day of disease severity assessment or the day before assessment were the most important weather variables in all ANN models. A set of weights from the ANN models was used to calculate the overall risk of anthracnose for the various sites. Sites with high and low anthracnose risk are present in both continents, and weather conditions at centres of diversity in Brazil and Colombia do not appear to be more conducive than conditions in Australia to serious anthracnose development.     

Effects of grass vegetation strips on soil conservation and crop yield under rainfed conditions in the Indian sub‐Himalayas

Vegetation strips (VS) along with conservation tillage, application of organic amendments and weed mulching improve crop yields by reducing run‐off and topsoil erosion. To investigate these issues, an experiment was conducted under rainfed conditions using grass VS for four and a half years (June 2007 to October 2011) at Dehradun, Uttarakhand, in the Indian Himalayan region. VS were incorporated in the experimental plots (Entisols) in a randomized complete block design in permanent 100 × 20 m (2000 m²) plots with a 2% slope to evaluate the effects of vegetation strips on run‐off, soil loss and crop yield. Three treatments were evaluated: (i) without VS with recommended NPK under conventional tillage, (ii) panicum as VS with recommended NPK under conventional tillage and (iii) palmarosa+ that consists of palmarosa as VS along with organic amendments (farmyard manure, vermicompost and poultry manure) and weed mulch under minimum tillage. The results show that soil loss and run‐off were significantly lower (P < 0.05) in plots under palmarosa+ than without VS treatment. Mean soil loss of 3.4, 5.2 and 7.1 t/ha was recorded from palmarosa+, panicum and without VS treated plots, respectively. Mean run‐off was 234, 356 and 428 mm from plots under palmarosa+, panicum and without VS, respectively. Maize yield was lower on the plots under palmarosa+ compared with panicum, but significantly higher (P < 0.05) than without a strip. The succeeding rainfed wheat yield was significantly greater in plots under palmarosa+ than in the initial years. The wheat yield equivalent was significantly higher in plots under palmarosa+ followed by panicum and without VS. Thus, vegetation strips are recommended for wider adoption to reduce run‐off and soil loss and to increase crop yield. The long‐term goal is to achieve a palmarosa+ system (palmarosa as a vegetation strip along with organic amendments, farmyard manure, vermicompost and poultry manure) and weed mulch under minimum tillage.