Fire effects on ecosystem nitrogen cycling in a Californian bishop pine forest

Fire can cause severe nitrogen (N) losses from grassland, chaparral, and temperate and boreal forest ecosystems. Paradoxically, soil ammonium levels are markedly increased by fire, resulting in high rates of primary production in re-establishing plant communities. In a manipulative experiment, we examined the influence of wild-fire ash residues on soil, microbial and plant N pools in a recently burned Californian bishop pine (Pinus muricata D. Don) forest. Ash stimulated post-fire primary production and ecosystem N retention through direct N inputs from ash to soils, as well as indirect ash effects on soil N availability to plants. These results suggest that redistribution of surface ash after fire by wind or water may cause substantial heterogeneity in soil N availability to plants, and could be an important mechanism contributing to vegetation patchiness in fire-prone ecosystems. In addition, we investigated the impact of fire on ecosystem N cycling by comparing ¹⁵N natural abundance values from recently burned and nearby unburned P. muricata forest communities. At the burned site, ¹⁵N natural abundance in recolonising species was similar to that in bulk soil organic matter. By contrast, there was a marked ¹⁵N depletion in the same species relative to the total soil N pool at the unburned site. These results suggest that plant uptake of nitrate (which tends to be strongly depleted in ¹⁵N because of fractionation during nitrification) is low in recently burned forest communities but could be an important component of eco- system N cycling in mature conifer stands. Received: 29 June 1999 / Accepted: 24 October 1999     

Production Dynamics and Characterization of Chitinolytic System of Streptomyces sp. NK1057, a Well Equipped Chitin Degrader

Streptomyces sp. NK 1057 produced four extracellular chitinases. Two (62 and 48 kDa) were endochitinaseswhile the other two (35 and 28 kDa) had chitobiosidaseactivity. Chi62 was produced in early growth phase whereas the other three were produced later. Chi48 was optimally active at pH 4.0 and 60 °C whereas Chi35 was optimally active at pH 6.0 and 40 °C. Both the enzymes had fairly good pH and temperature stability up to 50 °C, with Chi48 being more thermostable than Chi35. Chi48 was significantly inhibited by N-acetylglucosaminebut not by Hg²⁺ and the reverse was true for Chi35. Chi48 and Chi35 had isoelectric points of 5.1 and 6.0 and the N-terminal amino acid sequence of Chi35 determined uptofour amino acids, was Gln–Ser–Pro– Gly. Chi62 and Chi48 were able to inhibit the germination of Fusariumoxysporum spores by 57.4 and 61.2% respectively whereas; Chi35 and Chi28 did so by only 14.1 and 3.8%, suggesting endochitinaseto possess antifungal activity. Only Chi28 exhibited a lytic activity, 0.022 U ml^–1, towards Micrococcus lysodeikticus cells.     

Photosynthesis and respiration of a diatom biofilm cultured in a new gradient growth chamber

Abstract A diatom biofilm was grown in a chamber developed for culture of biofilms in chemical gradients. The diatoms grew on a polycarbonate membrane filter which separated a sterile reservoir, with added phosphate, from a reservoir without phosphate. Within 3 weeks of inoculation, a thick biofilm developed on the surface of the filter. The biofilms were homogeneous and therefore suitable for calculations of O₂ diffusion fluxes from concentration profiles of O₂. Profiles of O₂, pH, and gross photosynthesis at different light intensities and liquid medium concentrations of dissolved inorganic carbon and O₂ were measured with microelectrodes. Respiratory activity in a layer of the biofilm was determined as the difference between gross photosynthesis and outflux of O₂ from that layer. The photosynthetic activity in a well-developed biofilm grown at 360 μEinst m⁻² s⁻¹ and 2.4 mM HCO₃⁻ was limited by the supply of inorganic carbon. Exposure to light above 360 μEinst m⁻² s⁻¹ stimulated gross photosynthesis as well as respiratory processes without affecting net outflux of O₂. Higher concentrations of inorganic carbon, on the other hand, enhanced gross photosynthesis without concurrent increase in respiratory rate, resulting in an increased outflux of O₂. High concentrations of O₂ in the liquid medium decreased the net outflux of O₂ with little effect on the gross photosynthesis. The effects of inorganic carbon and O₂ on the metabolic activities of the biofilm were consistent with the presence of photorespiratory activity.     

Promotion of indole alkaloid production in Catharanthus roseus cell cultures by rare earth elements

Production of the indole alkaloids, ajmalicine or catharanthine, in cell suspension cultures of Catharanthus roseus was enhanced by cerium (CeO₂ and CeCl₃), yttrium (Y₂O₃) and neodymium (NdCl₃). The yield of ajmalicine in these treated-cultures reached 51 mg l^–1 (CeO₂), 40 mg l^–1 (CeCl₃), 41 mg l^–1 (Y₂O₃) and 49 mg l^–1 (NdCl₃) while catharanthine production reached to 36 mg l^–1 (CeO₂) and 31 mg l^–1 (CeCl₃). A major portion of increased alkaloids was released into medium in these treatments. But Sm₂O₃, SmCl₃, La₂O₃, LaCl₃, complex of chromium (III)-titanium (IV) and NaSeO₄ treatments had little effect on alkaloid production of C. roseus cell cultures.     

Nitric oxide inhibitory constituents from Siegesbeckia pubescens

Two new sesquiterpenoids (1 and 2) and a new ent-pimarane type diterpenoid (3), together with eighteen known compounds (4–21), were isolated from the whole plants of Siegesbeckia pubescens. The structures of the new compounds were determined on the basis of 1D-, 2D NMR and HRESIMS data. All compounds were evaluated for their inhibitory effects on LPS-induced nitric oxide production in RAW 264.7 macrophages. Of these, highly oxygenated germacrane type sesquiterpenoids (1–2 and 13–14) showed significant inhibitory effects with IC₅₀ values ranging from 3.9 to 16.8 μM.     

Shifting abundances of communities associated with nitrogen cycling in soils promoted by sugarcane harvest systems

Sugarcane cultivation supports Brazil as one of the largest world sugar and ethanol producer. In order to understand the impact of changing sugarcane harvest from manual to mechanized harvest, we studied the effect of machinery traffic on soil and consequently soil compaction upon soil microbial communities involved in nitrogen cycling. The impact of sugarcane harvest was dependent on soil depth and texture. At deeper soil layers, mechanized harvesting increases the abundance of nitrogen fixers and denitrifying communities (specifically nosZ clade I and II) while manual harvesting increases the abundance of ammonia oxidizers (specifically AOA) and increases denitrifying communities (nosZ clade I and II) on top and at intermediate depth. The effect of change on the harvest system is more evident on sandy soil than on clay soil, where soil indicators of compaction (bulk density and penetration resistance) were negatively correlated with soil microorganisms associated with the nitrogen cycle. Our results point to connections between soil compaction and N transformations in sugarcane fields, besides naming biological variables to be used as proxies for alterations in soil structure.     

Root growth dynamics linked to above-ground growth in walnut (Juglans regia)

Background and Aims Examination of plant growth below ground is relatively scant compared with that above ground, and is needed to understand whole-plant responses to the environment. This study examines whether the seasonal timing of fine root growth and the spatial distribution of this growth through the soil profile varies in response to canopy manipulation and soil temperature.Methods Plasticity in the seasonal timing and vertical distribution of root production in response to canopy and soil water manipulation was analysed in field-grown walnut (Juglans regia ‘Chandler’) using minirhizotron techniques.Key Results Root production in walnuts followed a unimodal curve, with one marked flush of root growth starting in mid-May, with a peak in mid-June. Root production declined later in the season, corresponding to increased soil temperature, as well as to the period of major carbohydrate allocation to reproduction. Canopy and soil moisture manipulation did not influence the timing of root production, but did influence the vertical distribution of roots through the soil profile. Water deficit appeared to promote root production in deeper soil layers for mining soil water. Canopy removal appeared to promote shallow root production.Conclusions The findings of this study add to growing evidence that root growth in many ecosystems follows a unimodal curve with one marked flush of root growth in coordination with the initial leaf flush of the season. Root vertical distribution appeared to have greater plasticity than timing of root production in this system, with temperature and/or carbohydrate competition constraining the timing of root growth. Effects on root distribution can have serious impacts on trees, with shallow rooting having negative impacts in years with limited soil water or positive impacts in years with wet springs, and deep rooting having positive impacts on soil water mining from deeper soil layers but negative impacts in years with wet springs.