Alternative method for rapidly screening microbial isolates for their potential to degrade volatile contaminants

Summary A method is described for rapidly screening the metabolic potential of bacteria to oxidize semivolatile and volatile compounds as a sole carbon source. The method is based on automated system that utilizes Microplates^TM manufactured by Biolog, Inc. (Hayward, CA, USA). This system detects bacterial respiratory activity from the oxidation of a carbon source introduced in volatile form. This is in contrast to the original design, which is based on inoculating a carbon source directly into each well. The 96-well (MT) microtiter plates contain nutrients and a tetrazolium dye. When a bacterial species is capable of oxidizing a volatile carbon substrate, the dye turns purple, and a spectrophotometric plate reader quantifies the response. As a test of this method 150 isolates, including isolates known to degrade some of the test compounds and negative controls were evaluated for their potential to oxidize carbon tetrachloride, toluene, ando-xylene. Thirty-seven isolates (25%) were qualitatively identified as contaminant oxidizers, and thirteen of these (35%) showed significant degradation capabilities for both toluene ando-xylene.Environmental Sciences Division Publication Number 4277.     

Short-term photosynthesis measurements predict leaf carbon balance in tropical rain-forest canopy plants

Diel (24 h) courses of net CO₂ exchange of leaves were determined in eight species of tropical rainforest plants on Barro Colorado Island, Panama, during 1990 and 1991. The species included three canopy trees, one liana, two epiphytes and one hemiepiphyte. One of the species studied was growing in a rain-forest gap. Daily carbon gain varied considerably across species, leaf age, and season. The analysis of data for all plants from 64 complete day/night cycles revealed a linear relationship between the diurnal carbon gain and the maximum rate of net CO₂ uptake, A_max. Nocturnal net carbon loss was about 10% of diurnal carbon gain and was positively related to A_max. We conclude that short-term measurements of light-saturated photosynthesis, performed at periodic intervals throughout the season, allow the annual leaf carbon balance in these rain-forest plants to be predicted.     

Ventilatory responses to exercise and carbon dioxide in elderly and younger humans

The present investigation examined the relationship between CO₂ sensitivity [at rest (S _R) and during exercise (S _E)] and the ventilatory response to exercise in ten elderly (61–79 years) and ten younger (17–26 years) subjects. The gradient of the relationship between minute ventilation and CO₂ production ( _E/ CO₂) of the elderly subjects was greater than that of the younger subjects [mean (SEM); 32.8 (1.6) vs 27.3 (0.4); P<0.01]. At rest, S _R was lower for the elderly than for the younger group [10.77 (1.72) vs 16.95 (2.13) 1 · min^–1 · kPa^–1; 1.44 (0.23) vs 2.26 (0.28) 1 · min^–1 · mmHg^–1; P<0.05], but S _E was not significantly different between the two groups [17.85 (2.49) vs 19.17 (1.62) l · min^–1 · kPa^–1; 2.38 (0.33) vs 2.56 (0.21) 1 · min^–1 · mmHg^–1]. There were significant correlations between both S _R and S _E, and _E/ CO₂ (P<0.05; P<0.001) for the younger group, bot none for the elderly. The absence of a correlation for the elderly supports the suggestion that _E/ CO₂ is not an appropriate index of the ventilatory response to exercise for elderly humans.     

Fire affects wood formation dynamics and ecophysiology of Pinus pinaster Aiton growing in a dry Mediterranean area

The increase in frequency and intensity of wildfires is seriously affecting forest ecosystems, especially in drought-prone areas. Trees’ recovery after fire is related to direct tree damage and is influenced by climate conditions, such as warm temperature and water shortage. In this study, we evaluate the post-fire effects on a Pinus pinaster Aiton forest growing in a hot and dry area of the Mediterranean region by comparing burned trees with severe crown reduction against unburned and not-defoliated trees. Inter-annual analyses of dendrochronology and stable isotopes in tree rings were combined with xylogenesis monitoring to investigate the effects of fire on tree growth, ecophysiological processes and wood formation. Tree-ring and isotope data showed a growth reduction and a decrease in photosynthetic activity in the burned trees, compared to control individuals, in the three years after fire. Further, the monitoring of cambial activity demonstrated a negative influence of warm and dry periods on wood formation, low xylem production, a delay in phenology and a reduction in xylem plasticity in burned trees. Our findings suggest that substantial photosynthetic limitations caused by crown defoliation and recurrent drought events could lead to severe growth decrease and reduction of trees ability to regain the pre-disturbance productivity rates.     

Crop responses to CO2 enrichment

Carbon dioxide is rising in the global atmosphere, and this increase can be expected to continue into the foreseeable future. This compound is an essential input to plant life. Crop function is affected across all scales from biochemical to agro-ecosystem. An array of methods (leaf cuvettes, field chambers, free-air release systems) are available for experimental studies of CO₂ effects. Carbon dioxide enrichment of the air in which crops grow usually stimulates their growth and yield. Plant structure and physiology are markedly altered. Interactions between CO₂ and environmental factors that influence plants are known to occur. Implications for crop growth and yield are enormous. Strategies designed to assure future global food security must include a consideration of crop responses to elevated atmospheric CO₂. Future research should include these targets: search for new insights, development of new techniques, construction of better simulation models, investigation of belowground processes, study of interactions, and the elimination of major discrepancies in the scientific knowledge base.     

滇南地区桃树种植模式对土壤有机碳组分及碳库管理指数的影响

经果林种植可改变土壤质量、改善生态环境,同时具有较高的经济效益。合理的种植模式可通过物种间的互补性提高资源利用效率,改善土壤碳库质量并提高综合效益。为探讨桃树种植模式对土壤有机碳组分及碳库管理指数的影响,以云南省开远市不同桃树种植模式(桃树单种-SP和桃树南瓜套种-PP)为研究对象,以毗邻的天然林地(CK)为对照,分析不同种植模式下活性碳库,即高锰酸钾氧化有机碳(POXC)、颗粒有机碳(POC),惰性有机碳库即矿物结合态有机碳(MAOC)在0—40 cm土层的分布情况,明确土壤有机碳组分与土壤理化性质的关系;计算碳库活度指数(CPAI)、碳库指数(CPI)以及碳库管理指数(CPMI),明确不同桃树种植模式的碳库变化情况。结果表明：桃树种植模式和对照的土壤有机碳组分的含量均随着土层深度的增加而减少,平均土壤有机碳(SOC)含量为：14.68 g/kg(CK)>9.57 g/kg(PP)>8.58 g/kg(SP)。平均活性有机碳组分所占比例与POC/MAOC均表现为：SP>CK>PP,PP的活性有机碳比例较低,具有较高的有机碳稳定性。两种桃树种植模式的CPMI在1...     

Land use induced changes of organic carbon storage in soils of China

Using the data compiled from China's second national soil survey and an improved method of soil carbon bulk density, we have estimated the changes of soil organic carbon due to land use, and compared the spatial distribution and storage of soil organic carbon (SOC) in cultivated soils and noncultivated soils in China. The results reveal that ～ 57% of the cultivated soil subgroups ( ～ 31% of the total soil surface) have experienced a significant carbon loss, ranging from 40% to 10% relative to their noncultivated counterparts. The most significant carbon loss is observed for the non‐irrigated soils (dry farmland) within a semiarid/semihumid belt from northeastern to southwestern China, with the maximum loss occurring in northeast China. On the contrary, SOC has increased in the paddy and irrigated soils in northwest China. No significant change is observed for forest soils in southern China, grassland and desert soils in northwest China, as well as irrigated soils in eastern China. The SOC storage and density under noncultivated conditions in China are estimated to ～ 77.4 Pg (10¹⁵ g) and ～ 8.8 kg C m^?2, respectively, compared to a SOC storage of ～ 70.3 Pg and an average SOC density of ～ 8.0 kg C m^?2 under the present‐day conditions. This suggests a loss of ～ 7.1 Pg SOC and a decrease of ～ 0.8 kg C m^?2 SOC density due to increasing human activities, in which the loss in organic horizons has contributed to ～ 77%. This total loss of SOC in China induced by land use represents ～ 9.5% of the world's SOC decrease. This amount is equivalent to ～ 3.5 ppmv of the atmospheric CO₂ increase. Since ～ 78% of the currently cultivated soils in China have been degraded to a low/medium productivities and are responsible for most of the SOC loss, an improved land management, such as the development of irrigated and paddy land uses, would have a considerable potential in restoring the SOC storage. Assuming a restoration of ～ 50% of the lost SOC during the next 20–50 years, the soils in China would absorb ～ 3.5 Pg of carbon from the atmosphere.     

Chirality differences in amino acid retention and release from the acid-extractable pool of cultured mammalian cells

In previous work, no chiral differences were found between D and L enantiomers of Leu in their ability to displace one another from the acid-extractable pool in mammalian cells. Recent evidence suggested otherwise. Our aim is to examine whether, in physiological range, D-amino acids have an equivalent ability to displace L-amino acids from the acid-extractable pool of HeLa cells, and vice versa. In the millimolar range, D-Leu and L-Leu have similar uptake and displacement properties with regard to the acid-extractable pool in HeLa cells, despite only the latter isomer being incorporated into protein. Below millimolar concentrations however, a distinct difference was found in the displacement of tritium-labelled L-Leu from the pool by unlabelled D-Leu compared with unlabelled L-Leu. Thus, unlabelled L-Leu in the external medium at 10⁻⁴ or 10⁻⁵ M displaced an equivalent amount of label from the pool as D-Leu introduced at a concentration approx. one order of magnitude higher, respectively. Reciprocal experiments, in which the acid-extractable pool was preloaded with ³H-D-Leu, confirmed this finding. The chirality difference was noted whether pool prelabelling was carried out at 37 or 0°C; but in order to avoid the complications of active transport mechanisms, the competition work reported here was done at 0°C. Similar chirality differences were observed with other hydrophobic amino acids, including His, Ile and Phe, such as, preferential displacement by the L-Leu racemer compared with the D-Leu racemer below mM levels. This was also true for the D and L forms of the non-utilisable isomer of Leu, norleucine (nLeu). We conclude that D-forms of hydrophobic amino acids have lower affinity for similar or the same intracellular binding sites involved in the acid-extractable pool than their L-forms. The significance of these chirality findings to amino acid pools in cells, and to the predominance of L-forms of amino acids in the biosphere is considered.     

Distribution of Plasma Membrane H+-ATPase and Polar Current Patterns in Leaves and Stems of Elodea canadensis*

The proton pumping ATPase in the plasma membrane of Elodea canadensis is believed to play a major role in inorganic carbon acquisition. To investigate potentially different carbon uptake strategies within the same plant, plasma membrane H⁺-ATPase distribution and polar current patterns were investigated in Elodea leaves and stems. Specific activity of plasma membrane H⁺-ATPase in leaf microsomal fractions was tenfold higher than in stem derived microsomes. Probing western blots with a monoclonal antibody specific for plasma membrane H⁺-ATPase, yielded strongly visible double bands at 100 kDa in leaf microsome preparations, whereas little antigen was detected in analogous stem microsome preparations. Using the same plasma membrane H⁺-ATPase specific antibody on tissue sections, the enzyme was found almost exclusively localized at the border of cells at the lower leaf surface. A positive ion current leaving the lower leaf surface was measured, using a vibrating probe device. Part of this current entered the upper leaf surface and part of it the internodes of the stem. The experimental results support the view, that Elodea leaves have different means of inorganic carbon uptake than stem internodes.