The relative uptake of Ca and Sr into tree foliage using a whole-watershed calcium addition

The use of strontium isotopes and ratios of alkaline earth elements (i.e., ⁸⁷Sr/⁸⁶Sr and Ca/Sr) to trace Ca sources to plants has become common in ecosystem studies. Here we examine the relative uptake of Ca and Sr in trees and subsequent accumulation in foliage. Using a whole-watershed Ca addition experiment at the Hubbard Brook Experimental Forest in N.H., we measured the uptake of Ca relative to Sr in foliage and roots of sugar maple (Acer saccharum), yellow birch (Betula alleghaniensis), American beech (Fagus grandifolia), and red spruce (Picea rubens). Vegetation was analyzed for Ca and Sr concentrations and the ⁸⁷Sr/⁸⁶Sr ratio. A comparison of the Ca/Sr ratio in the vegetation and the Ca/Sr ratio of the applied mineral allows for the calculation of a discrimination factor, which defines whether Ca and Sr are incorporated and allocated in the same ratio as that which is available. A discrimination factor greater than unity indicates preferential uptake of Ca over Sr; a factor less than unity reflects preferential uptake of Sr over Ca. We demonstrate that sugar maple (SM) and yellow birch (YB) have similar and small discrimination factors (1.14 ± 0.12,1σ and 1.16 ± 0.09,1σ) in foliage formation and discrimination factors of less than 1 in root formation (0.55–0.70). Uptake into beech suggests a larger discrimination factor (1.9 ± 1.2) in foliage but a similar root discrimination factor to SM and YB (0.66 ± 0.06,1σ). Incorporation into spruce foliage occurs at a much slower rate than in these other tree species and precludes evaluation of Ca and Sr discrimination in spruce foliage at this time. Understanding the degree to which Ca is fractionated from Sr in different species allows for refinement in the use of ⁸⁷Sr/⁸⁶Sr and Ca/Sr ratios to trace Ca sources to foliage. Methods from this study can be applied to natural environments in which various soil cation pools have different ⁸⁷Sr/⁸⁶Sr and Ca/Sr ratios. The results reported herein have implications for re-evaluating Ca sources and fluxes in forest ecosystems.     

Maternal androgens in eggs of communally breeding guira cuckoos (Guira guira)

Variation of maternal androgens in avian eggs may be a mechanism of maternal influence on offspring development, growth, and/or behavior. We studied yolk androgen concentrations in eggs of guira cuckoos (Guira guira) to understand how females might enhance the success of offspring in a complex communal breeding system. We measured concentrations of androstenedione, 5alpha-dihydrotestosterone, and testosterone in yolks and identified eggs and clutches of individuals in joint nests by yolk protein electrophoresis. Androstenedione had the highest yolk concentration, at least 10 times higher than that of testosterone and 5alpha-dihydrotestosterone. The first eggs of individual females that laid two or three eggs in a joint nest had lower androstenedione concentrations than their second and third eggs, the latter having a lower probability of being ejected from the nest. This implies that guira cuckoo females may influence offspring survival and competitiveness in communal nests by means of differential allocation of androstenedione and laying tactics. There was significant variation in yolk androstenedione among females, but the order in which females entered laying in the communal clutch had no effect on the concentrations. Androstenedione yolk concentrations increased with communal clutch size, which may indicate that higher levels of competition in larger groups lead to higher yolk androgen concentrations. Finally, androstenedione concentrations were higher in clutches in the later wetter periods of the rainy season than during the earlier drier period. This may be explained by the high frequency of large clutches in the later periods, with more females contributing to a joint clutch.     

Experimental and numerical study of heterogeneous pressure-temperature-induced lethal and sublethal injury of Lactococcus lactis in a medium scale high-pressure autoclave

The present contribution is dedicated to experimental and theoretical assessment of microbiological process heterogeneities of the high-pressure (HP) inactivation of Lactococcus lactis ssp. cremoris MG 1363. The inactivation kinetics are determined in dependence of pressure, process time, temperature and absence or presence of co-solutes in the buffer system namely 4 M sodium chloride and 1.5 M sucrose. The kinetic analysis is carried out in a 0.1-L autoclave in order to minimise thermal and convective effects. Upon these data, a deterministic inactivation model is formulated with the logistic equation. Its independent variables represent the counts of viable cells (viable but injured) and of the stress-resistant cells (viable and not injured). This model is then coupled to a thermo-fluiddynamical simulation method, high-pressure computer fluid dynamics technique (HP-CFD), which yields spatiotemporal temperature and flow fields occurring during the HP application inside any considered autoclave. Besides the thermo-fluiddynamic quantities, the coupled model predicts also the spatiotemporal distribution of both viable (VC) and stress-resistant cell counts (SRC). In order to assess the process non-uniformity of the microbial inactivation in a 3.3-L autoclave experimentally, microbial samples are placed at two distinct locations and are exposed to various process conditions. It can be shown with both, experimental and theoretical models that thermal heterogeneities induce process non-uniformities of more than one decimal power in the counts of the viable cells at the end of the treatment.     

Optimization of physical parameters for exo-biopolymer production in submerged mycelial cultures of two entomopathogenic fungi Paecilomyces japonica and Paecilomyces tenuipes

AIMS: In the present study, two different optimization techniques were used to determine the suitable operating parameters for exo-biopolymer production in submerged mycelial cultures of two entomopathogenic fungi Paecilomyces japonica and Paecilomyces tenuipes. METHODS AND RESULTS: First, the rotating simplex method, a nonstatistical optimization technique, was employed to obtain the best combination of physical parameters (viz. pH, agitation intensity, aeration rate) for maximum exo-biopolymer production by P. japonica in a batch bioreactor. The optimal combination was determined to be a pH of 8.06, an aeration of 3 vvm, without any impeller agitation, producing a 17-time increase in exopolymer production (34.5 g l(-1)) when compared with that achieved in unoptimized flask cultures. Second, the uniform design method, a statistical optimization technique, was employed to determine the best operating parameters for submerged culture of P. tenuipes. The optimal combination for mycelial growth was determined to be a pH of 4.88, an aeration of 2 vvm and an agitation of 350 rpm, while a pH of 4, an aeration of 2 vvm and an agitation of 150 rpm was best for exo-biopolymer production. CONCLUSIONS: The exo-biopolymer production in P. japonica optimized by the rotating simplex method was strikingly improved (max. 34.5 g l(-1)), and the exo-biopolymer production in P. tenuipes optimized by the uniform design method was also significantly increased (max. 3.4 g l(-1)). SIGNIFICANCE AND IMPACT OF THE STUDY: The successful application of these two different optimization techniques in this study implies that these methods are worthy of applying to other fermentation systems for the production of bioactive mycelial biomass and exo-biopolymers in liquid culture of higher fungi.     

Exploration of genes showing intramuscular fat deposition-associated expression changes in musculus longissimus muscle

Marbling, as defined by the amount of intramuscular fat, is an economically important trait in beef cattle. Intramuscular fat deposition is postulated to arise mainly from a series of adipogenic events in intramuscular adipocyte-lineage cells and in the physiological or anatomical milieux surrounding them. This study was designed to investigate gene-expression patterns associated with fat deposition in musculus longissimus muscle, including adipocyte-lineage cells and part of the milieux. Differential-display PCR (ddPCR) was used to examine expression differences between low-marbled and high-marbled steer groups at 8, 10, 12 and 14 months of age, encompassing the time that marbling starts to appear. Seventy-four of 2114 total bands on ddPCR gel-bands were significant (P < 0.05) for the group effect, the interaction effect between group and age, or both the group and the interaction effects. Sequence analysis of 72 of these bands revealed 77 genes, including 35 annotated genes and 42 novel sequences. Among the 35 annotated genes, 6 (BTG2, PDHB, SORBS1, TRDN, TTN and MGP) have been related to changes in intramuscular fat deposition, possibly by exerting effects on adipocyte-lineage cells or on the milieux surrounding them.     

Response of Oxidative Enzyme Activities to Nitrogen Deposition Affects Soil Concentrations of Dissolved Organic Carbon

Recent evidence suggests that atmospheric nitrate (NO ₃ ⁻ ) deposition can alter soil carbon (C) storage by directly affecting the activity of lignin-degrading soil fungi. In a laboratory experiment, we studied the direct influence of increasing soil NO ₃ ⁻ concentration on microbial C cycling in three different ecosystems: black oak–white oak (BOWO), sugar maple–red oak (SMRO), and sugar maple–basswood (SMBW). These ecosystems span a broad range of litter biochemistry and recalcitrance; the BOWO ecosystem contains the highest litter lignin content, SMRO had intermediate lignin content, and SMBW leaf litter has the lowest lignin content. We hypothesized that increasing soil solution NO ₃ ⁻ would reduce lignolytic activity in the BOWO ecosystem, due to a high abundance of white-rot fungi and lignin-rich leaf litter. Due to the low lignin content of litter in the SMBW, we further reasoned that the NO ₃ ⁻ repression of lignolytic activity would be less dramatic due to a lower relative abundance of white-rot basidiomycetes; the response in the SMRO ecosystem should be intermediate. We increased soil solution NO ₃ ⁻ concentrations in a 73-day laboratory incubation and measured microbial respiration and soil solution dissolved organic carbon (DOC) and phenolics concentrations. At the end of the incubation, we measured the activity of β-glucosidase, N-acetyl-glucosaminidase, phenol oxidase, and peroxidase, which are extracellular enzymes involved with cellulose and lignin degradation. We quantified the fungal biomass, and we also used fungal ribosomal intergenic spacer analysis (RISA) to gain insight into fungal community composition. In the BOWO ecosystem, increasing NO ₃ ⁻ significantly decreased oxidative enzyme activities (−30% to −54%) and increased DOC (+32% upper limit) and phenolic (+77% upper limit) concentrations. In the SMRO ecosystem, we observed a significant decrease in phenol oxidase activity (−73% lower limit) and an increase in soluble phenolic concentrations (+57% upper limit) in response to increasing NO ₃ ⁻ in soil solution, but there was no significant change in DOC concentration. In contrast to these patterns, increasing soil solution NO ₃ ⁻ in the SMBW soil resulted in significantly greater phenol oxidase activity (+700% upper limit) and a trend toward lower DOC production (−52% lower limit). Nitrate concentration had no effect on microbial respiration or β-glucosidase or N-acetyl-glucosaminidase activities. Fungal abundance and basidiomycete diversity tended to be highest in the BOWO soil and lowest in the SMBW, but neither displayed a consistent response to NO ₃ ⁻ additions. Taken together, our results demonstrate that oxidative enzyme production by microbial communities responds directly to NO ₃ ⁻ deposition, controlling extracellular enzyme activity and DOC flux. The regulation of oxidative enzymes by different microbial communities in response to NO ₃ ⁻ deposition highlights the fact that the composition and function of soil microbial communities directly control ecosystem-level responses to environmental change.     

Microbial Cycling of C and N in Northern Hardwood Forests Receiving Chronic Atmospheric NO 3 − Deposition

Sugar maple (Acer saccharum Marsh.)-dominated northern hardwood forests in the upper Lakes States region appear to be particularly sensitive to chronic atmospheric NO₃⁻ deposition. Experimental NO₃⁻ deposition (3 g NO₃⁻ N m⁻² y⁻¹) has significantly reduced soil respiration and increased the export of DOC/DON and NO₃⁻ across the region. Here, we evaluate the possibility that diminished microbial activity in mineral soil was responsible for these ecosystem-level responses to NO₃⁻ deposition. To test this alternative, we measured microbial biomass, respiration, and N transformations in the mineral soil of four northern hardwood stands that have received 9 years of experimental NO₃⁻ deposition. Microbial biomass, microbial respiration, and daily rates of gross and net N transformations were not changed by NO₃⁻ deposition. We also observed no effect of NO₃⁻ deposition on annual rates of net N mineralization. However, NO₃⁻ deposition significantly increased (27%) annual net nitrification, a response that resulted from rapid microbial NO₃⁻ assimilation, the subsequent turnover of NH₄⁺, and increased substrate availability for this process. Nonetheless, greater rates of net nitrification were insufficient to produce the 10-fold observed increase in NO₃⁻ export, suggesting that much of the exported NO₃⁻ resulted directly from the NO₃⁻ deposition treatment. Results suggest that declines in soil respiration and increases in DOC/DON export cannot be attributed to NO₃⁻-induced physiological changes in mineral soil microbial activity. Given the lack of response we have observed in mineral soil, our results point to the potential importance of microbial communities in forest floor, including both saprotrophs and mycorrhizae, in mediating ecosystem-level responses to chronic NO₃⁻ deposition in Lake States northern hardwood forests.     

Coupled Nitrogen and Calcium Cycles in Forests of the Oregon Coast Range

Nitrogen (N) is a critical limiting nutrient that regulates plant productivity and the cycling of other essential elements in forests. We measured foliar and soil nutrients in 22 young Douglas-fir stands in the Oregon Coast Range to examine patterns of nutrient availability across a gradient of N-poor to N-rich soils. N in surface mineral soil ranged from 0.15 to 1.05% N, and was positively related to a doubling of foliar N across sites. Foliar N in half of the sites exceeded 1.4% N, which is considered above the threshold of N-limitation in coastal Oregon Douglas-fir. Available nitrate increased five-fold across this gradient, whereas exchangeable magnesium (Mg) and calcium (Ca) in soils declined, suggesting that nitrate leaching influences base cation availability more than soil parent material across our sites. Natural abundance strontium isotopes (⁸⁷Sr/⁸⁶Sr) of a single site indicated that 97% of available base cations can originate from atmospheric inputs of marine aerosols, with negligible contributions from weathering. Low annual inputs of Ca relative to Douglas-fir growth requirements may explain why foliar Ca concentrations are highly sensitive to variations in soil Ca across our sites. Natural abundance calcium isotopes (δ⁴⁴Ca) in exchangeable and acid leachable pools of surface soil measured at a single site showed 1 per mil depletion relative to deep soil, suggesting strong Ca recycling to meet tree demands. Overall, the biogeochemical response of these Douglas-fir forests to gradients in soil N is similar to changes associated with chronic N deposition in more polluted temperate regions, and raises the possibility that Ca may be deficient on excessively N-rich sites. We conclude that wide gradients in soil N can drive non-linear changes in base-cation biogeochemistry, particularly as forests cross a threshold from N-limitation to N-saturation. The most acute changes may occur in forests where base cations are derived principally from atmospheric inputs.     

植物对Si的吸收、运输和沉积

本文综述了植物中的S i及其吸收、运输和沉积的研究进展:(1)植物含S i量因植物种、品种甚至无性系与器官的不同而有较大差异,S i在细胞中呈现区隔化分配;(2)植物中沉积的S i主要是非晶态的S iO2.nH2O(又称硅胶、植物蛋白石、植硅石等),是有机物质矿质化的产物,不同植物所形成的S i化结构及其形态不同,可用于植物分类、鉴定及古气候与环境变化的研究;(3)硅藻和高等植物主要吸收S i(OH)4,高等植物中存在S i主动吸收机制;(4)有机大分子物质(包括多胺、碳水化合物、纤维素)作为有机衬质参与了植物的S i沉积过程;(5)突变体的鉴定和应用,对S i营养研究具有重要作用.     

氮沉降增加对森林凋落物分解酶活性的影响

氮沉降增加对森林凋落物分解酶产生的影响在世界范围受到关注。综述了凋落物分解酶的种类、影响酶的因素、酶的生态学意义和土壤酶研究技术的研究发展趋势。根据森林凋落物底物性质的不同,将凋落物分解酶分为纤维素分解酶类、木质素分解酶类、蛋白水解酶类和磷酸酶类。目前普遍认为,氮沉降增加,磷酸酶类活性随之增加,其它三类酶活性未呈现规律性变化。此外,还对氮沉降增加与土壤酶之间关系的研究前景进行了探讨。