水分和热胁迫处理对4种针叶树苗木气体交换和水分利用效率的影响

以杉木、马尾松、花旗松和北美乔柏为研究对象 ,研究了水分和热胁迫对生长期间苗木的气体交换、瞬间水分利用效率和稳定碳同位素组成 (δ1 3C值 )等生理生态指标的影响 ,结果如下 :(1 )水分胁迫使杉木、马尾松、花旗松和北美乔柏 4个树种的净光合速率显著下降。但热胁迫只影响杉木和北美乔柏的净光合速率 ,对马尾松的净光合速率影响不大。 (2 )对针叶气孔导度的研究发现 ,水分和热胁迫均对马尾松苗木针叶气孔导度有显著影响 ,但对杉木和北美乔柏苗木针叶的气孔导度只有轻微影响。 (3)水分和热胁迫处理对马尾松苗木的瞬间水分利用效率有显著影响 ,但对杉木和北美乔柏的瞬间水分利用效率无显著影响。 (4 )水分胁迫处理对杉木、马尾松、花旗松和北美乔柏 4个树种的稳定碳同位素组成 (δ1 3C值 )均有显著影响 ,随着水分胁迫程度的加深 ,4个树种苗木针叶的δ1 3C值增大 (负值绝对值变小 ) ,说明其永久水分利用效率更高。 (5 )热胁迫对杉木和北美乔柏苗木针叶的δ1 3C值有显著影响 ,且在热胁迫下 ,两树种苗木针叶的δ1 3C值减小 (负值绝对值增大 ) ,即永久水分利用效率下降。但热胁迫对马尾松和花旗松苗木的δ1 3C值没有显著影响     

Nitrogen uptake from 15N-enriched fertilizer by four tree crops in an Amazonian agroforest

Mixed tree cropping systems have been proposed for sustainable nutrient management in the humid tropics. Yet, the nutrient interactions between intercropped trees have not been addressed sufficiently. In the present study we compare the temporal and spatial patterns of the uptake of applied ¹⁵N by four different tree crops in a mixed tree cropping system on a Xanthic Ferralsol in central Amazônia, Brazil, during one year. Most of the N uptake occurred during the first two weeks. Very little N was recovered by peach palm (Bactris gasipaes), more by cupuassu (Theobroma grandiflorum) and annatto (Bixa orellana) and most by Brazil nut (Bertholletia excelsa). Due to tree pruning the total accumulation of applied ¹⁵N in the above-ground biomass of annatto decreased throughout the year. It remained constant in cupuassu and peach palm and increased in Brazil nut. Brazil nut showed an extensive root activity and took up more fertilizer N applied to neighboring trees than from the one applied under its own canopy in contrast to the other three tree crops. Therefore, trees with wide-spread root systems may not need to receive N fertilizer directly but can take up N applied to other trees in the mixed cropping system. This means that such trees may effectively decrease N leaching when intercropped with trees that have dormant periods or places with low N uptake, but also exert considerable resource competition.This revised version was published online in November 2005 with corrections to the Cover Date.     

Nitrogen contribution by multipurpose trees to rice and cowpea in an alley cropping system in Sierra Leone

In an alley cropping experiment, a study was carried out on N₂ fixation by Gliricidia sepium, nitrogen (N) accumulation by prunings of Gliricidia, Senna siamea (formerly Cassia siamea) and Gmelina arborea, and the N contribution to associated crops of rice and cowpea.Total N accumulated by the hedgerow trees ranged from 297–524 kg N ha^–1 on average but varied between tree species and depended on the growing season. Gliricidia sepium accumulated 370 kg N ha^–1 on average and more than half of this came from fixation. Senna siamea and Gmelina arborea served as reference trees for estimating N₂ fixation. The estimates of N₂ fixation using Gmelina as a reference gave higher estimates than those using Senna.Although the dry matter and nitrogen yields of prunings from the hedgerow trees were high, their relative nitrogen contribution to the associated crops was generally low ranging from 5 to 29%. Higher crop yields and nitrogen contribution were observed with Gliricidia sepium prunings. The low N contribution from prunings was attributed to the lack of synchronization between the N released from the prunings and the crop's demand for N.     

Methane emissions and δ13C composition from beef steers consuming increasing proportions of sericea lespedeza hay on bermudagrass hay diets

An experiment was conducted to evaluate the effects of different proportions of ‘Au Grazer’ sericea lespedeza [SL, Lespedeza cuneata (Dum. Cours.) G. Don], a legume rich in condensed tannins (CT), on nutrient intake and digestibility, and to estimate methane (CH₄) emissions and ¹³C isotopic composition (δ¹³C_CH4) from beef steers consuming a forage-based diet. Twenty-five Angus-crossbred steers were distributed in a randomized complete block design (344 ± 48 kg initial BW), and randomly assigned to one of five treatments: 0SL, 25SL, 50SL, 75SL, and 100SL, diets containing 0%, 25%, 50%, 75%, and 100% of SL hay, respectively, mixed with ‘Tifton-85’ bermudagrass hay (Cynodon spp.). The study was carried out for two experimental periods of 21-d each. The statistical model included the fixed effect of treatment and random effects of block, experimental period, and their interaction. Apparent total tract digestibility of crude protein, neutral detergent fiber, and acid detergent fiber was linearly decreased (P < 0.001) by the inclusion of SL. No effects were observed for total CH₄ emissions per day, nor for CH₄ relative to organic matter intake or digestible organic matter with the inclusion of SL. However, emission of CH₄ in relation to intake of CT was affected by treatment (P < 0.001). A linear (P < 0.001) decrease and a quadratic effect (P < 0.001) were observed for δ¹³C of diets and gas, respectively, in which diets and enteric CH₄ with greater inclusion of SL were more depleted in ¹³C. Moreover, the difference in δ¹³C between diets and gas (Δδ¹³C) had a linear decrease (P = 0.001) with the inclusion of SL. The model developed to predict the C₃ proportions in the enteric CH₄ fitted to predicted values (P < 0.0001). Therefore, greater proportions of SL resulted in lesser CH₄ emission when CT intake was considered and the isotopic composition from enteric CH₄ was able to predict the contribution of SL in the emissions.     

Evaluation of the oral 13C-bicarbonate technique for measurements of energy expenditure in dogs before and after body weight reduction

Background

Overweight and obesity are the most common nutritional disorders in dogs and may lead to various secondary diseases and decreased lifespan. In obesity research, measurement of energy expenditure (EE) and determination of the energy requirements are essential. The objective with this study was to validate and evaluate the suitability of the oral ¹³C-bicarbonate technique (o¹³CBT) for measuring EE in dog obesity studies. A further objective was to investigate the impact of body weight (BW) reduction and changes in body composition on the EE when measured under conditions corresponding to the basal metabolic rate (BMR).

Results

The EE in five privately owned, overweight dogs was measured simultaneously with the o¹³CBT and indirect calorimetry (IC) for comparison of the results. Two measurements per dog were performed under the same standardised conditions (i.e. fasted and resting state) at the start, and after completing a 12-week BW reduction program. Additionally, measurements of body composition by Dual-energy X-ray absorptiometry (DEXA) were conducted at the beginning and at the end of the BW reduction program. There were no differences in EE results obtained by the o¹³CBT and IC. Overweight and the BW reduction did not affect the estimates for the respiratory quotient (RQ) or the recovery factor for the ¹³C-tracer (RF), both needed when using the o¹³CBT. The dogs lost 16% (SD ± 2.0) of their initial BW in reduced fat mass (P < 0.001), whereas fat free mass (FFM) remained unchanged. There was no effect of the BW reduction on the determined EE expressed in kJ/kg BW/d, or in kJ/kg BW^0.75/d. However, EE was lower (P < 0.001) after the BW reduction program when expressed in relation to FFM (kJ/kg FFM/d).

Conclusions

Results from the present study show that the o¹³CBT can be a used in obesity research to determine EE in fasted dogs and under resting conditions. Furthermore, the results suggest that the BMR does not change with reduced BW in overweight dogs as long as the FFM remains unchanged. This indicates that the BMR to maintain one gram of fat is equal to maintaining one gram of FFM in overweight dogs.     

Carbon source and trophic position of pelagic fish in coastal waters of south-eastern Izu Peninsula,Japan, identified by stable isotope analysis

ABSTRACT:   It is important to clarify trophic dynamics in marine ecosystems for management of the fishing ground. Organic carbon sources and trophic position of pelagic fishes in the coastal waters of the south-eastern Izu Peninsula, Japan, were examined on the basis of carbon and nitrogen stable isotope distributions. The δ¹³C of the fishes was mostly distributed from −19 to −16‰ for nektonic fishes (13 species of adults and immatures) and planktonic fishes (10 species of larvae and juveniles), close to the δ¹³C values of particulate organic matter and planktonic decapods. These δ¹³C signatures for the inhabitants of the water column were in contrast with the high δ¹³C values (mainly −16 to −13‰) for demersal fishes of Scorpaeniformes and benthic polychaetes collected in the surf zone. These results indicate that nektonic and planktonic fishes depend on phytoplankton for carbon supply. The δ¹⁵N signatures suggest that the trophic position ranged 3.1–4.5 for the nektonic fishes and 2.9–3.7 for the planktonic fishes, premised on trophic level 3 for larval Japanese anchovy Engraulis japonicus . Thus, planktivorous fishes should be mainly assigned to trophic levels 3 and 4 in this area.     

样本预处理方式对罗氏沼虾碳和氮稳定同位素比值检测的影响

为研究样本预处理方式对罗氏沼虾碳和氮稳定同位素比值检测的影响,分别选用3种保存温度(常温23℃/15 d、冷藏2℃/90 d、冷冻-18℃/360 d)、2种取样方式(虾仁取样、整虾取样),以新鲜沼虾样本为对照组,对比不同样本预处理方式对罗氏沼虾碳稳定同位素比值(δ¹³C)、氮稳定同位素比值(δ¹⁵N)、碳氮比(C/N)的影响。结果表明,不同保存温度和不同取样方式对罗氏沼虾δ¹³C、δ¹⁵N、C/N的影响明显。与对照组相比,常温保存条件下的δ¹⁵N偏移量最大(1.31‰~13.16‰,平均值为6.02‰),冷冻保存条件下的δ¹³C偏移量最大(2.34‰~2.84‰,平均值为2.57‰),室温保存条件下的C/N显著增加(P<0.05),冷藏和冷冻保存条件下的C/N显著减少(P<0.05)。不同取样方式对罗氏沼虾δ¹⁵N、δ¹³C的影响还取决于保存温度,在冷冻保存条件下,整虾取样的δ¹⁵N、δ¹³C显著高于虾仁取样,而在常温保存条件下,整虾取样的δ¹⁵N偏移量显著低于虾仁取样。因此,常温(23℃)和冷藏(2℃)条件不适合保存罗氏沼虾、冷冻(-18℃)保存罗氏沼虾的时间不宜超过60 d,建议新鲜沼虾采集后应立即干燥并开展碳和氮稳定同位素检测。本研究结果为水产品碳和氮稳定同位素比值检测的样本预处理方式提供了参考。     

滇中岩溶高原滇青冈原生林植物水分利用来源的稳定同位素分析

为阐明滇中岩溶高原滇青冈Cyclobalanopsis glaucoides原生林植物水分利用机理及其对岩溶干旱生境的适应策略,运用氧稳定同位素技术,分析了滇青冈,云南木樨揽Olea yue nnanensis,清香木Pistacia weinmannifolia等3种不同年龄阶段常见优势木琴植物小枝木质部水分及土壤水、表层岩溶带水氧同位素值的相关性,确定植物水分来源,并通过IsoSource模型计算不同潜在水源对滇青冈原生林的贡献。结果表明：滇青冈及其伴生的乔木水分利用层位及利用比例呈现时空差异,并形成明显的水分竞争关系。旱季,滇青冈、成熟云南木樨揽、幼龄清香木主要利用55～115 cm深层土壤水,成熟的滇青冈和清香木对表层岩溶带水利用比例增加。雨季,成熟的滇青冈、云南木樨揽、清香木和幼龄清香木因大气降水对浅表层土壤的补给主要利用20-55cm土壤水,利用比例分别为100％,33．3％,66．0％,37．4％,幼龄植株对表层岩溶带水的利用比例大于成熟植株。图2参23     

Stable isotopes and gut content show diet overlap among native and introduced piscivores in a large oligotrophic lake

Abstract – In past dietary studies kokanee Oncorhynchus nerka were prominent in the diet of Pend Oreille Lake's large piscivores: native bull trout Salvelinus confluentus, cutthroat trout O. clarki and northern pikeminnow Ptychocheilus oregonensis, and introduced lake trout S. namaycush and Kamloops rainbow trout O. mykiss gairdneri. However, kokanee have declined to 10–20% of their former abundance. We therefore initiated this study to understand current predation demands on kokanee and diet overlap among piscivores, using gut content samples and analysis of stable nitrogen (δ¹⁵N) and carbon (δ¹³C) isotopes from the lake's fish and invertebrate community. In gut content samples, kokanee were the main prey item of large [i.e., ≥400 mm total length (TL)] bull and lake trout; a conclusion that was affirmed by stable isotope analysis. Rainbow trout >500 mm TL consumed mostly kokanee, thus there was a high degree of diet overlap among large bull, lake and rainbow trout. Small (i.e., <400 mm TL) rainbow and cutthroat trout diets overlapped, and were composed mostly of littoral benthic invertebrates. However, gut content and stable isotope analysis did not accord for 400–500 mm TL rainbow trout, small lake trout, and large cutthroat trout. In these instances, a linear mixing model using stable isotope results predicted kokanee consumption for each species, but no kokanee were identified in rainbow or lake trout gut content. Gut content and stable isotope analysis of native northern pikeminnow indicated a diet of mostly littoral benthic invertebrates at smaller (100–150 mm TL) lengths, with kokanee becoming more prominent in the diet of individuals >300 mm TL. Percent of kokanee in the diet of northern pikeminnow has declined from a prior study; otherwise piscivore diets have apparently remained unchanged. In this study, judgments as to the feeding of some piscvores, based on gut content alone, would be tenuous because of small sample sizes, but stable isotope analysis provided an efficient means for confirming diets.