Oxygen isotope ratios of plant available phosphate in lowland tropical forest soils

Phosphorus (P) cycles rapidly in lowland tropical forest soils, but the process have been proven difficult to quantify. Recently it was demonstrated that valuable data on soil P transformations can be derived from the natural abundance of stable oxygen isotopes in phosphate (δ¹⁸O_P). Here, we measured the δ¹⁸O_P of soils that had received long-term nutrient additions (P, nitrogen, and potassium) or litter manipulations in lowland tropical forest in Panama and performed controlled incubations of fresh soils amended with a single pulse of P. To detect whether δ¹⁸O_P values measured in the incubations apply also for soils in the field, we examined the δ¹⁸O_P values after rewetting dry soils. In the incubations, resin-P δ¹⁸O_P values converged to ∼3.5‰ above the expected isotopic equilibrium with soil water. This contrasts with extra-tropical soils in which the δ¹⁸O_P of resin-P matches the expected equilibrium with soil water. Identical above-equilibrium resin-P δ¹⁸O_P values were also found in field soils that did not receive P additions or extra litter. We suggest that the 3.5‰ above-equilibrium δ¹⁸O_P values reflect a steady state between microbial uptake of phosphate (which enriches the remaining phosphate with the heavier isotopologues) and the release of isotopically equilibrated cell internal phosphate back to the soil. We also found that soil nutrient status affected the microbial turnover rate because in soils that had received chronic P addition, the original δ¹⁸O_P signature of the fertilizer was preserved for at least eight weeks, indicating that the off-equilibrium δ¹⁸O_P values produced during microbial phosphate turnover was not imprinted in these soils. Overall, our results demonstrate that ongoing microbial turnover of phosphate mediates its biological availability in lowland tropical soils.     

瘤胃上皮内的乳酸吸收及其转运载体蛋白研究进展

乳酸作为瘤胃内的中间代谢产物,其合理的清除与有效的利用在由高精料诱导的瘤胃酸中毒的研究中十分重要。现有研究表明,瘤胃上皮在乳酸吸收方面发挥着一定的作用,因此,本文从瘤胃上皮的乳酸吸收以及吸收过程中涉及的转运载体蛋白进行综述,为进一步了解乳酸在瘤胃内的转运过程提供理论依据。     

Characteristics of 18F-FDG and 18F-FDOPA PET in an 8-year-old neutered male Yorkshire Terrier dog with glioma: long-term chemotherapy using hydroxyurea plus imatinib with prednisolone and immunoreactivity for PDGFR-β and LAT1

An 8-year-old neutered male Yorkshire Terrier dog presented with head pressing, vestibular ataxia, neck tenderness, and no oculocephalic reflex. A demarcated lesion in the pons was identified on MRI. The patient was tentatively diagnosed with a glioma and was treated with hydroxyurea plus imatinib and prednisolone. After 30 days of therapeutic treatment, the patient showed a clear improvement in neurological signs, which lasted for 1117 days. On day 569 after the initiation of treatment, ¹⁸F-fluorodeoxyglucose (FDG)-positron emission tomography (PET) was performed with no significant findings on visual analysis. The average and maximal standardized uptake values (SUVs) were 1.92 and 2.29, respectively. The tumor-to-normal-tissue (T/N) ratio was 0.97. The first evidence of clinical deterioration was noticed on day 1147. On day 1155, 3,4-dihydroxy-6-[¹⁸F]-fluoro-l-phenylalanine (¹⁸F-FDOPA)-PET was performed. High uptake of ¹⁸F-FDOPA was observed in the intracranial lesion. The mean and maximal SUVs of the tumor were 1.59 and 2.29, respectively. The T/N ratio was 2.22. The patient was euthanized on day 1155 and histopathologic evaluations confirmed glioma (astrocytoma). This case shows that chemotherapy with hydroxyurea plus imatinib may be considered in the treatment of canine glioma. Furthermore, this is the first case describing the application of ¹⁸F-FDG and ¹⁸F-FDOPA in a dog with glioma.     

磷肥对甘肃临夏地区燕麦干草及种子生产的影响

为确定甘肃高寒雨养区燕麦(Avena sativa)种子生产中磷肥最佳用量,提高肥料利用效率,试验在氮肥(尿素)用量75 kg·hm^-2的固定水平下,设计4个磷肥(P₂O₅)水平(0(CK),65(C₁),100(C₂),135(C₃)kg·hm^-2),对各磷肥水平下干草产量、种子产量和相关性状的变化进行了研究。结果表明：施用磷肥使燕麦的株高、茎粗、分蘖和干草产量均有提高,灌浆期C₁,C₂,C₃干草产量较CK依次提高13.85%,25.96%,22.65%,干草产量与磷肥水平显著正相关(相关系数0.91);施用磷肥提高了燕麦的有效分蘖数、主穗长,显著提高主穗粒数、穗粒重、千粒重、种子产量和秸秆产量,C₁,C₂,C₃种子产量较CK依次提高12.37%,16.72%,14.38%,种子产量与磷肥水平显著正相关...     

利用32P示踪研究马铃薯(合作-88)对磷素营养的吸收及分布规律

应用3 2 P研究“合作 88”马铃薯对磷素营养的吸收和分布规律 ,结果显示 :马铃薯对磷素营养的吸收率随植株的生长而增加。吸收率与栽培生长时间呈显著正相关。磷素主要分布为茎 >根 >叶 ,随生育期茎中含量相对增加 ,而叶中含量相对减少 ,根的不变。     

植物对磷饥饿的反应研究进展

磷是构成生命的重要元素之一,也是土壤中有效性最低的一种营养元素。我国是世界上最大的小麦生产国。但是我国耕地中有59%的土壤缺磷。农作物的产量常受到缺磷的影响而受损。土壤缺磷并不是土壤中总磷量低,而是土壤中可供植物直接吸收利用的有效态磷含量低。植物在磷饥饿时会发生各种各样的变化,以尽最大可能满足自身对磷的需求。植物对缺磷的反应是一个复杂的网络过程。大约有100多个基因参与了植物对缺磷的反应。其中主要的有磷转运蛋白基因、核糖核酸酶基因、磷酸酶基因等。植物在吸收外界的磷的过程中磷转运蛋白发挥了重要作用。植物磷转运蛋白基因按照序列相似性可以划分为H+/Pi共转运家族(Pht1家族)和Na+/Pi共转运家族(Pht2家族)。按照吸收动力学的标准可以分为高亲和力磷转运蛋白和低亲和力磷转运蛋白两种。磷饥饿时植物对磷吸收能力的增强的原因之一是增加了磷转运蛋白分子的合成数目。目前尽管人们对植物吸收磷的理解已经有了长足的进步,但是在植物对磷的具体调控机制、磷的跨液泡膜运输等重要方面仍然没有明确的结果。     

棉花不同品种叶片和纤维中蔗糖磷酸合成酶活性变化 及其与糖含量的关系

利用山农棕02、丰抗6号、中棉45 3个品种在大田栽培的条件下，研究了叶片和纤维中蔗糖磷酸合成酶活性的变化及与糖含量的关系。结果表明，在3个品种的叶片和纤维中，蔗糖磷酸合成酶活性均出现双峰，在开花当天最高，花后18d次之，整体呈下降趋势；与此同时可溶性总糖和蔗糖的含量变化以及光合速率的变化也成相似的变化。3个品种中，丰抗6号蔗糖磷酸合成酶活性和含糖量最高，中棉45次之，山农棕02最低。3个品种的相应观测指标之间均呈极显著差异。     

农用运输车行驶平顺性的模拟计算与分析

提出了四轮农用运输车的八自由度随机振动系统模型，对整车行驶平顺性进行了计算机模拟计算和分析计算结果得到了试验验证。     

基于模糊分析的农用运输车双万向传动轴可靠性优化设计

将模糊可靠性设计应用于农用运输车传动轴的优化设计,提出了农用车双万向传动轴的模糊可靠性优化设计方法,建立了在满足给定模糊可靠性要求设计条件下优化设计数学模型,并进行了实例计算。     

加强农用运输车管理 做好交通事故预防

近年来因农用运输车所造成的交通事故不断发生,且逐年呈现上升势头,本文从驾驶员的因素、车辆自身因素以及驾驶环境条件、职能部门的监管等方面对农用运输车交通事故的原因作了分析,提出了一些预防事故发生的措施。