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南京直立人的U/Th和U/Pa年代 总被引：2，自引：0，他引：2
中国直立人化石的准确定年对于研究人类演化有着极为重要的意义。1993～1994年在南京汤山葫芦洞发现的两个直立人头盖骨化石和一枚牙化石被称为“南京直立人”。其中1号头盖骨化石之上的方解石钙板的U/Th年龄为53.3_(-1.2)~(+1.5)万年;但考虑到定年的准确性,则为53.3_(-3.0)~(+3.5)万年。其~(231)Pa/~(235)U活度比值为0.998±0.006。这表明“南京直立人”的年代应该大于50万年。与”南京直立人”伴生的动物牙化石U/Th年代为18.5～29.0万年;U/Pa年代为13.7～17.2万年。此外,对于同一颗牙化石,牙釉的年龄小于牙本质的年龄。同一样品的U/Pa年龄也显著小于其U/Th年龄。因此,牙化石的U摄取过程并不符合U早期摄取模式。多数牙化石分析点在~(234)U/~(238)U-~(230)Th/~(238)U图上落在位于U早期摄取和线性摄取模式曲线之间,指示牙化石的U摄取过程很可能介于上述两种模式之间。如果这一假设成立,那么牙化石的U/Th和U/Pa线性摄取模式年龄则为其年代的上限。因为不受U摄取过程~(234)U/~(238)U变化的影响,U/Pa线性摄取模式年龄比U/Th较为可靠。最小的U/Pa线性摄取模式年龄为1Ma,这是”南京直立人”上限年龄的估计。从定年结果看,”南京直立人”可能生活在海洋同位素(MIS)16阶段,但这不是最终结论。 相似文献
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Uptake and recovery of soil nitrogen by bryophytes and vascular plants in an alpine meadow 总被引：2，自引：2，他引：0
Due to their particular physiology and life history traits, bryophytes are critical in regulating biogeochemical cycles and functions in alpine ecosystem. Hence, it is crucial to investigate their nutrient utilization strategies in comparison with vascular plants and understand their responses to the variation of growing season caused by climate change. Firstly, this study testified whether or not bryophytes can absorb nitrogen(N) directly from soil through spiking three chemical forms of 15N stable isotope tracer. Secondly, with stronger ability of carbohydrates assimilation and photosynthesis, it is supposed that N utilization efficiency of vascular plants is significantly higher than that of bryophytes. However, the recovery of soil N by bryophytes can still compete with vascular plants due to their greater phytomass. Thirdly, resource acquisition may be varied from the change of growing season, during which N pulse can be manipulated with 15N tracer addition at different time. Both of bryophytes and vascular plants contain more N in a longer growing season, and prefer inorganic over organic N. Bryophytes assimilate more NH4+ than NO3– and amino acid, which can be indicated from the greater shoot excess 15N of bryophytes. However, vascular plants prefer to absorb NO3– for their developed root systems and vascular tissue. Concerning the uptake of three forms N by bryophytes, there is significant difference between two manipulated lengths of growing season. Furthermore, the capacity of bryophytes to tolerate N-pollution may be lower than currently appreciated, which indicates the effect of climate change on asynchronous variation of soil N pools with plant requirements. 相似文献
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FANG Zhanqiang 《中国海洋大学学报(英文版)》2006,5(1):49-54
Experiments were designed to expose the filter-feeding bivalve Perna viridis to different Cd-contaminated water environments in order to compare the different pathways through which Cd is accumulated. Results show that mussels can accumulate Cd through seawater, food, sediment and suspended particle pathways in a short period of time. Mussels＇ uptake of Cd through the seawater pathway reaches the highest concentration approximately 3 and 9 times larger than through the algae and sediment pathways respectively after 7 d. This indicates that the Cd-accumulation through seawater is most efficient. Results also indicate that the uptake directly through contaminated algae, particles or sediments ingested by mussels is less important when compared with the uptake of Cd by mussels through the seawater pathway. Metal uptake pathways and mechanisms of bioaccumulation by marine bivalve are also discussed in this paper. 相似文献
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铜绿微囊藻和四尾栅藻光合利用碳酸氢盐探讨 总被引：2，自引：0，他引：2
为了探讨羹类光合过程对碳酸氧盐的利用,研究不同pH值下铜绿微囊藻和四尾栅藻的净光合速率,并着重研究这两株藻的碳酸氢盐摄取速率.结果表明,从弱酸性到弱碱性,四尾栅藻的净光合速率都比铜绿微囊藻高.由pH值超过pH转折点后的无机碳摄取速率计算得到的碳酸氢盐摄取速率对铜绿微囊藻和四尾栅藻分别为142.14和314.08μmo1DIC/(g·h,FW),故这两株藻都可利用碳酸氢盐作为碳源进行光合,且均为强碳酸氧盐利用者;但是,四尾栅藻对碳酸氲盐的利用能力强于铜绿微囊藻.另外,与四尾栅藻相比,铜绿微囊藻的碳酸氧盐摄取速率更易受抑制剂的抑制. 相似文献
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海洋浮游植物对硒的摄取和转化 总被引：2，自引：0，他引：2
本文研究海洋浮游植物考长过程对硒的摄取和转化。结果表明，在藻类生长初期，快速选择摄取，并积累于藻相。在指数生长期，以溶解有机物形式排出体内多余硒。在稳定生长期各形态基本趋于稳定。藻类混种培养能提高对Ｓｅ的摄取程度及溶解有机硒代谢速度。 相似文献
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不同食物对紫红笛鲷幼鱼的生长和氮排泄的影响 总被引：3，自引：1，他引：3
以紫红笛鲷Lutjanusargentimaculatus幼鱼为研究对象,进行了摄食水平和食物种类对其生长和氮排泄影响的实验。结果表明,投喂鳗鱼饲料的紫红笛鲷幼鱼的特定生长率(SGR)为4.19%·d-1,投喂斑节对虾Penaeusmonodon肉和蓝圆Decapterusmaruadsi肉组的特定生长率分别为3.83%·d-1和3.90%·d-1;不同食物组的紫红笛鲷幼鱼的氮排泄率存在差异,以投喂鳗鱼饲料组的幼鱼最高,个体氮排泄率为4.080mg·尾-1·d-1,而投喂斑节对虾肉和蓝圆肉组的幼鱼个体氮排泄率分别为3.759和3.869mg·尾-1·d-1,摄取3种食物的紫红笛鲷幼鱼的氮排泄率(NE)和氮摄取率(NI)均为直线关系,直线方程分别为NE1=2.107+0.310NI1,NE2=1.749+0.316NI2,NE3=1.879+0.348NI3。 相似文献
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太湖铜绿微囊藻磷摄取动力学若干重要参数与其竞争优势相关研究 总被引：15，自引：0，他引：15
对从太湖分离的铜绿微囊藻(Microcystisaerugionosa)进行了不同氮磷比对生长影响的实验,以探索蓝藻生长优势形成的基础.实验结果虽然在一定程度上符合“氮磷摩尔比低于29蓝藻将会占据优势”的理论,但发现只在较低的营养水平时比较吻合.同时进行了不同磷营养条件下磷营养摄取与生长的实验,为太湖富营养化研究中应用的水质模型提供所需的参数值.微囊藻生长的磷半饱和常数Ks=16.21μM、磷摄取的半饱和常数Km=17.66μM、藻细胞最小的磷份额K=4.36μg/mg(dw);微囊藻在实验条件下的过度储磷系数Q0/Qmax=0.14;测定了磷饥饿和磷丰富时细胞最大的摄磷速率分别为1.66μg/(L·mg·h)和0.06μg/(L·mg·h).可见初始细胞内磷份额较低的藻细胞对磷的吸收速率要比胞内磷份额较高的藻细胞高. 相似文献
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