Phosphorus fractions and dynamics as affected by land-use changes in the Central Mexican highlands

Land-use change from forest to agriculture in the volcanic ash-derived soils of Mexico has increased over recent decades. It is likely that land uses and management practices, particularly fertilizer use have affected phosphorus (P) distribution and availability. The objective of this study was to evaluate the effects of land-use types (native forest and maize mono-cropping), and the related P addition, on the forms and distribution of soil P and their isotopic exchangeability. An Andisol, sampled from a cropping site, along with the contiguous area under native forest was treated with ³²P-labelled potassium phosphate (KH₂³²PO₄). The soil samples were extracted after incubation times of 7, 21, 35 and 49 days. Phosphorus content and ³²P recovery in fractions sequentially extracted were assessed for each incubation time. Total soil P was dominated by inorganic fractions (79 to 86%) in both land-use types. Resin-Pi, bicarbonate extractable inorganic P (Bic-Pi) and sodium hydroxide extractable inorganic P (NaOH_0.1-Pi) were all raised with P addition. However, the proportion of organic P fraction was reduced under cropped soil. The recovery of ³²P in soils with P addition indicates that resin-Pi, Bic-Pi and NaOH_0.1-Pi comprised nearly all the exchangeable P. In native soils with no P addition, more than 19% of the ³²P was recovered in Bic-Po and NaOH_0.1-Po forms. This finding indicates that organic P cycling is crucial when soil Pi reserves are presented in an inadequate amount. Ecologically based management has to be designed for replenishment and succeeding maintenance of soil organic P compounds to increase sustainable agricultural production.     

几种粘粒矿物和土壤表面吸附态磷的解吸 Ⅰ吸附和解吸滞后的机理(英文)

研究了可变电荷粘粒矿物和矿物学性质不同的代表性土壤对磷酸根的等温解吸特性。结果表明磷酸根的解吸等温线一般都滞后于吸附等温线。滞后的程度以铁、铝氧化物最大;含较多铁和铝氧化物的酸性土壤其次;高岭石、蒙脱石和中性、石灰性土壤较小。磷酸根的解吸率一般都随着吸附饱和度的增加而增加,但在各吸附饱和度下,解吸率都明显低于吸附磷的同位素(磷)交换率。在恒定pH和离子强度下,解吸主要涉及结合能较低的吸附态磷。可变电荷表面紧结合态吸附磷在同样条件下是极难解吸的,从而引起磷酸根吸附和解吸不可逆转。此外,吸附态磷还可能通过次生化学反应而转化成不溶性磷酸盐化合物,对这种形态磷就不能通过简单的水液平衡而发生可逆性的解吸作用,而必须加以某种化学处理(例如适当酸化或用有机物质)。     

Predation history and vulnerability: Conservation of the stickleback adaptive radiation

Recent adaptive radiations offer special insight into the processes that generate biodiversity. The loss of unique members of such radiations undermines their collective evolutionary potential, as well as the ability of scientists to compare divergent populations, thereby devaluing the entire radiation as a system of study. To illustrate our case, we consider the adaptive radiation of the threespine stickleback fish (Gasterosteus aculeatus) in light of anthropogenic threats. Specifically, we consider the effects of stocking with rainbow trout, Onchorynchus mykiss, on populations of stickleback in lakes of two types in the Cook Inlet Region of Alaska, USA: (1) those in which salmonids are native and (2) those historically devoid of predatory fish. Many populations in this second class exhibit reduced pelvic armor that is, in part, a consequence of the historical absence of piscine predators that prey upon stickleback. Long-term trapping data from 77 lakes show that stocking in lakes where trout are not native is associated with large fluctuations in stickleback abundance, relative to lakes in which trout are native, or to lakes in which trout are neither native nor stocked. Pelvic-reduced populations appear to be at most risk from stocking. We discuss how these populations have responded to, and may yet respond to such threats, and how the information we have on these populations can be used to identify evolutionarily significant units (ESUs: Ryder, 1986), and certainly, distinct populations segments (DPSs: [Green, 2005], [Moritz, 2002] and [Waples, 1991]) deemed worthy of protection under Section 3(15) of the 1973 US Endangered Species Act as amended in 1978. Finally, we consider relevance of our results to the conservation of other recent adaptive radiations.     

不同钝化剂和培养时间对Cd污染土壤中可交换态Cd的影响

原位化学钝化技术是修复重金属污染土壤的重要途径之一,通过施入一些钝化剂以降低土壤中重金属有效态含量,从而减少其迁移及对植物的毒害。选取羟基磷灰石（HA）、磷矿粉（PRX和PRH）、沸石、赤泥、新鲜植物残体、玉米秸秆粉末以及相应的处理共21种钝化剂,在同一培养条件和添加浓度下,比较其对人工Cd污染土壤中可交换态Cd含量的影响,并分析了其在不同培养时间对钝化效果的时间效应,试验的结果对于筛选Cd污染土壤钝化剂有着重要的意义。结果表明,纳米化赤泥、羟基磷灰石和纳米化酸洗赤泥可显著降低土壤中可交换态Cd含量,钝化比例高达35%-55%;赤泥、酸洗赤泥、沸石达15%-25%;富含巯基植物蒜苗、油菜、大葱植物残体也可达20%-25%。磷矿粉、大葱粉末、玉米秸秆和巯基化玉米秸秆的钝化效果相对较差;HA、铵型沸石、纳米赤泥、酸洗纳米赤泥、干油菜粉末、酸洗赤泥对可交换态Cd的钝化效果的时间效应不明显;赤泥、大葱残体、特别是玉米秸秆和巯基玉米秸秆随时间增长钝化效果增加显著,在8周和16周时段钝化效果较好。     

不同钝化剂和培养时间对Cd污染土壤中可交换态Cd的影响

原位化学钝化技术是修复重金属污染土壤的重要途径之一,通过施入一些钝化剂以降低土壤中重金属有效态含量,从而减少其迁移及对植物的毒害.选取羟基磷灰石(HA)、磷矿粉(PRX和PRH)、沸石、赤泥、新鲜植物残体、玉米秸秆粉末以及相应的处理共21种钝化剂,在同一培养条件和添加浓度下,比较其对人工Cd污染土壤巾可交换态Cd含量的影响,并分析了其在不同培养时间对钝化效果的时间效应,试验的结果对于筛选Cd污染土壤钝化剂有着重要的意义.结果表明,纳米化赤泥、羟基磷灰石和纳米化酸洗赤泥可显著降低土壤中可交换态Cd含量,钝化比例高达35%～55%;赤泥、酸洗赤泥、沸石达15%～25%;富含巯基植物蒜苗、油菜、大葱植物残体也可达20%～25%.磷矿粉、大葱粉末、玉米秸秆和巯基化玉米秸秆的钝化效果相对较差;HA、铵型沸石、纳米赤泥、酸洗纳米赤泥、干油菜粉末、酸洗赤泥对可交换态Cd的钝化效果的时间效应不明显;赤泥、大葱残体、特别是玉米秸秆和巯基玉米秸秆随时间增长钝化效果增加显著,在8周和16周时段钝化效果较好.