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.     

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。     

汾渭平原农户冬小麦氮磷养分投入调查与分析

为明确汾渭平原农户冬小麦施肥现状,并指导农户合理施肥,在汾渭平原冬小麦种植区选取22个区/县,连续2年进行农户冬小麦产量及氮、磷养分投入调查。结果表明,汾河平原和渭河平原农户冬小麦平均产量分别为6 949和6 442 kg·hm^-2,其中中等产量水平（5 500 kg·hm^-2）以上的农户超过80%。汾河平原农户冬小麦N和P₂O₅的平均投入量分别为272.6和139.1 kg·hm^-2,施氮不足、适中和过量的农户分别占11.84%、23.68%和64.47%,施磷不足、适中和过量的农户分别占14.03%、7.89%和78.07%。渭河平原农户N和P₂O₅的平均投入量分别为196.3和147.2 kg·hm^-2,施氮不足、适中和过量的农户分别占 28.63%、31.97%和39.40%,施磷不足、适中和过量的农户分别占5.95%、14.50%和79.56%。汾河平原农户冬小麦氮肥基肥和追肥比例分别为60.3%和39.7%,而渭河平原农户冬小麦氮肥基肥和追肥比例分别为 97.3%和2.7%。此外,汾河平原农户冬小麦N、P₂O₅的平均偏生产力分别为30.4和59.6 kg·kg^-1,渭河平原农户冬小麦N、P₂O₅的平均偏生产力分别为38.4和56.1 kg·kg^-1。总之,在汾渭平原农户冬小麦种植过程中,氮、磷肥过量施用依然严重,导致肥料利用率低,因此,未来需进一步加强对农民的宣传培训,使其科学合理施肥,促进农业绿色发展。     

三种鲟鱼血清及组织中磷酸酶和补体活性的比较

对施氏鲟、小体鲟和西伯利亚鲟的血清、肝脏、鳃及肠中碱性磷酸酶(AKP)、酸性磷酸酶(ACP)、补体C3及补体C4活性进行了测定和比较.AKP活性在小体鲟鳃和肠中显著高于施氏鲟和西比伯利亚鲟(P＜0.05),而其在三种鲟鱼的肝脏和血清中差异不显著(P＞0.05);ACP活性在小体鲟肠中显著高于施氏鲟和西比伯利亚鲟(P＜0.05),而其在三种鲟鱼的肝脏、鳃和血清中差异不显著(P＞0.05);补体C3活性在小体鲟肝脏和肠中显著高于施氏鲟和西比伯利亚鲟(P＜0.05),而其在三种鲟鱼的鳃和血清中差异不显著(P＞0.05);小体鲟血清中补体C4活性显著高于施氏鲟和西伯利亚鲟(P＜0.05),而补体C4活性在三种鲟鱼的肝脏、鳃及肠中差异不显著(P＞0.05).由此可见,虽然三种同为鲟科鲟属鱼类,但它们之间的AKP、ACP、补体C3及补体C4活性存在着种间差异.     

Application of Azotobacter enhances pond productivity and fish biomass in still water ponds

Two strains (derepressed-nitrogen fixing, Mac-27 and phosphate solubilizing, PS-21) of Azotobacter chroococcum were inoculated in fish culture ponds, singly and in combination with inorganic fertilizers (urea, single superphosphate–SSP). Physico-chemical parameters of pond waters, plankton production and fish biomass were studied. Inoculation of A. chroococcum (Mac-27) enhanced nitrogenase activity and rate of nitrogen fixation. A slight reduction in nitrogen fixation and nitrogenase activity was noticed when urea at 96 kg ha–1 y–1 was mixed with the biofertilizer (Mac-27). Inoculation of PS-21 enhanced phosphate solubilization, but Kjeldahl-nitrogen concentration values remained low in comparison with controls. On the other hand, inoculation of Azotobacter (either strain) enhanced the accumulation of ammonium-N, nitrite-N and nitrate-N. A significant (p < 0.05) reduction in dissolved oxygen (DO) concentration also took place when Azotobacter (both Mac-27 and PS-21) was inoculated in fish ponds. However, when used along with inorganic fertilizers, the reduction was not significant. The pH values were only slightly lowered when the phosphate-solubilizing strain (PS-21) of Azotobacter was inoculated. Inoculation of biofertilizer enhanced plankton production, net primary productivity and fish biomass. However, highest values in most of these parameters were noticed only in ponds that were treated with the higher doses of inorganic fertilizers (urea 192 kg and SSP 1500 kg ha–1 y–1). © Rapid Science Ltd. 1998     

充分发挥磷肥后效作用是实现玉米节本增效的重要举措

通过吉林省中等肥力黑土玉米磷肥13年田间与盆钵定位试验及室内大量化验分析得出磷肥当季虽具有较明显的增产效果,但其利用率(9.8%)并不高.四个量级磷肥(45、90、135和180kg/hm2)利用率最高的时期均在施后第二年(14.9%～38.8%)和第三年(12.3%～30.5%),到第四年虽能被玉米吸收利用一部分(9.1%～18.6%),但其增产效果已不显著.残留在土壤中的磷肥前两年利用率之和可达到27.4%～68.5%.产量与效益结果表明,磷肥在施用后的第二年和第三年,即磷肥前两年后效的年均增产(1003～1443 kg/hm2)增收(802～1154元/hm2)效果最高.     

不同磷源对橡胶树幼苗生长及土壤磷素组分特征的影响

通过盆栽试验及Hedley土壤磷素分组法研究了海南省玄武岩发育砖红壤上施用不同磷源对橡胶树幼苗生长的影响及土壤磷素组分变化。磷肥处理分别为不施磷处理、施用昆阳磷矿粉100 mg/kg(以全P计,下同)、施用昆阳磷矿粉250 mg/kg和施用普通过磷酸钙100 mg/kg。结果表明:施用磷矿粉和普通过磷酸钙均显著增加了橡胶树幼苗干物重、株高、茎粗和吸磷总量,但高磷矿粉处理和普通过磷酸钙处理橡胶树幼苗叶片磷含量显著降低;高磷矿粉处理取得了与普通过磷酸钙相当的肥效;磷矿粉施用后,土壤树脂提取态磷(Resin-P)、碳酸氢钠提取态无机磷(NaHCO_3-Pi)、氢氧化钠提取态无机磷(NaOH-Pi)、盐酸提取态磷(HCl-P)和残余态磷(Residual-P)等组分含量均显著增加,但碳酸氢钠提取态有机磷(NaHCO_3-Po)和氢氧化钠提取态有机磷(NaOH-Po)不受施磷影响;干物质重和吸磷总量均与土壤Resin-P、NaHCO_3-Pi和Na OH-Pi呈显著的正相关关系;磷矿粉施用11个月后,平均33.1%磷矿粉溶解在土壤中,平均43.5%的磷矿粉残留在土壤Residual-P组分中。为改善玄武岩发育砖红壤上有效磷及橡胶树磷素营养状况,应选择施用高活性磷矿粉以降低磷矿粉颗粒被大量包被的风险。