藏东南色季拉山林线过渡带7种灌木植物的叶氮回收潜力

在湿润的青藏高原东南部, 为什么常绿灌木广泛占据高海拔的林线过渡带及以上的高山带, 而落叶灌木只能零星分布?未来气候变暖对该区不同功能群物种的影响是否相同?通过测定西藏东南部色季拉山林线过渡带7种灌木凋落叶的氮含量, 比较了极端高海拔地区灌木不同表达单位的叶氮回收潜力在不同功能群间的差异, 以及不同海拔、不同坡向间的差异, 试图从养分限制的角度为解答上述科学问题提供基础数据。研究结果表明: 1)从基于单位质量叶氮含量(N_mass)的叶氮回收潜力来看, 常绿灌木裂毛雪山杜鹃(薄毛海绵杜鹃) (Rhododendron aganniphum var. schizopeplum)显著高于其他6种落叶灌木, 但由于受比叶重的影响, 基于单位面积叶氮含量(N_area)的叶氮回收潜力则表现为落叶灌木总体较高; 2)落叶灌木山生柳(Salix oritrepha)和拉萨小檗(Berberis hemsleyana)的叶氮回收潜力在不同海拔或不同坡向间均无显著差异, 但裂毛雪山杜鹃基于N_mass的叶氮回收潜力在高海拔地段明显偏高。在极端高海拔的林线过渡带, 通过降低凋落叶中的氮含量(增加叶氮回收潜力)以达到高效的养分利用可能是常绿灌木裂毛雪山杜鹃适应高寒胁迫环境的重要策略。与落叶灌木相比, 常绿灌木裂毛雪山杜鹃叶氮回收潜力对未来气候变暖可能更敏感。     

Leaf C,N, and P concentrations and their stoichiometry in peatland plants of Da Hinggan Ling,China

叶片碳(C)、氮(N)、磷(P)含量及其化学计量特征为植物养分状况和元素限制性提供依据。为了解不同生活型植物叶片C、N、P化学计量特征的变化,该研究测定、分析了大兴安岭地区18个泥炭地常见的3种草本植物——白毛羊胡子草(Eriophorum vaginatum)、玉簪薹草(Carex globularis)、小叶章(Deyeuxia angustifolia), 5种落叶灌木——柴桦(Betula fruticosa)、越桔柳(Salix myrtilloides)、细叶沼柳(Salix rosmarinifolia)、笃斯越桔(Vaccinium uliginosum)、越桔(Vaccinium vitis-idaea)和3种常绿灌木——杜香(Ledum palustre)、地桂(Chamaedaphne calyculata)、头花杜鹃(Rhododendron capitatum)的叶片C、N、P含量。结果表明: (1)落叶和常绿灌木叶片C、N、P含量总体高于草本植物而C:N、C:P、N:P低于草本植物, 说明不同生活型植物具有不同的养分利用策略,灌木叶片C、N、P储存高于草本植物而N、P利用效率低于草本植物; (2)小叶章和头花杜鹃叶片N:P小于10, 同时其N含量小于全球植物叶片平均N含量, 相比其他植物来说更易受N限制; (3)采样地点解释了叶片C、N、P指标变异的12.8%-40.8%, 植物种类对叶片C、N、P指标变异的解释量占9.3%-25.5%; (4)草本植物C、N、P指标的地点间变异系数高于落叶和常绿灌木, 草本植物C、N、P指标对地点因素变化的响应较灌木敏感; (5)草本植物N含量种间变异系数高于落叶和常绿灌木, 落叶灌木P含量种间变异系数高于草本植物和常绿灌木, 草本植物和落叶灌木N、P吸收的种间生理分化较常绿灌木高。     

大兴安岭泥炭地植物叶片碳氮磷含量及其化学计量学特征

叶片碳(C)、氮(N)、磷(P)含量及其化学计量特征为植物养分状况和元素限制性提供依据。为了解不同生活型植物叶片C、N、P化学计量特征的变化,该研究测定、分析了大兴安岭地区18个泥炭地常见的3种草本植物——白毛羊胡子草(Eriophorum vaginatum)、玉簪薹草(Carex globularis)、小叶章(Deyeuxia angustifolia), 5种落叶灌木——柴桦(Betula fruticosa)、越桔柳(Salix myrtilloides)、细叶沼柳(Salix rosmarinifolia)、笃斯越桔(Vaccinium uliginosum)、越桔(Vaccinium vitis-idaea)和3种常绿灌木——杜香(Ledum palustre)、地桂(Chamaedaphne calyculata)、头花杜鹃(Rhododendron capitatum)的叶片C、N、P含量。结果表明: (1)落叶和常绿灌木叶片C、N、P含量总体高于草本植物而C:N、C:P、N:P低于草本植物, 说明不同生活型植物具有不同的养分利用策略,灌木叶片C、N、P储存高于草本植物而N、P利用效率低于草本植物; (2)小叶章和头花杜鹃叶片N:P小于10, 同时其N含量小于全球植物叶片平均N含量, 相比其他植物来说更易受N限制; (3)采样地点解释了叶片C、N、P指标变异的12.8%-40.8%, 植物种类对叶片C、N、P指标变异的解释量占9.3%-25.5%; (4)草本植物C、N、P指标的地点间变异系数高于落叶和常绿灌木, 草本植物C、N、P指标对地点因素变化的响应较灌木敏感; (5)草本植物N含量种间变异系数高于落叶和常绿灌木, 落叶灌木P含量种间变异系数高于草本植物和常绿灌木, 草本植物和落叶灌木N、P吸收的种间生理分化较常绿灌木高。     

额尔齐斯河流域垂枝桦林群落结构特征与物种多样性相关分析

为阐明植物群落结构特征和物种多样性之间的相互关系,选择额尔齐斯河流域白桦林国家森林公园的天然垂枝桦(Betula pendula)纯林、垂枝桦苦杨混交林、垂枝桦白柳混交林为研究对象,分林层调查群落的基本特征参数(高度、枝下高、冠幅、胸径、盖度等),计算物种重要值、丰富度指数、多样性指数、均匀度指数,并进行典范对应分析。结果表明:(1)垂枝桦白柳混交林的乔木层树高、枝下高和灌木层的地径、盖度均最高;3种群落的草本层特征参数(除基径)均具有显著差异;垂枝桦白柳林的盖度分别比垂枝桦苦杨林和垂枝桦纯林高19.1%和51.8%。(2)3种群落的乔木层重要值最高为垂枝桦,灌木层为疏花蔷薇(Rosa laxa)、阿尔泰山楂(Crataegus altaica),草本层为莎薹草(Carex bohemica)。(3)3种群落类型中乔木层的丰富度指数R、Simpson指数、Shannon-Wiener指数和灌木层的Pielou指数、Alatalo指数呈现出相同规律,即垂枝桦白柳混交林>垂枝桦苦杨混交林>垂枝桦纯林;草本层中除Alatalo指数之外,其他指数均呈现垂枝桦纯林>垂枝桦苦杨混交林>垂枝桦白柳混交林(P>0.05)。(4)CCA排序结果表明,不同垂枝桦林群落结构特征与物种多样性关系有差异。其中,垂枝桦纯林中,对物种多样性影响最大的是乔木枝下高、灌木株高、冠幅以及草本盖度;垂枝桦苦杨混交林中,对物种多样性影响最大的是乔木高度和冠幅、灌木冠幅和草本高度;垂枝桦白柳林中,对物种多样性影响最大的是乔木胸径、灌木冠幅、盖度以及草本高度。研究表明,乔木枝下高度、灌木冠幅、草本高度是影响3种群落类型物种多样性的主要因素。     

模拟氮沉降对长白山苔原灌草混合群落中植物光合特性的影响

由于草本植物持续上侵长白山灌木苔原,形成了强烈的灌草群落种间竞争。本研究以牛皮杜鹃-小叶章群落（Comm.Rhododendron aureum-Deyeuxia purpurea）为对象,根据小叶章的入侵程度设置4种盖度差异显著的样方（无、轻度、中度、重度入侵）,并设3个施氮水平（自然状态、添加11.8 kgN·hm^-2·a^-1及添加23.6 kgN·hm^-2·a^-1）,进行原位氮沉降模拟实验,监测灌木牛皮杜鹃和草本植物小叶章光合特性的差异和变化趋势,研究小叶章入侵苔原带的内在生理机制。结果显示：（1）小叶章净光合速率大于牛皮杜鹃,小叶章盖度越高、其叶绿素含量越高,而牛皮杜鹃叶绿素含量降低,随着小叶章入侵程度的增加,其净光合速率增强;（2）施氮可以提高牛皮杜鹃和小叶章的叶绿素含量和净光合速率,促进植物生长,但小叶章的增幅更大,从而增强了小叶章的竞争优势;（3）施氮和小叶章入侵具有复合作用,小叶章盖度越大,对其施氮导致小叶章净光合速率与叶绿素含量的增幅越大,而牛皮杜鹃的增幅减小。所以小叶章的成功入侵可能与其具有较高的净光合速率有关,并且施氮有利于提高小叶章的净光合速率,随着氮沉降的继续增加,更有利于小叶章的生长并提高其竞争力。     

模拟氮沉降对长白山苔原灌草混合群落中植物光合特性的影响

由于草本植物持续上侵长白山灌木苔原,形成了强烈的灌草群落种间竞争。本研究以牛皮杜鹃-小叶章群落(Comm. Rhododendron aureum-Deyeuxia purpurea)为对象,根据小叶章的入侵程度设置4种盖度差异显著的样方(无、轻度、中度、重度入侵),并设3个施氮水平(自然状态、添加11.8 kgN·hm~(-2)·a~(-1)及添加23.6kgN·hm~(-2)·a~(-1)),进行原位氮沉降模拟实验,监测灌木牛皮杜鹃和草本植物小叶章光合特性的差异和变化趋势,研究小叶章入侵苔原带的内在生理机制。结果显示:(1)小叶章净光合速率大于牛皮杜鹃,小叶章盖度越高、其叶绿素含量越高,而牛皮杜鹃叶绿素含量降低,随着小叶章入侵程度的增加,其净光合速率增强;(2)施氮可以提高牛皮杜鹃和小叶章的叶绿素含量和净光合速率,促进植物生长,但小叶章的增幅更大,从而增强了小叶章的竞争优势;(3)施氮和小叶章入侵具有复合作用,小叶章盖度越大,对其施氮导致小叶章净光合速率与叶绿素含量的增幅越大,而牛皮杜鹃的增幅减小。所以小叶章的成功入侵可能与其具有较高的净光合速率有关,并且施氮有利于提高小叶章的净光合速率,随着氮沉降的继续增加,更有利于小叶章的生长并提高其竞争力。     

金沙江干旱河谷退化草地群落对氮磷施肥的反应

在云南省境内的金沙江干旱河谷区, 选择退化严重的草地群落研究氮磷施肥对群落动态的影响。经过一个生长季的施肥处理, 结果表明, 除大量施磷肥处理(20 g·a^-1·m^-2)时, 可能因施磷过多群落生物量和密度没有出现增加外。其余的施氮和施磷处理均导致群落地上生物量和密度增加, 而且施氮处理引起群落地上生物量和密度增加的程度都高于施磷处理。说明在干旱河谷退化严重的草地生态系统, 氮是限制系统恢复的主要因素。施肥后禾本科草本植物密度大量增加, 而乔灌木密度增加不明显, 群落在短期内变成以禾本科草本植物为主的状态。施氮和施磷没有引起群落种数量和植物多样性指数的明显变化。试验结束时土壤的铵态氮、硝态氮和有效磷浓度没因施肥而增加, 但施肥处理的植物体氮和磷浓度增加。     

长期不同施磷条件下玉米产量、养分吸收及土壤养分平衡状况

以设置在沈阳潮棕壤上的连续12年的田间定位磷微区试验为依托,研究在不同磷肥施用条件下(施用量和施磷频次),玉米产量、养分吸收以及土壤养分平衡状况。结果表明:磷素不是该研究区域玉米生产的主要限制因子;施肥促进养分吸收,其各处理间增加趋势为氮磷氮对照,并且一次性施磷肥方式优于每年施磷肥方式;与土壤本底值相比,施肥后土壤耕层(0~20 cm)全磷、速效磷、全氮、碱解氮呈增加趋势,由于长年没有外源钾的补充,土壤全钾和速效钾呈下降趋势,其各处理间下降趋势为氮磷氮对照;土壤速效磷在不施用肥料条件下有下降趋势,只施用氮肥条件下有增加趋势,只是两者变化并不很明显;在每年施磷条件下,土壤速效磷量呈缓慢上升趋势,而在一次性施磷条件下,施肥当年的土壤速效磷量激增,而后呈减小的趋势,即与每年施磷肥方式相比,一次性施磷方式更有利于建立土壤"宏大"有效磷库;为了保证土壤养分平衡,在施用足量氮肥的前提下,施用磷肥量为等于或略高于作物移出磷量,施氮磷比控制在1∶0.167到1∶0.5之间。     

Plant phenols contents and their changes with nitrogen availability in peatlands of northeastern China

气候变暖和大气氮沉降增加会改变北方泥炭地的养分状态,从而影响其植被的物种组成和固碳功能。酚类物质是植物用于 防御植食性动物和适应环境的次生代谢产物,由于其具有抗分解的特性,在调节泥炭地碳动态方面也起着重要的作用。然而,北方 泥炭地不同功能型植物的酚含量及其如何随氮有效性变化尚不清楚。本论文通过测定中国东北大兴安岭地区18个泥炭地共11 种植物的叶片总酚含量(Total Phenols Contents, TPC),研究了它们随叶片氮、磷含量的变化关系,并探讨了其潜在机制。结果表明,灌木叶片TPC高于草本植物,说明生长较快且无菌根的草本植物比生长较慢且具有菌根的灌木对防御的碳投入较少。灌木叶片TPC随叶片氮含量增 加而降低,表明其防御碳投入随氮有效性增加而减少。相反,草本植物叶片TPC随氮含量增加而增加,随磷含量增加而减少,由于草本植物相对于灌木具有较强的氮限制和较弱的磷限制,草本植物防御碳投入可能随养分有效性增加而增加。我们的结果表明,泥炭地在氮有效性随气候变暖和氮沉降增加而增加的背景下,灌木将投入相对较多的碳用于生长而非防御,而草本植物则与之相反。这些发现将有助于对北方泥炭地灌木入侵及其资源竞争机制的理解。     

氮磷添加对中亚热带常绿阔叶林土壤有效氮和pH值的影响

为了确定施肥类型和施肥时间对中亚热带常绿阔叶林土壤有效氮和p H值的影响,通过在浙江天童木荷林(Schima superba)设置4种施肥处理(对照:不添加;氮添加:100kg N·hm~(-2)·a~(-1);磷添加:15 kg P·hm~(-2)·a~(-1)和氮磷添加100 kg N·hm~(-2)·a~(-1)+15 kg P·hm~(-2)·a~(-1)),测定了氮磷添加后森林土壤有效氮和p H值的变化。结果表明:1)氮添加显著促进了土壤铵态氮和硝态氮含量的增加,增加幅度随着施氮时间的延长而增加;磷添加对土壤铵态氮含量无显著影响,但能显著降低土壤硝态氮含量;氮磷添加显著增加土壤硝态氮含量,随着施氮时间的延长,氮磷添加显著增加土壤铵态氮。2)随着施氮时间的延长,氮添加和氮磷添加均能显著降低土壤p H值;磷添加对土壤p H值无显著影响。3)相对硝态氮含量的增加而言,相同程度的土壤铵态氮含量的增加后土壤p H值降低的幅度更大。     

施磷对川西北高寒草地土壤磷形态及有效性的影响

以川西北高寒草地为研究对象,采用随机区组设计,设置0、10、20、30、40、50、60 g/m²的过磷酸钙(P₂O₅,16%)施肥试验,分析土壤不同形态磷含量和有效磷(Olsen-P)含量变化特征,探究施磷对川西北高寒草地土壤磷形态及有效磷的影响。结果表明：(1)随施磷量增加,土壤总磷(TP)含量先增加后趋于平稳而Olsen-P含量减少。高水平(50、60 g/m²)施磷下氢氧化钠有机磷(NaOH-Po)及残留磷(Residual-P)是高寒草地主要的磷素累积形态,其含量显著高于不施磷处理;(2)树脂交换态磷(Resin-Pi)、碳酸氢钠无机磷(NaHCO₃-Pi)、碳酸氢钠有机磷(NaHCO₃-Po)和氢氧化钠无机磷(NaOH-Pi)含量随施磷量增加整体呈先增加后降低趋势,表层土壤30 g/m²磷肥用量下其值均为最高,分别为21.54、22.94、65.86、64.48 mg/kg。酸溶性无机磷(HCl-Pi)随施磷量增加整体呈下...     

蓝藻胞外多糖的生态学意义及其工业应用

蓝藻能够合成胞外多糖并释放到细胞外围及周围环境中,这是其为适应复杂多变的环境而进化出的一种适应性机制.作为细胞与外界环境之间的保护性屏障,蓝藻胞外多糖可以起到抵抗干旱、紫外辐射、生物矿化和原生动物捕食等功能.蓝藻胞外多糖是一种酸性杂多糖,超过75％的多糖由6种以上单糖组成,葡萄糖是出现频率最高的单糖.胞外多糖的性质因种而异,多数蓝藻的胞外多糖呈现阴离子特性,这主要是由于糖醛酸和硫酸基团等带电基团的存在,硫酸基团同时也是多糖呈抗病毒特性的基础,而乙酰基团、缩氨酸部分及脱氧糖等疏水基团的存在使多糖呈乳化特性.因此,蓝藻胞外多糖在食品、化妆品、制药、污水处理等行业有广阔的应用前景.蓝藻胞外多糖的工业应用不仅能将水华蓝藻资源化,创造可观的经济效益,也能解决打捞蓝藻处置难题,避免随意堆放造成的二次污染.但截至目前,仍没有蓝藻胞外多糖类产品出现,理论研究与大批量工业生产之间仍然有很多技术性问题亟待解决.     

供磷水平及方式对杉木幼苗根系生长和磷利用效率的影响

为研究杉木幼苗根系生长、形态学指标及养分利用效率对土壤磷素异质分布的响应规律,选择杉木种子园单株采种培育的半同胞家系实生幼苗为研究对象,采用室内沙培控磷盆栽试验,设计低浓度供磷(8 mg/kg KH₂PO₄)、正常供磷(16 mg/kg KH₂PO₄)和高浓度供磷(32 mg/kg KH₂PO₄)3个供磷水平,每个供磷水平分别采用2种供磷方式(局部供磷和均匀供磷)进行根部施磷。结果表明:(1)从供磷水平来看,低浓度供磷下的杉木根长、根系生物量、根冠比、根系及全株的磷素利用效率均显著大于正常供磷和高浓度供磷,而根平均直径相反;随着供磷水平的提高,杉木苗高和地上部生物量无显著差异,而比根长表现出逐渐降低的趋势。(2)从供磷方式来看,局部供磷处理的杉木苗高、根长、根系表面积、比根长、地上部生物量、根系及全株的磷素利用效率均显著大于均匀供磷处理,而根平均直径和根冠比则相反。总体上,低浓度局部供磷处理下杉木可明显增强其根系的形态可塑性,从而优化根系在养分异质土壤里的...     

Distribution and release of sedimentary phosphorus in Lake Ladoga

Sedimentary phosphorus fractions and phosphorus release from the sediments were studied in Lake Ladoga at altogether 46 sampling sites, representing the full range of sediment types encountered in the lake. Determination of P fractions and physico-chemical analyses were made of surface sediment cores (10–20 cm long, each sampled at 3–4 levels) and in the overlying water. The range of total phosphorus per dry weight of sediment was 0.2–3.3 mg g^–1, and that of inorganic P 0.1–2.5 mg g^–1. The levels of interstitial soluble phosphorus, range 2–613 µg 1^–1 for total P and 1–315 µg 1^–1 for inorganic P, were higher than those of dissolved P concentrations in the overlying water. Diffusive fluxes of phosphate from sediment to the overlying water were estimated using three independent methods. The estimated range was 4–914 µg P m^–2 d^–1; the mean value for the whole bottom area, 0.1 mg P m^–2 d^–1, is lower than previously published estimates. The estimated annual contribution of sedimentary inorganic P flux to Lake Ladoga water is equal to 620 tons of P per year, which amounts to more than 10% of the estimated external P load into the lake. 68% of the total diffusive flux emanates from deep water sediments, which are not exposed to seasonal variation of conditions. In deep lakes, such as Lake Ladoga, phosphorus release from the sediments is controlled primarily by diffusive mechanisms. Wave action and currents as well as bioturbation are probably of importance mainly in shallow near-shore areas. Phosphorus release by gas ebullition and macrophytes is considered negligible.     

The uptake,translocation and release of phosphorus by Elodea densa

Short-term (16 h) laboratory studies of ³²P uptake by Elodea densa rooted in sediment demonstrated both foliar and root uptake, and that translocation occurred acropetally and basipetally. Root absorption is projected to provide 83–85% of total phosphorus uptake during 12–16 h photoperiod days. Measured foliar uptake and excretion rates suggest that there would be no net leakage of phosphorus into the water by undamaged actively-growing E. densa. Foliar uptake decreased and root uptake increased in the dark relative to rates under light.     

Uptake and transport of phosphorus by Agrostis capillaris seedlings from rapidly hydrolysed organic sources extracted from32 P-labelled bacterial cultures

Cultures of the soil bacterium Serratia liquifaciens grimesii were grown with³² P labelled phosphate, to produce a uniformly³² P labelled source of microbial P. Extracts of the bacteria were prepared by sonication, dialysis and filtration to provide a clear sterile solution which was characterised in terms of dissolved organic and condensed P (DOP and DCP) and molecular weight range. The extract was used as a source of P to Agrostis capillaris L. seedlings in nutrient solution from which orthophosphate was omitted. In a time course experiment, root surface phosphatase activity increased as soon as extract was added to the root medium, DOP was rapidly hydrolysed and orthophosphate concentration increased rapidly. These processes were complete within about 8 h, after which phosphatase activity fell to its original level, and the plants absorbed molybdate reactive P from the nutrient solution so that it reached its original concentration over 48 h. DCP concentrations did not change significantly throughout the experiment. This work clearly demonstrated that DOP but not DCP, as a component of a bacterial extract produced by a relatively straightforward method, was quickly hydrolysed and the P made available for plant uptake.     

热带亚热带常绿阔叶林维持酸性土壤有效磷水平的磷转化过程

热带和亚热带酸性土壤磷矿物的沉淀通常被认为会限制土壤有效磷的供应.选择以西双版纳山地季风常绿阔叶林和哀牢山中山湿性常绿阔叶林为代表的热带亚热带酸性土壤,探讨两类森林维持土壤有效磷水平的磷转化过程.哀牢山中山湿性常绿阔叶林腐殖质厚、而西双版纳山地季风常绿阔叶林的腐殖质几乎不存在.两地均显示土壤有效磷库随着土壤有机质含量的减少而降低.有机质含量较低的西双版纳表层矿质土（0～10 cm）的微生物生物量磷库大于有机质含量相对较高的哀牢山表层矿质土的微生物生物量磷库,且微生物对磷的固定占有效磷来源（磷矿物的溶解和有机磷的矿化）的比例为74%,高于哀牢山表层矿质土的63%.哀牢山表层矿质土的土壤有效磷库大于西双版纳,其土壤有效磷库可能更多的依赖于覆盖于其上的腐殖质分解后向下的磷输入.与两地的矿质土相比,哀牢山腐殖质具有高的磷净溶解率、总有机磷矿化速率和磷微生物固定速率.结果表明,热带山地季风常绿阔叶林主要通过微生物固定来避免土壤磷矿物的沉淀和保持土壤磷的有效供应;而亚热带中山湿性常绿阔叶林除具有较高的微生物固定外,地表腐殖质层的存在也帮助避免土壤磷矿物的沉淀而保持土壤有效磷的供应.     

Functions of Calcium-bound Phosphorus in Relation to Characteristics of Phosphorus Releasing Bacteria in Sediment of a Chinese Shallow Lake (Lake Wabu)

Sediment phosphorus (P) release accelerates lake eutrophication, while retention capacity and release potential of different P fractions, calcium-bound P (CaCO₃～P) in particular, still remains unclear. Fractionation and sorption behaviors of phosphorus were studied in sediment of a Chinese shallow lake (Lake Wabu) and two inflowing rivers from December 2011 to December 2012. Abundance of P releasing bacteria was analyzed, and their main species were isolated using a culture-dependent method and identified by their 16S rDNA sequences. CaCO₃～P release abilities of these bacteria were also tested. In sediments of both the lake and rivers studied, the rank order of the different P extracts was CaCO₃～P > iron-bound P > acid-soluble organic P > hot NaOH-extractable organic P. At the same time, CaCO₃～P content and equilibrium P concentration (EPC₀) values in river sediments were significantly higher than those in the lake. Additionally, EPC₀ changes non-monotonically with increasing CaCO₃～P content, forming a V-shaped curve, with the lowest EPC₀ at an intermediate CaCO₃～P content (around 180 mg kg^?1). Below this threshold, CaCO₃～P was a component strengthening P retention; moreover, CaCO₃～P became an active species responsible for P release. Noticeably, between the two parts divided by this threshold, the differences in abundance of inorganic phosphorus solubilizing bacteria (IPB) and organic phosphorus mineralizing bacteria (OPB) were insignificant and the dominant IPB species clustered together. By contrast, OPB was distinguished from each other, whose dominant species isolated from the part with higher CaCO₃～P content, namely Novosphingobium sp., exhibited a stronger ability to solubilize CaCO₃～P. Shortly, with lower content, CaCO₃～P tends to stabilize P in sediment; while with higher content or under eutrophic condition, it shifted into P source, with some OPB species becoming the main factors to drive its release.     

干旱绿洲灌区大白菜施磷效应与磷肥投入阈值

针对磷肥施用量大且利用率不高的问题,通过2011—2013年在甘肃省农业科学院张掖绿洲灌区农业生态环境重点野外台站进行定位试验,研究了不同施磷量对露地大白菜产量、磷肥利用率以及磷素平衡的影响.结果表明:大白菜产量随施磷量的增加先增加后呈下降的趋势.在施磷量为112.52 kg·hm^-2时产量达到最高(5489.1 kg·hm^-2),且显著高于其他处理,与不施磷处理相比,增产13.3%~23.8%,此时磷肥利用率为14.2%.土壤中土壤有效磷(Olsen-P)和可溶性总磷(CaCl-P)呈现较好的正相关性,土壤Olsen-P含量为24.22 mg·kg-12时对应的施磷量为111.1 kg·hm^-2,表明当土壤中Olsen-P含量小于24.22 mg·kg-1时,土壤中的磷素不发生盈余,对环境不造成污染.当施磷量为60.17 kg·hm^-2时,磷输入与输出达到平衡,即此施磷量水平能满足作物的需求.结合研究区的土壤肥力状况,综合产量、磷肥利用率及土壤有效磷含量,干旱绿洲灌区磷肥投入阈值在60.17~112.52 kg·hm^-2时,能保证露地大白菜高产,并且不会造成环境污染.     

Phosphorus characteristics correlate with soil fertility of albic luvisols

The information on phosphorus (P) characteristics of albic luvisols and their effect on plant P uptake is limited. Twelve soils representing typical albic luvisols were collected from farmland of four regions in northeast China, each with various levels of soil fertility. Phosphorus fractions, P adsorption and P supply capacity of the soils were analysed and were correlated with soil fertility and plant P nutrition. Total P in these soils ranged from 0.62–0.91 g kg^–1, and comprised 37–51% organic P, and 49–63% in inorganic forms among which the percentage of occluded P was the greatest, followed by Fe-P, Ca-P, Al-P and loosely bound P was the lowest (<1%). Whereas the % of organic P was not clearly affected by fertility, the % of occluded P increased with fertility. By contrast, both % and contents of other P forms decreased with decreasing soil fertility. Soil P adsorption maxima calculated from Langmuir isotherm ranged from 484 to 912 mg kg^–1. Soils with low fertility had the strongest P adsorption, and those with medium fertility had the weakest in all collection regions. The supply capacity of P was positively related to soil fertility. Plant growth correlated positively with P forms with available P correlating best, followed by Fe-P and P supply capacity. Organic C correlated with available P, Fe-P, total P, Al-P and P supply capacity but not with organic P. The results suggest that though the albic luvisols contained high total P, they had low P availability, and P application is required for optimal crop production on these soils.