不同磷源对磷高效利用野生大麦根际土壤磷组分的影响

在土培盆栽条件下,以野生大麦磷高效利用基因型IS-22-30、IS-22-25和低效基因型IS-07-07为材料,研究不施磷(CK)、无机磷(KH₂PO₄,Pi)、有机磷(phytate,Po)及二者混合(KH₂PO₄+phytate,Pi+Po)的方式施磷30 mg·kg^-1时,磷高效基因型野生大麦对磷素吸收利用能力及土壤磷组分特征.结果表明： Pi处理野生大麦干物质量和磷素积累量最大,Pi+Po处理其次,Po处理最小,均显著高于CK处理,且磷高效基因型物质生产和磷素吸收能力显著高于磷低效基因型.土壤有效磷在不同磷源处理间差异显著,Pi处理时含量最高,Pi+Po处理次之,且磷高效基因型野生大麦根际有效磷含量显著高于磷低效基因型.磷高效基因型野生大麦根际有效磷呈现亏缺现象,在Pi和Pi+Po处理时亏缺程度较大.根际与非根际土壤无机磷组分含量为Ca₁₀-P>O-P>Fe-P>Al-P>Ca₂-P>Ca₈-P,且其含量随着Pi的增加而增加.各磷源处理下,磷高效基因型野生大麦根际土壤Ca₂-P、Ca₈-P出现亏缺;Pi处理磷高效基因型野生大麦根际土壤Al-P、Fe-P出现富集.土壤中有机磷各组分含量为中活性有机磷>中稳性有机磷、高稳性有机磷>活性有机磷.野生大麦根际土壤活性有机磷和中活性有机磷呈现富集,其富集量在Pi处理时最大;中稳性有机磷和高稳性有机磷呈现亏缺.各磷源处理下,磷高效基因型野生大麦根际土壤活性有机磷含量显著高于磷低效基因型,中稳性有机磷和高稳性有机磷在基因型间差异不显著.Pi缺乏时,磷高效基因型野生大麦活化吸收Ca₂-P、Ca₈-P、Al-P和活性有机磷的能力较强.     

落叶松土壤有机磷形态与林木生长量的关系

采用Bowman-Cole有机磷分级体系,对落叶松人工林不同发育阶段根际与非根际土壤活性有机磷、中等活性有机磷、中稳性有机磷和高稳性有机磷含量的变化及其与有效磷和林木生长量的关系进行了研究。结果表明,构成落叶松人工林土壤有机磷的主要成分是中等活性有机磷和中稳性有机磷,两者之和占有机磷总量的77.07％～86．68％,根际土壤活性有机磷和中等活性有机磷是不同发育阶段土壤有效磷的主要来源,根际土壤有机磷总量、活性有机磷含量、中稳性有机磷含量和高稳性有机磷含量从幼龄林到近熟林随林龄递增而降低,近熟林之后有所增加,根际土壤中等活性有机磷含量随林龄变化不明显,非根际土壤各形态有机磷含量随林龄递增而呈波动性增加趋势,各发育阶段林木胸径、树高定期平均生长量与活性有机磷含量和有效磷含量关系最为密切。     

L value determination under paddy soil condition

Summary The L values of four paddy soils and one United Kingdom soil were determined under water-logged and aerobic conditions over a period of 7 weeks using rice and ryegrass as the respective test crops.Under water-logged conditions, the L values attained a constant level in the course of the growing period, indicating that isotopic equilibrium between the added P³² and the soil was achieved.Under aerobic conditions, the equilibrium L values tended to be lower than those determined under water-logged conditions.This was taken as an indication of an increase of labile soil phosphorus by reduction of ferric iron.     

长期施肥对黄土旱塬农田土壤有机磷组分及小麦产量的影响

研究长期施肥对黄土旱塬农田土壤有机磷组分及小麦产量的影响,可为提高磷素转化利用率及合理利用肥料提供理论支持。本研究依托长武旱塬农田生态系统长期(1984—2016年)定位试验站,选取不施肥(CK)、单施氮肥(N)、单施磷肥(P)、施氮磷肥(NP)、单施有机肥(M)、氮肥配施有机肥(MN)、磷肥配施有机肥(MP)、氮磷肥配施有机肥(MNP)8个处理,研究其对土壤有机磷组分、小麦产量和土壤性质的影响。结果表明: 长期施肥后土壤有机磷含量为244.7～429.1 mg·kg^-1,除N处理外,其余各处理有机磷含量比CK均显著增加了15.4%～47.9%。长期施用磷肥改变了黄土旱塬农田表层土壤(0～20 cm)各有机磷组分含量,MP、MNP处理显著提高了活性有机磷及中活性有机磷含量;N、P和NP处理显著降低了中稳性有机磷含量;N、P、NP、MN、MP、MNP处理均显著提高了高稳性有机磷含量。各处理土壤有机磷组分与总有机磷含量比值为:中活性有机磷>高稳性有机磷>活性有机磷>中稳性有机磷。长期施肥后,与CK相比,氮、磷肥配施,尤其是与有机肥配施,显著增加了小麦生物产量和籽粒产量。土壤指标中,有机质、速效磷和无机磷与小麦产量呈显著正相关。MP、M处理可以显著提高黄土旱塬黑垆土中的速效磷、总磷、总无机磷、活性有机磷和中活性有机磷含量,表明有机肥与磷肥配施可以提高该地区更容易被作物吸收的磷组分。总之,氮磷肥配施并配施有机肥可以提高该地区磷供给,对小麦增产有促进作用,对提高黄土旱塬地区土壤质量有重要意义。     

间伐和凋落物处理对华北落叶松人工林土壤磷形态的影响

土壤磷在维持生态系统功能稳定性中发挥重要作用,研究间伐和凋落物处理下的土壤磷组分特征及转化机理,对森林生态系统磷素管理和可持续发展具有重要意义。采用Tiessen改良的Hedley分级方法,探究了不同间伐强度(未间伐、轻度间伐、中度间伐、重度间伐)和凋落物处理(对照、加倍、去凋、切根去凋)下土壤磷形态的变化特征及其驱动因子。结果显示:随着间伐强度的增大,土壤活性磷(Resin-Pi、NaHCO_3-Pi和NaHCO_3-Po)、土壤微生物量磷和酸性磷酸酶活性呈先增加后降低的趋势,且在中度间伐最高。凋落物加倍(DL)显著增加了土壤活性磷(Resin-Pi、NaHCO_3-Pi和NaHCO_3-Po)、土壤微生物量磷和酸性磷酸酶活性。稳定态磷(HCl-Pi、浓HCl-Pi和浓HCl-Po)、残留态磷(Residual-P)不受间伐和凋落物处理的影响。冗余分析(RDA)显示,土壤微生物量磷、酸性磷酸酶活性和土壤有机碳是引起华北落叶松人工林表层土壤磷组分变化的重要因子。研究表明,适度的间伐和增加凋落物能够显著提高华北落叶松人工林表层土壤磷素的活化能力。本研究为华北落叶松人工林的可持续经营提供依据。     

缙云山4种林分土壤无机磷与活性铝的含量及分布

为探索不同林分对土壤中无机磷与活性铝的含量及分布的影响,以及无机磷与活性铝之间的相互关系,以在我国西南地区酸性土壤上的农林经营管理提供理论和实践依据。研究以缙云山广泛分布的4种林分类型：山莓、马尾松、楠竹和柑橘林土壤为对象,采用酸性土壤无机磷分级方法和铝试剂比色法测定了土壤剖面A、B和C层中各形态的无机磷与活性铝的含量,分析了不同林分土壤中无机磷和活性铝的含量和分布特征。结果表明,林分类型显著影响土壤中无机磷与活性铝的含量与分布,且铁磷(Fe-P)、交换态铝(Ex-Al)和羟基铝(Hy-Al)的含量和比例还受到土壤层次的影响。4种林分相比,山莓林能促进闭蓄态磷(O-P)的形成,而马尾松、楠竹和柑橘林则有利于Al-P、Fe-P和Ca-P的形成;柑橘林有利于低活性的腐殖酸铝(Al-AH)形成,而山莓、马尾松和楠竹林促进高活性的Ex-Al或Hy-Al溶出;Ex-Al、Al-P和Fe-P在土层的分布上有表层富集现象,而Hy-Al集中分布于B层。此外,土壤Ex-Al和Al-P与Fe-P之间,Hy-Al和Ca-P之间均呈显著(P<0.05)正相关。因此,林分类型显著影响土壤无机磷与活性铝的含...     

近自然化改造对马尾松人工林土壤团聚体有机磷组分含量变化的影响

有机磷(Po)是土壤磷库的重要组成部分。为探究马尾松人工林近自然化改造对土壤团聚体Po分布特征的影响,该研究以南亚热带的马尾松纯林(PP)和近自然化改造后的马尾松-阔叶树种混交林(CP)为对象,采集0～10 cm土样后利用干筛法将其筛分为>2 mm、0.25～2 mm和<0.25 mm三部分粒径团聚体,并测定原土及各粒径团聚体中各Po组分、微生物生物量磷(MBP)含量和酸性磷酸酶(ACP)活性。结果表明:(1)CP的土壤Po组分与PP相比发生了变化,高稳定性有机磷(HRO-P)和中度活性有机磷(MLO-P)在原土以及各团聚体径级中均显著高于PP(P<0.05),而活性有机磷(LO-P)和中度稳定性有机磷(MRO-P)在CP和PP中并无显著差异,PP和CP各组分Po在原土和各团聚体径级中无明显变化规律。(2)各形态Po在PP中占比大小为HRO-P>MRO-P>MLO-P>LO-P,而在CP中为HRO-P>MLO-P>MRO-P>LO-P。(3)CP中的MBP含量和ACP活性在原土及各团聚体径级中均显著高于PP,并且随着团聚体径级的减小,ACP活性上升。(4)冗余分析发现,土壤有效磷(AP)、土壤团聚体平均重量直径(MWD)、MBP和全氮(TN)为土壤Po组分的主要驱动因子。综上认为,近自然化改造有利于马尾松人工林土壤中磷的积累与转化,该研究结果为马尾松人工林土壤质量和生产力的提升提供了理论依据。     

Implications of soil organic carbon and the biogeochemistry of iron and aluminum on soil phosphorus distribution in flooded forests of the lower Orinoco River,Venezuela

Relationships among soil phosphorus distribution, soil organic carbon and biogeochemistry of iron and aluminum were studied along a flooded forest gradient of the Mapire river, Venezuela. Soil samples were collected during the dry season in three zones subjected to different flooding intensity: MAX inundated 8 months per year, MED inundated 5 months per year, and MIN inundated 2 months per year. Total labile phosphorus (resin + bicarbonate extractable fractions) was significantly higher in MIN than in MAX. The longer non-flooding period in MIN probably allowed a higher accumulation of microbial biomass in soils of this zone and consequently a greater release of the bicarbonate organic fraction. The moderately labile phosphorus fraction associated with the chemisorbed phosphorus on amorphous and some crystalline aluminum and iron was significantly lower in MAX than in MIN following the same tendency observed for crystalline iron oxides. This result allowed us to hypothesize that the combined effect of a long flood period and a high soil organic carbon content in the MAX, could be appropriate conditions for microbial reduction of stable forms of iron. The ratio of soil organic carbon to total organic phosphorus decreased from MAX to MIN, indicating higher mineralization of organic phosphorus in MIN. Our results suggests two distinct flood-dependent mechanisms operating for phosphorus release along the gradient. In MAX mineralization process appears to be limited, while microbial mineral dissolution appears to be an important source of phosphorus. In MIN supply of phosphorus is associated with the stability of soil organic matter.     

Reversibility of phosphorus sorption by ferruginous nodules

Ferruginous nodules sorb significant amounts of available soil and fertiliser phosphate. The effect of this sorption on phosphorus availability of an agricultural soil was tested by sequential extraction and by exhaustive cropping with millet (Pennisetum typhoides) in a greenhouse trial following fertilisation of the original soil containing 70% nodules and of prepared samples containing various mixes of separated soil fines and nodules. Phosphorus sorption maxima by the soil fines and nodules were 190 mg kg⁻¹ and 380 mg kg⁻¹ respectively. Samples of fines and nodules which had sorbed 110 and 194 mg kg⁻¹ were submitted to 8 successive extractions with 0.01 M KCl, after which P desorption amounted to 117 mg kg⁻¹ and 103 mg kg⁻¹ respectively. Hysteresis between sorption and desorption was negligible for the soil fines and increased with increasing nodule content of the samples. In the greenhouse experiment, P uptake at the first cropping was highest in the soil fines at all levels of phosphorus applied. Subsequent croppings, however, showed higher P uptake in the concretionary soils. These results indicate a higher initial P release from the soil fines with cropping followed by an earlier exhaustion of phosphorus. At the end of the greenhouse experiment, yields were low in spite of the large quantities of P still remaining in the soils. Phosphorus fractionation showed that, of the P left in the soil after cropping 20% was in labile, 29% in Fe or Al-associated, and 51% in low-availability forms.     

White lupin utilizes soil phosphorus that is unavailable to soybean

White lupin (Lupinus albus L. var. Ultra) and soybean (Glycine max L. var. Elgin) were grown in an acidic soil low an available phosphorus (P) to investigate their different capacities to acquire soil phosphorus. Experiments done in the controlled environment of a biotron were supplemented with four separate greenhouse experiments. Lupin and soybean were grown in monoculture and intercropped on a soil with low available P that was labeled with carrier-free ³²P as phosphate. Lupin had significantly lower values of specific activity of ³²P and higher values of isotopically exchangeable P than soybean in all cases. The results show that lupin utilizes soil P from a normally non-labile pool of soil P that is not utilized by soybean.     

减磷配施有机肥对水旱轮作紫色水稻土磷素淋失的消减效应

为探索长江流域稻油轮作系统水稻季减少农田磷素流失的最佳施肥模式和有效耕作措施,降低其对长江水质的威胁。采用渗漏池长期田间原位定点试验并结合室内实验分析,研究了化肥配施猪粪有机肥和水稻秸秆还田对土壤磷素淋溶迁移的影响。结果表明在水稻生长期内土壤淋溶水中磷素浓度随时间延长呈逐渐下降的趋势,前期波动幅度大且下降迅速,到55d之后逐步稳定达到平衡。总可溶性磷(TDP)是渗漏水磷素的主要形态。土壤淋溶水中总磷(TP)和总可溶性磷(TDP)含量均表现为优化施肥+猪粪有机肥(MP)优化施肥+秸秆还田(SP)优化施肥(P)优化施肥量磷减20%+猪粪有机肥(MDP)优化施肥量磷减20%+秸秆还田(SDP)不施磷肥(P0)。土壤总磷(TP)淋失负荷在0.295—0.493 kg/hm2之间。施用有机肥提高了淋溶水中的磷素含量,促进了土壤中磷素的淋失,同时显著提高了土壤中有效磷的含量,猪粪有机肥的促进作用比水稻秸秆大。减少化肥施用量有利于降低土壤磷素淋失。在综合考虑农业生产省本增效和控制农田面源污染的情况下,可以采取减量化肥配施有机肥的施肥模式。     

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...     

海拔梯度变化对武夷山黄山松林土壤磷组分和有效性的影响

土壤磷（P）是植物生长必需的养分元素,也是亚热带森林生产力的主要限制元素。目前,关于不同海拔土壤P组分和P有效性的变化规律尚无统一定论,其原因主要是忽略了植被类型变化导致的P组分和P有效性对海拔的响应更为复杂。因此,以武夷山不同海拔黄山松林为研究对象,通过测定土壤环境因素、理化性质、微生物生物量（SMB）、酸性磷酸单酯酶（ACP）和磷酸双酯酶（PD）活性以及土壤P组分,探究土壤P组分和P有效性的变化及其影响因素。结果表明,随海拔降低,速效P含量显著增加,而易分解P、中等易分解P、难利用P和总磷含量显著减少。冗余分析结果表明,微生物生物量磷和微生物生物量氮是影响土壤P组分和P有效性变化的关键因素。研究表明,随海拔降低,黄山松林土壤微生物通过提高ACP、PD活性和降低SMB含量的能量分配策略,促进更多较难分解P组分的矿化,从而提高速效P含量,以满足微生物对P的需求。因此,在低海拔地区,微生物通过能量分配策略获取更多有效P,可能有利于提高武夷山黄山松林土壤速效P的供应,但从长期来看,可能使P矿化速率提高和P损耗增加,导致P库的储备不足,不利于土壤P素养分的可持续供应。     

Impacts of long-term plant biomass management on soil phosphorus under temperate grassland

Aims

We assessed and quantified the cumulative impact of 20 years of biomass management on the nature and bioavailability of soil phosphorus (P) accumulated from antecedent fertiliser inputs.

Methods

Soil (0–2.5, 2.5–5, 5–10 cm) and plant samples were taken from replicate plots in a grassland field experiment maintained for 20 years under contrasting plant biomass regimen- biomass retained or removed after mowing. Analyses included dry matter production and P uptake, root biomass, total soil carbon (C), total nitrogen (N), total P, soil P fractionation, and ³¹P NMR spectroscopy.

Results

Contemporary plant production and P uptake were over 2-fold higher for the biomass retained compared with the biomass removed regimes. Soil C, total P, soluble and labile forms of inorganic and organic soil P were significantly higher under biomass retention than removal.

Conclusions

Reserves of soluble and labile inorganic P in soil were significantly depleted in response to continued long-term removal of P in plant biomass compared to retention. However, this was only sufficient to sustain plant production at half the level observed for the biomass retention after 20 years, which was partly attributed to limited mobilisation of organic P in response to P removal.

     

Recovery of soil phosphorus on former bauxite mines through tropical forest restoration

Soil phosphorus (P) is a major driver of forest development and a critically limited nutrient in tropical soils, especially when topsoil is removed by mining. This nutrient can be present in soils in the form of different fractions, which have direct consequences for P availability to plants and, consequently, for restoration success. Therefore, understanding how the stocks of different soil P fractions change over the restoration process can be essential for guiding restoration interventions, monitoring, and adaptive management. Here, we investigated the recovery of soil P fractions by forest restoration interventions on bauxite mine sites in the Brazilian Atlantic Forest. We assessed the concentration of different fractions of soil organic and inorganic P at (1) a bauxite mine prepared for restoration; (2) two former bauxite mines undergoing forest restoration for 6 and 24 years; and (3) an old‐growth forest remnant. Overall, restored areas recovered levels of labile organic P (P_o‐NaHCO₃) at 5–40 cm and of moderately labile organic P (P_o‐NaOH) at different depths, exhibiting concentrations similar to those found in a conserved forest. The use of P‐rich fertilizers and forest topsoil may have greatly contributed to this outcome. Some other fractions, however, recovered only after 24 years of restoration. Other inorganic P fractions did not differ among mined, restored, and conserved sites: nonlabile P_i (residual P and P‐HCl), labile P_i (P_i‐NaHCO₃), and moderately labile P_i (P_i‐NaOH). Forest restoration was able to promote efficient recovery of important soil P fractions, highlighting the value of restoration efforts to mitigate soil degradation by mining.     

林下养鸡年限对杨树人工林土壤磷素形态和生物有效性的影响

林下养殖是一种经济有效的林地空间利用方式,但长期高负载的林下养殖对林地土壤性状究竟产生何种影响,目前尚无定论.以不同林下养鸡年限(0年、1年、3年和5年)的美洲黑杨(Populus deltoides)人工林为对象,采用Hedley磷素分级法,分析其林地土壤的磷素组成和形态变化,探讨林下养鸡年限对土壤磷库特征及其生物有...     

大兴安岭森林火烧恢复年限对土壤磷及其有效性的影响

林火是大兴安岭地区森林生态系统的重要影响因子,对地下土壤养分,特别是磷及其有效性变化长时间序列研究,将有助于林火后植被恢复管理、模型模拟及科学评价。选择呼中、南瓮河、双河、图强、塔河、加格达奇、满归等地区火后恢复2-50年样地48块,并以火烧区域周边相似地形地貌、未经火烧区域为配对对照样地,野外调查记录地形地貌和地理位置数据,室内分析土壤全磷和速效磷。配对t检验、冗余排序分析、趋势分析、离散性分析等处理相结合,试图找出火烧后土壤磷及其有效性变化特征。研究结果表明：（1）整体数据平均值及离散程度表明,火后全磷及速效磷均值均稍低于对照,火后二者的离散程度为37%-49%,低于对照样地6-22个百分点;区分不同恢复时间,配对t检验未发现火烧样地土壤磷与对照间的显著差异。（2）以火烧对照比值及差值进行趋势分析发现,相对于对照,火烧后全磷呈现先增加后降低的变化趋势（R²=0.89-0.95,P=0.07-0.15）,火后20-30年间开始低于对照样地。速效磷也呈类似变化趋势,但是相关性较低（R²=0.44-0.67,P=0.44-0.66）;速效磷占比年代变化趋势不明显（R²=0.08-0.12,P > 0.95）。（3）RDA排序分析表明,火烧导致恢复年限成为影响磷变化的最主要因素（15.3%）,其次是经度（10.7%）;而在对照样地中,纬度是土壤磷变化最关键影响因素,能够解释其变化总量的27.6%。研究结果为森林火后土壤养分管理以及森林演替生态评价提供重要参数。     

Bioavailability of slowly cycling soil phosphorus: major restructuring of soil P fractions over four decades in an aggrading forest

Although low solubility and slow cycling control P circulation in a wide range of ecosystems, most studies that evaluate bioavailability of soil P use only indices of short-term supply. The objective here is to quantify changes in P fractions in an Ultisol during the growth of an old-field pine forest from 1957 to 2005, specifically changes with organic P (Po) and with inorganic P (Pi) associated with Fe and Al oxides as well as Ca compounds. Changes in soil P were estimated from archived mineral soil samples collected in 1962 shortly after pine seedlings were planted, and on six subsequent occasions (1968, 1977, 1982, 1990, 1997, and 2005) from eight permanent plots and four mineral soil layers (0–7.5, 7.5–15, 15–35, and 35–60 cm). Despite the net transfer of 82.5 kg ha⁻¹ of P from mineral soil into tree biomass and O horizons, labile soil P was not diminished, as indexed by anion exchange resins, and NaHCO₃ and Mehlich III extractants. An absence of depletion in most labile P fractions masks major restructuring of soil P chemistry driven by ecosystem development. During 28 years of forest growth, decreases were significant and substantial in slowly cycling Po and Pi associated with Fe and Al oxides and Ca compounds, and these accounted for most of the P supplied to biomass and O horizons, and for buffering labile soil fractions as well. Changes in soil P are attributed to the P sink strength of the aggrading forest (at 2.9 kg ha⁻¹ year⁻¹ over 28 years); legacies of fertilization, which enriched slowly cycling fractions of Po and Pi; and the changing biogeochemistry of the soil itself.     

定位施肥对紫色菜园土磷素状况的影响

基于紫色菜园土壤莴笋-白菜轮作3a的12季连续定位施肥试验,研究施肥对土壤磷素状况的影响。结果表明,在紫色土上以化肥为基础增施有机肥(泥炭或菜籽粕)既提高土壤磷含量,又增加无机磷组分中有效磷源和缓效磷源的比例,且不会增加磷素淋失的风险,是所有处理中最优者;增磷、增钾处理虽然提高了土壤磷含量,但未能提高速效磷源与缓效磷源的比例;增氮、增硼及常规施肥降低土壤磷含量和提高无效磷源的比例;无肥处理磷含量最低,无效磷源比例最高。紫色菜园土无机磷约为有机磷的4—6倍,无机磷各组分以钙磷为主,占I-P总量的60.89%—67.92%,显示紫色土风化程度较低。各形态磷素呈Ca10-P>Ca8-P>Fe-P≈Al-P≈OC-P>Ca2-P序列变化,其中Ca2-P和Al-P总共仅占无机磷总量的11.47%—19.43%,表明紫色土中对植物最有效的磷源不足;而Ca10-P和OC-P共占无机磷总量的42.48%—59.55%,意味着紫色土无机磷有一半左右是以作物不可利用的形态存在的。紫色土全磷与无机磷、有机磷、Ca2-P、Ca8-P、Al-P、Fe-P、OC-P及Ca10-P呈显著正相关;无机磷与多种形态磷呈显著正相关(除有机磷、Ca2-P、有效磷外);有机磷与全磷、Ca2-P显著正相关;有效磷与全磷、Ca2-P、Al-P、Fe-P显著正相关;无机磷组分间也都存在显著正相关关系(OC-P与Ca10-P间有极显著正相关,但它们与其它无机磷组分无相关性)。表明在土壤磷的整个循环系统中,不同组分无机磷与有机磷之间处于一个动态平衡中,它们之间存在着相互影响和制约。土壤pH与各形态磷关系密切。对土壤有效磷与无机磷组分间的关系进行系统分析,简单相关分析结果土壤有效磷与Ca2-P、Fe-P呈极显著正相关,与Al-P呈显著正相关,与Ca8-P、OC-P、Ca10-P正相关但不显著;通径分析结果对土壤有效磷直接影响较大的无机磷组分是Al-P、Ca8-P与Ca2-P,其中Ca8-P的直接影响为负效应;逐步回归分析结果与通径分析一致。综合分析得出,Ca2-P、Al-P是最有效的磷源,Fe-P、Ca8-P次之,Ca10-P与OC-P是非有效磷源。莴笋和白菜产量与紫色土壤Ca2-P、Ca8-P、Al-P、Fe-P呈显著正相关,与OC-P、Ca10-P无相关性。紫色土各形态无机磷与两种蔬菜产量的相关系数r大小依次为Ca2-P>Fe-P>AL-P>Ca8-P>Ca10-P>OC-P,这与各形态无机磷与有效磷简单相关分析的结果一致。     

Four decades of post-agricultural forest development have caused major redistributions of soil phosphorus fractions

Fertilisation of agricultural land causes an accumulation of nutrients in the top soil layer, among which phosphorus (P) is particularly persistent. Changing land use from farmland to forest affects soil properties, but changes in P pools have rarely been studied despite their importance to forest ecosystem development. Here, we describe the redistributions of the P pools in a four-decadal chronosequence of post-agricultural common oak (Quercus robur L.) forests in Belgium and Denmark. The aim was to assess whether forest age causes a repartitioning of P throughout the various soil P pools (labile P, slowly cycling P and occluded P); in particular, we addressed the time-related alterations in the inorganic versus organic P fractions. In less than 40 years of oak forest development, significant redistributions have occurred between different P fractions. While both the labile and the slowly cycling inorganic P fractions significantly decreased with forest age, the organic fractions significantly increased. The labile P pool (inorganic + organic), which is considered to be the pool of P most likely to contribute to plant-available P, significantly decreased with forest age (from >20 to <10% of total P), except in the 0-5 cm of topsoil, where labile P remained persistently high. The shift from inorganic to organic P and the shifts between the different inorganic P fractions are driven by biological processes and also by physicochemical changes related to forest development. It is concluded that the organic labile P fraction, which is readily mineralisable, should be taken into account when studying the bioavailable P pool in forest ecosystems.