适宜施氮量对粗齿冷水花根际微域土壤磷组分及磷酸酶活性的影响

  【目的】  适宜施氮可提高磷富集植物对磷过剩土壤的修复效率,研究适宜施氮处理下磷富集植物根际微域土壤磷组分的变化,可为利用磷富集植物提取土壤中过剩的磷提供理论依据。  【方法】  采用多隔层根箱土培试验,以磷富集植物矿山生态型粗齿冷水花为材料,非矿山生态型为对照,设磷处理的P质量浓度为800 mg/kg,氮处理的N质量浓度为0 (CK)和140 mg/kg,分析对比了两种生态型粗齿冷水花磷富集能力及根际微域土壤磷组分与磷酸酶活性的变化。  【结果】  1)适宜施氮量下,两种生态型粗齿冷水花地上部、地下部生物量和磷积累量均显著升高;矿山生态型地上部生物量和磷积累量分别为非矿山生态型的1.28和1.45倍。2)适宜施氮量下,两种生态型根际土壤中H₂O-P和NaHCO₃-Pi含量均增加;土壤H₂O-P和NaHCO₃-Pi含量均在距矿山生态型根际4 mm微域内显著高于非根际土壤,分别在距非矿山生态型根际4和2 mm微域内显著高于非根际土壤;土壤NaHCO₃-Po和NaOH-Pi、NaOH-Po含量在距两种生态型根际6 mm微域内显著低于非根际土壤;土壤HCl-Pi和HCl-Po和Residual-P含量在根际微域和非根际土壤之间无显著变化。不施氮和适宜施氮量下矿山生态型根际微域NaHCO₃-Pi含量均显著低于非矿山生态型,矿山生态型对土壤NaHCO₃-Pi的吸收利用能力更强。3)适宜施氮量下,两种生态型粗齿冷水花根际土壤磷酸酶活性均较对照增加,土壤酸性磷酸酶、碱性磷酸酶活性分别在距根际4和2 mm微域内显著高于非根际土壤,植酸酶活性在距根际8 mm微域内显著高于非根际土壤。不施氮和适宜施氮量下,矿山生态型根际微域土壤磷酸酶活性更高。  【结论】  高磷条件下,适宜施氮量 (140 mg/kg)增加了两种生态型粗齿冷水花根际微域土壤磷酸酶活性,且矿山生态型根际土壤磷酸酶活性更高,有利于根际微域土壤中磷由低有效态组分向高有效态组分转化,从而促进了植株的生长和磷素积累。     

Dynamics and availability of phosphorus in the rhizosphere of a temperate silvopastoral system

A field rhizosphere study was carried out over a period of 12 months on a 6-year-old silvopastoral trial in New Zealand. The trial comprised radiata pine (Pinus radiata) with lucerne (Medicago sativa) and perennial ryegrass (Lolium perenne) understoreys. The study was initiated because of the unique interrelationships between roots in silvopastoral systems and a paucity of understanding about the processes involved in phosphorus (P) dynamics in temperate silvopastoral systems. Improving our understanding in this area has important implications for nutrient management in silvopastoral systems. Rhizosphere soils were analysed to determine inorganic (Pi) and organic (Po) P fractions, macroporous resin Pi and Po, phosphatase enzyme activity, microbial biomass carbon and pH. Concentrations of labile Pi were consistently greater and Po lower in tree rhizosphere soil compared to the companion understorey, indicating that radiata pine when grown with a productive understorey mineralised Po to a greater extent than either understorey species. Tree rhizosphere soil from under lucerne and lucerne rhizosphere soil contained the lowest concentrations of total Pi and Po compared with tree under ryegrass and ryegrass rhizosphere soils. This was partly attributed to higher levels of phosphatase enzyme activity in the lucerne rhizosphere soils. The results suggest the combination of lucerne with radiata pine may enhance greater utilisation of soil P, although this requires further investigation. Lower levels of labile Po, and higher levels of labile Pi and phosphatase enzyme activity, were determined in tree and understorey lucerne and ryegrass rhizosphere soils in spring compared with autumn. This data confirmed that overall rates of soil organic P mineralisation are greatest in spring.     

Growth,P accumulation,and physiological characteristics of two ecotypes of Polygonum hydropiper as affected by excess P supply

The use of suitable plants that can accumulate excess phosphorus (P) from contaminated soil may serve as an attractive method for phytoremediation. In this study, pot experiments were conducted to investigate the effects of P incorporation on P accumulation and physiological mechanisms of Polygonum hydropiper in a mining ecotype (ME) and nonmining ecotype (NME) from a phosphorus mining and a noncontaminated agricultural area, respectively. The results demonstrate that the ME of P. hydropiper growing in soil supplied with 0, 100, 200, 400, 800, 1600 mg P (kg soil)^–1 showed a significantly higher biomass compared to the NME. Phosphorus accumulation of the ME was positively correlated with the soil P concentration. APase activity in roots of the ME significantly increased at 1600 mg P (kg soil)^–1 and phytase activity of the ME increased with increasing P supply. APase activity of the ME was more than twice that of the NME on average. A significant increase of superoxide dismutase (SOD) was observed compared with the NME at all supplied P levels. Peroxidase (POD) activity of the ME was significantly higher at 200 and 400 mg P (kg soil)^–1. No statistical differences in the catalase (CAT) activity of the ME were observed compared with the control. Activity of CAT in the NME was obviously induced after exposure to 100–800 mg P (kg soil)^–1. Malondialdehyde (MDA) concentration in leaves of the ME decreased with increasing P supply to reach a minimum at 400 mg P (kg soil)^–1. In the NME, an increase in MDA concentration compared to the control was observed at higher P levels. The APase and phytase induction and antioxidative defense allowed for the high P accumulation of the ME.     

Phytoextraction of arsenic contaminated soil by Chinese brake fern (Pteris vittata): Effect on soil microbiological activities

A greenhouse experiment was conducted to investigate the effect of phytoextraction by Chinese brake fern (Pteris vittata L.) on microbial activity and biomass in arsenic-contaminated soil (naturally occurring arsenic-contaminated soils of West Bengal, India). P. vittata was grown for two successive growing cycles (4 months each) with two phosphate sources (di-ammonium phosphate (DAP) and single superphosphate (SSP)). After phytoextraction by P. vittata, the rhizosphere soils were analyzed for microbial biomass C (MBC), C mineralization (C_min), dehydrogenase activity (DHA), phosphomonoesterase activities, and aryl sulphatase activity. All enzyme activities increased after two successive growing cycles of P. vittata as compared to one growing cycle and unplanted control. The arsenic (As) phytoextraction by this fern also increased the MBC by 34 %, C_min by 63 %, DHA by 38 %, acid phosphomonoesterase activity by 30 %, alkaline phosphomonoesterase activity by 6 %, and aryl-sulphatase activity by 33 % with two successive growing cycles over unplanted control. The di-ammonium phosphate was better as compared to single super phosphate for enhancing microbiological and biochemical parameters except phosphomonoesterase activities.     

Phosphorous accumulation and distribution of two ecotypes of Pilea sinofasciata grown in phosphorous-enriched soils

Water eutrophication and poultry manure require an efficacious remediation technology to decrease phosphorous (P) concentration. In this study, the P phytoremediation potential of a mining (ME) and nonmining ecotype (NME) of Pilea sinofasciata were analyzed by pot experiments employing different concentrations of P treatments (CK, P100, P200, P400, P800 and P1600) in tested soil. Growth, P accumulation and P-relevant enzyme activities of P. sinofasciata in ME and NME were assessed after 10 weeks’ plantation. The results showed that there was no significant difference between the shoot biomass of the ME and NME. Higher P concentration and accumulation were observed in the ME than NME for all treatments. Stem P concentration of the ME were 117%, 189%, 152%, 153%, 140% and 139% higher than the NME, and leaf P concentration were 122%, 146%, 138%, 144%, 137% and 113%. Maximum P uptake and phytoextraction was observed at P400 for the ME of P. sinofasciata. Elevated activities of acid phosphatase and phytase in roots were examined in P-enriched soil, and the ME presented higher activities compared with the NME. The results in this paper provide a theoretical basis for the use of ME of P. sinofasciata for phosphorus accumulators and suggest that ME of P. sinofasciata is a promising species for the excess P phytoextraction of P-enriched soils.     

矿山生态型和非矿山生态型粗齿冷水花富磷能力的比较

【目的】研究适宜施氮条件下磷富集植物粗齿冷水花的磷积累能力,可为有效利用该植物提取土壤中过剩的磷、减少磷的面源污染提供理论依据。【方法】以两种生态型粗齿冷水花 (Pilea sinofasciata) 为研究对象,进行土培盆栽试验,供试土壤为灰潮土,每盆 (8 L) 装土8 kg。分别施磷0、400、600、800 mg/kg,陈化8周。幼苗种植前,每盆施入140 mg/kg尿素。移栽9周后收获,测定植株生物量、磷含量,分析了土壤速效磷含量。【结果】1) 在供试施磷量范围内,两种生态型粗齿冷水花地上部、地下部生物量在施磷600 mg/kg时达最大,此时矿山生态型地上部、地下部生物量分别是其不施磷对照的2.37和3.69倍,非矿山生态型地上部、地下部生物量是其不施磷对照的4.63和7.36倍,矿山与非矿山生态型地上部生物量最大值分别可达28.6 g/株和31.9 g/株。矿山生态型生物量在不施磷和施磷400 mg/kg时显著大于非矿山生态型,在施磷600、800 mg/kg时两生态型间无明显差异。2) 随施磷量增加,两种生态型粗齿冷水花地上部磷含量和矿山生态型地下部磷含量均表现为先升高后降低,在施磷800 mg/kg时显著降低,而非矿山生态型地下部磷含量随施磷量增加而增加,在施磷800 mg/kg时达最高。各磷处理下,矿山生态型地上部磷含量均显著高于非矿山生态型,而地下部磷含量低于非矿山生态型。3) 高磷处理显著增加了两种生态型粗齿冷水花地上部、地下部磷积累量,且在施磷600 mg/kg时植株磷积累量最大,矿山生态型与非矿山生态型地上部磷积累量最高分别可达195 mg/株和182 mg/株。在不施磷和施磷400 mg/kg时,矿山生态型地上部磷积累量显著高于非矿山生态型,在施磷600、800 mg/kg时两生态型间无明显差异。4) 不同磷处理下,两种生态型磷富集系数远大于1,磷转移率大于80%;矿山生态型的磷提取率和移除量在不施磷和施磷400 mg/kg时均大于非矿山生态型,在施磷600、800 mg/kg时两生态型间无明显差异。【结论】适宜施氮条件下,粗齿冷水花在施磷600 mg/kg时表现出较强的磷富集能力。与非矿山生态型相比,矿山生态型在不施磷和施磷400 mg/kg时对磷的积累能力和富磷潜力更强;在施磷600、800 mg/kg时两生态型植株对土壤磷的富集能力无明显差异。     

高磷处理下矿山生态型水蓼根系耐受特征

  【目的】  磷富集植物对高磷具有良好的耐性是其应用于植物修复的前提。本研究探讨磷富集植物矿山生态型水蓼根系对高磷的耐受能力,为后期利用其修复环境中的过量磷提供一定的理论依据。  【方法】  采用矿山生态型和非矿山生态型水蓼(ME和NME)进行了水培试验,营养液中设置无机磷2、4、8、16 mmol/L 4个高浓度处理,以正常磷0.5 mmol/L浓度为对照,分析对比了两种生态型水蓼根系对高磷的耐受特征。  【结果】  随着磷浓度的增加,ME地上部和根系生物量和磷积累量均先显著增加后降低,在磷浓度4 mmol/L时出现峰值,而NME则大体呈降低趋势。高磷处理ME地上部和根系生物量分别为NME的1.35～2.56和1.18～1.86倍,除磷浓度16 mmol/L处理外,ME地上部和根系磷积累量分别为NME的1.35～2.58和1.36～1.96倍,磷积累能力更强。ME根系质膜开始受到明显损伤的营养液磷浓度是8 mmol/L,而NME是磷浓度4 mmol/L。随着磷浓度的增加,ME根系中H₂O₂、MDA和NME根系中的MDA含量均表现为先稳定后显著增加,而NME根系中的H₂O₂含量则持续增加;两种生态型水蓼根系SOD、POD和CAT活性均先显著增高后降低,分别在磷浓度4和2 mmol/L时显著高于对照。与NME相比,ME根系抗氧化酶活性更高,对H₂O₂和MDA的清除能力更强。两种生态型水蓼根系亚细胞组分磷含量均表现为可溶部分(含液泡)＞细胞壁＞细胞器。随着磷浓度的增加,两种生态型水蓼各亚细胞组分磷含量均显著增加,且在磷浓度2和4 mmol/L处理下,根系可溶部分(含液泡)磷分配比例明显高于对照,液泡是其磷素储存的重要场所。  【结论】  矿山生态型水蓼对高磷的耐受能力和磷积累能力均强于非矿山生态型水蓼。高磷处理下矿山生态型水蓼存在根系自由基和保护酶动态平衡、细胞壁固持和可溶部分的液泡区隔化现象,这是其根系的重要耐受特征。     

Seasonal effect of the exotic invasive plant Solidago gigantea on soil pH and P fractions

Invasions by alien plants can alter biogeochemical cycles in recipient ecosystems. We test if Early Goldenrod (Solidago gigantea) alters P fractions. To that end, we compare invaded plots and adjacent, uninvaded resident vegetation for specific fractions of organic and inorganic P, phosphomonoesterase (PME) activity in topsoil, and immobilization of P in above‐ and belowground organs and in soil microbial biomass. Invaded plots had lower soil pH and 20%–30% higher labile P fractions (resin‐P_i, bicarb‐P_i, NaOH‐Pi), and the difference was consistent across seasons. There was no difference in microbial P. Alkaline‐PME activity was 30% lower in topsoil of invaded plots. Annual P uptake in aboveground phytomass was not markedly higher in Solidago. In contrast, P in belowground organs steadily increased in autumn in invaded plots, due to both increased biomass and increased P concentrations. This indicated higher net P immobilization in Solidago, far in excess of both resorption from senescing shoots and P requirements for aboveground biomass in subsequent year. Higher turnover rates of P in belowground organs and mobilization of sparingly soluble P forms through rhizosphere acidification may be involved in the observed differences in soil P status between invaded and uninvaded plots.     

Seasonality of organic phosphorus mineralization in the rhizosphere of the native savanna grass, Trachypogon plumosus

Savanna ecosystems have low primary productivity, strong seasonality, and acid soils with low phosphorus (P) content. Organic P (Po) comprises around 50% of the total soil P and is plant-available only after mineralization. Rhizosphere processes mediated by plants, microorganisms and arbuscular mycorrhiza (AM) are important for plant P nutrition. We studied P transformation rates, Po-fractionation, acid phosphomonoesterase activity (APA), AM status, dehydrogenase activity (DHA), and bacterial and fungal plate counts in the rhizosphere of the native dominant grass Trachypogon plumosus. We collected samples from three acid savanna soils differing in order and P content (Entisol, Vertisol and Ultisol) at Estación Experimental La Iguana (Northeastern Venezuela) during the dry, rainy and transitional seasons over a 2-year-period. Less available Po fractions (moderately labile, moderately and highly resistant) seem to be involved in short-term P-cycling transformations as they significantly varied with season. During the rainy season plant P content (576-1160 mg P kg⁻¹ dry weight) and APA (44-200 mg PNP kg⁻¹ dry soil) were higher, while microbial number and activity (DHA) were lower. The higher P availability in the Entisol (6-9 mg P kg⁻¹ dry soil) resulted in a better plant nutritional status and inhibited APA. T. plumosus seems to be highly dependent on AM symbiosis (45-71% AM colonized root length, 0.6-8 AM spores g⁻¹ dry soil), especially during the rainy season. Po mineralization processes, mediated by biological associations in the rhizosphere, are crucial for understanding seasonal P-cycling and fertility in acid savanna soils.     

高磷对矿山生态型水蓼磷富集特性的影响

采用土培试验,以磷富集植物矿山生态型水蓼为研究对象,研究了高磷条件下（P 800 mg/kg）矿山生态型水蓼4周、 8周、 12周的磷富集特性,为利用矿山生态型水蓼提取土壤或水体中过量的磷, 防治磷的非点源污染提供理论依据。结果表明, 1）高磷处理下,矿山生态型水蓼根干重在4周、 8周、 12周时分别为不施磷处理的4.50、 8.12、 3.17倍;茎干重分别为不施磷处理的6.83、 11.47、 15.14倍;叶干重分别为不施磷处理的5.77、 10.49、 7.11倍。矿山生态型水蓼生物量在12周达到最大,增加幅度明显高于非矿山生态型。2）高磷处理下,矿山生态型水蓼各器官磷含量明显高于不施磷处理,且随着生长期延长逐渐降低。矿山生态型水蓼磷富集系数均大于1,且在高磷处理下高于非矿山生态型。各生长期下,矿山生态型磷迁移率均大于50%,且在高磷处理下分别为不施磷处理的1.21、 1.21、 1.20倍。矿山生态型水蓼地下部与地上部磷积累量在12周时,分别达到 9.76、 105.12 mg/plant, DW,为非矿山生态型的2.29、 3.29倍。 3）矿山生态型水蓼根系酸性磷酸酶活性在8周时达到峰值,在4周和8周时表现为高磷处理大于不施磷处理且显著高于非矿山生态型（P0.05）。而植酸酶活性随生长期延长逐渐降低,在12周时表现为高磷处理大于不施磷处理且高于非矿山生态型。表明在高磷处理下,矿山生态型水蓼对磷具有较强的吸收和积累能力,是一种理想稳定的磷富集材料。     

Correlations between Kinetic Parameters of Phosphate Uptake and Internal Phosphorus Concentrations in Maize Plants: Making it Possible to Estimate the Status of Phosphate Uptake according to Shoot Phosphorus Concentrations

Abstract

The relationship between internal phosphorus (P) concentration [P] and kinetics of phosphate (Pi) uptake was investigated in maize seedlings grown hydroponically at different Pi concentrations (0.1–1,000 µM) and in the phase of Pi deprivation (0–10 d). The results indicated when the internal [P] was higher than 85 µmol g^?1 dw, apparent K_m, C_min, and V_max were significantly (P<0.01) related to [P]s in shoots and roots; when the internal [P] was lower than 85 µmol g^?1 dw, K_m and C_min were small and only V_max was significantly related (P<0.01) to internal [P]s. Three equations were deduced from the linear regressions of the kinetic parameters and [P]s in shoots. Using these equations, the values of apparent K_m, C_min, and V_max of Pi uptake of seedlings grown in different circumstances were calculated according to [P]s in shoots. In all the circumstances involved, for K_m and C_min, there was a parallel relationship between the values estimated by [P]s in shoots and by the Pi‐depletion technique; for V_max, the values estimated by [P]s in shoots were consistent with those obtained from Pi‐depletion experiments except the period of supplying Pi to the Pi‐starved seedlings over several days. These results indicated it is possible to estimate the Pi‐uptake status according to shoot P concentrations in maize plants under experimental conditions, which might be helpful to estimate in‐season status of Pi uptake of maize plants in the field.     

根际pH对玉米利用磷酸单酯和双酯盐的影响

【目的】土壤有机磷在土壤全磷中占有很大比重,是植物潜在的有效磷源,但必须通过磷酸酶的水解作用释放出无机磷才能被植物利用。土壤中有机磷的主要形式为磷酸单酯和磷酸双酯。本研究中,我们探讨了无菌条件下不同形态的氮源引起的根际pH变化如何影响植物对这两种有机磷的活化利用。【方法】采用琼脂无菌培养体系种植玉米,向玉米植株供应两种形态的氮源和磷源, 氮源为硝态氮和铵态氮,磷源为植酸钙和卵磷脂,植酸钙属于磷酸单酯盐,卵磷脂属于磷酸双酯盐。不同的供氮形态会导致根际pH变化,进而研究根际pH变化对磷酸单酯盐和磷酸双酯盐的活化利用所产生的影响。【结果】当给玉米供应铵态氮时,根际pH从5.5降至4.0; 供应硝态氮时,根际pH升至6.6。测定玉米根际的琼脂中根系分泌的磷酸单酯酶和磷酸双酯酶活性发现,磷酸单酯酶活性在pH 6.0~7.0之间最高,磷酸双酯酶活性在pH 7.0~8.0之间达到最高。无论以植酸钙还是卵磷脂为有机磷源,相对于铵态氮处理,硝态氮处理能够使根际保持较高的磷酸单酯酶或磷酸双酯酶活性。有机磷的水解过程由磷酸酶活性和底物有效性两个因素控制,而植酸钙的水解受根际pH影响很大,在一定pH范围内,植酸钙的溶解度随根际pH值降低而升高,有效态磷浓度的增加,使得磷酸酶的底物有效性提高。在供应铵态氮时,根际pH值降低,玉米对植酸钙的利用效率高于硝态氮处理,尽管供硝态氮时磷酸单酯酶活性更高。同时,在供应铵态氮条件下,植株对植酸钙的利用率要显著高于卵磷脂,原因在于虽然磷酸双酯酶和磷酸单酯酶活性较低,由于植酸钙的溶解度较大,它的底物有效性更高。因此,植酸钙处理中植株的磷含量更高。相反,在供应硝态氮时,植酸钙溶解度减小而两种磷酸酶活性较高,卵磷脂处理中植株的磷含量更高。【结论】土壤中有机磷的水解过程由磷酸酶活性和有机磷底物有效性两个因素控制,酶活性与根际pH密切相关。本研究说明土壤有机磷的活化必须首先转化为溶解于水溶液中的状态,才能作为磷酸酶的底物被催化水解。我国长期施用化肥导致北方土壤大范围酸化,这种酸化无疑对土壤固有或随有机物料进入农田的有机磷的活化利用是具有重要贡献的,应该在北方土壤养分管理中应加以考虑。     

不同镉处理对两种生态型水蜈蚣镉富集特性的影响

采用室内盆栽试验,研究了在不同浓度cd处理下,两种生态型水蜈蚣的生长和对cd的吸收和富集特性。结果表明：（1）在2mg·kg^-1Cd处理时,Cd对两种生态型水蜈蚣生物量的影响较小。之后随着cd处理浓度的增加,两种生态型水蜈蚣生物量均呈降低的趋势,且差异显著。在200mg·kg^-1Cd处理时,矿山生态型水蜈蚣死亡,而非矿山生态型仍能维持一定生长,表现出较强的cd耐性。（2）在高浓度cd处理下,非矿山生态型水蜈蚣比矿山生态型具有更强的Cd富集能力。在2、10、50mg·kg^-1Cd处理时,两种生态型水蜈蚣Cd含量和积累量均呈增加的趋势。在200mg·kg^-1Cd处理时,非矿山生态型水蜈蚣地上部和地下部Cd含量分别达到498．66mg·kg^-1和1016．09mg·kg^-1,积累量分别为86．00μg·pot^-1和123．82μg·pot^-1,具有较强的cd富集能力。（3）在不同浓度Cd处理下,两种生态型水蜈蚣地上部富集系数均大于1,表现出较强的cd富集能力;矿山生态型水蜈蚣转移系数最大值为0．55,非矿山生态型为0．53。两种生态型水蜈蚣对cd均有一定的富集特性,而在高浓度Cd处理时非矿山生态型水蜈蚣的cd富集能力更强。     

Biological P cycling is influenced by the form of P fertilizer in an Oxisol

Phosphate rock (PR) is an alternative fertilizer to increase the P content of P-deficient weathered soils. We evaluated the effects of fertilizer form on indicators of biological cycling of P using an on-farm trial on a Rhodic Kandiudox in western Kenya. Treatment plots were sampled after 13 cropping seasons of P applications as Minjingu phosphate rock (PR) or as triple super phosphate (?TSP) (50 kg P ha^?1 season^?1), as well as a P-unfertilized control (0 kg P ha^?1 season^?1). Soils (0–15 and 15–30 cm) were analyzed for microbial biomass P (P_mic), activities of acid phosphomonoesterase, alkaline phosphomonoesterase, and phosphodiesterase, and sequentially extractable P fractions. P additions as Minjingu PR yielded 299% greater P_mic than TSP at 0–15-cm depth despite similar labile P concentrations in the two P fertilization treatments and stimulated activities of acid phosphomonoesterase (+39%). When added in the soluble form of TSP, a greater percentage of total soil P was present in mineral-bound forms (+33% Fe- and Al-associated P). Higher soil pH under Minjingu PR (pH 5.35) versus TSP (pH 5.02) and the P-unfertilized treatment (pH 4.69) at 0–15-cm depth reflected a liming effect of Minjingu PR. The form of P fertilizer can influence biological P cycling in weathered soils, potentially improving P availability under Minjingu PR relative to TSP via enhanced microbial biomass P and enzymatic drivers of P cycling.     

Faba bean (Vicia faba L.) varieties reveal substantial and contrasting organic phosphorus use efficiencies (PoUE) under symbiotic conditions

Background

The excessive use of inorganic P (Pi) in soils is alarming as it is causing numerous environmental problems and may lead to the depletion of rock phosphate reserves earlier than expected. Hence, to limit the over-dependence on Pi, there is the need to investigate organic phosphorus (Po), which is the dominant P form of soil P pool, as an alternate P source for plant growth.

Aim

The present study seeks to investigate organic P use efficiency of eight varieties of faba bean grown symbiotically.

Methods

The plants were grown in pots (6 kg soil) under greenhouse condition with three P source, namely, phytic acid (organic P, Po), KH₂PO₄ (inorganic P, Pi), and no-P. The P was applied at the rate of 1.79 g kg⁻¹ soil.

Results

The plants grown with Po and Pi produced similar amounts of root, shoot, and total dry matters. Despite producing statistically similar dry matters, P uptake by Pi-fertilized plants was twofold higher than by Po-fertilized plants. Meanwhile, Pi differed significantly from Po in terms of nodulation characteristics such as nodule dry biomass and individual nodule dry biomass. However, Po varied significantly from Pi in P utilization and acquisition efficiencies. Principal component analysis of Pi and Po revealed no significant variation and close association, confirming the nonsignificant differences between the two P treatments. Among the varieties tested, Tiffany tended to accumulate more dry matter, coupled with highest organic P utilization efficiency (0.48 g mg⁻¹) as well as the highest organic P beneficiary factor (80%).

Conclusion

These results provide a solid basis for further comparisons at physiological, biochemical, and molecular levels between Tiffany (Po-efficient) and Fuego (Po-inefficient) varieties, offering deep insights into and making it easier to understand the mechanisms that allow soil Po to be utilized under symbiotic conditions.     

Phosphorus and carbon status of a paddy soil under different fertilization regimes

Purpose

Phosphorus (P) in soil particulate fraction (PF; >53 μm) is suggested to have a significant importance in soil P cycling. However, the effects of continuous fertilization on P-PF and its association with soil organic carbon (SOC) in paddy soils have not been well studied.

Materials and methods

We sampled paddy soils at 0–20 cm from a long-term field experiment (initiated in 1981) conducted under humid subtropical conditions in China, which has five fertilization treatments with equivalent P input (135 kg P₂O₅?ha^?1 year^?1) except the control treatment (CK). Changes in total P (Pt), inorganic P (Pi), organic P (Po), and SOC under different fertilization managements were evaluated in the whole soil, in the PF, and in the mineral-associated fraction (MAF; <53 μm).

Results and discussion

Continuous fertilization increased the contents of SOC and P in all soil fractions. Both Po and organic carbon in PF were the most sensitive variables to fertilization, indicating that they constitute a useful tool to detect the effects of management practices. Among the fertilization treatments, organic amendments significantly increased Po-PF contents more than chemical fertilizer applied only (p?<?0.05), although they had equivalent P input. The paddy soil without fertilization showed a more significant decrease in Pi compared with Po. The SOC/Po ratios were significantly lower in fertilization treatments (especially those with manure or straw incorporation) than in CK and decreased from PF to MAF. A significant relationship was found between Po-PF contents and rice P uptake during the growing season.

Conclusions

These results demonstrate that Po-PF may also play a significant role in P cycling of paddy soil, and thus, it would be better to consider Po-PF in soil diagnosis to promote P management of paddy soil, especially for that under long-term organic amendments.

     

Effects of poultry manure amendment on phosphorus uptake by ryegrass,soil phosphorus fractions and phosphatase activity

Poultry manure (PM) contains a large proportion of phosphorus (P) in mineral-associated forms that may not be readily available for plant uptake. In addition, PM application influences both chemical and biotic processes, and can affect the lability of native soil P. To investigate the effects of PM on soil P availability, we grew ryegrass (Lolium perenne) in greenhouse pots amended with poultry manure. Biomass was harvested at 4, 8, and 16 weeks following PM application, with soil separated into rhizosphere and bulk fractions. Soil was sequentially extracted by H₂O, 0.5 M NaHCO₃, 0.1 M NaOH, and 1 M HCl, and inorganic P (P_i) and enzymatically hydrolyzable organic P (P_oe) were quantitated. Root P concentrations were 37% higher and total P uptake 59% higher with PM application than Control. At week 16, there was 30% more labile-P_i (H₂O- plus NaHCO₃-P_i) in the rhizosphere with PM than in Control. Phosphodiesterase activity increased with PM application. Furthermore, acid phosphomonoesterase, alkaline phosphomonoesterase, and phosphodiesterase activities were all higher in the rhizosphere than in bulk soil at week 16 with PM, indicating that increased labile-P_i was due primarily to stimulation of soil phosphatases to mineralize NaOH-P_oe. Soil pH increased with PM application and plant growth, and may have promoted P availability by decreasing sorption of Al- and Fe-associated inorganic and organic phosphates. These results demonstrate that whereas PM application may initially increase NaOH and HCl-P_i, these fractions can be readily changed into labile-P and do not necessarily accumulate as stable or recalcitrant P in soil.     

Effect of Different Phosphorus Treatments on the Physiological and Biochemical Characteristics of Pilea sinofasciata

Phosphorus (P) concentration and physiological and biochemical characteristics of the leaves of Pilea sinofasciata [both P-ME (ME) and nonME (NME)] grown in a greenhouse were determined under varying soil P conditions. Greater P concentration was observed in ME of P. sinofasciata. The concentration of chlorophyll a in the ME increased with an increase of P concentration in soil, whereas the reverse tendency was observed in the NME. A slight decrease of chlorophyll b concentration existed at 100 mg P kg^?1 soil for ME. Pilea sinofasciata of ME growing under high P concentration presented greater bioactivities of catalase (CAT), superoxide dismutase (SOD), and peroxidase (POD) and less concentrations of malondialdehyde (MDA) and free proline than under low-P conditions, whereas the opposite tendency was manifested in the NME, which demonstrated normal growing status and steady accumulation efficiency.     

根系分隔方式对玉米/大豆根际土壤碳含量及磷有效性的影响

【目的】豆科与禾本科间作体系中对磷有效性的影响主要集中在根系分泌物的活化作用,由根际沉淀引起的土壤碳含量与磷酸酶活性变化及其对红壤磷有效性的影响机制尚不清楚。【方法】本研究以间作玉米大豆为研究对象,设置根系完全分隔、尼龙网分隔、不分隔3种方式,在0、21.83、43.67、65.50和87.34 P mg kg-1（分别记为P0、P1、P2、P3和P4）磷肥施用水平下进行盆栽试验,研究根系分隔方式对间作玉米大豆根际土壤微生物量碳（MBC）、溶解性有机碳（DOC）、根际土壤有机碳（ROC）、酸性磷酸酶活性（ACP）、碱性磷酸酶活性（ALP）、速效磷和Hedley磷组分的影响。【结果】相比完全分隔,根系不分隔可提高玉米和大豆根际土壤MBC含量,显著降低玉米根际土壤DOC含量,低磷水平（P0、P1）时显著提高大豆DOC含量,显著提高玉米（仅在低磷时）和大豆根际土壤ACP活性,低磷时显著提高大豆根际土壤ALP活性。除玉米活性磷组分外,根系分隔方式对间作玉米大豆根际土壤速效磷、磷组分有显著或极显著影响。根系不分隔较完全分隔可通过降低大豆根际活性无机磷（Pi）(P0除外)和中活性Pi从而提高玉米根...     

Evaluation of Phosphorus Pools and Fractions in an Acid Tropical Soil Recapitalized with Different Phosphorus Sources

Abstract

Bray 1 phosphorus (B1P) and sequential phosphorus (P) fractions were determined on soils treated with triple superphosphate (TSP), Gafsa (GPR), and Christmas Island phosphate rocks (CIPR), respectively, with and without manure. The fractions extracted in decreasing lability were iron oxide–impregnated paper strip P (Pi‐strip P), inorganic (Pi), and organic (Po) bicarbonate (NaHCO3‐Pi and ‐Po), hydroxide [sodium hydroxide (NaOH)‐Pi and ‐Po], hydrochloric acid (HCl) P, and residual (residue P). The magnitude of B1P was in the order TSP>GPR=CIPR. Average B1P from PRs was two‐fold the amount in TSP, whereas that of the fractions was NaOH‐P>Residue P<sodium bicarbonate (NaHCO₃) P<Pi‐strip P <HCl. Bray 1 extracted mainly the most labile fractions (Pi‐strip P and NaHCO3‐Pi), and plant P uptake was correlated mainly to NaOH‐Po and NaHCO₃‐Pi. Magnitude of various fractions differed between TSP and PRs. Both B1P and the fractions were equally correlated to P uptake (R²=0.38**). Nevertheless, sequential fractionation appears to be a powerful tool to identify the P status and availability in soil.