根际养分状况数学模拟研究的进展

土壤养分有效性的核心问题是土壤中养分离子向根的迁移,而离子向根迁移则是由于植物根吸收水分和养分产生的梯度所引起。     

根际微生态系统养分有效性及植物适应性机理

文章从铁营养为例,从植物－土壤－微生物及其环境条件所组成的微生态系统角度,讨论了养分的迁移途径和植物对营养胁迫适应性反应的机理,及植物营养效率基因型差异的实质,对今后的研究重点提出了设想。     

南亚热带不同植被根际微生物数量与根际土壤养分状况

研究了包括尾叶桉、广东凤丫蕨、柳叶竹、大叶相思、青皮、木荷、湿地松在内的7种南亚热带不同植物植被下土壤根际微生物与根际养分状况及其相关关系。结果表明，根际环境对细菌有明显的正效应，对放线菌和真菌有正、负两方面的影响，但对根际微生物总量具有根际效应明显;在南亚热带森林生态系统中，在植物的某些生长季节，微生物的根际效应与土壤养分的根际效应一致。     

山西省玉米根际固氮特性研究

玉米根际固氮活性随品种和生态条件的不同而变化，在山西土壤气候条件下，测试品种中有９１．７％具有固氮活性，变异系数为６２．８％，固氮高出现在抽雄期，大约每公顷年固氮量８．１ｋｇ。在一定条件下，秸秆覆盖栽培，增施有机肥、磷肥、少量氮肥以及人工接种均有利于提高玉米根际的固氮作用。     

根际微域环境的研究

作者对根际环境研究的发展趋势和我国１０年来取得的成就进行了回顾,对今后重点的研究方向提出了见解,强调了根际物理环境,养分转化,特定分泌物与抗逆性等方面研究的重要意义。     

水稻钾素营养的根际效应

关于淹水条件下根际效应的研究迄今很少。而淹水土壤的根际环境与早作土壤十分不同。     

根际研究方法的特点及其进展

根际环境是指以微米或毫米计算的微区土壤范围内。     

VA菌根真菌对玉米生长及根际土壤微生态环境的影响

用两种不同的ＶＡ菌根真菌Ｇｌｏｍｕｓ ｍｏｓｓｅａｅ和Ｇｌｏｍｕｓ ｃａｌｅｄｏｎｉｕｍ接种玉米进行盆栽试验。结果表明,两种菌株均能侵染玉米,促进玉米生长,其中以Ｇｌｏｍｕｓ ｃａｌｅｄｏｎｉｕｍ的侵染率和作用较为明显。接种后,根区土壤中的细菌、放线菌、固氮菌的数量和微生物量明显增加,但真菌的数量则稍有下降。此外,菌根的形成也改善了根区土壤的微生态环境,为下一造作物的生长积累了养分基础。     

长期施肥及石灰后效对不同生育期玉米根际钾素的影响

依托祁阳红壤旱地定位施肥试验(始于1990年),选取施氮磷(NP)、氮磷+石灰(NPCa)、氮磷钾(NPK)、氮磷钾+石灰(NPKCa)、氮磷钾配施秸秆(NPKS)、氮磷钾配施秸秆+石灰(NPKSCa)6个处理,采集玉米不同生育期根际与非根际土壤,测定其钾、钙、镁、铝含量和p H。结果表明:与NP处理相比,施钾处理(NPK和NPKS)根际和非根际土壤速效钾含量显著提高。NP、NPK和NPKS处理根际速效钾在拔节期和灌浆期均处于亏缺状态,亏缺率分别平均为18.2%、34.2%和26.4%。与对应不施石灰处理相比,NPKCa和NPKSCa处理根际土壤速效钾含量在苗期分别降低46.0 mg kg~(-1)和26.5 mg kg~(-1),非根际分别降低68.5 mg kg~(-1)和56.0 mg kg~(-1);从拔节期至收获期,根际速效钾含量平均升高25.2 mg kg~(-1)和33.7 mg kg~(-1),非根际略微降低。NPCa、NPKCa和NPKSCa处理根际土壤速效钾盈亏率与不施石灰相比,整个生育期分别平均提高8.6%、33.2%和19.3%。根际和非根际土壤速效钾含量与相对应缓效钾含量、钾饱和度、K+/(Ca2++Mg2+)和K+/Al3+呈极显著正相关关系。缓效钾和钾饱和度相对变化率(交换性钙镁相对变化率)与速效钾相对变化率呈极显著正(负)相关关系。长期施氮磷钾肥基础上施石灰(NPKCa和NPKSCa)4年以后,根际土壤速效钾、缓效钾含量及钾饱和度均提高(苗期除外),根际土壤交换性钙镁含量提高幅度低于非根际,最终缓解根际土壤钾素的亏缺。     

玉米根际土壤中不同重金属的形态变化

采用根垫法研究了不同生长时期的玉米根际土壤中铜、镉、铅、锌和铬的形态变化。结果表明 ,玉米生长 1 0 0d内不同重金属的形态变化有显著差别。交换态铜 ,碳酸盐态铜和锌 ,铁锰态铜、铅和铬 ,有机态铜、铅和铬都有明显变化。在 1 0 0d生长期间 ,不同重金属在根际土壤中的相对变化有较大幅度的波动。植物吸收主要影响根际土壤交换态铜和碳酸盐态铜和锌的变化 ,对镉和铅形态变化影响不大。     

Atrazine mineralization in bulk soil and maize rhizosphere

An experiment was carried out in the greenhouse in order to compare atrazine mineralization in bulk soil and maize rhizosphere at different development stages. After 4, 8 and 12 weeks, we have (1) measured the soil microbial biomass C, (2) characterized the C substrate utilization profiles of the culturable microflora, and (3) analyzed atrazine mineralization. Microbial growth was stimulated in planted soil and different C substrate utilization patterns were obtained in bulk and rhizosphere soils during the first 2 months. During this period, laboratory tests for atrazine biodegradation revealed a lower mineralization potential in bulk than in planted soil. Atrazine mineralization was stimulated to a greater extent after atrazine application in the greenhouse but again the presence of plants had a favorable effect. After 12 weeks of cropping, the atrazine mineralization potential decreased in planted soil with or without prior atrazine application.     

Effect of slow releasing nitrogen fertilizers on nutrient status across wheat rhizosphere grown on volcanic ash

Abstract

The volcanic ash of the Mount Pinatubo in Philippines was used in this study. The major drawbacks of this ash for growing agricultural crops are nitrogen (N) and iron (Fe) deficiencies with low organic matter contents. The main objective of this study is to investigate the wheat grown on the volcanic ash to and determine the nutrient status across its rhizosphere using a rhizobox system. Either oxamide or polyolefinresin‐coated urea (PORCU) along with potash and phosphate fertilizers was applied to each rhizobox containing the volcanic ash. Plants were grown on the central compartment (CC) of the rhizobox. The nutrient status was examined by the assessment of distribution patterns of NH₄ ⁺‐N, NO₃ ^‐‐N, Ca²⁺, Mg²⁺, K⁺, Cl^‐, SO₄ ^2‐, PO₄ ^3‐, and associated pH. Although NH₄ ⁺‐N in both oxamide and PORCU treatments was accumulated to a somewhat considerable extent of the rhizosphere. The rhizosphere effect was more prominent in oxamide treatment. While NO₃ ^‐‐N concentrations in either of the treatment was low with a mere rhizosphere effect in PORCU treatment and a rugged distribution in oxamide treatment. Dominant anions and cations accumulated in the CC and the near by compartments of oxamide treatment were Cl^‐, SO₄ ^2‐ and Ca²⁺, respectively. In contrast, SO₄ ^2‐ and K⁺ were accumulated in the CC and the adjacent PORCU treated compartments. Thus the overall distribution of nutrients and pH across the wheat rhizosphere was rugged. Despite of this, it seems that with a rugged nutrient distribution and pH, the effects of slow releasing N fertilizers may well ensure the N benefit on plants while growing on the volcanic ash under circumstances of low N content.     

Glucose uptake by maize roots and its transformation in the rhizosphere

The flow of carbon from roots into the rhizosphere represents a significant C loss from plants. However, roots have the capacity to recapture low molecular weight C from soil although this is in direct competition with soil microorganisms. The aim of this study was to investigate the behaviour of glucose in rhizosphere and non-rhizosphere soil, the plant's potential to recapture sugars from soil and translocation and utilization of the recaptured sugars. In microcosms containing maize plants we injected ¹⁴C-glucose into the rhizosphere and followed its uptake into plants, upward and downward transport in the plant and soil, evolution as ¹⁴CO₂ and incorporation into the soil microbial biomass. These fluxes were compared with non-rhizosphere soil. Glucose was rapidly mineralized in soil and the rate of turnover was significantly greater in the rhizosphere in comparison to non-rhizosphere soil. The amount of glucose captured by the maize plants was low (<10% of the total ¹⁴C-glucose added) in comparison to that captured by the soil microbial biomass. Only small amounts of the ¹⁴C-glucose were transported to the shoot (0.6% of the total). The degree of glucose capture by maize roots whilst in competition with soil microorganisms was similar to similar experiments performed for amino acids. We conclude that while plant roots can recapture low molecular weight C from the rhizosphere, intense competition from soil microorganisms may reduce the efficiency of this process.     

Organic acid behaviour in a calcareous soil implications for rhizosphere nutrient cycling

Calcareous soils are frequently characterized by the low bioavailability of plant nutrients. Consequently, many vascular plant species are unable to successfully colonize calcareous sites and the floristic composition of calcareous and acid silicate soils has been shown to differ markedly. The root exudation of oxalate and citrate has been suggested to play a pivotal role in same nutrient acquisition mechanisms operating in calcareous soils. The aim of this study was therefore to investigate the nutrient extraction efficiency of three individual organic acids commonly identified in root exudates, i.e. citric, malic and oxalic acid. Our results clearly demonstrate the context dependent nature of nutrient release by organic acids. The degree of P extraction was highly dependent on which organic acid was added, their concentration and pH, and their contact time with the soil. P is generally more efficiently extracted by organic acids at a high pH and follows the series oxalate>citrate>malate. The opposite relationship between pH and extraction efficiency was apparent for most other cations examined (e.g. Zn, Fe), which are more efficiently extracted by organic acids at low pH. A serious constraint to the ecological importance of organic acid exudation in response to P deficiency is, however, their very low P mobilization efficiency. For every mol of soil P mobilized, 1000 mol of organic acid has to be added. It can, however, be speculated that in a calcareous soil with extremely low P concentrations it is still beneficial to the plants to exude organic acids in spite of the seemingly high costs in terms of carbon.     

Influence of municipal compost on temperature, water, nutrient status and the yield of maize in a temperate soil

Abstract. Composted domestic waste was applied either as a mulch or was incorporated into the topsoil. Mulching reduced the seasonal midday soil temperature ranges from between 14 °C and 27.5 °C to between 14 °C and 26 °C, averaging a 0.6 °C fall. However, at sub-optimal temperatures for maize production under the temperate conditions of South East England, the difference may be critical. Compost mulch also improved soil-water conservation in an average year, but not in a very dry year. Compost application increased soil-available N, but increased K uptake was considered to be more important for crop yield than either N additions or the effect on retained soil water. Overall, compost applied as a surface mulch, or incorporated into medium-textured soils in the south and east of England increased crop yield.     

Nutrient status of rhizosphere and phosphorus response of radish

Radish (Raphanus sativus L.) exhibits a high efficiency in the utilization of sparingly‐soluble phosphates. A greenhouse experiment was designed to investigate the growth response of radish to different phosphorus (P) sources and the nutrient status of the rhizosphere associated with radish growth and nutrient absorption. Radish plants were grown in pots with the roots confined in rhizobags, in such a manner that the concentration of roots was very high within the rhizobag. The rhizosphere soils and non‐rhizosphere soils were analyzed separately for active silicon (Si), aluminum (Al), iron (Fe), and manganese (Mn) using Tamm's solution and for “available”; P using the Bray P1 extraction reagent. The radish growth response was mostly attributable to phosphate amount and availability, and the lime level used in the experiment. Concentrations of active Fe, Si, Al, and Mn were reduced in the rhizosphere, especially when lime and rock phosphate (Ps) were added. Available soil P was accumulated in the rhizosphere under lime and Ps addition, whereas its concentration was reduced with the zero lime treatment. Phosphorus utilization, characterized by P accumulation in shoots, was in accordance with the concentration pattern for “available”; P in the rhizosphere, but not with the growth response of radish itself. The calcium (Ca) concentration of the shoot followed the same trend as the radish growth. There was an antagonism between potassium (K) and Ca absorption as well as between Ca and magnesium (Mg) absorption. With the addition of P, shoot Mn concentration increased, while shoot Fe and Al concentrations increased with no lime addition but decreased with lime addition. The high P efficiency of radish is discussed from the view of rhizosphere chemistry. The high Mn efficiency of radish may be influenced by the same rhizosphere processes that are involved in its high P efficiency. It was concluded that rhizosphere processes and the status of nutrients determined the nutrient efficiency of radish and thus influenced its growth response and nutrient uptake.     

Differential mobilization of P in the maize rhizosphere by citric acid and potassium citrate

The release of organic acid anions from plant roots into soil has been hypothesized to be a mechanism for enhancing phosphorus availability in the rhizosphere. Although these compounds are excreted from the cytoplasm as organic acid anions (e.g. citrate, malate), when the H⁺-ATPase is also upregulated there is evidence to suggest that they enter the soil as organic acids (e.g. citric acid, malic acid). The aim of this study was to evaluate the role of citric acid (H-citrate) and potassium citrate (K-citrate) in the mobilization and plant uptake of P from two acid soils contrasting in their P availability. Our results indicated that the mobilization of P from a labelled patch of soil was soil type dependent, was controlled by its intrinsic P status, and that more P was made available by K-citrate than H-citrate. Similarly, the uptake of ³³P from the rhizosphere by Zea mays L. was greatest in the presence of K-citrate in comparison to H-citrate. However, a significant increase in shoot ³³P content was only observed in the more acidic soil with high P sorption potential (Haplic podzol) while no significant increase was observed in the less acidic soil with low P sorption potential (Eutric cambisol). We conclude that the chemical form of organic acid anion excretion may have a significant impact on its P mobilization capability. The contrasting results with the two acid soils indicate that organic acids may not provide a universal mechanism for enhancing P uptake from soil.