The effect of soil moisture tension and nitrogen supply on nitrate reduction and accumulation in wheat seedlings

Summary The effect of soil moisture tension on nitrate reductase and on nitrate accumulation in wheat plants was studied. Nitrate reductase activity was inhibited when soil moisture tension was increased to about 3.0 bars associated with a drop in leaf relative water content to about 90 per cent. The decrease in nitrate reductase activity did not result in nitrate accumulation in short-term experiments (10 days) when plants were exposed to only 1–2 cycles of elevated soil moisture tensions. However, when the period of different moisture regimes was extended up to the flag-leaf stage, nitrate accumulated in stressed plants.Significant increase in plant nitrate concentration as a result of increased moisture tensions was only found at the high levels of added nitrogen. On the other hand, moisture tensions had no effect on the content of total nitrogen in wheat shoots, implying that nitrate reduction was rather limiting under stress conditions.An effect of soil moisture tension and nitrogen nutrition on dry matter production by wheat seedlings was also found in the long-term experiment. At the highest dose of soil nitrogen an increase in maximal soil moisture tension from 0.1 to 0.33 bars reduced plant growth; at intermediate nitrogen doses only tension higher than 2 bars reduced growth. Under complete nitrogen deficiency, plant dry matter production was very low and was not affected by soil moisture tensions.Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. 1972 Series, No. 2185-E.Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. 1972 Series, No. 2185-E.     

Nutrient sequestration potential of water primrose Ludwigia stolinefera (Guill. & Perr.) P.H. Raven: A strategy for restoring wetland eutrophication

The current work investigates the capacity of the water primrose (Ludwigia stolinefera) to sequester inorganic and organic nutrients in its biomass to restore eutrophic wetlands, besides its nutritive quality as fodder for animals. The nutrient elements and nutritive value of the water primrose were assessed seasonally in polluted and unpolluted watercourses. The water primrose plants’ highest biomass was attained during summer; then, it was significantly reduced till it reached its lowest value during winter. In the polluted canal, the plant root and shoot accumulated higher contents of all nutrient elements (except Na and Mg) rather than in the unpolluted Nile. They accumulated most investigated nutrients in the growing season during summer. The shoots accumulated higher contents of N, P, Ca, and Mg than the root, which accumulated higher concentrations of Na and K. Therefore, summer season is the ideal time to harvest water primrose for removing the maximum nutrients for restoring eutrophic watercourses. The aboveground tissues had the highest values of ether extract (EE) during spring and the highest crude fibers (CF) and total proteins (TP) during summer. In contrast, the belowground tissues had the lowest EE, CF, and TP during winter. In spring, autumn, and winter seasons, the protein content in the grazeable parts (shoots) of the water primrose was within the range, while in summer, it was higher than the minimum requirement for the maintenance of animals. There was a decrease in crude fibers and total proteins, while an increase in soluble carbohydrates content in the below- and above-ground tissues of water primrose under pollution stress. The total protein, lipids, and crude fibers of the aboveground parts of water primrose support this plant as a rough forage.     

新疆阜康绿洲荒漠过渡带植物群落物种多样性与土壤环境因子的耦合关系

对新疆阜康绿洲荒漠过渡带植物群落4个物种多样性指数和3层土壤19个指标进行回归分析,结果表明,土壤酸碱度,全盐量,Cl^-,K^ Na^ ,Mg^2 ,土壤有机质,全N和速效P与物种多样性有显著相关关系（P＜0．05）。酸碱度和有机质与多样性的最好拟合为二项式,即高的物种多样性出现在梯度中间位置。其余6个指标与物种多样性为显著线形负相关关系。表明全盐量,Cl^-,K^ Na^ ,Mg^2 含量越多,物种多样性越小,全N和速效P与均匀度均呈显著负相关,表明全N和速效P含量上升,均匀度显著下降,植物个体数与土壤水盐的回归分析表明,植物多度受土壤水分和盐分影响显著（P＜0．01）。     

Some aspects of the cation status of soil moisture

Summary A study was made of the effect of soil moisture tension (pF 0–3), regarding the soil moisture status and soil oxygen status as interrelated, on the growth and cation uptake byRaphanus sativus using a tension plate apparatus. A similar study was made usingBrassica sinensis in pots.Results suggested that the tension-plate apparatus would be useful in such studies, whereas the lack of adequate soil moisture control in the pot experiment made this type of method unsuitable.Increasing soil moisture tension resulted in an increase in the cation concentrations of both soil solution and plant material. The dilution and valency effect in the soil solution was demonstrated.The growth response to soil moisture tension was a reflection of changes in moisture status which in turn affected the soil oxygen tension.The value of logK–1/2log [Ca+Mg] in the plant was constant over the soil moisture tension range studied and was a reflection of the characteristic potassium intensity status of the soil solution, defined by pK–1/2p (Ca+Mg) which was also constant. The concentration ratio, K/Ca+Mg, in the plant varied with moisture tension in the same way as the ratio varied in the soil solution and was therefore a reflection of both the soil solution composition and soil moisture tension.The plant reflected the composition of the soil solution and it was concluded that both the adsorption and contact-exchange theories played no significant role in plant ion uptake.     

The effect of proline application on the physiology ofraphanus sativus plants grown under salinity stress

Transpiration rate, stomatal frequency, growth, contents of pigments, saccharides, total nitrogen, proteins and some nutritive elements (K, Ca, Mg, P) of radish plants were significantly lowere dwith the rise in salinization levels using NaCl. Spraying radish shoots with proline solution (200 g m-³) counteracted the above adverse effects, especially at low and moderate salinity.     

Fire and soil-plant nutrient relations in a pine-wiregrass savanna on the coastal plain of North Carolina

Summary Changes in soil and plant nutrient conditions were evaluated following various burn and clip treatments in a longleaf pine-wiregrass savanna in Bladen Co., N.C., USA. Ground fires were found to add substantial quantities of N, P, K, Ca, and Mg to the soil, though not necessarily in forms immediately available to plants. Less than 1% of the total nitrogen in the charred residue (ash) is present as nitrate or ammonium. Considerable quantities of all nutrients examined were lost to the atmosphere during burning. Green leaf tissue in recently burned areas was consistently higher in N, P, K, Ca, and Mg compared to unburned areas. Howerver, when compared to similar tissues from clipped plots, burned area tissues were significantly higher in N, Ca, and Mg only. Data presented here suggest that tissue age significantly affects nutrient content and must be considered in any analysis of tissue nutrient content following burning. Within 4–6 months following fire, burned-area tissue nutrient content decreases to concentrations found in the unburned area. Burning resulted in initial enrichment of available soil nutrients including PO₄, K⁺, Ca⁺⁺, and Mg⁺⁺, however, NO₃ ^-, and NH₄ ⁺ concentrations in burned soil were not significantly different from unbruned soil. Soil and plant nutrient changes in an area burned two years in succession indicate that repeated burning may diminish nutrient availability. Plant response to various nutrient enrichment treatments of the soil indicated that nitrogen is limiting growth in both burned and unburned soils and that burning may alter some factors other than nutrients which may retard plant growth in unburned areas.     

Role of magnesium in carbon partitioning and alleviating photooxidative damage

Magnesium (Mg) deficiency exerts a major influence on the partitioning of dry matter and carbohydrates between shoots and roots. One of the very early reactions of plants to Mg deficiency stress is the marked increase in the shoot-to-root dry weight ratio, which is associated with a massive accumulation of carbohydrates in source leaves, especially of sucrose and starch. These higher concentrations of carbohydrates in Mg-deficient leaves together with the accompanying increase in shoot-to-root dry weight ratio are indicative of a severe impairment in phloem export of photoassimilates from source leaves. Studies with common bean and sugar beet plants have shown that Mg plays a fundamental role in phloem loading of sucrose. At a very early stage of Mg deficiency, phloem export of sucrose is severely impaired, an effect that occurs before any noticeable changes in shoot growth, Chl concentration or photosynthetic activity. These findings suggest that accumulation of carbohydrates in Mg-deficient leaves is caused directly by Mg deficiency stress and not as a consequence of reduced sink activity. The role of Mg in the phloem-loading process seems to be specific; resupplying Mg for 12 or 24 h to Mg-deficient plants resulted in a very rapid recovery of sucrose export. It appears that the massive accumulation of carbohydrates and related impairment in photosynthetic CO2 fixation in Mg-deficient leaves cause an over-reduction in the photosynthetic electron transport chain that potentiates the generation of highly reactive O2 species (ROS). Plants respond to Mg deficiency stress by marked increases in antioxidative capacity of leaves, especially under high light intensity, suggesting that ROS generation is stimulated by Mg deficiency in chloroplasts. Accordingly, it has been found that Mg-deficient plants are very susceptible to high light intensity. Exposure of Mg-deficient plants to high light intensity rapidly induced leaf chlorosis and necrosis, an outcome that was effectively delayed by partial shading of the leaf blade, although the Mg concentrations in different parts of the leaf blade were unaffected by shading. The results indicate that photooxidative damage contributes to development of leaf chlorosis under Mg deficiency, suggesting that plants under high-light conditions have a higher physiological requirement for Mg. Maintenance of a high Mg nutritional status of plants is, thus, essential in the avoidance of ROS generation, which occurs at the expense of inhibited phloem export of sugars and impairment of CO2 fixation, particularly under high-light conditions.     

Nitrogen and potassium fertilization and environmental factors affecting the grass tetany hazard of wheat forage

Summary The effects of temperature and soil moisture levels on the chemical composition of wheat forage grown in growth chambers were studied. In addition to the environmental variables, K and N fertilization effects were studied. In all the studies, increasing levels of K fertilization depressed the Mg and Ca concentration of the shoots. Nitrogen fertilization increased the Mg concentration but had no effect on the Ca concentration of the plants. N fertilization depressed the K concentration in the soil moisture experiment, but had no effect on K concentration in the temperature experiment. Increasing the temperature from 10 to 20°C did not affect the Mg and Ca concentration of the shoots, but the K concentration declined due to dilution effects caused by the greater yield at the higher temperature. In the soil moisture level experiment the K, Mg and Ca concentration in wheat tended to decline with soil moisture level due to dilution effects. Calculations showed that uptake of K was regulated primarily by diffusion of K from the soil to the plant root and that the uptake of Mg was regulated by the uptake process of the plant root and not by the nutrient transport process through the soil.This study was part of the program of the Center for Root-Soil Research. Dept. of Agronomy paper #1532.     

农业活动对三江平原湿地主要植物种群生态位的影响

农业活动是三江平原湿地主要干扰方式之一,长期的农业活动已对该区域湿地生态环境产生显著影响。本研究以三江平原退化湿地20种主要植物为研究对象,分析其在土壤含水量、土壤有机碳、全氮、碱解氮、全磷、速效磷、全钾、速效钾8个资源维上的生态位宽度及生态位重叠特征,揭示农业活动导致的生境退化对湿地主要植物种群生态位产生的影响。研究结果表明：优势种中,小叶章具有最大生态位宽度,漂筏苔草具有最小生态位宽度。伴生种中,球尾花具有最大生态位宽度。湿地植物对不同资源的利用能力存在差异。60%的湿地植物对土壤有机碳表现为较窄的生态位宽度,70%以上的湿地植物在土壤含水量、氮、磷、钾资源维具有较高的生态位宽度。优势种在土壤含水量、土壤有机碳和氮资源维表现出不同的生态位宽度和生态位重叠,这种差异是影响湿地优势物种分布和种群生态位分化的主要原因之一。农业活动导致的土壤养分的变化,会引起植物种群间对有限资源的竞争,成为影响植物群落物种组成和群落动态的关键因素。     

Development and use of a short-term nutrient-absorption technique for evaluating soil magnesium status

Summary A greenhouse investigation was undertaken to study and evaluate the use of a short-term nutrient-absorption technique for evaluating soil magnesium status. Barley (Hordeum vulgare), variety Arivat, was used as the test plant. The investigation included four experiments with the following objectives: (1) to determine the need for base applications of nitrogen and phosphorus in a soil-magnesium study using a short-term nutrient absorption technique; (2) to study the effect of base applications of N and P on Mg-uptake by plants under three time periods of root-soil contact; (3) to study the effect of increasing soil moisture from 75 to 100 per cent of the soil moisture equivalent on the plant uptake of Mg; and (4) to evaluate the short-term nutrient-absorption technique in determining the magnesium status in six different soils: Gila silt loam, Tours silty clay loam, Cajon clay loam, La Palma fine sandy loam, Yavapai sandy clay loam, and Casa Grande loam. Magnesium was applied in the form of MgSO₄ and Sul-PO-Mag.Plant growth, potassium, calcium, and magnesium uptake were increased by the base application of nitrogen and phosphorus using a 7-day period of root-soil contact.Plant growth was not affected by soil moisture level. Potassium and calcium concentrations in the plant were decreased with increasing soil moisture, but the total plant uptake of these nutrients was not affected. Total plant uptake and concentration of magnesium were increased by increasing soil moisture level.The results obtained in this study agree with previous observations that soil response to Mg does not depend upon the amount of exchangeable magnesium in the soil.Published as Arizona Agr. Expt. Station Technical Publication No.848.     

Mineral Elements in Root of Wild Saposhnikovia divaricata and Its Rhizosphere Soil

Mineral elements are important components of medicinal herbs, and their concentrations are affected by many factors. In this study, Ca, Mg, Na, K, Fe, Mn, Cu, and Zn concentrations in wild Saposhnikovia divaricata and its rhizosphere soil collected from seven locations at two different times in China were measured, and influences of rhizosphere soil on those minerals in plant were evaluated. The results showed that mean concentrations of eight minerals in plant samples decreased in the order: Ca > Mg > Na > K > Fe > Zn > Mn > Cu, and those in the soil samples followed the following order: Na > Fe > Ca > K > Mg > Mn > Zn > Cu. Mean concentrations of Ca, Na, Mg, and K in plants were higher than those in soils, while higher mean concentrations of the other four minerals were found in soils. It was found that there was a positive correlation of Mg, Na, and Cu concentrations in the plant with those in the soil respectively, but a negative correlation of Mn concentration in plant with that in the soil. Except Ca, K, and Mn, the other five minerals in plant were all directly affected by one or more chemical compositions of soil. The results also indicate that pH value and concentrations of total nitrogen, Mg, Mn, and Cu in soil had significant correlations with multimineral elements in plant. In a word, mineral elements uptake of S. divaricata can be changed by adjusting the soil fertility levels to meet the need of appropriate quality control of S. divaricata.     

外源NO对缺镁胁迫下玉米幼苗生长和离子平衡的影响

研究了在缺镁胁迫下,外源NO对缺镁玉米幼苗生长、根系活力和离子含量的影响。结果表明,缺镁胁迫使玉米幼苗株高、根长和干鲜重下降,根系活力降低,N元素在地上部和根部分配失调,新叶和老叶中Mg2＋、Cu2＋、Fe3＋、Mn2＋等离子含量下降,Ca2＋、K＋、Zn2＋等离子含量上升。根中Mg2＋离子含量下降,Ca2＋、K＋、Zn2＋、Cu2＋、Fe3＋、Mn2＋等离子含量上升。用100μmol·L-1一氧化氮供体硝普钠（SNP）处理后,玉米幼苗株高、根长、干重和鲜重均提高,根系活力增强,改善了N代谢,新叶中Ca2＋、K＋和Zn2＋等离子含量下降,Mg2＋、Cu2＋、Fe3＋和Mn2＋等离子含量提高,老叶中Mg2＋、Ca2＋、K＋和Zn2＋等离子含量下降,Cu2＋、Fe3＋和Mn2＋等离子含量提高,根中Mg2＋、Ca2＋、K＋、Cu2＋、Zn2＋、Fe3＋和Mn2＋离子含量均下降。实验结果表明,NO保护玉米幼苗免受缺镁胁迫的影响。     

准噶尔盆地南缘两种典型禾本科植物根鞘土壤微生物群落功能多样性

以准噶尔盆地南缘两种禾本科植物的根鞘与其外围土壤为研究对象,采用Biolog-ECO微平板检测法对土壤微生物群落功能多样性进行了研究。结果表明:两种植物根鞘土壤的有机质、全氮、速效氮和速效钾均高于根鞘外围土壤;两种禾本科植物根鞘土壤的微生物平均颜色变化率(AWCD)、香农多样性指数、均匀度指数、优势度指数和丰富度指数均高于根鞘外围土壤;两种植物根鞘土壤微生物主要利用的碳源类型为羧酸、糖类和聚合物,其中芨芨草根鞘微生物是以利用羧酸、糖类、聚合物和氨基酸类物质为主,羽毛针禾根鞘土壤微生物是以利用糖类、氨基酸和聚合物为主;微生物平均颜色变化率与Shannon多样性指数、均匀度指数、速效钾和全氮呈显著相关性,除了全钾以外,与其余的土壤理化指标均存在正相关性。总而言之,根鞘结构改善了微生物的生存环境,提高了土壤微生物群落功能多样性,从而增强了缓冲外界不利影响的能力。     

Analysis of acid-soil stress in sorghum genotypes with emphasis on aluminium and magnesium interactions

Acid-soil stress in 12 sorghum (Sorghum bicolor (L.) Moench) genotypes was attributed mainly to aluminium (Al) toxicity. Root damage and magnesium (Mg) deficiency are two independent aspects of plant sensitivity to Al, either in acid soil or in nutrient solution. At moderate soil acidity, Mg deficiency dominantly limited growth whilst at high acidity root damage overruled the effect of Mg deficiency on the growth response. In nutrient solutions containing Al, increased Mg supply improved both root development and Mg nutrition of plants, whereas increased calcium (Ca) supply, or nutrition with ammonium (NH₄) instead of nitrate (NO₃), alleviated root damage but amplified Mg deficiency. At lowered pH the syndrome of Al toxicity was more profound. The implications of Mg-Al interactions, root damage, Mg supply and genotype selection are elucidated.     

植物群落演替与土壤发展之间的关系

本文运用植物群落中植物优势种的重要值与相对应子群落的土壤特征值直接相关联的分析方法,对湖北宜昌大老岭的桦(Betula)、栎(Quercus)、栗(Castanea)七个群落类型的三个演替途径的土壤动态进行分析,结果表明:在植物群落的演替过程中,土壤中的Ca、pH值减少;离子代换量增加;Na、Mg、NH_4+-N、速效P、速效K、有机质的含量是随着物种的变化而呈不同的趋势。因此,植物群落的演替是生态系统的动态过程。     

Herbivory and Stoichiometric Feedbacks to Primary Production

Established theory addresses the idea that herbivory can have positive feedbacks on nutrient flow to plants. Positive feedbacks likely emerge from a greater availability of organic carbon that primes the soil by supporting nutrient turnover through consumer and especially microbially-mediated metabolism in the detrital pool. We developed an entirely novel stoichiometric model that demonstrates the mechanism of a positive feedback. In particular, we show that sloppy or partial feeding by herbivores increases detrital carbon and nitrogen allowing for greater nitrogen mineralization and nutritive feedback to plants. The model consists of differential equations coupling flows among pools of: plants, herbivores, detrital carbon and nitrogen, and inorganic nitrogen. We test the effects of different levels of herbivore grazing completion and of the stoichiometric quality (carbon to nitrogen ratio, C:N) of the host plant. Our model analyses show that partial feeding and plant C:N interact because when herbivores are sloppy and plant biomass is diverted to the detrital pool, more mineral nitrogen is available to plants because of the stoichiometric difference between the organisms in the detrital pool and the herbivore. This model helps to identify how herbivory may feedback positively on primary production, and it mechanistically connects direct and indirect feedbacks from soil to plant production.     

The relationship of vegetation to environmental factors in Wangsuk stream and Gwarim reservoir in Korea: II. Soil environments

This paper presents a quantitative account of vegetation–soil environmental factor relationships in the Wangsuk stream (WS) and the Gwarim reservoir (GR) in Korea. Vegetation and the following soil variables were investigated in May, August and October 2004: pH, conductivity, water content, organic matter, total nitrogen content, NH₄–N content, PO₄–P content, total Ca, Mg, K, and Na content, extractable Ca, Mg, K and Na content, soil texture, distance from the channel, and elevation above water level. Species richness, diversity and ratio of hydrophyte occupation in WS were different from those in GR. Species richness was higher in WS, whereas the ratio of hydrophyte occupation was higher in GR. There were large temporal and spatial variations in plant distribution in the riparian and aquatic zones of WS but only slight variations in those of GR. These differences might have arisen from differences in flooding regime, distance from the stream channel related to elevation above water level, and soil properties such as soil texture and available nutrients. The median values of organic matter, total nitrogen, NH₄–N, PO₄–P and extractable Ca, Mg, K and Na contents in the soil were higher in GR than in WS. Sandy loam and loamy sand were common soil types in WS and clay loam and sandy clay loam in GR. Ten vegetation groups in WS and six in GR were identified using TWINSPAN. DCCA indicated that the distance from the stream channel was most strongly related to plant distribution and this reflected the spatial distribution of plant species in WS. In both WS and GR, NH₄–N content in soil and soil texture were important factors for the distribution of species in May, August and October. Spatial and temporal heterogeneity of soil variables were related to species distribution.     

滇南喀斯特地区不同季节土壤和灌木叶片化学计量特征及对水分添加的响应

干旱是影响南方喀斯特地区植物生长的重要限制因子, 气候变化会影响该地区的降水量和分布格局。研究该地区土壤和植物化学计量特征及其水分响应格局, 具有重要意义。自2017年4月开始, 在云南建水喀斯特植物群落进行加水试验, 2018年4月(旱季)和8月(雨季)分别采集土壤和优势灌木鞍叶羊蹄甲(Bauhinia brachycarpa)和假虎刺(Carissa spinarum)叶片样品, 测定碳、氢、氮、磷、硫、钾、钙、镁、铝、钠、铁、锰、锌、铜14种元素含量。结果表明, 水分添加影响了表层土壤中碳、氮、钠的含量, 相比于旱季, 雨季土壤中钠和硫含量明显减少, 其余土壤元素在水分添加和季节变化下并未表现出明显差异。土壤水分含量的增加使得鞍叶羊蹄甲和假虎刺叶片中钾含量下降, 钙含量上升。在水分条件变化下, 两种植物叶元素含量的稳定性与植物中元素的含量有关, 含量越接近极大值(基本元素碳、氢、氮等)或极小值(微量元素铜、锌等)的元素其变异系数越小(越稳定), 两种植物中含量接近于1 mg·g^-1的元素磷、硫、镁的变异系数最高。在土壤水分条件变化下, 假虎刺中碳、氮、磷等大量元素含量的稳定性显著高于鞍叶羊蹄甲。降水变化和水分添加导致的土壤水分变化, 对滇南喀斯特地区土壤和植物中不同元素含量的影响不同, 这些结果将为该地区的土壤、植被修复和管理提供科学参考。     

Spatial heterogeneity of soil nutrients and plant species in herb-dominated communities of contrasting land use

Recent interest in spatial pattern in terrestrial ecosystems has come from an awareness of the intimate relationship between spatial heterogeneity of soil resources and maintenance of plant species diversity. Soil and vegetation can vary spatially in response to several state factors of the system. In this study, we examined fine-scale spatial variability of soil nutrients and vascular plant species in contrasting herb-dominated communities (a pasture and an old field) to determine degree of spatial dependence among soil variables and plant community characteristics within these communities by sampling at 1-m intervals. Each site was divided into 25 1-m² plots. Mineral soil was sampled (2-cm diameter, 5-cm depth) from each of four 0.25-m² quarters and combined into a single composite sample per plot. Soil organic matter was measured as loss-on-ignition. Extractable NH₄ and NO₃ were determined before and after laboratory incubation (28 days at 27°C) to determine potential net N mineralization and nitrification. Cations were analyzed using inductively coupled plasma emission spectrometry. Vegetation was assessed using estimated percent cover. Most soil and plant variables exhibited sharp contrasts between pasture and old-field sites, with the old field having significantly higher net N mineralization/nitrification, pH, Ca, Mg, Al, plant cover, and species diversity, richness, and evenness. Multiple regressions revealed that all plant variables (species diversity, richness, evenness, and cover) were significantly related to soil characteristics (available nitrogen, organic matter, moisture, pH, Ca, and Mg) in the pasture; in the old field only cover was significantly related to soil characteristics (organic matter and moisture). Both sites contrasted sharply with respect to spatial pattern of soil variables, with the old field exhibiting a higher degree of spatial dependence. These results demonstrate that land-use practices can exert profound influence on spatial heterogeneity of both soil properties and vegetation in herb-dominated communities.     

Soil Nitrogen Conditions Approach Preinvasion Levels following Restoration of Nitrogen-Fixing Black Locust (Robinia pseudoacacia) Stands in a Pine–Oak Ecosystem

Restoring native plant communities on sites formerly occupied by invasive nitrogen‐fixing species poses unique problems due to elevated soil nitrogen availability. Mitigation practices that reduce available nitrogen may ameliorate this problem. We evaluated the effects of tree removal followed by soil preparation or mulching on native plant growth and soil nitrogen transformations in a pine–oak system formerly occupied by exotic nitrogen‐fixing Black locust (Robinia pseudoacacia) trees. Greenhouse growth experiments with native grasses, Andropogon gerardii and Sorghastrum nutans, showed elevated relative growth rates in soils from Black locust compared with pine–oak stands. Field soil nutrient concentrations and rates of net nitrification and total net N‐mineralization were compared 2 and 4 years since Black locust removal and in control sites. Although soil nitrogen concentrations and total net N‐mineralization rates in the restored sites were reduced to levels that were similar to paired pine–oak stands after only 2 years, net nitrification rates remained 3–34 times higher in the restored sites. Other nutrient ion concentrations (Ca, Mg) and organic matter content were reduced, whereas phosphorus levels remained elevated in restored sites. Thus, 2–4 years following Black locust tree removal and soil horizon mixing achieved through site preparation, the concentrations of many soil nutrients returned to preinvasion levels. However, net nitrification rates remained elevated; cover cropping or carbon addition during restoration of sites invaded by nitrogen fixers could increase nitrogen immobilization and/or reduce nitrate availability, making sites more amenable to native plant establishment.