Effect of the biocontrol agent Pseudomonas fluorescens F113 released as sugarbeet inoculant on the nutrient contents of soil and foliage of a red clover rotation crop

 The biocontrol agent Pseudomonas fluorescens F113, which produces the antimicrobial compound 2,4-diacetylphloroglucinol and inhibits soil-borne phytopathogenic fungi, might also affect non-target resident microorganisms involved in the cycling of soil nutrients. Analyses of soil nutrients and crop foliage were used to assess possible residual effects of the pseudomonad on soil fertility. The Bandon field site was sown in 1994 with sugarbeet seeds that were either untreated, inoculated with the spontaneous rifampicin-resistant mutant F113Rif, or treated with chemical fungicides. The field was cropped with uninoculated red clover in 1995. The inoculant was recovered at only 2.0 log CFU/root system at the first harvest of clovers, and the F113Rif treatment influenced 5 of 17 levels of readily available nutrients determined by electro-ultrafiltration (EUF) analysis of soil. However, this effect was essentially negligible since it was (1) small in magnitude and of little agronomic significance when compared with reference EUF levels, (2) similar in part to those of the commercial seed treatment and other farming practices followed at Bandon, and (3) not statistically significant when data were analysed at the plot level rather than using results from individual soil samples within plots. Clover leaf composition was investigated at two harvests. The F113Rif treatment had no effect on the 20 foliage parameters studied except a small (15%) transient decrease in foliage chlorine at the first harvest. EUF soil analysis and foliage analysis will be useful in future risk assessment studies of genetically modified derivatives of F113. Received: 24 June 1997     

樱桃根际土壤酶活性与土壤养分动态变化及其关系研究

通过盆栽试验研究了樱桃根际脲酶、磷酸酶活性与氮、磷、钾动态变化及其相互关系。结果表明,生长季前期樱桃根际脲酶、磷酸酶活性明显提高,根际酶活性显著高于根外,随物候期进展土壤酶活性及R/S值逐渐降低。氮、磷、钾元素在年生长周期内整体上呈下降趋势,生长季前期根际全氮、碱解氮及全磷亏缺明显,而根际有效磷、速效钾明显富集,这种作用亦随物候期进展逐渐减弱。土壤脲酶、磷酸酶活性与氮磷钾土壤营养元素含量间存在着一定的相关性,以春梢停长期相关程度最高。     

包膜控释尿素对保护地菜地土壤肥力及酶活性的影响

为探讨包膜控释尿素施用条件下土壤酶活性及其与土壤肥力的关系，对种植黄瓜、番茄、辣椒等蔬菜的保护地菜地土壤酶活性以及土壤养分因子含量进行了测定和分析。结果表明，施用包膜控释尿素比普通尿素能明显提高土壤有机质、全氮、碱解氮、硝态氮、铵态氮、速效钾含量，降低了土壤速效磷含量；包膜控释尿素可增强土壤多酚氧化酶、磷酸酶、脲酶活性，这些酶活性与土壤养分之间具有极显著或显著的相关性，施用包膜控释尿素未增强过氧化氢酶、转化酶的活性，过氧化氢酶、转化酶与土壤养分因子相关性不明显。在评价土壤酶活性与土壤养分的关系方面要根据不同的作物作具体的分析。     

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.     

黄土丘陵沟壑区典型林地土壤微生物、酶活性和养分特征

通过对陕西吴起县黄土沟壑区退耕还林地不同林分(沙棘、刺槐、油松、小叶杨)根际与非根际土壤养分、酶活性和微生物特征进行研究,比较4种典型林分及退耕草地“根际效应”及根际对养分的截留效应,评价根际效应对土壤特性产生不同改良效果,为黄土沟壑区退耕地人工林科学选择造林树种提供理论支持。研究表明:1根际与非根际土壤中有机质含量、有效磷含量、碱解氮含量和速效钾含量表现出显著差异,有机质、有效磷、速效钾含量均呈现明显的根际聚集现象。2根际土壤微生物数量和土壤酶活性总体高于非根际,仅油松样地中过氧化氢酶活性和小叶杨样地中脲酶活性根际低于非根际。3根际土壤中脲酶活性与细菌和真菌数量相关性达到显著水平,过氧化氢酶活性与真菌相关性达到显著水平;有机质含量与细菌、放线菌数量和脲酶活性相关性达到显著水平;碱解氮、有效磷含量均与细菌、真菌数量和脲酶活性相关性达到显著水平。在非根际土壤中,土壤养分含量与土壤微生物、土壤酶活性的相关性明显降低。4从土壤肥力综合水平看,根际土壤肥力水平综合得分总体上大于非根际土壤,其中根际土壤中沙棘小叶杨油松刺槐草地。沙棘能大幅度提高土壤肥力,具有较好的土壤改良效果。     

Clonal and seasonal shifts in communities of saprotrophic microfungi and soil enzyme activities in the mycorrhizosphere of Salix spp.

The species‐specific microbial root and rhizosphere colonization contributes essentially to the plant nutrient supply. The species number and colonization densities of cultivable saprotrophic microfungi and the activities of nutrient‐releasing soil enzymes (protease, acid and alkaline phosphatase, arylsulfatase) were investigated in the rhizosphere of one low mycorrhizal (Salix viminalis) and one higher mycorrhizal (S. × dasyclados) willow clone at a Eutric Cambisol in N Germany. After soil washing, in total 32 and 28 saprotrophic microfungal species were isolated and identified microscopically from the rhizosphere of S. viminalis and S. × dasyclados, respectively. The fungal species composition changed within the growing season but the species number was always lower under S. × dasyclados than under S. viminalis. Under both willow clones, the fungal colonization density was largest in spring, and the species number was largest in autumn. Acid‐phosphatase activity (p < 0.001) and protease activity (p < 0.003) were significantly affected by the Salix clone, whereas arylsulfatase and alkaline‐phosphatase activities did not show clone‐specific differences. All enzyme activities reached their maxima in the summer sampling. Rhizosphere colonization with Acremonium butyri, Cladosporium herbarum, and Penicillium janthinellum contributed significantly to explain the activities of acid phosphatase. Rhizosphere colonization with Cylindrocarpon destructans, Penicillium spinulosum, Plectosphaerella cucumerina, and Trichoderma polysporum contributed significantly to explain the arylsulfatase activities. Effects of the saprotrophic fungal colonization densities on the protease activities in the rhizosphere were low. Acid‐ and alkaline‐phosphatase and arylsulfatase activities in the rhizosphere soil were stronger affected by the composition of the saprotrophic fungal communities than by the Salix clone itself. In conclusion, the colonization density of some saprotrophic microfungi in the rhizosphere contributed to explain shifts in soil‐enzyme activities of the P and S cycles under different willow clones.     

陈山红心杉土壤养分、酶活性的根际效应及肥力评价

【目的】 陈山红心杉是国家级林木良种,获国家地理标志保护。土壤肥力状况影响林木的生长,根际是植物与土壤物质直接交换的场所,研究不同林龄陈山红心杉根际和非根际土养分含量、酶活性及综合肥力状况,可进一步了解土壤养分状况随林龄的演变规律,为陈山红心杉的养分管理和合理经营提供理论依据。 【方法】 以江西省安福县陈山林场不同林龄陈山红心杉为试验对象,测定了根际和非根际土壤养分 (有机质、全氮、全磷、全钾、碱解氮、有效磷和速效钾) 含量和酶活性 (过氧化氢酶、蛋白酶、蔗糖酶、脲酶和磷酸酶),分析了根际效应随林龄的变化规律,并进一步通过主成分分析对土壤肥力进行了综合评价。 【结果】 林龄对土壤养分、酶活性具有显著影响,仅碱解氮、全氮和全磷在根际和非根际间无显著差异。养分和酶活性在根际和非根际土中随林龄变化趋势一致,反映了根际受植物根系和林地土壤的共同影响。随着林龄的增加,有机质、氮素养分 (碱解氮和全氮)、钾素养分 (速效钾和全钾)、蛋白酶、脲酶和磷酸酶活性先下降后上升,总体以 10 年最低;有效磷变化趋势与之相反,全磷呈下降的趋势;蔗糖酶活性呈“下降 – 升高 – 下降”的趋势,过氧化氢酶活性变化趋势与蔗糖酶相反。有机质、碱解氮和酶活性的根际效应为正效应 (RE > 0),其余均为负效应 (RE < 0,除 20 年全氮和 40 年有效磷外),有机质和有效磷的根际效应在林龄间差异显著 (P < 0.05)。陈山红心杉根际和非根际土壤肥力综合指数 (IFI) 介于 –1.408～2.238,不同林龄土壤 (根际和非根际) IFI 变化趋势为 5 年 (2.238、2.413) > 40 年(– 0.313、0.065) > 20 a (– 0.773、–1.019) > 10 a (–1.203、–1.408)。5 年和 40 年土壤肥力综合指数表现为根际 < 非根际,主要由第二 (蔗糖酶)、第三 (速效磷和全磷) 主成分得分导致;而 10 年和 20 年土壤肥力综合指数表现为根际 > 非根际,主要是由第一主成分 (有机质、碱解氮、全氮、脲酶和蛋白酶等) 得分导致。 【结论】 随着林龄的增加,土壤肥力下降,尤其是 10 年前后最低,后虽有所恢复,但不能恢复到第 5 年水平。因此,在林木生长过程中,应在树龄 10 年左右适当补充林地土壤氮、磷养分。      

Temporal variations in phosphorus fractions and phosphatase activities in rhizosphere and bulk soil during the development of Larix olgensis plantations

Many studies have well reported nutrient deficiency and soil degradation focusing on soil N in pure plantations. However, few papers focused on soil P deficiency during pure plantation afforestation. We examined the variations in P fractions and phosphatase (P‐ase) activities in the rhizosphere and bulk soils in Larix olgensis plantations of 16, 23, 34, and 49 y. Correlation analysis was applied to identify the relationships between available P and other P fractions and P‐ase activities in the rhizosphere soil at different developmental stages. The stepwise regression models were established to explore their relationships with tree growth. The results showed that the deficiency of available P occurred in the rhizosphere micro‐region relative to the bulk soil in the 34‐ and 49‐y‐old stands, which was related to the lower acid phosphatase activity, the deficient Fe‐bound P, and occluded phosphate, as well as to soil pH in the rhizosphere soil during these periods. In addition, tree growth in the young and near‐mature stands was significantly correlated with soil P fractions, and the main P fractions closely related to tree growth were total P, organic P, available P and inorganic P, followed by Ca‐bound P and Fe‐bound P. The decreases in average DBH and average height growth in the near‐mature stand were related to the deficiency of available P in this period. Our results indicate that the development of Larix olgensis plantations affects the bioavailability of P through dynamic changes of P fractions and P‐ase activities, which provides a theoretical base in future afforestation with Larix olgensis plantations.     

Interactions between arbuscular mycorrhizal fungi and phosphate-solubilizing fungus (<Emphasis Type="Italic">Mortierella</Emphasis> sp.) and their effects on <Emphasis Type="Italic">Kostelelzkya virginica</Emphasis> growth and enzyme activities of rhizosphere and bulk soils at different salinities

This study investigated the interactions between two arbuscular mycorrhizal fungi (AMF) (Glomus aggregatum and Glomus mosseae) and a P-solubilizing fungus (Mortierella sp.), with respect to their effects on growth of Kostelelzkya virginica and urease, invertase, neutral phosphatase, alkaline phosphatase, and catalase activities of rhizosphere and bulk soils at different salinity levels (i.e., 0, 100, 200, and 300 mM NaCl). Percentage of AMF colonization, Mortierella sp. populations, pH, electrical conductivity, and available P concentration in soil were also determined. Combined inoculation of AMF and Mortierella sp. increased the percentage of AMF colonization and Mortierella sp. populations under salt stress (i.e., 100, 200, and 300 mM NaCl). The dual inoculation of Mortierella sp. with AMF (G. aggregatum or G. mosseae) had significant effects on shoot and root dry weights and available P concentrations, pH values, and electrical conductivities of rhizosphere and bulk soils under salt stress. The inoculation of Mortierella sp. significantly enhanced the positive effects of AMF on some enzyme activities (i.e., neutral phosphatase, alkaline phosphatase, and catalase in bulk soil; neutral phosphatase and urease in rhizosphere soil); on the contrary, it produced negative effects on urease activities in bulk soil and invertase activities in bulk and rhizosphere soils. The results indicated that the most effective co-inoculation was the dual inoculation with Mortierella sp. and G. mosseae, which may help in alleviating the deleterious effects of salt on plants growth and soil enzyme activities.     

糜子不同种植方式对土壤酶活性及养分的影响

【目的】土壤酶参与土壤中多种生化活动,是衡量土壤生产力的指标之一。本文比较分析了不同种植方式下糜子生育期间土壤酶活性的动态变化以及成熟期土壤养分含量和糜子产量,旨在探明糜子连作障碍和连作减产的产生机制,为糜子高产高效栽培提供理论依据。【方法】以西北农林科技大学农作一站小杂粮轮作连作长期定位试验为平台,设轮作(T1)、隔年种植(T2)、连作2年(T3)、连作3年(T4)4个处理,在糜子播种期、苗期、拔节期、抽穗期、灌浆期、成熟期测定0—20 cm根际土壤中过氧化氢酶、脲酶、碱性磷酸酶、蔗糖酶活性以及成熟期0—20 cm根际土壤养分含量,对同一时期不同处理间的酶活性和成熟期不同处理间土壤有机质、全氮、碱解氮、全磷、有效磷、全钾、速效钾含量以及土壤p H值进行方差分析,并分析土壤养分和酶活性以及糜子产量之间的相关性。【结果】1)土壤过氧化氢酶、脲酶、蔗糖酶活性随着连作年限的增加而降低;碱性磷酸酶在连作2年处理的活性较低。2)随着连作年限的增加土壤p H值升高,土壤速效钾严重积累,速效磷消耗较多,说明连作导致土壤盐碱化。3)过氧化氢酶、脲酶、碱性磷酸酶活性与糜子籽粒产量呈显著正相关,土壤p H值与籽粒产量呈显著负相关;蔗糖酶活性、有机质含量与产量具有一定的相关性。【结论】糜子连作改变了土壤酶活性及土壤养分含量,导致土壤腐殖化和熟化程度减慢,土壤次生盐渍化加重,土壤养分不均衡,植株生长发育受到影响,造成籽粒产量的下降。因此,在糜子生产上要进行合理的轮作倒茬,从而减缓连作障碍,实现糜子高产优质。     

The effect of root hairs on rhizosphere phosphatase activity

Background: Phosphatases in soil are of great importance for plant P acquisition. It is hypothesized that root hairs increase rhizosphere phosphatase activity as they release enzymes into soil and stimulate microbial activity. Methods: To test the effect of root hairs on soil phosphatase activity, we grew barley (Hordeum vulgare ‘Pallas') wild type and its root‐hairless mutant in rhizoboxes and determined phosphatase activity using soil zymography. Measurements were done at three moisture levels (30, 15, and 5% VWC). Rhizosphere phosphatase activity was estimated for the two genotypes and two locations along the root [root tip region (0–4 cm behind tip) and mature roots (> 7 cm behind tip)]. Results: Rhizosphere phosphatase activity was similar in the two locations along the root (root tip region vs. mature root parts). In contrast, rhizosphere phosphatase extension was two times larger for the root tip region of the wild type than for the mutant at 30% and 15% VWC. However, as phosphatase activities at the root surface of tips and mature root parts were slightly higher for the mutant than for the wild type, average enzyme activities were unaffected by the genotype. Conclusions: We conclude that the mutant seems to compensate for the lack of root hairs by increased phosphatase activity close to the root surface. However, the increased rhizosphere phosphatase extension for the wild type may be equally efficient as it allows P mobilization and uptake from large soil volumes.     

蚯蚓对As污染土壤酶活性及其P养分的影响

从湖南石门县的As矿区附近采集不同程度As污染的农田土壤,分别设置添加秸秆、接种蚯蚓等处理,研究蚯蚓对As污染土壤酶活性及其P养分供给的影响。结果发现,高浓度As土壤的脱氢酶活性显著低于中、低浓度As土壤,而酸性磷酸酶活性及有效P含量则与之相反。蚯蚓+20g秸秆处理在50d时脱氢酶活性最高,而酸性磷酸酶活性则是秸秆处理在100d时最高,且接种蚯蚓和施用秸秆有利于土壤P素的释放。结果表明在施用秸秆条件下接种蚯蚓有利于改善As污染土壤的养分供给,从而改善根际营养。     

连作对花生土壤酶活性、养分含量和植株产量的影响

通过盆栽试验,设置4个不同连作年限处理,研究连作对花生栽培种桂花17和野生种A.correntina土壤酶活性、养分含量和植株干物质产量影响的差异。结果表明:与对照相比,两个花生品种不同连作年限土壤有效养分含量和植株干物质产量均降低,A.correntina相比桂花17下降幅度小。桂花17各连作年限处理土壤的脲酶、转化酶、酸性磷酸酶活性随连作年限的增加有下降的趋势,处理间变幅大。而A.correntina各生育期土壤的脲酶、转化酶、酸性磷酸酶活性总体表现无一致性上升或下降的规律,处理间变幅小。两个花生品种在不同的连作年限间的过氧化氢酶活性的变化无规律性。连作条件下,花生野生种A.correntina的土壤理化和生物学性状的变化幅度更小。     

荒漠盐生植物根际土壤酶活性的变化

利用根袋法研究了荒漠盐土和灌耕灰漠土中6种不同荒漠盐生植物根际养分和酶活性特征.结果表明:两种土壤中,根际土全氮含量比非根际土高,但全磷却比非根际土低.根际土有效态养分的变化则与全态相反,6种植物的根际土有效氮含量均显著低于非根际土,除芦苇外,根际土有效磷含量均高于非根际土.6种植物中,钠猪毛菜根际土有效氮亏缺最高,有效磷富集也最少.分析测定了根际土和非根际土转化酶、蛋白酶、过氧化氢酶、脲酶、中性磷酸酶和碱性磷酸酶活性及其与土壤养分的关系.结果表明:过氧化氢酶、脲酶和蛋白酶在两种土壤的植物根际表现出相反的变化,荒漠盐土中,根际土3种酶的活性均高于非根际土;而灌耕灰漠土的根际土3种酶活性均低于非根际土.荒漠盐土碱性磷酸酶、过氧化氢酶和转化酶与几种主要养分含量有很强的相关性,较好地体现了荒漠盐土根际的养分状况,也说明盐生植物对荒漠盐土酶活性有较大的影响.     

苹果园土壤微生物生态特征研究

2003—2004年开展对9个有代表性的不同产量的苹果园秋季土壤的养分、微生物类群及土壤酶活性的研究,获得不同产量苹果园的土壤微生物生态状况。结果表明,各苹果园的土壤养分、微生物数量、多样性和酶活性均表现出较大差异。随土壤碱解氮、速效磷、速效钾、总碳含量的增加,产量水平呈增高趋势。高产园土壤微生物数量高,多数土壤酶活性强,微生物多样性好。土壤微生物中细菌数量、微生物多样性、蛋白酶、磷酸酶活性可作为评价果园土壤肥力的生物指标。果树产量与土壤微生物类群和数量具有显著正相关,与速效磷、速效钾、碱解氮和全氮含量显著正相关,且与蛋白酶和磷酸酶显著正相关。     

长期定位施肥对黄绵土酶活性及土壤养分状况的影响

本研究以25年的肥料长期定位试验为平台,探讨了长期不同施肥处理对土壤活性有机质、氮磷养分及土壤酶活性的影响。结果表明:长期施肥土壤活性有机质、全氮、碱解氮及速效磷含量显著提高,土壤转化酶和碱性磷酸酶活性增强,其中有机肥化肥配施(NPM)的作用明显大于施用化肥(N、NP);长期施肥不能增强土壤过氧化氢酶活性。相关分析表明,土壤脲酶、转化酶及碱性磷酸酶活性与土壤活性有机质、氮磷养分含量呈显著正相关,且三种酶活性间呈极显著正相关关系。综合土壤养分与土壤主要酶活性的密切关系,认为将土壤酶与土壤养分相结合进行土壤肥力研究,对该区培肥土壤具有重要的指导意义。     

不同树龄茶树根际土壤酶活性的变化分析

以不同种植年限黄金桂茶树根际土壤为研究对象,分析茶树树龄对土壤酶活性的影响。结果表明,茶树根际土壤中与养分循环相关的酸性磷酸酶、脲酶、蔗糖酶活性随着茶树树龄的增加而上升,且与茶树树龄呈显著正相关,中性磷酸酶、碱性磷酸酶则相反;茶树根际土壤中与抗性相关的多酚氧化酶活性随着茶树树龄的增加而上升且与茶树树龄呈显著正相关,而过氧化物酶、过氧化氢酶、脱氢酶活性则呈下降趋势,与茶树树龄呈显著负相关。土壤酶对茶树树龄的敏感性分析结果表明,不同土壤酶响应茶树树龄变化的趋势为过氧化氢酶脲酶脱氢酶蔗糖酶过氧化物酶多酚氧化酶酸性磷酸酶中性磷酸酶碱性磷酸酶。可见,在茶树生产管理过程中应适当提高磷肥的施用量,老茶树应当加强土壤松耕,以提高土壤中抗性酶活性。     

黄土高原旱地轮作与施肥长期定位试验研究 Ⅱ.土壤酶活性与土壤肥力

本文分析了长期试验土壤酶活性与土壤有机C、全N、有效P含量、主要微生物类群之间的关系。相关分析表明,土壤脲酶、碱性磷酸酶、蛋白酶活性随土壤有机C含量的增加而增加,蔗糖酶、过氧化氢酶活性与有机C之间的关系因施肥种类及种植方式的不同而不同;微生物数量仅真菌与脲酶、蛋白酶活性之间的相关性达到显著水平。除过氧化氢酶外,其它4种酶的活性均与当年种植冬小麦处理的产量存在显著相关关系。利用主成分分析与通径分析揭示了土壤酶活性与养分之间的内在关系及酶活性对土壤养分的影响。根据主成分分析结果,旱地土壤肥力状况用脲酶、碱性磷酸酶、蛋白酶活性作为综合评价指标优于过氧化氢酶与蔗糖酶。     

Changes in enzyme activities of spruce (Picea balfouriana) forest soil as related to burning in the eastern Qinghai-Tibetan Plateau

The effect of forest fire on soil enzyme activity of spruce (Picea balfouriana) forest in the eastern Qinghai-Tibetan Plateau was assessed. Six specific enzymes were chosen for investigation: invertase, acid phosphatase, proteinase, catalase, peroxidase and polyphenoloxidase. It was found that the activities of invertase and proteinase were reduced by burning, but the activities of acid phosphatase, polyphenoloxidase and peroxidase increased. Meanwhile, burning significantly (P < 0.05) resulted in the decrease of concentrations of available N and K of 0–20 cm depth layer soil, and significantly (P < 0.05) decreased concentrations of organic matter content, total N and P, as well as available N, P and K in soil at both 20–40 and 40–60 cm depths except for available P at 20–40 cm soil depth. These results illustrated that burning could influence the enzyme activities and chemical properties of soil not only of upper but also lower soil layers. Correlation analysis indicated that invertase activities in 0–20 cm depth layer soil were significantly positively correlated with organic matter, total N and P, as well as available N and P. Furthermore, all six enzymes studied were sensitive to fire disturbance, and thus could be used as indicators of soil quality. Our study also showed that soil enzyme activities were associated with soil depth, decreasing from top to bottom in both burned and unburned spruce forests. The distribution pattern of soil enzyme activities suggested that the rate of organic matter decomposition and nutrient cycling depended on soil depth, which had important structural and functional characteristics in nutrient cycling dynamics and implications in plantation nutrient management. The finding that burning effects on enzyme activities and soil properties between different soil layers were homogenized was attributed to the 8-years’ regeneration of forest after burning.     

Effect of Transgenic Bt Cotton on Bioactivities and Nutrients in Rhizosphere Soil

The influence of transgenic Bacillus thuringiensis (Bt) cotton (BtXincai1) and its corresponding nontransgenic isoline (Xincai1) on the microorganisms, enzyme activity, and nutrient content of rhizosphere soil was studied through experiments in potted plants. The calcareous drab soil samples were collected (0–15 cm deep) from an experimental field in Shanxi Agricultural University (China) in 2005. The pots were categorized in different groups with replicates for each variety (transgenic BtXincai1 and general Xincai1). The rhizosphere soil samples were collected at different growth periods (seedling, bud, flowering, peak boll, boll opening, and harvest). The Bt protein and other microbial properties in the soil samples were determined by using selected methods (material and methods session). The results demonstrated that the concentration of the Bt protein in the rhizosphere soil of BtXincai1 reached a peak at 56.14 ng g^?1 during the flowering period. However, the Bt protein would not continuously accumulate in the soil. The rhizosphere soil of BtXincai1 was more suitable for the growth and proliferation of bacteria and fungi but it had no significant impact on the number of actinomycetes. BtXincai1 had some inhibitory effects on alkaline phosphatase activity in the rhizosphere soil, and it might promote dehydrogenase activity during the blooming period. However, it had no significant influence on protease, urease, or sucrase activities. Further, it had no significant impact on the contents of organic matter, total nitrogen, available nitrogen, or potassium in rhizosphere soil. It could significantly decrease the content of available phosphorus during the flowering period. Based on this study, the sensitive reactions of microorganisms and the activities of alkaline phosphatase and dehydrogenase might be considered as three potential indexes for assessing the risk posed by transgenic Bt cotton to soil ecology.