毛竹和林下植被芒箕凋落物分解特征研究

[目的]探讨竹林与其林下植被凋落物叶之间相互影响的潜在机制,为合理经营管理毛竹林林下植被提供理论参考。[方法]采用原位分解袋法研究了四川长宁毛竹与林下植被芒箕凋落物叶分解和养分释放过程。[结果](1)芒箕凋落物叶初始C、N、P含量和羟基碳高于毛竹(P 0. 05),而C∶N、C∶P、烷基碳、氧烷基碳和芳香碳低于毛竹(P 0. 05)。(2)凋落物叶分解和养分释放速率芒箕整体高于毛竹,芒箕和毛竹分解常数(k)分别为0. 58±0. 03和0. 73±0. 02,C、N、P养分释放均表现为净释放。(3)凋落物叶混合对分解速率没有显著影响,但抑制了N、P元素整个分解周期和C元素中后期的释放。(4)凋落物叶分解过程中元素含量变化格局表现为C含量和C∶N比整体呈下降趋势,N含量和N∶P比有小幅上升,P含量有微弱的下降趋势,C∶P比呈波动性变化。(5)凋落物叶分解速率与土壤温度、初始凋落物叶N和P含量呈显著正相关(P 0. 01),与初始凋落物叶的C∶N和C∶P呈极显著负相关(P 0. 01),与土壤含水量相关不显著。[结论]单独分解过程中,毛竹凋落物叶分解速率低于林下植被芒箕,养分释放特征均表现为直接释放;混合分解过程中,毛竹和芒箕凋落物叶分解速率无显著混和效应,但养分释放的混合效应表现出一定负效应和不同阶段性。     

模拟氮沉降对华西雨屏区天然常绿阔叶林凋落叶分解过程中K、Ca、Mg元素释放的影响

[目的]研究氮沉降背景下凋落叶分解过程中钾(K)、钙(Ca)、镁(Mg)元素的释放动态,揭示森林生态系统在氮沉降持续增加背景下养分元素的循环过程。[方法]在华西雨屏区天然常绿阔叶林中设置对照(CK)、低氮(L)、中氮(M)和高氮沉降(H)4个处理,以NH4NO3为氮源,采用尼龙网袋法对凋落叶进行模拟氮沉降分解试验,研究了凋落叶分解过程中K、Ca、Mg元素浓度及残留率,探讨氮沉降对凋落叶分解过程中养分释放的影响。[结果]经过1年的分解,模拟氮沉降显著抑制了凋落叶分解过程中K元素浓度的下降,显著促进了Ca元素浓度的下降,对Mg元素浓度无显著影响。在各处理中,K元素呈净释放模式,Ca元素表现为释放-富集的交替模式,Mg元素呈富集-释放模式,模拟氮沉降未改变凋落叶分解中K、Ca、Mg元素的释放模式。分解1年后,L、M和H处理的K元素残留率分别比CK高3.91%、10.27%和13.91%,模拟氮沉降显著抑制了凋落叶分解过程中K元素的释放;L、M和H处理的Ca元素残留率分别比CK低6.39%、6.51%和15.93%,模拟氮沉降显著促进了凋落叶分解过程中Ca元素的释放;L、M和H处理的Mg元素残留率与CK差异不显著,模拟氮沉降对凋落叶分解过程中Mg元素的释放无显著影响。[结论]模拟氮沉降未改变凋落叶分解过程中K、Ca、Mg元素的释放模式,但对凋落叶分解过程中K、Ca、Mg元素的释放速率产生了不同的影响。     

华西雨屏区常绿阔叶林凋落叶分解过程中木质素降解对模拟氮、硫沉降的响应

[目的]探索亚热带常绿阔叶凋落叶分解过程中木质素降解对氮、硫沉降的响应。[方法]采用氮、硫双因素3水平试验设计方法,设置对照(CK)、低氮(LN, 50 kg·hm~(-2)·a~(-1))、高氮(HN, 150 kg·hm~(-2)·a~(-1))、低硫(LS, 200 kg·hm~(-2)·a~(-1))、高硫(HS, 400 kg·hm~(-2)·a~(-1))、低氮低硫(LNLS)、高氮低硫(HNLS)、低氮高硫(LNHS)和高氮高硫(HNHS)9个处理,分析氮、硫沉降对华西雨屏区常绿阔叶林凋落叶分解过程中木质素降解的影响。[结果]模拟氮、硫沉降1年时间,LN、LNLS和HNLS对木质素残留率、多酚氧化酶和过氧化氢酶活性的影响不显著;LS显著降低了木质素残留率,显著增加了凋落叶C/N、纤维素损失率、多酚氧化酶和过氧化物酶活性;HN、HS、LNHS和HNHS显著增加了木质素残留率,显著降低了凋落叶C/N、纤维素损失率、多酚氧化酶和过氧化物酶活性;氮沉降和硫沉降对木质素降解的交互作用显著。[结论]不同氮、硫沉降水平对华西雨屏区常绿阔叶林凋落叶分解过程中木质素降解及相关酶的影响不同,在氮、硫沉降量持续增加的背景下,氮、硫沉降相互作用,共同影响凋落叶分解过程中木质素的降解,进而影响凋落叶分解过程。     

模拟氮沉降对华西雨屏区巨桉林凋落叶分解的影响

2008-01—2010-01,对华西雨屏区巨桉人工林进行氮沉降模拟试验,氮沉降水平分别为对照(CK,0gN.m-2a-1)、低氮(5gN.m-2a-1)、中氮(15gN.hm-2a-1)和高氮(30gN.m-2a-1),把年施氮量分12等份,每月下旬对各处理施氮(NH4NO3),探讨氮沉降持续增加对巨桉凋落叶分解和养分释放过程的影响,及巨桉凋落叶分解过程中是否存在限制值。结果表明:巨桉凋落叶在分解初期存在一个质量快速损失的淋溶期,而分解后期(14个月以后)质量损失极其缓慢,残留凋落物处于较稳定状态;氮沉降显著抑制了巨桉凋落叶后期分解,并且低氮处理抑制作用最强,但氮沉降对凋落物养分释放过程无明显影响;自然分解状态下,巨桉凋落叶分解限制值大约为90%(CK),而氮沉降使得这一限制值降低,并且低氮(限制值大约为72%)与对照之间差异达到显著水平。     

毛竹叶片生物量、养分及与土壤的耦合特征

叶片对植物的生长、发育和生活史的完成具有极其重要的作用,叶生物量(叶量)及其养分含量将直接影响树体对光能的接收与利用,而土壤为植物的生长发育提供了所需的养分元素。本研究对不同年龄毛竹的叶量、叶片和土壤养分含量及其相互关系进行了研究。结果表明:(1)毛竹叶量随着径阶的增大而增大。(2)5块样地中,样地1和3的毛竹叶量明显高于其他3块样地,样地4的毛竹叶量最小。(3)毛竹叶片中镁含量随着年龄的变化差异不显著(p>0.05);氮、总磷、有机磷、钾、钙含量在1度毛竹叶片与其他年龄毛竹叶片含量差异显著(p<0.05);2度以上各年龄毛竹叶间氮含量差异显著(p<0.05);毛竹叶无机磷含量仅1度竹叶与4度竹叶含量差异显著(p<0.05);叶片中的氮磷比值(N/P)随年龄增加先增大后减小;相同年龄不同径阶毛竹的叶片养分含量虽有变化却不存在显著差异(p>0.05)。(4)竹叶中氮含量与有机磷、全磷、钾、钙含量呈极显著相关(p<0.01);总磷、无机磷、有机磷含量与钙、钾含量显著相关(p<0.05);钾与钙含量呈极显著负相关(p<0.01)。(5)毛竹林土壤pH值与叶片镁含量显著负相关(p<0.05);土壤中镁含量与叶片中钙含量显著负相关(p<0.05),而与叶片全氮、总磷、有机磷、镁含量呈极显著负相关(p<0.01)。     

模拟氮沉降对毛竹非结构性碳的影响

【目的】分析不同强度氮沉降对毛竹体内非结构性碳水化合物(NSC)含量的影响,为全面认识氮沉降对毛竹林生态系统的影响提供科学依据。【方法】在临安市毛竹林长期试验基地,采用典型选样法,设置12块20 m×20 m样地,包括低氮(30 kg·hm~(-2)a~(-1))、中氮(60 kg·hm~(-2)a~(-1))、高氮(90 kg·hm~(-2)a~(-1))和对照(0 kg·hm~(-2)a~(-1))4种处理,每处理设3个重复样地,处理32个月,探讨模拟氮沉降对1龄和3龄毛竹NSC含量的影响。【结果】可溶性糖和淀粉在NSC中所占比例分别为80%和20%,NSC主要以可溶性糖的形式存在;竹叶NSC含量最高,分别是枝和秆的1.32和1.27倍;3龄竹枝和秆NSC含量显著高于1龄竹(P0.05),竹龄对竹叶NSC含量影响不显著(P0.05);氮沉降显著降低毛竹叶、3龄竹枝和1龄竹秆的NSC含量(P0.05);氮沉降和竹龄的交互作用对毛竹枝、秆的NSC含量影响显著(P0.01),对毛竹叶影响不显著。【结论】氮沉降显著影响毛竹地上器官的NSC含量及其分配,且随竹龄而显著变化,高强度的氮沉降不利于毛竹NSC的积累和固碳。     

模拟N沉降对滇中亚高山典型森林凋落物分解及土壤微生物的影响

[目的]模拟N沉降下凋落物分解及土壤微生物特征,为研究森林生态系统碳、氮循环对氮沉降的响应机制提供依据。[方法]以滇中亚高山常绿阔叶林、华山松(Pinus armandii)林、高山栎(Quercus semicarpifolia)林和云南松(Pinus yunnanensis)林凋落物为研究对象,采用凋落物袋法,于2018年2月至2019年1月,通过模拟N沉降和原位分解实验,研究不同模拟N沉降下(CK, 0;LN, 5;MN, 15;HN, 30 g·m~(-2)·a~(-1))凋落物碳氮、土壤微生物量碳(MBC)、微生物量氮(MBN)及土壤微生物数量变化特征。[结果]分解1年后,不同N沉降处理下,常绿阔叶林和高山栎林凋落物C含量均显著增加(0.40%～8.16%),华山松林和云南松林凋落物C含量呈LN减少(2.67%),HN增加(4.09%);各林分凋落物N含量均显著增加(1.45%～69.01%),C/N则显著降低(0.34%～37.92%);相同N沉降下土壤微生物量随土层的加深而减小,N沉降对土层垂直分布格局影响不显著;N沉降对常绿阔叶林和高山栎林土壤MBC和MBN的影响表现为抑制,对华山松林和云南松林表现为低N促进,高N抑制;4种林分土壤MBC/MBN介于5.31～11.26之间,N沉降对不同林分不同土层的MBC/MBN影响存在差异,但均受到高N的抑制作用。[结论]滇中亚高山4种典型森林凋落物分解主要受森林类型影响,N沉降次之;土壤微生物量和数量主要受森林类型影响,土壤深度次之,N沉降最小。     

增温和氮添加对中亚热带杉木人工林土壤氮矿化和N2O排放的影响

[目的]研究增温和氮沉降对中亚热带森林土壤氮矿化和氧化亚氮(N₂O)排放的影响,以期深入认识全球变化背景下中亚热带森林土壤氮循环过程。[方法]选取经过野外增温和氮添加处理的中亚热带杉木人工林土壤,将野外非增温处理和增温处理的土壤置于不同温度(20、25℃)培养箱中,同时对野外氮添加处理的土壤继续添加不同梯度的氮素(0.1、0.2 g·kg^-1,以干土计),进行为期28 d的室内培养,研究增温和氮添加对土壤氮矿化和N₂O排放的影响。[结果]与对照相比,增温和氮添加及二者交互处理增加了土壤铵态氮、硝态氮和矿质氮含量,且氮添加水平越高增加越明显,增温处理增加不显著。与对照相比,培养28 d后增温处理的土壤净铵化速率、净硝化速率和净氮矿化速率变化不显著,低氮、增温+低氮显著增加土壤净硝化速率,而高氮、增温+高氮显著降低土壤净氮矿化速率。与对照相比,增温和氮添加及二者交互处理总体降低土壤N₂O排放速率,土壤N₂O累积排放量也显著降低(P<0.05),其中,单独增温、低氮、高氮、增温...     

施氮条件下森林凋落物分解早期的碳和氮动态

通过13周实验室培养试验,研究了施氮和树种对森林凋落物早期分解过程中碳和氮动态的影响,新鲜凋落物样品包括针叶（红松）和两种阔叶（蒙古栎和紫椴）,采自长白山北坡阔叶红松林。试验共包括3个施氮梯度（0、30和50kg&#183;ha^-1．a^-1 NH4NO3）。以质量减少和呼吸速率表征的凋落物分解速率随可溶性氮的增加而显著增加,阔叶凋落物质量减少和累积CO2—C释放量比针叶凋落物高,不同物种之间凋落物沥出物中溶解性有机碳（DOC）浓度变化较大,但施氮处理对DOC的影响不大。除了施氮率,施氮处理和物种对凋落物沥出物中溶解性有机氮（DON）浓度都没有显著影响。有52—78％的外加氮滞留在凋落物中,氮滞留率与凋落物质量减少呈正相关（R^2=0．91,P〈0．05）,这表明易分解凋落物覆盖的森林地面比分解较慢的凋落物覆盖的森林地面有更高的N汇潜力。图3表1参40。     

不同种植年限尾巨桉人工林叶片-凋落物-土壤碳氮磷化学计量特征

[目的]为了解雷州半岛尾巨桉速生人工林生态系统的C、N、P分配格局及化学计量特征。[方法]采用空间换时间的方法,选取雷州半岛4种不同林龄(1、3、5、7 a)的尾巨桉人工林为研究对象,对尾巨桉叶片、凋落物及土壤的C、N、P含量及化学计量特征进行测定分析。[结果]表明:C、N含量表现为叶片凋落物土壤,P含量表现为叶片土壤凋落物,且3个库间差异显著;土壤的C含量随林龄增加而增加,N、P含量差异不显著,土壤C∶N随林龄的增加而增加,说明土壤有机质分解速率逐渐下降;凋落物的C∶N为54. 07 92. 18 ( 25),表明尾巨桉林下凋落物分解速率较慢,N元素成为主要限制凋落物分解的元素,凋落物的C∶N随林龄的增加先增加后下降,凋落物分解速度先降低后升高;叶片的N∶P为10. 80 12. 98,说明中幼林龄尾巨桉受N限制较明显。相关性分析表明:凋落物养分元素含量受叶片限制,土壤养分含量受凋落物限制,表明生态系统内部C、N、P元素在植物、凋落物与土壤之间实现了运输和转换。[结论]雷州半岛尾巨桉中、幼林龄时期土壤有机质及凋落物分解速率较慢;随林龄的增加,土壤有机质、凋落物分解速率下降,N元素成为其主要分解限制性元素,林分生长受N限制明显。     

Vertebrate and insect pests and hemi-parasitic plants of Parkia biglobosa and Vitellaria paradoxa in Nigeria

This study investigated the occurrence and diversity of hemi-parasitic plants, vertebrate and insect pest species of Parkia biglobosa (Keay), and Vitellaria paradoxa (Gaertn.) as well as the strategies for their control in the parklands of the Nigerian humid savanna. Results indicated that of the two major hemi-parasitic plants encountered, Tapinanthus globiferus was the more widespread with wider host range than T. dodonifolius. Mechanical control by cutback of infested branches was ineffective for both species. The major vertebrate pests consist of 6 avian species from 3 families: Nectaridae, Plocidae and Cuculidae; a fruit bat, Epomops frangueti and an unidentified squirrel. The species fed on both the fruits of the trees and the seeds of the hemi-parasitic plants. Twenty insect species from 14 families were encountered on P. biglobosa compared to 33 species from 17 families on V. paradoxa in all the ecological zones covered in the study. Species diversity was comparatively higher in the fallow than in the cultivated land. The majority of the insects encountered was of little significance and may not warrant application of control. Cirina forda (Saturnidae:lepidoptera) was a major pest causing 60%–90% defoliation of mature trees of V. paradoxa. All larval stages were destructive but control at this stage is not advised because it provides incidental source of food to locals. Control after pupation using a slow-release insecticide with a soil penetration depth of 15–20 cm is suggested.This revised version was published online in November 2005 with corrections to the Cover Date.     

Populations of adult fungus gnats and shore flies in British Columbia container nurseries as related to nursery environment,and incidence of fungi on the insects

Adult fungus gnat and shore fly populations were monitored in four container nurseries near Victoria, British Columbia. In general, populations of both insects were larger in summer than in winter. Also, both insects were more abundant in the nursery with a plastic-covered, soil floor, which favored moisture accumulation and build up of algae, liverworts and mosses, than in nurseries with other types of floors such as cement. Results of fungus isolations revealed that gnats and flies both harbor the seedling pathogens Botrytis cinerea and species of Fusarium and Phoma, plus several non-pathogenic fungi. The results are discussed in relation to nursery sanitation practices, their effects on gnat and fly populations, and some possible roles of these insects in seedling disease epidemiology.     

Trees and shrubs as sources of fodder in Australia

Experience with browse plants in Australia is briefly reviewed in terms of their forage value to animals, their economic value to the landholder and their ecological contribution to landscape stability. Of the cultivated species only two have achieved any degree of commercial acceptance (Leucaena leucocephala and Chamaecytisus palmensis). Both of these are of sufficiently high forage value to be used as the sole source of feed during seasonal periods of nutritional shortage. Both are also leguminous shrubs that establish readily from seed. It is suggested that a limitation in their present use is the reliance on stands of single species which leaves these grazing systems vulnerable to disease and insects. Grazing systems so far developed for high production and persistence of cultivated species involve short periods of intense grazing followed by long periods of recovery. Similar management may be necessary in the arid and semi-arid rangelands where palatable browse species are in decline.     

Rehabilitation of diseased cacao fields in Peru through shade regulation and timing of biocontrol measures

The objective of this case study was to test the effectiveness of biocontrol for the rehabilitation of abandoned, diseased (moniliasis, witches' broom and black pod) cocoa and to develop testable hypotheses regarding the effect of shade and biocontrol timing. Three trial fields differed in their shade regimes. Biocontrol was administered starting either at flowering or pod filling. Disease incidence and yield were compared with cultural control alone. Biocontrol reduced moniliasis from 49% to 25%, independent of the shading regime and application time. Witches' broom was most severe without shade and unaffected by biocontrol. No significant effects on black pod were observed. Although biocontrol increased percentage healthy fruit independent of shading and timing, only the shaded plot with biocontrol from flowering onwards responded with increased yield. Our hypothesis is: 'In the rehabilitation of abandoned cacao, only fields under sustainable shade management and early onset of biocontrol can realise their production potential.' This revised version was published online in June 2006 with corrections to the Cover Date.     

Growth, nitrogen fixation and mineral acquisition of Alnus sieboldiana after inoculation of Frankia together with Gigaspora margarita and Pseudomonas putida

The role of tetrapartite associations among Frankia, Gigaspora margarita (an arbuscular mycorrhizal fungus), Pseudomonas putida (rhizobacterium), and Alnus sieboldiana in growth, nitrogen fixation, and mineral acquisition of A. sieboldiana was investigated. Seedlings of A. sieboldiana were inoculated with Frankia isolated from root nodules of alder, followed by inoculation of G. margarita and P. putida, and were grown for 5 months in a greenhouse. The seedlings inoculated with Frankia and G. margarita together produced the highest biomass of shoots and root nodules. Nitrogen-fixation activity, measured by acetylene reduction assay, was observed when Frankia was inoculated. The activity, on a per-nodule gram basis, decreased after G. margarita inoculation, but on a per-plant basis there was no significant difference in the activity among inoculation treatments. The mineral content in the seedlings changed after inoculation with Frankia, but not after inoculation with P. putida and/or G. margarita. The results showed a synergistic interaction among Frankia, the mycorrhizal fungus, and the rhizobacterium on the growth of A. sieboldiana.     

Root diseases in bareroot and container nurseries of the Pacific Northwest: epidemiology, management, and effects on outplanting performance

In forest and conservation nurseries in the Pacific Northwest USA, seedling production can be limited by root diseases caused by fungi in the genera Fusarium Link:Fr., Cylindrocarpon Wollenw., Phytophthora de Barry, and Pythium Pringsh. Fusarium, Cylindrocarpon, and Pythium are the most ubiquitous, whereas incidence of Phytophthora is mostly associated with coastal bareroot nurseries. All of these root pathogens are encouraged by water saturated soils or media. Seedlings infected with Fusarium, Phytophthora, or Pythium often appear chlorotic or necrotic with extensive root decay. Cylindrocarpon often causes serious root decay without shoot symptoms. The best approach to mitigate losses from these diseases is to use a holistic integrated pest management program. This program should combine chemical controls with cultural practices, particularly those that increase soil permeability and drainage and reduce potential sources of inoculum, especially by disinfesting seeds and containers reused for crops. In general, we found that seedlings meeting nursery specifications for outplanting on forest soil (proper height, root collar diameter, healthy shoot color, lack of disease symptoms) but having these disease organisms on their root systems perform as well as non-infected seedlings.     

Biomass and production of fine and coarse roots of trees under agrisilvicultural practices in north-east India

An understanding of the rooting pattern of tree species used in agroforestry systems is essential for the development and management of systems involving them. Seasonal variation, depth wise and lateral distribution of biomass in roots of different diameter classes and their annual production were studied using sequential core sampling. The investigations were carried out in four tree species under tree only and tree+crop situations at ICAR Research Farm, Barapani (Meghalya), India. The tree species were mandarin (Citrus reticulata), alder (Alnus nepalensis), cherry (Prunus cerasoides) and albizia (Paraserianthes falcataria). The contribution of fine roots to the total root biomass ranged from 87% in albizia to 77% in mandarin. The bulk of the fine roots (38% to 47%) in the four tree species was concentrated in the upper 10 cm soil layer, but the coarse roots were concentrated in 10–20 cm soil depth in alder (46%) and albizia (51%) and at 0–10 cm in cherry (41%) and mandarin (48%). In all the four tree species, biomass of both fine- and coarse-roots followed a unimodal growth curve by showing a gradual increase from spring (pre-rainy) season to autumn (post rainy) season. Biomass to necromass ratio varied between 2 to 3 in the four tree species. The maximum (3.2) ratio was observed during spring and the minimum (2) in the rainy season. In alder and albizia, the fine roots were distributed only up to 1 m distance from the tree trunk but in the other two species they were found at a distance up to 1.5 m from the tree trunk. The annual fine root production varied from 3.6 Mg ha^–1 to 6.2 Mg ha^–1 and total production from 4.2 to 8.4 Mg ha^–1 in albizia to mandarin, respectively. Cherry and mandarin had a large number of woody roots in the surface layers which pose physical hindrance during soil working and intercultural operations under agroforestry. But the high biomass of roots of these two species may be advantageous for sequential or spatially separated agroforestry systems. However, alder and albizia have the most desirable rooting characteristics for agroforestry systems.This revised version was published online in November 2005 with corrections to the Cover Date.     

Antinephritis and radical scavenging activity of prenylflavonoids

Antinephritis activity of 5 prenylflavonoids similar to glabridin (1-5), isolated from Morus alba, Artocarpus communis, Glycyrrhiza uralensis and G. inflata, was evaluated in mice with glomerular disease (Masugi-nephritis). Oral administrations of artonin E (2) or licochalcone A (4) for 10 days (30 mg kg(-1) day(-1)) reduced the amount of urinary protein excretion compared to nephritic mice. ESR spectroscopy demonstrated that morusin (1) and licorisoflavan A (5) increased the radical intensity of sodium ascorbate by about two times. Morusin, licoricidin (3), licochalcone A and licorisoflavan A showed weak scavenging activity against superoxide anion radical.     

Decomposition and nutrient loss from prunings of different contour hedgerow species in tea plantations in the sloping highlands of Sri Lanka

Contour hedgerows of multipurpose tree species in the sloping tea lands of Sri Lanka are expected to reduce soil erosion and also add significant amounts of plant nutrients to the soil via periodic prunings. The objective of this experiment was to characterize the biomass decomposition pattern and quantify the amount of nutrients added through prunings of six tree species (Calliandra calothyrsus, Senna spectabilis, Euphatorium innulifolium, Flemingia congesta, Gliricidia sepium and Tithonia diversifolia) currently being used in hedgerows associated with tea. Withered leaf and stem prunings (50 g) were enclosed in 2-mm litter bags, placed at 5-cm depth and retrieved after one, three, six, nine and 12 weeks. Loss of initial dry weight, N, P and K was measured. Single exponential decay function adequately described both dry weight and nutrient loss. Tree species differed significantly in their rate of breakdown with decomposition constants (k) varying from 0.0299 to 0.2006 week⁻¹ for leaves and from 0.0225 to 0.0633 week⁻¹ for stems. Gliricidia showed the highest k for leaves with the rest in the following descending order: Senna > Tithonia ≥ Euphatorium > Calliandra > Flemingia. A similar pattern was observed for loss of all nutrients with Calliandra and Flemingia always having lower k values than the rest. Although N immobilization was not observed, immobilization of P and K was observed during the first week of incubation in some species, particularly in stem prunings. Annual biomass of prunings differed significantly between tree species in the following descending order: Calliandra > Senna > Flemingia > Tithonia > Gliricidia > Euphatorium. Calliandra added the greatest amount of nutrients annually to the soil with Euphatorium adding the least. Calliandra prunings provided the annual total K requirement and 49% of the N requirement of mature tea. However, none of the species provided more than 5% of the P requirement. It is concluded that among the tree species tested, Calliandra and Flemingia are the most suitable for contour hedgerows in tea plantations of this agroclimatic region because of their higher soil nutrient enrichment capacity and slower decomposition rates which would minimize leaching losses. This revised version was published online in June 2006 with corrections to the Cover Date.     

兰花致病真菌拮抗细菌的筛选与鉴定

[目的]为获得高效拮抗3种兰花病原真菌胶孢炭疽菌、尖孢镰孢菌和腐皮镰孢菌的菌株。[方法]使用平板对峙法筛选拮抗菌株,结合形态特征观察、生理生化试验和16S rRNA基因序列分析的方法对目的菌株进行鉴定。[结果]筛选获得5株同时拮抗三种病原菌的菌株,其中菌株GT312拮抗效果明显。16S rRNA基因序列分析显示,该菌株与Bacillus amyloliquefaciens(模式菌株FZB42T)相似性最高,为99.93%。菌株形态特征观察、生理生化试验结果与B.amyloliquefaciens描述一致。[结论]菌株GT312可同时拮抗3种兰花病原真菌,鉴定为解淀粉芽孢杆菌,为兰花病害的生物防治提供了菌株资源。