外源氮添加对高寒草地门源草原毛虫种群密度的影响

近几十年以来,中国陆地生态系统的大气氮沉降持续增加。这种外源氮输入会影响植物多样性和生产力,进而影响植食性昆虫的种群动态。门源草原毛虫(Gynaephora menyuanensis)是青藏高原东北部高寒草地的主要植食性昆虫,种群数量爆发时会造成巨大的生态经济损失。为了探明草原毛虫种群密度如何响应氮沉降加剧,依托青海海北高寒草地“外源氮添加梯度”控制实验平台(0、25、50、100 kg N hm^-2 a^-1),详细调查了门源草原毛虫的种群密度及其相关的食物数量、质量和栖息地环境变化。结果表明：(1)外源氮添加显著影响门源草原毛虫的虫口密度(ANOVA:F=3.29,P=0.04),且草原毛虫虫口密度随氮添加量的增加呈线性增加趋势(R~2=0.31,P=0.005)。(2)外源氮添加梯度下,食物质量(叶片氮含量),而非食物数量(植物地上生物量和禾草地上生物量)和栖息地环境(土壤温度、湿度和光照条件),是草原毛虫虫口密度变化的关键影响因素。基于上述结果,可以预测：未来氮沉降的加剧可能促进青藏高原高寒草地门源草原毛虫的虫害爆发。研究将为全球变化背...     

Influence of rainfall,temperature and somes oil physico-chemical variables on seasonal population structure and vertical distribution of earthworms in two semi-arid tropical grassland soils

Two semi-arid tropical grasslands, one of an alfisol and the other on vertisol were sampled for earthworm populations during July 1985 to July 1987. The soil of the alfisol grassland was slightly acidic while that of the vertisol was slightly alkaline. The alfisol grassland has a lower range of soil moisture, soil temperature, electrical conductivity, organic carbon, available nitrogen and potassium, and a higher range of phosphorus compared to the vertisol. The alfisol grassland was inhabited byOctochaetona phillotti (Michaelsen) with rare occurrence ofBarogaster annandalei (Stephenson) whereas the vertisol grassland was inhabited only byB. annandalei. The total population ofO. phillotti ranged between 16 and 96/m² while its juvenile population ranged between 3.2 and 25.6/m², pre-adult population between 5.3 and 53.6/m² and adult population between 0 and 28.8/m². The total population ofB. annandalei ranged between 3.2 and 58.3/m² and its juvenile population between 0 and 26.6/m², pre-adult population 0 and 10.6/m² and adult population between 0 and 22.4/m². The earthworms migrated to deeper layers during winter and summer,O. phillotti reaching a maximum depth of 40 cm andB. annandalei reaching a depth of 45 cm, and seen in quiescent stage. Their seasonal population structure was significantly influenced by the seasonal patterns in rainfall, soil temperature, pH, electrical conductivity and phosphorus. These variables along with organic carbon, available nitrogen and potassium together accounted for 32–63% and 79–91% respectively, of the variation in seasonal population fluctuation of differentO. phillotti andB. annandalei age groups. The physical factors of the soil were collectively more effective in causing the seasonal variation in their population size than the chemical factors.Visiting scientist (under the Rockefeller Foundation Environmental Research Fellowship in International Agriculture) in Resource Management Programme of ICRISAT, Andhra Pradesh, India     

川西北高寒草地沙化过程中土壤氮素变化特征

草地沙化是我国最严重的环境问题之一,但关于草地沙化过程中氮素变化特征的研究报道多集中于干旱半干旱地区,而半湿润地区的相关报道还比较缺乏。通过野外调查,研究了川西北半湿润地区高寒沙质草地沙化过程中土壤氮素变化特征。结果表明,草地沙化对0—100cm土层土壤氮素具有显著影响,全氮、碱解氮、铵态氮(NH_4~+-N)、硝态氮(NO_3~--N)和微生物量氮(MBN)均呈现极显著下降的变化特征,极度沙化阶段较未沙化阶段分别减少了73.95%、77.72%、76.75%、79.77%和84.12%。其中,0—20cm土层变化最显著,全氮、碱解氮、NH_4~+-N、NO_3~--N和MBN含量分别减少了86.43%、83.52%、82.11%、88.82%和91.77%。随着土层深度增加,不同程度沙化草地土壤氮素含量及其变化量逐渐减少;草地沙化过程中,不同沙化阶段土壤氮素损失数量不尽相同,其中,以轻度沙化阶段氮素损失最严重,全氮、碱解氮、NH_4~+-N、NO-3-N和MBN含量分别降低了41.18%、35.17%、46.74%、43.46%和46.88%。草地沙化过程中,土壤全氮、碱解氮、NH_4~+-N、NO_3~--N和MBN含量与土壤粉粒、粘粒含量和植被群落盖度均呈极显著正相关特征,与土壤沙粒含量呈极显著负相关特征。研究区土壤氮素损失与风蚀选择性吹蚀土壤粉粒、粘粒及地表植物覆盖状况逐渐变差密切相关,因此该区域治沙的关键是采取措施降低风蚀对地表土壤吹蚀作用,提高沙化草地地表植被覆盖。同时,还应及时对沙化前期阶段及潜在沙化的草地进行生态治理,从而避免草地沙化继续恶化。     

Altitudinal gradients of grassland carbon and nitrogen isotope composition are recorded in the hair of grazers

Aim The hair of grazers provides an isotopic record of environmental and nutritional signals. Here, we assess the effect of altitude on the carbon and nitrogen isotope composition of the hair of ruminant grazers and its relation to grassland vegetation, to evaluate the use of hair isotope data for ecosystem reconstruction, animal nutritional ecology and biogeochemical studies in montane environments. Location European Alps. Methods We sampled grassland vegetation (pure C₃) and the hair of ruminants along an altitudinal gradient (400–2500 m), and analysed their isotope composition (δ¹³C and δ¹⁵N). Results were compared with published effects of altitude on ¹³C in C₃ plants at the species level and on ¹⁵N at the community level. The study was complemented with a comparison of diet and hair isotope composition in ruminants held in confinement. Results δ¹³C of hair increased (c. 1.1‰ km⁻¹) and δ¹⁵N decreased (c. 1.1‰ km⁻¹) with altitude. The same changes occurred in local grassland vegetation, and in regional to global grassland data sets. Offsets between hair and vegetation ¹³C or ¹⁵N (‘diet–hair shift’) were independent of altitude. Sheep (Ovis aries) and cattle (Bos taurus) exhibited a ¹³C shift near +3‰, but that of goats (Capra hircus) was larger (+4.2‰) in alpine environments and in confinement. The diet–hair shift for ¹⁵N was more variable (+2.1 to +3.6‰). Main conclusions Grazer hair provides a faithful spatially and temporally integrated record of grassland isotope composition, useful for ecosystem and environment reconstruction. The effect of altitude on hair ¹⁵N is important for studies of trophic relationships: an altitude shift of 2000 m produced the same effect in hair ¹⁵N as would a shift from an animal tissue‐based to a plant‐based diet. The similarity of altitude effects on δ¹³C of individual plant species, vegetation and hair indicates that the effect of altitude on species‐level ‘intrinsic water use efficiency’ scales up linearly to the community and landscape level.     

SHORT-TERM IMPACTS OF FORMULATIONS OF BACILLUS THURINGIENSIS VAR. ISRAELENSIS DE BARJAC AND THE ORGANOPHOSPHATE TEMEPHOS,USED IN BLACKFLY (DIPTERA: SIMULIIDAE) CONTROL,ON RHEOPHILIC BENTHIC MACROINVERTEBRATES IN THE MIDDLE ORANGE RIVER,SOUTH AFRICA

Summary

The impacts of larvicides used in the control of blackflies (Diptera: Simuliidae) on macroinvertebrates in the stones-in-current biotope were assessed during 8 field trials in the middle Orange River, South Africa. Two Bacillus thuringiensis var. israelensis (B.t.i.) products (Vectobac^R 12AS and Teknar^R HP-D) and the organophosphate temephos (Abate^R 200EC) were applied at recommended and high dosages to simulate “operational” and “worst-possible” scenario's respectively. Mortality was evaluated either by direct counting of invertebrates on stones before and after application, or by ranking invertebrates on a 4-point relative abundance scale before and after application. In addition, the re-appearance of benthic invertebrate population densities after temephos application was examined.

At the recommended dosage (1.2 ppm/10 min), B.t.i. significantly reduced blackfly larval numbers (P<0.001) and those of the chironomid Rheotanytarsus fuscus Freeman (P<0.05). At high dosage (20 ppm/10 min), numbers of the filter-feeding mayfly Tricorythus discolor (Burmeister) (P<0.01) and the chironomid Cardiocladius sp. (P<0.05) were also significantly reduced. No Simulium predators were directly affected by B.t.i., but there were indications of food shortage amongst Hydropsychidae and Hirudinea.

Temephos caused significant reductions in the relative abundance of 5 taxa at 0.05 ppm, 3 to 6 taxa at 0.1 ppm, and 9 taxa at 1.0 ppm (P<0.05). “Non-target” organisms which were most affected included the chironomid R. fuscus, the mayflies Baetis glaucus Agnew and Choroterpes elegans Barnard, and the caddisflies Cheumatopsyche thomasseti Ulmer and Amphipsyche scottae Kimmins. The mayfly T. discolor was tolerant of temephos, even at high dosage (1.0 ppm/10 min). In winter, most taxa re-appeared within 19 days, and population densities were back to pre-treatment levels within 35 days.

It is concluded that good reduction of blackfly populations may be obtained with minimal direct impact on the “non-target” fauna, provided recommended dosages of temephos are not exceeded. Overdosing with temephos may result in high mortality of “non-target” organisms, including blackfly predators, and should be avoided.     

内蒙古温带草原大针茅叶片光合生理特性对氮添加的响应

大气氮沉降增加生态系统氮有效性,优势种植物对不同水平氮输入的响应影响草原生态系统结构和功能。研究设置4个氮添加水平,分析内蒙古温带草原优势种大针茅（Stipa grandis）光合生理特性对不同梯度氮添加的响应。结果表明：低氮（0-2 g m^-2 a^-1）处理时,大针茅叶片氮含量较低,叶绿素含量和1,5-二磷酸核酮糖羧化/加氧酶的活性不高,光能利用效率低,导致光系统II出现过剩激发能,光合器官受到抑制,净光合速率相对较低。适量氮添加（5-10 g m^-2 a^-1）提高了大针茅叶片羧化系统和电子传递系统的氮分配,进而提高了1,5-二磷酸核酮糖羧化/加氧酶的活性以及电子传递速率,净光合速率增大。高氮（25 g m^-2 a^-1）处理时,叶片氮含量较高,但光合氮分配比例下降,降低了光合氮利用效率。大针茅光抑制程度增大,叶绿素含量、1,5-二磷酸核酮糖羧化/加氧酶的活性下降,不利于生物量积累。研究结果有助于进一步了解全球变化背景下草原生态系统优势种的生理响应机制,并为草原的可持续发展提供一定的理论依据。     

荒漠草原植物群落结构及其稳定性对增水和增氮的响应

通过在荒漠草原开展增水和增氮野外控制试验,研究增水和增氮对荒漠草原植物群落结构、物种多样性及群落稳定性的影响。结果表明：（1）增水和增氮处理显著影响了荒漠草原植物群落结构和地上生物量,而对植物群落稳定性影响不显著（P>0.05）。增水处理显著增加了豆科和禾本科植物地上生物量（101.3%和57.9%）（P<0.05）;增水+增氮处理显著增加了植物群落盖度（43.2%）和地上生物量（112.4%）及不同功能群（禾本科和杂类草）植物盖度（75.5%和47.3%）和地上生物量（139.3%和85.7%）（P<0.05）。与增氮处理相比,增水+增氮处理显著增加了植物群落和不同功能群（禾本科和杂类草）植物高度、盖度和地上生物量（P<0.05）。（2）增水、增氮和增水+增氮处理均显著降低了植物群落Pielou指数（11.7%、8.7%和10.2%）（P<0.05）。（3）增水和增水+增氮处理提高了荒漠草原植物群落稳定性,而增氮处理降低了荒漠草原植物群落稳定性。增水处理荒漠草原植物群落稳定性效应大于增水+增氮处理。研究表明,荒漠草原植物群落结构受到氮沉降和降水增加的共同影响。增加降水对荒漠草原植物群落稳定性的积极效应可能会抵消部分氮沉降的消极影响,荒漠草原植物群落地上生物量及群落稳定性可能有所增加。     

Influence of phosphate and zinc on growth,nodulation and mineral composition of chickpea (Cicer arietinum L.) under salt stress

Zn²⁺ at 5 ppm and phosphate at 20 and 40 ppm improved the growth and nodulation of chickpea (Cicer arietinum L.) at two levels of salinity (4.34 and 8.3 dS m^–1). Augmentation with Zn²⁺ at 5 ppm provided protection to the plant under saline conditions by reducing the Na⁺:K⁺ ratio in the shoot. The shoot nitrogen content with 5 ppm Zn²⁺ and 20 ppm phosphate was equal to that of a non-saline control. No significant effect on nitrogenase activity was observed.     

Growth performance of an inland population of Plantago maritima in response to nitrogen and salinity

The inland distribution of Plantago maritima in Ireland and Britain is strongly western and generally associated with base-rich soils or with flushes in more acidic upland soils. Plants from an eastern Irish salt marsh and from an inland population growing on shallow calcareous soils in east County Clare, Ireland, were grown in culture solutions with a range of seawater dilutions (10–100%) and nitrogen (2.8–140 ppm N) concentrations added as ammonium nitrate. A low nitrogen supply (2.8 ppm N) resulted in very low dry matter production but with increased nitrogen, plant growth increased, even of inland population plants in 50% seawater. Some inland plants survived 100% seawater, but growth was much reduced. The relatively high salinity tolerance of this inland population is discussed.Nomenclature follows Flora Europaea (Tutin et al., 1964–80) for angiosperms, Watson (1968) for bryophytes and Hawksworth et al. (1980) for lichens.Thanks are due to the Central Marine Services Unit and Michael Coughlan, Microbiology Department at University College Galway for Mullaghmore soil nitrogen analyses.     

黄土区不同恢复年限草地群落生物量及根冠比对氮添加的响应

大气氮沉降增加作为全球变化的主要环境问题之一,已引发人们的广泛关注,持续的氮沉降对草地生态系统的组成、结构和功能产生重要影响。为深入了解草地恢复进程中群落生物量和根冠比对氮沉降的响应,以黄土区3个不同恢复年限（初期12a、中期28a和后期37a）的天然草地为研究对象,通过设置6个氮添加水平,CK （0）、N1（2.34g m^-2a^-1）、N2（4.67g m^-2a^-1）、N3（9.34g m^-2a^-1）、N4（18.68g m^-2a^-1）、N5（37.35g m^-2a^-1）来测定草地群落地上生物量、地下生物量和总生物量,并计算根冠比和氮响应效率（NRE）。结果表明：（1）地上生物量在恢复中期最大,随氮添加梯度增加,地上生物量在恢复初期和恢复后期呈不显著上升趋势,对氮添加表现为非线性的正响应（ΔNRE>0）,在恢复中期呈不显著下降趋势,对氮添加表现为非线性的负响应（ΔNRE<0）。（2）群落地下生物量对氮添加无显著响应,总生物量只有在恢复后期的N4添加水平下,与对照存在显著差异。（3）根冠比在恢复初期时,N3添加水平下显著高于对照和其他氮添加水平,其余恢复年限对氮添加无显著响应。综上所述,通过分析比较黄土区不同恢复年限草地群落的地上、地下及总生物量和根冠比对氮添加的响应。建议对该区域开展试点实验,实行适应性草地管理,如进行两年一次刈割或轻度放牧（2只羊/hm²）,来探寻更科学有效的管理措施,使草地实现系统性恢复,进而满足生态系统容量和社会需求的变化。     

氮素和水分添加对贝加尔针茅草原植物多样性及生物量的影响

为了解草原植物群落物种多样性和植物地上生物量对氮沉降增加和降水变化的响应,在内蒙古贝加尔针茅(Stipa baicalensis)草原,分别设置对照(N0)、1.5 g/m2(N15)、3.0 g/m2(N30)、5.0 g/m2(N50)、10.0 g/m2(N100)、15.0 g/m2(N150)、20.0g/m2(N200)和30.0 g/m2(N300)(不包括大气沉降的氮量)8个氮素(NH4NO3)添加梯度和模拟夏季增加降水100mm的水分添加交互试验,研究氮素和水分添加对草原群落植物物种多样性和几种常见植物地上生物量的影响。结果表明:(1)氮素和水分的添加降低了草原群落植物物种多样性,且氮素和水分有显著的互作效应。在水分添加的条件下,随着施氮水平的增加,群落植物物种多样性减小;在无水分添加的条件下,随着施氮水平的增加,群落植物物种多样性呈先增加后减小的"单峰"变化趋势。(2)不同植物对氮素和水分添加的响应不同,随着施氮水平的增加,羊草地上生物量显著增加;贝加尔针茅、羽茅、糙隐子草、寸草苔和冷蒿先增加后减少,呈单峰曲线;星毛委陵菜、牧马豆、扁蓄豆和线叶菊地上生物量则逐渐减少。而且氮素和水分对贝加尔针茅、羽茅、扁蓄豆地上生物量有显著的交互作用。     

长期不同施氮水平对草原植物群落结构的影响

为探讨施氮对贝加尔针茅草原植物群落结构的影响,该研究于内蒙古贝加尔针茅草原设置不同施氮水平0(N0)、15(N15)、30(N30)、50(N50)、100(N100)、150(N150)、200(N200)和300(N300)kg·hm-2·a-1,研究连续施氮9年后贝加尔针茅草原群落物种组成、重要值、多样性及生物量等指标对不同施氮水平的响应。结果表明:(1)长期施氮导致植物群落物种组成发生了明显的变化,在高浓度氮素添加量下群落物种数最低,但可显著提高优势种在群落中的重要值(P<0.05)。(2)长期施氮使贝加尔针茅草原植物多样性指数不同程度地降低,使优势度指数增加,其中N300添加水平效果最为明显(P<0.05)。(3)长期施氮使草原植被生产力(地上、地下生物量)整体呈先上升后下降的趋势,地上生物量在N100水平时出现峰值,地下生物量在N50水平时出现最大值(P<0.05),且根系分布具有明显的表聚特征(0~10 cm)。(4)RDA分析表明,寸草苔和狭叶柴胡地上生物量与土壤pH呈显著正相关关系(P<0.05);展枝唐松草和二裂委陵菜地上生物量与土壤有机质含量呈显著正相关关系(P<0.05)。研究认为,长期不同施氮水平均可改变贝加尔针茅草原群落物种组成,降低物种多样性,对植物群落结构有着明显的影响。     

氮素添加对贝加尔针茅草原土壤团聚体微生物群落的影响

大气氮沉降增加作为全球气候变化的重要因素,其对土壤生态系统影响的研究受到了生态学家的广泛关注。土壤微生物是有机物分解和养分循环的主要参与者,在维持土壤的功能多样性和可持续发展方面发挥着重要的作用。氮沉降的激增会引起土壤微生物群落结构和功能的改变。土壤中营养物质在不同团聚体组分中分布的不均匀,为微生物提供了空间异质微生境。为揭示草原土壤不同粒径团聚体中微生物群落分布及其对氮素添加响应特征。自2010年起,在内蒙古贝加尔针茅草原典型地段设置N₀（0 kg hm^-2 a^-1）、N₁₅（15 kg hm^-2 a^-1）、N₃₀（30 kg hm^-2 a^-1）、N₅₀（50 kg hm^-2 a^-1）、N₁₀₀（100 kg hm^-2 a^-1）、N₁₅₀（150 kg hm^-2 a^-1）6个氮素添加处理模拟氮沉降野外控制试验。采用磷脂脂肪酸（phospholipid fatty acid,PLFA）法测定>2 mm、0.25-2 mm和<0.25 mm 3个粒径土壤团聚体中微生物PLFA含量,探讨氮素添加对土壤团聚体微生物群落结构的影响。结果表明：氮素添加提高了土壤碳、氮含量,降低了土壤pH。氮素添加显著提高了0.25-2 mm土壤团聚体微生物群落磷脂脂肪酸总量、真菌磷脂脂肪酸含量和真菌/细菌（Fungi/bacteria,F/B）、革兰氏阳性菌/革兰氏阴性菌（Gram-positive bacteria/gram-negative bacteria,G⁺/G^-）的比值（P<0.05）,降低了土壤团聚体微生物Margalef丰富度指数（P<0.05）。相关性分析表明,土壤团聚体微生物总PLFAs、真菌PLFAs含量、G⁺/G^-、F/B与土壤有机碳、全氮含量呈显著正相关关系,与C/N值负相关。综合研究表明,连续8年氮素添加显著提高了土壤有机碳和全氮含量、降低了土壤pH;提高了0.25-2 mm土壤团聚体真菌群落,土壤有机碳、全氮的固持与真菌群落的增加有关。     

The influence of fungal food quality on the growth and fecundity of Folsomia candida (Collembola: Isotomidae)

Summary The Basidiomycete fungi Coriolus versicolor and Hypholoma fasciculare were grown in liquid media containing 2, 20, 200 and 2,000 ppm nitrogen (as asparagine) and fed to cultures of Folsomia candida. Collembola feeding on both species of fungi exhibited trends of increased moulting and egg laying rates up to 200 ppm N and an inhibition of growth and fecundity at 2,000 ppm N. The differences in moulting rates between individual treatments were small for both species of fungi and not all the pair wise comparisons of treatments were significantly different. Egg laying rates of collembola fed C. versicolor showed a highly significant response to all levels of N in the growth medium and egg production at 200 ppm N was over three times higher than at 2 ppm N. Collembola fed H. fasciculare showed a less marked fecundity response to the different nitrogen levels and egg production at 200 ppm was approximately 1.5 times higher than at 2 ppm N. Both moulting and egg laying rates were significantly affected by the species of fungus presented as food to the collembola. The patterns of growth and reproduction of starved control groups of F. candida as well as those fed the test fungi demonstrate the adaptability of this species to changes in the quality and quantity of available food.     

Effects of continuous nitrogen application and nitrogen preconditioning on nodulation and growth ofCeanothus griseus varhorizontalis

Rooted cuttings ofCeanothus griseus varhorizontalis were irrigated with 0, 10, 20, 50, 75 or 100ppm nitrogen as NH₄NO₃ for eight weeks prior to inoculation with infectiveFrankia. After inoculation, half of the plants for each treatment nitrogen level continued to be irrigated with the preconditioning nitrogen level and half were given no more supplemental nitrogen. For plants continuously receiving nitrogen, nodule initiation (nodule number) was inversely correlated with increasing supplemental nitrogen levels, and suppressed above 50 ppm N. Leaf nitrogen above 2% in continuous-N plants correlated with greatly reduced or suppressed nodulation. Plants maintained after inoculation without supplemental nitrogen showed influence of the prior nitrogen treatment on nodulation. Preconditioning at 50 ppm and above greatly reduced the number of nodules formed. The evidence suggests that stored internal nitrogen can regulate nodulation.Plant biomass accumulated maximally when nodulation was suppressed, at 75 and 100 ppm supplemental N applied continuously. Internode elongation during the nodulation period occurred only on nodulated plants, or in the presence of supplemental N (10 ppm and above).     

Decolorization of Azo Dye (Orange MR) by an Autochthonous Bacterium, <Emphasis Type="Italic">Micrococcus</Emphasis> sp. DBS 2

Soil and sediment samples obtained from Orange MR dye contaminated habitat were screened for heterotrophic bacterial population. The heterotrophic bacterial density of dye-contaminated soil was 2.14 × 10⁶ CFU/g. The generic composition of heterotrophic bacterial population was primarily composed of 10% of Proteus sp., 15% Aeromonas sp., 20% Bacillus sp., 25% Pseudomonas sp. and 30% Micrococcus sp. The bacterial strain that decolorized the azo dye Orange MR up to 900 ppm was identified as Micrococcus sp. The optimum inoculum load, pH and temperature were found to be 5%, 6 and 35°C, respectively. The rate of decolorization was assessed using spectrophotometer at 530 nm and the percentage of decolorization was ascertained. The autochthonous bacterial isolate was able to utilize the dye as both nitrogen and carbon source.     

短期氮添加对祁连山亚高山草地生产力及植物多样性的影响

全球氮沉降速率的急剧增加已显著地改变了生态系统的生产力及稳定性,特别是在受N限制较严重的亚高山草地生态系统。虽然氮沉降增加对草地生产力和植物多样性影响的研究报道已经很多,但是氮素沉降的生态系效应因气候区、草地系统类型、加氮水平、氮肥类型和试验时间长短等不同而差别很大。为了评估氮沉降增加对亚高山草地植物物种多样性和生产力的影响,通过在祁连山中部亚高山草地设置不同氮添加水平（0、2、5、10、15、25 g N m^-2 a^-1和50 g N m^-2 a^-1）的短期氮沉降增加模拟试验,探讨了生产力和物种多样性对不同水平氮添加的响应。结果显示：氮添加增加了禾本科（垂穗披碱草、赖草和草地早熟禾）和莎草科（矮嵩草）的地上生产力及其在群落生产力中所占的比例,主要表现在氮添加增加了禾本科和莎草科的株高和株数,降低了其他科（鹅绒委陵菜和葛缕子）的株高和株数;与生产力相比,植物多样性对氮添加的响应较慢,总体随着氮添加量的增加呈下降趋势但未达到显著水平;植物多样性与生产力呈显著的负相关关系。研究结果表明氮添加有助于提高禾本科和莎草科的生产力,进而提高群落生产力,但其他科的植物会被逐渐替代,导致群落植物物种多样性降低。研究结果可为我国亚高山草地的持续性管理提供一定的理论基础。     

湘西石漠化区3种造林模式土壤真菌群落结构差异

湘西石漠化地区是我国生态系统脆弱而又敏感的区域,土壤微生物在维持石漠化区森林生态系统结构和功能稳定中发挥重要作用。选取石漠化地区立地条件相同的32年生的马尾松纯林、光皮桦纯林及马尾松-光皮桦混交林为研究对象,以立地条件相似的未造林荒地演变成的灌草群落作为对照,比较分析石漠化地区不同造林模式对土壤真菌群落结构和多样性的影响及其主要驱动因素。采用Illumina HiSeq第二代高通量测序技术,分析了3种森林土壤真菌群落组成及多样性。结果表明,不同造林模式下土壤真菌优势类群不同,光皮桦、马尾松-光皮桦混交林以及石漠化灌草地土壤真菌优势门均为子囊菌门(Ascomycota),且在石漠化灌草地相对丰度最大,为64.0%;马尾松则以担子菌门(Basidiomycota)为优势类群,其相对丰度占57.9%。混交林土壤真菌物种总数和Shannon指数显著高于马尾松和光皮桦林地,整体上真菌群落多样性表现为：未造林灌草地>混交林>马尾松林>光皮桦林。与未造林灌草地相比,马尾松-光皮桦混交林和光皮桦纯林显著提升了土壤有机碳(SOC)和全氮(TN)含量。Mantel test检验结果显示,...     

Survivorship of a monocarpic bamboo grass,Sasa kurilensis,during the early regeneration process after mass flowering

The survivorship of a monocarpic bamboo grass,Sasa kurilensis, during the early regeneration process was documented by a 10 year observation of the seedling population after mass flowering in the Hakkoda Mountains, northern Japan. Three phases were recognized: the establishment, density-stable and thinning phases. The mortality of the densely germinated seedlings (932.9m⁻² in aBetula ermanii forest and 1222.3 m⁻² in aSasa grassland) was high, up to 0.5 year⁻¹, in the establishment phase (0–1 year after germination) and low in the density-stable phase (1–3 years after germination). After reaching full density state, the seedling population showed a nearly constant mortality of 0.18 year⁻¹ due to self-thinning (the thinning phase). The high C/F ratio presumably caused suppressed seedlings to die. Recovery of theS. kurilensis population was estimated to requireca 20 years in the study plots, judging from the height growth and the decrease in culm density of the seedling population. The illuminance on the ground was higher in the flowered population than in the unflowered one for 5 years after mass death. The duration of high ground illuminance is an important factor affecting the dynamics of forests withSasa undergrowth, because tree seedlings need to establish under high ground illuminance for the successful regeneration of the forests.     

Influences of fertilization on Aphis gossypii and insecticide usage

Abstract: Fertilization levels for ornamental crops may influence pest population dynamics, crop quality, and pest management strategy. We examined the effect of fertilization on population growth and within‐plant distribution of melon or cotton aphid, Aphis gossypii Glover, on potted chrysanthemum, Dendranthema grandiflora (Tzvelev). In terms of pest management implications, we also investigated the effect of fertilization on the number of insecticide applications needed to control A. gossypii on potted chrysanthemum. Population growth rate of A. gossypii increased with fertilization levels from 0 to 38 ppm N and reached a plateau from 38 to 488 ppm N. Increased fertilization beyond 38 ppm N, 10% of the commercial standard, did not result in higher aphid number. Aphids responded to nutrient availability of plants by distributing themselves in areas with higher level of nitrogen. More aphids were found in the apical and middle strata of the plants than the basal stratum, which had the lowest nitrogen content. Leaf nitrogen content increased with increased fertilization level and was consistently higher in the apical and middle strata than the basal stratum. Increased fertilization from 0 to 375 ppm N did not result in higher number of insecticide applications. All three insecticides (bifenthrin, kinoprene or pymetrozine) were effective in keeping the aphid infestation below a pre‐determined level, five aphids per plant, but pymetrozine required the least number of applications. For chrysanthemum, a fast‐growing crop and heavy utilizer of nitrogen, increased fertilization shortened the time to flowering, which would allow growers to harvest their crop sooner and reduce the time for aphid population growth. Reduction in time to harvest could result in significant reduction of insecticide usage by reducing the time for aphid population growth. As a result, high fertilization together with minimal runoff may be a useful tactic to an integrated pest management (IPM) programme for managing A. gossypii on potted chrysanthemums.