黄土丘陵小流域土壤侵蚀的时空变异及其影响因子

采用土壤侵蚀模型LISEM(Limburg Soil Erosion Model)模拟黄土丘陵沟壑区大南沟小流域5种土地利用格局下立地尺度上土壤侵蚀量的空间分布,从土壤侵蚀量与环境因子的关系分析入手,研究黄土丘陵小流域立地尺度上土壤侵蚀的时空变异性及其影响因子.研究结果表明,立地尺度上平均土壤侵蚀强度以1975年>1998年>退耕格局,可见优化土地利用格局(陡坡农地退耕)可以有效地降低立地尺度上的土壤侵蚀强度.各种土地利用方案下土壤侵蚀强度的空间变异都很显著,相对来说以1975年<1998年<退耕格局,可见优化土地利用格局可以提高土壤侵蚀的空间变异性,降低土壤侵蚀危险的空间聚集度.土壤侵蚀量与降雨呈现显著正相关性,相关性以LU75>LU98>退耕格局,可见合理的土地利用格局可以有效地削弱降雨对土壤侵蚀强度的影响.土地利用方式对土壤侵蚀空间分布具有显著影响.从1975年、1998年到3种退耕格局,陡坡农地退耕还林还草,植被覆盖度增加,林地/灌木地、果园/经济林地、农地和休闲地的平均土壤侵蚀强度都逐渐降低.相关分析表明,林地/灌木地上土壤侵蚀量最小,荒草地相对最严重;果园、休闲地和农地居中.土壤侵蚀强度还存在显著的地形分异.水平凹凸度和相对海拔对土壤侵蚀空间分布的影响比较显著,而坡向、坡度和垂直凹凸度的影响较小.土壤侵蚀强度以水平凸坡大于水平凹坡、垂直凹坡略大于垂直凸坡、偏南坡大于偏北坡、低海拔大于高海拔.对1975年和1998年土地利用格局来说,土壤侵蚀强度以偏西坡大于偏东坡、陡坡大于缓坡;对3种退耕格局而言则正相反.可见,优化土地利用格局(陡坡农地退耕),可以有效地削弱甚至逆转地形对土壤侵蚀强度的影响.     

岷江冷杉针叶林下穿透雨空间分布特征

森林对降水的截留作用、林下穿透雨的水文学及生态学意义一直是生态水文学研究中的热点 ,但是关于林下穿透雨空间分布特征的研究还比较少。在四川西部的卧龙自然保护区研究了岷江冷杉林下穿透雨的空间分布特征。在岷江冷杉针叶林下布设了 8个雨量筒用以测量林下穿透雨 ,对两年共 35次降雨的穿透雨研究结果表明 ,林下各观测点的穿透雨率同林外降雨量之间的关系都可以用逻辑斯谛曲线方程较好地模拟 ,与传统的对数方程模拟相比 ,前者的相关程度显著高于后者 ,而且用逻辑斯谛方程进行模拟时 ,方程中的各参数具有一定的生态学意义。此外 ,研究发现林下各点的穿透雨率具有显著的差异 ,位点 4下的穿透雨存在着明显的聚集效应 ,此处的平均穿透雨率达到了 10 3.2 %。对林下 8个点穿透雨进行聚类分析表明 ,林下位点 4和位点 8的穿透雨特征与其余 6个点的穿透雨特征有显著的差异。对影响岷江冷杉林下穿透雨空间分布的因素分析表明 ,观测点上方的冠层覆盖度、枝叶层厚度与降雨量之间均有一定的负相关关系 ,但其影响未达到显著水平 ;观测点到树干的距离与林下的穿透雨之间的关系可以较好地用二次多项式方程模拟 ,方程的相关程度很高 (R=0 .94 91) ;各观测点正上方的冠层以及枝叶性质也对穿透雨的空间分布特征有一定的     

第2代杉木幼林生态系统水化学特征

对第 2代杉木幼林生态系统的降雨、穿透水、茎流、地表和地下径流等水文过程中 N、P、K、Ca、Mg、Cu、Fe、Zn和 Mn9种养分元素含量进行了连续 5 a的测定 ,结果表明 :降雨通过林冠后其化学特性发生明显变化 ,p H值出现酸化现象 ,穿透水中 Zn和 Org-N为负淋溶 ,其余各元素浓度有所增加。树干茎流的富集作用比穿透水强 ,其中 Zn为负 ,其它元素的浓度均比林外降雨的高。地表径流中 Zn>Org-N>NO3 -N,与降雨中含量相比较为淋失迁移型 ,Ca>K>Cu>Mg>P>NH4 -N>Mn>Fe为内贮型 ,p H值增大。地下径流中 Zn>Org-N>NH4 -N>K>Mn为淋失迁移型、Ca>Mg>Cu>NO3 -N>P>Fe为内贮型。该系统的水循环中 Ca>Mg>Fe>P为净损失、Zn>K>Org-N>NH4 -N>Mn>NO3 -N>Cu为净积累 ,与第 1代杉木林相比 ,第 2代杉木幼林水化学过滤与吸贮功能较差 ,系统稳定性也较弱 ,生态功能的恢复需要一定的时间     

贡嘎山峨眉冷杉林原生扰动土壤溶质运移的持续降雨模拟研究

以人工持续(5d)降雨模拟方式研究了贡嘎山物眉冷杉林原生土壤地表覆被层破坏后土壤中矿质元素与营养盐的迁移输出动态与规律。模拟降雨采用当地最为常见的小到中雨雨型（5.7-26mm/h),壤中流以垂直入渗为主,并滞后于降雨0.2-4.2h,通过0模拟实验发现,降雨总量和降雨事件的持续时间对壤中流产生量的影响比单位时间降雨强度的影响更为明显,在持续降雨影响下,主要离子（Mg^2 ,Ca^2 ,Cl^-,SO4^2-和Na^ K^ ）和营养盐（NH4^ -N,NO3^--N和活性磷酸盐）在短期内急剧流失,模拟降雨的第1天,壤中流结束时离子浓度仅为初始时浓度的29%,营养盐浓度为初始浓度的21%-55%。至第3天,上述离子和营养盐输出浓度趋于恒定,约为首日降雨壤中流初始浓度的1%-15%,在主要矿质元素流失后,原生土壤内过程转为有机质控制的HCO3^-输出过程,伴随着土壤矿质养分的输出,土壤缓冲能力下降,壤中流pH值由6.1降为5.2,研究结果表明,贡嘎山区峨眉冷杉林原生土壤系统十分脆弱,养分易于流失,对人类活动的敏感性很高。     

模拟降雨条件下施肥方法对坡面磷素流失的影响

采用模拟降雨的方法研究了3种施肥方法对P素流失形态与流失过程的影响。结果表明,P肥在土壤中的混匀程度越高,则越容易导致生物有效P（BAP）的流失,混施条件下,径流中水溶态P（DP）与AP含量,DP／BAP与BAP／TP（总P）比值均较高;其次为穴施;实施条件下DP,BAP含量最低,DP／BAP与BAP／TP比值也相对较低,与对照间的差异不明显。施肥方法对径流中TP含量影响较小,从减少P素肥料流失的角度来讲,3种施肥方法作用大小顺序为：条施＞穴施＞混施。     

Rainfall, phycocyanin, and N:P ratios related to cyanobacterial blooms in a Korean large reservoir

Nutrient concentrations and other environmental factors were measured in the Daechung Reservoir for 25 weeks from spring until autumn in 1999. The high irradiance after heavy rainfall provided optimal meteorological conditions for bloom formation during summer, therefore, rain would also appear to forecast imminent bloom. The bloom formation was largely governed by cyanobacteria, in particular, Microcystis spp. and Anabaenaspp. Phycocyanin showed higher correlation with cyanobacteria (r = 0.744, P < 0.001) compared to chlorophyll-a(r = 0.599, P < 0.01). Therefore, phycocyanin was more accurate and useful than chlorophyll-a in quantitatively measuring cyanobacterial blooms. The atomic N:P ratio of the particulate form also showed a high correlation with cyanobacteria (r = 0.541, P < 0.01), increasing from 4.3 to 14.6 during bloom formation, while that of the dissolved form decreased from 25.5 to 8.7. These results indicated that the algae assimilated N significantly without comparable P uptake during the blooming season, which was in sharp contrast to the excessive storage of P during the spring.     

The reproductive flight phenology of a neotropical ant assemblage

1. Alate flights reflect an ant colony's investment in sexual reproduction and dispersal yet little is known about community‐wide patterns of alate phenology. Two Malaise traps (for 2 years) and two light traps (for 1 year) were used to explore the flight phenologies of 22 common neotropical species from Barro Colorado Island, Panama. 2. The traps caught 23 182 individuals and 286 species/morphospecies. The two trap methods shared only 18 species. Samples also differed in sexual composition: light trap samples were 80% female, Malaise trap samples were 2.6% female. 3. Of 22 common species, all but one flew over half the year, with about half flying every month of the year. These data, combined with a literature review, suggest a latitudinal gradient in alate flight season: one north temperate assemblage (42°N) averaged 1.6 lunar months per species. The ever‐warm tropical year provides a larger flight window that allows a diversity of phenologies, from continuous to strongly pulsed. 4. Rainfall was correlated with alate flights in one‐third of the species. Quantile regression suggested that high weekly rainfall was necessary but not sufficient to produce alate flights in about a quarter of the species. 5. By decreasing the number of nests releasing alates on a given day, long flight seasons may lower the probability of finding a mate. At the same time, long flight seasons may increase the opportunity of finding vacant nest sites. High population densities and high incidence of nest disturbance in this community may ameliorate the first cost while enhancing the second benefit.     

Explaining geographical variation in the isotope composition of mouse lemurs (Microcebus)

Aim We sought to quantify geographical variation in the stable isotope values of mouse lemurs (Microcebus) and to determine whether this variation reflects trophic differences among populations or baseline isotopic differences among habitats. If the latter pattern is demonstrated, then Microcebus can become a proxy for tracking baseline habitat isotopic variability. Establishing such a baseline is crucial for identifying niche partitioning in modern and ancient communities. Location We studied five species of Microcebus from eight distinct habitats across Madagascar. Methods We compared isotopic variation in C₃ plants and Microcebus fur within and among localities. We predicted that carbon and nitrogen isotope values of Microcebus should: (1) vary as a function of abiotic variables such as rainfall and temperature, and (2) covary with isotopic values in plants. We checked for trophic differences among Microcebus populations by comparing the average difference between mouse lemur and plant isotope values for each locality. We then used multiple regression models to explain spatial isotope variation in mouse lemurs, testing a suite of explanatory abiotic variables. Results We found substantial isotopic variation geographically. Ranges for mean isotope values were similar for both Microcebus and plants across localities (carbon 3.5–4.0‰; nitrogen 10.5–11.0‰). Mean mouse lemur and plant isotope values were lowest in cool, moist localities and highest in hot, dry localities. Rainfall explained 58% of the variation in Microcebus carbon isotope values, and mean plant nitrogen isotope values explained 99.7% of the variation in Microcebus nitrogen isotope values. Average differences between mouse lemur and plant isotope values (carbon 5.0‰; nitrogen 5.9‰) were similar across localities. Main conclusions Isotopic data suggest that trophic differences among Microcebus populations were small. Carbon isotope values in mouse lemurs were negatively correlated with rainfall. Nitrogen isotope values in Microcebus and plants covaried. Such findings suggest that nitrogen isotope values for Microcebus are a particularly good proxy for tracking baseline isotopic differences among habitats. Our results will facilitate future comparative research on modern mouse lemur communities, and ecological interpretations of extinct Holocene communities.     

Oviposition behaviour of the grasshopper Zonocerus variegatus

Abstract. 1. Long-term changes in the numbers of Zonocerus at oviposition sites reflect changes in the maturity of the general population.
2. Short-term changes in the numbers of Zonocerus at oviposition sites are associated partly with normal diurnal behaviour in which roosting occurs at night.
3. Immigration of Zonucems , particularly females, into the oviposition site occurs prior to periods of oviposition activity. Emigration follows oviposition.
4. The majority of Zonocerus move upwind into the oviposition site suggesting an odour and/or sound attraction.
5. Periods of intense oviposition activity follow heavy rainfall.