养分资源脉冲供给对几种微藻种间竞争的影响

以淡水生态系统常见的5种微藻为研究对象,通过稳态条件下单一培养的方式获取各微藻在氮素或磷素缺乏条件下对应的生长特征参数和R*值,同时将5种微藻在养分资源脉冲供给的方式下进行混合培养,进而检测养分资源脉冲供给对几种微藻种间竞争的影响作用,并与基于稳态条件下所预测的微藻种间竞争结果进行比较。研究结果显示,在稳态条件下具有最小R*值的纤细角星鼓藻在与其它微藻的种间竞争过程中始终保持优势地位,而其余4种微藻在混合培养状态下的相对比重亦与其稳态条件下的R*值紧密相关。然而,资源脉冲供给条件下的竞争优势种纤细角星鼓藻能与其它种群数量较小的微藻共存。此外,在氮素和磷素的不同供给比例情况下,对应微藻群落的结构也会发生相应的变化。实验养分资源脉冲作用下多种微藻的共存现象与自然水体中的观测现象相一致,显示了资源脉冲可能是维持生物多样性水平的一个重要机制。

资源脉冲对外来植物入侵影响的研究进展和展望

全球变化背景下,诸如营养、水分等资源的波动是非稳态的,往往以脉冲的形式出现,呈现出频率低、强度高和持续时间短的特征。资源脉冲往往会打破植物群落固有的平衡状态,进而影响全球变化的另一重要组分——外来植物入侵。目前,全球变化对外来植物入侵影响的研究往往关注资源的稳态变化,忽略了资源的波动性,特别是脉冲的作用。该文通过综述资源脉冲对外来植物入侵影响的研究,简要评述了资源脉冲的形成原因、类型及影响,讨论了不同类型的资源脉冲对外来植物入侵的作用。此外,该文根据现有的研究进展提出了一些未来可能的研究方向,如资源脉冲的不同属性,多种资源脉冲交互作用对植物入侵的影响及其机制等。

Contribution of Adventitious Roots to Water Use Strategy of Juniperus sabina in a Semiarid Area of China

duniperus sabina Linnaeus, an evergreen shrub with prostrate life form, can effectively prevent sand moving and is an important tree species for reforestation in semiarid areas of China. It has laterally distributed adventitious roots and a deeply distributed main root system. To detect water movement between the main root system and adventitious roots, we adopted heat pulse sensors using the Heat Ratio Method, a high precision method for measuring low sap flow rates. Two sensors were implanted in each individual in the stem between the main root system and adventitious roots, and another two in lateral stems distal to all the roots. Positive sap flows during nighttime, even under saturated air moisture conditions, were detected only between the main root system and adventitious roots under drought conditions, and the rate of flow increased as drought progressed and decreased or disappeared after rain events. The results demonstrated the existence of water movement from the main root system to adventitious roots, and combined with the high contribution of nighttime sap flow to transpiration （11%-16%） the results indicate that it also involves the process of hydraulic lift, a water movement from moist subsoil to dry surface soils. Integrated water use strategy between the main root system and adventitious roots via the process of hydraulic lift of soil water maximizes water acquisition efficiency from both subsoil water and water from rain pulses on the soil surface; this increases survivability in the water-limited environment of semiarid areas.

OPTIMAL IMPULSIVE HARVESTING FOR FISH POPULATIONS

In this paper the management model a two-species fishery involving impulsesis investigated by using optimal impulsive control theorem. Optimal impulsive harvesting times andthe corresponding optimal harvesting population levels in different cases are obtained.