DETRITUS ABUNDANCE AND BENTHIC INVERTEBRATE CATCH IN ARTIFICIAL SUBSTRATE SAMPLES FROM MOUNTAIN STREAMS1

ABSTRACT: Artificial substrates were designed using rock filled polyethylene bags which were perforated with holes. The substrates trapped waterborne sediment and detritus which enhanced microhabitat complexity. Colonization was compared in side-by-side tests with multiple plate samplers in mountain streams ranging from second to seventh order. After 41 days the bag samples contained more sediment and detritus and more animals than did multiple plates. Plastic bags exceeded multiple plate samples by a factor of nearly 8 for individuals and 1.5 for taxa expressed as numbers/sampler. Although detritus amounts differed significantly between samplers, catch composition was similar in habitat preference and functional groups. Most taxa were “lotic erosional” or “lotic erosional-depositional” detritivores. The plastic bags better represented the streambed fauna judged by their greater similarity to dip net samples. Bag samplers had 4.5 × the colonization area of multiple plates, hence would be expected to support more species. Catch/m² of colonization area was not significantly different between samplers. Functionally the plastic bags act as detritus retention devices, offering a diverse, highly dynamic microhabitat for colonization. Results are interpretable in terms of research on microdistribution of stream benthos and the river continuum model. This study supports the conclusion that stream benthos abundance and diversity are related to the amount of detritus. Maximum diversity and numbers of individuals occurred in samples from third and fourth order streams. Grazers reached peak abundances in the same streams where the continuum model predicts P>R Shredders reached maximum abundances in third and fourth order streams where the riparian canopy was greatest. Predator abundance changed little with stream size. Although bag samples required more sorting time, the samplers are catch effective, inexpensive, and adaptable.     

Impacts of urbanization: diversity and the symbiotic relationships of rural,urban, and spaces in-between

This Impacts article proposes strategies for mitigating negative impacts of urbanization in rural locations in the United States. Issues addressed include impacts of population growth and development, loss of agricultural lands, and impacts of climate change on agriculture and rural communities. Conclusions are supported by stakeholder survey data, geographic information systems-based data, and desktop reviews of research journal publications. We propose a sustainable, diversified approach that supports mitigation of issues, including increasing demand on food production and decline of rural communities. A key issue that we address is where we will find suitable landscapes to reduce enough food for 9.6 billion people living in 2050.

Urban and rural development planners are grappling with solutions to escalating impacts global populations, stresses on food production, and effects of climate change. Solutions are identified, including strengthening rural and urban contexts by establishing connected and interdependent links that support diversification of rural and urban contexts as viable solutions to these issues.

Diversified rural-to-urban sustainable agriculture production is a promising approach to addressing climate change impacts. Organic agriculture principles exhibit strong diversity and are accredited by United States Department of Agriculture as the only federally certified sustainable agriculture practice in the United States. Sustainable agriculture practices are evolving into profitable diversified alternative food sources. We offer substantiated alternative solutions for remediating impacts of urbanization on rural agriculture and communities. Collectively, these solutions can strengthen symbiotic relationships between sustainable agriculture and rural communities, addressing our growing population issues and preserving our dwindling farmlands and rural communities.     

Water budget and the consequent duration of canopy carbon gain in a teak plantation in a dry tropical region: Analysis using a soil–plant–air continuum multilayer model

A soil–plant–air continuum multilayer model was used to numerically simulate canopy net assimilation (A_n), evapotranspiration (ET), and soil moisture in a deciduous teak plantation in a dry tropical climate of northern Thailand to examine the influence of soil drought on A_n. The timings of leaf flush and the end of the canopy duration period (CDP) were also investigated from the perspective of the temporal positive carbon gain. Two numerical experiments with different seasonal patterns of leaf area index (LAI) were carried out using above-canopy hydrometeorological data as input data. The first experiment involved seasonally varying LAI estimated based on time-series of radiative transmittance through the canopy, and the second experiment applied an annually constant LAI. The first simulation captured the measured seasonal changes in soil surface moisture; the simulated transpiration agreed with seasonal changes in heat pulse velocity, corresponding to the water use of individual trees, and the simulated A_n became slightly negative. However, in the second simulation, A_n became negative in the dry season because the decline in stomatal conductance due to severe soil drought limited the assimilation, and the simultaneous increase in leaf temperature increased dark respiration. Thus, these experiments revealed that the leaflessness in the dry season is reasonable for carbon gain and emphasized the unfavorable soil water status for carbon gain in the dry season. Examining the duration of positive A_n (DPA) in the second simulation showed that the start of the longest DPA (LDPA) in a year approached the timing of leaf flush in the teak plantation after the spring equinox. On the other hand, the end appeared earlier than that of all CDPs. This result is consistent with the sap flow stopping earlier than the complete leaf fall, implying that the carbon assimilation period ends before the completion of defoliation. The model sensitivity analysis in the second simulation suggests that a smaller LAI and slower maximum rate of carboxylation likely extend the LDPA because soil water from the surface to rooting depth is maintained longer at levels adequate for carbon gain by decreased canopy transpiration. The experiments also suggest that lower soil hydraulic conductivity and deeper rooting depth can postpone the end of the LDPA by increasing soil water retention and the soil water capacity, respectively.     

植物根系吸收土壤水分的研究综述

植物根系吸收土壤水分是土壤－植物－大气连续体中水分运动的一个重要环节．本文从土壤－植物－大气连续体入手，对植物根系吸收土壤水分的影响因素，植物根系吸收土壤水分的微观模型及植物根系吸收土壤水分的宏观模型等，进行了介绍和评述．     

Trait differences between naturalized and invasive plant species independent of residence time and phylogeny

The ability to predict which alien plants will transition from naturalized to invasive prior to their introduction to novel regions is a key goal for conservation and has the potential to increase the efficacy of weed risk assessment (WRA). However, multiple factors contribute to plant invasion success (e.g., functional traits, range characteristics, residence time, phylogeny), and they all must be taken into account simultaneously in order to identify meaningful correlates of invasion success. We compiled 146 pairs of phylogenetically paired (congeneric) naturalized and invasive plant species in Australia with similar minimum residence times (i.e., time since introduction in years). These pairs were used to test for differences in 5 functional traits (flowering duration, leaf size, maximum height, specific leaf area [SLA], seed mass) and 3 characteristics of species’ native ranges (biome occupancy, mean annual temperature, and rainfall breadth) between naturalized and invasive species. Invasive species, on average, had larger SLA, longer flowering periods, and were taller than their congeneric naturalized relatives. Invaders also exhibited greater tolerance for different environmental conditions in the native range, where they occupied more biomes and a wider breadth of rainfall and temperature conditions than naturalized congeners. However, neither seed mass nor leaf size differed between pairs of naturalized and invasive species. A key finding was the role of SLA in distinguishing between naturalized and invasive pairs. Species with high SLA values were typically associated with faster growth rates, more rapid turnover of leaf material, and shorter lifespans than those species with low SLA. This suite of characteristics may contribute to the ability of a species to transition from naturalized to invasive across a wide range of environmental contexts and disturbance regimes. Our findings will help in the refinement of WRA protocols, and we advocate the inclusion of quantitative traits, in particular SLA, into the WRA schemes.     

连续光源火焰原子吸收法测定土壤速效钾

采用连续光源原子吸收光谱仪原子吸收法，选择404nm为测定波长，检测国家土壤标准样品的速效钾。结果表明，该方法检测结果准确度高，精密度好，测试方法快速简单。     

PROCESS DOMAINS AND THE RIVER CONTINUUM1

ABSTRACT: The concept of process domains is proposed as an alternative to the River Continuum Concept for the influence of geomorphic processes on aquatic ecosystems. Broadly defined, the Process Domain Concept is a multi-scale hypothesis that spatial variability in geomorphic processes governs temporal patterns of disturbances that influence ecosystem structure and dynamics. At a coarse scale, regional climate, geolog vegetation, and topography control the suite of geomorphic processes that are distributed over a landscape. Within the broad context so defined, stream channel classification can guide identification of functionally similar portions of a channel network, but the response of otherwise similar reaches can depend upon their geologic and geomorphic context. Within geomorphic provinces defined by differences in topography, climate history, and tectonic setting, areas with generally similar geology and topography define lithotopo units, which are useful for stratifying different suites of dominant geomorphic processes. Process domains are spatially identifiable areas characterized by distinct suites of geomorphic processes, and the Process Domain Concept implies that channel networks can be divided into discrete regions in which community structure and dynamics respond to distinctly different disturbance regimes. The concepts of process domains and lithotopo units provide both a framework for the application of patch dynamics concepts to complex landscapes and a context for addressing the effects of watershed processes on the ecology of mountain drainage basins.     

煤矿风险预控连续统一体理论研究

为了使煤矿被动式的安全管理模式真正转变为主动式预控管理模式,从而打造本质安全型矿井,借鉴领导方式连续统一体理论,提出煤矿风险预控连续统一体理论,建立煤矿风险梯度控制框架。将煤矿风险预控对象划分为4种类型,即稳定的安全系统、失稳的安全系统、事故紧急状态和事故,针对不同预控对象所实施的安全管理模式就构成风险预控的"连续统一体"。对煤矿风险应实施梯度控制,控制方案从高梯度到低梯度依次为预防控制、校正控制、应急控制和事故控制。研究表明:只有做好每一个风险阶段的安全管理工作,才能实现煤矿本质安全的目的。