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1.
Oil palm plantations have expanded rapidly in recent decades. This large‐scale land‐use change has had great ecological, economic, and social impacts on both the areas converted to oil palm and their surroundings. However, research on the impacts of oil palm cultivation is scattered and patchy, and no clear overview exists. We address this gap through a systematic and comprehensive literature review of all ecosystem functions in oil palm plantations, including several (genetic, medicinal and ornamental resources, information functions) not included in previous systematic reviews. We compare ecosystem functions in oil palm plantations to those in forests, as the conversion of forest to oil palm is prevalent in the tropics. We find that oil palm plantations generally have reduced ecosystem functioning compared to forests: 11 out of 14 ecosystem functions show a net decrease in level of function. Some functions show decreases with potentially irreversible global impacts (e.g. reductions in gas and climate regulation, habitat and nursery functions, genetic resources, medicinal resources, and information functions). The most serious impacts occur when forest is cleared to establish new plantations, and immediately afterwards, especially on peat soils. To variable degrees, specific plantation management measures can prevent or reduce losses of some ecosystem functions (e.g. avoid illegal land clearing via fire, avoid draining of peat, use of integrated pest management, use of cover crops, mulch, and compost) and we highlight synergistic mitigation measures that can improve multiple ecosystem functions simultaneously. The only ecosystem function which increases in oil palm plantations is, unsurprisingly, the production of marketable goods. Our review highlights numerous research gaps. In particular, there are significant gaps with respect to socio‐cultural information functions. Further, there is a need for more empirical data on the importance of spatial and temporal scales, such as differences among plantations in different environments, of different sizes, and of different ages, as our review has identified examples where ecosystem functions vary spatially and temporally. Finally, more research is needed on developing management practices that can offset the losses of ecosystem functions. Our findings should stimulate research to address the identified gaps, and provide a foundation for more systematic research and discussion on ways to minimize the negative impacts and maximize the positive impacts of oil palm cultivation.  相似文献   

2.
Tropical forest conversion to agricultural land leads to a strong decrease of soil organic carbon (SOC) stocks. While the decrease of the soil C sequestration function is easy to measure, the impacts of SOC losses on soil fertility remain unclear. Especially the assessment of the sensitivity of other fertility indicators as related to ecosystem services suffers from a lack of clear methodology. We developed a new approach to assess the sensitivity of soil fertility indicators and tested it on biological and chemical soil properties affected by rainforest conversion to plantations. The approach is based on (non-)linear regressions between SOC losses and fertility indicators normalized to their level in a natural ecosystem. Biotic indicators (basal respiration, microbial biomass, acid phosphatase), labile SOC pools (dissolved organic carbon and light fraction) and nutrients (total N and available P) were measured in Ah horizons from rainforests, jungle rubber, rubber (Hevea brasiliensis) and oil palm (Elaeis guineensis) plantations located on Sumatra. The negative impact of land-use changes on all measured indicators increased in the following sequence: forest < jungle rubber < rubber < oil palm. The basal respiration, microbial biomass and nutrients were resistant to SOC losses, whereas the light fraction was lost stronger than SOC. Microbial C use efficiency was independent on land use. The resistance of C availability for microorganisms to SOC losses suggests that a decrease of SOC quality was partly compensated by litter input and a relative enrichment by nutrients. However, the relationship between the basal respiration and SOC was non-linear; i.e. negative impact on microbial activity strongly increased with SOC losses. Therefore, a small decrease of C content under oil palm compared to rubber plantations yielded a strong drop in microbial activity. Consequently, management practices mitigating SOC losses in oil palm plantations would strongly increase soil fertility and ecosystem stability. We conclude that the new approach enables quantitatively assessing the sensitivity and resistance of diverse soil functions to land-use changes and can thus be used to assess resilience of agroecosystems with various use intensities.  相似文献   

3.
Summary   All forests, including commercial plantations, provide a range of habitats for conserving and enhancing elements of native biodiversity. However, the biodiversity values of commercial plantations will depend on the management practices adopted on site, as well as the landscape context of the plantation. The present study describes a generic, quantitative method for assessing the potential biodiversity benefits that might be derived from a plantation, depending on the management practices adopted. This method is based on existing ecological design and management principles. The Plantation Biodiversity Benefits Score (PBBS) was designed to be repeatable and practical to apply. The method can be used either as a stand-alone tool or as part of an integrated framework to assess and compare the commercial and environmental benefits that can be derived from different layouts, management practices and locations of plantations anywhere in Australia.  相似文献   

4.
The planting of non‐timber forest products (NTFPs) in the understory of tropical forests is promoted in many regions as a strategy to conserve forested lands and meet the economic needs of rural communities. While the forest canopy is left intact in most understory plantations, much of the midstory and understory vegetation is removed in order to increase light availability for cultivated species. We assessed the extent to which the removal of vegetation in understory plantations of Chamaedorea hooperiana Hodel (Arecaceae) alters understory light conditions. We also examined how any changes in light availability may be reflected by changes in the composition of canopy tree seedlings regenerating in understory plantations. We employed a blocked design consisting of four C. hooperiana plantation sites; each site was paired with an adjacent, unmanaged forest site. Hemispherical canopy photographs were taken and canopy tree seedlings were identified and measured within 12 3 × 2 m randomly placed plots in each site for a total of 96 plots (4 blocks × 2 sites × 12 plots). Plantation management did not affect canopy openness or direct light availability but understory plantations had a higher frequency of plots with greater total and diffuse light availability than unmanaged forest. Comparisons of canopy tree seedling composition between understory plantations and unmanaged forest sites were less conclusive but suggest that management practices have the potential to increase the proportion of shade‐intolerant species of tree seedlings establishing in plantations. Given the importance of advanced regeneration in gap‐phase forest dynamics, these changes may have implications for future patterns of succession in the areas of forest where NTFPs are cultivated.  相似文献   

5.
分析高校科学研究型实验室管理的现状,成功开发出基于C/S、B/S结合模式、集成多种实验室管理相关模块的新型实验室集成信息管理系统(Laboratory Information Management Systems,LIMS)。系统以实验室为核心、对人员、仪器、试剂耗材及整体环境进行全方位的综合管理。其应用及推广,对进一步提高科研型实验室管理水平,提高仪器使用效率,合理利用资源具有重要意义。可满足高校研究型实验室集成化信息管理的新需要。  相似文献   

6.
In this paper, we focus on the impact on soil organic carbon (SOC) of two dedicated energy crops: perennial grass Miscanthus x Giganteus (Miscanthus) and short rotation coppice (SRC)‐willow. The amount of SOC sequestered in the soil is a function of site‐specific factors including soil texture, management practices, initial SOC levels and climate; for these reasons, both losses and gains in SOC were observed in previous Miscanthus and SRC‐willow studies. The ECOSSE model was developed to simulate soil C dynamics and greenhouse gas emissions in mineral and organic soils. The performance of ECOSSE has already been tested at site level to simulate the impacts of land‐use change to short rotation forestry (SRF) on SOC. However, it has not been extensively evaluated under other bioenergy plantations, such as Miscanthus and SRC‐willow. Twenty‐nine locations in the United Kingdom, comprising 19 paired transitions to SRC‐willow and 20 paired transitions to Miscanthus, were selected to evaluate the performance of ECOSSE in predicting SOC and SOC change from conventional systems (arable and grassland) to these selected bioenergy crops. The results of the present work revealed a strong correlation between modelled and measured SOC and SOC change after transition to Miscanthus and SRC‐willow plantations, at two soil depths (0–30 and 0–100 cm), as well as the absence of significant bias in the model. Moreover, model error was within (i.e. not significantly larger than) the measurement error. The high degrees of association and coincidence with measured SOC under Miscanthus and SRC‐willow plantations in the United Kingdom, provide confidence in using this process‐based model for quantitatively predicting the impacts of future land use on SOC, at site level as well as at national level.  相似文献   

7.
When pasture land is abandoned, there are, in many cases, inhibitory factors that slow the rate of transition to a natural vegetation. Accordingly, the planned management of restoration has become an important issue in various parts of the world, where environmental conditions can vary widely. Although tree plantations are widely used as a management tool for restoration, there have been few studies addressing the practical aspects of the procedure. I examined effects of tree plantations within the framework of an evaluation of methods for restoring abandoned pasture on Hokkaido, northern Japan. I developed and analyzed vegetation maps spanning the past 57 years for the old-growth site influenced by artificial disturbance; the procedure revealed the pattern of change in the vegetation cover. Matrix model analysis showed that intensive use of plantations contributed to reduction of the area occupied by dwarf bamboo and pasture land (i.e., superior to simple abandonment). Furthermore, the field study of vegetation types and changes in species composition over 20 years suggests that plantations have contributed to a reduction in the effects of factors that inhibit revegetation. However, the establishment of monoculture plantations is frequently viewed skeptically as a procedure that is applied without fundamental ecological knowledge. For sustained management, adequate historical and ecological information on the restoration site should be provided to all stakeholders. An erratum to this article can be found at  相似文献   

8.
The density of colonies of leaf-cutting ants, Atta cephalotes L. (Hymenoptera: Formicidae), was measured and compared among coffee (Coffea arabica L.) plantations in five management categories: monoculture conventional, diversified conventional, diversified organic, highly diversified conventional, and highly diversified organic. Twenty-four small farms (<4 ha) in Turrialba, Costa Rica, were included in this study. Within-farm and off-farm (landscape) variables were measured and tested for their relationship with A. cephalotes colony density. Total ant colony density (colonies per ha) and density of new colonies shortly after a nuptial flight were significantly greater in the coffee monoculture conventional system, compared with all other systems. Total ant colony density and density of new colonies were inversely related to percentage of shade within the farms. Within farms, colony density was greater near edges adjacent to riparian forest than those adjacent to nonforested land. Regardless of edge type, plots closer to the edge (0-30 m) had greater colony density than those furthest from the edge. At the landscape scale, density of new colonies was positively related to fallow land use coverage within a 2,000-m buffer radius and to forest coverage within a 500-m radius. Results indicate that coffee farm management practices and landscape level factors can affect A. cephalotes colony densities. Understanding such practices and factors could assist in the development of better management methods of these injurious insects in coffee farms. Increased diversification in coffee farms, possibly due to the greater shade associated with it, may reduce colonization by the ants, which are considered forest gap specialists.  相似文献   

9.
2004~2005年,对珠海市斗门区有机、常规和天然荔枝园的蜘蛛群落进行了系统的调查和分析,结果表明,不同类型荔枝园蜘蛛群落丰富度S值天然>有机>常规荔枝园;多样性指数H'值有机>天然>常规荔枝园;均匀度E值有机>天然>常规荔枝园.说明进行有机管理的荔枝园对蜘蛛群落的多样性影响较小,有利于保护和发挥天敌的自然控制力.有机、常规荔枝园的优势类群均为园蛛科、皿蛛科和球蛛科,而天然荔枝园除这三者外,跳蛛科也明显增加.除天气因素外,更重要的还与人为农事活动干扰程度直接相关.有机荔枝园不使用化学农药,蜘蛛种类多,个体数也较多.而常规荔枝园由于频繁地使用了化学合成物质,蜘蛛种类和数量较少.说明施用大量的化学农药,对蜘蛛的影响较大.  相似文献   

10.
Nutrient cycling, nutrient use efficiency and nitrogen fixation in an age series of Alnus-cardamom plantations were studied in the eastern Himalaya. The impact of stand age (5, 10, 15, 20, 30 and 40 years) on the nutrient dynamics of mixtures of N2-fixing (Alnus nepalensis) and non-N2-fixing (large cardamom) plants was assessed. Foliar nutrient concentrations of Alnus decreased with advancing age groups of plantations and showed an inverse relationship with stand age. Annual N fixation increased from the 5-year-old stand (52 kg ha(-1)), peaking in the 15-year-old stand (155 kg ha(-1)) and then decreased with increasing plantation age. Nitrogen and phosphorus uptake was lowest in the 40-year-old stand, and highest in the 15- and 5-year-old stand, respectively. Nutrient storage in understorey cardamom was very high: up to 31 % N and 59 % P of the stand total in the 15-year-old stand. Nutrient use efficiency was higher (with faster turnover times) in younger stands and decreased (with slower turnover times) in older plantations. Nitrogen retranslocation showed a strong positive relationship with stand age, while that of P was inversely related to stand age. Nutrient standing stock, uptake and return were also highest in the 15-year-old stand. Nitrogen and P cycling in Alnus-cardamom plantations was functionally balanced. Nutrient cycling and dynamics indicated that Alnus-cardamom plantations performed sustainably up to 15-20 years. The management practice should be altered to incorporate replantation after this age.  相似文献   

11.
Frosty pod rot or moniliasis is a very destructive disease of cocoa plantations in Latin America. The conventional methods to control this disease such as the use of chemical pesticides have failed or are too expensive for smallholders. Nowadays, biological alternatives are being investigated to improve yields and to keep moniliasis controlled. Xenorhabdus and Photorhabdus bacteria and their exudates were evaluated against Moniliophthora roreri. All bacteria demonstrated antifungal action reaching up to 97% after 13 days of exposure, whereas some exudates demonstrated more than 70%. Moniliophthora roreri did not sporulate in bacteria presence and sporulation was reduced by their exudates in 70%. The bacteria and exudates were compared with a commercial fungicide used by Venezuelan farmers; better performance of the bacteria and exudates was found and the fungicide was unable to control M. roreri. These experiments showed promising results of Xenorhabdus and Photorhabdus as biocontrol agents for being included in the integrated disease management programmes in Venezuela.  相似文献   

12.
Logging in the boreal forest may benefit moose by increasing food availability. However, the influence of tree plantations on moose behavior, especially on moose spatial ecology, is poorly understood. We assessed the impacts of black spruce plantations on moose winter distribution at a landscape scale in the Bas-Saint-Laurent region (Québec, Canada). We used winter aerial surveys to examine relationships among plantation characteristics and other habitat variables known to affect moose distribution. The total area of plantations positively influenced moose abundance, but highly aggregated plantations resulted in fewer moose. Moose abundance was also positively associated with food availability and the density of edges between stands providing cover and stands offering high food availability, but moose abundance was negatively associated with road density. Although plantation characteristics were less influential than habitat variables related to foraging and predator avoidance, we demonstrate that the area of black spruce plantations and their configuration should be considered in moose management. We conclude that an integrated management strategy is needed to find a balance between overdeveloped road networks (needed to join homogeneously distributed plantations) and agglomerated plantations in order to mitigate impacts on moose winter distribution. © 2012 The Wildlife Society.  相似文献   

13.
Nanoparticles are widely suggested as targeted drug-delivery systems. In photodynamic therapy (PDT), the use of multifunctional nanoparticles as photoactivatable drug carriers is a promising approach for improving treatment efficiency and selectivity. However, the conventional cytotoxicity assays are not well adapted to characterize nanoparticles cytotoxic effects and to discriminate early and late cell responses. In this work, we evaluated a real-time label-free cell analysis system as a tool to investigate in vitro cyto- and photocyto-toxicity of nanoparticles-based photosensitizers compared with classical metabolic assays. To do so, we introduced a dynamic approach based on real-time cell impedance monitoring and a mathematical model-based analysis to characterize the measured dynamic cell response. Analysis of real-time cell responses requires indeed new modeling approaches able to describe suited use of dynamic models. In a first step, a multivariate analysis of variance associated with a canonical analysis of the obtained normalized cell index (NCI) values allowed us to identify different relevant time periods following nanoparticles exposure. After light irradiation, we evidenced discriminant profiles of cell index (CI) kinetics in a concentration- and light dose-dependent manner. In a second step, we proposed a full factorial design of experiments associated with a mixed effect kinetic model of the CI time responses. The estimated model parameters led to a new characterization of the dynamic cell responses such as the magnitude and the time constant of the transient phase in response to the photo-induced dynamic effects. These parameters allowed us to characterize totally the in vitro photodynamic response according to nanoparticle-grafted photosensitizer concentration and light dose. They also let us estimate the strength of the synergic photodynamic effect. This dynamic approach based on statistical modeling furnishes new insights for in vitro characterization of nanoparticles-mediated effects on cell proliferation with or without light irradiation.  相似文献   

14.
Aim We present an integrated approach for predicting future range expansion of an invasive species (Chinese tallow tree) that incorporates statistical forecasting and analytical techniques within a spatially explicit, agent‐based, simulation framework. Location East Texas and Louisiana, USA. Methods We drew upon extensive field data from the US Forest Service and the US Geological Survey to calculate spread rate from 2003 to 2008 and to parameterize logistic regression models estimating habitat quality for Chinese tallow within individual habitat cells. We applied the regression analyses to represent population spread rate as a function of habitat quality, integrated this function into a logistic model representing local spread, and coupled this model with a dispersal model based on a lognormal kernel within the simulation framework. We simulated invasions beginning in 2003 based on several different dispersal velocities and compared the resulting spatial patterns to those observed in 2008 using cross Mantel’s tests. We then used the best dispersal velocity to predict range expansion to the year 2023. Results Chinese tallow invasion is more likely in low and flat areas adjacent to water bodies and roads, and less likely in mature forest stands and in pine plantations where artificial regeneration by planting seedlings is used. Forecasted invasions resulted in a distribution that extended from the Gulf Coast of Texas and Louisiana northward and westward as much as 300 km, representing approximately 1.58 million ha. Main conclusions Our new approach of calculating time series projections of annual range expansion should assist land managers and restoration practitioners plan proactive management strategies and treatments. Also, as field sampling continues on the national array of FIA plots, these new data can be incorporated easily into the present model, as well as being used to develop and/or improve models of other invasive plant species.  相似文献   

15.
Vegetation changes, particularly those involving transitions between tree‐ and grass‐dominated covers, often modify evaporative water losses as a result of plant‐mediated shifts in moisture access and demand. Massive afforestation of native grasslands, particularly important in the Southern Hemisphere, may have strong yet poorly quantified effects on the hydrological cycle. We explored water use patterns in Eucalyptus grandis plantations and the native humid grasslands that they replace in Central Argentina. In order to uncover the interactive effects that land cover type, soil texture and climate variability may have on evaporative water losses and water use efficiency, we estimated daily evapotranspiration (ET) in 117 tree plantations and grasslands plots across a soil textural gradient (clay‐textured Vertisols to sandy‐textured Entisols) using radiometric information from seven Landsat scenes, existing timber productions records, and 13C measurements in tree stems. Tree plantations had cooler surface temperatures (?5°C on average) and evaporated more water (+80% on average) than grasslands at all times and across all sites. Absolute ET differences between grasslands and plantations ranged from ~0.6 to 2 mm day?1 and annual up‐scaling suggested values of ~630 and ~1150 mm yr?1 for each vegetation type, respectively. The temporal variability of ET was significantly lower in plantations compared with grasslands (coefficient of variation 36% vs. 49%). Daily ET increased as the water balance became more positive (accumulated balance for previous 18 days) with a saturation response in grassland vs. a continuous linear increase in plantations, suggesting lower ecophysiological limits to water loss in tree canopies compared with the native vegetation. Plantation ET was more strongly affected by soil texture than grassland ET and peaked in coarse textured sites followed by medium and fine textured sites. Timber productivity as well as 13C concentration in stems peaked in medium textured sites, indicating lower water use efficiency on extreme textures and suggesting that water limitation was not responsible for productivity declines towards finer and coarser soils. Our study highlighted the key role that vegetation type plays on evapotranspiration and, therefore, in the hydrological cycle. Considering that tree plantations may continue their expansion over grasslands, problematic changes in water management and, perhaps, in local climate can develop from the higher evaporative water losses of tree plantations.  相似文献   

16.
The decline in distribution and abundance of biodiversity requires evidence-based guidelines for cost-effective conservation management and systematic quantitative assessments of its effects. We investigated the efficiency of a habitat restoration programme aimed at reducing the risk of extinction of the Iolas blue Iolana iolas (Ochsenheimer, 1816), one of the rarest butterflies of Central Europe. Using occupancy and capture-mark-recapture (CMR) models accounting for probability of detection, we assessed habitat patch occupancy, habitat selection, demography and dispersal with the aim of testing and refining restoration measures. Count surveys performed at 38 plantations dedicated to the species’ unique host plant resulted in an occupancy rate of 50 %, with mostly very low relative abundance indices. The site-occupancy habitat analysis demonstrated that species abundance was best explained by host plant vitality, habitat patch connectivity, and solar radiation. CMR surveys yielded very high catchability (82 %), individual detectability (86 %) rates and limited dispersal capacity. These results form the basis for future efficient count surveys to assess species distribution and abundance. They also provide evidence-based recommendations for improving ongoing habitat restoration: (i) the attractiveness of host plant plantations must be enhanced by promoting mass blossoming, which can be achieved through systematic autumn pruning of the extant plantations; (ii) new plantations should be created in order to fill in the gaps in the landscape matrix, to increase meta-population capacity through improved habitat connectivity. Finally, this study demonstrates the relevance of efficiency tests as an integral, adaptive phase of any conservation research activity.  相似文献   

17.
Luk VN  Fiddes LK  Luk VM  Kumacheva E  Wheeler AR 《Proteomics》2012,12(9):1310-1318
Proteolytic digestion is an essential step in proteomic sample processing. While this step has traditionally been implemented in homogeneous (solution) format, there is a growing trend to use heterogeneous systems in which the enzyme is immobilized on hydrogels or other solid supports. Here, we introduce the use of immobilized enzymes in hydrogels for proteomic sample processing in digital microfluidic (DMF) systems. In this technique, preformed cylindrical agarose discs bearing immobilized trypsin or pepsin were integrated into DMF devices. A fluorogenic assay was used to optimize the covalent modification procedure for enzymatic digestion efficiency, with maximum efficiency observed at 31 μg trypsin in 2-mm diameter agarose gel discs. Gel discs prepared in this manner were used in an integrated method in which proteomic samples were sequentially reduced, alkylated, and digested, with all sample and reagent handling controlled by DMF droplet operation. Mass spectrometry analysis of the products revealed that digestion using the trypsin gel discs resulted in higher sequence coverage in model analytes relative to conventional homogenous processing. Proof-of-principle was demonstrated for a parallel digestion system in which a single sample was simultaneously digested on multiple gel discs bearing different enzymes. We propose that these methods represent a useful new tool for the growing trend toward miniaturization and automation in proteomic sample processing.  相似文献   

18.
An integrated pest management programme for control of the psyllid,Ctenarytaina thysanura (Ferris & Klyver) (Hemiptera: Psyllidae) in commercial boronia plantations was developed and implemented from 1986–1989. The programme involved spraying boronia stems only with the systemic organophosphate mevinphos at peak incidence of late stage nymphs. At this time, the majority of parasitoids were pupating within mummified hosts. Consequently, actively feeding nymphs were potentially susceptible to mevinphos but the parasitoids were not. Stem application negated any contact effect on parasitoids and predators. The conservation of natural enemies subsequently reduced psyllid numbers and no insecticide has been required since 1989. In economic terms the benefit to cost ratio of the IPM programme was $22.40: $1.0 and this was 40 times greater than the conventional 10 demeton-S-methyl sprays used by growers prior to the study.  相似文献   

19.
整体医疗管理是在整体论和医学整体观启发下产生的医院医疗管理新理论。医院整体医疗管理弥补了传统医院医疗管理模式的不足,对促进医院服务由医疗救治模式向院前、院内、院后全程化,预防、医疗、保健、康复一体化的健康服务模式转化具有重要意义。文章论述了实行医院整体医疗管理的必要性,讨论了其思想基础、变革目标以及基本运作模式。  相似文献   

20.
The incongruency of diurnally varying resources essential to plants may detrimentally affect plants early in their development as indicated by reduced water use efficiency and carbon gain. Typical diurnal patterns of light and CO(2) availability in a midsized temperate herbaceous or forest gap were simulated in specially designed growth chambers. A sinusoidally varying CO(2) treatment (400 ppm minimum, 800 ppm maximum) approximated the diurnal cycle of CO(2) at the soil surface, while a steady-state CO(2) treatment (600 ppm) with the same average CO(2 )concentration provided a control. Crossed with these two CO(2) treatments were two light regimes, one with 3 h of high light (850 μmol·m·s) in the morning (west side of a gap), and the other with 3 h of high light in the afternoon (east side). All treatments received baseline low light (55 μmol·m·s) for 14 h during the day. Rumex crispus was selected as a model species because of its rosette leaves, which grow close to the ground where diurnal CO(2 )variation is greatest. The relative timing of diurnal variations in light and CO(2) significantly affected seedling water use efficiency, carbon gain, and morphology. Total biomass, photosynthetic rates, daily integrated carbon, water use efficiency, and leaf area were enhanced by morning exposure to high light. Seedlings that were exposed to peak values of light and CO(2) incongruently, i.e., those plants receiving intense afternoon light with diurnally varying CO(2), were detrimentally affected relative to control plants receiving intense afternoon light with steady-state CO(2). The results of this experiment indicate that the incongruent availability of required resources-such as light and CO(2)-can detrimentally affect performance relative to when resources are congruent. These contrasting resource regimes can occur on the east and west side of gaps.  相似文献   

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