Indirect Effects Of Environmental Factors Research Articles

Temperature related to the spatial heterogeneity of wetland soil total nitrogen content in a frozen zone

Changes in soil total nitrogen (N) content would affect wetland function and the global N cycle. Determination of spatial heterogeneity controlling factors of wetland soil total N content per unit mass is essential to assess responses of ecosystem N cycle to global change. However, such information is limited in permafrost zones because few soil profiles have been acquired and methods to predict spatial distributions of wetland soil total N content in large areas are inefficient, which increase uncertainty in evaluations of N cycle at national or global scales. To determine the spatial heterogeneity of wetland soil total N content at different soil depths and frozen zones and the factors controlling wetland soil total N content in the frozen zones of Northeast China, the spatial pattern of wetland soil total N content was investigated by using a random forest method that combined field samples with environmental factors. Vertically, wetland soil total N content decreased with increasing soil depth, with the highest content in the top soil layer (0–30 cm). Spatially, wetland soil total N content decreased from northwest to southeast, with relatively high total N content in a continuous permafrost zone and relatively low total N content in a seasonally frozen zone. The overall coefficient of variation of wetland soil total N content in the frozen zones of Northeast was 29.58 %, indicating moderate variation. Land surface temperature, mean annual temperature, and mean annual humidity significantly affected total N content in 0–30 and 30–60 cm soil layers, suggesting that variations in temperature and humidity altered sequestration processes of wetland soil total N content. In the 60–100 cm soil layer, compared with other environmental factors, mean annual humidity, altitude, and mean annual precipitation had the greatest influence on the spatial distribution of wetland soil total N content. The study unravels the spatial pattern of soil total N content in frozen zones of Northeast China and reflects the direct and indirect effects of environmental factors on total N content. This provides a basis for the management and protection of wetland ecosystems.

Diversity-biomass relationships are shaped by tree mycorrhizal associations and stand structural diversity at different spatial scales

Diversity-biomass relationships (DBRs) in terrestrial ecosystems tend to vary across spatial scales, but, particularly in hyperdiverse forests, the mechanisms driving these trends remain uncertain. Until now, few have simultaneously investigated the connections between tree species diversity, stand structural diversity, mycorrhizal associations, and ecosystem functioning. In addition, DBRs have only been studied at limited spatial scales, with limited focus on the direct and indirect effects of environmental factors. We addressed these research gaps using a 30-ha forest dynamics plot located in Pu'er City, Southwest China. Through piecewise structural equation models, we quantified the direct effects of tree species diversity (α, β, γ), stand structural diversity, mycorrhizal associations (AM, EcM), and the environmental factors (soil fertility and topography), as well as the indirect effects of the environmental factors on aboveground tree biomass across spatial scales ranging from 400 to 230,400 ​m2. We hypothesized that complex interactions among these factors underpin the variation in DBRs in natural ecosystems across spatial scales. Our results showed that environmental conditions indirectly affected the tree biomass via changes in tree species diversity, and these effects became stronger as the spatial scale increased. At small to moderate spatial scales, environmental factors were more predictive of tree biomass than tree species diversity (or its components); the effects of stand structural diversity on biomass also gradually increased with spatial scale. Conversely, from the intermediate to the largest spatial scales, mycorrhizal associations gradually became the best predictors of DBR dynamics. Our research offers novel empirical evidence demonstrating the importance of environmental conditions, structural diversity, and mycorrhizal associations in shaping cross-scale DBRs. Future comprehensive studies should consider these factors to assess the mechanisms shaping scale-dependent DBRs in complex natural ecosystems.

Effects of land-use intensity on vegetation dynamics across elevation in Savanna Grassland, Southern Ethiopia

The rangeland ecosystem is currently one of the area’s most sensitive to biodiversity because of both natural and human effects. There is still much to learn about the sustainable management of dry and semi-arid rangelands in order to protect their rich biodiversity resources. This is due to the uncertain indirect effects of environmental factors, such as dryness, on vegetation species, which are mediated by shifting both living and non-living components. The purpose of this project was to ascertain the effects of land use intensity (LUI) on the various species of rangeland flora along the elevation gradient in the Borana Rangeland. We gathered a total of 37 plant species, comprising 22 grasses, 7 graminoids, and 8 forbs, from the nine sampling locations, which were exposed to LUI and included three locations within each elevation range of 500–900, 1000–1400, and 1500–1900 m.a.s.l. At every sampling site, we evaluated the dynamics of the plant species, taking into account their diversity, richness, percentage of undesirable species, and properties of the soil. We used structural equation modeling (SEM) to examine the effects of LUI on the different vegetation species along the elevation gradient. We found that the density and diversity of vegetative species decreased and the fraction of undesired species increased as elevation climbed (from lower to higher). Because of the heavy livestock grazing, these impacts were substantially linked with high LUI at lower elevations. According to our research, the complex relationships between elevation gradient and LUI have a big influence on the diversity and density of the flora. This demonstrates that we need to account for environmental gradients in order to generalize LUI's effects on rangeland biodiversity. This study sheds important light on the complex interactions between vegetation dynamics and LUI in savanna grasslands. To create practical strategies for maintaining ecosystem health and biodiversity in the Southern Ethiopian Savanna Grasslands, policymakers, environmentalists, and land managers should take these findings into account.

Vegetation canopy structure mediates the response of gross primary production to environmental drivers across multiple temporal scales

Gross primary production (GPP) is a critical component of the global carbon cycle and plays a significant role in the terrestrial carbon budget. The impact of environmental factors on GPP can occur through both direct (by influencing photosynthetic efficiency) and indirect (through the modulation of vegetation structure) pathways, but the extent to which these mechanisms contribute has been seldom quantified. In this study, we used structural equation modeling and observations from the FLUXNET network to investigate the direct and indirect effects of environmental factors on terrestrial ecosystem GPP at multiple temporal scales. We found that canopy structure, represented by leaf area index (LAI), is a crucial intermediate factor in the GPP response to environmental drivers. Environmental factors affect GPP indirectly by altering canopy structure, and the relative proportion of indirect effects decreased with increasing LAI. The study also identified different effects of environmental factors on GPP across time scales. At the half-hourly time scale, radiation was the primary driver of GPP. In contrast, the influences of temperature and vapor pressure deficit took on greater prominence at longer time scales. About half of the total effect of temperature on GPP was indirect through the regulation of canopy structure, and the indirect effect increased with increasing time scale (GPPNT-based models: 0.135 (half-hourly) vs. 0.171 (daily) vs. 0.189 (weekly) vs. 0.217 (monthly); GPPDT-based models: 0.139 vs. 0.170 vs. 0.187 vs. 0.215; all values were reported in gC m−2 d−1 °C−1, P < 0.001); while the indirect effect of radiation on GPP was comparatively lower, accounting for less than a quarter of the total effect. Furthermore, we observed a direct, negative-to-positive impact of precipitation on GPP across timescales. These findings provide crucial information on the interplay between environmental factors and LAI on GPP and enable a deeper understanding of the driving mechanisms of GPP.

Evaluation and mapping soil organic carbon in seasonally frozen ground on the Tibetan Plateau

Seasonally frozen ground (SFG) significantly contributes to global carbon sinks. Global warming and anthropogenic-induced disturbances threaten the carbon storage capacity of SFG. Challenges in evaluating the SFG carbon storage potential include the lack of understanding of the control mechanisms of soil organic carbon (SOC) variations and timely spatial estimates of SOC. In this study, we investigated SOC stocks in SFG in the Tibet Autonomous Region, China, in 2020 and 2021. We employed partial least squares structural equation modeling (PLS-SEM) to explore the effect of complex processes (interacting roles of climate, plant physiology and phenology, freeze–thaw cycle, soil environment, and C inputs) on SOC and mapped SOC stocks in the topmost 30 cm. We identified four causal pathways: (1) an indirect pathway representing the effect of climate on plant physiology and phenology through changes in freeze–thaw cycles and soil environment, (2) an indirect pathway representing the effect of climate on C inputs through changes in freeze–thaw cycles, soil environment and plant physiology and phenology, (3) an indirect pathway representing the effect of climate on freeze–thaw cycles, and (4) an indirect pathway representing the effect of climate on the soil environment through changes in freeze–thaw cycles. C inputs exerted the greatest control on SOC. The effect of these factors decreased with increasing soil depth. We used PLS-SEM to generate maps of SOC stocks in SFG at a 500 m resolution with a moderate accuracy. The estimated mean SOC stocks in the 0–30 cm layer reached 6.87 kg m−2, with a 95% confidence interval ranging from 6.2 to 7.5 kg m−2. Our results indicated that it is critical to consider the depth dependence of the direct and indirect effects of environmental factors when assessing the control mechanisms of SOC variations. In this work, we also demonstrated that spatially explicit SOC estimates based on timely investigations are important for assessing C stocks against the background of considerable environmental changes across the Tibetan Plateau.

Interaction Processes of Environment and Plant Ecophysiology with BVOC Emissions from Dominant Greening Trees

In global greening, biogenic volatile organic compound (BVOC) emissions and their influencing factors have been considered due to their significant roles in the biosphere and atmosphere. Many studies have reported relationships of BVOC emissions with environmental factors and plant ecophysiology. However, the direct and indirect effects of environmental factors on BVOC emissions remain unclear, and the causal relationships between plant ecophysiology and BVOC emissions are ambiguous. We measured the isoprene and monoterpene emissions from dominant greening plants using a dynamic enclosure system and quantified the interactions of environment–-plant and ecophysiology–BVOC emissions using a path analysis model. We found that isoprene emission was directly affected by photosynthetic rate, and indirectly affected by photosynthetically active radiation and air temperature (Tair). Monoterpene emissions were directly affected by atmospheric pressure, relative air humidity and specific leaf weight, and indirectly affected by Tair.

Co-regulation of temperature and moisture in the irrigated agricultural ecosystem productivity

Agroecosystem photosynthesis is key to coping with global climate change. In farmland where human activities are highly involved, the interaction between environmental factors and their influences on gross primary productivity (GPP) are insufficiently understood. Particularly, the irrigation and mulching in water-saving agriculture can alter the crop responses to environmental change. Based on eddy covariance measurements of maize fields under mulched drip irrigation (DM) and mulched border irrigation (BM) in arid areas of Northwest China from 2014 to 2018, we systematically studied the interaction between multiple environmental factors and their independent effects on GPP using structural equation modeling, partial correlation coefficient and decoupling analysis by bins. The top three factors exerting the largest total effects on the GPP were soil temperature (Ts), canopy temperature (Tc) and vapor pressure deficit (VPD), among which Ts (0.75) and Tc (0.66) had the largest total effect on GPP under DM and BM, respectively. The independent effects of Ts, soil water content (SWC) and VPD on GPP were different under the two irrigation methods. SWC after excluding the influence of Ts showed a negative effect on GPP under DM (−1.24 g Cm−2d−1), while a positive effect under BM (0.02 g Cm−2d−1). By contrast, SWC after excluding the influence of VPD showed a positive effect on GPP under DM (0.59 g Cm−2d−1), while a negative effect under BM (−0.05 g Cm−2d−1). Interestingly, higher Ts, lower SWC and higher VPD had the potential to increase GPP under the two irrigation methods. We also found that the total effects of irrigation and VPD as well as the indirect effects of environmental factors on GPP should not be ignored. Our study will provide important reference for dealing with the effect of high temperature and drought stress on agro-ecosystem GPP and evaluating the response of vegetation to environmental factors.

Ship navigation disturbance alters multiphase distribution of perfluoroalkyl acids and increases their ecological risk in waterways

As a global persistent organic pollutant, perfluoroalkyl acids (PFAAs) have aroused great public concern. However, little is known regarding the effect of ship navigation disturbance on the transport and fate of PFAAs in inland waterways developed regions. In the present study, overlying water, pore water, suspended particulate matter (SPM), and sediment were collected from waterways (WWs), non-navigable channels (NCs), and ports (PTs) in Taihu Lake Basin. The results revealed that the total concentrations of PFAAs (ΣPFAAs) in WWs, NCs, and PTs varied considerably in different media. In overlying water, the mean ΣPFAAs in WWs were the highest, while those of NCs were relatively higher in the remaining three media. A comparison of PFAA distribution coefficients revealed that the values in NCs were generally higher than those of WWs and PTs, suggesting the critical role of ship navigation in PFAA transport. Furthermore, a structural equation model was applied to estimate direct and indirect effects of environmental factors on PFAA partitioning behavior. The results revealed that ship traffic volume (STV) exerted indirect effects on PFAA distribution between solid and dissolved phases by influencing dissolved oxygen, total suspended solid concentration, clay and sand contents, and median diameter. PFAAs were more readily to be released into overlying water from pore water than in sediment, and the ΣPFAAs carried per gram of SPM decreased with an increase in STV. Ecological risk assessment and Monte Carlo simulation results revealed that ship navigation could exert adverse effects on aquatic organisms, making the average probability of RQmix values to exceed corresponding risk values in WWs, which were 1.3–2-fold higher than in NCs. The present study provides crucial information for simulating the environmental behaviors of PFAAs under the influence of ship navigation and is significant for the integration of inland water transport development and aquatic environmental protection.

Direct and indirect effects of environmental factors, spatial constraints, and functional traits on shaping the plant diversity of montane forests.

Understanding the relative importance of the factors driving the patterns of biodiversity is a key research topic in community ecology and biogeography. However, the main drivers of plant species diversity in montane forests are still not clear. In addition, most existing studies make no distinction between direct and indirect effects of environmental factors and spatial constraints on plant biodiversity. Using data from 107 montane forest plots in Sichuan Giant Panda habitat, China, we quantified the direct and indirect effects of abiotic environmental factors, spatial constraints, and plant functional traits on plant community diversity. Our results showed significant correlations between abiotic environmental factors and trees (r = .10, p value = .001), shrubs (r = .19, p value = .001), or overall plant diversity (r = .18, p value = .001) in montane forests. Spatial constraints also showed significant correlations with trees and shrubs. However, no significant correlations were found between functional traits and plant community diversity. Moreover, the diversity (richness and abundance) of shrubs, trees, and plant communities was directly affected by precipitation, latitude, and altitude. Mean annual temperature (MAT) had no direct effect on the richness of tree and plant communities. Further, MAT and precipitation indirectly affected plant communities via the tree canopy. The results revealed a stronger direct effect on montane plant diversity than indirect effect, suggesting that single‐species models may be adequate for forecasting the impacts of climate factors in these communities. The shifting of tree canopy coverage might be a potential indicator for trends of plant diversity under climate change.

Direct and indirect effects of environmental factors on daily CO2 exchange in a rainfed maize cropland—A SEM analysis with 10 year observations

The carbon budget of agricultural ecosystems is of great importance to the global carbon balance. In this study, the structural equation modeling (SEM) method was employed to quantify the direct and indirect effects of environmental factors on daily net ecosystem CO2 exchange (NEE) in a rainfed maize cropland, northeast China. The results showed that net radiation (Rn) was the most important factor controlling daily NEE, followed by the leaf area index (LAI), air temperature (Ta), vapor pressure deficit (VPD), and clearness index (Kt). The strong effect of Rn was mainly attributed to its direct effect, while Ta and VPD showed comparable or even higher indirect effects than direct effects, indicating that Ta and VPD influenced NEE mainly through regulating canopy development on a daily scale. Moreover, the responses of NEE to individual environmental factors differed greatly among multiyear climatic conditions. Ta and VPD were shown to be more important in warm (WM) years and warm and dry (WD) years than in normal (NM) years and cold and wet (CW) years. LAI was the primary controlling factor of daily NEE in WD years, resulting in large indirect effects of Ta and VPD on NEE. Kt had a large effect on daily NEE only in CW years. SWC had significant effects on daily NEE in WM and WD years but in the opposite direction, i.e., daily NEE increased with SWC in WD years but decreased with SWC in CW years. The partitioning of direct and indirect effects of environmental factors with SEM can greatly enhance the understanding of the controlling mechanism of NEE and remind researchers to consider the distinct effects of environmental factors on NEE among multiyear climatic conditions in future models.

Relative effects of wind-induced disturbances and vegetation on tetrabromobisphenol A cycling in shallow lakes: Direct and indirect effects

The environmental concerns regarding the possible threats of tetrabromobisphenol A (TBBPA) to aquatic environments are increasing. However, information about TBBPA cycling in the water-vegetation-sediment systems of shallow lakes is limited. In a shallow lake, wind-induced disturbance is considered as the key factor of affecting the cycling of contaminants. To address this issue, the TBBPA distribution and elimination processes were simulated for three typical wind speeds by using an annular flume. Four forms of TBBPA were studied in these systems, including water, suspended solids (SS), vegetation and sediment. The results showed that the mass distributions of TBBPA in water, SS and vegetation increased remarkably while enhancing the wind-induced disturbances, which resulted from the release of TBBPA from the sediment through resuspension and adsorption-desorption processes. However, most of the TBBPA (up to 94%) still accumulated in the sediment. Wind-induced disturbances and vegetation both increased the TBBPA elimination rate in the water-vegetation-sediment systems. The half-life (T1/2) of TBBPA in the fast wind condition was 16.1 ± 0.2 days, which was shorter than that in the static condition (29.8 ± 0.9 days). Compared to the systems without vegetation, the presence of vegetation shortened the T1/2 by 7.3 days in the static condition. Furthermore, a structural equation model (SEM) was used to assess the direct and indirect effects of environmental factors on the TBBPA amounts in each form. The main effects of wind speed and vegetation in the TBBPA cycling of each form (except for the TBBPA on vegetation) were indirect by affecting the dissolved oxygen (DO), velocity and suspended solids concentration (SSC). Overall, the findings provide useful information about the fate of TBBPA and other related organic contaminants in shallow lake systems.

Phylogenetic constraints to soil properties determine elevational diversity gradients of forest understory vegetation

Elevational diversity gradients (EDGs) of vegetation are shaped by the evolutionary histories of plants as well as by ecological factors. However, few studies of EDGs have focused on the roles of phylogenetic constraints and the effects of complicated interactions among environmental factors. Here, we examine the direct and indirect effects of environmental factors in forming EDGs of forest understory vegetation. The study plots were selected along elevational gradients in cool-temperate and sub-alpine forests in the University of Tokyo Chichibu Forest of central Japan. Tree seedlings and herbs were identified, and environmental factors (elevation, soil temperature, soil pH, soil CN ratio, forest type, basal area, canopy openness, and slope) were measured in these plots. Structural equation modeling (SEM) including taxonomic and phylogenetic diversity was used to consider the causal relationships between environmental conditions and the diversity of understory vegetation. In addition, phylogenetic signals in habitat requirements were tested. The taxonomic and phylogenetic diversities of tree seedlings increased monotonically with elevation, and the same pattern was found for the taxonomic diversity of herbs. The SEM indicated that both the taxonomic and phylogenetic diversity of tree seedlings were most affected by soil properties, although the phylogenetic diversity of herbs was determined by light conditions. These results highlight the importance of environmental filtering by soil properties in shaping EDGs of tree seedlings. This study implies that phylogenetic constraints in the adaptation to soil properties should be considered when predicting changes in EDGs under environmental fluctuations.

Direct and indirect effects of environmental factors on dietary niches in size‐structured populations of a wild salmonid

Dietary plasticity of populations can be associated to ontogenetic diet preferences and depends on the size‐structure of populations. Dietary niche characterizes the functional role of organisms in a food web, as it reflects both resources' diversity used by a consumer and trophic interactions in the system. Dietary niches are controlled both by biotic and abiotic factors, but their interactions in natural systems remain poorly studied. Here, we investigated the variability of dietary niche in salmonid wild populations focusing both on inter‐population and intra‐population (through time) trophic changes, using marble trout (Salmo marmoratus) living in Slovenian headwater streams as a model system. Stable isotope analysis showed high variability of dietary niche and trophic diversity among six of the seven remnant marble trout populations. We observed substantial differences in dietary niche width among populations and within populations through time. Results of partial least square path modelling highlighted opposite effects of immature and mature trout on trophic niche structure. Direct effects of temperature and slope (stream and watershed) were opposite; temperature narrowed dietary niches while slope increased them. Environmental factors (e.g., temperature, stream and watershed slope) had indirect effects on trophic niches after accounting for fish density. Our results showed that size‐distribution and sexual maturity are key determinants of the dietary niche width in a population. Increasing density of immature trout tended to widen the dietary niche while increasing density of mature trout tended to narrow it. Environmental factors had direct effects both on resources and consumers densities and indirect effects. Direct and indirect effects were often antagonistic.

Climatic Factors as Determinants of International Migration

AbstractWe examine natural disasters and long‐run climatic factors as potential determinants of international migration, implementing a panel dataset of bilateral migration flows from 1960 to 2000. We find no direct effect of long‐run climatic factors on international migration across our entire sample. These results are robust when conditioning on origin‐country characteristics, when considering migrants returning home, and when accounting for the potential endogeneity of migrant networks. Rather, we find evidence of indirect effects of environmental factors operating through wages. We find that epidemics and miscellaneous incidents spur international migration, and there is strong evidence that natural disasters beget greater flows of migrants to urban environs.

Critical effects of gas exchange parameters in Tamarix chinensis Lour on soil water and its relevant environmental factors on a shell ridge island in China's Yellow River Delta

Photosynthetic parameters of the leaves of a three-year-old Tamarix chinensis Lour tree growing on a shell ridge island were assessed under different soil water conditions with a LI-6400 portable photosynthesis system. The objective of the study was to relate the critical effects of the net photosynthetic rate (Pn), transpiration rate (Tr), water use efficiency (WUE) and other physiological parameters of T. chinensis Lour to soil water and to classify its productivity. The direct and indirect effects of environmental factors under different relative water content (RWC) regimes on Pn and Tr were calculated using path analysis. The results indicated that when the RWC was between 36% and 85%, both the net photosynthetic rate (Pn) and transpiration rate (Tr) exhibited a double-peak curve. The decline in Pn was mainly caused by stomatal limitation in morning and non-stomatal limitation in afternoon. The maximum value of Pn (8.3±1.7mmolm−2s−1) appeared at an RWC value of 75%. There was significant difference in the response of water use efficiency (WUE) among levels of RWC: diurnal changes in WUE exhibited a modest single-peak curve when the RWC was greater than 49% and were highest (daily average, 2.56±0.68μmolmol−1) when the RWC was 49%. According to the quantitative relations between the Pn, Tr, WUE and RWC, the suitable RWC for T. chinensis Lour growth is between 36% and 75%. Based on photosynthetic and physiological parameters, soil water availability and productivity was classified and evaluated. An RWC of more than 93% or less than 36% resulted in medium yield and efficiency, and an RWC between 19% and 27% was classified as low yield and efficiency. RWCs ranging from 75% to 85% and 49% to 75% were classified as high yield-medium efficiency and high yield-high efficiency, respectively. Our statistical analysis indicated that photosynthetic active radiation (PAR) was the most important ecological factor affecting Pn and Tr, followed by air CO2 concentration (Ca). With the intensification of water stress, the atmospheric temperature (Tc) evidently restrained Pn and Tr.

吉林不同生境防风夏季光合特性

PDF HTML阅读 XML下载 导出引用 引用提醒 吉林不同生境防风夏季光合特性 DOI: 10.5846/stxb201208081122 作者: 作者单位: 吉林农业大学,中国科学院东北地理与农业生态研究所,吉林农业大学,吉林农业大学,吉林省和龙市科学技术情报研究所,吉林农业大学 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金（31300270）；国家科技支撑计划项目（2011BAI03B01-02）；教育部博士点新教师基金（20112223120004）；吉林省科技发展计划项目（20130522048JH） Photosynthetic characteristics of Saposhnikovia divaricata in different habitats in summer Author: Affiliation: College of Chinese Medicinal Materials,Jilin Agricultural University,Northeast Institute of Geography and Agroecology,Chinese Academy of Sciences,College of Chinese Medicinal Materials,Jilin Agricultural University,College of Chinese Medicinal Materials,Jilin Agricultural University,Helong Institute of Scientific and Technical Information of Jilin Province,College of Chinese Medicinal Materials,Jilin Agricultural University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:采用LCpro+全自动便携式光合仪同时测定了长春、长岭和白城3个生境防风的光合作用及环境因子，研究不同生境防风净光合速率、蒸腾速率及水分利用效率等日变化特征及其与生态因子之间关系，并采用通径分析法分析各环境因子对防风净光合速率的直接和间接影响，探讨防风的光合生理规律，为进一步研究防风的光合生理提供依据。结果表明，各环境因子之间存在相互作用，在影响防风光合作用的环境因子中，光合有效辐射（PAR）是驱动因子，它的变化驱动了大气温度（Ta）、叶片温度（Tl）变化，Ta升高引起空气密度的变化是午间相对湿度（RH）和大气浓度CO2（Ca）降低的一个重要原因。环境因子中对Pn直接作用由大到小长春为Tl >Ta > PAR >Ca >RH ，长岭为PAR >Tl > RH > Ca >Ta，白城为Ta >Tl >RH > PAR >Ca。长春、长岭PAR与Pn相关系数最大，而白城地区Ca与Pn相关系数最大，说明防风叶片对不同环境因子的反应有所不同。8月份3个地区防风净光合速率日变化均呈双峰型曲线，具有明显的光合"午休"现象。长春、长岭地区防风光合"午休"现象主要由气孔因素引起，白城地区防风光合"午休"现象主要由非气孔因素引起的。3个生境防风的Pn与Gs之间均呈显著的正相关关系，白城的Gs比长春、长岭地区的低44%左右，这是防风为适应高温干旱的环境而形成的生理反应。不同生境土壤含水量间差异显著，白城地区土壤水分含量很低，只有20.35%，仅是长春土壤含水量的56.50%，而空气温度较高，强辐射使气孔叶片蒸腾失水加剧，导致叶片含水量也很低，仅仅为56.60%，高温干旱使防风叶温升高，防风磷酸化、电子传递、酶活性等受到抑制，导致光合速率降低。因此，白城地区长期高温胁迫是限制防风Pn的主要原因。 Abstract:Photosynthesis of Saposhnikovia divaricata (Turcz.) Schischk. and environmental factors were measured by using LCPro+ portable photosynthesis system in Changchun, Changling and Baicheng, the diurnal changes in net photosynthetic rate (Pn), transpiration rate (E) and water use efficiency (WUE) of S. divaricata and their relationships with environmental factors were studied, and direct and indirect effects of environmental factors on net photosynthetic rate were calculated through the path analysis in different habitats in order to discuss photosynthetic physiology rule of S. divaricata . This knowledge could provide basis for further study the photosynthetic physiology of S. divaricata . The results showed that there were significant interactions among environmental factors, variation of photosynthetically active radiation (PAR) triggered the fluctuations of air temperature (Ta) and leaf temperature (TL), and Ta was closely related to the air density, which had significant impacts on the air CO2 concentration (Ca) and relative humidity (RH), the reduce of air density affected by increase of Ta was the one of important causes, which decreased the RH and Ca at noon. Environmental factors driven intrinsically by PAR superposed an integrative effect on Pn. And the responses of the species to the environmental factors were different in different habitats, and the direct effects of environmental factors in three different habitats were of the order: Tl >Ta > PAR >Ca >RH in Changchun, PAR >Tl >RH >Ca >Ta in Changling and Ta >Tl >RH > PAR >Ca in Baicheng. The correlation coefficients between PAR and Pn were the biggest in Changchun and Changling, but Ca and Pn was the biggest in Baicheng. The diurnal changes in Pn of the species in different habitats were similar and could be expressed as two-hump curves, reflecting a significant middy depression at noon. The decrease in Pn during midday was mainly resulted from stomatal limitation in Changchun and Changling, but non-stomatal limitation occurred in Baicheng. There were significant positive correlations between Pn and Gs in three ecological regions, Gs in Baicheng was about 44% lower than in Changchun and Changling, this was a physiological reaction in order to response to high temperature and drought in Baicheng. The soil water content differed significantly in different habitats, it was only 20.35% in Baicheng, and that was 56.50% of that in Changchun, but air temperature in Baicheng was high, leaf water content was only 56.60%, which resulted from leaf strong transpiration and water loss affected by intense radiation. So the net photosynthetic rate decreased because of that the phosphorylation, electron transfer and enzyme activities of S. divaricata were restrained by high leaf temperature. So heat-stress was one of critical factors constraining Pn in Baicheng. 参考文献 相似文献 引证文献

Climatic Factors as Determinants of International Migration

We examine environmental change as a potential determinant of international migration. We distinguish between unexpected short-run factors, captured by natural disasters, as well as long-run climate change and climate variability captured by deviations and volatilities of temperatures and rainfall from and around their long-run averages. Starting from a simple neo-classical model we use a panel dataset of bilateral migration flows for the period 1960-2000 that allows us to control for numerous time-varying and time invariant factors. We find no direct impact of climatic change on international migration across our entire sample. These results are robust when conditioning on characteristics of origin countries as well as when further considering migrants returning home and the potential endogeneity of our network variable. In contrast, there is evidence of indirect effects of environmental factors going through wages. We further find strong evidence that natural disasters beget greater flows of migrants to urban environs.

甜瓜幼苗叶片光合变化特性

为探讨甜瓜光响应变化特性与环境因子的关系,选择光响应曲线适宜测定的时段,以甜瓜幼苗为试材,将1 d分为3个时段:10:00-12:00、12:00-15:00和15:00-17:00,每个叶位叶片测定1 d,并采用直角双曲线修正模型拟合光响应曲线,研究不同时段下甜瓜叶片光响应曲线、光响应参数的变化趋势和不同叶位叶片光响应参数特性。结果表明:当环境中光合有效辐射增强,叶面温度(<em>Tl</em>)升高,空气相对湿度(<em>RH</em>)降低;当环境中光合有效辐射减弱,<em>Tl</em>降低,<em>RH</em>升高。10:00-12:00光响应曲线和12:00-15:00的第1-4叶光响应曲线呈双曲线,在强光下趋向饱和状况,12:00-15:00的第5叶光合速率和15:00-17:00光合速率在强光下出现明显的光抑制现象。1 d的不同时段均表现为10:00-12:00最大净光合速率(<em>P</em>_max)和光饱和点(<em>LSP</em>)最高,12:00-17:00降低;12:00-15:00光补偿点(<em>LCP</em>)和暗呼吸速率(<em>R</em>_d)较高,其它两个时段较低,10:00-17:00光补偿点量子效率(<em>φ</em>_c)、气孔导度(<em>G</em>_s)和胞间CO₂浓度(<em>C</em>_i)总体呈降低趋势,气孔限制值(<em>L</em>_s)升高。10:00-15:00相同时段测得的不同叶位叶片光响应参数,以第4-5叶光合性能较好,15:00-17:00以第3叶<em>P</em>_max最高,第5叶次之;10:00-17:00 <em>G</em>_s和<em>C</em>_i以第5叶较低,第1叶较高,<em>L</em>_s以第5叶较高,第1叶较低。<em>RH</em>为影响<em>P</em>_max的主要决策因子,测定时段、叶面饱和蒸汽压亏缺(<em>Vpdl</em>)和<em>Tl</em>为主要限制因子。10:00-12:00适宜进行光响应曲线测定,气孔限制为不同时段光合作用不同的主要因素,非气孔限制为影响不同叶位叶片光合作用的主要因素。;Plant light response curves reflect dynamic charateristics of photosynthesis with the photosynthetic active radiation (<em>PAR</em>). The data collection for the curves is time-consuming and the photosynthesis is sensitively affected by surrounding environmental factors, so it is vital to establish suitable time interval for data determination in one day. Muskmelon is top ten most popular fruit in the world. However, researches on dynamic characteristics of photosynthesis in muskmelon seedling leaves were rarely reported. In order to probe into the relationships between characteristics of muskmelon photosynthesis in light response and environmental factors, suitable time intervals for measuring light response curves were optimized with potted muskmelon seedlings as test material, and the light response curves and several parameters of photosynthesis for different position leaves and environmental factors were measured by LI-6400 portable photosynthesis system from 18 October to 23 October, 2009. Each leaf position was measured at 3 intervals of time:10:00-12:00, 12:00-15:00 and 15:00-17:00 in one day. All of light response curves were fitted with the modified rectangular hyperbola model, which was widely applied and could fit light response curves that photosynthesis rate decreased obviously under intensive irradiation. Maximum net photosynthetic rate (<em>P</em>_max) was selected as an indicator of photosynthetic capacity. Direct and indirect effects of environmental factors on <em>P</em>_max were calculated through the path analysis. The results show that when photosynthetic active radiation in environment increased, leaf temperature (<em>Tl</em>) rose, and air relative humidity (<em>RH</em>) decreased; photosynthetic active radiation in environment decreased, <em>Tl</em> decreased, and <em>RH</em> increased. Light response curves between 10:00-12:00 and light response curves of leaf 1-4 between 12:00-15:00 were characterized by hyperbolic curves and the photosynthetic capability approached saturation under intensive irradiation, while photosynthesis rate of leaf 5 between 12:00-15:00 and photosynthesis rate between 15:00-17:00 decreased obviously under intensive irradiation. <em>P</em>_max and light saturation point (<em>LSP</em>) were the highest between 10:00-12:00 and declined between 12:00-17:00 during one day. Light compensation point (<em>LCP</em>) and dark respiration (<em>R</em>_d) were higher between 12:00-15:00 than that under the other two time intervals. Quantum efficiency at light compensation point (<em>φ</em>_c), stomatal conductance (<em>G</em>_s), and intercellular CO₂ concentration (<em>C</em>_i) all generally displayed a declining trend, however, stomatal limitation value (<em>L</em>_s) increased from 10:00 to 17:00. Stomatal limitation was the key factor for different time intervals influencing photosynthesis. Light responsive parameters of leaf 4-5 were positive at the same time interval between 10:00-15:00, the <em>P</em>_max of leaf 3 was the highest, leaf 5 was the second between 15:00-17:00. <em>G</em>_sand <em>C</em>_i of leaf 5 were lower than that of leaf 1, while <em>L</em>_s of leaf 5 was higher than that of leaf 1 between 10:00-17:00. Non-stomatal limitation was the major factor of influencing photosynthesis for different position leaves. <em>RH</em> was the primary determining factor that influenced <em>P</em>_max; measuring time (Time), vapor pressure deficit at the leaf surface (<em>Vpdl</em>) and <em>Tl</em> were main limiting factors, so it was helpful to improve <em>P</em>_max by increasing <em>RH</em>, limiting Time, <em>Vpdl</em>, and <em>Tl</em>. The suitable time period for measuring light response curves was between 10:00-12:00.

Stomatal sensing of the environment

The effects of environmental factors on stomatal behaviour are reviewed and the questions of whether photosynthesis and transpiration control stomata or whether stomata themselves control the rates of these processes is addressed. Light affects stomata directly and indirectly. Light can act directly as an energy source resulting in ATP formation within guard cells via photophosphorylation, or as a stimulus as in the case of the blue light effects which cause guard cell H+ extrusion. Light also acts indirectly on stomata by affecting photosynthesis which influences the intercellular leaf CO2 concentration (Ci). Carbon dioxide concentrations in contact with the plasma membrane of the guard cell or within the guard cell acts directly on cell processes responsible for stomatal movements. The mechanism by which CO2 exerts its effect is not fully understood but, at least in part, it is concerned with changing the properties of guard cell plasma membranes which influence ion transport processes. The Ci may remain fairly constant for much of the day for many species which is the result of parallel responses of stomata and photosynthesis to light. Leaf water potential also influences stomatal behaviour. Since leaf water potential is a resultant of water uptake and storage by the plant and transpirational water loss, any factor which affects these processes, such as soil water availability, temperature, atmospheric humidity and air movement, may indirectly affect stomata. Some of these factors, such as temperature and possibly humidity, may affect stomata directly. These direct and indirect effects of environmental factors interact to give a net opening response upon which is superimposed a direct effect of stomatal circadian rhythmic activity.