In this study we assessed the current status of coral reefs along the Saudi Arabian coast of the Red Sea. Among the three growth forms of Acroporid corals, the branching forms were found to dominate in the Farassan Is...In this study we assessed the current status of coral reefs along the Saudi Arabian coast of the Red Sea. Among the three growth forms of Acroporid corals, the branching forms were found to dominate in the Farassan Islands （44.55%±11.10% cover） fol-lowed by tabular forms in the Doga Islands （ranging between 18%±6.47% and 18.30%±9.47% cover）. Digitate forms were rarely found along the coast except at Maqna. Among the five growth forms of non-Acroporid corals, we observed maximum cover of branching forms in the Yanbu offshore area （58.89%±15.11% cover） followed by the Jeddah coast （24.76%±14.04% cover）. The Millepora spp., a non-Scleractinian coral, was abundant at all the near-shore sites, such as Jeddah （10.70%±8.21%） and A1-Wajh （9.81%±6.69%）. The live coral cover （including both Scleractinian and non-Scleractinian corals） of Saudi Red Sea coast was seen to be higher in the north and gradually decrease towards the south. Principal Component analysis showed that the contribution of Acro- porid corals was greater in the southern region than in the northem and middle regions, but vice-versa in the case of non-Acroporid corals. Bray-Curtis cluster analysis categorized all the study sites into two major clusters with 60% similarity. Among them, one cluster-forming sites from Maqna to Masturah （Northem region） and the second one comprised the middle and southem regions （Jeddah to Farassan Islands）, and one outlier Rabigh.展开更多
Cactaceae is an important plant family in the semi-arid ecosystems of the Americas.However,few studies have analyzed their responses after wildfires.In this study,we assessed the survival rate and resprouting capacity...Cactaceae is an important plant family in the semi-arid ecosystems of the Americas.However,few studies have analyzed their responses after wildfires.In this study,we assessed the survival rate and resprouting capacity of cacti from different growth forms one year after a wildfire in the Córdoba Mountains,central Argentina.Eight species are present in the study area,which were classified into four growth forms;then we established 158 plots and recorded the status(dead or alive)of each cactus and size-related variables.We also documented microenvironmental characteristics(percentage cover of grasses,forbs,shrubs,rock and bare ground)and topographic information(slope and slope orientation)for each plot,estimating the resprouting capacity of each growth form.Survival rates and resprouting capacity varied among growth forms.The survival rate for arborescent growth form was 25%,while for globose,opuntioid and short columnar forms were 84%,69%and 55%,respectively.Microenvironmental and topographic factors influenced resprouting capacity,though effects varied among growth forms.Globose growth form showed the highest recovery capacity after the wildfire,contrasting with arborescent growth form,of which only 2%of the individuals resprouted,predominantly on south-and north-facing slopes.In contrast,short columnar and opuntioid growth forms showed no significant relationship between survival or resprouting capacity,and the measured variables.These findings provide key insights into the role of fire in shaping cacti populations and highlight the need to consider species-specific and environmental interactions in conservation and management strategies for the Chaco forest.展开更多
The present study was conducted in the alpine pastures of Tungnath （30° 14＇ N and 79° 13＇ E） to observe life-form and growth-form patterns of alpine plant species under grazed and ungrazed conditions and...The present study was conducted in the alpine pastures of Tungnath （30° 14＇ N and 79° 13＇ E） to observe life-form and growth-form patterns of alpine plant species under grazed and ungrazed conditions and to work out the plant life form spectrum. Species were categorized as plant habit, height and length of growth-cycle and life-form classes according to Raunkiaer＇s system. The results show that in total of 68 species at grazed site, hemicryptophytes （He） accounted for 50.00% species, followed by cryptophytes （26.47%）, chamaephytes （16.18%）, phanemphytes （4.41%） and therophytes （2.94%）. At the ungrazed site in 65 plant species, hemicryptophytes （He） accounted fo＇r 49.23% species, cryptophytes （26.15%）, chamaephytes （15.38%）, phanerophytes （6.15%） and ther6phytes （3.08 % species）. In general, hemicrptophyte are dominant^in both sites i.e. graged and ungrazed. Growth form categories were classified as forbs, shrubs, grasses and sedges＇and undershrubs, according to plant habit and height. On the basis of length of the growth cycle, species were categorized as plant species of short growth cycle, intermediate growth cycle and long growth cycle. The short forbs of plant habit and height, had the highest emergence, and grasses and sedges had the lowest emergence in representative species. Percentage of species with long growth cycle was highest in both sites.展开更多
Wind is an environmental stimulus that stresses plants of all growth forms at all life-stages by influencing the development,architecture,and morphology of roots and shoots.However,comparative studies are scarce and n...Wind is an environmental stimulus that stresses plants of all growth forms at all life-stages by influencing the development,architecture,and morphology of roots and shoots.However,comparative studies are scarce and no study directly investigated whether shoot and root morphological traits of trees,grasses and forbs differ in their response to short wind pulses of different wind intensity.In this study,we found that across species,wind stress by short wind pulses of increasing intensity consistently changed root morphology,but did not affect shoot morphological traits,except plant height in four species.Wind effects in roots were generally weak in tree species but consistent across growth forms.Furthermore,plant height of species was correlated with changes in specific root length and average diameter.Our results indicate that short-pulse wind treatments affect root morphology more than shoot morphology across growth forms.They further suggest that wind stress possibly promotes root anchorage in young plants and that these effects might depend on plant height.展开更多
The spectrum variance m0, peak frequency ω0 and peakness factor p are expressed in terms of nondimensional fetch and duration by making use of relations which are derived through comparing and analyzing existing empi...The spectrum variance m0, peak frequency ω0 and peakness factor p are expressed in terms of nondimensional fetch and duration by making use of relations which are derived through comparing and analyzing existing empirical formulas for the growth of significant wave height and period. The main features of spectrum growth as specified by these parameters agree with those of the JONS-WAP experiments. For given wind speed and fetch, the high frequency parts beyond the peaks of shallow water spectra almost coincide with that of the corresponding deep water spectrum, whereas the low frequency parts differ appreciably. The method developed in this paper predicts smaller significant wave height as well as smaller wave period for shallow water spectra in contrast to the theoretical result of Kitaigorodskii ef al, in which the peak frequency, and consequently the significant wave period, remains basically unchanged for different water depths. Spectra are further reduced to a form in which only significant wave height and period are left as parameters, the peakness factor being replaced by the wave steepness through an empirical relation between them. Spectra in this form have been verified by observations.展开更多
The grain growth behavior in reactive spray formed 7075+2.91 vol percent TiCAl alloy was studied and compared with that of spray formed 7075 Al alloy at semi-solid state. Theeffects of in-situ TiC particles on the mic...The grain growth behavior in reactive spray formed 7075+2.91 vol percent TiCAl alloy was studied and compared with that of spray formed 7075 Al alloy at semi-solid state. Theeffects of in-situ TiC particles on the microstructure of spray formed 7075 Al alloy were alsoinvestigated. The specimens were heat-treated isothermally at various temperatures between thesolidus and liquidus of 7075 Al alloy for times in the range of 10-60 min, then quenched in water.The microstructure of reheated specimens was characterized using scanning electron microscopy andoptical microscopy. The grain size was measured using a mean linear intercept method. Results showthat the in-situ TiC particles can effectively retard grain growth and refine the grain at a limitedsize. The grain growth exponent in Arrhenius equation increases from 2 to 3, which indicates thatthe in-situ TiC particles have the significant pinning effect on grain coarsening in the semi-solidstate.展开更多
The current study performed a finite element analysis of the strain localization behavior of a voided ductile material using a non-local plasticity formulation in which the yield strength depends on both an equivalent...The current study performed a finite element analysis of the strain localization behavior of a voided ductile material using a non-local plasticity formulation in which the yield strength depends on both an equivalent plastic strain measurement (hardening parameter) and Laplacian equivalent. The introduction of gradient terms to the yield function was found to play an important role in simulating the strain localization behavior of the voided ductile material. The effect of the mesh size and characteristic length on the strain localization were also investigated. An FEM simulation based on the proposed non-local plasticity revealed that the load-strain curves of the voided ductile material subjected to plane strain tension converged to one curve, regardless of the mesh size. In addition, the results using non-local plasticity also exhibited that the dependence of the deformation behavior of the material on the mesh size was much less sensitive than that with classical local plasticity and could be successfully eliminated through the introduction of a large value for the characteristic length.展开更多
The grain growth behavior of spray-formed Al-70wt.%Si alloys was studied in the semi-solid state. The specimens were isothermally heat-treated at various temperatures between the solidus and liquidus of Al-Si alloys a...The grain growth behavior of spray-formed Al-70wt.%Si alloys was studied in the semi-solid state. The specimens were isothermally heat-treated at various temperatures between the solidus and liquidus of Al-Si alloys and then quenched in water. The microstructure of reheated specimens was characterized using optical and scanning electron microscopies. The isothermal holding experiment was carried out to investigate grain growth behavior as a function of holding time and temperature in the semi-solid state. The coarsening mechanism and the effect of porosity on microstructure were also studied.展开更多
Invasive species are increasingly spreading,particularly in rangeland ecosystems.It is essential to evaluate the effectiveness of different methods for controlling invasive plants in these ecosystems.This study aimed ...Invasive species are increasingly spreading,particularly in rangeland ecosystems.It is essential to evaluate the effectiveness of different methods for controlling invasive plants in these ecosystems.This study aimed to investigate the effects of three strategies-21-year grazing exclusion(21-YES),mowing-grazing in rotation in alternate years(MGRS),and moderate grazing(MGS)-on the change in cover,density,and biomass of Leucanthemum vulgare Lam.(Ox-eye Daisy=OED)and the plant community.To accomplish this,three sites selected for each treatment.In 2021,270 vegetation plots were sampled using a random systematic method.Subsequently,we recorded the density and canopy cover of all growth forms(forbs,grasses,and ferns),the OED biomass,and the ground cover.The results indicated that MGS reduced OED density,OED canopy,and OED biomass.Furthermore,this strategy demonstrated the highest density and canopy cover of the plant community(including total,forbs,grasses,and ferns).Additionally,the strongest correlation was observed between the total canopy and the OED density(R2=-0.91,-0.95,-0.94 in 21-YES,MGRS,and MGS,respectively),as well as between the total canopy and the OED canopy(R2=-0.51,-0.98,-0.97 in 21-YES,MGRS,and MGS,respectively).The MGS led to an increase in diversity indices.In general,the grazing strategy has proven to be effective in controlling the spread of invasive OED and has also resulted in an increase in canopy cover,density,and diversity indices of the plant community.The study highlights the importance of ongoing management efforts to control invasive species,with moderate grazing potentially serving as a more practical,culturally accepted,and costeffective short-term control strategy for widespread rangeland weed infestations.展开更多
Aerosol particle pollution has become an increasing serious environmental problem,and urban vegetation plays a long-lasting and positive role in mitigating it.This study compared the particle capture abilities of tree...Aerosol particle pollution has become an increasing serious environmental problem,and urban vegetation plays a long-lasting and positive role in mitigating it.This study compared the particle capture abilities of trees,shrubs,and herbs,and examined the compositions and influence of aerosol particles accumulated on leaf functional traits.Retained particles primarily contained Ca^(2+),K^(+),SO_(4)^(2-),NO_(3)^(-)and NH_(4)^(+),indicating their anthropogenic origins.The leathery-leaved tree Osmanthus fragrans and the papery-leaved herb Alternanthera sessilis demonstrated the higher competence in particle accumulation than other plants,and leaf morphologic structures(e.g.,leaf grooves,trichomes,waxy layers,and stomata characteristics)were closely associated with particle capture by plant species.Particle retention negatively impacted stomata,impeding photosynthesis,and reducing transpiration.In response to particle accumulation,plants tended to decrease specific leaf area and adjust stomatal conductance.Both growth form and leaf texture significantly influenced the particle capture abilities of different plant species.The substantial contribution of plants,particularly herbs in the lower vegetation strata,to particle removal should not be overlooked.Vegetation with a tree-shrub-herb configuration excels at particle capture,offering potential advantages in mitigating particle pollution and enhancing ecological benefits.展开更多
文摘In this study we assessed the current status of coral reefs along the Saudi Arabian coast of the Red Sea. Among the three growth forms of Acroporid corals, the branching forms were found to dominate in the Farassan Islands （44.55%±11.10% cover） fol-lowed by tabular forms in the Doga Islands （ranging between 18%±6.47% and 18.30%±9.47% cover）. Digitate forms were rarely found along the coast except at Maqna. Among the five growth forms of non-Acroporid corals, we observed maximum cover of branching forms in the Yanbu offshore area （58.89%±15.11% cover） followed by the Jeddah coast （24.76%±14.04% cover）. The Millepora spp., a non-Scleractinian coral, was abundant at all the near-shore sites, such as Jeddah （10.70%±8.21%） and A1-Wajh （9.81%±6.69%）. The live coral cover （including both Scleractinian and non-Scleractinian corals） of Saudi Red Sea coast was seen to be higher in the north and gradually decrease towards the south. Principal Component analysis showed that the contribution of Acro- porid corals was greater in the southern region than in the northem and middle regions, but vice-versa in the case of non-Acroporid corals. Bray-Curtis cluster analysis categorized all the study sites into two major clusters with 60% similarity. Among them, one cluster-forming sites from Maqna to Masturah （Northem region） and the second one comprised the middle and southem regions （Jeddah to Farassan Islands）, and one outlier Rabigh.
基金supported by grants from the Research Committee of the Cactus and Succulent Society of America and Secretaría de Ciencia y Tecnología-Universidad Nacional de Córdoba,and a PIP-CONICET grant[11220220100196],Argentina.
文摘Cactaceae is an important plant family in the semi-arid ecosystems of the Americas.However,few studies have analyzed their responses after wildfires.In this study,we assessed the survival rate and resprouting capacity of cacti from different growth forms one year after a wildfire in the Córdoba Mountains,central Argentina.Eight species are present in the study area,which were classified into four growth forms;then we established 158 plots and recorded the status(dead or alive)of each cactus and size-related variables.We also documented microenvironmental characteristics(percentage cover of grasses,forbs,shrubs,rock and bare ground)and topographic information(slope and slope orientation)for each plot,estimating the resprouting capacity of each growth form.Survival rates and resprouting capacity varied among growth forms.The survival rate for arborescent growth form was 25%,while for globose,opuntioid and short columnar forms were 84%,69%and 55%,respectively.Microenvironmental and topographic factors influenced resprouting capacity,though effects varied among growth forms.Globose growth form showed the highest recovery capacity after the wildfire,contrasting with arborescent growth form,of which only 2%of the individuals resprouted,predominantly on south-and north-facing slopes.In contrast,short columnar and opuntioid growth forms showed no significant relationship between survival or resprouting capacity,and the measured variables.These findings provide key insights into the role of fire in shaping cacti populations and highlight the need to consider species-specific and environmental interactions in conservation and management strategies for the Chaco forest.
文摘The present study was conducted in the alpine pastures of Tungnath （30° 14＇ N and 79° 13＇ E） to observe life-form and growth-form patterns of alpine plant species under grazed and ungrazed conditions and to work out the plant life form spectrum. Species were categorized as plant habit, height and length of growth-cycle and life-form classes according to Raunkiaer＇s system. The results show that in total of 68 species at grazed site, hemicryptophytes （He） accounted for 50.00% species, followed by cryptophytes （26.47%）, chamaephytes （16.18%）, phanemphytes （4.41%） and therophytes （2.94%）. At the ungrazed site in 65 plant species, hemicryptophytes （He） accounted fo＇r 49.23% species, cryptophytes （26.15%）, chamaephytes （15.38%）, phanerophytes （6.15%） and ther6phytes （3.08 % species）. In general, hemicrptophyte are dominant^in both sites i.e. graged and ungrazed. Growth form categories were classified as forbs, shrubs, grasses and sedges＇and undershrubs, according to plant habit and height. On the basis of length of the growth cycle, species were categorized as plant species of short growth cycle, intermediate growth cycle and long growth cycle. The short forbs of plant habit and height, had the highest emergence, and grasses and sedges had the lowest emergence in representative species. Percentage of species with long growth cycle was highest in both sites.
文摘Wind is an environmental stimulus that stresses plants of all growth forms at all life-stages by influencing the development,architecture,and morphology of roots and shoots.However,comparative studies are scarce and no study directly investigated whether shoot and root morphological traits of trees,grasses and forbs differ in their response to short wind pulses of different wind intensity.In this study,we found that across species,wind stress by short wind pulses of increasing intensity consistently changed root morphology,but did not affect shoot morphological traits,except plant height in four species.Wind effects in roots were generally weak in tree species but consistent across growth forms.Furthermore,plant height of species was correlated with changes in specific root length and average diameter.Our results indicate that short-pulse wind treatments affect root morphology more than shoot morphology across growth forms.They further suggest that wind stress possibly promotes root anchorage in young plants and that these effects might depend on plant height.
文摘The spectrum variance m0, peak frequency ω0 and peakness factor p are expressed in terms of nondimensional fetch and duration by making use of relations which are derived through comparing and analyzing existing empirical formulas for the growth of significant wave height and period. The main features of spectrum growth as specified by these parameters agree with those of the JONS-WAP experiments. For given wind speed and fetch, the high frequency parts beyond the peaks of shallow water spectra almost coincide with that of the corresponding deep water spectrum, whereas the low frequency parts differ appreciably. The method developed in this paper predicts smaller significant wave height as well as smaller wave period for shallow water spectra in contrast to the theoretical result of Kitaigorodskii ef al, in which the peak frequency, and consequently the significant wave period, remains basically unchanged for different water depths. Spectra are further reduced to a form in which only significant wave height and period are left as parameters, the peakness factor being replaced by the wave steepness through an empirical relation between them. Spectra in this form have been verified by observations.
基金This work was financially supported by the National Natural Science Foundation of China (No.50171010)
文摘The grain growth behavior in reactive spray formed 7075+2.91 vol percent TiCAl alloy was studied and compared with that of spray formed 7075 Al alloy at semi-solid state. Theeffects of in-situ TiC particles on the microstructure of spray formed 7075 Al alloy were alsoinvestigated. The specimens were heat-treated isothermally at various temperatures between thesolidus and liquidus of 7075 Al alloy for times in the range of 10-60 min, then quenched in water.The microstructure of reheated specimens was characterized using scanning electron microscopy andoptical microscopy. The grain size was measured using a mean linear intercept method. Results showthat the in-situ TiC particles can effectively retard grain growth and refine the grain at a limitedsize. The grain growth exponent in Arrhenius equation increases from 2 to 3, which indicates thatthe in-situ TiC particles have the significant pinning effect on grain coarsening in the semi-solidstate.
文摘The current study performed a finite element analysis of the strain localization behavior of a voided ductile material using a non-local plasticity formulation in which the yield strength depends on both an equivalent plastic strain measurement (hardening parameter) and Laplacian equivalent. The introduction of gradient terms to the yield function was found to play an important role in simulating the strain localization behavior of the voided ductile material. The effect of the mesh size and characteristic length on the strain localization were also investigated. An FEM simulation based on the proposed non-local plasticity revealed that the load-strain curves of the voided ductile material subjected to plane strain tension converged to one curve, regardless of the mesh size. In addition, the results using non-local plasticity also exhibited that the dependence of the deformation behavior of the material on the mesh size was much less sensitive than that with classical local plasticity and could be successfully eliminated through the introduction of a large value for the characteristic length.
文摘The grain growth behavior of spray-formed Al-70wt.%Si alloys was studied in the semi-solid state. The specimens were isothermally heat-treated at various temperatures between the solidus and liquidus of Al-Si alloys and then quenched in water. The microstructure of reheated specimens was characterized using optical and scanning electron microscopies. The isothermal holding experiment was carried out to investigate grain growth behavior as a function of holding time and temperature in the semi-solid state. The coarsening mechanism and the effect of porosity on microstructure were also studied.
基金the University of Mohaghegh Ardabili,Department of Natural Resources,Iran for financial support。
文摘Invasive species are increasingly spreading,particularly in rangeland ecosystems.It is essential to evaluate the effectiveness of different methods for controlling invasive plants in these ecosystems.This study aimed to investigate the effects of three strategies-21-year grazing exclusion(21-YES),mowing-grazing in rotation in alternate years(MGRS),and moderate grazing(MGS)-on the change in cover,density,and biomass of Leucanthemum vulgare Lam.(Ox-eye Daisy=OED)and the plant community.To accomplish this,three sites selected for each treatment.In 2021,270 vegetation plots were sampled using a random systematic method.Subsequently,we recorded the density and canopy cover of all growth forms(forbs,grasses,and ferns),the OED biomass,and the ground cover.The results indicated that MGS reduced OED density,OED canopy,and OED biomass.Furthermore,this strategy demonstrated the highest density and canopy cover of the plant community(including total,forbs,grasses,and ferns).Additionally,the strongest correlation was observed between the total canopy and the OED density(R2=-0.91,-0.95,-0.94 in 21-YES,MGRS,and MGS,respectively),as well as between the total canopy and the OED canopy(R2=-0.51,-0.98,-0.97 in 21-YES,MGRS,and MGS,respectively).The MGS led to an increase in diversity indices.In general,the grazing strategy has proven to be effective in controlling the spread of invasive OED and has also resulted in an increase in canopy cover,density,and diversity indices of the plant community.The study highlights the importance of ongoing management efforts to control invasive species,with moderate grazing potentially serving as a more practical,culturally accepted,and costeffective short-term control strategy for widespread rangeland weed infestations.
基金supported by the National Natural Science Foundation of China(No.31700475).
文摘Aerosol particle pollution has become an increasing serious environmental problem,and urban vegetation plays a long-lasting and positive role in mitigating it.This study compared the particle capture abilities of trees,shrubs,and herbs,and examined the compositions and influence of aerosol particles accumulated on leaf functional traits.Retained particles primarily contained Ca^(2+),K^(+),SO_(4)^(2-),NO_(3)^(-)and NH_(4)^(+),indicating their anthropogenic origins.The leathery-leaved tree Osmanthus fragrans and the papery-leaved herb Alternanthera sessilis demonstrated the higher competence in particle accumulation than other plants,and leaf morphologic structures(e.g.,leaf grooves,trichomes,waxy layers,and stomata characteristics)were closely associated with particle capture by plant species.Particle retention negatively impacted stomata,impeding photosynthesis,and reducing transpiration.In response to particle accumulation,plants tended to decrease specific leaf area and adjust stomatal conductance.Both growth form and leaf texture significantly influenced the particle capture abilities of different plant species.The substantial contribution of plants,particularly herbs in the lower vegetation strata,to particle removal should not be overlooked.Vegetation with a tree-shrub-herb configuration excels at particle capture,offering potential advantages in mitigating particle pollution and enhancing ecological benefits.
