Aims Facilitation by nurse plants is a common interaction in harsh environments and this positive plant-plant interaction may promote vegetation recovery in ecosystems affected by human activities.Determining the rele...Aims Facilitation by nurse plants is a common interaction in harsh environments and this positive plant-plant interaction may promote vegetation recovery in ecosystems affected by human activities.Determining the relevance of this process,however,requires assessing how nurse plants influence the establishment of other species,as well as the proportion of species in the regional species pool that would benefit from the presence of nurse plants in human-disturbed areas.Further,since vegetation recovery is a time-dependent process,the community-level consequences of facilitation are likely to vary among landscapes with different disturbance history.Thus,an integrative perspective of the relevance of nurse plants for vegetation recovery could be obtained by measuring their effects across different human-disturbed landscapes of the target region.This study focuses on these issues and uses a regional-scale approach to assess the community-level effects of a widespread nurse plant of American deserts,the creosotebush(Larrea tridentata).Methods This study was conducted in the southernmost portion of Chihuahuan Desert because most floodplain valleys of this region have been affected by human activities during the past centuries.For this study,we selected 10 floodplain valleys differing in their age(i.e.the time elapsed after human activities were ceased).At each landscape,we measured the cover of creosotebushes and the proportion of plant species positively associated with them,as well as the density of seeds in the soil beneath creosotebush canopies.All these data were regressed against the age of the landscapes.Further,to assess whether positive association patterns were due to facilitation or other processes,we conducted field experiments and measured the ecophysiological performance of plant species established beneath and outside creosotebush canopies.Important Findings Most plant species from the target region were positively associated to creosotebushes,and our field experiments and ecophysiological measures indicated that these distribution patterns can be attributed to facilitative interactions.In most landscapes,the density of seeds was higher beneath creosotebushes than in the surrounding habitats,suggesting that these shrubs may also act as seed traps.The community-level effects of creosotebushes increased with landscape age and creosotebush cover,indicating that magnitude of these effects depends on the disturbance history of each site.These results highlight the relevance of performing large-scale assessments for identifying the consequences of facilitation on vegetation recovery across space and time.We then propose that this kind of large-scale approach should be taken into account in the development of conservation programs aimed at the recovery and preservation of plant biodiversity in harsh environments.展开更多
Aims Light requirements for cactus seed germination have been considered to be associated with their adult plant height and seed mass,but this has not been thoroughly studied for other succulent species.In order to un...Aims Light requirements for cactus seed germination have been considered to be associated with their adult plant height and seed mass,but this has not been thoroughly studied for other succulent species.In order to understand seed photosensitivity from desert species belonging to Asparagaceae(subfamily Agavoideae)and Cactaceae,we performed a germination experiment with and without light for 12 species and 2 varieties from 1 species from the Southern Chihuahuan Desert.We also determined if adult growth is totally determined by seedling‘growth form’in cacti.Methods We performed a germination experiment using light and darkness for 13 species from Southern Chihuahuan Desert:10 rosette species(Asparagaceae),as well as 1 globose,1 columnar and 2 varieties from 1 depressed-globose species(Cactaceae).The response variables were seed germination percentage and relative light germination(RLG).In addition,in order to determine if adult-globose cacti could have cylindrical seedlings,we calculated the shape index(height/width ratio)for Coryphanta clavata and Mammillaria compressa.Important Findings All species were considered neutral photoblastic.Eleven species had similar seed germination in both light and dark conditions,and three taxa(M.compressa and the two varieties of Ferocactus latispinus)showed higher germination with light than without it.Agave salmiana,M.compressa and the two varieties of F.latispinus had higher RLG than the other species.Seed mass was an important factor because with higher seed mass there was lower dependence to light.These findings support the hypothesis that small seed mass and light requirements have coevolved as an adaptation to ensure germination.One adult-globose cactus species,M.compressa,and one adult-columnar species,C.clavata,had small seeds and neutral fotoblasticism.Seedlings from these two species exposed to light were cylindrical and those under darkness conditions were columnar.Perhaps seeds from this species are able to germinate in the dark because they produce columnar seedlings with the ability to emerge from greater soil depths where sunlight cannot penetrate.展开更多
基金Secretaría de Educación Pública-Consejo Nacional de Ciencia y Tecnología of México(Project CB-2010-156205).
文摘Aims Facilitation by nurse plants is a common interaction in harsh environments and this positive plant-plant interaction may promote vegetation recovery in ecosystems affected by human activities.Determining the relevance of this process,however,requires assessing how nurse plants influence the establishment of other species,as well as the proportion of species in the regional species pool that would benefit from the presence of nurse plants in human-disturbed areas.Further,since vegetation recovery is a time-dependent process,the community-level consequences of facilitation are likely to vary among landscapes with different disturbance history.Thus,an integrative perspective of the relevance of nurse plants for vegetation recovery could be obtained by measuring their effects across different human-disturbed landscapes of the target region.This study focuses on these issues and uses a regional-scale approach to assess the community-level effects of a widespread nurse plant of American deserts,the creosotebush(Larrea tridentata).Methods This study was conducted in the southernmost portion of Chihuahuan Desert because most floodplain valleys of this region have been affected by human activities during the past centuries.For this study,we selected 10 floodplain valleys differing in their age(i.e.the time elapsed after human activities were ceased).At each landscape,we measured the cover of creosotebushes and the proportion of plant species positively associated with them,as well as the density of seeds in the soil beneath creosotebush canopies.All these data were regressed against the age of the landscapes.Further,to assess whether positive association patterns were due to facilitation or other processes,we conducted field experiments and measured the ecophysiological performance of plant species established beneath and outside creosotebush canopies.Important Findings Most plant species from the target region were positively associated to creosotebushes,and our field experiments and ecophysiological measures indicated that these distribution patterns can be attributed to facilitative interactions.In most landscapes,the density of seeds was higher beneath creosotebushes than in the surrounding habitats,suggesting that these shrubs may also act as seed traps.The community-level effects of creosotebushes increased with landscape age and creosotebush cover,indicating that magnitude of these effects depends on the disturbance history of each site.These results highlight the relevance of performing large-scale assessments for identifying the consequences of facilitation on vegetation recovery across space and time.We then propose that this kind of large-scale approach should be taken into account in the development of conservation programs aimed at the recovery and preservation of plant biodiversity in harsh environments.
基金Secretaría de Educación Pública-Consejo Nacional de Ciencia y Tecnología(CB-2010-156205).
文摘Aims Light requirements for cactus seed germination have been considered to be associated with their adult plant height and seed mass,but this has not been thoroughly studied for other succulent species.In order to understand seed photosensitivity from desert species belonging to Asparagaceae(subfamily Agavoideae)and Cactaceae,we performed a germination experiment with and without light for 12 species and 2 varieties from 1 species from the Southern Chihuahuan Desert.We also determined if adult growth is totally determined by seedling‘growth form’in cacti.Methods We performed a germination experiment using light and darkness for 13 species from Southern Chihuahuan Desert:10 rosette species(Asparagaceae),as well as 1 globose,1 columnar and 2 varieties from 1 depressed-globose species(Cactaceae).The response variables were seed germination percentage and relative light germination(RLG).In addition,in order to determine if adult-globose cacti could have cylindrical seedlings,we calculated the shape index(height/width ratio)for Coryphanta clavata and Mammillaria compressa.Important Findings All species were considered neutral photoblastic.Eleven species had similar seed germination in both light and dark conditions,and three taxa(M.compressa and the two varieties of Ferocactus latispinus)showed higher germination with light than without it.Agave salmiana,M.compressa and the two varieties of F.latispinus had higher RLG than the other species.Seed mass was an important factor because with higher seed mass there was lower dependence to light.These findings support the hypothesis that small seed mass and light requirements have coevolved as an adaptation to ensure germination.One adult-globose cactus species,M.compressa,and one adult-columnar species,C.clavata,had small seeds and neutral fotoblasticism.Seedlings from these two species exposed to light were cylindrical and those under darkness conditions were columnar.Perhaps seeds from this species are able to germinate in the dark because they produce columnar seedlings with the ability to emerge from greater soil depths where sunlight cannot penetrate.
