Aims Fire has important consequences on vegetation dynamics.In fire-prone areas,natural selection favors plant species,characterized by a large soil seed bank,and that their germination is stimu-lated by fire.Although...Aims Fire has important consequences on vegetation dynamics.In fire-prone areas,natural selection favors plant species,characterized by a large soil seed bank,and that their germination is stimu-lated by fire.Although seed germination stimulated by fire heat is common in the eastern Mediterranean Basin,only little is known about germination stimulation by smoke.We examined the inter-active effect of aerosol smoke and fire history on the germina-ble soil seed bank(GSSB)community in eastern Mediterranean woodlands.Methods We collected soil samples from sites that have been subjected to different fire frequencies during the last four decades and exposed them to aerosol smoke,with or without watering.By document-ing the seed germination patterns characterizing these samples,we could test for changes in the abundance and richness of the germi-nable seeds in the soil.Important Findings Total GSSB density was higher in sites that were burned more fre-quently during the last four decades.Exposure to aerosol smoke increased the GSSB density,and this pattern was more pronounced in samples originating from sites burned more frequently,as well as among annual species.Notably,exposing wet samples to aerosol smoke caused a significant reduction in GSSB density and richness.These results highlight the importance of exploring germination responses using intact soil samples,rather than synthetic seed com-munities.Moreover,our findings emphasize the important role smoke plays in shaping post-fire succession processes in the Mediterranean Basin,mainly by stimulating the germination of annual species.展开更多
Aims Release of carbon from plant roots initiates a chain of reactions involving the soil microbial community and microbial predators,eventually leading to nutrient enrichment,a process known as the‘microbial loop’....Aims Release of carbon from plant roots initiates a chain of reactions involving the soil microbial community and microbial predators,eventually leading to nutrient enrichment,a process known as the‘microbial loop’.However,root exudation has also been shown to stimulate nutrient immobilization,thereby reducing plant growth.Both mechanisms depend on carbon exudation,but generate two opposite soil nutrient dynamics.We suggest here that this difference might arise from temporal variation in soil carbon inputs.Methods We examined how continuous and pulsed carbon inputs affect the performance of wheat(Triticum aestivum),a fast-growing annual,while competing with sage(Salvia officinalis),a slow-growing perennial.We manipulated the temporal mode of soil carbon inputs under different soil organic matter(SOM)and nitrogen availabilities.Carbon treatment included the following two carbon input modes:(i)Continuous:a daily release of minute amounts of glucose,and(ii)Pulsed:once every 3 days,a short release of high amounts of glucose.The two carbon input modes differed only in the temporal dynamic of glucose,but not in total amount of glucose added.We predicted that pulsed carbon inputs should result in nutrient enrichment,creating favorable conditions for the wheat plants.Important FindingsCarbon addition caused a reduction in the sage total biomass,while increasing the total wheat biomass.In SOM-poor soil without nitrogen and in SOM-rich soil with nitrogen,wheat root allocation was higher under continuous than under pulsed carbon input.Such an allocation shift is a common response of plants to reduced nutrient availability.We thus suggest that the continuous carbon supply stimulated the proliferation of soil microorganisms,which in turn competed with the plants over available soil nutrients.The fact that bacterial abundance was at its peak under this carbon input mode support this assertion.Multivariate analyses indicated that besides the above described changes in plant biomasses and bacterial abundances,carbon supply led to an accumulation of organic matter,reduction in NO_(3)levels and increased levels of NH_(4)in the soil.The overall difference between the two carbon input modes resulted primarily from the lower total wheat biomass,and lower levels of NO_(3)and soil PH characterizing pots submitted to carbon pulses,compared to those subjected to continuous carbon supply.Carbon supply,in general,and carbon input mode,in particular,can lead to belowground chain reactions cascading up to affect plant performance.展开更多
Aims Resource allocation in plants can be strongly affected by competition.Besides plant–plant interactions,terrestrial plants compete with the soil bacterial community over nutrients.Since the bacterial communities ...Aims Resource allocation in plants can be strongly affected by competition.Besides plant–plant interactions,terrestrial plants compete with the soil bacterial community over nutrients.Since the bacterial communities cannot synthesize their own energy sources,they are dependent on external carbon sources.Unlike the effect of overall amounts of carbon(added to the soil)on plant performance,the effect of fine scale temporal variation in soil carbon inputs on the bacterial biomass and its cascading effects on plant growth are largely unknown.We hypothesize that continuous carbon supply(small temporal variance)will result in a relatively constant bacterial biomass that will effectively compete with plants for nutrients.On the other hand,carbon pulses(large temporal variance)are expected to cause oscillations in bacterial biomass,enabling plants temporal escape from competition and possibly enabling increased growth.We thus predicted that continuous carbon supply would increase root allocation at the expense of decreased reproductive output.We also expected this effect to be noticeable only when sufficient nutrients were present in the soil.Methods Wheat plants were grown for 64 days in pots containing either sterilized or inoculated soils,with or without slow-release fertilizer,subjected to one of the following six carbon treatments:daily(1.5mg glucose),every other day(3mg glucose),4 days(6mg glucose),8 days(12mg glucose),16 days(24mg glucose)and no carbon control.Important Findings Remarkably,carbon pulses(every 2–16 days)led to increased reproductive allocation at the expense of decreased root allocation in plants growing in inoculated soils.Consistent with our prediction,these effects were noticeable only when sufficient nutrients were present in the soil.Furthermore,soil inoculation in plants subjected to low nutrient availability resulted in decreased total plant biomass.We interpret this to mean that when the amount of available nutrients is low,these nutrients are mainly used by the bacterial community.Our results show that temporal variation in soil carbon inputs may play an important role in aboveground–belowground interactions,affecting plant resource allocation.展开更多
基金This research was co-supported by the United States-Israel Binational Science Foundation(BSF Grant 2012081).
文摘Aims Fire has important consequences on vegetation dynamics.In fire-prone areas,natural selection favors plant species,characterized by a large soil seed bank,and that their germination is stimu-lated by fire.Although seed germination stimulated by fire heat is common in the eastern Mediterranean Basin,only little is known about germination stimulation by smoke.We examined the inter-active effect of aerosol smoke and fire history on the germina-ble soil seed bank(GSSB)community in eastern Mediterranean woodlands.Methods We collected soil samples from sites that have been subjected to different fire frequencies during the last four decades and exposed them to aerosol smoke,with or without watering.By document-ing the seed germination patterns characterizing these samples,we could test for changes in the abundance and richness of the germi-nable seeds in the soil.Important Findings Total GSSB density was higher in sites that were burned more fre-quently during the last four decades.Exposure to aerosol smoke increased the GSSB density,and this pattern was more pronounced in samples originating from sites burned more frequently,as well as among annual species.Notably,exposing wet samples to aerosol smoke caused a significant reduction in GSSB density and richness.These results highlight the importance of exploring germination responses using intact soil samples,rather than synthetic seed com-munities.Moreover,our findings emphasize the important role smoke plays in shaping post-fire succession processes in the Mediterranean Basin,mainly by stimulating the germination of annual species.
基金supported by the Sol Leshin UCLABGU Program(8721991).
文摘Aims Release of carbon from plant roots initiates a chain of reactions involving the soil microbial community and microbial predators,eventually leading to nutrient enrichment,a process known as the‘microbial loop’.However,root exudation has also been shown to stimulate nutrient immobilization,thereby reducing plant growth.Both mechanisms depend on carbon exudation,but generate two opposite soil nutrient dynamics.We suggest here that this difference might arise from temporal variation in soil carbon inputs.Methods We examined how continuous and pulsed carbon inputs affect the performance of wheat(Triticum aestivum),a fast-growing annual,while competing with sage(Salvia officinalis),a slow-growing perennial.We manipulated the temporal mode of soil carbon inputs under different soil organic matter(SOM)and nitrogen availabilities.Carbon treatment included the following two carbon input modes:(i)Continuous:a daily release of minute amounts of glucose,and(ii)Pulsed:once every 3 days,a short release of high amounts of glucose.The two carbon input modes differed only in the temporal dynamic of glucose,but not in total amount of glucose added.We predicted that pulsed carbon inputs should result in nutrient enrichment,creating favorable conditions for the wheat plants.Important FindingsCarbon addition caused a reduction in the sage total biomass,while increasing the total wheat biomass.In SOM-poor soil without nitrogen and in SOM-rich soil with nitrogen,wheat root allocation was higher under continuous than under pulsed carbon input.Such an allocation shift is a common response of plants to reduced nutrient availability.We thus suggest that the continuous carbon supply stimulated the proliferation of soil microorganisms,which in turn competed with the plants over available soil nutrients.The fact that bacterial abundance was at its peak under this carbon input mode support this assertion.Multivariate analyses indicated that besides the above described changes in plant biomasses and bacterial abundances,carbon supply led to an accumulation of organic matter,reduction in NO_(3)levels and increased levels of NH_(4)in the soil.The overall difference between the two carbon input modes resulted primarily from the lower total wheat biomass,and lower levels of NO_(3)and soil PH characterizing pots submitted to carbon pulses,compared to those subjected to continuous carbon supply.Carbon supply,in general,and carbon input mode,in particular,can lead to belowground chain reactions cascading up to affect plant performance.
基金Sol Leshin UCLA-BGU Program,grant number 8721991.
文摘Aims Resource allocation in plants can be strongly affected by competition.Besides plant–plant interactions,terrestrial plants compete with the soil bacterial community over nutrients.Since the bacterial communities cannot synthesize their own energy sources,they are dependent on external carbon sources.Unlike the effect of overall amounts of carbon(added to the soil)on plant performance,the effect of fine scale temporal variation in soil carbon inputs on the bacterial biomass and its cascading effects on plant growth are largely unknown.We hypothesize that continuous carbon supply(small temporal variance)will result in a relatively constant bacterial biomass that will effectively compete with plants for nutrients.On the other hand,carbon pulses(large temporal variance)are expected to cause oscillations in bacterial biomass,enabling plants temporal escape from competition and possibly enabling increased growth.We thus predicted that continuous carbon supply would increase root allocation at the expense of decreased reproductive output.We also expected this effect to be noticeable only when sufficient nutrients were present in the soil.Methods Wheat plants were grown for 64 days in pots containing either sterilized or inoculated soils,with or without slow-release fertilizer,subjected to one of the following six carbon treatments:daily(1.5mg glucose),every other day(3mg glucose),4 days(6mg glucose),8 days(12mg glucose),16 days(24mg glucose)and no carbon control.Important Findings Remarkably,carbon pulses(every 2–16 days)led to increased reproductive allocation at the expense of decreased root allocation in plants growing in inoculated soils.Consistent with our prediction,these effects were noticeable only when sufficient nutrients were present in the soil.Furthermore,soil inoculation in plants subjected to low nutrient availability resulted in decreased total plant biomass.We interpret this to mean that when the amount of available nutrients is low,these nutrients are mainly used by the bacterial community.Our results show that temporal variation in soil carbon inputs may play an important role in aboveground–belowground interactions,affecting plant resource allocation.
