What to take home. Resource Compe,,on Removing things Compe,,on: One plant depletes a resource; that deple,on has a deleterious effect on another.

Transcription

1 Plant- Plant Interac,ons What to take home Plants interact passively Plants remove things from the environment (generally resource compe,,on) Plants add things to the environment (organic chemicals [allelochemics], salt, organic etc) Interac,ons can be posi,ve or nega,ve Outcome of interac,on depends on plant adapta,ons and the environmental condi,ons Interac,ons among plants include resource compe,,on, allelopathy, and other modifica,ons of the environment that enhance or inhibit species. Resource Compe,,on Removing things Compe,,on: One plant depletes a resource; that deple,on has a deleterious effect on another. Historical Principle of Compe,,ve Exclusion (Gause 1930 s) Plant Compe,,on (vs. Animal) Plants all have essen,ally the same requirements Spa,al/Temporal separa,on Plas,c Responses (mortality may not result) 1

2 Plas,c Responses (sunflower exp.) Area Or Height Basal Area For which resource might mortality be a larger issue? Height Leaf Area High plant density ->low plant density How measure compe,,on? Raise plants together in pots? Problem: edge of pot has no compe,,on Variety of designs, some sample only the middle of pots, others require both greenhouse and field experiments, etc Pot experiments De Wit Method Reciprocal Replacement method Propor,on of species range from 100% to 0% Density of plants in pot kept constant >100% sp A + 0% sp B >50% sp A + 50% sp B >25% sp A + 75% sp B, etc De Wit Results (Reciprocal Replacement) Chris,e and Detling 1982 Biomass Total per species per pot Species A Species B B wins B loses Sp A 100% 50% 0% Sp B 0% 50% 100% 2

3 Shiiing results this experiment provides an important insight on compe,,on Outcome of compe,,on depends upon ADAPTATIONS of the species and how they differ CONDITIONS under which they compete Whether or not a nega,ve effect occurs Outcome may shii as environment changes Allelopathy allelo = other pathy = suffering Allelochemics Adding things allelopathy is the introduc,on of organic chemicals into the environment that may inhibit the growth or survival of another species How are chemicals added to the environment? vola,liza,on li@er secre,on or excre,on (root exudates) passive leaching by rain or fog Characteris,cs highly selec,ve (suppresses some species and not others) depends on environmental condi,ons (reduc,on in growth may not result in observable response if soils don t accumulate the chemicals, like sandy soils) can circumvent other interac,ons Example of allelopathy Quercus falcata var pagodaefolia (compared with Liquidambar styraciflua) Forest cleared, 1 tree per hectare left. Beneath cherrybark oak, only grasses. Woody plants outside of canopy Example of allelopathy Quercus falcata var pagodaefolia (compared with Liquidambar styraciflua) Salicylic Acid leached from the canopy by rain inhibited Salicylic Acid establishment of woody species. Hook and Stubbs 1967, DeBell 1971 Hook and Stubbs 1967, DeBell

4 Other examples Salvia species in California Weedy thistles in Great Basin may inhibit other species Introduced species may be more suscep,ble to na,ves, or may be more inhibitory to na,ves (Eucalyptus, thistles) Geographic differences in allelopathic impact: example of an invasive species, Centaurea diffusa This native of central Eurasia was introduced to western North America. It associates with similar plants in both places (genera). In central Eurasia this is a relatively uncommon plant. But in North America this has become a terrible invasive. Root exudates directly affect neighbors, and directly affect soil microbes and mycorrhizae, influencing NAm na,ve hosts Diffuse coevolu,on of the physiology of plants and soil organisms to each other More exudate in N. Am. More invasion w/ N. Am. Natives & soil The Centaurea example shows that local communi,es may coevolve tolerances to each other s impact on the environment (in this case chemical root exudates) The net allelopathic impact in this case depended on a previous history of coevolu,on or lack of it Origin of the chemicals? waste products? an,- herbivore compounds? an,- fungal agents? etc coffee seeds filled with mitosis inhibitors, seeds divide cells first, embryo germinates just by cell expansion (an,- seed predator, pathogen). Outcome of allelopathy depends upon ADAPTATIONS of species involved ENVIRONMENTAL CONDITIONS under which chemical inhibi,on should occur Why do I keep emphasizing this? 4

5 Other deple,on/addi,on reac,ons Mesembryanthemum crystalinum adds NaCl to habitat Heavy addi,ons in deciduous forest inhibits many understory species like Aster acuminatus (experiments with plas,c in England show that chemicals aren t necessarily involved). Nurse plants (logs and hemlock; shrubs in desert). Mineral nutri,on/moisture enhanced beneath tree canopies in grasslands (light depleted). How do we evaluate impacts in the field? Asymmetric: seedlings vs adults Wetland zona,on Grasslands, forests, shrublands? 5