1. Luna Morcillo, Diana Turrión, Susana Bautista
Plant-plant interactions in semiarid steppes as a function of resource availability
Luna Morcillo, Diana Turrión, Susana Bautista
Dpt. Ecology. University of Alicante. Apdo Alicante, Spain.
ABSTRACT
The outcome of plant-plant interactions in semiarid ecosystems depends on the specific traits of the species involved and on the biotic and abiotic conditions prevailing in the area. Yet, studies are not conclusive about the role of increasing environmental stress, leading to an ongoing debate on this topic. We examined the net balance of the interactions between mature Stipa tenacissima tussocks and Olea europaea seedlings, in response to changes in resource availability, in two steppe areas in southern Spain (Alicante). We planted O. europaea seedlings nearby and away from S. tenacissima tussocks, and manipulated the availability of two key resources by applying inputs of water and nutrients to the planting microsites. All across the abiotic gradient established and the between-site differences in resource availability, the negative effects of S. tenacissima on O. europaea largely prevailed against the facilitative effects. The results suggest that S. tenacissima tussocks outcompeted O. europaea in exploiting the water and nutrient inputs provided.
MAIN QUESTION
How does the net balance of the interaction between Stipa tenacissima and Olea europaea seedlings change across a gradient of resource availability?
MATERIAL and METHODS
Study area:
Target species: S. tenacissima (Benefactor sp) / O. europaea seedling (Beneficiary sp)
Experimental design
Semiarid Steppes areas in South East Spain
Soil type Lithic Calciorthid
South facing slopes .
Control and Watering treatments applied on both Microsites:
Stipa (upper)
Open (bottom)
W-N- :Control treatment
W-N+ : Nutrient addition (Compost)
W+N- : Watering treatment
W+N+: Nutrient and Water addition
Petrer site
Crevillent site
High differences in resource availability between sites during the study period.
Total rainfall:
Crevillent = XXX mm
Petrer = XXX mm
Organic matter (SOM), Nitrogen (N) and assimilable Phosphorus (P) content
RESULTS
Higher soil moisture values in Open microsite, particularly in the driest site: Crevillent
CONCLUSIONS
Competitive effects of S. tenacissima on O. europaea dominate positive effects across the wide abiotic gradient assessed. Potential changes towards a positive net balance in response to changes in resource availability are not supported by the results.
Competitive effect of S. tenacissima increased with nutrient availability.
The results do not support previous predictions based on the response of broad species traits (competitive/stress-tolerant), and suggest that predictions on the net balance of plant-plant interactions should be based on more specific traits.
Higher survival of Olea europaea seedlings in Open microsite
Negative effect of Stipa microsite on Olea europaea survival increased with nutrient addition.
Higher basal-diameter growth of Olea europaea seedlings in Open microsite.
Positive effect of Nutrient addition on basal-diameter growth of Olea europaea in Open microsite; neutral or negative effect in Stipa microsites.
No effect of Watering treatment
Acknowledgement: This research was supported by PATTERN (AGL2008/05532) project. Luna Morcillo Is supported by a FPI fellowship from the Spanish Ministry of Innovation and Science.