Species-specific traits determine shrub-annual interactions during a growing season
GeFei ZHANG, WenZhi ZHAO*
Linze Inland River Basin Research Station, Key Laboratory of Ecohydrology of Inland River Basin, Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou 730000, China
Species-specific traits determine shrub-annual interactions during a growing season
GeFei ZHANG, WenZhi ZHAO*
Linze Inland River Basin Research Station, Key Laboratory of Ecohydrology of Inland River Basin, Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou 730000, China
摘要 Stress gradient hypothesis predicted that facilitative interactions usually increase in intensity and are importance with abiotic stress. By contrast, facilitation may be lost in time, when it involves the growth of benefactors or beneficiaries. Less is known about which response pattern is more common in arid desert. We present an empirical study to explore shrub-annual interactions at the community and individual level along the course of a single growing season in a desert steppe in northwest China. Here the severity of drought stress may increase in time due to uneven precipitation during plant growing season. We assessed growth responses of annuals in understory where two dominant shrubs were removed. Annuals responses showed a switch from weakly positive to more strongly positive beneath Calligonum mongolicum, whereas from positive to negative beneath Nitraria sphaerocarpa during the growing season. Additionally, annual species with contrasting functional traits showed distinct growth responses to canopies removal. There was evidence of an increase in soil moisture below the canopy of shrubs, but a decrease in potential evaporation rate and photosynthetically active radiation, which can partly explain these species-specific responses. We conclude that the balance between competitive and facilitative effects in shrub-annual interactions is not only governed by the severity of stress but also determined by plant traits, such as canopy structure of shrubs and functional traits of their understory annuals.
Abstract: Stress gradient hypothesis predicted that facilitative interactions usually increase in intensity and are importance with abiotic stress. By contrast, facilitation may be lost in time, when it involves the growth of benefactors or beneficiaries. Less is known about which response pattern is more common in arid desert. We present an empirical study to explore shrub-annual interactions at the community and individual level along the course of a single growing season in a desert steppe in northwest China. Here the severity of drought stress may increase in time due to uneven precipitation during plant growing season. We assessed growth responses of annuals in understory where two dominant shrubs were removed. Annuals responses showed a switch from weakly positive to more strongly positive beneath Calligonum mongolicum, whereas from positive to negative beneath Nitraria sphaerocarpa during the growing season. Additionally, annual species with contrasting functional traits showed distinct growth responses to canopies removal. There was evidence of an increase in soil moisture below the canopy of shrubs, but a decrease in potential evaporation rate and photosynthetically active radiation, which can partly explain these species-specific responses. We conclude that the balance between competitive and facilitative effects in shrub-annual interactions is not only governed by the severity of stress but also determined by plant traits, such as canopy structure of shrubs and functional traits of their understory annuals.
This work was financial supported by the National Basic Re-search Program of China (2013CB429903) and the National Natural Science Foundation of China (41301603).
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2015, Vol. 7 
