Hultine Kevin R, Bean Dan W, Dudley Tom L, Gehring Catherine A
*Department of Research, Conservation and Collections, Desert Botanical Garden, Phoenix, AZ, USA
Palisade Insectary, Colorado Department of Agriculture, Palisade, CO, USA.
Integr Comp Biol. 2015 Oct;55(4):587-601. doi: 10.1093/icb/icv019. Epub 2015 Apr 22.
Desert riparian ecosystems of North America are hotspots of biodiversity that support many sensitive species, and are in a region experiencing some of the highest rates of climatic alteration in North America. Fremont cottonwood, Populus fremontii, is a foundation tree species of this critical habitat, but it is threatened by global warming and regional drying, and by a non-native tree/shrub, Tamarix spp., all of which can disrupt the mutualism between P. fremontii and its beneficial mycorrhizal fungal communities. Specialist herbivorous leaf beetles (Diorhabda spp.) introduced for biocontrol of Tamarix are altering the relationship between this shrub and its environment. Repeated episodic feeding on Tamarix foliage by Diorhabda results in varying rates of dieback and mortality, depending on genetic variation in allocation of resources, growing conditions, and phenological synchrony between herbivore and host plant. In this article, we review the complex interaction between climatic change and species introductions and their combined impacts on P. fremontii and their associated communities. We anticipate that (1) certain genotypes of P. fremontii will respond more favorably to the presence of Tamarix and to climatic change due to varying selection pressures to cope with competition and stress; (2) the ongoing evolution of Diorhabda's life cycle timing will continue to facilitate its expansion in North America, and will over time enhance herbivore impact to Tamarix; (3) defoliation by Diorhabda will reduce the negative impact of Tamarix on P. fremontii associations with mycorrhizal fungi; and (4) spatial variability in climate and climatic change will modify the capacity for Tamarix to survive episodic defoliation by Diorhabda, thereby altering the relationship between Tamarix and P. fremontii, and its associated mycorrhizal fungal communities. Given the complex biotic/abiotic interactions outlined in this review, conservation biologists and riparian ecosystem managers should strive to identify and conserve the phenotypic traits that underpin tolerance and resistance to stressors such as climate change and species invasion. Such efforts will greatly enhance conservation restoration efficacy for protecting P. fremontii forests and their associated communities.
北美沙漠河岸生态系统是生物多样性热点地区，支撑着许多敏感物种，且该地区正经历北美一些最高的气候变化速率。弗里蒙特杨（Populus fremontii）是这片关键栖息地的基础树种，但它受到全球变暖和区域干旱以及一种非本土乔木/灌木——柽柳属（Tamarix spp.）的威胁，所有这些都可能破坏弗里蒙特杨与其有益菌根真菌群落之间的共生关系。为控制柽柳而引入的专食性食叶甲虫（Diorhabda spp.）正在改变这种灌木与其环境之间的关系。Diorhabda对柽柳树叶的反复间歇性取食导致不同程度的枯死和死亡，这取决于资源分配的遗传变异、生长条件以及食草动物与寄主植物之间的物候同步性。在本文中，我们回顾了气候变化与物种引入之间的复杂相互作用及其对弗里蒙特杨及其相关群落的综合影响。我们预计：（1）由于应对竞争和压力的选择压力不同，弗里蒙特杨的某些基因型对柽柳的存在和气候变化的反应会更有利；（2）Diorhabda生命周期时间的持续进化将继续促进其在北美的扩张，并随着时间的推移增强食草动物对柽柳的影响；（3）Diorhabda造成的落叶将减少柽柳对弗里蒙特杨与菌根真菌共生关系的负面影响；（4）气候和气候变化的空间变异性将改变柽柳在遭受Diorhabda间歇性落叶后存活的能力，从而改变柽柳与弗里蒙特杨及其相关菌根真菌群落之间的关系。鉴于本综述中概述的复杂生物/非生物相互作用，保护生物学家和河岸生态系统管理者应努力识别和保护那些构成对气候变化和物种入侵等压力源耐受性和抗性基础的表型特征。这些努力将大大提高保护弗里蒙特杨森林及其相关群落的保护恢复效果。
