Abstract
Open top chambers (OTCs) are a popular method for studying the biological effects of climate change through passive heating, but their effects on biotic interactions are poorly understood, especially for pollination. Here we use the subalpine plants Delphinium nuttallianum and Potentilla pulcherrima to examine the possibility that the effects of OTCs on plant reproduction are not the result of warming but rather OTCs acting as barriers to pollinator movement. Pollinator observations were conducted and stigmas collected from plants inside and outside of OTCs in a meadow in the Rocky Mountains of Colorado, USA. Very few visitors were observed inside of OTCs, which led to severe reductions in visitation rates, by 92% in Delphinium and 85% in Potentilla. The number of conspecific pollen grains on stigmas was 73% lower in OTCs for Delphinium but not Potentilla, likely because it is capable of autogamous self-pollination. This study clearly shows that OTCs can reduce animal pollination, which is also likely to reduce plant reproductive output of outcrossing plants via decreases in the quantity or quality of pollen. OTCs may therefore confound effects of warming on plant reproduction with pollination effects. Although the unintended effects of OTCs on abiotic conditions are well-studied, this study highlights that their effects on biotic interactions require further investigation.
Highlights
Climate change affects various aspects of plant performance, including survival and reproduction (Hedhly et al 2009; Miller-Rushing et al 2010; Cleland et al 2012)
Open top chambers (OTCs) significantly reduced the mean number of conspecific pollen grains on Delphinium stigmas by 73%; in contrast, we did not detect a significant effect of OTCs on pollen deposition to Potentilla
We show that OTCs can substantially reduce both pollinator visitation and pollen deposition in a subalpine ecosystem
Summary
Climate change affects various aspects of plant performance, including survival and reproduction (Hedhly et al 2009; Miller-Rushing et al 2010; Cleland et al 2012). Open top passive warming chambers (hereafter OTCs) are widely used as an experimental manipulation to study how plant performance responds to climate change, because they consistently and passively increase air temperatures in the field (Marion et al 1997). OTCs can increase or decrease rates of insect herbivory depending on the herbivore and the study system (Barrio et al 2016; Brikemoe et al 2016), but so far have not been shown to affect plant-pollinator interactions (Robinson & Henry 2018). Visitors may stay inside chambers if the abiotic conditions inside OTCs are preferable, which could increase visitation rates. The only study of which we are aware that directly examines the effect of OTCs on pollinator behavior finds that OTCs have no effect on pollinator visitation rates to three Arctic plant species (Robinson & Henry 2018). We expect any effects of OTCs on pollinator behavior to have larger consequences for pollen deposition in Delphinium, which requires pollinators to set seed (Waser & Price 1981), compared to Potentilla, which is capable of autogamous self-pollination (Burkle & Irwin 2010)
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