PS 43-151 - A large-scale analysis of passive experimental warming effects on plant communities

Abstract: Average global temperatures are predicted to increase by 1.8-4.0 °C during the twenty-first century. Anthropogenic climate change can have many major effects on plants, such as altering phenology, plant composition, plant traits, and more. There are many past and present experiments in which scientists try to mimic these increasing temperatures to determine how plants may respond. One common method for in situ temperature manipulation is open-top chambers (OTCs). OTCs are structures that passively warm on average from 1-3 °C daily, have an open top to allow for natural levels of sunlight, precipitation, and gas exchange, are relatively inexpensive to create and maintain, and do not require an external power source. Nearly a decade ago, synthesis research of warming studies found large variation in vegetation responses over space and time. However, these studies were either limited in scope (i.e., restricted to tundra and alpine zones), had small sample sizes, or combined warming techniques (i.e., passive and active warming). A comprehensive large-scale meta-analysis of OTC experiments is needed to quantify the short- vs. long-term effects of warming across different contexts (e.g., latitude, plant community type, chamber design, etc.), identify knowledge gaps, and help guide future research. To address these knowledge gaps, we conducted a meta-analysis of 110 OTC studies across the globe. For each study, we calculated the effect of warming on measured plant traits (e.g., biomass, height, N content, etc.) using Hedges’ g effect sizes and evaluated these responses across different plant contexts (family, genus, functional group, etc.) and experimental design attributes (chamber temperature, study length, and latitude).

Here we show that plant responses to warming vary among plant traits. For example, growth traits, such as biomass or shoot length, often increased under warming. However, traits such as N content declined in warmer conditions. These trends also depended upon the plant functional group; species such as bryophytes or lichens experienced decreased growth traits under warming. Latitude also played a role in plant responses to warming, with plants in higher latitudes typically having stronger responses to warming than plants in lower latitudes. In conclusion, this meta-analysis reveals both how plants across the globe vary in their responses to warming and what factors contribute to this variation.