Differential responses of invasive and native plants to warming with simulated changes in diurnal temperature ranges.

Bao-Ming Chen,Hui-Xuan Liao,Yang Gao,Shao-Lin Peng

doi:10.1093/aobpla/plx028

Abstract

Although many studies have documented the effects of global warming on invasive plants, little is known about whether the effects of warming on plant invasion differ depending on the imposed change in different diurnal temperature ranges (DTR). We tested the impact of warming with DTR change on seed germination and seedling growth of eight species in the family Asteraceae. Four of these are invasive (Eupatorium catarium, Mikania micrantha, Biodens pilosa var. radiate, Ageratum conyzoides) in China, and four are native (Sonchus arvensis, Senecios candens, Pterocypsela indica, Eupatorium fortunei). Four temperature treatments were set in growth chambers (three warming by 3 °C with different DTRs and control), and experiments were run to mimic wintertime and summertime conditions. The control treatment (Tc ) was set to the mean temperature for the corresponding time of year, and the three warming treatments were symmetric (i.e. equal night-and-day) (DTRsym), asymmetric warming with increased (DTRinc) and decreased (DTRdec) DTR. The warming treatments did not affect seed germination of invasive species under any of the conditions, but DTRsym and DTRinc increased seed germination of natives relative to the control, suggesting that warming may not increase success of these invasive plant species via effects on seed germination of invasive plants relative to native plants. The invasive plants had higher biomass and greater stem allocation than the native ones under all of the warming treatments. Wintertime warming increased the biomass of the invasive and wintertime DTRsym and DTRinc increased that of the native plants, whereas summertime asymmetric warming decreased the biomass of the invasives but not the natives. Therefore, warming may not facilitate invasion of these invasive species due to the suppressive effects of summertime warming (particularly the asymmetric warming) on growth. Compared with DTRsym, DTRdec decreased the biomass of both the invasive and native plants, while the asymmetric summer warming treatments (DTRinc and DTRdec) decreased the biomass of the invasive but not the native plants. In addition, wintertime DTRinc did not enhance the biomass of all the plants relative to DTRsym. Our results were obtained in an unrealistic setting; the growth conditions in chambers (e.g. low light, low herbivory, no competition) are quite different from natural conditions (high light, normal herbivory and competition), which may influence the effects of warming on the seedling establishment and growth of both invasive and native plants. Nonetheless, our work highlights the importance of asymmetric warming, particularly in regards to the comparison with the effects of symmetric warming on both invasive and native plants. Conclusions regarding the effects of future warming should be made cautiously because warming with different DTRs may suggest different implications for invasion, and effects of warming may be different in different seasons.

Highlights

Mean temperatures have increased 1.0–1.6 C globally, with daily minimum temperature (Tmin) showing a more rapid increase than daily maximum temperature (Tmax), resulting in a decrease of 0.066 C per decade in the diurnal temperature range (DTR, Tmax - Tmin) between 1950 and 2004 (Vose et al 2005; IPCC 2013)
In order to test these hypotheses, we addressed the following questions: (i) do the responses to warming with different diurnal temperature ranges (DTR) differ between plants native to a region and related introduced invaders, and (ii) does warming with DTR change have different effects on plant invasion compared with symmetric warming? We selected four invasive alien species (Eupatorium catarium, Mikania micrantha, Biodens pilosa var. radiate, Ageratum conyzoides) and four native species (Sonchus arvensis, Senecios candens, Pterocypsela indica, Eupatorium fortunei) from the Asteraceae family to examine their seed germination and seedling establishment, which are critical to population invasion and persistence and are important factors in species’ responses to global change (Williams et al 2007)
Under simulated summertime temperature changes, the results showed that the biomass of the invasive plants decreased under DTRdec and DTRinc compared with the corresponding control (Tc) and DTRsym, but not the native plants (Fig. 2B)

Summary

Introduction

Mean temperatures have increased 1.0–1.6 C globally, with daily minimum temperature (Tmin) showing a more rapid increase than daily maximum temperature (Tmax), resulting in a decrease of 0.066 C per decade in the diurnal temperature range (DTR, Tmax - Tmin) between 1950 and 2004 (Vose et al 2005; IPCC 2013). In addition to the increases in mean annual temperatures, climate warming is asymmetric (i.e. warming with different DTRs) for different periods, seasons and continents (Liu et al 2004; Wild et al 2007; Rohde et al 2013; Tan et al 2015). The DTR in India has increased as a result of a decrease in the minimum temperature (Rai et al 2012). While an analysis conducted in southern China, the location of the present study, found an increase in DTR from 1984 to 2005 (Li and Chen 2009) and an increase in DTR from 1950 to 2100 was estimated with modelling study (Stone and Weaver 2003)

Methods

Results

Discussion

Conclusion