Interactions of herbivore exclusion with warming and N addition in a grass-dominated temperate old field

Abstract

Field experiments used to explore the effects of global change drivers, such as warming and nitrogen deposition on plant productivity and species composition, have typically focused on bottom-up processes. However, both direct and indirect responses of herbivores to the treatments could result in important interactions between top-down and bottom-up effects. These interactions may be complicated by the simultaneous effects of multiple herbivore taxa. We used rodent and mollusc exclosures in the plots of a warming and N addition field experiment to examine how herbivore removal would influence plant biomass responses to the treatments. The effect of rodent exclusion on grass biomass more than doubled in response to nitrogen addition, but did not respond to warming, whereas the effect of mollusc exclusion on grass biomass increased in response to warming, but not nitrogen. In contrast, the effect of rodent exclusion on total biomass (grasses and forbs combined) increased in response to both nitrogen and warming, while the effect of mollusc exclusion on total biomass was insensitive to nitrogen and warming. In no cases were there interactions between nitrogen and warming with respect to their influence on exclosure effects. Overall, our results demonstrated substantial and variable effects of multiple herbivore taxa on plant biomass responses to warming and N addition, despite the absence of conspicuous damage to the plant canopy. These results therefore highlight the potential importance of interactions between top-down and bottom-up factors in global change field experiments.

Soil freezing and N deposition: transient vs multi‐year effects on plant productivity and relative species abundance

“…However, the chronic effects of moderate rates of N deposition could potentially affect productivity through changes in species composition over the longer term (Wedin & Tilman, 1996;Isbell et al, 2013). In addition, in the context of the broader ecosystem, herbivores can play an important role in plant responses to climate change and N availability in our system (Moise & Henry, 2012), and the limited spatial scale of our experiment (both the mesocosms and the 1-m 2 area plots) was such that the herbivores would not have always been directly exposed to the treatments.…”

Climate change alters slug abundance but not herbivory in a temperate grassland

“…Slugs can both positively and negatively affect plant biomass production depending on a myriad of environmental and biological factors [14][15][16] and can alter overall plant species composition of vegetative stands through highly selective foraging [17]. For example, in pasture and grassland settings, gastropods have been reported to selectively graze seedlings [16], although this depends on plant species [18], seedling age [18], and nitrogen (N) content [19].…”

“…Furthermore, slug herbivory is likely to be impacted by climate change through both direct and indirect interactions [12,15]. Climate change is expected to increase global average annual temperatures by 1.4-5.8˚C and alter hydrological regimes world-wide, in part by altering the timing and magnitude of rain events [20].…”

“…However, in some systems, since slugs can influence the composition of vegetation through seedling herbivory, any direct effects on the slug community from climate change may result in concomitant changes to the plant community [27]. In a factorial study of warming, N addition, and slug exclusion, Moise and Henry [15] found that long-term warming (three years) in an old-field pasture reduced overall plant productivity but that slug exclusion in warmed plots negated the negative effect on biomass of warming alone. These results suggest that the negative effect of warming on grassland productivity was mostly a direct effect of warming increasing slug herbivory [15].…”

Biomass Production of Selected Grassland, Wetland and Cropland Vegetation Communities

“…It is strongly related to the flow of matter through an ecosystem (Mooney, 1991) and thus plays a key role in landscape functions (Wiegand et al, 2004). Besides the physiology of plants forming a plant community and their ecologic strategies biomass production is significantly influenced by environmental factors such as climate and microclimate and the resulting water supply (Palmer and Yunusa, 2011), soil properties, especially the nutrient regime (Čížková et al, 2001) and pressure from the herbivores (Moise and Henry, 2012) orin case of agricultural ecosystemsan extra supply of nutrients, harvest and other farming practices (Heggenstaller et al, 2009). The methods to determine biomass production can be generally divided into destructive and non-destructive types.…”