Simple additive effects are rare: a quantitative review of plant biomass and soil process responses to combined manipulations of CO₂ and temperature

Abstract

In recent years, increased awareness of the potential interactions between rising atmospheric CO2 concentrations ([ CO2 ]) and temperature has illustrated the importance of multifactorial ecosystem manipulation experiments for validating Earth System models. To address the urgent need for increased understanding of responses in multifactorial experiments, this article synthesizes how ecosystem productivity and soil processes respond to combined warming and [ CO2 ] manipulation, and compares it with those obtained in single factor [ CO2 ] and temperature manipulation experiments. Across all combined elevated [ CO2 ] and warming experiments, biomass production and soil respiration were typically enhanced. Responses to the combined treatment were more similar to those in the [ CO2 ]-only treatment than to those in the warming-only treatment. In contrast to warming-only experiments, both the combined and the [ CO2 ]-only treatments elicited larger stimulation of fine root biomass than of aboveground biomass, consistently stimulated soil respiration, and decreased foliar nitrogen (N) concentration. Nonetheless, mineral N availability declined less in the combined treatment than in the [ CO2 ]-only treatment, possibly due to the warming-induced acceleration of decomposition, implying that progressive nitrogen limitation (PNL) may not occur as commonly as anticipated from single factor [ CO2 ] treatment studies. Responses of total plant biomass, especially of aboveground biomass, revealed antagonistic interactions between elevated [ CO2 ] and warming, i.e. the response to the combined treatment was usually less-than-additive. This implies that productivity projections might be overestimated when models are parameterized based on single factor responses. Our results highlight the need for more (and especially more long-term) multifactor manipulation experiments. Because single factor CO2 responses often dominated over warming responses in the combined treatments, our results also suggest that projected responses to future global warming in Earth System models should not be parameterized using single factor warming experiments.

Effects of increased temperature on plant communities depend on landscape location and precipitation

“…Indeed, the productivity response to experimental warming varies with soil moisture, but not in a consistent manner (Elmendorf et al., 2011, 2012; Wu et al., 2011). Other ecosystem factors, such as species composition, and environmental factors like soil type and infiltration rates (Dieleman et al., 2012; Way & Oren, 2010) are likely also important and potentially explain the inconsistent relationship between soil moisture and the response to increased temperature. Furthermore, experimental warming tends to increase productivity more strongly near the poles (Rustad, Campbell, Marion, Norby, & Mitchell, 2001), indicating another context dependency of warming effects.…”

“…We expected that warming and drying from the OTC (Liancourt et al., 2012) would negatively impact plant productivity and diversity, and especially so in the warmer, drier location, where plants might be operating closer to their thermal optima (Wertin, Reed, & Belnap, 2015), and be more water limited. As such, we would expect the drying effects of the warming treatment to be more consequential than the temperature effects (Dieleman et al., 2012). We further hypothesized that additional precipitation could moderate much of the negative impact of the OTC.…”

Interactions among ecosystem stressors and their importance in conservation

“…survival, growth, abundance, behaviour e.g. species diversity, biomass, total primary production additive antagonistic Crain et al [15] Darling & Côté [16] Dieleman et al [32] Gruner et al [26] Harvey et al [47] Przelawski et al [22] Wu et al [31] Stephens et al [29] Wahl et al [33] Jackson [27] Figure 4. Links between various categories of responses to multiple stressors and the types of interactions occurring between these stressors.…”

Physiological and molecular alterations in plants exposed to high [CO2] under phosphorus stress

“…Many experiments have been carried out to study the responses of plants to high [CO 2 ] at various levels ranging from the ecosystem to the genome (e.g. Ainsworth and Long 2005;Luo et al, 2006;Teng et al, 2006;Niu et al, 2011;Dieleman et al, 2012;AbdElgawad et al, 2014;Zinta et al, 2014). Such studies revealed that elevated [CO 2 ] increases plant growth and crop yield by the stimulation of carboxylation and suppression of oxygenation activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) particularly in C3 plants, whereas the effects are marginal in C4 plants because Rubisco is already saturated at ambient [CO 2 ] (reviewed by Bowes 1991;Ghannoum et al, 2003;Feng et al, 2014).…”