Abstract
A major frontier in global change research is predicting how multiple agents of global change will alter plant productivity, a critical component of the carbon cycle. Recent research has shown that plant responses to climate change are phylogenetically conserved such that species within some lineages are more productive than those within other lineages in changing environments. However, it remains unclear how phylogenetic patterns in plant responses to changing abiotic conditions may be altered by another agent of global change, the introduction of non-native species. Using a system of 28 native Tasmanian Eucalyptus species belonging to two subgenera, Symphyomyrtus and Eucalyptus, we hypothesized that productivity responses to abiotic agents of global change (elevated CO2 and increased soil N) are unique to lineages, but that novel interactions with a non-native species mediate these responses. We tested this hypothesis by examining productivity of 1) native species monocultures and 2) mixtures of native species with an introduced hardwood plantation species, Eucalyptus nitens, to experimentally manipulated soil N and atmospheric CO2. Consistent with past research, we found that N limits productivity overall, especially in elevated CO2 conditions. However, monocultures of species within the Symphyomyrtus subgenus showed the strongest response to N (gained 127% more total biomass) in elevated CO2 conditions, whereas those within the Eucalyptus subgenus did not respond to N. Root:shoot ratio (an indicator of resource use) was on average greater in species pairs containing Symphyomyrtus species, suggesting that functional traits important for resource uptake are phylogenetically conserved and explaining the phylogenetic pattern in plant response to changing environmental conditions. Yet, native species mixtures with E. nitens exhibited responses to CO2 and N that differed from those of monocultures, supporting our hypothesis and highlighting that both plant evolutionary history and introduced species will shape community productivity in a changing world.
Highlights
IntroductionIn contrast to the implied paradigm that all plants should produce more biomass in response to increased soil N, a growing body of research shows that not all species respond positively, or even at all, to increased soil N, especially in elevated CO2 conditions [5,6,7,8,9,10]
Several analyses of primary productivity at community, biome and global levels have indicated that soil nitrogen (N) generally limits carbon sequestration, but have failed to address whether individual species respond differently to increased soil N [1,2,3,4]
Consistent with our hypothesis that plant productivity responses to abiotic agents of global change are contingent upon both evolutionary history and novel species interactions, full models of total and aboveground biomass identified a significant interaction among atmospheric CO2, soil N, species pair type, and subgenus (x254.2151, p50.040; x254.1311, p50.042) (Table 1; Fig. 1)
Summary
In contrast to the implied paradigm that all plants should produce more biomass in response to increased soil N, a growing body of research shows that not all species respond positively, or even at all, to increased soil N, especially in elevated CO2 conditions [5,6,7,8,9,10]. This is likely because plants have evolved different capacities to compete for soil resources [11]. Understanding how past evolution and contemporary biotic interactions shape plant species responses to environmental change could provide key insight into how plant diversity and function may be altered in global change scenarios
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