Rhizosphere interactions, carbon allocation, and nitrogen acquisition of two perennial North American grasses in response to defoliation and elevated atmospheric CO2

Abstract

Carbon allocation and N acquisition by plants following defoliation may be linked through plant-microbe interactions in the rhizosphere. Plant C allocation patterns and rhizosphere interactions can also be affected by rising atmospheric CO(2) concentrations, which in turn could influence plant and microbial responses to defoliation. We studied two widespread perennial grasses native to rangelands of western North America to test whether (1) defoliation-induced enhancement of rhizodeposition would stimulate rhizosphere N availability and plant N uptake, and (2) defoliation-induced enhancement of rhizodeposition, and associated effects on soil N availability, would increase under elevated CO(2). Both species were grown at ambient (400 μL L(-1)) and elevated (780 μL L(-1)) atmospheric [CO(2)] under water-limiting conditions. Plant, soil and microbial responses were measured 1 and 8 days after a defoliation treatment. Contrary to our hypotheses, we found that defoliation and elevated CO(2) both reduced carbon inputs to the rhizosphere of Bouteloua gracilis (C(4)) and Pascopyrum smithii (C(3)). However, both species also increased N allocation to shoots of defoliated versus non-defoliated plants 8 days after treatment. This response was greatest for P. smithii, and was associated with negative defoliation effects on root biomass and N content and reduced allocation of post-defoliation assimilate to roots. In contrast, B. gracilis increased allocation of post-defoliation assimilate to roots, and did not exhibit defoliation-induced reductions in root biomass or N content. Our findings highlight key differences between these species in how post-defoliation C allocation to roots versus shoots is linked to shoot N yield, but indicate that defoliation-induced enhancement of shoot N concentration and N yield is not mediated by increased C allocation to the rhizosphere.

Grassland Management Affects Delivery of Regulating and Supporting Ecosystem Services

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Elevated CO2 induces substantial and persistent declines in forage quality irrespective of warming in mixedgrass prairie

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Grazing enhances belowground carbon allocation, microbial biomass, and soil carbon in a subtropical grassland

“…Strategic management of pastures and rangelands can enhance sequestration of SOC (Conant, Paustian, & Elliott, ), reverse historic declines, and potentially offset a significant portion of fossil carbon emissions. Although there is robust literature on the role of large herbivores in shaping grassland plant composition, structure, and productivity (Fuhlendorf & Engle, ; Fuhlendorf, Engle, Elmore, Limb, & Bidwell, ; McNaughton, ; McNaughton, Banyikwa, & McNaughton, ), there remains considerable uncertainty about how large grazers affect belowground carbon allocation (Augustine, Dijkstra, Iii, & Morgan, ; Derner, Boutton, & Briske, ; McNaughton, Banyikwa, & McNaughton, ), and SOC stocks (McSherry & Ritchie, ).…”