Abstract
Shoot defoliation by grazers or mowing can affect root traits of grassland species, which may subsequently affect its aboveground traits and ecosystem functioning (e.g., aboveground primary production). However, experimental evidence for such reciprocal feedback between shoots and roots is limited. We grew the perennial grass Leymus chinensis–common across the eastern Eurasian steppe–as model species in a controlled-hydroponics experiment, and then removed half of its shoots, half of its roots, or a combination of both. We measured a range of plant aboveground and belowground traits (e.g., phenotypic characteristics, photosynthetic traits, root architecture) in response to the shoot and/or root removal treatments. We found the regenerated biomass was less than the lost biomass under both shoot defoliation and root severance, generating a under-compensatory growth. Root biomass was reduced by 60.11% in the defoliation treatment, while root severance indirectly reduced shoot biomass by 40.49%, indicating a feedback loop between shoot and root growth. This defoliation-induced shoot–root feedback was mediated by the disproportionate response and allometry of plant traits. Further, the effect of shoot defoliation and root severance on trait plasticity of L. chinensis was sub-additive. That is, the combined effects of the two treatments were less than the sum of their independent effects, resulting in a buffering effect on the existing negative influences on plant persistence by increased photosynthesis. Our results highlight the key role of trait plasticity in driving shoot–root reciprocal feedbacks and growth persistence in grassland plants, especially perennial species. This knowledge adds to earlier findings of legacy effects and can be used to determine the resilience of grasslands.
Highlights
Grasslands that are dominated by perennial species, which cover the largest terrestrial land area worldwide (Gibson, 2009), are commonly used by livestock grazing or mowing for haymaking and provide essential services for human (Dixon et al, 2014; Fetzel et al, 2017)
To investigate defoliation-induced legacy effects on plant performance due to the changes in root trait, we asked three questions: (1) How do functional traits of shoots and roots differentially respond to defoliation? (2) How do shoot performances feedback to root plasticity? (3) Is the effect of shoot defoliation and root severing on trait variation additive or non-additive? Answering these questions can improve our understanding of the grazing stress tolerance and interannual stability of this important forage species
We found that the effect of experimental defoliation and root severance on trait plasticity of L. chinensis was sub-additive, may resulting in a buffering effect on plant performances under grazing or mowing
Summary
Grasslands that are dominated by perennial species, which cover the largest terrestrial land area worldwide (Gibson, 2009), are commonly used by livestock grazing or mowing for haymaking and provide essential services for human (Dixon et al, 2014; Fetzel et al, 2017). Shoot-Root Interaction Under Defoliation mowing of grasslands (Lü et al, 2012; Wang B. et al, 2020) With both grazing and mowing, the removal of plant shoot tissue (i.e., “defoliation”) is the main mechanism underlying the effects on plant performance and ecosystem function of grasslands (Liu et al, 2015; Lezama and Paruelo, 2016). In addition to the three major drivers described above, the feedback loop between shoot and root plasticity may be essential for determining the growth and persistence of perennial plant species. To investigate defoliation-induced legacy effects on plant performance due to the changes in root trait, we asked three questions: (1) How do functional traits of shoots and roots differentially respond to defoliation? To investigate defoliation-induced legacy effects on plant performance due to the changes in root trait, we asked three questions: (1) How do functional traits of shoots and roots differentially respond to defoliation? (2) How do shoot performances feedback to root plasticity? (3) Is the effect of shoot defoliation and root severing on trait variation additive or non-additive? Answering these questions can improve our understanding of the grazing stress tolerance and interannual stability of this important forage species
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