Semiarid ecosystem sensitivity to precipitation extremes: weak evidence for vegetation constraints

Area of Science:

• Ecology
• Climate Change Biology
• Ecosystem Science

Background:

• Semiarid regions face vegetation constraints on plant growth, potentially limiting net primary productivity (NPP).
• Climate change predictions suggest shifts from linear to saturating NPP-precipitation (PPT) relationships due to increased PPT extremes.

Purpose of the Study:

• To experimentally test the hypothesis that vegetation constraints limit NPP in semiarid regions.
• To investigate ecosystem process responses (ANPP, Rs) to a gradient of growing season precipitation (GSP) extremes.

Main Methods:

• A replicated gradient of 11 growing season precipitation levels was imposed in a semiarid grassland.
• Responses of aboveground net primary productivity (ANPP) and soil respiration (Rs) were measured.
• Plant community composition changes were analyzed under varying GSP conditions.

Main Results:

• Both ANPP and Rs showed linear responses to GSP, with greater sensitivity to wet than dry extremes.
• Responsiveness peaked at moderate GSP levels and declined at extreme levels.
• Plant compositional shifts, particularly increased forb cover, were driven by extreme wet GSP and mediated ANPP responses.

Conclusions:

• Plant compositional change is a key mediator of semiarid ecosystem responses to altered precipitation patterns.
• Ecosystem processes like ANPP and Rs exhibit complex responses to GSP extremes, influenced by vegetation dynamics.
• The sensitivity of semiarid ecosystems to precipitation extremes may be modulated by shifts in plant community structure.