PLANT AND MICROBE CONTRIBUTION TO COMMUNITY RESILIENCE IN A DIRECTIONALLY CHANGING ENVIRONMENT

摘要: To understand the role biota play in resilience or vulnerability to environmental change, we investigated soil, plant, and microbial responses a widespread increased nitrogen (N). Our aim was test plant-soil threshold hypothesis: that changed biotic structure influences accumulated changes N. For six years, removed one of two codominant species, Geum rossii Deschampsia caespitosa, moist- meadow alpine tundra Colorado, USA. We also manipulated nutrient availability by adding carbon (C) N, separately combination with species removals. Consistent our hypothesis, associated soil feedbacks slowed rates N cycling cycling. After four- year initial period, dramatically declined (by almost 70%) due increasing availability. In contrast, abundance did not respond supply; it only responded removal Geum. Forbs graminoids more positively than removal, indicating stronger competitive effects Deschampsia. The interactions appear have community-level consequences: after years (but Deschampsia) evenness community over 35%. Increased affected soil-microbial feedbacks, particularly association Microbial biomass at higher as activities C-acquiring N- acquiring extracellular enzymes. presence Geum, fertilization activity phenol oxidase, tannin-degrading enzyme, suggesting microbes shift from degrading Geum-derived compounds. absence acid phosphatase increased, phosphorus limitation With continued deposition forecast for this system, these results suggest will be overwhelmed through elimination feedbacks. Once declines, loss indirectly facilitate via release. Because exerts strong on subordinate may accompanied community-wide drop diversity. conclude can influence exogenous contribute dynamics.