Shifting soil resource limitations and ecosystem retrogression across a three million year semi-arid substrate age gradient

摘要: The current paradigm of plant nutrient limitation during ecosystem development predicts a change from nitrogen (N) when substrates are young to phosphorus (P) sub- strates old. However, there surprisingly few direct tests this model. We evaluated theory experimentally along three million year semi-arid substrate age gradient using resource additions intercanopy spaces dominated by the C4 bunchgrass Bouteloua gracilis. Unlike other gradients in tropical and temperate ecosystems, soil water avail- ability also increases strongly across system due finer texture with age. found that aboveground net primary production (ANPP) B. gracilis was limited both N on 55 ky substrate; not N, P, or 750 P alone 3000 kysubstrate.Notably, measures offoliarnutrient concentration N:P mass ratios were unable predict limitations these systems. In unamended plots, mean ANPP declined dramatical- ly at compared younger sites, presumably progressive P. This decline late is consistent reduction total carbon storage site provides mechanism for successional retrogression structure function. Our results unify biogeochemical disparate ecosystems while illustrating important water-nutrient interactions semi- arid further define nature terrestrial ecosystems.