Shifting soil resource limitations and ecosystem retrogression across a three million year semi-arid substrate age gradient
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The current paradigm of plant nutrient limitation during ecosystem development predicts a change from nitrogen (N) limitation when substrates are young to phosphorus (P) limitation when substrates are old. However, there are surprisingly few direct tests of this model. We evaluated this theory experimentally along a three million year semi-arid substrate age gradient using resource additions to intercanopy spaces dominated by the C4 bunchgrass Bouteloua gracilis. Unlike other gradients in subtropical and temperate ecosystems, soil water availability also increases strongly across this semi-arid system due to finer texture with substrate age. We found that aboveground net primary production (ANPP) of B. gracilis was limited by both water and N on the 55 ky substrate; not limited by N, P, or water on the 750 ky substrate; and limited by P alone on the 3000 ky substrate. Notably, measures of foliar nutrient concentration and N:P mass ratios were unable to predict nutrient limitations in these semi-arid systems. In unamended plots, mean ANPP declined dramatically at 3000 ky compared to the younger substrate age sites, presumably due to progressive limitation by P. This decline in ANPP late in ecosystem development is consistent with a reduction in soil total carbon and N storage at this site and provides a mechanism for successional retrogression in ecosystem structure and function. Our results unify biogeochemical theory across disparate ecosystems while illustrating the important water-nutrient interactions in these semi-arid ecosystems to further define the nature of nutrient limitations in terrestrial ecosystems.
KeywordsChronosequence Nitrogen N:P stoichiometry Phosphorus Piñon–juniper Soil development
This research was supported, in part, by McIntire-Stennis appropriations to NAU and the State of Arizona. K. Hess was instrumental in field and laboratory work and D. Guido provided essential laboratory assistance. We thank M. Sundqvist, T. Kolb, and two anonymous reviewers for valuable comments and D. Binkley, T. Whitham, and C. Gehring for thoughtful discussions that significantly improved the manuscript.
- Aerts R, Chapin FS III (1999) The mineral nutrition of wild plants revisited: a re-evaluation of processes and patterns. Adv Ecol Res 30:1–67Google Scholar
- Bonham CD (1989) Measurements of terrestrial vegetation. Wiley, New YorkGoogle Scholar
- Chapin FS III, Matson PA, Mooney HA (2002) Principles of terrestrial ecosystem ecology. Springer, New YorkGoogle Scholar
- Emerson AA (2010) Atmospheric inputs and plant nutrient uptake along a three million year semi-arid substrate age gradient. Dissertation, Northern Arizona UniversityGoogle Scholar
- Hooper DU, Johnson L (1999) Nitrogen limitation in dryland ecosystems: responses to geographical and temporal variation in precipitation. Biogeochemistry 46:247–293Google Scholar
- Jenny H (1941) Factors of soil formation: a system of quantitative pedology. Dover Publications, New YorkGoogle Scholar
- Selmants PC (2007) Carbon, nitrogen, and phosphorus dynamics across a three million year substrate age gradient in northern Arizona, USA. PhD Dissertation, Northern Arizona UniversityGoogle Scholar
- Vitousek PM (2004) Nutrient cycling and limitation: Hawai’i as a model system. Princeton University Press, NJGoogle Scholar