Influence of Non-nitrogenous Soil Amendments on Soil CO2 Efflux and Fine Root Production in an N-Saturated Northern Hardwood Forest
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Non-nitrogenous mineral nutrients may be an important constraint on forest productivity and belowground processes in many ecosystems. We measured responses of soil CO2 efflux (FCO2), fine root production, and root-free incubation soil respiration to experimental additions of non-nitrogenous mineral nutrients (phosphorus (P) + potassium (K) fertilizer, dolomitic lime, and P + K plus lime) over 2 years in a sugar-maple-dominated forest in central Ontario; this region receives some of the highest anthropogenic nitrogen (N) inputs in North America, and evidence exists for co-limitation by P, magnesium (Mg), and calcium (Ca) of the growth of dominant trees. Soil amendments, in particular P + K fertilization, reduced FCO2, fine root production and microbial respiration, with decreases in FCO2 of 28–51% in fertilized compared to control plots. Partial regression analyses indicated that soil available P had a negative effect on FCO2, fine root production, and microbial respiration, but detected no significant effects of N, Ca, or Mg. Path analysis further suggested that available P reduced both fine root production and microbial respiration, and that these effects were largely responsible for reduced FCO2. There was also a residual direct negative relationship between available P and FCO2, which may represent reduced metabolic activity of roots. The study indicates that P is a critical nutrient dominating belowground processes in an N-saturated forest ecosystem, and suggests that additions of P may enhance C sink strength in managed forests in part through reductions in soil CO2 efflux.
KeywordsAcer saccharum forest management fertilization soil respiration microbial respiration fine root production phosphorus soil pH
We thank Tomasz Gradowski for assistance with establishing the experiment and with field measurements. This research was financially supported by the Canadian National Science and Engineering Research Council (NSERC) and Ontario’s Premier’s Research Excellence Award program. Y. Peng is grateful to the University of Toronto for a Connaught scholarship.
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