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Influence of Non-nitrogenous Soil Amendments on Soil CO₂ Efflux and Fine Root Production in an N-Saturated Northern Hardwood Forest

Peng, Yuanying, Thomas, Sean C.
Ecosystems 2010 v.13 no.8 pp. 1145-1156
adverse effects, calcium, carbon dioxide, carbon sinks, ecosystems, fertilizers, fine roots, hardwood forests, magnesium, nitrogen, nutrients, phosphorus, potassium, regression analysis, soil, soil amendments, soil respiration, trees, Ontario
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.