Soil microbial nutrient constraints along a tropical forest elevation gradient: a belowground test of a biogeochemical paradigm

[摘要] Aboveground primary productivity is widely considered to be limited byphosphorus (P) availability in lowland tropical forests and by nitrogen (N)availability in montane tropical forests. However, the extent to which thisparadigm applies to belowground processes remains unresolved. We measuredindices of soil microbial nutrient status in lowland, sub-montane and montanetropical forests along a natural gradient spanning 3400 m in elevation inthe Peruvian Andes. With increasing elevation there were marked increases insoil concentrations of total N, total P, and readily exchangeable P, but adecrease in N mineralization determined by in situ resin bags. Microbialcarbon (C) and N increased with increasing elevation, but microbialC : N : P ratios were relatively constant, suggesting homeostasis. Theactivity of hydrolytic enzymes, which are rich in N, decreased withincreasing elevation, while the ratio of enzymes involved in the acquisitionof N and P increased with increasing elevation, further indicating anincrease in the relative demand for N compared to P with increasingelevation. We conclude that soil microorganisms shift investment in nutrientacquisition from P to N between lowland and montane tropical forests,suggesting that different nutrients regulate soil microbial metabolism andthe soil carbon balance in these ecosystems.

[学科分类] 地球化学与岩石