Breakdown of green and senescent leaves in Amazonian streams: a case study

Allochthonous organic matter in low-order streams is, in general, mainly composed of senescent leaves. However, in tropical streams green leaves can represent an important source of energy. The present study evaluated the decomposition of green and senescent leaves in Amazonian streams using leaves of three plant species: Inga stipularis D.C. 1876, Tococa guianensis Aubl. 1775 and Vochysia ferruginea Mart. 1826. The leaves were incubated for 120 days in four streams in the municipality of Santarém in western Pará State, Brazil. Senescent leaves were collected using nylon nets suspended 1 m above the ground, while green leaves were collected manually, directly from the trees. Green leaves exhibited better nutritional status: higher values for nitrogen and phosphate and lower values for carbon. Toughness and percentages of tannin and lignin of the green and senescent leaves varied among the studied species. Mass loss of green leaves was ~ 3.5 times higher than that of senescent leaves after 120 days. Higher values of phosphate and nitrogen and lower values of carbon, tannin, and lignin in green leaves were fundamental in explaining the difference in decomposition between green and senescent leaves. These differences reinforce the importance of understanding the role of green leaves in aquatic environments. © 2020, The Japanese Society of Limnology