Woody debris dominates the exports of carbon and nitrogen from headwater streams in an alpine forest.

The exports of carbon and nitrogen with water flowing in the headwater streams could be important components of material mitigation in forest ecosystems. Plant debris is a major source of dissolved organic matter for headwater streams, but few studies have investigated the differences between the impacts of woody debris and non‐woody debris inputs on headwater streams in terms of carbon and nitrogen exports. Here, we assessed the effects of plant debris (i.e., woody debris, non‐woody debris and mixed debris) on the concentrations and exports of dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) in the headwater streams of an alpine forest on the eastern Tibetan Plateau. Woody and non‐woody debris only weakly affected the DOC and TDN concentrations in the headwater streams. Compared with those in the reference stream excluding plant debris, woody debris increased the exports of DOC and TDN by 19% and 13%, whereas non‐woody debris decreased the exports of DOC and TDN by 22% and 25%, respectively. However, when fall approached, the role of non‐woody debris reversed to enhance the stream‐water exports of DOC and TDN. The effect of non‐woody debris during the fall season differed from that during the overall growing season, indicating that restricting non‐woody debris inputs might improve the ability of the stream to retain forest carbon and nitrogen. Notwithstanding the relatively limited experimental period, this work revealed the critical importance of plant debris for carbon and nutrients within water conservation regions like alpine forests. [ABSTRACT FROM AUTHOR]