Headwater Stream Dissolved Organic Carbon Under Four Different Vegetation Types Along An Altitudinal Gradient In The Wuyi Mountains Of China

Stream DOC is a major constituent of the global carbon cycle. Compared with researches oncarbon cycle of vertical direction (soil-vegetation-atmosphere continuum system) along analtitudinal gradient, litter is known on carbon cycle of horizontal direction (terrestrial-streamwater continuous system or soil-freshwater system), especially dynamics of headwater streamdissolved organic carbon (DOC) along an altitudinal gradient. In this dissertation, headwaterstream DOC concentrations, dissolved organic matter (DOM) composition, and biodegradabilityof dissolved organic carbon (BDOC) were studied under four different vegetation types,including evergreen broadleaf forest (EBF), coniferous forest (CF), subalpine dwarf forest (SDF)and alpine meadow (AM), along an altitudinal gradient in Wuyi Mountains of China.In the first study (stream DOC concentrations, chapter3), we examined the pattern ofheadwater stream DOC concentrations in relation to riparian soil organic carbon (SOC) contents,riparian water-extractable soil organic carbon (WSOC) contents, temperature and riparian soilC:N ratio under four different vegetation types along an altitudinal gradient. We found thatheadwater stream DOC concentrations were lower in AM than in EBF, CF, and SDF. Headwaterstream DOC concentrations were negatively correlated with riparian SOC as well as WSOCcontents, and were unrelated to riparian soil C:N ratio. Our findings suggest that altitudinalpattern of headwater stream DOC concentrations under four different vegetation types were notdriven by SOC. Higher precipitation, lower temperature, as well as higher soil clay content athigher elevation may play an important role in determining DOC concentrations in headwaterstreams under four different vegetation types along an altitudinal gradient in the WuyiMountains.In the second study (stream DOM composition, chapter4), we explored the use ofexcitation-emission matrix fluorescence spectroscopy (EEMs) and parallel factor analysis(PARAFAC) to detect the composition of headwater stream DOM. Two humic-like (C1and C2)and one tryptophan-like (C4) components were identified in headwater stream. Humic-likecomponent accounted for86.9394.01%of DOM in headwater stream. The relativecontributions of C1and C2in headwater stream were not substantially different under fourdifferent vegetation types along an altitudinal gradient, and the relative contributions ofheadwater stream C4in EBF and AM were higher than CF and SDF. Fluorescence index (FI)showed that soil was the predominant source of DOM in headwater stream, but composition ofheadwater stream DOM was different from that of water-extractable soil organic matter (WSOM).Our findings suggested that vegetation change along an altitudinal gradient didn’t lead to changein type of DOM components and the relative contributions of DOM dominant component(humic-like C1, C2) in headwater stream. And the composition of headwater stream DOM wasn’tfully controlled by soil organic matter (SOM) composition, but might also depend on siteconditions of temperature, light and dominant species. These different in site conditions oftemperature, light and dominant species might lead to consequently feature differentbio-degradation in soil, and bio-and photo-degradation and release of recently fixed carbon in stream.In the third study (stream BDOC, chapter5), we conducted a spatially comprehensive studyof stream BDOC during30days incubation under four vegetation types along an altitudinalgradient, and investigated the factors controlling altitudinal pattern of stream BDOC. StreamBDOC was significantly higher in EBF and CF than in SDF and AM. And stream BDOC waspositively correlated with initial stream dissolved organic carbon (DOC) and nitrateconcentrations, and negatively related to stream fluorescence index (FI), but was independentfrom initial stream dissolved organic matter (DOM) composition contents and ammoniumconcentrations. The altitudinal gradient of stream BDOC under four different vegetation types inWuyi Mountains was most likely a function of differences in initial stream DOC concentrations,stream nitrate nutrient, and the proportion of terrestrial DOC.