Variations Of Soil Organic Carbon In Soil Aggregates Along An Altitudinal Gradient In Wuyi Mountains

Mountain primary forests, which are the important component of global carbon sink, haveattracted huge attention for their vulnerability. Forest soils play a key role in attenuating globalwarming. Labile carbon, as the most active part of SOC, is a very sensitive indicator toindicate future SOC dynamics. Soil structure can regulate many biological processes toinfluence the decomposition and storage of SOC. We set experiments in four differentelevations of Wuyi Mountain located in the subtropical area of southeastern China. Frombottom to top, there are subtropical evergreen broad-leaved forest (EBF), coniferous forest (CF),subalpine dwarf forest (DF), and alpine meadow (AM). We studied soil organic carbon,hot-water extractable organic C (HWOC), mineral nutrients,such as calcium (Ca), magnesium(Mg), potassium (K), iron (Fe), natrium (Na), phosphorus (P) and microorganism metabolismprofiles(CLPP). We analyzed their temporal and spatial variations and the reasons for thesevariations. The results showed that:(1) Along the elevation, the proportions of macroaggregates and MWD increased. SOCand HWOC in different soil aggregates also increased. The sequences of SOC in different soilaggregates under the four vegetations were different. At EBF, the sequence was silt and clayparticles> microaggregates> macroaggregates; At AM, it was macroaggregates>microaggregates> silt and clay particles. The sequence of HWOC under different vegetations at0-10cm was macroaggregates> microaggregates> silt and clay particles. But the sequences ofHWOC under different vegetations at10-25cm were different, such as, at AM, the sequence wasmicroaggregates> macroaggregates>silt and clay particles; at DF, the sequence was silt and clayparticles> macroaggreages> microaggregates. In soil aggregates, HWOC also had goodrelationship with SOC.(2) Along the elevation, mineral nutrients in three soil aggregates showed different altitudechange. But all illustrated that from macroaggregates to microaggregates, nutrient amountdecreased and then increased in silt and clay particles. Only Mg and P had significantrelationship with SOC and HWOC. There was P limitation at CF, this lead OC at CF increasedat a low rate. Pathway Analysis proved that minearal nutrients influenced SOC inmicroaggregates and silt and clay particles, and path coefficient was0.35and0.45, respectively.They combined with HWOC could explain at least90%of variances in soil aggregates.(3) HWOC and C/N changes of different layers showed the influence of root on HWOC.Pathway Analysis manifested that path coefficients of root to HWOC were0.61,0.38and0.50in macroaggregates, microaggregates and silt and clay particles, respectively. Root togetheredwith total nitrogen could explain more than90%variances of SOC in soil aggregates.(4) CLPP showed that only soil microoragnisms diversity correlated significantly withHWOC. Factor analysis and cluster analysis showed that organic carbon in different aggregatesunder different vegetations had distinct C constitutes.(5) With increased elevation, SOC stored in macroaggregates also increased. But thelability of macroaggregates lead the SOC stored in it were very sensitive to environmentalteration. Global warming increased the possibility of SOC stored in macroaggregates torelease to the atmosphere. May forest soil decreased carbon sink ability and aggravate globalwarming.