Vertical Distribution, Seasonal Dynamics And Controls Of Soil Organic Carbon In Phyllostachy Edulis Porests

Moso bamboo (Phyllostachys edulis), a major component of bamboo forests, not only can bring substantial revenue to farmer, and also is regarded as one of the most suitable candidate tree species in mitigating climate change in China. Compared with other trees, bamboo is managed intensively by human and more likely to release carbon from bamboo forests significantly. A better understanding of carbon stock and its dynamics of bamboo forests is the basis for clarifying the magnitude, spatial distribution, and driving factors, as well as enhancing the role of bamboo forest in response to climate change. A smaller variation of soil carbon pool can lead to large fluctuations in atmospheric CO2 concentration, and thus soil carbon plays an important role in the carbon cycle at various levels. Actually, many researches on soil organic carbon (SOC) of bamboo forests have been conducted, but vertical distribution, seasonal dynamic and controls of Moso bamboo forests are poorly known.Three oriented management, shoot-oriented stand (Type I, SOS), timber and shoot-oriented stand (Type II, TSOS) and timber-oriented stand (Type III, TOS), and two unmanged stand, pure Moso bamboo stand (Type IV, PMS) and mixed Moso bamboo-Cunninghamia lanceolata stands (MBS) was studies to clarify the magnitude, vertical distribution, seasonsal dynamics and controls of TSOC and four labile organic carbon (LOC) (i.e., MBC, microbial biomass carbon; DOC, dissolved organic carbon; HWOC, hot water-extractable organic carbon; ROC, readily oxidizable organic carbon) in South Anhui Province. The main conclusions are as follows:(1) The mean contents of TSOC, MBC, DOC, HWOC and ROC in managed Moso bamboo forests were approximately 11.84 g/kg,70.14 mg/kg,36.33 mg/kg, 40.54 mg/kg and 3.93 g/kg. Compared to managed stands, TSOC contents in the unmanaged PMS and MBS were low, having respective contents of 9.84 and 8.23 g/kg. MBS possessed lower HWOC (28.33 vs.38.31 mg/kg), but higher MBC (87.04 vs.48.05 mg/kg) than PMS (P<0.05). About 50% of SOC including TSOC and the four labile organic carbons was distributed at the soil surface (0-20 cm in depth) in both managed and unmanaged bamboo forests.(2) At each soil layer, TSOC, MBC, DOC and HWOC content were not significantly different among different oriented managements (P> 0.05); however, ROC at the upper soil surface (i.e.,0-20 cm and 20-40 cm in depth) was significantly different, suggesting that oriented managements (namely, different management measures) had a significant impact on ROC content only.(3) Regardless of oriented managements, TSOC, MBC, HWOC and ROC showed significant difference among soil layers (P<0.001), and decreased continually with soil depth, while DOC had no significant difference (P=0.98). No significant difference was also found for all the percentages of LOC, except ROC, which reduced significantly with soil depth (P=0.03). In unmanaged MBS, all forms of SOC indicated a significant difference (P<0.01), except DOC, while no significant difference was found for all the percentages of LOC. As soil depth increased, TSOC, MBC, ROC and HWOC in MBS decreased significantly.(4) In oriented management, TSOC decreased first and then increased with month (i.e., season), and decreased in each season with soil depth; significant variations were found for the four months among the soil layer, except in Ocotober (P <0.001). With soil depth, MBC increased first and then decreased, and significant variations were also found decreases in January, July or October; MBC decreased with soil depth in the four seasons. Overall, HWOC decreased with month, and indicated significant differences among soil layer in all the seasons, showing a decreasing trend with soil depth. The changing trend of DOC was similar to HWOC, wth the highest content in January, followed by April and July, and lowest in Ocotober; the highest DOC was the 40 times as the lowest one, and DOC also dereased with soil depth. However, no significant seanson variation of ROC was found.(5) TSOC in PMS indicated a significant difference among seasons (P<0.05), while TSOC in MBS didn’t (just significant at the soil layer of 40-60 cm). Significant differences in MBC contents of the two unmanaged stands were found at the upper (0-20 cm) and the lowest layers (40-60 cm) (P<0.05), but not at the soi layer with a depth of 20-40 cm; MBC first increased and then decreased with season. For HWOC, th contents of PMS in January and July had significant differences from that in April and October only at the surface soil (0-20 cm), while no significant variation was found among season in MBS. DOC and HWOC in the two stands had similar changing trend with season, with the highest in January, followed by April and July and the lowest in October. DOC in each soil layer varied significantly with season. In the soil surface (0-20 cm), PMS showed an obvious difference in ROC content among season, while no difference was found in MBS, implying that no effect of season on ROC in MBS.(6) For the proportion of LOC in TSOC in unmanaged stands in Central Hunan. ROC had the largest percentage (27.32%-41.54%), followed by MBC (0.58%-1.17%), HWOC and DOC had the lowest (0.29%-0.41% and 0.26%-0.46%, respectively). The percentage of all the LOCs in TSOC was larger in MBS than that in PMS. Significant positive correlations were found between TSOC and ROC, between HWOC, DOC or ROC and MBCor HWOC, between HWOC and DOC.(7) The relationships between soil temperature or moisture and SOC fitted well with power functions. Soil temperature had the larger effect on TSOC and LOCs than soil moisture, which just affected DOC and HWOC. However, the contribution to SOC was generally less than 50%, indicating that additional factors also controlled SOC, besides soil temperature and moisture.(8) All LOCs showed a significant positive correlation with soil organic matter (P<0.01), except DOC, suggesting that probably environmental factors drived DOC content Such soil nutrients as total N, available N, total P, available P, total K and available K also had little effect on the DOC, but significant effect on MBC; all the soil nutrients influenced ROC and HWOC significantly, except total P and available P. All nutrients correlated with TSOC significantly, except total K; among the microbes (bacteria, fungi and actinomycetes), only fungi was negatively correlated with SOC significantly (P<0.01); only catalase in the five enzymes (urease, protease, invertase, polyphenol oxidase and catalase) were significantly correlated (P<0.01) with TSOC, MBC, ROC and HWOC.(9) Stepwise regression showed that TSOC could be predicted by the jointly C/N ratio, total N and catalase content, which explained 98% of variance. In contrast, factors introduced by stepwise regression could explain less than 60% of variation of LOCs, but no significant regression relationship was found between DOC and the 26 factors (including physicochemical, nutrient, enzymatic and microbial factors), suggesting that DOC were more likely be controlled by other factors. Specificallty, MBC was mainly controlled by soil organic matter, C/N ratio and soil catalase, ROC by soil organic matter and total K, and HWOC by natural moisture content and catalase content, respectively.