秸秆碳的田间原位分解和微生物量碳的周转特征

应用14 C示踪技术研究了杂交狼尾草秸秆在稻麦轮作田中为期 1年的原位分解。结果表明 :秸秆用量对其分解率影响甚微 ,1年后秸秆C分解了 72 %左右 ,分解速率常数为 2 7× 1 0 - 3d- 1,但秸秆用量的多少与土壤原有碳的分解和土壤有机碳平衡密切相关。黄棕壤原有C年分解率为 5 4 5 %～ 6 0 7% ,分解速率常数在 1 0 4× 1 0 - 4～ 1 1 8× 1 0 - 4d- 1之间。随秸秆用量增加 ,黄棕壤原有C分解率和分解量均增加 ,土壤有机碳的亏缺减少。微生物量14 C占加入秸秆14 C的 3 79%～ 1 0 63% ,占土壤残留14 C的 1 2 2 7%～1 7 4 3% ,其大小变化及减少程度均较微生物量12 C显著。微生物量12 C约为微生物量14 C的 0 74～ 3 85倍 ,说明大多数情况下 ,土壤原有C仍是土壤微生物活动所需能量和养分的主要来源。微生物量14 C的周转率在 1 1 0～ 1 1 8a- 1之间 ,微生物量12 C的周转率在 0 97～ 1 0 6a- 1之间。增加秸秆用量可加快土壤微生物量C的周转速度 ,反过来微生物量C周转速度的加快又加速了秸秆C和土壤原有C的分解。土壤原有C和秸秆C的分解进程与微生物量12 C和微生物量14 C的动态变化趋势一致 ,说明有机碳分解的快慢是土壤微生物活动强弱的外在表现。

STRAW CARBON DECOMPOSITION IN SITU IN FIELD AND CHARAC-TERISTICS OF SOIL BIOMASS CARBON TURNOVER

Decomposition of hybrid elephant straw ¹⁴C in situ in the field was studied using the ¹⁴C-tracer technique in yellow-brown earth under a wheat-rice rotation system for one year.Results indicated that the amount of straw added had little effect on its decaying rate.After one year, straw ¹⁴C decomposed by about 72% with a decaying rate constant of 2.7×10^-3 d^-1.However, straw addition was closely related to decomposition of native soil C and balance of soil carbon.Soil native carbon decomposed by 5.45% ~ 6.07% annually with a decaying rate constant from 1.04×10^-4 d^-1 to 1.18×10^-4 d^-1.With straw addition, decomposition of straw ¹⁴C increased in both amount and rate, while the net loss of soil organic C decreased.Biomass ¹⁴C accounted for 3.79%~10.63% of input ¹⁴C and 12.27%~17.43% of soil residual ¹⁴C.Its variat ion was much significant than that of biomass ¹²C.The ratio of biomass ¹²C to biomass ¹⁴C varied from 0.74 to 3.85, which indicated that under most situations, native soil C was still the major source of energy and nutrients for microorganisms.Turnover rates of soil biomass ¹⁴C and ¹²C were 1.10~1.18 a^-1 and 0.97~1.06 a^-1 respectively.Straw addition could accelerate turnover of soil organisms, and in turn increase in the turnover rate of soil organisms accelerate the decaying rate of straw C and soil native C.Decomposition processes of soil native C and straw C showed similar trends to dynamics of soil biomass ¹²C and soil biomass ¹⁴C, which indicated that decomposition rates of organic C were the apparent indication of activity of soil organisms.