火烧对长期封育草地土壤碳固持效应的影响

Effects of prescribed fire on carbon sequestration of long-term grazing-excluded grasslands in Inner Mongolia

火烧是内蒙古典型草原的自然现象,对长期封育草地碳固持效应具有潜在的重要影响。基于野外控制火烧实验(未火烧、1a火烧1次、2a火烧1次、4a火烧1次),采用土壤和土壤粒级组分相结合的指标体系,分析了火烧以及火烧频率对长期封育草地土壤碳贮量的影响。结果表明:火烧会降低长期封育草地0—30 cm土壤碳贮量;其中,频繁火烧将显著降低草地土壤碳贮量,而4a 1次的火烧对土壤碳贮量影响较小。火烧对0—10 cm土壤碳贮量影响明显,而对10—30 cm土层影响较小。此外,火烧对长期封育草地土壤砂粒和粉粒碳氮贮量影响较大、对粘粒碳氮贮量影响较小。火烧后表层土壤砂粒和粉粒C∶N比下降,表层土壤有机质的稳定性有所提高。与自由放牧草地相比,连续遭受火烧处理的长期封育草地仍具有较高的碳贮量。总之,火烧会一定程度降低长期封育草地的碳贮量,但并不会彻底改变其显著的碳固持效应。

Natural and prescribed fires are common in the typical temperate grasslands in Inner Mongolia and are considered to have a significant impact on the terrestrial ecosystems and even on regional carbon（C） balance because they profoundly alter the biota,land cover,and biogeochemical cycles.Natural and prescribed fires may play important roles and increase the uncertainty in the evaluation of C sequestration in the long-term grazing-excluded grasslands in this region. By conducting a field fire experiment at 4 different frequencies（no burning,and burning every 1,2,and 4 years） and measuring the C and nitrogen（N） storage in both soil and soil particle-size fractions,researchers have investigated the effects of fire and fire regimes on soil C and N storage in the long-term grazing-excluded grasslands in Inner Mongolia,China.Understanding the effects of fire on soil C storage would help us scientifically evaluate C sequestration of long-term fenced grasslands under different fire regimes in the future. The results of the 4-year prescribed fire experiment showed that fire treatment significantly decreased C storage in the 0-to 30cm soil layer in the approximately 30yearfenced grassland,particularly under frequent fire perturbation.Moreover,the influence of prescribed fire was more apparent in the 0 to 10cm soil layer than in the 10 to 30cm layer.We also found that prescribed fire had an apparent influence on soil organic C in different soil particlesize fractions;the decline of C storage in the sand fraction was higher than that in the silt and silt fractions,indicating that prescribed fire redistributed the organic C in the sand,silt,and clay fractions and significantly affected the stability of soil organic matter（SOM）.Compared to freegrazing grasslands outside the fences,long-term fenced grasslands of northern China were found to have tremendous capacity to sequester C in soil,even when these were subjected to different fire regimes. To summarize,fire and fire regimes have significant effect on C storage in soil and soil fractions in these long-term grazingexcluded grasslands in Inner Mongolia;frequent fire significantly decreased soil C storage,and lowfrequency fire（burning every 4 years） decreased soil C storage to a lesser extent.Importantly,the stability of SOM in the surface layer was enhanced after burning in view of the decrease in the C ∶ N ratio in the sand and silt fractions.Compared to the unburned grasslands,the grasslands exposed to lowfrequency burning showed a decrease in soil C storage to a less extent and simultaneous enhancement in SOM stability;therefore,we suggest that lowfrequency fire should,to some extent,be a useful management approach for increasing C storage in these long-term-grazingexcluded grasslands in Inner Mongolia.