西南峡谷型喀斯特坡地土壤微生物量C、N、P空间变异特征

Spatial heterogeneity of soil microbial biomass carbon,nitrogen,and phosphorus in sloping field in a groge Karst region,Southwest China

土壤微生物是陆地生态系统中最活跃的成分,它推动着生态系统的能量和物质循环,被公认为土壤生态系统变化的预警及敏感指标。以西南峡谷型喀斯特坡地为研究对象,基于网格法取样,结合经典统计学和地统计学方法,揭示了土壤微生物生物量的空间分布与格局及其主要影响因子。结果表明,西南峡谷型喀斯特坡地土壤微生物生物量碳(MBC)、氮(MBN)、磷(MBP)、碳氮比(MBC/MBN)、碳磷比(MBC/MBP)适宜,MBC、MBN、MBP变异均很大;空间自相关性明显,除MBP最佳拟合模型为球状模型外,其他指标均为指数模型。C0/(C0+C)均<25%(4.9%—6.2%),呈强烈的空间相关,这主要由结构性变异引起。Kriging等值线图表明,MBC、MBN的高值区集中在坡中上部;MBP的格局明显不同,高值区集中在坡脚;MBC/MBN斑块较大,变化缓和;MBC/MBP的空间分布规律不明显,斑块多而破碎。西南峡谷型喀斯特坡地土壤微生物量空间分布的影响因子很多,其中,影响土壤微生物量碳和氮的主要因子有土层厚度、pH、碱解氮。西南峡谷型喀斯特坡地土壤微生物不仅存在着小尺度的空间分布格局,而且不同土壤微生物属性的空间分布不同。因此,应采取适宜措施,激活土壤微生物活性。

Soil microorganisms are among the most active components of terrestrial ecosystems,as promoters of energy and nutrient recycling of ecosystems. They are also recognized as early warning and sensitive indicators of soil ecosystems.Here,we conducted a field study to analyze the soil microbial biomass in the Karst gorge region in Southwestern China. The study was conducted over a typical area of sloping farmland in the Karst gorge region. The total study area of（ 300 × 200）m2was divided into（ 20 × 20） m2grids using an Electronic Total Station,yielding 212 sample points. We examined thespatial patterns of soil microbial biomass using geo-statistical and statistical methods. The spatial patterns of soil microbial biomass and their main influencing factors were revealed by grid sampling methods,combining classical statistics and geostatistics methods. The soil microbial biomasses of carbon（ Cmic） and phosphorus（ Pmic） and their ratio（ Cmic/Nmic）were moderately high in this Karst region of Southwestern China. The ＂ average soil microbial biomasses of carbon（ MBC）,nitrogen（ MBN）,and phosphorus（ MBP） were 75. 62 mg /kg,25. 23 mg /kg and 24. 06 mg /kg,respectively. The ratios of MBC to MBN（ MBC /MBN） and MBC to MBP（ MBC /MBP） were 3. 87 and 5. 61,respectively. The variation coefficients of the biomasses ranged from 14. 193 to 182. 756%,while those of the ratios ranged from 14. 192% to 114.512%. The values of all five variables were moderately high and widely varying. The smallest Moran＇s I result for MBC,MBN,MBP,MBC /MBN and MBC /MBP was- 0. 0965,- 0. 0556,- 0. 0913,- 0. 0682 and- 0. 0654,respectively,suggesting strong spatial heterogeneity of the soil microbial biomass. The MBC,MBN,MBP,and MBC /MBN were best fitted to an exponential model,while the MBC /MBP was consistent with a spherical model. The RSS values were very small,indicating good model fitting. The nugget（ C0） was low（ 0.0245—13.4） and all C0/（ C0＋C） values were less than25%,indicating that the soil microbial biomasses are strongly autocorrelated over the study region,and that their spatial patterns are influenced by structural factors. These spatial patterns varied over a small range（ 30. 9—60. 6 m）. The ranges of the MBN and MBP patterns were similar（ 40. 5 m and 30. 9 m,respectively）,and were smaller than that of MBC（ 60. 6m）. On Kriging contour maps,the regions of high MBC occupied the middle and upper parts of the slope,while high MBN was found on the upper parts and foot of the slope. The MBP displayed a clear spatial distribution pattern with high values at the foot of the slope. The MBC /MBN pattern was characterized by larger patches with an alleviate variation,while that of MBC /MBP was unobvious and was fragmented into many patches. Numerous factors influence the spatial patterns of soil microbial biomasses in the sloped Karst gorge region. Soil depth,pH,and available nitrogen are the main influencers of carbon and nitrogen biomass. In addition to the small-scale spatial distributional patterns of microbial biomass in the study region,different spatial patterns were observed in the soil microbial variables. Therefore,by adopting appropriate statistical and analytical techniques,we can elucidate the extent and distribution of microbial activity in soils.