Connin S L, Virginia R A, Chamberlain C P
Department of Earth Sciences, Dartmouth College, Hanover, NH 03755, USA Fax: 520-670-6806; e-mail: lachlan @sun1paztcn.wr.usgs.gov, , , , , , US.
Environmental Studies Program, Dartmouth College, Hanover, NH 03755, USA, , , , , , US.
Oecologia. 1997 Apr;110(3):374-386. doi: 10.1007/s004420050172.
Over the past century, overgrazing and drought in New Mexico's Jornada Basin has promoted the replacement of native black grama (Bouteloua eriopoda Torr.) grass communities by shrubs, primarily mesquite (Prosopis glandulosa Torr.). We investigated the effects of shrub expansion on the distribution, origin, turnover, and quality of light (LFC) and heavy (HFC) soil organic matter (SOM) fractions using δC natural abundance to partition SOM into C (grass) and C (shrub) sources. Soil organic matter beneath grasses and mesquite was isotopically distinct from associated plant litter, providing evidence of both recent shrub expansion and Holocene plant community changes. Our δC analyses indicated that SOM derived from mesquite was greatest beneath shrub canopies, but extended at least 3 m beyond canopy margins, similar to the distribution of fine roots. Specific C activities of LFC indicated that root litter is an important source of SOM at depth. Comparison of turnover rates for surface LFC pools in grass (7 or 40 years) and mesquite (11 or 28 years) soils and for HFC pools by soil depth (∼150-280 years), suggest that mesquite may enhance soil C storage relative to grasses. We conclude that the replacement of semiarid grasslands by woody shrubs will effect changes in root biomass, litter production, and SOM cycling that influence nutrient availability and long-term soil C sequestration at the ecosystem level.
在过去的一个世纪里，新墨西哥州乔纳达盆地的过度放牧和干旱促使原生黑格兰马草（Bouteloua eriopoda Torr.）群落被灌木取代，主要是豆科灌木（Prosopis glandulosa Torr.）。我们利用δC自然丰度将土壤有机物质（SOM）划分为C（草）和C（灌木）来源，研究了灌木扩张对轻质（LFC）和重质（HFC）土壤有机物质（SOM）组分的分布、来源、周转和质量的影响。草和豆科灌木下的土壤有机物质在同位素上与相关植物凋落物不同，这为近期灌木扩张和全新世植物群落变化提供了证据。我们的δC分析表明，源自豆科灌木的土壤有机物质在灌木树冠下含量最高，但至少延伸到树冠边缘以外3米处，类似于细根的分布。LFC的特定C活性表明，根凋落物是深层土壤有机物质的重要来源。比较草（7年或40年）和豆科灌木（11年或28年）土壤中表层LFC库以及不同土壤深度（约150 - 280年）HFC库的周转率，表明相对于草而言，豆科灌木可能会增强土壤碳储存。我们得出结论，木本灌木取代半干旱草原将导致根系生物量、凋落物产量和土壤有机物质循环发生变化，从而在生态系统层面影响养分有效性和长期土壤碳固存。
