Regulation of the Hydrologic and C Cycles by Native Shrubs in Soils of Sub-Sahelian Africa

土著SHRUBSIN南萨赫勒地区的水文和C循环的调整。俄勒冈州立大学科瓦利斯分校的迪克·皮迪，与南萨赫勒非洲沙漠化有关的土壤退化是一个主要问题。半干旱土地的农民被认为是为在土壤中隔离碳的做法而获得报酬，这可能使脆弱生态景观中的农民能够采用促进可持续性并改善土壤质量和退化环境的做法。然而，在这一半干旱地区，评估土壤退化和固碳潜力在空间和时间上都是复杂的。特别是，我们在广袤的半干旱萨赫勒地区的地貌中发现了一种基本上未被认识到的成分，即木本灌木(Piliostigma reetatum和Guiera senegalens)，它们在夏季作物季节过后自愿在农民的田地里重新生长。在调节碳输入/固存和水文过程方面，这些灌木似乎比树木或其他有机投入(如动物粪便)在景观层面上重要得多。在目前的管理下，每年春天砍伐和焚烧灌木生物量的农民没有有效地利用这些有机物。一个耐人寻味的辅助理论是，这些灌木可能会起到“液压提升”的作用。这在其他半干旱地区也有记载，这是水分从潮湿的下层土壤向干燥的表层移动的过程，利用根系作为管道，在蒸腾停止的时期(通常在夜间)，水分可以从根向周围土壤释放。这可以驱动“干燥”土壤中的根际过程，如养分矿化和移动性，并可能在干旱时期为浅根作物物种提供少量的水。总体目标是(1)量化亚萨赫勒农业生态系统中两种主要灌木的年度碳循环和储存、水平衡和凋落物分解；(2)将生物地球化学和水文结果的本地知识与这些灌木的生态相结合；(3)在景观水平上利用模型来确定不同灌木管理制度对土壤碳和土壤质量的影响。这项工作对西非萨赫勒以南的大片地区有影响，这些地区的农业生态系统与塞内加尔相似。这种方法将是多学科的，这些灌木的生态研究将为农业养分和水管理的实际应用奠定基础，并作为一种可行的管理工具来抵消土壤退化和促进碳固存，以减少全球气候变化。

ABSTRACTREGULATION OF HYDROLOGIC AND C CYCLES BY NATIVE SHRUBSIN SUB-SAHELIAN AFRICAR.P. Dick PI, Oregon State University, Corvallis ORSoil degradation in relation to desertification of Sub-Sahelian Africa is a major concern. Farmers of semiarid land are being considered to be paid for practices that sequester C in soils, which could enable farmers in vulnerable ecological landscapes to adopt practices that promote sustainability and improve soil quality and degraded environments. However, assessing soil degradation and the potential to sequester C is spatially and temporally complex in this semiarid landscape. In particular, we have identified a largely unrecognized component in the landscape of the vast semi-arid Sahel, namely woody shrubs (Piliostigma reticulatum and Guiera senegalensis) that voluntarily regrow in farmers' fields after the summer cropping season. These shrubs seem to be much more important than trees or other organic inputs such as animal manure at the landscape level in regulating C inputs/sequestration and hydrologic processes. Under current management farmers who cut and burn the shrub biomass each spring are not utilizing this organic matter effectively. An intriguing ancillary theory is that these shrubs may do "hydraulic lift". This has been documented in other semiarid regions and is the process of water movement from moist subsoil to dry surface layers using root systems as a conduit which can be released from roots to surrounding soil during periods when transpiration ceases (usually at night) This could drive rhizosphere processes in "dry" soil such as nutrient mineralization and mobility and possibly provide small amounts of water to shallow rooting crop species during dry periods.The overall objectives are to (1) quantify annual C cycling and storage, water balance, and litter decomposition of two dominant shrubs of Sub-Sahelian agroecosystems; (2) couple indigenous knowledge to biogeochemical and hydrological results with the ecology of these shrubs; and (3) use modeling to determine the effect of alternative shrub management systems on soil C and soil quality at the landscape level. The work has implications for large areas of Sub Sahelian West Africa that have similar agroecosystems to Senegal. The approach will be multidisciplinary and the ecological research of these shrubs would be a basis for practical applications in agricultural nutrient and water management, and as a viable management tool to off set soil degradation and promote C sequestration to reduce global climate change.