Interactive effects of climate and land-use on soil organic carbon, nitrogen, and phosphorous pools in tropical Africa (Zambia, Mozambique)

热带土壤含有约26%-30%的全球土壤有机碳(SOC)和相关养分，其中大部分通常在原生开阔草原或木本稀树草原被转化为农田时流失。我们假设，这些损失的程度取决于气候和管理。为了验证这一假设，我们将在三种不同的土地利用系统(I)天然稀树草原牧场生态系统(最好在保育区)下，(Ii)退化耕地(耕地，集约化管理至少50年)，以及(Iii)两个热带国家传统耕作方式下的毗邻耕地(赞比亚和莫桑比克)下，测定气候序列(年降雨量300 mm至1000 mm)下表层和底层土壤中的SOC、N和P库。将在不同深度(0-10、10-20、20-30、30-50 cm)对土壤进行采样。基础土壤和养分分析将由合作大学进行测量。在波恩，我们将评估碳、氮和磷的总量以及它们在粒度(2微米、2-20微米、20-250微米和250微米)和集合体部分(微集料和大集料250微米)中的分布。此外，我们将根据Hedley分馏方案评估不稳定到稳定的P库，并通过生物标记物(氨基糖)和31-P-核磁共振分析来研究选定样品中C、N和P的来源。为了阐明温度升高对有机碳和有机结合N和P的命运的潜在影响，使用RESPICOND VIII系统在黑暗中培养表层土壤样品，以便监测不同温度下的二氧化碳释放以及N和P添加的影响。这是赞比亚、莫桑比克和德国之间独特的三方合作，使参与国之间能够进行方法和样本交流以及知识转让。双方将通过聘用两名已在本国科研机构担任领先科学职位的博士生来建立长期合作关系。

Tropical soils contain about 26-30% of global soil organic carbon (SOC) and associated nutrients, of which large parts are usually lost when native open or woody savannah are converted to agricultural fields. We hypothesize that the degree of these losses depends on both climate and management. To test this hypothesis, we will determine SOC, N- and P pools in top- and subsoils of a climosequence (300 to > 1000 mm annual precipitation) under three different land use systems (i) native savannah rangeland ecosystems, preferably in conservation areas, ii) degraded arable lands (arable field, intensively managed for at least 50 years), and iii) adjacent arable lands under traditional farming practice in two tropical countries: Zambia and Mozambique. Soil will be sampled in different depths (0-10, 10-20, 20-30, 30-50cm). Basic soil and nutrient analyses will be measured by the partner universities. In Bonn, we will assess total C, N, and P stocks as well as their distribution into particle-size (< 2 µm, 2-20 µm, 20-250 µm, and > 250 µm) and aggregate fractions (microaggregates < 250 µm; macroaggregates > 250 µm). In addition, we will assess labile to stable P-pools according to the Hedley fractionation scheme, and investigate the origin of C, N and P by biomarker (amino sugars) and 31-P-NMR analyses at selected samples. To elucidate potential effects of temperature rise on the fate of SOC and organically bound N and P, topsoil samples are incubated using the RESPICOND VIII system in the dark, allowing monitoring CO2 release at different temperatures as well as effects of N and P additions. It is a unique trilateral collaboration between Zambia, Mozambique and Germany, that allows method and sample exchange as well as knowledge transfer between the participating countries. A long-term collaboration will be established through the employment of two PhD candidates that already have leading scientific positions at their home scientific institutes.