This study investigated seasonal changes in litter and soil organic carbon contents of deciduous and coniferous forests at two altitudes (500 and 1000 m a.s.l.), which were used as proxies for temperature changes. To this aim, adjacent pine (P500 and P1000) and deciduous forests (downy oak forest at 500 m a.s.l. and beech forest at 1000 m a.s.l., D500 and D1000, respectively) were selected within two areas along the western slope of a calcareous massif of the Apennine chain (central Italy). Periodic sampling was carried out within each site (a total of 19 sampling dates: 6 in autumn, 4 in winter and spring, and 5 in summer), taking each time an aliquot of the upper mineral soil horizon and measuring litter thickness and CO2 emission from the soil. The samples were then analyzed for their content of organic C, total N, water-soluble organic C and N (WEOC and WEN, respectively), and the natural abundance of 13C and 15N. Soil and litter C and N stocks were calculated. The chemical and isotopic data suggested that organic C and N transformations from litter to the upper mineral soil horizon were controlled not only by temperature but also by the quality (i.e. C:N ratio) of the plant material. In particular, the more the temperature decreased, the more the quality of the organic matter would influence the process. This was clearly showed by the greater 13C fractionation from litter to soil organic matter (SOM) in D1000 than in P1000, which would indicate a higher degree of transformation under the same thermal condition of the plant residues from the deciduous forest, which were characterized by a more balanced C:N ratio than the pine litter. However, while at 500 m altitude a significant SOM 13C fractionation and a parallel increase in soil CO2 emissions occurred in the warmer seasons, no seasonal delta 13C variation was observed at 1000 m for both forests, despite the different quality of SOM derived from deciduous and coniferous forests. Our findings suggested that organic C and N transformations from litter to the upper soil mineral horizon were greatly controlled by the quality of the plant residues, whereas soil temperature would seem to be the major driver for the seasonal evolution of SOM. This study, by considering two different vegetation types (deciduous and coniferous), allowed to evaluate the combined interactions between the plant residue quality and temperature in controlling litter and SOM mineralisation/accumulation processes.

该文针对高原冻土地区公路路面的主要病害问题,通过马歇尔试验确定AC-13C沥青混合料配合比并对其路用性能进行试验研究。依托国道109线那曲至拉萨公路改建工程,结合AC-13C改性沥青混合料在不同油石比和矿料级配条件下进行了最佳配合比设计;采用浸水马歇尔试验、低温弯曲试验、车辙试验、冻融循环试验等研究了沥青混合料的水稳定性、高温稳定性、低温抗裂性、耐久性及抗渗水性能等路用性能;并铺筑试验路段进行路面厚度、平整度和弯沉检测,验证了使用该配合比厂拌沥青混合料的实际路用性能。结果表明:110-A级沥青配合当地集料进行混合料配合比优选设计,得到最佳油石比为5.0%,沥青用量为4.76%,空隙率为4.6%。该配合比下沥青混合料各项技术指标满足规范要求,并在试铺阶段效果良好,满足高原冻土地区公路路面性能要求。

沉水植物碳同位素分馏同水中溶解无机碳浓度有一定的关系 ,因而可以通过青藏高原多年冻土区的湖相沉积物中埋藏沉水植物———龙须眼子菜 (Potamogetonpectinatus)植物屑的碳同位素组成重建该地大气CO2 浓度的变化情形 .研究结果表明 ,该地在 9 176 77kaBP间 ,大气CO2 浓度是整个研究时间段中最低的 ,其后在 6 774 5 6kaBP时期大气CO2 浓度增加 ,在 4 5 6 2 17kaBP之间 ,大气CO2 浓度是整个研究时间内CO2 浓度最高的阶段 .植物屑的碳同位素组成反映了溶解无机碳浓度的变化 ,从而可用以重建大气CO2 浓度的变化情况