中国森林和草地凋落物现存量的空间分布格局及其控制因素

凋落物是陆地生态系统的重要组成部分,它对生态系统的养分循环非常重要。凋落物现存量是凋落物输入量与分解量的净累积量,理论上影响凋落物输入过程和分解过程的因素都会对凋落物现存量产生重要影响。目前,我国科学家对部分区域典型陆地生态系统凋落物现存量及其影响因素进行了探讨,但迄今为止,全国尺度下的关于凋落物现存量评估的结果还未见报道。因此,如何准确地评估凋落物现存量对揭示生态系统应对全球变化具有重要意义。收集了2000—2014年公开发表文献中的森林和草地凋落物现存量数据(共1864个样点),并结合气候、土壤和地上生产力探讨了中国森林和草地凋落物现存量的空间格局及其主要控制因素,此外,还利用森林和草地凋落物的碳氮含量,结合凋落物现存量估算了不同区域和全国尺度的凋落物的碳氮贮量。分析结果表明:中国森林和草地的凋落物现存量存在较弱的经度和纬度格局,然而按照不同经度和纬度间隔整理数据后凋落物现存量表现出显著的空间分布格局。森林的凋落物现存量表现为随着经度和纬度的增加而逐渐增加,主要控制因素为温度。草地的凋落物现存量表现为随着经度的增加而逐渐升高,其主要影响因素为降水。森林和草地凋落物现存量在局部(或区域内)存在非常大的变异,这是造成其大尺度格局较弱的重要原因。结合1∶100万中国植被图的森林和草地面积数据,估算出中国森林的凋落物现存量约为1135.56 Tg,其碳氮贮量约为517.93 Tg C和15.33 Tg N;此外,中国草地的凋落物现存量约为119.63 Tg,其碳氮贮量分别为47.11 Tg C和1.59 Tg N。首次尝试对全国尺度森林和草地凋落物现存量及其碳氮贮量进行估算,其研究结论有助于揭示凋落物在碳氮循环中的重要作用,并可为准确评估中国陆地生态系统碳氮贮量提供重要参考。

Spatial patterns of litter density and their controlling factors in forests and grasslands of China

Litter is an important component of terrestrial ecosystems and plays significant role in nutrient cycles. The accumulation of litter (or litter density) on the soil surface depends on the balance of the process of litter input and decomposition. Theoretically, any factors influencing the processes of litter input or decomposition will affect the accumulation of litter. Therefore, the accurate assessment of litter density is important in illustrating the ecosystem response of carbon (C) and nitrogen (N) cycles to global climate change. However, to date in China, spatial patterns of litter density and their influencing factors have not been reported. In this study, we collected the litter density data of forests and grasslands in China, published from 2000 to 2014; the data of 1864 sampling sites, including litter density, mean annual precipitation, mean annual temperature, climate, soil, and productivity, were obtained to explore the spatial patterns of litter density and their main controlling factors. In addition, we estimated the C and N storages of litter at different scales and the total C and N contents of forests and grasslands in China. Our results showed that the litter density in the forests and grasslands of China exhibited weak latitudinal and longitudinal distribution patterns; however, after the division with a different latitudinal and longitudinal interval, it showed significant spatial distribution. Litter density in the forests increased with increasing latitude and longitude and was mainly controlled by temperature. Litter density in the grasslands increased with increasing longitude; the main controlling factor of spatial patterns was precipitation. Apparent variations in the litter density were observed at the local or regional scale for forests and grasslands, which attenuated the expected spatial patterns of litter density. The total estimated amount of litter in the forests was 1135.56 Tg, and the C and N storages were 517.93 TgC and 15.33 TgN, respectively. The total amount of litter in the grasslands was 119.63 Tg, with 47.11 TgC and 1.59 TgN. To the best of our knowledge, this is the first study to evaluating the spatial patterns and C and N storages of litter in the forests and grasslands of China, which provide important information on the significance of litter in ecosystem nutrient cycles, especially for the accurate estimation of C and N storages in terrestrial ecosystems at the national scale.