黄土高原人工苜蓿草地固碳效应评估

苜蓿草地作为黄土高原草地的重要组成部分，在黄土高原草地生态系统碳循环占有重要地位。同时由于苜蓿具有固氮和固碳的双重作用，使它在低碳农业的发展中具有重要意义。本文以一年生（建植初期）、三年生（盛产期）、五年生（稳产期）和十年生（衰败期）的人工苜蓿草地为研究对象，利用地上地下生物量和土壤碳贮量，定量分析了人工苜蓿草地不同发育阶段的固碳能力；结合种植面积，对黄土高原区人工苜蓿草地的总固碳效应进行了评价。研究结果表明：苜蓿草地地上生物固碳能力以三年生和五年生最强，并显著高于其他年限；地下生物固碳和土壤固碳量均以十年苜蓿草地最高，且显著高于其他年限。总体而言，人工苜蓿草地以土壤固碳为主，并集中在0~80cm土壤，各年限0-80cm土层土壤固碳量分别占到总固碳量的41.02%、39.43%、41.56%、39.59%；而地下生物固碳主要发生在0~20cm土层，各年限该层生物固碳量分别占到地下生物总固碳量的45.74%、 55.68%、53.12%和 43.28%。苜蓿草地在整个生命周期中总固碳量随生长年限逐年增长，但增长速度不明显，各年限单位面积总固碳量分别为12.69kg/m2、13.49 kg/m2、13.31 kg/m2和14.83 kg/m2。估算得到黄土高原的人工苜蓿草地年总固碳量为1.430?1011 Kg（143.0 Tg），其中地上、地下、土壤分别为5.43Tg、1.15Tg和136.4Tg。本研究结果为正确分析区域碳循环和发展低碳大农业提供了重要理论参考。

Evaluation on carbon sequestration effects of artificial alfalfa pastures in the Loess Plateau area

Carbon of grasslands is an important component in the global carbon cycle and often plays a dominant role in continental and regional carbon budgets. Identifying Carbon dynamics in grassland ecosystems is significant to predict the response of grassland ecosystems to future climate change. As the important component of the grasslands on Loess Plateau, alfalfa pastures which have both effects of nitrogen fixation and carbon sequestration, not only have great influences on the carbon cycle of the grasslands on Loess Plateau, but also play a significant role in low carbon agriculture. However, the carbon sequestration effects of alfalfa pastures on Loess Plateau are poorly understood. This research studied the carbon sequestration effects of alfalfa pastures which have grown one year(initial stage of establishment), three years(high yielding period), five years(stable production period) and ten years(obviously decline phase). With measuring the carbon content of the above-ground vegetation, below-ground vegetation, and soil, the research quantitatively analysed the carbon sequestration effects of alfalfa pastures with different planting ages, meanwhile, evaluated the carbon sequestration effects of the alfalfa pastures on Loess Plateau. The results showed that alfalfa pastures with the growth of 3 and 5 years owned the strongest ability of above-ground vegetation carbon sequestration, while the 10-year-old had the highest ability of carbon sequestration of both below-ground vegetation and soil. The soil carbon sequestration focused on 0-80cm soil layer, while the below-ground vegetation focused on 0-20cm. The soil carbon sequestration amount of 0-80 cm soil layer of different planting ages accounted for 41.02%,39.43%,41.56% and 39.59% of their total soil carbon sequestration amount respectively whilst the below-ground vegetation occupied 45.74%,55.68%,53.12% and 43.28% respectively. The total fixed carbon amounts of alfalfa pastures were growing with the increase of planting age, but the rate was not very obvious, and the total fixed carbon amount per unit area of different planting ages were 12.69kg/m²,13.49kg/m²,13.31 kg/m² and 14.83 kg/m² respectively. According to the age structure of alfalfa pastures on Loess Plateau, we estimated that the yearly total fixed carbon of alfalfa pastures on Loess Plateau was 1.430×10¹¹ kg(143.0 Tg).This study provided theory references for regional studies of carbon cycles and low carbon agriculture.