内蒙古草原植硅体封碳潜力和土地利用变化影响研究

Phytolith-occluded carbon (PhytOC) is an inert form of organic carbon that is bio-sequestered within plants and accumulated in soils after plant decomposition. As phytOC has a long residual time in soil (on a millennial scale), it pays an important role in carbon bio-sequestration from a long-term perspective, which can off-set the increase in atmospheric carbon dioxide concentration. The phytOC production and turnover rate as well as its potential in carbon sequestration has recently emerged as a focus in the search for the methods to mitigate the climate change...The grassland ecosystems cover about one fifth of the world's land surface, and have a great potential for carbon sequestration. However, the research on the phytOC production in grassland is very limited, with only some rough estimation of phytOC production based on the above-ground net productivity (ANPP) and the mean phytOC content of major plant species in grasslands. The phytOC content and production has not yet been sufficiently determined in grassland plant shoots (ANPP), and not at all evaluated in grassland plant roots (BNPP, below-ground net productivity). In addition, the impacts of grassland use, such as animal grazing and crop cultivation, on phytOC production has not yet been assessed. As the BNPP is generally around 10-times greater than the ANPP in semi-arid grassland, and the grassland use has profound impats on grassland species composition (which has different phytOC content) and productivity, we speculate that grassland BNPP has a.significant contribution to total phytOC production in grassland, and that land use through animal grazing and crop cultivation reduces grassland phytOC production...In present project, we will determine the ANPP, BNPP and the phytOC production of major plant species of the main grassland vegetation types in Inner Mongolia under three contrast conditions: intact natural, grazing degraded and under reclamation, and measure the total organic carbon and phytOC content in soil profiles. Thus we can (1) determine total phytOC production rate under varying conditions, and establish the relations between phytOC production and climate and soil factors; (2) upscale the results at the representative grassland sites to grassland regions to quantify the carbon sequestration potential via phytOC production in grassland regions, and (3) evaluate the long-term effects of land use change on soil carbon storage for the development of grassland management systems.

在植物固定的有机碳中，植硅体闭蓄有机碳（简称植硅体碳PhytOC)可长期存留于土壤，对减缓大气CO2浓度增加具有重要意义。生态系统中植硅体碳的生产、周转和增碳潜力正成为全球变化研究的一个重要方面。草原生态系统面积辽阔，增碳潜力巨大，但对草原植硅体固碳的研究目前只有依据植物地上生产力及其植硅体碳平均含量而做的粗略估算。草原地上部分植硅体碳测定不足，地下部分完全忽略；不同土地利用对植硅体碳生产的影响尚无研究。基于草原地下生产力是地上生产力约十倍的事实和人为利用对草原植物组成和生产力的影响，我们推测草原植物地下生产是植硅体碳生产的主要部分，草原利用将降低植硅体碳的生产。本项目选择我国主要草原类型，通过测定其在天然、退化和开垦状态下植物地上与地下生产力及其植硅体碳含量以及土壤植硅体碳含量，计算草原植硅体碳生产通量，评价草地利用对土壤碳库的长期影响，为草原碳汇计算和草原增碳措施制定提供理论依据。

围绕草原植物植硅体长期固碳潜力估算和挖掘，测定了内蒙古草原区不同气候带和土壤环境中草原优势植物地上和地下部分植硅体和植硅体碳含量，估算了植硅体碳年生产通量和长期固碳潜力，研究了放牧、割草、短期和长期围封等对草原植硅体碳生产通量和长期碳汇的影响，分析了草原植硅体固碳潜力与区域地质和气候干燥度的关系。结果表明 ① 草原植物地下部分具有巨大的植硅体固碳潜力和储量。典型草原植物地下部分的植硅体碳含量（0.67 g kg-1）显著高于地上部分（0.20 g kg-1），同时地下生产力是地上生产力的8-15倍，因此地下植硅体碳储量是地上储量的40倍左右，地下植硅体碳生产率（8.1-15.8 kg ha-1 yr-1）是地上生产率的25-51倍。表明地下生产力在草原植硅体碳生产中起着主要作用，彻底改变了草原植硅体长期固碳潜力的估算方法和精度。② 草地利用如果没有导致植物群落发生类型演替则对植硅体碳生产通量没有显著影响。草原放牧、割草、短期和长期围封等利用影响植物生物量和植硅体碳含量；放牧和割草具有降低草原地上生物量的趋势，却没有显著降低植硅体碳的生产通量。③ 玄武岩和花岗岩区域草原植物植硅体固碳潜力没有显著差异。尽管玄武岩区土壤比花岗岩区土壤具有较高的有效硅含量，但两个区域采集的所有优势植物的植硅体或植硅体碳含量，总体上没有显著差异，而且建群植物大针茅（Stipa grandis）的植硅体含量在玄武岩区反而偏低，否定了玄武岩土壤有效硅含量高会导致植硅体生产通量高的假设。④ 气候湿润度梯度上，草原植物植硅体和植硅体碳含量有显著增加的趋势。草原优势植物羊草（Leymus chinensis）的植硅体含量与降水量显著正相关；生长季增雨50%条件下植物的植硅体及植硅体碳含量，比自然降雨条件下显著增加。说明半干旱区降水增加或灌溉对植物蒸腾吸水形成植硅体的促进大于对植物生物量积累的促进。这些研究结果加深了对草原植硅体碳生产和形成机制的认识，并为估算草原植硅体长期固碳潜力提供了科学数据和依据。