柱花草生物固氮作用修复干热河谷中度退化土壤的机制研究

The characteristics of dry-hot valley are ecologically fragile, soil serious degradation, and lack of nitrogen and phosphorus , which restrict the ecological restoration and the development of agricultural economy in the area. It was focused on the effect of the leguminous crops artificial community nitrogen fixation for the degradation soil in the previous research.There was little research on the remediation mechanism of using Stylosanthes guianensis to increase the soil nitrogen content, and of interplanting with gramineous herbage to restore the phosphorus content in degraded ecosystems. For this science problem, it will be studied on the soil ecosystem of the cultivated Stylosanthes guianensis and interplanting with gramineous herbage in the moderate degradation soil of Jinsha river dry-hot valleys typical area in yuanmou. They will be used in this research, which are fixed point and position, the combination of field test and indoor test methods. Using interspecific interaction technology and natural 15N abundance method, we will research the δ15N biological nitrogen fixation quantity, δ15N biological nitrogen fixation quantity and phosphorus Content residued in the soil, and the influence of the vegetation characters in the whole samples plot for Stylosanthes guianensis monoculture and intercropping with gramineous herbage. It will be further revealed the mechanism of biological nitrogen fixation of Stylosanthes guianensis for improving the productivity of degradation soil system.

干热河谷生态脆弱，土壤严重退化，氮磷含量匮乏，制约了本区生态恢复及农业经济的发展。以往研究侧重豆科作物人工群落固氮效应的研究，少有利用柱花草减少作物吸收退化土壤氮含量以及与禾本科牧草间种逐渐恢复退化生态系统含磷量的理论开展退化土壤修复机制的研究。针对以上科学问题，项目以金沙江干热河谷典型区元谋山地中度退化土壤人工种植柱花草、以及间种禾本科牧草样地土壤生态系统为研究对象，采用定点定位、田间试验和室内试验相结合的方法。应用种间互作技术、15N自然丰度法，研究柱花草单作、与区域禾本科优势牧草混作的δ15N生物固氮量、残留在土壤中的δ15N生物固氮量和磷含量、对整个样地植被性状的影响等，进一步揭示种植柱花草生物固氮作用提高退化土壤系统生产力的机制。

柱花草(Stybsanthes guianensis)为多年生豆科草本植物，具有生物固氮和提高土壤氮素的作用。本项目针对区域干旱和中度退化土壤氮磷含量低的现状，通过土培和水培两种方法，从22个柱花草中，筛选了幼苗期抗旱及耐低磷柱花草-灌木型柱花草，灌木型柱花草在水培试验低/高磷处理中，对磷转化效率低，且在干旱胁迫时植株幼苗受到影响小，同时项目组获得了豆科固氮植物的δ15N值和不同部位的氮磷含量，形成了豆科固氮植物植物体取样部位的技术方法，为准确计算植物对土壤氮磷吸收和柱花草的δ15N值和固氮量提供了技术支撑。研究表明：柱花草单独种植时，固氮量为14.30g/株，与种植之前相比，土壤氮含量增幅6.39%，0～30 cm氮残留量为4.09g/m3；当柱花草分别与扭黄茅、孔颖草等禾本科牧草间作时，土壤氮含量分别增幅10.54%和11.82%，0～30 cm耕作层土壤氮残留量分别为11.43 g/m3和14.33 g/m3；全磷分别增幅3.18%、0.79%。这是由于禾本科牧草耕作层水平根系大于50 cm，与柱花草根系交叉后，种间根系相互作用促进了间作柱花草根瘤的发育和生物固氮，与柱花草草单作比较，其根瘤平均增幅为6.15%，提高间作样地氮含量；间作体系的扭黄茅和孔颖草根系分泌物活化土壤难溶性的磷，与柱花草单作比较，间作样地土壤全磷增幅10.8%和8.41%。由此可见，间作地0～30 cm土层氮、磷含量呈增加趋势。研究结果为在退化土壤（退化草地）区域，选择以柱花草/禾本科草互作种植提供了科学依据。项目发表论文5篇，出版专著1部，获发明专利2项。