摘要:为研究喀斯特退耕地不同植物根际土壤碳氮水解酶活性的空间分布特征，采用喀斯特区域农田表层土壤，选择当地粮食作物玉米、牧草苜蓿及弃耕后常见草本植物莎草，进行室内根盒培养试验。利用根际土壤原位酶谱分析技术，研究不同植物根际与非根际土壤β-葡萄糖苷酶（βG）和N-乙酰氨基葡萄糖苷酶（NAG）活性的分布模式。结果发现：1）3种植物在根尖和根伸长区都存在酶活性热点区，最大根际酶活性热点区范围为苜蓿 > 莎草 > 玉米；2）玉米βG和NAG根际酶活性热点范围在根尖与根伸长区范围相近约为1.13 mm，苜蓿根际βG热点区范围是根伸长区（1.98 mm） > 根尖（1.19 mm），而NAG热点区范围是根尖（0.91 mm） > 根伸长区（0.59 mm），莎草根际βG和NAG活性热点区范围均是根尖（1.38-1.86 mm） > 根伸长区（0.93-1.16 mm）；3）豆科植物苜蓿的根系和根际微生物偏好碳需求，这可能与豆科植物的固氮功能有关，缓解氮养分需求；而莎草根系和根际微生物偏好氮养分，这与喀斯特土壤氮养分限制有关。总体上，苜蓿根际酶活性热点范围最广，根系和根际微生物偏好碳需求，而且其特有的固氮功能可缓解氮养分需求，对于喀斯特生态恢复效果更好。本研究的土壤原位酶谱法可为在根际酶活性热点区范围进行微生物养分获取机制提供定量依据。



Abstract:In order to study the spatial distribution of carbon (C) and nitrogen (N) acquiring hydrolase activity hotspots in rhizosphere in karst ecosystems, we incubated maize (one of main grain crops in locality), alfalfa (forage grass), and sedge (common grass in abandoned farmland) in rhizoboxes, which were filled with the collected topsoil of sloping farmland in a karst region of Guizhou province, China. The distribution of β-glucosidase (βG) and N-acetyl glucoaminosidase (NAG) activities in rhizosphere and non-rhizosphere soils was in situ detected by zymography. The results show that: 1) the hotspots of βG and NAG activities were located at both tip and elongation zones of roots for the three plants. The largest hotspot extent ranked in order: alfalfa > sedge > maize. 2) The hotspot extent of βG and NAG activities in maize rhizosphere was similar in size between root tip and elongation zones (about 1.13 mm). Alfalfa had larger hotspot extent of C-acquiring hydrolase activity in its root elongation zone (1.98 mm) than in root tip zone (1.19 mm), but larger hotspot extent of N-acquiring hydrolase activity in root tip zone (0.91 mm) than in root elongation zone (0.59 mm). Sedge had larger hotspot extent for both βG and NAG activities in root tip zone (1.38-1.86 mm) than root elongation zone (0.93-1.16 mm). 3) Rhizosphere microbes of leguminous alfalfa with N-fixing capacity preferred carbon, probably due to their low demand for nitrogen. Rhizosphere microbes of sedge preferred nitrogen, which might be caused by nitrogen limitation in the karst soil. On the whole, alfalfa had largest hotspot extent of βG and NAG activities activities in rhizosphere, where microbes preferred C to meet requirements for N fixation. Therefore, planting alfalfa can alleviate nitrogen limitation for ecological restoration in abandoned sloping farmland in karst regions. The in situ zymography in this study provides a quantitative tool for exploring microbial nutrient-acquiring mechanisms in rhizosphere.





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