草地利用和管理方式对地木耳生物量的影响

地木耳(Nostoc commune)是一种固氮蓝藻，其固氮活性是可逆的，在天然草地氮素循环中起着非常重要的作用。本研究分析了放牧、刈割、烧荒以及围封对地木耳生长动态的影响，以期为合理利用和管理天然草地提供理论依据。结果表明，围栏封育样地地木耳的生物量最高，适度放牧和刈割样地次之，重度放牧显著抑制了地木耳生长，其总生物量仅相当于围栏封育的11.2%～35.1%；烧荒处理当年地木耳生长受到抑制，但随着凋落物的积累，其生长量逐渐增加；地木耳生物量与凋落物、立枯物的量呈显著正相关（P<0.05），凋落物和立枯物的量是影响地木耳生长的主要因素。因此，适度放牧和围栏封育有利于草地固氮蓝藻--地木耳的生长和增加草地氮素供应。

Effects of grassland management and utilization on biomass of Nostoc commune

Nostoc commune belongs to Nitrogen fixing blue algae, and the characteristic of its nitrogen fixing is reversible. It plays an important role in the nitrogen cycle of natural grassland. In order to provide an information on grassland utilization and management, the effects of grazing, cutting, firing and fencing on the biomass dynamics of N.commune in Bashang grassland were investigated in this study. The results indicated that fencing promoted the growth of N.commune, and the highest total biomass occurred in fencing treatment, followed by moderate grazing and cutting, the lowest biomass occurred in heavy grazing treatment and it only accounted for 11.2%-35.1% of those in fencing treatment. Firing showed significant negative effects on the growth of N.commune, there was no N.commune in year one after firing, but with the standing dead litter and litter increasing in year two after firing, N.commune began to grow and increased. Biomass of N.commune showed positive correlationship with standing dead litter and litter. Biomass of standing dead litter and litter were the main determinated factors on biomass of N.commune in Bashang natural grassland. In conclusion, fencing and moderate grazing promoted growth of N.commune and increased nitrogen fixing in grassland.