封育年限对典型草原大针茅无性系构件组成与生长的影响

研究不同封育年限对黄土高原大针茅(Stipa grandis)无性系构件结构组成和生长的影响，可为阐明无性系构件组成和资源分配提供一定基础。在黄土高原典型草原选取不同封育年限区(10和20年)和放牧地(对照)作为试验样地，采用整个无性系完整挖掘的方法进行大针茅无性系构件特征的研究。结果表明：1)与放牧相比，封育10年显著增加了大针茅无性系丛径、生殖枝高度和花序高度(P < 0.05)，而封育20年则显著提高了大针茅无性系丛径、总枝数、生殖枝数、营养枝数、分蘖芽数、生殖枝高度、花序高度、地上总生物量、营养枝生物量和花序生物量(P < 0.05)。封育降低了大针茅生殖枝数、生殖枝高度、花序高度、地上总生物量、生殖枝生物量和花序生物量的变异系数。2)随封育年限增加，营养枝生物量比例明显提高，生殖枝生物量比例下降，但花序生物量比例基本不变。3)封育措施显著提高了营养株单株生物量(P < 0.05)，但生殖株单株生物量和全体分枝单株生物量与放牧处理差异不显著(P > 0.05)。4)大针茅丛径与地上总生物量、生殖枝数、生殖枝生物量、花序生物量呈极显著正相关关系(P < 0.001)，与营养枝生物量呈极显著正相关关系(P < 0.01)，与总枝数呈显著正相关关系(P < 0.05)。而地上总生物量与生殖枝数、营养枝数、总枝数、营养枝生物量呈极显著正相关关系(P < 0.001)，与分蘖芽数、生殖枝生物量和花序生物量呈极显著正相关关系(P < 0.01)。分蘖芽数与营养枝数、总枝数、营养枝生物量呈极显著正相关关系(P < 0.001)，与地上总生物量呈极显著正相关关系(P < 0.01)。综上所述，短期封育提高了大针茅的生殖分配，使大针茅迅速成为群落优势种，而长期封育使大针茅更依靠无性繁殖进行种群更新。

Effects of grazing exclusion years on module structure and growth pattern of Stipa grandis clones in a typical steppe

In this study, we selected different grasslands subjected to varying periods of grazing exclusion (10 and 20 years) and grazed grassland (control) as sites on the Loess Plateau. We harvested the whole clones to study the effects of number of grazing exclusion years on module structures and growth patterns of Stipa grandis clones, which provides a theoretical basis for studying module structures and resource allocation. We found that: 1) compared with grazing, grazing exclusion for 10 years significantly increased the size, reproductive height, and inflorescence height of S. grandis (P < 0.05), and grazing exclusion for 20 years markedly improved the size, total tillers, reproductive tillers, vegetative tillers, total buds, reproductive height, inflorescence height, total aboveground biomass, biomass of vegetative tillers, and biomass of inflorescence (P < 0.05). In addition, grazing exclusion reduced the coefficient of variation (CV) of reproductive tillers, reproductive height, inflorescence height, total aboveground biomass, biomass of reproductive tillers, and biomass of inflorescence. 2) For the biomass allocation ratio, vegetative tiller significantly increased, reproductive tiller decreased, and inflorescence showed no significant change (P > 0.05) with increase in grazing exclusion years (P < 0.05). 3) The biomass of vegetative tillers was significantly higher in grazing exclusion grasslands than in grazed grasslands (P < 0.05); however, there was no significant difference in the biomass of reproductive tillers and total tillers (P > 0.05). 4) The S. grandis size showed a significant positive correlation with the total aboveground biomass, reproductive tiller number, biomass of reproductive tiller, and biomass of inflorescence (P < 0.001). It also showed a significant positive correlation with biomass of vegetative tillers (P < 0.01) and a positive correlation with total tiller numbers (P < 0.05). Total aboveground biomass had a significant positive correlation with reproductive tiller numbers, vegetative tiller numbers, total tillers, and biomass of vegetative tillers (P < 0.001); it also had a significant positive correlation with total buds, biomass of reproductive tillers, and biomass of inflorescence (P < 0.01). Finally, total bud numbers showed a significant positive correlation with vegetative tiller numbers, total tiller numbers, and biomass of vegetative tillers (P < 0.001) and a significant positive correlation with total aboveground biomass (P < 0.01). In conclusion, short-term grazing exclusion improves the reproductive allocation of S. grandis and results in S. grandis rapidly becoming the dominant species, while long-term exclusion results in generation of S. grandis mainly through asexual reproduction.