Adaptive regulation in reproductive strategy of two bunchgrasses under mowing disturbance in Inner Mongolia grassland

doi:10.3773/j.issn.1005-264x.2010.03.002

Abstract

Abstract:

Aims Stipa grandis and Cleistogenes squarrosa are two important bunchgrass species in Inner Mongolia typical steppe. Stipa grandis is a dominant species in undisturbed communities, while C. squarrosa becomes the dominant species in degraded communities. It is important to understand the regulation mechanisms of the two populations under mowing disturbance, especially those regulating sexual and asexual reproduction. We addressed four questions: 1) Do the two populations exhibit density-dependent regulation under mowing disturbance? 2) If so, how do they regulate sexual and asexual reproduction? 3) Do the species modify their biomass allocation patterns under mowing disturbance, and, if so, how do they change their allocation patterns? 4) Does mowing disturbance affect plant basal area and tiller number?

Methods This study was conducted in a long-term fenced site and a long-term mowed site at the Inner Mongolia Grassland Ecosystem Research Station of Chinese Academy of Sciences in 2007. We examined the density regulation and resource allocation regulation of S. grandis and C. squarrosa under different management regimes.

Important findings Under mowing disturbance, S. grandis exhibited no significant change in population biomass, while C. squarrosa significantly increased. Because mean plant biomass of S. grandis decreased significantly and that of C. squarrosa did not change, density increase plays an important role for the two species in population biomass production. The two species exhibited different strategies in density-dependent regulation of asexual and sexual reproductive processes. For S. grandis, density increased in non-reproductive plants, but was unchanged in reproductive plants under mowing disturbance, which led to relative density increasing in non-reproductive plants and decreasing in reproductive plants. For C. squarrosa, the densities of both reproductive and non-reproductive plants increased significantly at the mowed site. The relative density increased in reproductive plants, but decreased in non-reproductive plants. The two species showed opposite reproductive allocation manipulation strategies under mowing disturbance. Stipa grandis significantly decreased reproductive biomass allocation by decreasing the biomass fraction of spikes in reproductive tillers. In contrast, C. squarrosa significantly increased reproductive biomass allocation by increasing the fraction of reproductive tiller biomass in plant biomass. No significant changes were found in S. grandis basal area and tiller number under mowing disturbance. Likewise, no significant change was found in C. squarrosa tiller number, but its basal area significantly decreased.

Key words: density regulation, Inner Mongolia typical steppe, reproductive strategy, resource allocation

ZHANG Xiao-Na, HADA ChaoLu, PAN Qing-Min. Adaptive regulation in reproductive strategy of two bunchgrasses under mowing disturbance in Inner Mongolia grassland[J]. Chin J Plant Ecol, 2010, 34(3): 253-262.

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URL: https://www.plant-ecology.com/EN/10.3773/j.issn.1005-264x.2010.03.002

https://www.plant-ecology.com/EN/Y2010/V34/I3/253

Figures/Tables 5

Fig. 1 Population characteristics of Stipa grandis (sg) and Cleistogenes squarrosa (cs) (mean ± SE, p = 0.05).

Fig. 2 Density (A) and relative density (B) of nonreproductive plants in Stipa grandis (sg) and Cleistogenes squarrosa (cs) (mean ± SE, p = 0.05).

Fig. 3 Density (A) and relative density (B) of reproductive plants in Stipa grandis (sg) and Cleistogenes squarrosa (cs) (mean ± SE, p = 0.05).

Fig. 4 Biomass reproductive allocation of Stipa grandis (sg) and Cleistogenes squarrosa (cs) (mean ± SE, p = 0.05). A, Fraction of reproductive tiller in plant biomass. B, Fraction of spike in reproductive tiller biomass.

Fig. 5 Basal area (A) and tiller number (B) in Stipa grandis (sg) and Cleistogenes squarrosa (cs) (mean ± SE, p = 0.05).

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