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2 Polish Journal of Ecology

2 2011

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Effects of Salix sphaeronymphe Gorz shrubs on herbaceous community in forest secondary succession (Tibetan Plateau)

Wang Y., Bao W., Wu N.

Polish Journal of Ecology

2011

Vol. 59, nr 3

495-505

In the present study, we selected a total of 26 Salix sphaeronymphe Gorz shrubs of various sizes on a cutover in the eastern Tibetan Plateau to evaluate the effects of shrub size on richness, cover and biomass of the understorey herbaceous community, grasses and forbs, as well as litter cover and biomass. Results indicated that the richness of herbaceous community, grasses and forbs significantly increased with the increased area of both undershrub canopies and open field. However, the cover and biomass of the herbaceous community beneath the shrub canopies decreased with increasing shrub size. Grasses and forbs, as different functional groups, responded differently to the increasing area of shrubs: the cover and biomass of grasses decreased while those of forbs increased. The cover and biomass of herbaceous community, grasses and forbs in the open field did not obviously vary with area. Under the shrub canopies, the cover and mass of litter positively correlated to area, but this was not the case in the open field. Our results suggest that shrubs have a positive effect on diversity and a negative effect on the cover and productivity of the herbaceous community in forest secondary succession on the alpine cutovers, and that these effects are size.dependent. Moreover, different functional groups of herbaceous plants can respond differently to the presence of shrubs.

Biomass fraction of graminoids and forbs in N-limited alpine grasslands: N:P stoichiometry

Zhang R., Gou X., Bai Y., Zhao J., Chen L., Song X., Wang G.

Polish Journal of Ecology

2011

Vol. 59, nr 1

105-114

It is known that the dominance of graminoid species is promoted by N addition; however, there has been relatively little effort to examine the pattern induced by natural N fertility. Since nutriet use efficiency (NUE) is an important trait determining plant competitive ability, we expected that the species guild with higher NUE (lower nutrient content) may be more competitive on infertile soils. We explored the relationships between relative forbs biomass share, soil N and productivity by the linear regressi on analysis on a natural alpine meadow in northeast of Qinghai Tibetan Plateau (3600 m a.s.l.). To test the variety of leaf N:P stoichiometry, paired t test and general linear model multivariate (GLM) analysis were also used. We found that the leaf N:P ratios of the whole community were below 13 in studied sites, which may be consistent with the N limitation on the vegetation. Graminoids retained lower concentrations of leaf N and P than forbs in community on the N limited grassland. Consistent with our prediction, we found that the biomass fraction of graminoids declined with soil N content and aboveground production on the grassland. Different from the pattern along fertility gradients induced by N fertilization, our results showed that gr aminoids with lower internal nutrient content were able to resist low levels of nutrient availability on the natural alpine grassland when compared to forbs.