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Effects of the Conversion of a Degraded Alpine Kobresia Meadow on the Organic Carbon and Nitrogen of Soil and Plants

Qiao Y., Duan Z., Li X., Quan X., Liang H.

Polish Journal of Ecology

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2015

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Vol. 63, nr 4

500--511

EN

Three sites with both degraded alpine Kobresia meadow (DM) and adjacent mix-seeded perennial grasses pastures (MSP) in the headwater region of the Yellow River, Qinghai-Tibetan Plateau, were selected to investigate plant and soil organic carbon (SOC), total nitrogen (TN) and their isotope composition. The SOC and TN in the top soil layer to a depth of 10 cm were significantly affected by ploughing and planting mix-seeded perennial grasses. The SOC content in 0–10 cm soil layer of MSPs was 25.6%, 5.5% and 12.9% lower than those of DMs at the I-III sites, respectively, and the rate of OC density loss was 23.8, 14.5 and 18.2%, respectively. The soil TN content in 0–10 cm soil layer of MSPs was 16.6%, 2.2% and 9.4% lower than those of the DMs at three sites, respectively, and the TN density was 15.6, 10.6 and 15.3% lower than those of DMs, respectively. The plant and soil 13C values (-27.03‰, -25.16‰, respectively) suggest that the vegetation of both DMs and MSPs are C3 plant communities. The 15 N value in the soil (>4‰) was significantly greater than in plants (<2‰). No differences of either 13C or 15N abundance between MSPs and DMs at Site I and II, but were found at Site III, indicating that the effects were site specific. The rehabilitation of a degraded Kobresia meadow has a significant influence on the soil properties, SOC and TN. Caution should be taken in site selection before performing conversion.

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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

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2011

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Vol. 59, nr 1

105-114

EN

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.

3

Trade-off of sexual and asexual recruitment in a dominant weed Ligularia virgaurea (Maxim.) In alpine grasslands (China)

Wu G., Hu T., Liu Z.

Polish Journal of Ecology

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2010

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Vol. 58, nr 1

81-86

EN

Ligularia virgaurea (Maxim.) is a typical naturally-occurring native noxious weed, widely distributed in alpine grasslands of the Tibetan Plateau, China. Three field sampling plots (30 m ' 50 m) dominated by L. virgaurea were selected to study its population colonization mode and the relationship between sexual- and clonalrecruitment in alpine meadow of the Qinghai-Tibetan Plateau, NW China. Field investigations were conducted on its soil seed bank, seed rain and the individuals of new recruitment (seedlings and ramets) to study its sexual and asexual recruitment. And, 46 individuals which produced the seeds were selected randomly to study their relationship between seed production and ramet production. Results showed that there were more ramets (26.23 ramets m[^-2]) and less seedlings (6.70 seedlings m[^-2]) and a mean value of seed rain was close to 8.04 seeds m[^-2], but the soil seed bank for this species was not found in study sites. Significantly negative correlations (r = -0.416, P <0.001) between seed number per individual and ramet number per adult individual were found for L. vrigaurea in studied alpine grasslands. Our results revealed that clonal reproduction was the main population colonization mode. In addition, there was a significantly negative relationship between seed production and ramets for this species.