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2 Polish Journal of Ecology

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Effects of elevated CO2 and temperature on growth and morphology of fir (Abies faxoniana, Rehd. e t Wils.) and native herbs in a treeline ecotone: an experimental approach

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Hou Y. , Luo Z. , Jenerette G. D. , Qiao Y. , Wang K.

Polish Journal of Ecology

2010

tom 58

nr 2

Determining how changes in atmospheric CO₂ concentrations and climate affects growth of species is helpful for understanding plant community species shift in response to future environmental changes. In the present study, fir (Abies faxoniana) and native herbs from treeline ecotone of east Qinghai-Tibetan Plateau (altitude: 3230–3300 m) were exposed to ambient CO₂ or ambient +350 μmol·mol⁻¹ CO₂ concentration in combination with ambient or ambient +2°C air temperature for two years in enclosedtop chambers. The results showed that elevated CO₂ , elevated temperature and the combination of elevated CO₂ and temperature increased biomass, height and diameter of fir compared to the control. Elevated CO₂ decreased biomass of Deyeuxia scabrescens, but increased for Fragaria orientalis and Cardamine tangutorum. Except for Fragaria orientalis, herbaceous biomass decreased by elevated temperature. The combination stimulated growth of Fragaria orientalis and Cardamine tangutorum, but suppressed for Deyeuxia scabrescens and Carex kansuensis. The results also demonstrated that elevated CO₂ and temperature increased the crown size and altered the morphology of fir, with benefits for resource capture, and did not affect growth of herbs. Larger root to shoot ratio of fir contributed the enhancement of biomass, while negatively influencing the growth of some herbs. This indicates morphological changes of trees may modify their growth responses and species around them to environmental changes. The different effects of elevated CO₂ and temperature on the growth of species in treeline ecotone suggest that climate change may alter community composition and structure.

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Peng G. , Wu C. , Xu X. , Yang D.

tom 60

nr 2

In woody perennials, leaf structure and biochemistry vary with tree age under changing environments. However, the related eco-physiological mechanisms have not been elucidated yet. In this study, we investigated agerelated responses of juvenile and mature subalpine fir trees (Abies faxoniana Rehder & E.H. Wilson.) growing at altitudes between 2,500 and 3,500 m in the Wanglang Natural Reserve in southwest China, to study the adaptive strategies of different age trees to suit changing environments. We found that there were distinct age- and altituderelated changes in the structural and biochemical characteristics of leaves. At all altitudes, mature trees exhibited higher area- and mass-based leaf nitrogen content (Narea, Nmass), leaf mass per area (LMA) and stable isotope carbon composition (δ13C), and a lower chlorophyll (Chl) content than those juvenile trees, except for Nmass at 3,000 m as well as LMA at 2,750 m, where the values of Nmass and LMA in mature trees were slightly lower than those in juvenile trees. Furthermore, leaf characteristics showed significant differences in the change rates with altitude between different age groups. Our results indicated that assimilative organs in mature trees do not suffering from nutrient deficiency and that juvenile and mature trees possess different adaptive growth strategies under changing environments, as indicated by higher leaf N content in mature trees and the opposite patterns of LMA and Chl content between two age groups. We also concluded that juvenile could be more sensitive to global warming due to a greater altitudinal influence on the leaf traits in juvenile trees than those in mature trees.