Ecophysiological responses of two dominant subalpine tree species Betula albo-sinensis and Abies faxoniana to intra-and interspecific competition under elevated temperature

Seedlings of tree species Abies faxoniana and Betula albo-sinensis were grown under different competition regimes (single plant, monoculture or mixture) at ambient temperature (AT) and elevated temperature (ET) to evaluate the impact of inter-and intraspecific competition on photosynthesis capacity, N resorption efficiency, N uptake patterns, water use efficiency (foliar carbon isotope composition, delta C-13) and root carbon reserve accumulation. Our results showed that ET did not have significant effects on relative height growth rate (RGR(H)), relative diameter growth rate (RGR(D)), chlorophyll fluorescence parameters(F-v/F-m,Phi(PSll)), light-saturated photosynthetic rate (A(1400)) and nitrogen uptake in A. faxoniana, but it significantly reduced the values of these parameters in B. albo-sinensis. On the other hand, RGR(H) of A. faxoniana was not influenced by intraspecific competition irrespective of temperature regimes, while in B. albo-sinertsis intraspecific competition was severer under AT than under ET. Decreased photosynthetic capacity and reduced plant size detected in B. albo-sinensis under ET likely contribute to its low intraspecific competitive ability. However, we found positive effects of interspecific competition on A. faxoniana but negative effects on B. albo-sinensis under ET, as A. faxoniana exposed to interspecific competition showed higher RGR(H,) RGR(D), A(1400), chlorophyll fluorescence parameters, foliar delta C-13, foliar N, and percentages of N-15-ammonium and N-15-nitrate recovery than did A. faxoniana exposed to intraspecific competition or no competition. The results indicate that A. faxoniana is a better competitor than B. albo-sinensis under ET. Further, A. faxoniana altered resource use patterns and had a high plasticity in its ammonium uptake in mixtures compared with monocultures under ET, while B. albo-sinensis did not change its N use pattern. In all, our results showed that high temperature stress tolerance (e.g., higher root carbon accumulation), high ability to keep carbon balance (e.g., higher water use efficiency, lower leaf respiration rate, higher F-v/F-m), as well as a better N acquisition ability make A. faxoniana a better competitor when compared to B. albo-sinensisg under ET. (c) 2014 Elsevier B.V. All rights reserved.