Chin J Plan Ecolo ›› 2004, Vol. 28 ›› Issue (6): 803-809.DOI: 10.17521/cjpe.2004.0105

• Research Articles • Previous Articles     Next Articles

CHANGES IN BIOMASS ALLOCATION AND GAS EXCHANGE CHARACTERISTICS OF LEYMUS CHINENSIS IN RESPONSE TO SOIL WATER STRESS

WANG Yun-Long1 XU Zhen-Zhu1 and ZHOU Guang-Sheng1,2*   

  1. (1 Laboratory of Quantitative Vegetation Ecology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China)
  • Online:2004-11-10 Published:2004-11-10
  • Contact: ZHOU Guang-Sheng

Abstract: Global environmental change has already been and will continue to reallocate water and heat resources at a global scale, and, as a result, will affect the structure and function of terrestrial ecosystems. For temperate zone steppe ecosystems, aridification currently is the most significant environmental problem and this may be intensified due to global warming. The responses of the dominant species of these ecosystems to water stress will be important for understanding how terrestrial ecosystems will respond to global change and how species will adapt to the aridification under the backdrop of global warming as well as the impact on the global carbon budget. The response of leaf relative water content, leaf photosynthetic rate, biomass allocation and net population CO2 exchange rate of Leymus chinensis to soil water stress were studied using a pond cultivation experiment from May to July 2002. Five soil water treatment levels were used: 75%-80% (control), 60%-65%, 50%-55%, 35%-40% and 25%-30% of soil water holding capacity. The results are summarized below. 1) The relationship between leaf relative water content of L. chinensis and soil water stress could be expressed as a single peak curve with its maximum value appearing in the 50%-55% soil water treatment. 2) Leaf photosynthetic rates decreased with an increase in soil water stress, and the diurnal pattern of leaf photosynthetic rates in the soil water treatments of 75%-80%, 60%-65% and 50%-55% were different than that under the drier conditions of 35%-40% and 25%-30%. 3) The total biomass, root biomass, sheath biomass and leaf biomass of L. chinensis decreased with an increase in soil water stress. 4) Soil water stress promoted the allocation of carbon to roots and increased the root to shoot ratio of L. chinensis at the early growth stage but not at late growth stages. These results imply that increasing the root to shoot ratio is an adaptive strategy for tolerating drought conditions. The relationship between the biomass of roots and sheaths and the percent of carbon allocation to soil water stress could also be expressed as a single peak curve with the maximum value of root and sheath biomass (1.28 g·plant-1) appearing at the 50%-55% soil water treatment and the maximum allocation to root and sheaths (48.5%) at 35%-40% soil water content. 5) The net population CO2 exchange of L. chinensis decreased with an increase in soil water stress. The relationship between daily net population CO2 exchange of L. chinensis and soil water stress showed a single peak with the maximum value occurring at 60%-65%. Negative values of daily net population CO2 exchange of L. chinensis occurred at 25%-30% soil water content. Moreover, the results indicated that 40% soil water holding capacity might be the tolerance threshold for L. chinensis below which this species is not able to survive.