Abstract:

Aims The issue of rationally classifying plant species into plant functional types at different scales has been a major challenge in ecosystem sciences, especially ecosystem simulation. A typical steppe in Inner Mongolia of China was chosen for study. We asked: 1) Can plant species be classified into several plant functional groups according to their ecophysiological characteristics of stomatal conductance and net photosynthesis? 2) Are there common ecophysiological traits of each plant functional group? 3) What are the advantages and disadvantages of this classification method in ecological modeling?

Methods Diurnal stomatal conductance and net photosynthetic rate of nine plant species were measured in the field during May, July, and late August 2005. Ecophysiological characteristics of these species were quantified by applying models of stomatal conductance and net photosynthesis to the field data. The models were fitted to the data to obtain model parameters for each species. The analysis showed that the model explained up to 55.87% and 78.19% of the variation in the stomatal conductance and net photosynthetic rate, respectively. Cluster analysis was then applied to identify plant functional types on the basis of the model parameters, which are regarded as ecophysiological traits of plant species.

Important findings Nine plant species were classified into three plant functional groups: 1) highly drought-resistant plants with moderate photosynthetic efficiencies, including Stipa krylovii, Heteropappus altaicus, Artemisia frigida, Convolvulus ammannii and Caragana microphylla; 2) medium drought-resistant plants with high photosynthetic efficiencies, including Leymus chinensis, Achnatherum splendens and Iris lacteal; 3) low drought-resistant plants with low photosynthetic efficiencies, including Phlomis mongolica. This study suggests that plant species in natural ecosystems can be classified into several plant functional groups using our methods. Therefore, the complexity of ecological models and calculation times can be reduced by substituting plant functional groups for individual species. Our approach can be an effective way to quantitatively distinguish plant traits, thus contributing to scaling up of ecosystem simulation.

Key words: ecosystem model, parameter fitting, aggregation of plant functional group, cluster analysis, scaling up, plant functional type