NITROGEN AND PHOSPHORUS RESORPTION IN TWO SYMPATRIC DECIDUOUS SPECIES ALONG AN ELEVATION GRADIENT

Abstract

Some leaf traits (N and P concentrations, N/P ratio, specific leaf area, mean residence time of nitrogen and phosphorus (MRTN and MRTP) and foliar resorption were investigated in two sympatric deciduous species (Amelanchier rotundifolia (Lam.) Dum.-Courset subsp. rotundifolia and Rhamnus oleoides L. subsp. graecus) which are the most characteristic species of steppe and rocky vegetation along an elevation gradient to determine which leaf traits were related to nitrogen and phosphorus efficiency (NRE and PRE) and proficiency (NRP and PRP). Statistically significant differences were found along the elevation gradient between the two sympatric deciduous species with respect to green leaf N/P ratio, NRE, MRTN, MRTP and leaf longevity. NRE was below the threshold values for deciduous species in A. roundifolia subsp. rotundifolia although PRE was higher than threshold values. Both NRE and PRE were higher than threshold values for deciduous species in R. oleoides subsp. graecus. Soil phosphorus concentrations were found to be rather low along the elevation gradient. Leaf N/P ratios varied between 25.54 and 37.11 in A. rotundifolia subsp. rotundifolia, and 11.59 to 21.96 in R. oleoides subsp. graecus and these values indicate P rather than N-limitation for these species. As with NRE and PRE mean residence time of nutrients (MRT) both MRTN and MRTP were considerably higher in R. oleoides subsp. graecus. It has been found that A. rotundifolia subsp. rotundifolia has low green leaf P concentration and high N/P ratio and has a CS (competitor/ stress-tolerant) strategy, whilst R. oleoides subsp. graecus has a C/CS (competitor/ competitor stress-tolerant) transitional type strategy In conclusion, higher MRTN and MRTP would provide a competitive advantage of a certain species in mixed-deciduous species stands and also enable. higher PRE along an elevation gradient.