Physiological and morphological variations of Picea asperata populations originating from different altitudes in the mountains of southwestern China

Population differences in dry matter accumulation and allocation, conifer leaf nitrogen status, stomata parameters and water use efficiency were studied in a 7-year-old Picea asperata Mast. plantation that contains seven populations grown from seed collected from different altitudes in the mountains of southwestern China. In our study, we measured dry matter accumulation (DMA), total projected leaf area (LA), specific projected leaf area (SLA), root/shoot ratio (RS), root mass/projected leaf area ratio (R/LA), projected leaf area/stem cross-sectional area ratio (LA/SA), leaf stomatal density (SD), stomatal length (SL) and total stomatal length (TSL), nitrogen content per unit leaf mass (Nmass) and nitrogen content per unit projected leaf area (Narea), and carbon isotope composition (δ13C). Significant differences in these properties among the populations were detected, but these morphological and physiological responses to altitudinal gradients of origins varied non-linearly with increasing altitude. We found that seed source near 2950 m altitude was likely an optimum zone for P. asperata; growth was most vigorous at this altitude, and with increasing altitudinal distance from this optimum the growth decrease. In addition, seedling early growth, including DMA and LA, negatively correlated with RS, R/LA, Nmass, Narea and δ13C, and positively correlated with SLA, LA/SA, SD, SL and TSL. Our results provided strong evidence that variations in these physiological and morphological properties of P. asperata populations reflected genetic adaptations to native habitats. These differences may be used as criteria for genotype selection in the mountains of southwestern China.