Variations in leaf functional traits along the altitude gradient of Pinus tabuliformis and its environmental explanations in Beijing Songshan Mountain

  Objective  In this study, we explored the responses of leaf functional traits of Pinus tabuliformis to altitude gradients and quantified the contribution of topography and soil to intraspecific trait variation. This work aims to provide a basis for predicting the spatial-temporal variations and its mechanism of leaf functional trait caused by climate change in the future.

  Method  Leaves of Pinus tabuliformis on the southern slope of Songshan Mountain area in Beijing at an altitude of 789−1106 m were collected to measure 8 leaf functional traits, including leaf area (LA), specific leaf area (SLA), leaf dry matter content (LDMC), nitrogen concentration per unit mass (M_N), phosphorous concentration per unit mass (M_P), nitrogen concentration per unit of area (A_N), phosphorous concentration per unit of area (A_P) and leaf nitrogen to phosphorus ratio (L_N:P). Correlation between these traits and its response to altitude gradients were analyzed. The responses of these traits to topography and soil were also examined in this study.

  Result  (1) LA, SLA and M_P showed a decreasing trend with the altitude gradient, while LDMC, M_N, A_N and L_N:P showed an increasing trend along the altitude gradient. A_P did not respond to the altitude. The leaf functional traits of Pinus tabuliformis showed significant intraspecific variations and the variation coefficient was between 10.33% and 27.59%. The order of variation was LA > A_N > A_P > SLA > L_N:P > M_N > M_P > LDMC. (2) A significant synergy or trade-off was observed among some functional traits as the altitude changed, where SLA of Pinus tabuliformis was negatively correlated with LDMC (P < 0.05) and it was extremely negatively correlated with A_N and A_P (P < 0.001). (3) The variation of leaf functional traits was affected by various environmental factors. We found that LA, SLA and L_N:P of Pinus tabuliformis were mainly affected by altitude and soil phosphorus content (TP), while LDMC was mainly affected by soil nitrogen to phosphorus ratio and soil water content. Both M_N and A_N were mainly affected by soil pH and TP, and M_P was mainly affected by altitude and slope. (4) Altitude and soil could only explain 6.28%−41.1% of the variation in leaf functional traits of Pinus tabuliformis.

  Conclusion  In the study area, leaf functional traits of Pinus tabuliformis adapt to altitude gradient change by certain character variation and combination, among which the dominant factors and extent of the character variation were different.