广西猫儿山不同海拔常绿和落叶树种的营养再吸收模式

Nutrient resorption patterns of evergreen and deciduous tree species at different altitudes on Mao′er Mountain,Guangxi

土壤养分供给性大小是否影响植物氮和磷再吸收效率仍存在争议。调查了广西猫儿山不同海拔常绿和落叶树种成熟和衰老叶片的氮和磷含量,探讨营养再吸收是否受到叶片习性和海拔的影响。所有树种氮和磷再吸收效率的平均值分别为56.5%和52.1%。常绿树种比落叶树种有显著较高的氮再吸收效率(P<0.001)和磷再吸收效率(P<0.01),这与前者有较低的衰老叶片氮和磷含量密切相关。随着海拔的上升,氮再吸收效率显著下降(P<0.01),磷再吸收效率显著提高(P<0.05)。氮再吸收效率与土壤氮:磷比(r=-0.41,P<0.05)和成熟叶片氮:磷比(r=-0.37,P<0.05)负相关,磷再吸收效率与土壤氮:磷比(r=0.44,P<0.05)和成熟叶片氮:磷比(r=0.47,P<0.01)正相关,表明了树种对低海拔氮限制的适应逐渐转变为对高海拔磷限制的适应。此外,氮再吸收效率与年均温正相关(r=0.43,P<0.05)而磷再吸收效率与年均温负相关(r=-0.45,P<0.01),这表明气温也是调节树木营养再吸收格局的重要影响因素。不同海拔树种氮和磷再吸收模式的差异可能是引起广西猫儿山常绿树种沿海拔形成双峰分布的原因之一。

Nitrogen （N） and phosphorus （P） resorption from senesced leaves are hypothesized to improve plant nutrient conservation. However, whether the availability of nutrients in soil affects the resorption efficiency of N and P is still under debate. The present study investigated N and P contents in mature and senesced leaves of co- existing evergreen and deciduous tree species in evergreen broad-leaved forest at low altitude, beech mixed forest at middle altitude, and hemlock mixed forest at high altitude on Mao＇er Mountain, Guangxi. The present study also determined if nutrient resorption was affected by leaf habit and altitude. N resorption efficiency （NRE） and P resorption efficiency （PRE） for the total species averaged 56.5% and 52.1%, respectively, supporting our hypothesis that nutrient resorption from senesced leaves is very important for plant nutrient conservation. NRE and PRE for the total evergreen species averaged 61.8% and 57.0%, respectively. NRE and PRE for the total deciduous species averaged 51.2% and 47.3%, respectively. Evergreen species exhibited significantly higher NRE （P〈0.001） and PRE （P〈0.01） than deciduous species, which were closely associated with lower N and P contents in senesced leaves in evergreen species. These shifts of NRE and PRE between leaf habits suggested that evergreen species were more conservative than deciduous species in terms of nutrient resorption. On average, at low, middle, and high altitude, NRE was 61.8%, 55.8%, and 52.0%, while PRE was 47.1%, 51.5%, and 57.8%, respectively. As altitude increased, NRE decreased significantly （P〈0.01）, while PRE increased significantly （P〈0.05）. NRE was negatively correlated to the soil N ：P ratio （r=- 0.41, P〈0.05） and mature leaf N ：P ratio （r=- 0.37, P〈 0.05）, whereas PRE was positively correlated to the soil N ：P ratio （r= 0.44, P〈0.05） and mature leaf N ：P ratio （r= 0.47, P〈0.01 ）.The pattern of NRE vs. PRE was indicative of the plant adaptation from N limitation at low altitude to P limitation at high altitude. In addition, mean annual temperature was positively related to NRE （r = 0.43, P〈 0.05） but negatively related to PRE （r=- 0.45, P〈0.01 ）, suggesting that air temperature was also an important factor in the regulation of nutrient resorption patterns in tree species. The combined effects of soil and temperature on nutrient resorption indicated that plants were not responding to altitude directly, but rather to a suite of factors such as soil and temperature that co-varied with altitude. Overall, this study suggests that surveying leaf nutrient content and resorption could provide information about plant adaptation to altitude-induced changes in soil and temperature and explain the bimodal distribution of evergreen tree species along the altitudes on Mao＇ er Mountain. This study also provides insight into the nutrient management and ecosystem conservation in montane forests and delivers information for future meta-studies and model simulations of global leaf nutrient resorption.