海岸梯度上黑松针叶化学计量特征的变化规律

Variation in needle stoichiometric characters of Pinus thunbergii along a coastal-inland gradient

风对树木形态、生理和生长的影响一直是生态学研究的热点和难点问题,目前主要采用模拟风速或机械刺激的方式来研究树木对风胁迫的响应与适应变化,无法准确反映出树木在风环境下的长期适应机制。揭示自然环境下树木对风胁迫的长期适应机制,测定了海岸梯度上迎风面和背风面60年生黑松林(Pinus thunbergii)针叶有机碳、氮、磷、钾、钙、钠、镁元素含量,并分析元素含量及其化学计量特征的变化规律。结果表明:黑松林迎风面针叶有机碳含量随离海岸距离的减小显著降低(P<0.05);而氮、磷、钾、钙、钠、镁含量则显著增加(P<0.05);氮磷比保持相对稳定。黑松林背风面针叶除钙和钠含量随离海岸距离的减小逐渐增加外,其他元素含量变化规律均不明显;距海岸500 m内黑松针叶化学计量特征差异显著(P<0.05),其后趋于相对稳定。黑松林迎风面针叶化学计量特征普遍存在相关关系,背风面仅针叶氮和磷、钙和钠间存在相关关系,且与迎风面存在共同的SMA斜率和截距。研究表明,海岸梯度上风胁迫会显著改变黑松针叶化学元素含量,但其比值相对稳定;随海岸距离减少,风胁迫增加,针叶碳同化能力受到明显影响,黑松通过针叶氮、磷、钾、钙、钠、镁含量的增加来提高耐风胁迫的能力,这可能是自然环境下黑松对长期风胁迫的一种适应策略。

The effects of wind on the morphology,physiology and growth of trees have been a hot topic and difficulty in ecology.Previous studies examined response and adaptation of trees to wind through short-time wind simulation or mechanical stimulation,which cannot reflect the long-term adaptation mechanism of trees in the natural windy environment.To fill such knowledge gap,we measured the concentrations of carbon,nitrogen,phosphorus,potassium,calcium,sodium and magnesium in needles of a 60-year-old Pinus thunbergii forest along a coastal-inland gradient,and analyzed the variations of element concentration and stoichiometric characteristics.The results showed that organic carbon concentration in needle on windward of P.thunbergii decreased from inland to coast,the concentrations of nitrogen,phosphorus,potassium,calcium,sodium and magnesium increased(P<0.05),and N∶P ratio remained stable.However,there were no significant differences for these variables on leeward along the coastal-inland gradient,except that calcium and sodium concentrations decreased.Needle stoichiometric characters were significantly different between windward and leeward within 500 m from coastline,and then kept stable over distance.The correlations among windward needle stoichiometry were pervasive,but on the leeward side,only significant relationships between nitrogen and phosphorus and between calcium and sodium existed.Standardized major axis(SMA)fitted between windward and leeward were not different in slope and intercept(P>0.05).In sum,the needle chemical composition of P.thunbergii was significantly affected by wind stress,but the ratio was relatively stable.The needle carbon assimilation function was significantly affected with the increases of sea wind stress.Meanwhile,P.thunbergii improved its tolerance to wind stress by increasing needle nitrogen,phosphorus,potassium,calcium,sodium and magnesium concentrations,which may be an adaptive strategy for P.thunbergii to long-term wind stress in natural environment.