光氮耦合作用对化香幼苗碳平衡的影响

Effects of Light and Nitrogen Supply on the Carbon Balance of Seedling of Platycarya strobilacea

为了研究大气氮沉降和次生林冠层郁闭度增加对化香幼苗更新的影响,本文通过模拟鄂东南典型次生林光环境和土壤氮素供给的变化趋势,研究了化香幼苗叶功能性状、生物量分配及气体交换对光氮变化的响应,最后应用全株碳平衡模型模拟了整株光补偿点的变化(LCP-wholeplant)。结果表明:光对化香幼苗叶功能性状和生物量分配均存在显著影响,氮素供给增加对其叶功能性状和生物量分配影响不明显,但是,光和氮素供给互作对根质量比(RMR)影响显著。幼苗叶片的表观量子效率(Ф)、最大光合速率(Amax)在郁闭光(3.0%,6.0%透光率)下随氮素供给增加而降低,在林窗光条件下(12.0%,25.0%透光率)随氮素供给增加而增加。富氮营养导致郁闭条件下(6.0%,3.0%透光率)化香幼苗的整株光补偿点(LCP-wholeplant)升高,但却导致林窗条件下(25.0%,12.0%透光率)化香幼苗的整株光补偿点(LCP-wholeplant)降低。因此,大气氮沉降将使化香种群更加依赖于林窗和干扰更新。

Platycarya strobilacea is widely distributed in the sub-tropical area of China. To study the potential effect of atmosphere nitrogen deposition on its seedling regeneration, the seedling leaf functional traits, biomass allocation, gas exchange and seedling carbon balance to low light （3.0%, 6.0%, 12.0% and 25.0% PAR of open sky light） and nitrogen （ 15.0 and 3.0 mmol ~ L-1 ） treatments were determined in a greenhouse experi- ment. The results showed that light deeply affected leaf functional traits and biomass allocation. In contrast, ni- trogen supply had no influence on them, though the interactions of low light and nitrogen supply could signifi- cantly affect RMR. We also found that the maximum photosynthesis rate （Amax ） and apparent photon efficiency （q）） decreased with increasing nitrogen supply under low light （3.0% and 6.0% of full sun light）, vice versa in a relatively higher light （ 12.0% and 25.0% of full sun light）. Hence, the interactions of light and nitrogen deeply influenced leaves gas exchange of seedlings of P. strobilacea. The results simulated with a whole plant car- bon balance model indicated that light compensation point of P. strobilacea seedlings （LCP,_wholeplant） increased with increasing nitrogen under 3.0%, 6.0% PAR of open sky light, while it decreased with increasing nitrogen supply under 12.0% and 25.0% conditions. Therefore, we suggested that atmosphere nitrogen deposition would deteriorate P. strobilacea regeneration under lower light environment conditions, but increase its survival under disturbance and gap conditions.