【目的】通过比较不同遮荫水平下香榧苗期的生长指标、气体交换参数、光合色素含量和叶氮含量的差异，初步探讨不同遮荫水平下香榧苗期光合作用及氮分配的响应机制。【方法】以2年生香榧苗为材料，测定不同遮荫水平(0，50%，75%和90%遮荫水平)下香榧苗的苗高、地径、生物量及叶片的光响应、二氧化碳( CO2)响应曲线、叶绿素和叶氮含量等指标。【结果】随遮荫水平的增加，香榧苗叶色逐渐增绿；地径增量和生物量均呈先增加后降低的趋势，其中50%和75%遮荫水平下的地径增量最高，分别为0遮荫下的215.2%和233.6%( P ＜0.05)，为90%遮荫下的161.4%和175.2%(P ＜0.05)；75%遮荫水平下的生物量最高，分别为0，50%，90%遮荫下的141.0%，111.5%和114.0%(P＜0.05)。随遮荫水平的增加，香榧苗的根冠比逐渐降低，但其叶片的叶绿素 a(Chl a)、叶绿素 b( Chl b)和类胡萝卜素( Car)含量均呈逐渐升高的趋势。随遮荫水平的增加，香榧苗期叶片的光饱和点(LSP)、光补偿点(LCP)呈逐渐下降的趋势；其表观量子效率(AQY)呈逐渐升高的趋势；其最大净光合速率(Pmax)、最大 RuBP羧化速率(Vcmax)及 RuBP再生的光合电子传递速率(Jmax)均呈先升高后降低的趋势，且这些参数在50%和75%遮荫水平下最高；但其单位面积上的叶氮含量( Na )呈逐渐降低的趋势。随遮荫水平的增加，分配到羧化作用的 N素(Nc)、能量代谢的 N素(NB)、捕光色素的 N素(NL)、光合氮素利用效率(PNUE)均呈先增加后降低的趋势，除 NL外其他参数均在75%遮荫水平下最高。【结论】遮荫处理能有效地促进香榧苗的生长；有效加强香榧苗对早晨或傍晚弱光的利用，这有利于植物体的生长发育。而过度遮荫(90%遮荫水平)的香榧苗 Pmax显著降低，这可能与其为了捕获更多的光能，将更多资源用于捕光蛋白上，而导致光合能力下降有关。与50%遮荫水平相比，75%遮荫水平的香榧苗将更多的氮素分配到光合机构( Nc 和 NB )中，从而显著提高 PNUE。综上所述，前期苗木培育中，给予香榧苗75%遮荫水平有利于其生长发育。
Response of Photosynthesis and Nitrogen Distribution of Torreya grandis‘Merrilli’Seedlings in Different Light Regimes
[Objective]To elucidate the mechanism of photosynthetic characteristics and nitrogen allocation of Torreya grandis‘Merrilli’seedlings under different shading levels,the growth,gas exchanges parameters,chlorophyll content and leaf nitrogen content were measured. [Method]We measured the height,ground diameter,biomass,light response curve,CO2 response curve,chlorophyll content,leaf nitrogen content of T. grandis‘Merrilli’seedlings under different shading levels( 0%,50%,75% and 90%) .[Result]The results showed that the leaf color of seedlings became much greener with the increasing level of shade levels. However,the diameter increment and biomass of seedlings showed an increase at first,followed by a decreased trend with increasing shade level. The seedlings at 50% and 75% shade levels had the greatest diameter increment,which was 215. 2% and 233. 6% of that at 0% shade level and 161. 4% and 175. 2% of that at 90% shade level,respectively. The biomass at 75% shade level was significanly higher than the other shade treatments,and was 141. 0%,111. 5% and 114. 0% compared with that at 0%,50% and 90% shade level respectively. The root/shoot ratio of seedlings reduced gradually,while the chlorophyll a ( Chl a) ,chlorophyll b ( Chl b) and carotenoid ( Car) content increased with increasing of shade levels. LCP ( light compensation point) ,and LSP ( light saturation point ) decreased while the apparent quantum efficiency ( AQY ) increased with increasing of shade level. Maximum net photosynthetic rate ( Pmax ) , maximum RuBP carboxylation rate ( Vcmax ) and RuBP regeneration of photosynthetic electron transport rate (Jmax) showed an increase at first,followed by a decreased trend with increasing of shade level and the highest parameters were observed at 50% and 75% shade levels. However,the leaf nitrogen content per unit area ( Na ) showed a decrease trend with increasing of shade level. Moreover,the fraction of leaf nitrogen allocated to carboxylation ( N C ) ,the fraction of leaf nitrogen allocated to bioenergetics ( N B ) ,the fraction of leaf nitrogen allocated to light-absorbing pigment (NL),and photosynthetic nitrogen utilization efficiency (PNUE) showed a decrease trend with increasing of shade levels,and the highest values of these parameters except NL were observed at 75% shade level.[Conclusion]Shade treatment can effectively promote the growth of T. grandis‘Merrilli’seedlings. The seedlings grown under shade treatment can effectively use the lower light intensity at early morning or late afternoon in comparison to that grown at full sun light. Heavy shading (90% shading level) significantly decreased the Pmax,which may be related to the capacity to capture more light,and thus more resources were used to the light protein,resulting in a decline in photosynthetic capacity. Compared with the 50% shade level,the 75% shade level had more nitrogen allocated to the photosynthetic mechanism,such as in Nc and NB,and significant higher PNUE. Thus,our results indicate that T. grandis‘Merrilli’seedlings likely grow better at 75% shade level for seedling cultivation.
国家科技期刊平台
NSTL
万方数据
维普
