延长光周期对罗汉松和鸡爪槭苗期生长及养分吸收利用的影响

Growth,nutrient uptake and utilization responses of Buddhist pine and Japanese maple seedlings to the extended photoperiod

采用盆栽试验,通过每天将光周期延长至约18h的处理对罗汉松和鸡爪槭容器苗木进行培育,以自然光周期为对照,研究2种苗木在养分吸收和利用方面的响应。结果表明:和自然光周期处理相比,在延长光周期培育下罗汉松和鸡爪槭的苗高增幅分别达到17%(P=0.004 8)和20%(P=0.023 0),但新根数分别下降了31%(P=0.044 2)和21%(P=0.026 5),地径和根长均未出现显著响应;光周期延长也使鸡爪槭苗木的生物量(P=0.005 5)和氮(N)(P=0.018 3)、磷(P)(P=0.012 5)、钾(K)(P=0.001 4)含量均显著增加,却并未引起罗汉松体内P和K含量发生变化;试验结束时,罗汉松体内N、P、K质量分数分别为(1.57±0.14)%、(0.93±0.25)%和(1.21±0.15)%,分别比鸡爪槭高8%(P=0.045 8)、87%(P<0.000 1)和110%(P<0.000 1);延长光周期会同时提高苗木对N的吸收和利用效率,但是不会影响养分淋溶。总体上,虽然延长光周期处理对2种苗木的生长和养分吸收产生了一定的促进作用,但也容易导致苗木出现"头重脚轻"的形态,并且在苗体养分浓度稀释方面存在极大的隐患。

Illumination enables plants to assimilate carbon by photosynthesis.Under the extended photoperiod,plants could continue to grow through uninterrupted carbohydrate production,leading to increase of dry mass accumulation.Physiological responses under these driven-changes have been fully studied for photosynthesis,such as carbon（C）and nitrogen（N）balance,and N utilization.The purposes of most studies were to understand the mechanism of plant growth in the extended photoperiod,for application in culture of tree seedling.However,the application was limited by lack of evidence for the establishment of inherent nutrient reserve,acting as the most determinative factor for an acceptable seedling quality.High-valued ornamental tree seedlings usually ownanaturally slowly growing rate.Hence,they are usually suggested to be cultured under the extended photoperiod so as to stimulate their growth to meet the standard morphologies for selling.However,this manipulation may be fatal for the survival of these slowly growing ornamental tree seedlings,because quite little attention has been paid to their inherent nutrient reserve,and their quality would have been impaired at the end of nursery culture.Recently,research on one typical ornamental tree seedling of Buddhist pine（Podocarpus macrophyllus [Thunb.]D.Don）found coexistence of nutrient dilution with dry mass accumulation under the extended photoperiod.However,results and conclusions therein were limited by the unique tree species in the experiment.Meanwhile,the evidence for effects of nutrient leaching on nutrient utilization remained insufficient.Therefore,the application of extended photoperiod on culture of slowly growing ornamental seedlings remains debatable.In the present study,seedlings of Buddhist pine and Japanese maple（Acer palmatum Thunb.）were raised in an extended photoperiod（EP）treatment of 18-hour light per day,while the natural photoperiod was employed as a control,in a practical greenhouse at Flower Research and Development Center,Zhejiang Academy of Agricultural Sciences in Xiaoshan District of Hangzhou City,China.The experiment commenced at 17 June 2014and ended until the termination on 17 December 2014.In the last month before the experiment terminated,leachates were collected to determine the nutrient contents once a week.The results indicated that compared to the control,seedling height increased by 17%（P=0.004 8）and 20%（P=0.023 0）,but new root number decreased by 31%（P=0.044 2）and 21%（P=0.026 5）for Buddhist pine and Japanese maple seedlings under the EP,respectively.However,both root-collar diameter（RCD）and root length did not respond at all;additionally,whole-plant biomass accumulation（P=0.005 5）and nutrient contents of N（P=0.018 3）,P（P=0.012 5）and K（P=0.001 4）in Japanese maple seedlings were all promoted in the longer photoperiod,whilst the contents of P and K did not show any significant response in Buddhist pine seedlings.At the end of experiment,the concentrations of N,P and K were determined to be（1.57±0.14）%,（0.93±0.25）% and（1.21±0.15）%in Buddhist pine seedlings,which were higher than those in Japanese maple seedlings by 8%（P=0.045 8）,87%（P〈0.000 1）and 110%（P〈0.000 1）,respectively.In conclusion,for slowly growing ornamental seedlings,such as Buddhist pine and Japanese maple,an extended photoperiod can effectively promote biomass accumulation,height growth and nutrient uptake efficiency,but has no influence on the growth of RCD and root length,also invalid effect is found on nutrient leaching.The seedlings cultured in the extended photoperiod tend to present a morphological feature of＂big head but light feet＂,and have potential risks on within-body nutrient dilution.