亚热带地区不同林分下植物水分利用的季节差异

以长沙地区针阔混交林(样地一)内的刺杉(Cunninghamia lanceolate)、栀子花(Gardenia jasminoides)和低矮经济林(样地二)内的板栗树(Castanea mollissima)、野茶花(Camellia japonica)为研究对象,基于2018年9月-2019年8月期间降水、土壤水和植物茎杆水中稳定同位素数据并结合Iso-Source模型,分析了4种植物水分利用来源的季节变化。旨在揭示亚热带湿润地区不同植物水分利用状况。结果表明:观测期内,土壤水和植物茎杆水中稳定同位素对降水的响应存在时滞。通过比较不同水分条件下4种植物茎杆水线(XWL)和各层土壤水线(SWL)的斜率,可以定性判别4种植物水分利用来源,其结果与Iso-Source模型模拟结果基本一致。在降水较为丰富的10月至次年5月,刺杉、栀子花和野茶花分别主要利用0-20、0-10和0-10cm土壤水,利用比例分别为69.2%、89.6%和56.2%;在雨、旱季过渡期的6-7月,3种植物分别主要利用20-100、0-20和0-60 cm土壤水,利用比例分别为69.5%、63.6%和80.7%;在干旱严重的8-9月,3种植物均主要利用60-100 cm深层土壤水,利用比例分别为78.1%、59.7%和76.8%。板栗树在落叶期(12月至次年3月)几乎不利用土壤水;在10-11月和4月,板栗树主要利用0-10 cm表层土壤水,利用比例均大于40%;而在5-9月,板栗树对深层土壤水利用比例超过40%。研究发现,4种植物水分利用对环境水分的变化较为敏感,均能通过合理的水分利用策略应对季节性干旱。

Seasonal Differences in Water-Uptake Pattern of Plants under Different Forest Types in Subtropical Regions

The typical plant species Cunninghamia lanceolate,Gardenia jasminoides in the Needle-broad leaf mixed forest(plot 1)and Castanea mollissima,Camellia japonica in the economic forest(plot 2)in Changsha were selected as target species.Based on the stable isotope composition of different water bodies investigated from September 2018 to August 2019 and the Iso-Source Model,the seasonal variations of the water-uptake patterns of different plant species were analysed,which were used to reveal the differences in water-uptake patterns for the four plant species in a subtropical humid region.The results show that during the observation period,there were delays in responses of stable isotopes of soil water and plant xylem water to precipitation inputs.Based on the comparison of the slopes of the xylem water line(XWL)and soil water line(SWL)of the four plants under different water conditions,the water use sources of the four plants were qualitatively determined,which was mainly consistent with the simulation results of the Iso-Source Model.Sufficient precipitation occured from October 2018 to May 2019,the C.lanceolate,G.jasminoides and C.japonica mainly used soil water at the depth of 0–20 cm,0–10 cm and 0–10 cm respectively,and the corresponding utilization proportion was 69.2%,89.3%and 56.2%,respectively.During the transition period of wet and dry season(between June and July),the three plants mostly uptook soil water at the depth of 20–100 cm,0–20 cm and 0–60 cm,respectively,and the utilization proportion was 69.5%,63.6%and 80.7%.From August to September,the three plants generally used the soil water at the depth of 60–100 cm due to severe drought,and the proportion was 78.1%,59.7%and 76.8%,respectively.In addition,C.mollissima hardly used soil water during leaves fallen period(from December 2018 to March 2019).During the periods of October to November and April,it primarily used soil water within 0–10 cm depths,and the utilization proportion exceeded 40%.From May to September,it mainly used deep soil water constituting more than 40%of total utilization proportion.In summary,the mentional plants above are susceptible to the variations in changes of environmental water,and they formed reasonable water use strategies in response to seasonal drought.