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岷江柏(Cupressus chengiana)是柏科柏木属乔木,为国家Ⅱ级重点保护野生植物、川甘特有种,一般生于海拔1200—2 900 m的干燥阳坡[1],其抗逆性强,是干旱河谷地区水土保持和植被恢复的重要乡土树种[2-3]。2014年以来,毛康珊等证实岷江柏依流域分为3个独立单元[4-5],Maerki D.等发表新种甘肃柏木Cupressus gansuensis Maerki & J.Hoch,重新定义大渡河柏木Cupressus fallax Franco,形成“三江三柏”[6],得到国内外植物学界的普遍承认,至此,岷江柏分布区域变窄,仅为汶川、理县、茂县等岷江流域的干旱河谷地区,濒危程度加剧。根据《四川省古树名木目录》(四川省绿化委员会,2020年),现有岷江柏古树12株,分别为阿坝藏族羌族自治州理县6株、茂县6株。经过调查发现,理县现存岷江柏古树仅5株(一级古树3株,二级古树1株,三级古树1株),均得到当地政府妥善管护,生长健康,未发生破坏及砍伐等情况。古树是在气候变化、人为因子、管理措施及传统文化的长期综合作用下保存下来的[7-11],蕴藏有长寿、抗逆、抗病虫害等多种基因的,遗传改良的宝贵种质材料[12-15]。相关研究表明植物的生殖能力一般随着年龄的增长而下降,进而衰老死亡[16],且可能是从花或种子中形成促衰老因子,进而导致其他部位开始衰老[17],在古银杏(Ginkgo biloba)、古楸树(Catalpa bungei)的种子活力及萌发率的研究结果亦是如此[18]。柏科植物具有长寿、生命力旺盛的特点[19],剑阁县古柏的生长状况与树龄无显著相关性[20],古侧柏(Platycladus orientalis)的种子生理机能亦没有明显的衰退迹象[21]。前人已对岷江柏种群结构[22]、种实表型特征[23]、种子萌发[24]、育苗造林[25]、抗性[26-28]、迁地保护[29]等进行了系列研究,而对岷江柏古树的研究鲜见报道,其种子表型、生理特征如何,是否具有繁殖能力尚未可知。因此,为保护古树资源、保存珍贵基因、扩大古树种群数量,以理县岷江柏古树种子为研究对象,通过对种子形态特征、生活力、发芽指数等指标进行测定,研究岷江柏古树种子的萌发特性,探究岷江柏古树种子活力,为古树育苗与珍贵基因保护提供理论基础。
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2020年9—10月,对研究区域范围内古树(见表1和图1)种子进行采集。选择两年生成熟果,呈绿褐色、鳞片微裂、隐约可见其中褐色种子,利用高枝剪摘果与自然人工承接。采集的球果平铺于阳光照射、通风干燥的房间内晾晒。种鳞开裂后,木棒敲打球果、脱出种子、风扬去杂,去除干瘪、霉变和过小种子。用0.5%的高锰酸钾消毒30 min后用蒸馏水洗净、晾干,装入网袋中存放于室内阴凉通风处[30]。
采集点 树龄/a 级别 经纬度 海拔/m 树高/m 胸径/cm 冠幅/m 古城 1200 一级 31°33′14.4″N,103°28′54.9″E 1480 42 168 9 城区 600 一级 31°26′21″N,103°10′4.2″E 1860 26 120 11 独柏树 550 一级 31°24′55.8″N 103°7′22″E 1 930 24 71 7 新店子 350 二级 31°26′0.5″N,103°1′46.7″E 2120 32 60 7 Table 1. Seed collection points and ancient tree information of ancient C. chengiana
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每株古树随机选取100粒种子,用游标卡尺测量种子的长度、宽度及厚度,用百分之一天平测量种子百粒重。每株3个重复,共1200粒种子,并以20树龄岷江柏300粒健康种子为对照,采集地点为四川省阿坝藏族羌族自治州金川县。
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每株古树挑选外形饱满的种子30粒,参考《1996国际种子检验规程》,开展种子生活力测试。测试方法为氯化三苯基四氮唑(TTC)法,胚、胚乳均染色或胚乳少部分未染色均视为种子有生活力[31]。每株3个重复,共360粒种子,并以90粒健康种子为对照。
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2021年1月~2月,在四川省林业科学研究院沙河堡实验中心开展不同温度岷江柏古树种子萌发试验。试验开始前,将种子用45 ℃的温水浸泡24 h后,放在铺有2层滤纸的培养皿中分别置于15、20、25 ℃的恒温培养箱(型号:GZX-250光照培养箱)中进行萌发实验。每个温度每株古树选取100粒种子,每个处理3个重复,共1200粒,并以300粒健康种子为对照。
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当种子胚根长至1 mm时视为发芽,每天10:00观察并记录发芽种子数、始发芽时间,并将发芽种子挑出,计算发芽率、发芽势及发芽指数。试验时间共40 d[25]。
发芽率(%)=(正常发芽的种子粒数/参试种子的总粒数)×100%
发芽势(%)=(发芽试验规定期限的最初1/3期间内的种子发芽数/参试种子的总粒数)×100%
发芽指数=每日发芽数/发芽天数之和
采用单因素方差分析(One-way ANOVA)和LSD(Least significant difference)检验温度处理对古树种子形态特征及萌发的差异性影响[5],绘图采用Excel 2019,指标参数以“平均值±标准误”表示。
Seed Morphology and Germination Characteristics of Rare and Endangered Plant Cupressus chengiana
doi: 10.12172/202303160001
- Received Date: 2023-03-16
- Available Online: 2023-10-10
- Publish Date: 2023-12-28
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Key words:
- Ancient tree /
- Cupressus chengiana /
- Morphological characteristic /
- Seed germination /
- Temperature
Abstract: Cupressus chengiana is a rare and endangered species in China, a national class II key protected wild plant and endemic to Sichuan and Gansu Province. The ancient C. chengiana trees contain a variety of genes and are valuable genetic germplasm materials. The seeds of 4 ancient C. chengiana trees (350-1200 years) in Lixian County, Aba Prefecture were used as test materials, and the seeds of C. chengiana (20 years old) in Jinchuan County was used as control. Based on the study of the seed morphological characteristics and germination characteristics of ancient C. chengiana, the germination characteristics of their seeds were revealed. The results showed that the average seed length, width and of thickness of ancient C. chengiana trees was 3.83mm, 3.20mm and 1.29mm, and the average number of seeds in a single cone was 42.42. Compared with the control, the 100-seed weight, viability and germination rate of seeds decreased significantly, which were only 0.25g, 28.27%, 14.59%. The initial germination time and the germination period (13.75 days and 35 days) increased significantly, showing obvious physiological function decline. The initial germination time of 1200-year-old ancient trees was significantly lower than that of other ancient trees, and there was no significant difference in germination rate, germination potential and germination index among different ancient trees. The suitable germination temperature of ancient tree seeds was 20 ℃, the germination rate, germination potential and germination index were 14.58%, 5.42% and 0.29 respectively, and the average initial germination time was 13.46 days.