| Second or multiple shooting is one of the important events in the process of woody species life history. Researching second shooting may reflect life history characteristics of woody species, to a certain extent, which can help to understand the ecology adaptation strategies of species. Systematic reports about second shooting are seldom so far. The features of second shooting of woody species are still unclear.We selected woody plants from deciduous broad-leaves forest of Xianlin, Nanjing, Jiangsu Province to survey the proportion of the second shooting at the level of species, individual and shoot, compare leaf and shoot dynamic, functional traits of mature shoot between the two sets of shooting (First shooting and second shooting was called in short respectively as FS. and SS in the following) aiming to understand characteristic of SS in deciduous broad-leaves forest of north subtropical region. The main results were as follows:(1) In late-July 2014, we set three 120 m long and 4 m wide line transects to survey proportion and position of SS. The results showed:i) At the level of species, we recorded 37 woody species in all. Among them,18 species had the phenomena of SS with the mean proportion of three line transects of 46.5±5.4%.12 species had SS out of 21 single leaf species, while only 6 species had SS out of 16 compound leaf species. The result indicated that the protortion of single leaf species (57.1%) was greater than that of compound leaf species (37.5%).13 species had SS among 24 tree species, and 5 species had SS among 13 shurb leaf species, indicating the protortion of tree species (54.2%) was greater than that of shurb species (38.5%). ii) At the level of individual, we recorded 1043 woody individuals in all,361 individuals having SS among them. The mean proportion of SS of 18 species was 62.8±7.8%. The mean porpotion of single leaf species (67.4±8.9%) was not different from that of compound leaf species (53.3±15.6%). The mean porpotion of tree species (30.5±8.5%) was not different from that of shurb species (41.8±18.7%). iii) At the level of shoot, the mean proportion of SS of 18 species was 34.6±6.0%. The mean porpotion of single leaf species (24.4±4.9%) was not different from that of compound leaf species (55.1±11.9%). The mean porpotion of shurb species (47.4± 17.4%) was significantly higher than that of tree species (29.7±5.1%) (P<0.05).The positions of SS occurred in terminal bud, axillary bud, adventitious bud on the first current-year shoot. According to the position of the SS, those species in the forest are divided into four types:ⅰ) Only terminal bud grew SS, including five species (Quercus serrata, Quercus dentate, Populus adenopoda, Pistacia chinensis, Maclura tricuspidata). ii) Both of terminal bud and axillary bud had SS, including four species (Symplocos paniculata, Triadica sebifera, Styrax confuses, Dalbergia hupeand). iii) Both of axillary bud and adventitious bud grew SS, including two species (Platycarya strobilacea, Pterocarya stenoptera) with the proportion of 11.1%. iv) Only axillary bud grew SS, including seven species (such sa Indigofera bungeana, Liquidambar formosana, Celtis sinensis and so on).(2) From late-March 2014 to mid-December 2014, the result of leaf number dynamic of two shooting phases for 16 representative woody species showed:The beginning time of leaf emergence of FS was relatively concentrated from mid-March to mid-April and SS was quite dispersive from late-May to mid-July. The ending time of leaf emergence of FS was from mid-March to early-June and SS was from mid-May to mid-August. FS and SS shared the same leaf emergence pattern, showing a succeeding type or flushing type of leaf emergence. However, the duration of leaf emergence was much longer in SS (31.4±4.2 d) than in FS (23.4±3.4 d) (P<0.05). The result of correlation analysis of the leaf emergence phenology parameter showed: The beginning, ending, duration time of leaf emergence between FS and SS had no significant correlation. The ending time of leaf emergence of FS showed an extremely significant positive correlation (P<0.01) with the duration of leaf emergence of SS. The correlation between FS and SS of leaf emergence duration was extremely significant positive (P<0.01).The beginning time of leaf abscission of FS from late-May to late-November was much earlier than SS which was from early-June to early-December. The ending time of leaf abscission of FS was from late-June to mid-December and SS was from early-August to mid-December, but there were no significant difference between them. The duration of leaf abscission was much longer in FS (55.7±7.6 d) than in SS (51.2 ±5.9 d) (P<0.05). The result of correlation analysis of the leaf abscission phenology parameter showed:The beginning time of leaf abscission of FS showed an extremely significant positive correlation (P<0.01) with the ending, duration time of SS. The ending time of leaf abscission of FS showed an extremely significant positive correlation (P<0.01) with the beginning, duration time of SS. The duration of the two processes of shooting was significantly positive (P<0.05).(3) From late-March 2014 to early-August 2014, the result of leaf area dynamic between the first and SS for 16 woody species showed:In term of the duration mean of leaf expansion, FS (23.7±1.6 d) was not significantly different from SS (25.6±2.1 d). And the leaf expansion rate between FS (0.20±0.01) and SS (0.18±0.01) was not significantly different as well.(4) According to the relationship between the ending growth time of FS and the beginning growth time of SS,16 measured species were divided into three types:i) There was a overlapping period between the two shooting phases. This type included four species (C. sinensis, Phyllanthus glaucus, Ulmus pumila, Indigofera bungeana). ⅱ) When the first shoot stopped elongating, the second shoot extended at once. This type included two species (A. fruticose, T. sebifera). ⅲ) There was a quiescent period between the two shooting phases. This type included ten species (such as Q. serrata, Q. dentate, S. confuses and so on).(5) In late-July 2014, the result of leaf and shoot traits of mature shoot between FS and SS for 14 woody species showed:In term of leaf traits, six leaf traits (including leaf number, total leaf area, total leaf mass, leaf mass per area, individual leaf area and individual leaf mass) of FS were higher than those of SS. In term of stem traits, twig stem length, diameter and mass were significantly smaller in SS than in FS, indicating lower twig allocation during SS. In term of the relationship between leaf and stem, leafing intensity was significantly smaller in FS than in SS. Leaf area ratio and stem mass fraction showed that FS were higher than SS. |
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