| Zenia insignis Chun is a rare and endangered species under second-class national protection in China. It is a broad-leaf deciduous tree species in Caesalpiniaceae family with pale yellow stem and can produce light, straight and infestation avoiding wood for construction, interior decoration, furniture manufacturing, transportation and other industries. It is the unique species widely used in karst mountain forestation in Guangxi, as it grows rapidly, penetrates soil by strong rooting system, capable of sprouting regeneration and adapting to various habitats. Young plantations of Z. insignis were investigated in this paper, to compare their characteristics in phenology, growth and photosynthesis in relation to seasons, slope positions and growth potentials, analyzing the interactions and correlations among these factors. The main results were as follows:1 Phenophase characteristics of young Z. insignis plantations(1) In Central Guangxi (WeiDu forest farm), phenophases of 6-yr plantations of Z. insignis were 20 d earlier than the referenced phenophases observed at the arboretum of Guangxi Forestry Academy. Buds emerged in mid to late February, swelled in early March, leaf initially exhibited in early April, the first shooting completed in mid to late April, defoliating began in early December and finished in early January. The earlier phenophase might be contributed to differences in latitude and longitude.(2) Effects of slope positions on the phenophase were moderate. Phenophases of tree at upper slope were earlier 3-5 d than that at lower slope; while growth potential effects on phenophases were almost negligible:the phenophase of average trees (averages) was nearly the same as that of inferior trees (inferiors), and superior trees (superiors) had a little difference (1-3 d) In that comparing to the averages and inferiors.2 Changes of photosynthesis in different seasons(1) Diurnal net photosynthetic rate (Pn) and transpiration rate (TR) presented unimodal or bimodal curves. Trees at slope positions exhibited unimodal Pn curves in both spring and autumn, and bimodal Pn curves in summer; while displayed unimodal TR curve in spring, bimodal TR curve in summer. In autumn, trees at upper slope showed bimodal TR curve and trees at downhill assumed unimodal TR curve. Trees of different growth potentials were also compared and we found that they all showed unimodal Pn curve in spring and autumn, but in summer things were different that superiors and averages presented bimodal Pn curves and inferiors unimodal Pn curves. TR curves were always unimodal in spring, and bimodal in summer; but in autumn, superiors exhibited unimodal TR curve, while averages and inferiors displayed bimodal TR curves.(2) In different seasons, trees at slope positions had highest Pn in spring, moderate Pn in summer and lowest Pn in autumn; and in the 3 seasons, trees at upper slope often had higher Pn than those at downhill. Trees at upper or lower slopes had highest TR in summer, moderate TR in autumn, and lowest TR in spring. Trees at upper slope had higher TR than those at lower slope in all seasons. Water use efficiency (WUE) of trees at upper or lower slopes changed in consistent to Pn, being highest in spring, moderate in summer and lowest in autumn. In spring, trees at downhill had higher WUE than that at upper slope; but in summer, trees at downhill had lower WUE than trees at upper slope. In autumn, trees at upper slope and downhill almost had the same WUE.(3) Pn of trees with different growth potentials varied as season changed. In spring, summer and autumn, superiors had higher Pn than averages and inferiors, and averages had higher Pn than inferiors. In different seasons, all of superiors, averages and inferiors had highest Pn in summer. Superiors and averages' Pn in autumn were greater than in spring; and for inferiors, autumn Pn was smaller than spring Pn. As for TR, no matter of growth potentials, the species presented highest TR in summer, moderate TR in autumn and lowest TR in spring. In spring, the averages and inferiors had equal TR, and the superiors had lower TR. In summer, the TR order was inferiors> averages> superiors. In autumn, the averages had greatest TR, and the superiors' TR were slightly higher than inferiors'. All the 3 types of trees presented highest WUE in spring; superiors and inferiors' WUEs were greater in autumn than in summer, and averages' WUEs were higher in summer than in autumn. In spring and summer, the order of WUEs was superiors> averages> inferiors. In autumn the order of WUEs changed to superiors> inferiors> averages.3 Correlations among tree growth, phenophases and photosynthesis(1) Five phenophases (bud forming, leaf sprouting, shoot developing, leaf color changing, defoliating) were slightly different from that of the references, varied in initiating time, completing time and duration, depending on tree heights, diameter at breast height (DBH), and crown widths.(2) Pn was strongly and positively correlated to tree height, DBH and crown width, indicating that higher Pn giving higher growth, and the order of Pn in trees of different growth potentials was:superiors> averages> inferiors. TR also significantly correlated to tree height, DBH, crown width, Pn and WUE. WUEs were positively and very significantly correlated to DBH, and positively and significantly correlated to tree height, crown width and Pn.(3) Phenophase had not significant correlation with Pn, TR and WUE. Growth potentials, slope positions had some effects on the phenophases; but the phenological variations induced by growth potentials and slope positions did not give rise to qualitative changes in the photosynthesis. |
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