千岛湖次生林优势种植物光合生理生态特性

对千岛湖次生林优势种马尾松(Pinus massoniana)、苦槠(Castanopsis sclerophylla)、石栎(Lithocarpus glaber)、青冈(Cyclobalanopsis glauca)在不同季节的光合作用日变化、光响应、CO2响应以及相对叶绿素含量进行了分析,以期了解群落演替的内在机制。结果表明:(1)马尾松的净光合速率(Pn)日变化在4个季节均呈"单峰"曲线;苦槠在8月呈"双峰"曲线,其他3个月份均呈"单峰"曲线;石栎和青冈在5月、8月和11月的Pn日变化均为"双峰"曲线,有明显的光合"午休"现象,2月为"单峰"曲线。(2)马尾松和苦槠的Pn日积累值为8月最高,石栎和青冈为11月最高,且均与其他3个月均差异显著。4种优势种在4个季节的Pn日积累值的平均值大小为马尾松苦槠青冈石栎,差异显著。(3)4个季节中,光饱和点(LSP)、光补偿点(LCP)、最大净光合速率(Amax)、暗呼吸速率(Rd)、最大羧化速率(Vcmax)、最大电子传递速率(Jmax)均以马尾松最高,表观量子效率(AQY)为马尾松最低。青冈在4个季节中具有最低的LSP、Rd和最高的AQY。苦槠和石栎的光合特性介于马尾松和青冈之间。(4)相对叶绿素含量以青冈最高,马尾松最低。总之,马尾松属强阳性树种,苦槠为阳性树种,石栎具有一定的耐荫性,青冈的耐荫性较强。

Photo-ecological characteristics of the dominant plant species in the secondary forest surrounding Qiandao Lake, Zhejiang, China

The main factors that influence community succession in an evergreen broadleaf forest are differences in the ecological adaptability and eco-physiological traits of the various dominant plant species. Studies of the eco-physiological traits of these dominant species allow researchers to better understand the physiological demands and ecological traits of dominant species in their forest habitat and these studies also help researchers to recognize and understand the intrinsic mechanisms involved in forest regeneration and the mechanisms driving ecological succession in an evergreen broadleaf forest at the individual species level. In this study, we used a portable photosynthesis system to determine various physiological parameters associated with plant growth. We investigated the seasonal dynamics of the diurnal variations of photosynthesis, the responses to both light and CO₂, and the relative chlorophyll content of the dominant plant species in the secondary forest surrounding Qiandao Lake, Zhejiang, China. The species included Pinus massoniana, Castanopsis sclerophylla, Lithocarpus glaber and Cyclobalanopsis glauca. The results showed the following. (1) Diurnal variations of the net photosynthesis rate (R_n) of P. massoniana exhibited a monomodal curve in all four seasons, while the variations in R_n for C. sclerophylla were bimodal in August but had a single curve in the other three time seasons investigated. Diurnal variations of R_n of L. glaber and C. glauca exhibited a typical bimodal curve with obvious "midday depression" in May, August and November but had a monomodal curve in February. (2) The diurnal integral values of R_n of P. massoniana and C. sclerophylla were significantly higher in August than those in the other three seasons, while those of L. glaber and C. glauca were significantly higher in November than those in the other three time periods investigated. The average value of the diurnal integral value of R_n in the four dominant species differed significantly in all four seasons and was ranked in the order of: P. massoniana > C. sclerophylla > L. glaber > C. glauca; (3) Compared with the other three dominant species, for P. massoniana, the light saturation point (LSP), light compensation point, maximum net photosynthetic rate, dark respiration rate (R_d), maximum rate of carboxylation and maximum rate of electron transport were highest in all four seasons, while the apparent quantum yield (AQY) was the lowest. The LSP and R_d of C. glauca were the lowest, while the AQY of C. glauca was the highest in the four seasons. Photosynthetic characteristics of C. sclerophylla and L. glaber were moderate among the four species. (4) In all four seasons, the relative chlorophyll content of C. glauca was the highest among the four dominant species, while that of P. massoniana was the lowest. All these results indicate that P. massoniana and C. sclerophylla are shade intolerant species and moderately shade intolerant species, respectively, while L. glaber and C. glauca are strongly shade tolerant species, although C. glauca is more strongly shade tolerant when compared with L. glaber. Based on these findings, we concluded that P. massoniana and C. sclerophylla will withdraw from the community during the succession. L. glaber and C. glauca will become the dominant species in the secondary forest surrounding Qiandao Lake as these forests mature.