Study On Photosynthetic Characteristics Of Several Plants In Forest Canopy Gap Of The Cypress Plantation

The cypress plantation is the main types of the protection froest in the central Sichuan hilly region. Early completion it greatly improved the ecological environment in the region.And its efficiency significantly of soil and water conservation. Due to the planting design, seedling quality, post management and other factors, most of the cypress artificial forest became inefficient forest.Urgent need to improve forest ecosystems through reasonable ways and means services. To study the growth, photosynthetic characteristics and physiological of planted Cinnamomum septentrional and Toona sinensis and various plants of vegetation natural regeneration(trees:Ligustrum lucidum, Rosaceae broussonetia, Vernicia fordii; shrubs:Vitex negundo, Rhus chinensis, Rutaceae Zanthoxylum; herbaceous: Arthraxon hispidus, Carex brunnea, Ficus tikoua) under different size of forest gaps, to know the response of the light intensity, we were selected three different size of forest gaps including 50 m2(Ⅰ),100 m2 (Ⅱ),200 m2 (Ⅲ) and opening field (KD), which were in a cypress plantation in the central Sichuan hilly region. The main results were found as follows:(1) The photosynthetically active radiation and temperature of gaps Ⅲ was significantly higher than the gaps and gaps Ⅰ or Ⅱ (p<0.05), while air humidity is lower (p<0.05). The photosynthetically active radiation and temperature diurnal variation exhibited a single peak. The peak of photosynthetically active radiation was at 12:00, and temperature’s was 14:00. The diurnal variation of air humidity was two peaks and valleys appear in 14:00. The magnitude of diurnal variation of photosynthetically active radiation, temperature and air humidity in gaps Ⅲ was greater than gaps Ⅰ and gaps Ⅱ. By principal component factor analysis showed differences in the kind of habitat is mainly affected by the photosynthetically active radiation. The photosynthetically active radiation appeared the change of gradient by gap center>gap pericenter>gap edge and gap center had a significant difference with gap edge (p< 0.05). The PAR gradually increased with the increase of the gap size, light intensity heterogeneity reduces in turn. There were no significant difference between gap Ⅰ and gap Ⅱ (p> 0.05).(2) The growth characteristics of Cinnamomum septentrional and Toona sinensis. Cinnamomum septentrional and Toona sinensis’s tree height, diameter and crown area were the highest in the gaps Ⅱ. And which in full light of open areas (KD) was minimum. The timber volume of height growth of Cinnamomum septentrional has increased and diameter growth reduced compared with the first growing season. The amount of tree height and diameter growth of Toona sinensis showed an increasing trend. The tree height, diameter and crown area of Toona sinensis were significantly higher than Cinnamomum septentrional. The leaf morphological characteristics of Cinnamomum septentrional and Toona sinensis:The dry weight ratio (LMA) of Cinnamomum septentrional and Toona sinensis were increased with the increase of the gap size. The leaf of Cinnamomum septentrional and Toona sinensis was significantly smaller blade becomes thickened.The leaf thickness of Cinnamomum septentrional were significantly higher than Toona sinensis.(3) The net photosynthetic rate (Pn) of diurnal variation of Cinnamomum septentrional in gapsIII and Cinnamomum septentrional and Toona sinensis in KD has obvious "midday depression of photosynthesis".The Pn of Cinnamomum septentrional reduction was mainly affected by stomatal factors, and Toona sinensis is a non-stomatal dominant limiting factor. The Pn and gas exchange parameters (stomatal conductance (Cond), transpiration rate (Tr), stomatal limitation value (Ls) and water use efficiency (WUE)) of Cinnamomum septentrional and Toona sinensis were gradually increased with the increase in forest area of the window (p<0.05). But the intercellular carbon dioxide concentration (Ci) of Cinnamomum septentrional and Toona sinensis decreased (p<0.05). In the same area of forest gap, the Pn, Cond, Tr, WUE of Toona sinensis were higher than Cinnamomum septentrional (p<0.05) and Ci, Ls were relatively lower (p<0.05).(4) The maximum of light response parameters (initial quantum efficiency (a), maximum net photosynthetic rate (Pmax), dark respiration rate(Rd)) and CO2 response parameters (apparent carboxylation efficiency (CE), maximum photosynthetic rate table (Pnmax)) of Cinnamomum septentrional and Toona sinensis were in gaps II or III. The light compensation point (Lcp) of Cinnamomum septentrional and Toona sinensis overall with increasing gap size increases. And the light saturation point (Lsp) in the gaps difference was not significant (p> 0.05), but significantly higher than the all-optical environment open areas. In the same area of forest gap, the a, Pmax, Rd, CE, Pnmax of Toona sinensis higher than Cinnamomum septentrional, while Vcmax and Jmax low.(5) The leaf chlorophyll a (Chla), chlorophyll b (Chl b), carotenoids (Cars) of Cinnamomum septentrional and Toona sinensis is reduced with increasing of forest size. But the Chla/Chlb value and soluble protein (SP), malondialdehyde (MDA) content and superoxide dismutase (SOD) activity increases. In the second growing season, the MDA of Cinnamomum septentrional and Toona sinensis were significantly decreased than the first growing season (p<0.05).(6) With the increase of gap size, the total nitrogen (Nm), nitrogen content per unit leaf area (Naera), light nitrogen utilization (PNUE) and leaf nitrogen in bio-energetics component (photosynthetic electron transfer and photosynthetic phosphorylation carrier protein component) partition coefficient (PB), leaf nitrogen in carboxylation system partition coefficient (Pc) of Cinnamomum septentrional and Toona sinensis were significantly increased (p<0.05). The leaf nitrogen in chlorophyll-protein complexes (PS Ⅰ, PS Ⅱ, LCH Ⅱ) in the distribution coefficient (PL) is gradually reduced (p<0.05).The NmT Naera, Pmax, PNUE, Pc of Toona sinensis was significantly higher than Cinnamomum septentrional (p<0.05), while the PL is lower, and the PB was not significant (p> 0.05). The PNUE of Cinnamomum septentrional and Toona sinensis with Nm negatively correlated and correlation reached a significant level (p< 0.01), while the relationship with the LMA did not reach significant levels (p> 0.05). The Pmax of Cinnamomum septentrional and Toona sinensis increases with increasing Nm, but did not reach significant levels (p> 0.05). The Pmax was negatively correlated with the LMA, but the relationship was not significant (p> 0.05).(7) The LMA, Naera, Pn, Cond, Tr, a, Pmax, Rd, Lcp and PNUE of various plants in the gao were higher understory (p<0.05). But the Ci was significantly lower than the understory (p<0.05). The Naera, Pn, Cond, Tr, a, Pmax, Rd, Lcp of various plants were decreased when the gap size more than 100m2. But the LMA still showed an increasing trend. The LMA of various plants rendered tree layer> shrub layer> herb layer (p<0.05). The PNUE of shrub and herb layers was higher than the tree layer. The LMAof various plants was negatively correlated with PNUE. The LMA of shrub layer and herb layer was positively correlated with Pmax. The LMA of tree layer is negatively correlated with Pmax.In summary, a appropriate forest gap (100-200 m2) has showed a significant role in promoting photosynthetic capacity and growth of Cinnamomum septentrional and Toona sinensis. On the same time, the photosynthetic capacity of natural regeneration has also been improved significantly (50-100 m2). It can make a contribution to not only maintaining and improving ecosystem services, but also enhancing the adjustment of tree structure.