Studies On The Photosynthetic Characteristics Of Dominant Shrubs In Different Restoration Stages In Degraded Shrub Of Upper Reaches Of Minjiang River

According to the time series of ecological restoration, the 8-year abandoned fields, 19-year natural community, and 12-year and 19-year artificial community were selected in Dagou valley in Maoxian, upper reaches of Minjiang River. Using portable photosynthesis system CI-310, main photosynthetic indices of four dominant species, Rubus setchuenensis, Corylus yunnanensis, Campylotropis macrocarpa and Quercus liaotungensi, were measured, including daily variations of net photosynthetic rate (Pn), photosynthetic photon flux density (PPFD), CO₂ concentration, leaf temperature (T_leaf), relative humidity (RH), evaporation (Tr), intercellular CO₂ concentration (Ci), stomatal conductance (Gs). Using plant canopy analyzer (LAI-2000), canopy structure parameters were measured, including gap fraction (GF), leaf area index (LAI) and mean leaf angle (MLA). Variation of canopy structure and light environment in different restoration stages were summarized. Results were as follows:For photosynthetic characteristics: the average net photosynthetic was in the order of C. macrocarpa,Q. liaotungensis,C. yunnanensis , R. setchuenensis. Similar to C. yunnanensis, R. setchuenensis had a high compensation point (LCP). C. macrocarpa was was lowest in light saturation point (LSP) and LCP. Q. liaotungensis was the hightest LCP.A11 above implied that the photosynthesis system of C. macrocarpa had a higher efficiency under low irradiation while Q. liaotungensis had a higher efficiency under high irradiation.The traits of daily Pn--PPFD curve were that the maximum Pn appear at 10:00, the diurnal variation of net photosynthetic rate of Q. liaotungensis and C. macrocarpa showed unimodal rise-and-fall pattern , however, R. setchuenensis and C. yunnanensis were twin-peaked pattern, which appeared "phytosynthetic depressed"in the noon that related to stometal restriction factors. C. macrocarpa photosynthesis system showed "high photosynthetic rate and high transpiration rate"characteristic, and R. setchuenensis revealed opposite results. Among these species, C. macrocarpa had higher net photosynthetic rates(Pn), transpiration rates(Tr), dark respiration(Rd), and lowest water use efficiency(WUE) and LCP. Q. liaotungensis had the highest Pn, LCP, and lower WUE and Tr. So these made it in a favourable position to get dominating status for occupying the community space. The physiological index of phytosynthesis, respiration, transpiration for R.setchuenensis and C. yunnanensis were relatively weak among these four dominant species.With the time of degraded shrubs community restoration, the indices related to photosynthesis :Pn, LCP, LSP, Rd, Gs, Ci were decrease. But Chl concentration, Nitrogen concentration increased. Canopy structure parameters as: PPFD, GF and MLA decrease accordingly. LAI has a trend of increase. The restoration of natural forest with good ecological function, and to promote the degradation of the effective restoration of vegetation.