The Physiological Characteristic Of Drought Resistant And Fluorescence Dynamical Mechanism Of Main Trees In Losses Hill Area

The semi-arid hill area of Loess Plateau is the typical fragile area in our country. In this region, moisture is the key factor to limit the vegetation restoration and reconstruction. Considering semi-arid hill area of Loess Plateau scarce water resource, eight trees of Fraxinus rhynchophyila Hance., Rosa roxburghii Tratt., Rhus typhina L., Acer buergerianum Miq., Morus mongolica Schneid., Morus alba Linn., Xanthoceras sorbifolia Bunge. and Acer mono Maxim. were chose as experimental material to carry out pot experiment in Chemingyu forestry center, Zhongyang county, Shanxi province. Mensuration technology, an analysis theory of gas exchange and chlorophyll fluorescence, was used. In this study, we clarified continuous variety process of gas exchange parameters, such as photosynthesis rate, transpiration rate and water use efficiency etc., and chlorophyll fluorescence parameters from soil saturation humidity to languish humidity; revealled the critical soil moisture in which photosynthesis characteristic parameters took remarkable changes, and its mechanism of taking remarkable changes; and also confirmed the fitting soil moisture range mainting higher photosynthesis rate and water use efficiency. The results have the theoretic value to the practical meaning of scientific directing the reasonable tree choice and fitting area and trees in semi-arid Loess Hilly region. The main results are as follows:(1) The gas exchange parameters of eight trees have notable threshold response value to soil moisture and photosynthetic active radiation.â‘ The range of relative water content (RWC) being suitable for the growth of Fraxinus rhynchophyila Hance., Rosa roxburghii Tratt., Rhus typhina L., Acer buergerianum Miq., Morus mongolica Schneid., Morus alba Linn., Xanthoceras sorbifolia Bunge. and Acer mono Maxim. was 39.5%～71.1%, 43.6%～73.3%, 37.9%～72.4%, 37.3%～71.5%, 41.6%～79.3%, 42.7%～70.3%, 42.7%～70.3%, 44.2%～73.2% and 49%～74.1% respectively. The maximum soil moisture deficit was 31.7%, 36.5%, 28.8%, 29.8%, 34.6%, 34.7%, 37.6% and 33.1%, respectively. The range of most suitable PAR was 500～1100, 300～1100, 300～1300, 300～900, 500～900, 500～1100, 500～1100 and 500～1300μmol·m^-2·s^-1, respectively. According to maximum soil moisture deficit, the drought resistance are Rhus typhina L., Acer buergerianum Miq., Fraxinus rhynchophyila Hance., Acer mono Maxim., Morus mongolica Schneid., Morus alba Linn., Rosa roxburghii Tratt. and Xanthoceras sorbifolia Bunge. in succession.â‘¡The apparent quantum yield (Φ), dark respiration rate (R_d) and light compensation points (LCP) was affected by soil moisture apparently and had notable threshold response to RWC. According to the utilization of low light intensity, the sequence was Rhus typhina L., Morus mongolica Schneid., Fraxinus rhynchophyila Hance., Morus alba Linn., Acer buergerianum Miq., Acer mono Maxim., Rosa roxburghii Tratt. and Xanthoceras sorbifolia Bunge.. According to the consume photosynthesis production, the sequence was Morus mongolica Schneid., Rhus typhina L., Fraxinus rhynchophyila Hance., Morus alba Linn., Xanthoceras sorbifolia Bunge., Acer buergerianum Miq., Rosa roxburghii Tratt. and Acer mono Maxim.. Based on the ability of shade enduring, the sequence was Fraxinus rhynchophyila Hance., Rosa roxburghii Tratt., Rhus typhina L., Acer buergerianum Miq., Morus mongolica Schneid., Morus alba Linn., Xanthoceras sorbifolia Bunge. and Acer mono Maxim.(2) Soil moisture effected CO₂ response process of gas exchange parametersâ‘ Research on CO₂ response process of gas exchange parameters under different soil moisture is meaningful to clarify the response characteristic to CO₂ concentration and soil moisture. When RWC was higher than 75%, T_r and Gs appeared degressive trend, but P_n did not; When RWC was 60%～75%, P_n reduced slowly after CO₂ saturation points, T_r and Gs reduced sharply, while WUE maintained higher value. With the increase of water threatening, the CO₂ saturation points of P_n, T_r and Gs reduced notably and the trait of fighting a drought was improved. P_n, T_r and Gs all kept at very low level under severe water stress.â‘¡The carboxylation efficiency (CE), CO₂ compensation points (Γ) and photorespiration rate (R_p) had notable threshold value to the variety of soil moisture. The CE and R_p increased gradually and reached to the maximal value when RWC was about 70%, and then fell gradually. WhileΓpresented the opposite rule. When RWC was about 60.1%～70.3%, it reached to the minimal value. Rosa roxburghii Tratt. had the highest CE, the next was Fraxinus rhynchophyila Hance.. The results also presented that all of the eight trees are typical C₃ plants, and the R_p of Fraxinus rhynchophyila Hance. and Rosa roxburghii Tratt. was higher than that of others.(3) The response process and mechanism of daily dynamics of photosynthesis characteristic parameters to the variety of soil moistureâ‘ Soil moisture effected daily dynamics process of gas exchange parameters notablyWhen RWC was higher than 75%, the curve type of P_n, T_r and Gs was single curve, and the difference of WUE was unapparent; When RWC was 60%～75%, Fraxinus rhynchophyila Hance., Acer buergerianum Miq., Morus alba Linn. and Acer mono Maxim. did not present notable midday photosynthesis depression, and the curve type of T_r, Gs and WUE was double curve; When RWC was 45%～60%, the curve type of P_n, T_r and Gs was double curve, and the curve type of WUE of Rosa roxburghii Tratt., Acer buergerianum Miq. and Xanthoceras sorbifolia Bunge. was single curve, the other trees'curve was double curve; When RWC was lower than 40%, P_n and T_r presented severe middy depression and typical concave curve. The WUE of the other trees all maintained higher value except Morus alba Linn..â‘¡Soil moisture effected photosynthesis efficiency significantlyWhen RWC was higher than 75%, the daily average value of P_n in eight trees was equable; When RWC was 60%～75%, the P_n of other trees maintained maximal except Acer mono Maxim., Fraxinus rhynchophyila Hance. had the highest P_n, and had unconspicuous differentia with Morus alba Linn.; When RWC was 45%～60%, Acer mono Maxim. had the highest P_n, Morus alba Linn. was the second, and Acer buergerianum Miq. had the minimal P_n.When RWC was higher than 75%, the T_r in eight trees changed obviously, among them, Rhus typhina L. had the highest T_r, Acer buergerianum Miq. was second, and Acer mono Maxim. had the minimal T_r; When RWC was 60%～75%, the T_r maintained the highest, Rhus typhina L., Morus alba Linn. and Xanthoceras sorbifolia Bunge. had higher T_r than Rosa roxburghii Tratt., Acer mono Maxim., Fraxinus rhynchophyila Hance., Acer buergerianum Miq. and Morus mongolica Schneid.; When RWC was 45%～60%, Morus alba Linn. had the highest T_r.When RWC was higher than 75%, Acer mono Maxim. had the highest WUE, Fraxinus rhynchophyila Hance. was the second, and Acer buergerianum Miq. had the minimal WUE; When RWC was 60%～75%, Fraxinus rhynchophyila Hance. had th highest WUE, Morus mongolica Schneid. was second, and Rhus typhina L. had the minimal WUE; When RWC was 45%～60%, the WUE maintained the highest, Fraxinus rhynchophyila Hance. had the highest WUE, the other was Morus mongolica Schneid., Xanthoceras sorbifolia Bunge., Acer mono Maxim., Morus alba Linn., Acer buergerianum Miq., Rosa roxburghii Tratt. and Rhus typhina L. in turn, in addition, Acer buergerianum Miq., Rosa roxburghii Tratt. and Rhus typhina L. had unconspicuous differentia.â‘¢Soil moisture affected photosynthesis photoinhibition, the increase of thermal dissipation was the main mechanism to resist photoinhibitionWhen RWC was higher than 75%, photosynthesis photoinhibition did not occurred in eight trees, the fall of P_n in the afternoon was caused by non-stomatal limitation; When RWC was 45%～75%, obvious photosynthesis photoinhibition appeared in eight trees, and the degree of photoinhibition fell with the melioration of water stress,. The reason causing P_n fall turned from stomatal limitation to non-stomatal limitation after 13:00. When RWC was lower than 40%, the photosynthetic apparatus photooxidation was destroyed. Nonphotochemical quenching coefficient hoist in the middy under different soil moisture, indicating that the increase of thermal dissipation was one of the main mechanism to resist photoinhibition and relief middy photosynthesis depression.(4) The leaf gas exchange parameters had seasonal variation and diurnal dynamicsIn CK condition, the P_n of Morus alba Linn. and Acer buergerianum Miq. showed a single curve; In T₁ disposal, the maximal value and daily average value of Morus alba Linn. and Acer buergerianum Miq. all reached to the highest in July, and to the lowest in September. the P_n showed a double curve in May and September, and single curve in July. In T₂ disposal, Morus alba Linn. showed a single curve, Acer buergerianum Miq. showed a double curve in May, and a single curve in July and September. The maximal value and daily average value of Morus alba Linn. presented obvious seasonal variation, and had conspicuous differentia in different growth period.In CK condition, the T_r of Morus alba Linn. was the highest in July, and had conspicuous differentia with the T_r in May and September, but the T_r of Acer buergerianum Miq. had unconspicuous differentia in May and July. The daily average value of two trees had conspicuous differentia. In T₁ disposal, two trees took on double curve in May and July; In T₂ disposal, two trees took on transpiration middy depression in May, and put up single curve in July and September. The Tr of Morus alba Linn. was higher than that of Acer buergerianum Miq. obviously; In T₃ disposal, the Tr of two trees always maintained very low value.The curve of WUE of two trees changed tardily, and took on unconspicuous double curve. In a word, the WUE in the forenoon was higher than that in the afternoon. The WUE of Acer buergerianum Miq. was higher than that of Morus alba Linn. in different growth period. The maximum value of WUE took on in T₂ disposal under different water disposal, the next is in T₁ disposal. The WUE in May was higher.(5) The photosynthesis photoinhibition, photochemistry efficiency and thermal dissipation in different growth periodIn CK condition, Morus alba Linn. and Acer buergerianum Miq. did not take on obvious photoinhibition and electron transport efficiency depression. The value of maximal quantum yield of PSâ…¡in the dark (F_v/F_m), actural photochemistry efficiency of PSâ…¡(Φ_PSâ…¡) and non-photochemical quenching coefficient (NPQ) was higher in July, the next was in May. In T₁ and T₂ disposal, two trees all took on obvious photoinhibition and electron transport efficiency depression, and the time occurring photoinhibition brought forward. Morus alba Linn. had higher ability to resist photoinhibition and electron transport efficiency than that of Acer buergerianum Miq.. Two trees had higher ability to consume surplus energy.In CK condition, the fall of P_n was caused by non-stomatal limitation. In T₁ disposal, the fall of P_n in the forenoon was caused by stomatal limitation, and then turned to non-stomatal limitation in the afternoon. In May and September, the turning point occurring non-stomatal limitation was at 13:00, and brought forward 11:00 in July. With the aggravation of water stress, the time occurring non-stomatal limitation forward. In T₃ disposal, the fall of P_n was caused by non-stomatal limitation.