Study On The Ecophysiological Characteristics Of Desert Plant-Yucca Brevifolia Seedlings

In order to ascertain the befitting environment for growth of Yucca brevifolia seedlings in greenhouse, such as soil matrix, illumination and moisture, experiments were done to research the effects of different ratios of sand to soil on photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Gs), water use efficiency (WUE), osmotic adjustment substances and antioxidant enzyme of biennial seedlings. Based on this, the change rules of physiological indicators such as morphology, relative water content (RWC), photosynthetic characteristics, SPAD value, soluble sugar, proline of triennial Yucca brevifolia seedlings under the condition of shading treatment (natural light,60%luminousness,20%luminousness) and water stress (normal, moderate, severe) were studied. The experimental results proved that:(1) When the ratio of sand to soil was about7:3, Pn, Tr and Gs of the seedlings were maximal, while WUE was minimum. When the ratio of sand to soil was around5:5, the daily mean WUE was highest (7.366μmol·m-2·s-1).(2) With the increase of sand in soil, the Pro of seedlings rose firstly, then began decreasing tardily. When the ratio of sand to soil was5:5,the Pro of the seedlings was highest (4.886μgμg-1), and the mass fractions of soluble protein (Pr) was higher(15.554mg-g-1). The activity of CAT reduced with the sand ratio increasing.(3)The effects of shading treatments and water stress on ecophysiological characters of triennial seedlings were that water stress led the decline of Pn, Gs and WUE of seedlings. And the severer the water stress was, the more the indexes declined. The highest Pmax (8.103μmol·m·s-1) occurred under the condition of natural light and normal water supply, and the lowest Pmax(2.541μmol·m·s-1) occurred under the condition of20%luminousness and severe water stress. LSP under all treatments were severe water stress>normal water supply>moderate water stress. The change rules of WUE were similar under all treatments. But the highest WUE under natural light and severe water stress was11.756μmol·m-2·s-1, obviously higher than other treatments.(4)Under water stress,60%luminousness made leaf width of seedlings larger and Pn, Tr, Gs obviously higher. While20%luminousness made all ecophysiological indexes obviously decreased. Under the same illumination, SPAD value obviously decreased with the severer of water stress. Under the same moisture condition, the SPAD value of seedlings increased with the light transmittance decreased. Under the same illumination intensity, RWC decreased with the severer of water stress. Under the of the same moisture condition, RWC increased with the light transmittance decreased. Under the same moisture condition, soluble sugar decreased with the decreasing of light transmittance. Under the condition of normal water supply and severe water stress, mass fraction of Pro decreased with the decreasing of light transmittance. While the change rule is opposite when moderate water stress. Under the condition of shading treatment, Pro increased with the severer the water stress was. There were few differences in total nitrogen content of seedlings under the condition of natural illumination and60%luminousness. The total nitrogen content obviously increased under20%luminousness and water stress condition. There were few differences in TOC under all treatments. Under the same moisture condition, cellulose content of seedlings decreased with the light transmittance decreased. In summary, the Yucca brevifolia nursery,under the sand ratio of about5:5substrate can improve the ability of osmotic and water use efficiency, it is good for improve the ability of seedling to respond to environmental stress in the sand environment; In greenhouse cultivation, choosing natural light and severe water stress can increase WUE and LSP of seedlings, and decrease LCP of seedlings. it is good for seedlings’adaptability to high light intensity and severe water shortages after transplanting to sandy zone; after transplanting seedlings to sandy area, to reduce damage due to dramatic changes in the growing environment of the seedlings, you can make the appropriate shading to seedlings (shading transmittance is approximately60%after shading). It’s in favor of improving the survival rate and photosynthetic capabilities of transplanted seedlings. It plays an important role for successfully transplanting of Yucca brevifolia in the desert regions of our country.