Response Of Indicator Species(Iris Lactea Pall. Var. Chinensis Koidz) Of Grassland Degradation In Songneng Plain To Saline-alkali Environment

Vegetational and edaphic indicators were screened to assess different degree of degeneration of grassland in Songnen Plain. An indicator plant positive to degeneration was confirmed. In different degree of saline and alkali conditions controlled in lab or under field, contents as followed were determined: the absorption, transportation and distribution of major cations (Na⁺, K⁺, Ca²⁺and Mg²⁺) in indicator plant; organic solute (proline and soluble sugar), and antioxidase activities, including superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD); characteristics of individual, population and community of the plant. Responses of the indicator plant to environment from physiological to community aspects were systemically discussed in this document.(1) Vegetional characteristics and edaphic indicators including bare patch index, dry biomass, percent cover by perennial plants, growth indicators of Leymus chinensis, soil organic matter and pH were sensitive to saline-alkali grassland degeneration. We also used the indicators screened to classify the study sites by the cluster analysis method and got four groups: health, light degeneration, middle degeneration and severe degeneration grassland. Iris lactea Pall. var. chinensis Koidz was present in the grassland of middle degeneration. I. lactea was the dominant species in grassland of severe degeneration. I. lactea was the indicator plant of grassland of middle and severe degeneration.(2) Treatments of NaCl, Na2CO3 and the mixture of the two salts caused increases in Na⁺ concentration, proline content and Electrolyte leakage rate (REL) and decreases in root Mg²⁺ and K⁺ content. Increased Ca²⁺ and antioxidase activities were observed at lower external Na⁺ concentrations. However, at higher external Na⁺ levels, decreased Ca²⁺ and antioxidase activities were detected. Alkaline salt resulted in more damage to I. lactea than neutral salt, including lower SOD, POD and CAT activities and decreased proline content relative to neutral salt. High Na⁺ and low K⁺ in I. lactea intensified ion toxicity under alkaline condition. Alkaline salt caused greater harm to plants than neutral salt, the primary reason of which might be the lower Ca²⁺ content in the plant under alkaline salt stress.(3) The cation contents in I. lactea varied in different months. Contents of the four cations increased with growth of I. lactea before June. Ca²⁺ and Na⁺ contents in roots were highest in July with the value of 2.30% and 0.51%, respectively. K⁺ and Mg²⁺ in roots were highest in September (0.27%) and October (0.28%), respectively. The Leaf Na⁺ content in July was highest with the value of 0.57%.The highest values of K⁺, Ca²⁺ and Mg²⁺ in leaves were 1.30%, 2.69% and 0.47%, respectively, which all presented in August. In July and August, the selective absorption (SA) by I. lactea for K⁺ over Na⁺ was higher, while the selective transport (ST) was lower. The cation contents in I. lactea were significantly higher than those in soil, which indicated that I. lactea had high accumulation capacity of these cations. The accumulation of cations by I. lactea was mainly distributed from 40cm underground to 30cm aboveground. The distributions of Na⁺, K⁺, Ca²⁺and Mg²⁺ in the individual of I. lactea aboveground were 9.11, 4.07, 0.98 and 2.27 times of those in the underground, respectively.(4) Electric conductivity (EC) and pH had negative relation with K⁺ content, positive relation with Na⁺ content, and no significant relation with Ca²⁺, Mg²⁺ and Ca²⁺/Na⁺ ratio in I. lactea. K⁺/Na⁺ in I. lactea decreased with increasing of EC and pH, which showed exponential relationship. Conditions with higher saline and alkali levels were favourable to competition of Na⁺ for K⁺. High pH enhanced poison of Na⁺ for plants. K⁺, K⁺/Na⁺ ratio in leaves were significantly negative to soil Na⁺, CO32-, HCO3-, Cl- and moisture, and significantly positive to soil Mg²⁺,Ca²⁺/Na⁺ and K⁺/Na⁺ ratio. Na⁺ contents in leaves were significantly negative to soil K⁺/Na⁺ ration, and significantly positive to soil Na⁺, CO32-, HCO3-, Cl- and moisture. Ca²⁺ and Mg²⁺ content in leaves had no significant relationship with all the ions in soil, except that Mg²⁺ was significantly positive to soil K⁺/Na⁺. Enhancing K⁺/Na⁺,Ca²⁺/Na⁺ in soil was better for increasing tolerance to saline-alkali environment than only increasing Ca²⁺ content.(5) Soluble sugar (SS) and proline in leaves increased with pH and EC, they are both compatible solutes for I. lactea. Soil Na⁺, CO32-, HCO3-, Cl- contents and moisture were significantly positive to the contents of SS and proline in leaves, and were main stress factors for plants. Ca²⁺, Ca²⁺/Na⁺, K⁺/Na⁺ ratio and organic matter could possibly eliminate stress effects by ions stated above.(6) SOD, POD and CAT activities had decreasing trend in the growing season. The highest activities of SOD, POD and CAT were present in May, June and May, respectively. The lowest value of SOD, POD and CAT was present in August, September and August, respectively. EC and pH had linear and exponent curve, respectively. SOD, POD and CAT activities were significantly positive to soil Na⁺, CO32-, HCO3-, Cl- and moisture. SOD activities were significantly negative to soil Ca²⁺, organic matter and K⁺/Na⁺ ratio; POD activities were significantly negative to soil Ca²⁺, organic matter, Ca²⁺/Na⁺ and K⁺/Na⁺ ratio. CAT activities were significantly negative to soil Ca²⁺/Na⁺ and K⁺/Na⁺ ratio. (7) Caloric value of leaves and roots in I. lactea increased gradually with growth and reached the highest in September, then decreased. The caloric value of different organs was different. The order of caloric value of organs was seed >leaf >root >flower. Seasonal dynamics of caloric value was mainly because climatic factors. The energy stored by I. lactea aboveground was mainly distributed from 0 to 40cm underground, with occupied 91.6% of the total energy aboveground. The energy stored by I. lactea underground was mainly distributed from 0 to 80cm underground, with occupied 88.6% of the total energy underground. The caloric value of leaves was significant positively to soil pH and EC, which was perhaps due to the increase of soluble sugar and proline with soil pH and EC. The caloric value of leaves had no significant relationship with soil moisture and organic matter, however it showed quadraticy curve(y = -64358x2 + 8975.6x + 3663.2) with soil N content. The caloric value of roots had no significant relationship with soil moisture, pH, EC, N, and organic matter.(8) Soil pH had no significant relationship with abundance, biodiversity index, average height and density in I. lactea community, but had significantly negative to biomass per unit of I. lactea. Soil pH from 9.358 to 10.069 was most suitable for I. lactea growth. The relationships with soil EC, N content, organic matter and moisture and abundance, biodiversity index, average height and density in I. lactea community were not significant. Soil EC and moisture had negative effects on I. lactea growth. Soil N content had no significant effects on the biomass per unit of I. lactea.