The type, position and age effect on the cutting reproduction of Picea crassifolia and its rooting mechanism in the Qilian Mountains

Picea crassifolia Kom, a perennial arbor spe- cies is recognized as one of the most adaptable plants found to date in Qilian Mountains. To explore the cutting reproduction technology of P. crassifolia and reveal its rooting mechanism, cuttings of P. crassifolia with different cutting types （softwood, hardwood and root）, positions （top, upper, middle and bottom） and ages （7, 10, 15, 20, 25 year-old） were cultivated in a field experiment. One- year old softwood and hardwood cuttings were collected from 7-, 10-, 15-, 20-, and 25 year-old healthy ortets to analyze the changes from endogenous hormones and organic nutrients. Results indicate that the softwood cut- tings （0.5-1.0 cm in diameter） from upper branches of 15 year-old ortets shows better growth performance by improving rooting indexes, including a significant increasein rooting rate and a decrease in basal rot rate. Concomi- tantly, increasing rooting quantity and root length also increased. It is noteworthy that the high rooting rate of P. crassifolia cuttings due to its ability to accumulate high concentrations of indole-3-acetic acid （IAA） and total carbon （TC） rather than abscisic acid （ABA） and total nitrogen （TN）. The rooting rate was mainly regulated by the IAA/ABA and TC/TN ratio. In summary, our results suggest that the softwood cuttings （0.5-1.0 cm in diameter） from upper branches of 15 year-old P. crassifolia can be considered as an effective strategy to improve cutting rooting rate, and the IAA/ABA and TC/TN ratio was one of the main factors limiting the cutting rooting rate of P. crassifolia.

Sand-fixing characteristics of Carex brunnescens and its application with straw checkerboard technique in restoration of degraded alpine meadows

Carex brunnescens（Pers.）, a typical clonal species, is considered to be the only herb found to date that can develop on sand dunes in Maqu alpine region of northwestern China. However, the characteristics that C. brunnescens resists to harsh alpine environment have not been documented. In this study, we conducted a field investigation to determine the morphological, reproductive, and sand-fixing characteristics of C. brunnescens. Concomitantly, we transplanted the belowground rhizomes of C. brunnescens to sand dunes and compared the abilities to restore degraded alpine meadows among sand dunes that had no further treatment（SD＋N）, sand dunes that had straw checkerboard technique but no transplanted rhizomes of C. brunnescens（SD＋SCT）, and sand dunes that had both SCT and transplanted rhizomes of C. brunnescens（SD＋SCT＋P）. We found that belowground vertical rhizomes and horizontal rhizomes（including branching rhizomes and main rhizomes） of C. brunnescens were highly developed and that population reproduction was dominated by horizontal rhizomes. C. brunnescens exhibited a significant sand-fixation effect under following conditions： population density was 145–156 ramets/m^2, vegetation cover was 31.2%–39.3%, total length of belowground rhizomes was 11,223 cm/m^2, total length of belowground first-order roots was 9161–10,524 cm/m^2, fresh weight of aboveground part was 198.5–212.6 g/m^2, and fresh weight of belowground part was 578.8–612.4 g/m^2. It should be particularly noted that SD＋SCT＋P treatment（sand dunes that had both straw checkerboard technique and transplanted rhizomes of C. brunnescens） was the best and SD＋N（sand dunes that had no further treatment） was the worst in terms of following biotic indicators： total number of reproductive ramets, total number of belowground rhizomes, and fresh weight of aboveground and belowground parts of C. brunnescens, contents of soil organic carbon, available nitrogen, microbial biomass carbon, and microbial biomass nitrogen. It implies that applying SCT in sand dunes and transplanting belowground rhizomes to sand dunes with SCT could improve both soil fertility and growth of C. brunnescens. These results suggest that the SCT-promoted high reproductive abilities of belowground rhizomes of C. brunnescens can successfully facilitate the establishment of ramets and can thus be an effective strategy to restore degraded vegetation in Maqu alpine region of northwestern China.

Effects of separate and mutual application of Na and Si on drought resistance of Haloxylon ammodendron

We studied pot cultivated Haloxylon ammodendron＇s growth, physiological changes and drought resistance under NaC1, H2SiO3, and NaCl＋H2SiO3 treatments. Results show that 0.3 g/kg NaC1, 0.2 g/kg HzSiO3 or 0.3 g/kg NaCI＋0.1 g/kg H2SiO3 treatments can effectively promote growth and improve the drought resistance of/-L, ammodendron. Compared with that without NaCI treatment, H. ammodendron＇s height, crown diameter and fresh weight increased by 42%, 91% and 62% respectively under 0.3 g/kg NaC1 treatment, and its main stem diameter, main root diameter and main root length increased by 40%, 39% and 23%, respectively. Compared with that without H2SiO3 treatments, H. ammodendron＇s height, crown diameter and flesh weight increased by 36%, 45% and 27% respectively under 0.2 g/kg HeSiO3 treatment, and its main stem diameter, main root diameter and main root length increased by 23%, 23% and 20%, respectively. Compared with that under 0.3 g/kg NaC1 treatment, H. ammodendron＇s height, crown diameter and fresh weight and main root length increased by 9%, 10%, 17% and 12% respectively under 0.3 g/kg NaCI＋0.1 g/kg H2SiO3 treatment. Compared with that under 0.1 g/kg H2SiO3 treatment, H. ammodendron＇s height, crown diame- ter and fresh weight increased by 28%, 76% and 68% respectively under 0.3 g/kg NaCI＋0.1 g/kg H2SiO3 treatment, and its main stem diameter, main root diameter and main root length increased by 30%, 32% and 27%, respectively. This suggests that moder- ate levels of NaCI＋H2SiO3 interaction can effectively promote growth and improve drought resistance of/-L, ammodendron than separate applications of NaC1 or H2SiO3.