Growth and physiological responses of Agriophyllum squarrosum to sand burial stress

Agriophyllum squarrosum is an annual desert plant widely distributed on mobile and semi-mobile dunes in all the sandy deserts of China. We studied the growth and physiological properties of A. squarrosum seedlings under different sand burial depths in 2010 and 2011 at Horqin Sandy Land, Inner Mongolia to understand the ability and mechanism that A. squarrosum withstands sand burial. The results showed that A. squarrosum had a strong ability to withstand sand burial. Its survival rate, plant height and biomass increased significantly at a burial depth 25% of seedling height and decreased significantly only when the burial depth exceeded the height of the seedlings; some plants still survived even if the burial depth reached 266% of a seedling height. The malondialdehyde （MDA） content and membrane permeability of the plant did not change significantly as long as the burial depth was not greater than the seedling height; lipid peroxidation increased and cell membranes were damaged if the burial depth was increased further. When subjected to sand burial stress, superoxide dismutase （SOD） and peroxidase （POD） activities and free proline content increased in the seedlings, while the catalase （CAT） activity and soluble sugar content decreased. Sand burial did not lead to water stress. Reductions in photosynthetic area and cell membrane damage caused by sand burial may be the major mechanisms increasing mortality and inhibiting growth of the seedling. But the increases in SOD and POD activities and proline content must play a certain role in reducing sand burial damage.

Afforestation effects on soil microbial abundance, microbial biomass carbon and enzyme activity in dunes of Horqin Sandy Land, northeastern China

In order to investigate the effects of afforestation on soil microbial abundance, microbial biomass carbon and enzyme activity in sandy dunes, 20-year-old Pinus sylvestris var. mongolica Litv. （PSM） and Populus simonii Carri6re （PSC） mature forests were se- lected in Horqin Sandy Land, and mobile dunes was set as a control （CK）. Results show that PSM and PSC plantations can im- prove soil physicochemical properties and significantly increase microbiological activity in mobile dunes. Soil microbial abun- dance, microbial biomass carbon and enzyme activity show an order of PS〉PSM〉CK. Total soil microbial abundance in PSM and PSC was respectively 50.16 and 72.48 times more than that in CK, and the differences were significant among PSM, PSC and CK Soil microbial biomass carbon in PSM and PSC was respectively 23.67 and 33.34 times more than that in CK, and the difference was insignificant between PSM and PSC. Soil enzyme activity, including dehydrogenase （DEH）, peroxidase （PER）, protease （PRO）, urease （URE） and cellobiohydrolase （CEL） in PSM and PSC were respectively 19.00 and 27.54, 4.78 and 9.89, 4.05 and 8.67, 29.93 and 37.46, and 9.66 and 13.42 times of that in CK. R sylvestris and P. simonii can effectively improve soil physico- chemical and microbiological properties in sandy dunes and fix mobile dunes in Horqin Sandy Land. The Cmic：C ratio is an appli- cable indicator to estimate soil stability and soil water availability, and based on an overall consideration of plantation stability and sustainability, R sylvestris is better than R simonii in fixing mobile dunes in sandy land.

Effects of sand burial on survival and growth of Artemisia halodendron and its physiological response

There is a great deal of literature on the effects of sand burial upon the survival and growth of desert plants, but the physiological adaption mechanisms of desert plants to sand burial have as yet rarely been studied. Artemisia halodendron is widely distributed in the semi-arid deserts of China and is a dominant species in semi-moving dune vegetation. The growth and physiological properties ofA. halodendron seedlings under different sand burial depths were studied in 2010 and 2011 in the Horqin Sand Land, Inner Mongolia, to better understand the ability and physiological mechanism by which desert plants withstand sand burial. The results showed that A. halodendron as a prammophyte species had a stronger ability to withstand sand burial compared to non-prammophytes, with some plants still surviving even if buried to a depth reaching 225% of seedling height. Although seedling growth was inhibited significantly once the depth of sand burial reached 50% of the seedling height, seedling survival did not decrease significantly until the burial depth exceeded 100% of the seedling height. Sand burial did not result in significant water stress or MDA （Malondialdehyde） accumulation in the seedlings, but membrane permeability increased significantly when the burial depth exceeded 100% of the seedling height. After being subjected to sand burial stress, POD （Peroxidase） activity and proline content increased significantly, but SOD （Superoxide Dismutase） and POD activities and soluble sugar content did not. The primary mechanism resulting in in- creased mortality and growth inhibition were that cell membranes were damaged and photosynthetic area decreased when subjected to the severe stress of sand burial, while proline and POD played key roles in osmotic adjustment and protecting cell membranes from damage, respectively.

Screening of cellulose decomposing fungi in sandy dune soil of Horqin Sandy Land

Cellulose decomposing fungi play an important role in litter decomposition and are decisive in nutrient cycling in sandy land ecosystems. Thirty-one strains were isolated to select efficient cellulose decomposers, and four efficient cellulose decomposing fungi （NM3-1, NM3-2, NM3-3, and NM3-4） were screened using a CMC （carboxymethyl cellulose） carbon source in dune soil of Horqin Sandy Land. They were identified as Asperigillus calidoustus, Fusarium oxysporum, Fusarium solani, and Hypocrea lixii by rDNA-ITS molecular biological methods. Cloth decomposition rates were 15.71%, 15.89%, 17.29%, and 17.89% by the four efficient decomposers incubated for 30 days, respectively. Screening of efficient cellulose decomposers can not only increase the dune soil functional microbe bank, but can also accelerate litter decom- position and available nutrient input in the Horqin Sandy Land.