Responses of Caryopsis Germination, Seedling Emergence, and Development to Sand Water Content of Agropyron cristatum （L.） Gaertn. and Bromus inermis Leyss.

Responses of caryopsis germination, seedling emergence, and development of Agropyron cristatum （L.） Gaertn. （Gramineae） and Bromus inermis Leyss. （Gramineae）, two dominant perennial grasses in the Otindag Sandland of China, to different sand water content （SWC; 1%, 2%, 3%, 4%, 6%, 8%, 12%, 16%, and 20%） were studied comparatively. The results showed that the germination responses of the two grasses to SWC were similar （i.e. caryopses could not germinate when the SWC was below 3%; at SWC ranging from 3% to 12%, the higher the SWC, the higher the germination percentage; and at a SWC of 12%-20%, germination reached similarly high percentages）. At a sand burial depth of 0.5 cm, the threshold of SWC for seedling emergence was 6% forA. cristatum and 8% forB. inermis; at 12%-20% SWC, the seedling emergence of both species reached similarly high percentages. The seedling growth responses of these two species to SWC gradients were different. For A. cristatum, the biomass of seedlings increased with SWC from 6% to 12%, and decreased with SWC from 12% to 20%. For B. inermis, the biomass of seedlings always increased with SWC from 8% to 20%. The results also showed that the seedlings of both species allocated more biomass to the roots with decreases in SWC. The SWC changes from April to October in natural microhabitats of both species suggested that the SWC may play an important role in caryopsis germination, seedling emergence, and the growth characteristics of the two grasses. The responses of caryopsis germination, seedling emergence, and the growth characteristics of these two species to SWC may determine their distribution pattems in the Otindag Sandland.

Drought tolerance in three hybrid poplar clones submitted to different watering regimes

Aims Poplars grownin North Chinamay experience water-deficient periods in their life cycle.The aim of the present paper was to quantify the response of three clones to different watering regimes and to determine whichcloneamongthe three is the best adapted to drought conditions.Methods Three hybrid poplar clones(clone DN-34,R-247 and OP-367)were used in the present experiment.The seedlings of the three clones were grown under four watering regimes:control(well watered,100%field water capacity(FC))and three drought treatments(drought stress I,50%FC;drought stress II,40%FC;drought stress III,30%FC).Changes in morphological,physical and biochemical indicators of the three hybrid poplar clones were investigated.Important Findings Drought treatment(50%,40%and 30%FC)decreased net photosynthetic rate(Pn),transpiration rate(Tr),stomatal conductance(gs),shoot height,total biomass and chlorophyll(Chl)content in all the three clones and it increased activities of antioxidant enzymes and free proline content.The highest values of the above-mentioned morphological and physiological parameters were recorded in clone OP-367 under 30%FC,followed by clone DN-34 and R-247.Relative leaf water content(RWC)and stem diameter(sd)markedly declined in clone R-247 and DN-34 under drought stress I,II and III,whereas RWC and sd declined in clone OP-367 only under drought stress II and III.Clone OP-367 had more RWC and sd than DN-34 and R-247.Only the 30%FC induced an increase in the root-to-shoot ratio(rs)and water use efficiency(WUE)in all the three clones.OP-367 was the most efficient clone in water absorption and use,for plants of the clone had the highest values of rs and WUE.Our data demonstrate that among the three clones,OP-367 was better able to maintain photosynthesis and growth and lower the damage caused by drought.