| Picea crassifolia is widely distributed in Qilian Mountains,which is the dominate tree species and play important roles in climate regulation,biodiversity conservation,carbon sequestration,oxygen release and ecological conservation of ecological services as well as important ecological security in arid and semi-arid areas where the ecological environment is vulnerable,northwest of China.In which,the role of water conservation of Picea crassifolia in the poverty of water resource in the region is the most important,which is related to the industrial and agricultural water using in Hexi Corridor area of Gansu Province as well as some areas of Inner Mongolia.Currently,the ecological environment safety of National Nature Reserve of Qilian Mountain has upgraded to the national ecological security strategy.Since the 1960 s,however,deforestation and unreasonable using of land resources as well as mismanagement of Picea crassifolia forest lead to poor recruitment of Qinghai spruce,furthermore,affecting the ecological service function of Picea crassifolia forest.In order to clarify the factors that affects the recruitment of Picea crassifolia,the article focus on the Picea crassifolia forest,studying on the biotic and abiotic factors that influnced the recruitment of Picea crassifolia;both the temporal-spatial and local characteristics of Picea crassifolia are revealed by the field investigations,laboratory experiments and model simulation;the main results are as follows:1.Effects of environmental variables on the recruitment of Picea crassifolia?1?On slope scale,the spatial distribution of seedling-saplings of Picea crassifolia is first affected by the altitude gradient?34.3% of the total variation?,the results showe that the seedling-saplings of Picea crassifolia are the most in the meddle altitude?2900-3250 m?then followed by other environmental factors such as slope,aspect and distance from the parent tree?27.7% of the total variation?and etc.?2?On local scale,the seedling-saplings of Picea crassifolia are affected by moss.The results show that the moss layer with the thickness about 5 cm or the coverage about 50% is the threshold,in which the number of seedling-saplings is the most.2.Effects of moss on the recruitment and seedling-saplings' mortality of Picea crassifolia along autitude gradients?1?The results show that thin moss?5 cm?promotes the recruitment of Picea crassifolia,while thick moss?10 cm?inhibites the recruitment.?2?After the removal of moss?bare soil?,the recruitment of Picea crassifolia decreases with the increase of altitude gradients.In the presence of moss,which promotes the recruitment of Picea crassifolia,the results provide direct evidence for the “stress gradient hypothesis”,indicating that the positive interaction between species is enhanced with the increase of the stress gradient.?3?The results show that in the case of low altitude gradient?2750 m?,moss inhibits the survival of the seedling-saplings of Picea crassifolia,however,with the increase of the altitude gradient,moss decreases the mortality of seesling-saplings,indicating that moss has the “nurse effect” on the recruitment of Picea crassifolia in the harsh environment,implying that the presence of moss potentially expand the niche of Picea crassifolia,also increases the survival rate of Picea crassifolia at the end of stress gradient.3.Effects of allelopathy of moss on germination as well as the moisture gradients on seedling establishment of Picea crassifolia?1?The results show that high concentrations of(50 mg ml-1)of WSE?water solube extracts?inhibits the germination of Picea crassifolia,while low concentrations(0.5 mg ml-1 and 5 mg ml-1)improve the germination.The highest germination rate of Picea crassifolia is 70 ± 7% when the concentration of WSE is 0.5 mg ml-1.?2?In the dry?air moisture 50%?and intermediate moist?air moisture 70%?environment,moss has a positive "nurse effect" on the emergence of Picea crassifolia,and in the moist?air moisture 90%?environment,moss inhibits the emergence of Picea crassifolia;the result implies that both the positive and negative effects of moss on regeneration of Picea crassifolia.?3?The presence of moss changed the morphological characteristics of the seedlings of Picea crassifolia,resulting in the seedlings of Picea crassifolia grown in moss layer are weak and slender(5.41 × 10-4 ± 6.7 × 10-5 g cm-1;dry weight of seedlings / seedling length);with seedlings grown on the bare soil are strong(6.58 × 10-4 ± 8.5 × 10-5 g cm-1;seedling dry weight / seedling length);however,the seedling number of Picea crassifolia in moss is higher than that of which on bare soil.In a word,the presence of moss plays a positive role in the recruitment of Picea crassifolia.4.Simulating the biomass of seedling-saplings of Picea crassifolia on variational spatio-temporal scales.?1?The results of FAREAST model showe that the accumulated biomass of seedling-saplings of Picea crassifolia within 60 years has a significant linear trend over time in the altitudinal gradients.?2?With the increase of the altitude gradient,the relationship between the biomass accumulation of seedling-saplings of Picea crassifolia and the altitude gradient is a quadratic polynomial,that is,the biomass of seedling-saplings increases firstly,after peaking,decreases with the increase of altitude gradient.?3?The number of altitude gradients and the highest or lowest altitudinal gradient can be simulated for the biomass of seedling-saplings of Picea crassifolia in the western,middle or eastern parts of Qilian Mountains are different,which is related to the climatic variables such as the soil variables,topographic variables and biological environment variables. |
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