生命科学学院知识库

青海云杉（Picea crassifolia）广泛分布于祁连山区，是该地区的优势乔木树种。青海云杉林承担着气候调节、生物多样性维持、固碳释氧和水源涵养的生态服务功能，是生态环境脆弱的西北地区的重要生态屏障。其中青海云杉林所承载的水源涵养功能对水资源贫乏的西北内陆来说乃是重中之重，这关系到甘肃河西走廊地区及部分内蒙古地区工农业用水问题，是有关国计民生的大事。目前，祁连山国家级自然保护区的生态环境安全已上升为国家生态安全战略层面。然而自上世纪60年代以来，森林砍伐、土地资源不合理利用以及青海云杉林经营管理不善导致青海云杉更新不良，对青海云杉林的可持续发展产生威胁，进而影响青海云杉林生态服务功能的发挥。为了理清影响青海云杉更新的因素，本文以青海云杉为研究对象，以影响青海云杉更新的生物因素和非生物因素为切入点，通过野外调查、室内实验以及模型模拟等方法揭示青海云杉更新的时空特征，主要研究结果如下：

环境变量对青海云杉更新的影响（1）在坡面尺度上，青海云杉幼苗幼树的分布首先受海拔梯度的影响（约占总变异的34.3%），调查结果显示青海云杉幼苗幼树在中等海拔梯度（2900-3200 m）分布最多，其次受其他环境要素如坡度、坡向及距母树的距离（约占总变异的27.7%）的影响。（2）在样方尺度上，青海云杉幼苗幼树受苔藓层的影响。研究结果显示厚度约为5 cm和盖度约为50%的苔藓层是影响青海云杉更新的阈值；即当苔藓层厚度约为5 cm、盖度约为50%时，生长在苔藓层上的幼苗幼树最多。2．苔藓沿海拔梯度对青海云杉更新的影响（1）在相同海拔梯度薄苔藓层（5 cm）促进青海云杉更新，降低幼苗幼树死亡率，而厚苔藓层（10 cm）抑制青海云杉的更新。（2）去除地表苔藓层后（裸地）随着海拔梯度的升高青海云杉的更新能力下降；在未去除地表苔藓处理中，随着海拔梯度的升高，苔藓对青海云杉的更新产生积极的促进作用；该研究结果为“胁迫梯度假说”提供了直接证据，即随着胁迫梯度的增强，物种间的正相互作用在增强。（3）在较低海拔梯度上（2750 m），苔藓抑制了青海云杉幼苗幼树的存活，而随着海拔梯度的升高，苔藓降低了青海云杉幼苗幼树的死亡率，说明在环境条件较为恶劣的情况下苔藓对青海云杉产生了“保育作用”；暗示着苔藓植物潜在扩张了青海云杉幼苗幼树的生态位，在胁迫梯度的末端提高了幼苗幼树的存活率。3．苔藓化感作用对青海云杉种子萌发和湿度梯度对出苗的影响（1）高浓度（50 mg ml^-1）苔藓水提液抑制青海云杉种子萌发，而低浓度（0.5 mg ml^-1和5 mg ml^-1）苔藓水提液促进青海云杉种子萌发，在水提液浓度为0.5 mg ml^-1时，青海云杉种子的萌发率最高，约为70% 。（2）在干燥（空气湿度50%）和中等湿度（空气湿度70%）的环境中，苔藓植物对青海云杉出苗具有积极的“保育作用”，而在潮湿（空气湿度90%）的环境中苔藓对青海云杉出苗产生抑制作用。该结果意味着苔藓对青海云杉更新具有双重影响。（3）苔藓层改变了青海云杉幼苗的形态学特征，导致生长在苔藓层中的青海云杉幼苗柔弱纤细（5.41×10^-4 ± 6.7×10^-5 g cm^-1；幼苗干重/幼苗长度），而生长在裸土上的青海云杉幼苗较为粗壮（6.58×10^-4 ± 8.5×10^-5 g cm^-1；幼苗干重/幼苗长度），但是苔藓层中的青海云杉出苗率高于裸土上的青海云杉出苗率，综合以上结果，苔藓对青海云杉更新起到积极的促进作用。4．不同时空尺度青海云杉幼苗幼树的生物量特征（1）FAREAST模型模拟显示，60年内青海云杉幼苗幼树的生物量在任何一个海拔梯度上随着时间的推移均呈显著的线性增长趋势。（2）青海云杉幼苗幼树的生物量与海拔梯度呈二次多项式关系，即生物蓄积量随着海拔梯度的增加而增加，达到峰值后再降低。（3）模拟结果显示青海云杉幼苗幼树的生物量在祁连山西、中和东段不同，幼苗幼树分布的海拔梯度的上限和下限有所差异，这与不同模拟站点的气候变量、土壤变量、地形变量以及生物环境变量密切相关。

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 1960s, 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.