Nitrogen economy of alpine plants on the north Tibetan Plateau: Nitrogen conservation by resorption rather than open sources through biological symbiotic fixation

Nitrogen (N) is one of the most important factors limiting plant productivity, and N fixation by legume species is an important source of N input into ecosystems. Meanwhile, N resorption from senescent plant tissues conserves nutrients taken up in the current season, which may alleviate ecosystem N limitation. N fixation was assessed by the ¹⁵N dilution technique in four types of alpine grasslands along the precipitation and soil nutrient gradients. The N resorption efficiency (NRE) was also measured in these alpine grasslands. The aboveground biomass in the alpine meadow was 4–6 times higher than in the alpine meadow steppe, alpine steppe, and alpine desert steppe. However, the proportion of legume species to community biomass in the alpine steppe and the alpine desert steppe was significantly higher than the proportion in the alpine meadow. N fixation by the legume plants in the alpine meadow was 0.236 g N/m², which was significantly higher than N fixation in other alpine grasslands (0.041 to 0.089 g N/m²). The NRE in the alpine meadows was lower than in the other three alpine grasslands. Both the aboveground biomass and N fixation of the legume plants showed decreasing trends with the decline of precipitation and soil N gradients from east to west, while the NRE of alpine plants showed increasing trends along the gradients, which indicates that alpine plants enhance the NRE to adapt to the increasing droughts and nutrient‐poor environments. The opposite trends of N fixation and NRE along the precipitation and soil nutrient gradients indicate that alpine plants adapt to precipitation and soil nutrient limitation by promoting NRE (conservative nutrient use by alpine plants) rather than biological N fixation (open sources by legume plants) on the north Tibetan Plateau.     

不同类型高寒草地群落结构与生产对施氮的响应及其敏感性

大气氮沉降增加被认为是目前重要的环境问题,会引起生物多样性的丧失和生态系统稳定性的降低。但作为草地改良的管理措施,养分添加被广泛应用于退化草地的恢复。但由于不同类型草地所处气候与群落组成的差异,对氮输入的响应可能不同。通过在藏北高原高寒草甸与高寒草甸草原设定长期氮添加梯度试验(对照, 25, 50, 100, 200 kg N hm~(-2) a~(-1)),来探讨氮输入对生物多样性与生产的影响,并估算不同类型高寒草地的氮饱和阈值。施氮对高寒草甸物种多样性指数无影响,而随着施氮量的提高高寒草甸草原植物物种数和多样性指数均逐渐降低。开始施肥前两年,随着施氮量提高高寒草甸地上生物量呈现逐渐增加趋势,随着施肥时间的延长地上生物量呈现先增加后降低的趋势。在高寒草甸草原随着施氮量提高地上生物量均呈现先增加后降低的趋势。随着施氮量提高,开始施氮前三年高寒草甸禾草植物地上生物量逐渐提高;随着施氮时间的延长,禾草和豆科植物地上生物量呈现先增加后降低的趋势。高寒草甸莎草植物地上生物量由施氮开始时的逐渐增加转变为先增加后降低趋势,最后变为逐渐降低的趋势,这说明施氮不利于莎草植物的生长。施氮只在施肥第四年显著提高杂草植物地上生物量。高寒草甸草原呈现不同的规律,开始施氮前三年随着施氮量提高,禾草植物地上生物量呈现先增加后降低的趋势;随着施氮时间的延长,禾草地上生物量逐渐提高。莎草和杂草植物地上生物量呈现先增加后降低趋势。利用对氮输入响应最敏感的植物功能群禾草生物量估算的高寒草甸和高寒草甸草原的氮饱和阈值分别是109.5、125.8 kg N hm~(-2) a~(-1),这说明高寒草甸氮敏感性显著高于高寒草甸草原。由此可见,未来氮沉降增加会对不同类型高寒草地产生不同的影响,在不同类型高寒草地进行施肥恢复时也应将氮饱和阈值的差异考虑在内。     

青藏高原高寒草地AM真菌分布及其对近自然恢复的生态作用

超载过牧以及全球气候变化等导致大部分青藏高原高寒草地呈现持续退化态势。青藏高原高寒草地退化致使地上植物群落逐渐发生更替,地下土壤微生物群落多样性和丰富度发生改变。本文旨在探析青藏高原高寒草地丛枝菌根（arbuscular mycorrhizal,AM）真菌的分布特征、对近自然恢复的生理生态效应及其作用机制。青藏高原高寒草地中已报道4目14属61种AM真菌,约占已知AM真菌物种的20%。高寒草地禾本科植物根围AM真菌物种丰度最高,而莎草科植物根围AM真菌孢子密度最高。3种高寒草地植被类型中,高寒草原AM真菌丰度最高（33种）,山地灌丛草原次之（32种）,高寒草甸最低（22种）。高寒草原以光壁无梗囊霉Acaulospora laevis和闪亮和平囊霉Pacispora scintillans为优势种,山地灌丛草原以摩西斗管囊霉Funneliformis mosseae为优势种,高寒草甸以光壁无梗囊霉A. laevis、近明球囊霉Claroideoglomus claroideum和闪亮和平囊霉P. scintillans为优势种。高寒草地土著AM真菌与植物构建的菌根网络可以通过调节营养元素吸收、分配,促进植物建植和生长;但是毒杂草入侵可以改变土著AM真菌物种多样性和菌根网络,限制本地植被的实际生态位扩张。退化高寒草地中,AM真菌群落具有高的环境适应性和恢复力,其不仅调控地上植物群落建植和多样性,同时AM真菌建植也增加了代谢产物-球囊霉素相关土壤蛋白产生,进而协同改善地下土壤微生态系统,为退化高寒草地早期植被恢复塑造土壤生境。因此,AM真菌在退化高寒草地近自然恢复中具有较大的应用潜力。     

内蒙古草甸草原与典型草原地下生物量与生产力季节动态及其碳库潜力

地下根系是草原生态系统的重要组成部分,其生物量及其净生产力对地下碳库具有直接与间接作用,分析地下生物量季节动态与周转对深入揭示草原生态系统碳库动态及其固碳速率与潜力具有重要意义。应用钻土芯法对不同利用方式或管理措施下内蒙古草甸草原、典型草原地下生物量动态及其与温度、降水的相关性研究表明:草甸草原和典型草原地上生物量季节动态均为单峰型曲线,与上月降水显著正相关(P0.05),但地下生物量季节动态表现为草甸草原呈"S"型曲线,典型草原则是双峰型曲线,与温度、降水相关性均不显著(P0.05);两种草原根冠比和地下生物量垂直分布均为指数函数曲线,根茎型草原地下生物量集中在土壤0—5 cm,丛生型草原地下生物量集中于土壤5—10 cm,根冠比值在生长旺季(7—8月份)最小。草甸草原地下净生产力及碳储量范围分别为2167—2953 g m-2a-1和975—1329 gC m-2a-1,典型草原为2342—3333 g m-2a-1和1054—1450 gC m-2a-1,地下净生产力及其碳储量约为地上净生产力及其碳储量的10倍,具有较大的年固碳能力,且相对稳定;地下净生产力与地上净生产力呈显著负相关性(P0.05);地下生物量碳库是地上生物量碳库的10倍左右,适度放牧可增加地下生产力,但长期过度放牧显著降低其地下生物量与生产力,并使其垂直分布趋向于浅层化。     

降水量变化对藏北高寒草地养分限制的影响

生态系统净初级生产养分限制的模式是现代生态学关注的重要问题。养分的可利用性是草原生态系统生产力动态变化的关键决定因素, 但土壤养分可利用性与整个生态系统中养分限制之间的关系尚不清楚。该研究通过在藏北降水梯度上4种类型高寒草地(从东到西依次是高寒草甸、高寒草甸草原、高寒草原和高寒荒漠草原)设置氮磷养分添加试验, 系统研究氮磷养分添加对不同类型高寒草地的影响, 并探讨降水梯度上高寒草地的氮磷限制模式。结果表明: (1)氮磷添加对不同高寒草地的影响存在差异: 氮添加显著提高了高寒草甸和高寒草甸草原地上生产力, 而对高寒草原和高寒荒漠草原无影响; 单独磷添加对4种高寒草地均无显著影响, 而氮磷添加对4种高寒草地地上生产力均有促进作用。(2)通过计算氮磷共同限制指数发现: 随着降水量减少, 高寒草地氮限制指数从1.18逐渐降低到0.52-0.64, 养分限制模式从氮限制过渡到氮磷共同限制; 磷限制指数在高寒草甸草原和高寒草原为负值, 说明单独磷添加对高寒草甸的生产力有负向作用, 高寒草甸主要受氮限制; 高寒草甸草原介于氮限制与氮磷限制之间, 受到氮磷共同限制, 单独磷添加有负向作用; 高寒荒漠草原受到氮磷共同限制。研究表明, 高寒草地氮磷限制模式存在环境梯度上的递变规律, 随着降水量减少, 高寒草地养分限制模式从氮限制逐渐过渡到氮磷共同限制。由此推断, 未来气候变化条件下氮沉降增加对不同类型高寒草地的影响可能存在差异。同时, 利用养分添加恢复不同类型退化高寒草地时也应将氮磷限制模式的差异考虑进去。     

新疆天山中段巴音布鲁克高山草地碳含量及其垂直分布

对新疆天山中段巴音布鲁克高山草地(高山草原和高山草甸)的生物量和土壤有机碳进行了测定。结果表明积分和分层两种估算方法得到的土壤有机碳含量没有显著差异,但积分算法的优势在于能推算不同深度的土壤有机碳含量,便于与以往的研究进行比较;高山草甸的生物量和土壤有机碳含量均大于高山草原;其地上生物量分别为71.4和94.9 g C·m^-2,地下生物量分别为1 033.5和1 285.2 g C·m^-2; 1 m深度的土壤有机碳含量分别为25.7和38.8 kg·m^-2;地上生物量呈现较为明显的垂直分布格局,即随着海拔的增加,地上生物量先呈增加趋势,但当海拔超过一定界限后生物量突然下降;土壤含水率是导致南坡(阳坡)土壤有机碳含量空间分异的重要因素,但北坡(阴坡) 土壤有机碳含量还可能与地形、土壤质地等其它因素有关;两种高山草地(高山草原和高山草甸)的根系集中分布在40 cm以内,0~20 cm根系分别占其总量的76%和80%;土壤有机碳集中分布在60 cm以内,0~20 cm土壤有机碳分别占其总量的55%和49%;高山草原根系分布比高山草甸深,但较低的地下/地上比使得其有机碳分布比高山草甸浅。     

Variations in the nitrogen saturation threshold of soil respiration in grassland ecosystems

Over the last century, anthropogenic activities have increased nitrogen (N) deposition considerably, which significantly affects ecosystem processes and has the potential to induce N saturation in the future. The continuous increase in N deposition may cause a non-linear response in soil respiration (Rs), an important component of carbon (C) cycling. However, little is known about N saturation threshold of soil respiration. In this study, we conducted coordinated experiments in four grassland types across northern China with four N addition levels to explore patterns in the Rs saturation threshold. Our results showed that an Rs saturation threshold generally exists in grassland ecosystems in response to N addition gradients. The N saturation threshold of Rs occurred at an average rate of 50 kg N ha⁻¹ yr⁻¹, but varied widely with grassland type; the N saturation threshold occurred at rates of 100, 50, 50, and 25 kg N ha⁻¹ yr⁻¹ in the alpine meadow, meadow steppe, typical steppe, and desert steppe, respectively. Autotrophic respiration (Ra) and heterotrophic respiration (Rh) responded to N addition gradients differently. Ra increased initially and became saturated at a rate of 50 kg N ha⁻¹ yr⁻¹ and declined thereafter. In contrast, Rh decreased monotonically after N addition. Structural equation models further confirmed that the effects of N addition gradients on Rs were primarily determined by the non-linear response of belowground biomass. Interestingly, the compiled global dataset showed that the N saturation threshold of Rs increased with precipitation and soil moisture. These findings indicate that the stimulating effect of N deposition on Rs and Ra might diminish with increasing N deposition in the future, especially in dry grassland ecosystems.

     

青藏高原草地植被覆盖变化及其与气候因子的关系

为揭示气候变化对青藏高原草地生态系统的影响及其生态适应机制,利用1982~1999年间的NOAA/AVHRR NDVI数据和对应的气候资料,研究了近20年来青藏高原草地植被覆盖变化及其与气候因子的关系。结果表明,18年来研究区生长季NDVI显著增加(p=0.015),其增加率和增加量分别为0.41% a^-1和0.001 0 a^-1。生长季提前和生长季生长加速是青藏高原草地植被生长季NDVI增加的主要原因。春季为NDVI增加率和增加量最大的季节,其增加率和增加量分别为0.92% a^-1和0.001 4 a^-1;夏季NDVI的增加对生长季NDVI增加的贡献相对较小,其增加率和增加量分别为0.37% a^-1和0.001 0 a^-1。3种草地(高寒草甸、高寒草原、温性草原)春季NDVI均显著增加(p<0.01;p=0.001; p=0.002); 高寒草甸夏季NDVI显著增加(p=0.027),而高寒草原和温性草原夏季NDVI呈增加趋势,但都不显著(p=0.106; p=0.087);3种草地秋季NDVI则没有明显的变化趋势(p=0.585; p=0.461; p=0.143)。3种草地春季NDVI的增加是由春季温度上升所致。高寒草地(高寒草甸和高寒草原)夏季NDVI的增加是夏季温度和春季降水共同作用的结果。温性草原夏季NDVI变化与气候因子并没有表现出显著的相关关系。高寒草地植被生长对气候变化的响应存在滞后效应。     

Responses of Soil Microbial Communities to Experimental Warming in Alpine Grasslands on the Qinghai-Tibet Plateau

Global surface temperature is predicted to increase by at least 1.5°C by the end of this century. However, the response of soil microbial communities to global warming is still poorly understood, especially in high-elevation grasslands. We therefore conducted an experiment on three types of alpine grasslands on the Qinghai-Tibet Plateau to study the effect of experimental warming on abundance and composition of soil microbial communities at 0–10 and 10–20 cm depths. Plots were passively warmed for 3 years using open-top chambers and compared to adjacent control plots at ambient temperature. Soil microbial communities were assessed using phospholipid fatty acid (PLFA) analysis. We found that 3 years of experimental warming consistently and significantly increased microbial biomass at the 0–10 cm soil depth of alpine swamp meadow (ASM) and alpine steppe (AS) grasslands, and at both the 0–10 and 10–20 cm soil depths of alpine meadow (AM) grasslands, due primarily to the changes in soil temperature, moisture, and plant coverage. Soil microbial community composition was also significantly affected by warming at the 0–10 cm soil depth of ASM and AM and at the 10–20 cm soil depth of AM. Warming significantly decreased the ratio of fungi to bacteria and thus induced a community shift towards bacteria at the 0–10 cm soil depth of ASM and AM. While the ratio of arbuscular mycorrhizal fungi to saprotrophic fungi (AMF/SF) was significantly decreased by warming at the 0–10 cm soil depth of ASM, it was increased at the 0–10 cm soil depth of AM. These results indicate that warming had a strong influence on soil microbial communities in the studied high-elevation grasslands and that the effect was dependent on grassland type.     

Precipitation and nitrogen addition enhance biomass allocation to aboveground in an alpine steppe

There are two important allocation hypotheses in plant biomass allocation: allometric and isometric. We tested these two hypotheses in an alpine steppe using plant biomass allocation under nitrogen (N) addition and precipitation (Precip) changes at a community level. An in situ field manipulation experiment was conducted to examine the two hypotheses and the responses of the biomass to N addition (10 g N m^?2 y^?1) and altered Precip (±50% precipitation) in an alpine steppe on the Qinghai–Tibetan Plateau from 2013 to 2016. We found that the plant community biomass differed in its response to N addition and reduced Precip such that N addition significantly increased aboveground biomass (AGB), while reduced Precip significantly decreased AGB from 2014 to 2016. Moreover, reduced Precip enhanced deep soil belowground biomass (BGB). In the natural alpine steppe, the allocation between AGB and BGB was consistent with the isometric hypotheses. In contrast, N addition or altered Precip enhanced biomass allocation to aboveground, thus leading to allometric growth. More importantly, reduced Precip enhanced biomass allocation into deep soil. Our study provides insight into the responses of alpine steppes to global climate change by linking AGB and BGB allocation.     

The microbially mediated soil organic carbon loss under degenerative succession in an alpine meadow

Land‐cover change has long been recognized as having marked effect on the amount of soil organic carbon (SOC). However, the microbially mediated processes and mechanisms on SOC are still unclear. In this study, the soil samples in a degenerative succession from alpine meadow to alpine steppe meadow in the Qinghai–Tibetan Plateau were analysed using high‐throughput technologies, including Illumina sequencing and geochip functional gene arrays. The soil microbial community structure and diversity were significantly (p < .05) different between alpine meadow and alpine steppe meadow; the microbial ɑ‐diversity in alpine steppe meadow was significantly (p < .01) higher than in alpine meadow. Molecular ecological network analysis indicated that the microbial community structure in alpine steppe meadow was more complex and tighter than in the alpine meadow. The relative abundance of soil microbial labile carbon degradation genes (e.g., pectin and hemicellulose) was significantly higher in alpine steppe meadow than in alpine meadow, but the relative abundance of soil recalcitrant carbon degradation genes (e.g., chitin and lignin) showed the opposite tendency. The Biolog Ecoplate experiment showed that microbially mediated soil carbon utilization was more active in alpine steppe meadow than in alpine meadow. Consequently, more soil labile carbon might be decomposed in alpine steppe meadow than in alpine meadow. Therefore, the degenerative succession of alpine meadow because of climate change or anthropogenic activities would most likely decrease SOC and nutrients medicated by changing soil microbial community structure and their functional potentials for carbon decomposition.     

藏北高原典型植被样区物候变化及其对气候变化的响应

植被物候作为陆地生态系统对气候变化的响应和反馈的重要指示,已成为区域或全球生态环境领域研究的热点。基于非对称高斯拟合方法重建了2001—2010年MODIS EVI时间序列影像,利用动态阈值法提取藏北高原植被覆盖2001—2010年每年关键物候参数。选取研究区内东部高寒灌丛草甸、中部高寒草甸及西部高寒草原和高寒荒漠4种典型植被类型,并结合附近的4个气象台站气候资料,分析典型植被物候在近10a对关键气候因子的响应特征。研究结果表明:(1)4种不同典型植被的物候特征(EVImax降低、返青期延后和生长季长度缩短)均表现出高寒灌丛草甸→高寒草甸→高寒草原→高寒荒漠草原的过渡;(2)藏北高原近10a的年平均气温及春、夏、冬三个季度的平均气温均呈显著升高的趋势,升温幅度在0.8—3.9℃/10a,降水减少趋势不显著,在这种水热条件下典型植被均表现出返青提前(7.2—15.5d/10a)、生长季延长(8.4—19.2d/10a)的趋势,而枯黄出现时间为年际间自然波动;(3)高寒灌丛草甸EVImax主要受春季降水量和气温影响,且降水的影响程度大于气温;对高寒草甸植被而言,春、夏季的气温和降水均有较大的影响;而高寒草原和高寒荒漠草原主要受夏季平均气温和降水量影响;(4)高寒灌丛草甸的返青时间主要受前一年秋季降水量的影响,相关系数达-0.579;而高寒草甸、高寒草原和高寒荒漠草原主要受春季平均气温影响,高寒荒漠草原的特征最为明显(r=-0.559)。     

Considerable methane uptake by alpine grasslands despite the cold climate: in situ measurements on the central Tibetan Plateau, 2008–2013

The uptake of CH₄ by aerate soil plays a secondary role in the removal of tropospheric CH₄, but it is still highly uncertain in terms of its magnitude, spatial, and temporal variation. In an attempt to quantify the sink of the vast alpine grasslands (1 400 000 km²) of the Tibetan Plateau, we conducted in situ measurements in an alpine steppe (4730 m) and alpine meadow (4900 m) using the static chamber and gas chromatograph method. For the alpine steppe, measurements (2008–2013) suggested that there is large interannual variability in CH₄ uptake, ranging from ?48.8 to ?95.8 μg CH₄ m^?2 h^?1 (averaged of ?71.5 ± 2.5 μg CH₄ m^?2 h^?1), due to the variability in precipitation seasonality. The seasonal pattern of CH₄ uptakes in the form of stronger uptake in the early growing season and weaker uptake in the rainy season closely matched the precipitation seasonality and subsequent soil moisture variation. The relationships between alpine steppe CH₄ uptake and soil moisture/temperature are best depicted by a quadratic function and an exponential function (Q₁₀ = 1.67) respectively. Our measurements also showed that the alpine meadow soil (average of ?59.2 ± 3.7 μg CH₄ m^?2 h^?1) uptake less CH₄ than the alpine steppe and produces a similar seasonal pattern, which is negatively regulated by soil moisture. Our measurements quantified – at values far higher than those estimated by process‐based models – that both the alpine steppe and alpine meadow are considerable CH₄ sinks, despite the cold weather of this high‐altitude area. The consecutive measurements gathered in this study also highlight that precipitation seasonality tends to drive the interannual variation in CH₄ uptake, indicating that future study should be done to better characterize how CH₄ cycling might feedback to the more extreme climate.     

Temporal intraspecific trait variability drives responses of functional diversity to interannual aridity variation in grasslands

Interannual climate variation alters functional diversity through intraspecific trait variability and species turnover. We examined these diversity elements in three types of grasslands in northern China, including two temperate steppes and an alpine meadow. We evaluated the differences in community‐weighted means (CWM) of plant traits and functional dispersion (FDis) between 2 years with contrasting aridity in the growing season. Four traits were measured: specific leaf area (SLA), leaf dry matter content (LDMC), leaf nitrogen concentration (LNC), and the maximum plant height (H). CWM for SLA of the alpine meadow increased in the dry year while that of the temperate steppe in Qinghai showed opposing trends. CWM of LDMC in two temperate steppes became higher and CWM of LNC in all grasslands became lower in the dry year. Compared with the wet year, FDis of LDMC in the alpine meadow and FDis of LNC in the temperate steppe in Qinghai decreased in the dry year. FDis of H was higher in the dry year for two temperate steppes. Only in the temperate steppe in Qinghai did the multi‐FDis of all traits experience a significant increase in the dry year. Most of the changes in CWM and FDis between 2 years were explained by intraspecific trait variation rather than shifts in species composition. This study highlights that temporal intraspecific trait variation contributes to functional responses to environmental changes. Our results also suggest it would be necessary to consider habitat types when modeling ecosystem responses to climate changes, as different grasslands showed different response patterns.     

祁连山3种典型生态系统土壤微生物活性和生物量碳氮含量

 测定分析了祁连山高寒草甸、山地森林和干草原土壤中微生物活性、生物量碳氮含量。结果显示：就土壤微生物生物量碳含量,森林比干草原和高寒草甸中分别高60%和120%以上,干草原比高寒草甸中高40%以上(p<0.05)。就土壤微生物生物量氮含量,0～5 cm土层,森林比高寒草甸和干草原中分别高64%和111%以上,高寒草甸比干草原中高29%;5～15 cm土层,森林比干草原和高寒草甸中分别高7%和191%以上,干草原比高寒草甸中高171% 以上(p<0.05)。森林和干草原中土壤微生物生物量碳比例比高寒草甸中高32%以上,0～5和5～15 cm土层,森林和干草原中土壤微生物生物量氮比例比高寒草甸中高150%以上（p<0.05）。就土壤微生物活性,0～5和5～15 cm土层,森林和高寒草甸比干草原中高26%以上;15～35 cm土层,森林比干草原和高寒草甸中高28%以上 (p<0.05)。土壤微生物生物量碳氮含量与有机碳含量及微生物生物量氮含量和比例与微生物生物量碳含量和比例呈现正相关（r²>0.30,p<0.000 1）。土壤微生物生物量氮含量、微生物生物量碳氮含量比例、微生物活性与土壤pH值呈显著负相关,土壤微生物生物量碳氮含量及其比例、微生物活性与土壤湿度呈正相关。说明祁连山3种生态系统土壤中微生物生物量和活性受气候要素、植被、有机碳、pH值和湿度等因素 的共同影响。     

Occurrence and distribution of arbuscular mycorrhizal fungal species in three types of grassland community of the Tibetan Plateau

Arbuscular mycorrhizal (AM) fungal spore communities and distribution patterns were surveyed in montane scrub grassland, alpine steppe, and alpine meadow sites at altitudes ranging from 3,500 to 5,200 m a.s.l. on the Tibetan Plateau. Thirty-two representative soil samples were collected from the root zone of the dominant and common plant species in late May 2004. Twenty-three AM fungal species representing six genera (Acaulospora, Entrophospora, Glomus, Pacispora, Paraglomus, and Scutellospora) were detected and species richness varied from 5.3 ± 0.8 to 10.5 ± 2.5 per site. Some AM fungal species were restricted to one vegetation type and Glomus mosseae, Glomus intraradices, and Scutellospora calospora were detected in all three vegetation types. Glomus species were found to be the most frequent and abundant in all three vegetation types. Acaulospora occurred mostly in the alpine steppe and alpine meadow. Scutellospora occurred mostly in montane scrub grassland. At the species level, Glomus mosseae was dominant in the montane scrub, Acaulospora laevis and Pacispora scintillans were dominant in the alpine steppe, and Acaulospora laevis, Pacispora scintillans, and Glomus claroideum dominated the alpine meadow. It was evident from the distribution pattern of AM fungi in the different vegetation types that the abundance and diversity of AM fungal species were lowest in the montane scrub grassland than the other two plant communities. Climatic conditions, especially temperatures, and intensity of land use may be the most important factors influencing the AM fungal community.     

中国北方草地植物群落季节生长格局模拟

中国北方草地横跨干旱、半干旱及亚湿润干旱气候区,水分是限制中国北方草地植物群落生产力的主要气候因子.采用基于水分平衡过程的、简单的植物群落模型,利用460个气象站40年气象数据的月平均值,模拟中国北方7种草地类型的季节及年生长、叶片投影盖度(FPC)、蒸发系数(k)及净第一性生产力(NPP).野外观测数据对模型的验证显示模拟结果与观测值相符较好.温性草地自东向西,青藏高原自东南向西北,植物群落的k、NPP与FPC呈递减趋势,显示了中国温性草地自东向西,青藏高原自东南向西北逐渐干旱的水分梯度;其中高寒草甸的3个模拟参数值均最高,高寒草原FPC次于高寒草甸,而NPP却与温性典型草原相近,温性典型荒漠的3个参数最低.高寒草甸、高寒草原、温性草甸草原、温性典型草原、温性荒漠草原、温性草原化荒漠和温性典型荒漠等7种类型草地的畜群承载力约为每公顷5.2、2.3、3.6、2.1、1.0、0.6和0.2只羊单位,区域最适恢复植被盖度分别以93%、79% 、56%、50%、44%、38%和37%为宜.     

环青海湖地区天然草地时序光谱特征参量分析

获取了环青海湖地区4类主要天然草地2003年5~10月共16个时相的地面高分辨率光谱数据,并利用植被指数技术、导数光谱技术、植被光谱维特征提取模型及包络线归一化技术提取了多个光谱特征参量,通过对各参量在生育期内分布规律的分析,给出了能较好地表征草地生长发育规律时序特征参量的具体分布;最后计算了4类天然草地各时序特征参量的平均散度,结果表明黄边位置λY、红边位置λV、红边斜率SV、绿峰半高宽wλG、红谷半高宽wλR、去包络红谷净面积AR'和归一化植被指数NDV I对于天然草地分类更有效。     

The interactive effects of nitrogen addition and increased precipitation on gross ecosystem productivity in an alpine meadow

氮水添加对高寒草甸生态系统生产力的影响 降水变化和大气氮沉降增加对草原生态系统碳交换具有重要的影响,进而影响草地生产力、群落组成和生态系统功能。然而,氮水添加对高寒草甸生态系统碳交换的影响目前尚不清楚。因此,本研究在青藏高原高寒草甸布设氮水添加试验,设置4种不同处理：对照、 加氮、加水和同时添加氮水,对生态系统碳交换过程进行了连续4年的原位观测。研究结果发现,氮添加可以增加总生态系统生产力(GEP)、植物地上生物量、群落盖度和群落加权平均高度(CWMh),而水分添加没有显著影响。生态系统碳交换对氮水添加的响应在干湿年存在显著差异。水分添加仅在干旱年对净生态系统碳交换(NEE)具有显著影响,原因是GEP的增加量大于生态系统呼吸(ER)。相反,氮添加仅在湿润年显著提高了生态系统碳交换,其中GEP的增加归因于NEE的增加量大于ER。结构方程结果表明,氮添加主要通过增加优势种的盖度从而提高NEE。本研究强调了降水和优势物种在调节高寒草甸生态系统响应环境变化中的重要作用。     

藏北高寒草地土壤有机质化学组成对土壤蛋白酶和脲酶活性的影响

土壤酶作为生态系统的生物催化剂, 是土壤有机体的代谢驱动力, 在土壤物质循环和能量转化过程中起着重要作用。该研究以藏北5种不同类型高寒草地(高寒草甸、高寒草原、高寒草甸草原、高寒荒漠草原和高寒荒漠)为研究对象, 利用热裂解气质联用技术(Py-GC/MS)分析不同类型草地土壤有机质化学组成, 并建立其与土壤蛋白酶和脲酶活性之间的相互关系。结果表明, 5种高寒草地土壤(0-15 cm)的酶活性表现出一定差异性, 高寒荒漠草原土壤的脲酶活性显著高于蛋白酶活性, 而其余类型高寒草地的脲酶和蛋白酶活性之间的差异未达到显著水平; 蛋白酶活性在5种高寒草地土壤之间的差异显著, 而脲酶活性在5种草地土壤之间的差异未达到显著水平。相关分析发现, 土壤蛋白酶活性与土壤有机质烷烃、烯烃和芳香烃的相对丰度和糠醛:吡咯的值密切相关, 土壤脲酶活性与土壤有机质化学组成之间相关性未达到显著水平。综上所述, 高寒草地类型和土壤有机质化学组成是影响高寒草地土壤蛋白酶活性的重要因素, 而对土壤脲酶活性的影响均未达到显著水平, 其影响因素有待进一步深入的研究。