Modeling gross primary productivity of alpine meadow in the northern Tibet Plateau by using MODIS images and climate data

The Vegetation Photosynthesis Model (VPM) was used to simulate the gross primary productivities (GPP) of the alpine meadow ecosystem in the northern Tibet Plateau at three different spatial resolutions of 0.5 km, 1.5 km and 2.5 km, respectively. The linear relationships between enhanced vegetation indices (EVI) and GPP, with higher correlative coefficients, were better than those between normalized difference vegetation indices (NDVI) and GPP at the three resolutions. VPM could well simulate the seasonal changes and inter-annual variations of GPP, with similar trends at the three resolutions. There were significant differences (P < 0.0001) among the three modeled GPP with the three resolutions. Therefore, the modeled GPP at high resolution could not be directly extrapolated to low resolution, and vice versa. The contribution levels of different model parameters, including photosynthetically active radiation (PAR), air temperature (Ta), NDVI, EVI and land surface water indices (LSWI), to modeled GPP could vary with spatial resolution based on multiple stepwise linear regression analysis. This indicated that it was important to choose parameters properly and consider their effects on modeled GPP.     

Modeling gross primary productivity of alpine meadow in the northern Tibet Plateau by using MODIS images and climate data

The Vegetation Photosynthesis Model (VPM) was used to simulate the gross primary productivities (GPP) of the alpine meadow ecosystem in the northern Tibet Plateau at three different spatial resolutions of 0.5 km, 1.5 km and 2.5 km, respectively. The linear relationships between enhanced vegetation indices (EVI) and GPP, with higher correlative coefficients, were better than those between normalized difference vegetation indices (NDVI) and GPP at the three resolutions. VPM could well simulate the seasonal changes and inter-annual variations of GPP, with similar trends at the three resolutions. There were significant differences (P < 0.0001) among the three modeled GPP with the three resolutions. Therefore, the modeled GPP at high resolution could not be directly extrapolated to low resolution, and vice versa. The contribution levels of different model parameters, including photosynthetically active radiation (PAR), air temperature (Ta), NDVI, EVI and land surface water indices (LSWI), to modeled GPP could vary with spatial resolution based on multiple stepwise linear regression analysis. This indicated that it was important to choose parameters properly and consider their effects on modeled GPP.     

Leaf area index and net primary productivity along subtropical to alpine gradients in the Tibetan Plateau

Aim Our aims were to quantify climatic and soil controls on net primary productivity (NPP) and leaf area index (LAI) along subtropical to alpine gradients where the vegetation remains relatively undisturbed, and investigate whether NPP and LAI converge towards threshold‐like logistic patterns associated with climatic and soil variables that would help us to verify and parameterize process models for predicting future ecosystem behaviour under global environmental change. Location Field data were collected from 22 sites along the Tibetan Alpine Vegetation Transects (TAVT) during 1999–2000. The TAVT included the altitudinal transect on the eastern slope of the Gongga Mountains in the Eastern Tibetan Plateau, with altitudes from 1900 m to 3700 m, and the longitudinal‐latitudinal transect in the Central Tibetan Plateau, of approximately 1000 km length and 40 km width. Methods LAI was measured as the product of foliage biomass multiplied by the ratio of specific leaf area. NPP in forests and shrub communities was estimated as the sum of increases in standing crops of live vegetation using recent stem growth rate and leaf lifespan. NPP in grasslands was estimated from the above‐ground maximum live biomass. We measured the soil organic carbon (C) and total and available nitrogen (N) contents and their pool sizes by conventional methods. Mean temperatures for the year, January and July and annual precipitation were estimated from available meteorological stations by interpolation or simulation. The threshold‐like logistic function was used to model the relationships of LAI and NPP with climatic and soil variables. Results Geographically, NPP and LAI both significantly decreased with increasing latitude (P < 0.02), but increased with increasing longitude (P < 0.01). Altitudinal trends in NPP and LAI showed different patterns. NPP generally decreased with increasing altitude in a linear relationship (r² = 0.73, P < 0.001), whereas LAI showed a negative quadratic relationship with altitude (r² = 0.58, P < 0.001). Temperature and precipitation, singly or in combination, explained 60–68% of the NPP variation with logistic relationships, while the soil organic C and total N variables explained only 21–46% of the variation with simple linear regressions of log‐transformed data. LAI showed significant logistic relationships with both climatic and soil variables, but the data from alpine spruce‐fir sites diverged greatly from the modelled patterns associated with temperature and precipitation. Soil organic C storage had the strongest correlation with LAI (r² = 0.68, P < 0.001). Main conclusions In response to climatic gradients along the TAVT, LAI and NPP across diverse vegetation types converged towards threshold‐like logistic patterns consistent with the general distribution patterns of live biomass both above‐ground and below‐ground found in our earlier studies. Our analysis further revealed that climatic factors strongly limited the NPP variations along the TAVT because the precipitation gradient characterized not only the vegetation distribution but also the soil N conditions of the natural ecosystems. LAI generally increased with increasing precipitation and was well correlated with soil organic C and total N variables. The interaction between LAI growth and soil N availability would appear to have important implications for ecosystem structure and function of alpine spruce‐fir forests. Convergence towards logistic patterns in dry matter production of plants in the TAVT suggests that alpine plant growth would increase in a nonlinear response to global warming.     

青藏高原高寒草甸生态系统净二氧化碳交换量特征

高寒草甸是青藏高原广泛分布的植被类型之一,面积约120万km2,地处青藏高原腹地的当雄草原站即位于该类植被的典型分布区。以2003年8~10月中旬在该站用涡度相关法连续观测的CO2通量数据资料为基础,分析了高寒草甸生态系统8~10月份净二氧化碳交换量(NEE)的日变化规律,及其与光合有效辐射、降水、温度等环境因子之间的关系。结果表明,8~10月份的日均NEE有明显的日变化,表现为单峰型,通常在地方时11:00~12:00左右达到碳吸收的最大值,平均为-0.2680mgCO2/(m2·s)(-6.0800μmolCO2/(m2·s))。白天的NEE与光合有效辐射之间符合很好的直角双曲线关系,表观量子产额平均为0.0203μmolCO2/μmolPAR,表观最大光合速率平均为9.7411μmolCO2/(m2·s)。夜晚的NEE与5cm地温有很好的指数函数关系。     

Characteristics of net ecosystem carbon dioxide exchange (NEE) from August to October of Alpine meadow on the Tibetan Plateau, China

The Alpine meadow is one of the vegetation types widely distributed on the Tibetan Plateau in China with an area of about 1.2 million square kilometers. The Damxung rangeland station, located in the hinterland of the Tibetan Plateau, is covered with an typical vegetation. The continuous carbon flux data (from August to middle October, 2003) measured with the open-path eddy covariance system was used to analyze the diurnal variation pattern of net ecosystem carbon dioxide exchange (NEE) and its relationship with the environmental factors, such as photosynthetically active radiation (PAR), precipitation, and temperature. Results showed that NEE presented obvious diurnal variation pattern with single-peak of diurnal maximum carbon assimilation at 11: 00–12: 00 (local time) with an average of −0.268 mg CO₂·m⁻²·s⁻¹, i.e., −6.08 μmol CO₂·m⁻²·s⁻¹. During the daytime, NEE fitted fairly well with PAR in a rectangular hyperbola function with the apparent quantum yield (0.020 3 μmol CO₂ μmol⁻¹ PAR) and maximum ecosystem assimilation (9.741 1 μmol CO₂·m⁻²·s⁻¹). During the night-time, NEE showed a good exponential relation with the soil temperature at 5 cm depth. __________ Translated from Acta Ecologica Sinica 2005, 25(8): 1948–1952 [译自: 生态学报, 2005, 25(8): 1948–1952]     

Characteristics of net ecosystem carbon dioxide exchange(NEE) from August to October of Alpine meadow on the Tibetan Plateau,China

The Alpine meadow is one of the vegetation types widely distributed on the Tibetan Plateau in China with an area of about 1.2 million square kilometers.The Damxung rangeland station,located in the hinterland of the Tibetan Plateau,is covered with an typical vegetation.The continuous carbon flux data (from August to middle October,2003) measured with the open-path eddy covariance system was used to analyze the diurnal variation pattern of net ecosystem carbon dioxide exchange (NEE) and its relationship with the environmental factors,such as photosynthetically active radiation (PAR),precipitation,and temperature.Results showed that NEE presented obvious diurnal variation pattern with single-peak of diurnal maximum carbon assimilation at 11:00-12:00 (local time) with an CO2.m-2-s-1.During the daytime,NEE fitted fairly well with PAR in a rectangular hyperbola function with the apparent the night-time,NEE showed a good exponential relation with the soil temperature at 5 cm depth.     

青藏高原高寒草甸非生长季温室气体排放特征及其年度贡献

高寒草甸是青藏高原地区的主要植被类型,目前对其温室气体研究多集中于生长季.本文利用静态箱-气相色谱法,对非生长季高寒草甸温室气体排放特征及其与主要环境因子的关系进行了研究.结果表明:非生长季高寒草甸表现为CO2和N2O的源、CH4的汇.其中非生长季CO2通量平均值为89.33 mg·m-2·h-1,累积排放通量为280.01g· m-2;CH4通量平均值为-11.35 μg·m-2·h-1,累积吸收通量为124.74 mg·m-2;N2O通量平均值为8.02 μg·m-2·h-1,累积排放通量为39.51 mg·m-2.非生长季CO2、CH4和N2O累积排放通量分别占全年的13.33％、53.47％和62.67％.冻融期(2012年4月)CH4累积吸收通量较小,只占非生长季的4.5％;而CO2和N2O累积排放通量较大,分别占非生长季的25.8％和20.8％.非生长季CO2通量与温度(气温、5和10 cm土壤温度)和5 cm土壤湿度均存在显著正相关关系,而CH4和N2O通量仅与5 cm土壤湿度存在显著正相关.研究表明,虽然冻融期CH4累积吸收通量在非生长季累积量中比重较小,但非生长季CH4和N2O累积排放量却占全年累积排放量的1/2以上,在温室气体累积通量评估中不容忽视.     

青藏高原高寒湿地GPP变化特征及对生长季积温的响应

基于涡度相关系统,利用2004—2016年的涡度相关系统观测资料,做了青藏高原高寒湿地生长季总初级生产力(GPP)在不同时间尺度上对生长季有效积温(GDD)响应的研究。结果表明:高寒湿地生态系统在生长季的日GPP、GDD与月际GPP、GDD都表现为先增大后减小的单峰变化趋势,都在7月或8月达到峰值,在5月达到最小值。在整个生长季尺度上,GPP与GDD变异性较大,没有明显的变化趋势。2004—2016年整个生长季GPP与GDD的均值分别为(458.82±25.78) gC m^-2季^-1和(1060.89±84.07)℃。在日尺度、月尺度、生长季尺度上,GPP与GDD都呈极显著正相关关系(P<0.01)。但是,通过比较生长季分别每个月GPP与GDD的关系发现,5、9月的GPP与GDD没有显著相关性(P>0.05),而在7月相关性最为显著(P<0.01)。整体上看,高寒湿地生态系统植被的总初级生产力与热量条件表现为正相关关系,由此说明在全球气候变暖的背景下,将会提高青藏高原高寒湿地生态系统植被的光合生产能力。     

A simulation of the importance of length of growing season and canopy functional properties on the seasonal gross primary production of temperate alpine meadows

Background and Aims: Along snowmelt gradients, the canopies of temperate alpine meadowsdiffer strongly in their structural and biochemical properties.Here, a study is made of the effects of these canopy dissimilaritiescombined with the snow-induced changes in length of growingseason on seasonal gross primary production (GPP). Methods: Leaf area index (LAI) and community-aggregated values of leafangle and leaf nitrogen content were estimated for seven alpineplant canopies distributed along a marked snowmelt gradient,and these were used as input variables in a sun–shadecanopy bulk-photosynthesis model. The model was validated forplant communities of early and late snowmelt sites by measuringthe instantaneous CO₂ fluxes with a canopy closed-chamber technique.A sensitivity analysis was conducted to estimate the relativeimpact of canopy properties and environmental factors on thedaily and seasonal GPP. Key Results: Carbon uptake was primarily related to the LAI and total canopynitrogen content, but not to the leaf angle. For a given levelof photosynthetically active radiation, CO₂ assimilation washigher under overcast conditions. Sensitivity analysis revealedthat increase of the length of the growing season had a highereffect on the seasonal GPP than a similar increase of any otherfactor. It was also found that the observed greater nitrogencontent and larger LAI of canopies in late-snowmelt sites largelycompensated for the negative impact of the reduced growing season. Conclusions: The results emphasize the primary importance of snow-inducedchanges in length of growing season on carbon uptake in alpinetemperate meadows. It was also demonstrated how using leaf-traitvalues of the dominants is a useful approach for modelling ecosystemcarbon-cycle-related processes, particularly when continuousmeasurements of CO₂ fluxes are technically difficult. The studythus represents an important step in addressing the challengeof using a plant functional-trait approach for biogeochemicalmodelling.     

青藏高原高寒草甸不同季节土壤理化性质及酶活性对施肥处理的响应

分析了青藏高原东缘高寒草甸不同施肥处理对土壤全量养分、速效养分、pH、含水量、有机碳和土壤脲酶活性的影响,以揭示高寒草甸土壤养分和酶活性对施肥的响应。结果表明:(1)随施肥量的增加,土壤pH明显趋于降低,施肥引起高寒草甸土壤酸化;全磷、速效磷均显著增大;(2)土壤全氮、有机碳和脲酶活性随施肥量增加呈单峰曲线变化,在施肥量为30或60g·m-2时最高,施肥量增加到90g·m-2时土壤资源逐渐降低;(3)季节变化对土壤养分也有一定的影响,全氮和全磷含量均于9月份较高,而速效氮含量一般于9月份较低,而速效磷含量5月份较低;(4)施肥对土壤养分的影响并不是简单的线性正相关关系,30~60g·m-2施肥量可作为高寒草甸最佳施肥水平。施肥处理下土壤有机碳和脲酶活性可作为衡量土壤肥力和土壤质量变化的重要指标。高施肥量(≥90g·m-2)可作为影响高寒草甸土壤养分及土壤酶活性的阈值。     

Grazing intensifies degradation of a Tibetan Plateau alpine meadow through plant–pest interaction

Understanding the plant–pest interaction under warming with grazing conditions is critical to predict the response of alpine meadow to future climate change. We investigated the effects of experimental warming and grazing on the interaction between plants and the grassland caterpillar Gynaephora menyuanensis in an alpine meadow on the Tibetan Plateau in 2010 and 2011. Our results showed that grazing significantly increased nitrogen concentration in graminoids and sward openness with a lower sward height, sward coverage, and plant litter mass in the community. Grazing significantly increased G. menyuanensis body size and potential fecundity in 2010. The increases in female body size were about twofold greater than in males. In addition, grazing significantly increased G. menyuanensis density and its negative effects on aboveground biomass and graminoid coverage in 2011. We found that G. menyuanensis body size was significantly positively correlated with nitrogen concentration in graminoids but negatively correlated with plant litter mass. Even though warming did not significantly increased G. menyuanensis performance and the negative effects of G. menyuanensis on alpine meadow, the increases in G. menyuanensis growth rate and its negative effect on aboveground biomass under the warming with grazing treatment were significantly higher than those under the no warming with grazing treatment. The positive effects of grazing on G. menyuanensis performance and its damage were exacerbated by the warming treatment. Our results suggest that the fitness of G. menyuanensis would increase under future warming with grazing conditions, thereby posing a greater risk to alpine meadow and livestock production.     

藏北高原草甸土壤固碳微生物群落特征随海拔和季节的变化

研究土壤固碳微生物丰度、群落结构、多样性差异及其影响因子对了解青藏高原土壤碳循环和固碳潜力具有重要意义。采用定量PCR(qPCR)、末端限制性片段分析(T-RFLP)、克隆文库和测序方法,研究了青藏高原草甸土壤固碳微生物丰度与群落结构随海拔和季节的变化,主要结果如下:1)随海拔升高高寒草甸土壤固碳微生物丰度显著升高,但季节变化不明显,不同类别微生物固碳基因cbbL丰度依次为:Form ICForm IABForm ID,其中Form IC类固碳微生物可达10~8拷贝数/g土壤,cbbL基因丰度与海拔、土壤含水量和铵态氮含量(NH_4~+-N)呈正相关关系,与土壤温度和pH值负相关;2)固碳微生物多样性和丰富度随海拔升高而升高,在4800m达到最大,且二者受季节影响较小,其群落结构随海拔升高而逐渐变化,主要受土壤pH值、海拔和土壤水分影响;3)Form IC类固碳微生物主要包括放线菌门和和变形菌门,其中α变形菌门是高寒草甸土壤优势固碳微生物类群。本研究有助于理解土壤微生物群落功能及其在土壤碳循环过程中的作用,为更准确评估高寒草甸土壤碳循环过程提供了科学依据。     

Calibration of Terra/MODIS gross primary production over an irrigated cropland on the North China Plain and an alpine meadow on the Tibetan Plateau

This paper evaluated the MODerate resolution Imaging Spectroradiometer (MODIS) gross primary production (GPP) product (MOD17) by using estimated GPP from eddy‐covariance flux measurements over an irrigated winter wheat and maize double‐cropping field on the North China Plain in 2003–2004, and an alpine meadow on the Tibetan Plateau in 2002–2003. The mean annual GPP from MOD17 accounted for 1/2–2/3 of the surface estimated mean annual GPP for the alpine meadow, but only about 1/5–1/3 for the cropland. This underestimation was partly attributed to low estimates of leaf area index by a MODIS product (MOD15) because it is used to calculate absorbed photosynthetically active radiation in the MOD17 algorithm. The main reason is that the parameter maximum light use efficiency (ε_max) in the MOD17 algorithm was underestimated for the two biomes, especially for the cropland. Contrasted to the default, ε_max was optimized using surface measurements. The optimized ε_max for winter wheat, maize and meadow was 1.18, 1.81 and 0.73 g C/MJ, respectively. By using the surface measurements and optimized ε_max , the MOD17 algorithm significantly improved the accuracy of GPP estimates. The optimum MOD17 algorithm explained about 82%, 68%, and 79% of GPP variance for winter wheat, maize, and meadow, respectively. These results suggest that it is necessary to adjust the MOD17 parameters for the estimation of cropland and meadow GPP, particularly over cropland.     

藏北高山嵩草草甸群落特征及生产力对模拟增温幅度的响应

青藏高原气候严酷,陆地表层生态系统脆弱,其高寒植物群落特征及生态系统生产力对气候变化的响应极其敏感。利用开顶箱(OTCs,Open Top Chambers)式装置在藏北高山嵩草(Kobresia pygmaea)草甸设置不同增温梯度实验(W1、W2、W3、W4),探究增温对高寒草甸植物群落特征及地上生产力的影响。研究结果表明:1)与对照样地相比,增温减少了植物群落总盖度(2015年,W1、W2、W3、W4分别显著减少了28%、23%、59%、60%; 2016年,W4显著减少了83%)和高山嵩草盖度(2015年,W1、W2、W3、W4分别显著减少了26%、33%、681%、64%; 2016年,W4显著减少了85%),而低幅度增温(W1、W2)对委陵菜属植物盖度无显著影响,高幅度增温(W3、W4)显著减少了委陵菜属植物盖度(2015年,W3、W4分别显著减少了58%和60%;2016年,W4显著减少了71%); 2)对整个植物群落而言,增温幅度较低时,增温对群落的生长和生物量的积累有促进作用,当温度升高超过一定程度,这种促进作用会逐渐减弱甚至变成抑制作用(2015年,W4显著减少了地上生物量69%; 2016年,W4显著减少了地上生物量82%); 3)高山嵩草盖度和其他物种总盖度存在显著的年际差异,而委陵菜属植物盖度无明显的年际变化。研究结果预示着,一定程度的升温会促进高寒草甸植物群落的生长,但温度升高超过一定幅度时,会导致草地生产力下降,草地退化加剧,同时当地群落中委陵菜属植物在全球变化背景下相对稳定,这类物种在未来气候变暖的背景下可能具有更强的竞争力。     

Root-shoot competition interactions cause diversity loss after fertilization: a field experiment in an alpine meadow on the Tibetan Plateau

Aims A decrease in species diversity after fertilization is a common phenomenon in grasslands; however, the mechanism causing it remains highly controversial. The light competition hypothesis to explain loss of diversity has received much attention. The aim of the present paper was to test this hypothesis.Methods Fertilization was used to control above- and belowground resources simultaneously, while shade was used to control aboveground resource in an alpine meadow on the Tibetan Plateau. Univariate general linear models was used to estimate the effects of fertilization and shade on above- and belowground vegetation characteristics, including photosynthetically active radiation (PAR) in the understory, aboveground biomass, belowground biomass, R:S ratio, species richness and Simpson's diversity index.Important findings PAR was similar in the understory of shaded and fertilized plots, but only fertilization reduced species richness and diversity, suggesting that light competition alone could not explain diversity loss after fertilization. The root biomass and R:S ratio had a significant increase in shaded plots, but the richness and diversity did not change, suggesting that root competition alone also could not explain diversity loss after fertilization in this community. Our results illustrated that the root–shoot competition interactions, investigated from a functional groups perspective, should be the most reasonable explanation leading to the diversity loss due to fertilization.     

Approaches of climate factors affecting the spatial variation of annual gross primary productivity among terrestrial ecosystems in China

Analyzing the approaches that climatic factors affect the spatial variation of annual gross primary productivity (GPP_yr) would improve our understanding on its spatial pattern. Based on network eddy covariance measurements and published data in literature, we separated GPP_yr into radiation use efficiency (RUE) and annual absorbed photosynthesis active radiation (APAR_yr), where APAR_yr can be regarded as the product of the fraction of absorbed annual photosynthesis active radiation (FPAR_yr) and annual PAR (PAR_yr). Given that PAR_yr affects the spatial variation of GPP_yr directly through itself, we investigated factors affecting the spatial variations of RUE and FPAR_yr, to reveal how climatic factors affect the spatial variation of GPP_yr. Results suggest that the spatial variation of RUE was directly affected by annual mean air temperature (MAT) and annual mean CO₂ mass concentration (ρ_cyr). The increasing MAT and ρ_cyr directly enhanced RUE. The increasing annual precipitation (MAP) directly prompted FPAR_yr. Therefore, MAT and ρ_cyr affected the spatial variation of GPP_yr through altering RUE while the effect of MAP was achieved through altering FPAR_yr. Our study could also provide an alternative way for regional GPP_yr assessment.     

Net primary productivity and spatial distribution of vegetation in an alpine wetland,Qinghai-Tibetan Plateau

To initially describe vegetation structure and spatial variation in plant biomass in a typical alpine wetland of the Qinghai-Tibetan Plateau, net primary productivity and vegetation in relationship to environmental factors were investigated. In 2002, the wetland remained flooded to an average water depth of 25 cm during the growing season, from July to mid-September. We mapped the floodline and vegetation distribution using GPS (global positioning system). Coverage of vegetation in the wetland was 100%, and the vegetation was zonally distributed along a water depth gradient, with three emergent plant zones (Hippuris vulgaris-dominated zone, Scirpus distigmaticus-dominated zone, and Carex allivescers-dominated zone) and one submerged plant zone (Potamogeton pectinatus-dominated zone). Both aboveground and belowground biomass varied temporally within and among the vegetation zones. Further, net primary productivity (NPP) as estimated by peak biomass also differed among the vegetation zones; aboveground NPP was highest in the Carex-dominated zone with shallowest water and lowest in the Potamogeton zone with deepest water. The area occupied by each zone was 73.5% for P. pectinatus, 2.6% for H. vulgaris, 20.5% for S. distigmaticus, and 3.4% for C. allivescers. Morphological features in relationship to gas-transport efficiency of the aerial part differed among the emergent plants. Of the three emergent plants, H. vulgaris, which dominated in the deeper water, showed greater morphological adaptability to deep water than the other two emergent plants.     

Measurement of net ecosystem exchange,productivity and respiration in three spruce forests in Sweden shows unexpectedly large soil carbon losses

Measurement of net ecosystem exchange was made using the eddy covariance method above three forests along a north-south climatic gradient in Sweden: Flakaliden in the north, Knottåsen in central and Asa in south Sweden. Data were obtained for 2 years at Flakaliden and Knottåsen and for one year at Asa. The net fluxes (N_ep) were separated into their main components, total ecosystem respiration (R_t) and gross primary productivity (P_g). The maximum half-hourly net uptake during the heart of the growing season was highest in the southernmost site with ?0.787 mg CO₂ m^?2 s^?1 followed by Knottåsen with ?0.631 mg CO₂ m^?2 s^?1 and Flakaliden with ?0.429 mg CO₂ m^?2 s^?1. The maximum respiration rates during the summer were highest in Knottåsen with 0.245 mg CO₂ m^?2 s^?1 while it was similar at the two other sites with 0.183 mg CO₂ m^?2 s^?1. The annual N_ep ranged between uptake of ?304 g C m^?2 year^?1 (Asa) and emission of 84 g C m^?2 year^?1 (Knottåsen). The annual R_t and P_g ranged between 793 to 1253 g C m^?2 year^?1 and ?875 to ?1317 g C m^?2 year^?1, respectively. Biomass increment measurements in the footprint area of the towers in combination with the measured net ecosystem productivity were used to estimate the changes in soil carbon and it was found that the soils were losing on average 96–125 g C m^?2 year^?1. The most plausible explanation for these losses was that the studied years were much warmer than normal causing larger respiratory losses. The comparison of net primary productivity and P_g showed that ca 60% of P_g was utilized for autotrophic respiration.     

青藏高原高寒草地植物物种丰富度及其与环境因子和生物量的关系

在青藏高原进行了大范围的群落调查 ,研究高原的两种主要草地群落类型———高寒草甸和高寒草原的植物物种丰富度及其变化。结果表明 :(1)在 5 0个样地 2 5 0个 1m× 1m的样方中 ,共出现 2 6 7种植物 ,其中高寒草甸179种 ,高寒草原 135种。在高寒草甸 ,1m2 样方内物种数最多为 32种 ,最少的仅为 3种 ;在高寒草原 ,物种数最多为 18种 /m2 ,最少的仅为 2种 /m2 。 (2 )物种丰富度随经度和纬度的增加呈增加趋势 ;随海拔的上升呈减少趋势。对物种丰富度与环境因子之间进行逐步回归 ,发现物种丰富度与生长季降水和温暖指数呈显著正相关。 (3)物种丰富度与地上生物量呈显著正相关。     

基于地形因素的高寒草甸土壤温湿度和物种多样性与初级生产力关系研究

山地是高寒草甸的主要分布区,地形变化引起了土壤温湿度和物种的差异性分布,进而影响到草地生态系统生产功能。为明晰高寒草甸山地环境因子(土壤温湿度)和物种多样性(丰富度、多度、均匀度、优势度)与初级生产力的关系,本研究以青藏高原东北缘马牙雪山支脉的高寒草甸山体为研究对象,选择阶地、阴坡、山脊和阳坡与3个海拔梯度段,调查了189个样方的植物群落组成和土壤温湿度。采用线性回归法分析土壤温湿度和物种多样性与初级生产力之间的关系。结果表明:(1)以山地高寒草甸整体为研究单元,初级生产力只随物种多度的增加而显著增加(R~2=0.07 P=0.01)。(2)坡向影响初级生产力的因素不同,阴坡初级生产力与物种丰富度正线性相关;山脊初级生产力与土壤湿度正线性相关,也随物种丰富度增加而显著增加;阳坡初级生产力与物种多度正线性相关;阶地初级生产力随均匀度增加而显著增加,随优势度增加而显著降低。(3)只有低海拔区(2860-2910 m)初级生产力随物种多度和丰富度的增加而显著增加。综上所述,山地高寒草甸土壤温湿度和物种多样性与初级生产力关系受坡向比海拔的影响更大,且物种多样性对初级生产力的影响大于土壤温湿度。建议山地高寒草甸生态系统生产和生态管理过程中要重点考虑坡向对植物多样性和初级生产力的影响。