Spatial and Temporal Variations in Available Soil Nitrogen—A Case Study in Kobresia Alpine Meadow in the Qinghai-Tibetan Plateau, China

Elucidating the factors that determine the effects of temporal and spatial variation of nutrients is important for analyzing the characteristics of an ecosystem. The goal of this paper was to estimate how values obtained using a particular sampling approach correlated with the actual data for an entire plot. The mesh partition method was employed to divide an integrated observing field (IOF) located at the Haibei National Field Research Station of an alpine grassland ecosystem, China, into 25 subplots. Five of the 25 subplots were randomly selected for soil sampling and to determine the source of variations in soil nutrient content from 2001 to 2012. The results showed that, contributions of temporal and spatial variation in available nitrogen in the 0 - 10 cm soil layer accounted for 47.3% and 52.7%, respectively. The contribution of spatial variance was higher than that of temporal variance especially in the surface soil layers. The available soil nitrogen content in the alpine meadow was not obviously affected by fluctuations in rainfall and temperature. Increasing the number of samples could reduce calculation errors in measuring available soil nitrogen content, while collecting a reasonable number of samples can save time and labor.

Correlation between Different Morus alba L. Leaf Nodes and the Change in Leaf Size or Mass

This paper aimed to explore the correlation between Morus alba L. leaf node and its size or mass change and provide a theoretical basis for the development of scientific Morus alba L. cultivation technology. During 2016-2017,the correlation between Morus alba L. leaf node and its size or mass change was investigated and researched. Results showed that through the correlation coefficient analysis,there was a weakly positive correlation between the leaf node and some indicators such as( leaf length ÷ leaf width) and petiole length,there was a weakly negative correlation between the leaf node and some indicators such as leaf width,( leaf length + leaf width),( leaf length × leaf width) and leaf mass,and there was a weakly negative correlation between the leaf node and the other indicators; there was a highly positive correlation between the leaf mass and some indicators such as Morus alba L. leaf length,leaf width,( leaf length + leaf width) and( leaf length × leaf width),there was a significantly positive correlation between the leaf mass and some indicators such as petiole transverse diameter in width and petiole mass,and there was a weakly positive correlation between the leaf mass and some indicators such as petiole transverse diameter in thickness. In terms of significant level of difference,it was found that there was no significant difference in the correlation coefficients between the leaf nodes on the Morus alba L. shoots and some indicators such as leaf length,leaf width,( leaf length + leaf width),( leaf length × leaf width) and leaf mass; there was an extremely significant difference in the correlation coefficients between the leaf mass and some indicators such as Morus alba L. leaf length,leaf width,( leaf length + leaf width),( leaf length × leaf width),petiole transverse diameter in width and petiole mass; there was no significant difference in the correlation coefficients between the leaf mass and the other indicators. The regression analysis was performed on the leaf node and leaf length,leaf width,( leaf length + leaf width),( leaf length × leaf width),( leaf length ÷ leaf width),petiole length,petiole diameter in width,petiole diameter in thickness,petiole mass and leaf mass. Significance F values were0. 4864,0. 1995,0. 2888,0. 3004,0. 2350,0. 2407,0. 8925,0. 5227,0. 7022 and 0. 2000,respectively,that is,there was an extremely significant difference between Morus alba L. leaf node and petiole diameter in width,there was a significant difference between Morus alba L.leaf node and petiole mass,and there was no significant difference between Morus alba L. leaf node and the other indicators. The comparative analysis of quadratic curve regression equation and linear regression equation was performed on some indicators such as leaf length,and it was found that the R value between the leaf node and petiole diameter in width was in line with the logarithmic curve regression equation,and the other R values of quadratic curve regression equation was larger than the other R values of linear regression equation,indicating that different Morus alba L. leaf nodes,leaf length,leaf mass and other indicators were in line with the quadratic curve regression equation. It was concluded that by investigating the leaf node on the Morus alba L. shoots and regression equation,we could predict the leaf size,leaf mass and other indicators,and we could take the leaf node on the Morus alba L. shoots as a main factor affecting the Morus alba L. leaf size and mass.

Two Ultraviolet Radiation Datasets that Cover China

Ultraviolet（UV） radiation has significant effects on ecosystems, environments, and human health, as well as atmospheric processes and climate change. Two ultraviolet radiation datasets are described in this paper. One contains hourly observations of UV radiation measured at 40 Chinese Ecosystem Research Network stations from 2005 to 2015. CUV3 broadband radiometers were used to observe the UV radiation, with an accuracy of 5%, which meets the World Meteorology Organization＇s measurement standards. The extremum method was used to control the quality of the measured datasets. The other dataset contains daily cumulative UV radiation estimates that were calculated using an all-sky estimation model combined with a hybrid model. The reconstructed daily UV radiation data span from 1961 to 2014. The mean absolute bias error and root-mean-square error are smaller than 30% at most stations, and most of the mean bias error values are negative, which indicates underestimation of the UV radiation intensity. These datasets can improve our basic knowledge of the spatial and temporal variations in UV radiation. Additionally, these datasets can be used in studies of potential ozone formation and atmospheric oxidation, as well as simulations of ecological processes.

The Correlation between Different Fruiting Branch Diameters of Actinidia chinensis and Fruit Quality Change in Post-ripening Period

he research aimed to explore the correlation between fruiting branch diameter of A. chinensis and fruit quality change during the post-ripening period and the mechanism,which could provide theoretical basis for making scientific management measures during A. chinensis fruit post-ripening period. In this paper,correlation analysis between fruiting branch diameter of A. chinensis and fruit quality change during post-ripening period during 2013- 2015 was conducted. Results were as below:(i) correlation coefficient analysis showed that fruiting branch diameter was highly positive correlation with number of fruit ventricle,significantly positive correlation with single fruit weight when picking and the indexes after the fruit ripening single(single fruit weight,loss rate of single fruit weight,longitudinal diameter of fruit and width of fruit core),lowly positive correlation with sugar content of fruit juice,and positive correlation with thick transverse diameter of fruit after ripening.(ii) Standard errors of regression analysis between fruiting branch diameter and single fruit weight,longitudinal diameter of fruit,wide transverse diameter of fruit,thick transverse diameter of fruit,fruit core length and sugar content of fruit juice were 12. 4248,4. 2731,2. 6452,2. 0260,0. 1337 and 1. 0035 respectively; significance F values of variance analysis were 0. 0743,0. 0658,0. 1950,0. 5733,0. 2600 and 0. 1517 respectively. It showed that fruiting branch diameter had a significant difference with thick transverse diameter of fruit and insignificant differences with other indicators; quadratic curve regression equation and linear regression equation of residual curve,observed value curve,forecast value curve and normal probability curve of were analyzed,and the results were all in line with the law of quadratic curve.(iii)The larger the fruiting branch diameter,the greater the indexes after post-ripening(single fruit weight,longitudinal diameter of fruit,wide transverse diameter of fruit,thick transverse diameter of fruit and sugar content of fruit juice),the better the fruit quality. It was clear that fruiting branch diameter could be as one of important bases of fruit quality change during post-ripening period. Through investigating fruiting branch diameter and the regression equation,it could predict single fruit weight,longitudinal and transverse diameters of fruit,and sugar content of fruit juice index after the ripening.

高寒小嵩草草甸可能成为青藏高原相同地理和气候单元下多种类型草地的偏途演替状态

高寒嵩草(Kobresia)草甸是青藏高原冬春放牧草场的主体,在放牧强度分异的条件下可以形成特征迥异的稳态。然而,目前还不清楚在不同放牧强度下其他类型草地是否可以演替成为这些稳态。本研究通过土壤剖面特征推断其历史植物群落特征,以植物群落现场调查确定其现实植物群落特征,以非结构式问卷调查确定草地放牧强度,采用多元回归树模型分析导致草地稳态转化的节点。研究结果表明,高寒灌丛草甸和旱化沼泽草甸在过度放牧条件下均可转化成为高寒矮嵩草(K.humilis)草甸和高寒小嵩草(K.pygmaea)草甸,从而使高寒灌丛草甸和旱化沼泽化草甸进入高寒矮嵩草草甸退化演替序列,最终转化成为黑土滩-杂类草次生裸地。以放牧强度为分节点,最多可以将这些植物群落划分为4类稳态,各稳态转化的节点依次为11.0、8.0、5.5羊/ha。所有研究草地总体表现为随放牧强度的增高地上总生物量呈下降趋势。其中,11.0羊/ha是草地转化成为黑土滩杂类草次生裸地的节点。放牧强度改变可以影响植物群落特征及其演替方向,进而改变草地的畜牧生产服务能力,因此放牧强度可以作为反映牧场畜牧生产服务能力的表观指标。未来牧场的可持续发展策略应以草畜平衡为主,合理控制放牧强度,增加草地生产附加值和延伸畜牧业产业链以实现区域草场生态和生产效益的双赢。

Self-stabilizing maintenance process in plant communities of alpine meadows under different grazing intensities

Backgrounds:Grazing prohibition and reduced grazing intensity,as two important“vegetation close-to-nature recovery”methods,have been suggested as economical and effective technologies for enhancing forage production.However,numerous studies have found that the yield of forage could be increased by removing or reducing grazing in a short time in some steady stage of alpine Kobresia meadows,but not in others.To reveal the mechanism behind this phenomenon,we proposed a series of experiments.Methods:We monitored the plant and soil characteristics in the key steady stages of Kobresia meadows under reduced and prohibited grazing conditions in the same geographic and climatic environments in the northeastern Qinghai-Tibet Plateau for 6 years.We estimated the relationships between the plant community and soil nutrients and obtained the following results.Results:All measured variables were positively correlated with each other.The plant community structure had higher path coefficients to aboveground biomass,soil organic matter,total nitrogen,and nitrate nitrogen than to other factors.The plant community structure played an important role in response to grazing intensity.Different plant functional groups(PFGs)had different responses to grazing intensity,which led to plant community re-establishment or re-organization under different grazing intensities.Poaceae and Kobresia were more sensitive to grazing intensity than other PFGs,and the ratio of Kobresia biomass(including Kobresia humilis and Kobresia pygmaea)to the total biomass of Poaceae and Kobresia could be used as an indicator of regime shifts within plant communities.With Kobresia pygmaea as the dominant species,the prohibition of grazing was not an efficient approach to increase the yield in the steady stages because this treatment needed more time to recover aboveground biomass.If Poaceae is the dominant PFG,grazing should only be prohibited for 3 years in the steady stages because the aboveground biomass will decrease if grazing is prohibited for more than 3 years.Conclusions:Therefore,the different steady stages of alpine meadows require different recovery methods to increase recovery efficiency and speed.

Synergies between microsites of plant communities and steady-stage alpine meadows on the Qinghai-Tibetan Plateau

Background:Due to the effects of climate change and overgrazing in recent decades,alternative stable states in the alpine Kobresia meadow degradation process have coexisted in the same geographical and climatic environment,with variations occurring among microsites.Methods:We used a space-for-time substitution approach to explore the synergies of microsite variation according to its numerical characteristics and the proportion of each stable state at various stages of succession in alpine Kobresia meadows on the Qinghai-Tibetan Plateau.Results:(1)The highest average aboveground biomass in summer was 196.2±20.3 gm^(-2),with significantly higher levels of biomass in≤3.65 sheep unit ha^(-1) than in other levels of grazing intensity,while the parameters showed no significant differences among grazing intensity levels in>3.65 sheep unit ha^(-1).(2)The importance of plant functional groups,aboveground biomass,and niche breadth of Poaceae and Cyperaceae significantly decreased as the grazing intensity increased.(3)The effects of≥0°C accumulated temperature,total precipitation,altitude,longitude,and latitude cumulatively contributed less than 20%of the variation in the distribution of functional group characteristics across microsites.Conclusions:(1)Overgrazing decreases primary production in alpine Kobresia meadows,but ecosystem responses regulate plant community structure and botanical components so as to partially counteract grazing disturbance.(2)Overgrazing changed the proportion of microsites,which in turn led to regime shift in the plant community and subsequent synergies between the microsites of plant communities and their stable states.

祁连山南麓高寒草甸2002~2016年生长季CO_(2)通量对气温日较差的响应

全球气候变化背景下气温日较差(amplitude of diurnal temperature,ADT)的减小将会对高寒生态系统的碳收支产生重要影响.基于涡度相关系统观测资料,研究祁连山南麓高寒草甸2002~2016年生长季(6~9月)ADT在日、月、年尺度上对CO2通量影响,为预测高寒草甸生态系统碳平衡对未来气候变化的响应具有重要参考价值.结果表明,2002~2016年的生长季中,最高气温(maximal air temperature,MaxTa)和最低气温(minimal air temperature,MinTa)呈先升高后降低的单峰变化趋势,ADT没有呈现明显的变化趋势.总初级生产力(gross primary production,GPP)和生态系统呼吸(ecosystem respiration,Re)呈先增加后降低的单峰趋势,净生态系统CO_(2)交换(net ecosystem exchange,NEE)呈先下降后上升的“V”型变化趋势.高寒草甸整个生长季总NEE、GPP和Re平均值分别为–230.4±17.3、668.8±25.5、438.3±27.5 g C m^(-2),表现为较强的碳汇.在月尺度和年尺度上,高寒草甸生长季ADT对NEE没有显著影响(P>0.05).在日尺度上,整个生长季的逐日NEE与ADT呈显著的二次曲线关系(P<0.001),阈值为19.8℃;但是,线性回归分析表明,在6~9月的日NEE与日ADT呈极显著负相关(P<0.001).整体上,仍能说明高寒草甸ADT的增大有利于生态系统的碳固持,暗示在未来气候变化背景下ADT的减小将会削弱高寒草甸生态系统的碳汇能力.

祁连山南麓高寒灌丛生态系统生长季CO_(2)通量动态年际特征及环境驱动

高寒生态系统对全球碳循环发挥着至关重要的作用,然而对高寒生态系统长时间尺度上碳平衡动态及驱动机制的研究仍相对薄弱.本文以青藏高原东北部高寒金露梅灌丛为研究对象,分析了基于涡度相关系统观测的高寒灌丛2003~2016年生长季(5~9月)CO_(2)通量动态及影响机制.结果表明,总初级生产力(gross primary production,GPP)和生态系统呼吸(ecosystem respiration,Re)呈先增加后降低的单峰趋势,净生态系统CO_(2)交换(net ecosystem exchange,NEE)呈先下降后上升的"V"型变化趋势.高寒灌丛整个生长季总NEE、GPP和Re平均值分别为-143.8±30.5、509.0±65.1和365.2±34.6 g Cm^(-2),表现为碳汇.在月尺度,分类回归树分析(classification and regression trees,CART)表明,生长季积温(aggregated growing season degree days,GDD)是月GPP和月NEE的最重要控制因素,而土壤温度(soil temperature,T_(s))是月Re的最主要控制因素.线性回归分析表明,高寒灌丛生长季的热量条件(GDD、T_(a)和T_(s))是CO_(2)通量动态变化的关键控制因素.在年际尺度上,生长季总CO_(2)通量主要受到土壤含水量(soil water content,SWC)和GDD的影响.生长季GDD与GPP呈显著正相关(P<0.05),与生长季NEE呈显著负相关(P<0.05),但生长季GDD与Re没有显著相关性(P<0.05),说明高寒灌丛生态系统的生长季GPP相较于Re对温度的响应更加敏感.该结果对预测高寒灌丛生态系统碳平衡对未来气候变化的响应具有重要参考价值.

Large-scale estimates of gross primary production on the Qinghai-Tibet plateau based on remote sensing data

Vegetation gross primary production(GPP)is an important variable for the carbon cycle on the Qinghai-Tibetan Plateau(QTP).Based on the measurements from 12 eddy covariance flux sites,we validated a light use efficiency model(i.e.EC-LUE)to evaluate the spatial-temporal patterns of GPP and the effect of environmental variables on QTP.In general,EC-LUE model performed well in predicting GPP at different time scale over QTP.Annual GPP over the entire QTP ranged from 575 to 703 Tg C,and showed a significantly increasing trend from 1982 to 2013.However,there were large spatial heterogeneities in long-term trends of GPP.Throughout the entire QTP,air temperature increase had a greater influence than solar radiation and precipitation(PREC)changes on productivity.Moreover,our results highlight the large uncertainties of previous GPP estimates due to insufficient parameterization and validations.When compared with GPP estimates of the EC-LUE model,most Coupled Model Intercomparison Project(CMIP5)GPP products overestimate the magnitude and increasing trends of regional GPP,which potentially impact the feedback of ecosystems to regional climate changes.