Ecosystem-Dependent Responses of Vegetation Coverage on the Tibetan Plateau to Climate Factors and Their Lag Periods

The spatiotemporal variation characteristics of the Normalized Difference Vegetation Index (NDVI) and its climate response patterns are of significance in deepening our understanding of regional vegetation and climate change. The response of vegetation to climate factors varies spatially and may have lag periods. In this paper, we studied the spatiotemporal responses of vegetation to climatic factors on an ecosystem-dependent scale using GIMMS NDVI3g data and climatic parameters. Pure pixels with a single vegetation type were firstly extracted to reduce the influence of mixed vegetation types. Then, a lag correlation analysis was used to explore the lag effects of climatic parameters affecting NDVI. Finally, the stepwise regression method was adopted to calculate the regression equation for NDVI and meteorological data with the consideration of effect lag times. The results show that precipitation has significant lag effects on vegetation. Temperature is the main climatic factor that affects most vegetation types at the start of growing season. At the end of growing season, the temperate desert, temperate steppe, and temperate desert steppe are greatly affected by precipitation. Moreover, the alpine steppe, alpine desert, alpine meadow, and alpine sparse vegetation are greatly affected by temperature. The needleleaf forest, subalpine scrub, and broadleaf evergreen forest are sensitive to sunshine percentage during almost the whole growing season. These findings could contribute to a better understanding of the drivers and mechanisms of vegetation degradation on the Tibetan Plateau.

Soil fertility evaluation and spatial distribution of grasslands in Qilian Mountains Nature Reserve of eastern Qinghai-Tibetan Plateau

The study assessed the overall soil characteristics of grasslands on Qilian Mountains and rated the soil nutrient status with classification standard of the second national soil survey of China. Nemerow index method was used to evaluate the soil fertility of different grassland types. GIS was used to analyze the spatial distribution of the soil nutrients and provided a database for the grassland’s ecological protection and restoration. The study graded the soil organic matter (SOM), total N, and available K at level 2 (high) or above for most regions, available soil-P at level 4, while the soil bulk density, total porosity and pH were 0.77–1.32 g cm−3, 35.36–58.83% and 7.63–8.54, respectively. The rank of comprehensive soil fertility index was temperate steppe (TS) > alpine meadow (AM) > alpine steppe (AS) >upland meadow (UM) >alpine desert (AD)> lowland meadow (LM)> temperate desert steppe (TDS)> temperate desert (TD). The areas with high, medium and low soil fertility accounted for 63.19%, 34.24% and 2.57% of the total grassland area. Soil fertility of different grassland types had different main limiting factors, for instance, the pH, total N and SOM were the main factors limiting soil fertility in LM, while pH and available P were the main factors limiting soil fertility in UM, AM, TS and AS. In summary, the grassland soil fertility was generally at the mid-upper level, and the main limiting factors were found in the different types of the grasslands and their spatial distributions were figured out. Our findings also indicated that the typical grasslands and meadows may require phosphorus application, while for desert grasslands, both nitrogen and phosphorus were required to improve their comprehensive soil fertility and grassland productivity.

Spatial Scale-Depended Characteristic Of Moss and Soil C, N, P and K Stoichiometry and Their Relationships In A Temperate Desert of Central Asia

Background and aims: Previous studies showed that moss stoichiometric characteristics were influenced by moss patch size and shrubs in desert. Study of moss stoichiometry in different spatial scales is crucial for understanding of growth and adaptation strategy of the mosses in temperate desert. Methods: In this study, the dominant moss (Syntrichia caninervis Mitt.) of biological soil crusts, and soil under the moss patches in the Gurbantunggut Desert were selected to determine their stoichiometry in different dunes and sites. Carbon (C), nitrogen (N), phosphorus (P) and potassium (K) contents of the moss and soil, and soil available nutrients were measured. Results: Moss stoichiometry and soil available nutrients were significantly influenced by changes in spatial distance scales except for moss C. The scaling exponents of moss N, P and K elements between above-ground and below-ground parts were 0.251, 0.389, 0.442, which were less than 1. The N vs. P scaling exponents were 0.71, 0.84 in above-ground and below-ground parts of moss. Moss C, P and K elements content in above-ground parts higher than that in below-ground parts. Moreover, moss N, P and K elements were influenced by MAP, longitude and soil nutrients. Conclusion: This study provided the C, N, P and K stoichiometric characteristics of desert moss and explored their relationships with environmental variables, which can help understand nutrient stoichiometry patterns and utilization strategy of N, P and K and their potential responses to global climate changes in the desert ecosystem of central Asia.

Carbon and nitrogen isotopes in grasslands of northern China

<p>Carbon (C) and nitrogen (N) isotopes are important traits to characterize terrestrial ecosystems. Studying the relationships between carbon and nitrogen isotopes of soils and plants in different grassland types and under different environmental conditions is of great importance to the reconstruction of past climate. In this study, we selected three different grassland ecosystems (temperate meadow steppe, temperate typical steppe and temperate desert steppe) in northern China, collected meteorological data and plant and soil samples, determined the basic physical and chemical properties, C and N isotopes to explore the patterns and controlling factors of C and N isotopes in plants and soils of grasslands in northern China. The results showed that there were significant differences in soil δ<sup>13</sup>C and δ<sup>15</sup>N between different grassland types in the northern temperate zone. The soil δ<sup>13</sup>C and δ<sup>15</sup>N of different depths of the northern temperate grassland soil increased with the increase of soil depth. The surface soil δ<sup>13</sup>C of temperate meadow steppe and temperate desert steppe had a good correlation with plant sample δ<sup>13</sup>C. The surface soil δ<sup>15</sup>N temperate typical steppe and temperate desert steppe had a good correlation with plant sample δ<sup>15</sup>N. Mean annual temperature (MAT) and mean annual precipitation (MAP) had a complicated relationship with carbon and nitrogen isotopes of surface soil and plant sample in northern temperate grassland. The surface soil δ<sup>13</sup>C and δ<sup>15</sup>N and the plant sample δ<sup>15</sup>N can be used as indicators of the change of MAT.</p><p><em>Keywords:</em> carbon isotopes, nitrogen isotopes, grasslands, climate, soil depth</p>