Pujia Yu

Spatiotemporal change of diurnal temperature range and its relationship with sunshine duration and precipitation in China

We examined the spatiotemporal variation in diurnal temperature range (DTR) and discussed the reasons for the changes of DTR in China based on data from 479 weather stations from 1962 to 2011. Results showed that DTR decreased rapidly (0.291°C/decade) from 1962 to 1989 due to slightly decreased Tmax and significantly increased Tmin, but the decrease in DTR has stopped since 1990 as Tmax and Tmin kept pace with each other. During 1990–2011, DTR remained trendless, with slight increase in the 1990s and slight decrease after 2000. During the whole study period from 1962 to 2011, DTR decreased at a rate of 0.157°C/decade nationally. Spatially, decreases in DTR were greatest in Northeast China and lowest in Southwest China with a transect running from northeast to southwest showing the decreasing trends change from high to low. Seasonally, DTR decreases were greatest in winter and lowest in summer, and the magnitudes of decrease reduced from the north to south of China. The changes in DTR were closely correlated with changes in sunshine duration (SD) in China except the Tibetan Plateau, suggesting that SD decrease is an important contributor to the decrease of DTR through its influence on Tmax. In addition to the contribution of SD decrease, the increasing of precipitation played an important role in DTR decrease in Northwest China, the most arid region of China. It appeared that changes of cloud cover (CC) were not the reasons for DTR changes in the past 50 years as CC has decreased during the study period.

Grass-legume mixtures impact soil N, species recruitment, and productivity in temperate steppe grassland

AimsIn this study, we aimed to understand effects and mechanisms of legume species and their relative abundance on soil N, species recruitment, and productivity in mixed grassland. We also assessed the utilization prospect of several legumes in natural grassland.MethodsIn 2006, grass-legume combinations (GLCs) with different ratios (GLR) were established using Leymus chinensis and four legume species (Medicago ruthenica, Lespedeza daurica, Medicago falcata, and Medicago sativa). In 2009, plant and soil samples were taken to examine the differences in soil nitrogen (N) properties, biological N fixation (BNF), recruitment characteristics, and aboveground biomass of the community under different mixture patterns.ResultsSoil total N and available N concentration increased when legume component increased from GLR 1:0 (grass monoculture) to GLR 1:1 (grass:legume 1:1) but decreased as legume component increased further from GLR 1:3 (grass:legume 1:3) to GLR 0:1 (legume monoculture). GLR 1:1 had the highest BNF in most GLCs except for L. chinensis-M. falcata. For any GLR with legume, L. chinensis-M. sativa combination (L-MS) had higher soil total N, available N, water content, and BNF. The legume combinations with a GLR lower than 1:1 resulted in more species recruitments compared with the grass monoculture, and L-MS induced relatively more species recruitments than other GLCs, which were correlated with improved soil water and NO3−-N status. The grassland productivity increased as the GLR decreased; in any GLRs with legume, higher productivity was found under L-MS combination, and current results showed that grassland productivity was positively linked to soil NO3−-N availability influenced by grass-legume mixture.ConclusionsWe concluded that the species and relative abundance of legumes had great impact on soil N status, species recruitment, and productivity in this temperate grassland ecosystem. In this study site, legume introduction can be considered as an alternative to N fertilization for increasing grassland productivity. M. sativa has the greatest economic and ecological potential species to be mixed into natural temperate steppe grassland, and grass-legume ratio 1:1 is the best combination in mixed communities.

Selecting the minimum data set and quantitative soil quality indexing of alkaline soils under different land uses in northeastern China

Understanding the influences of land use conversions on soil quality (SQ) and function are essential to adopt proper agricultural management practices for a specific region. The primary objective of this study was to develop soil quality indices (SQIs) to assess the short-term influences of different land uses on SQ in semiarid alkaline grassland in northeastern China. Land use treatments were corn cropland (Corn), alfalfa perennial forage (Alfalfa), monoculture Lyemus chinensis grassland (MG) and successional regrowth grassland (SRG), which were applied for five years. Twenty-two soil indicators were determined at 0-20cm depth as the potential SQ indicators. Of these, thirteen indicators exhibited treatment differences and were identified as the total data set (TDS) for subsequent analysis. Principal component analysis was used with the TDS to select the minimum data set (MDS), and four SQIs were calculated using linear/non-linear scoring functions and additive/weighted additive methods. Invertase, N:P ratio, water-extractable organic carbon and labile carbon were identified as the MDS. The four SQIs performed well, with significant positive correlations (P<0.001, n=16) among them. However, the SQI calculated using the non-linear weighted additive integration (SQI-NLWA) had the best discrimination under different land-use treatments due to the higher F values and larger coefficient of variance as compared to the other SQIs. The SQI value under the MG treatment was the highest, followed by that under the SRG and Alfalfa treatments, and all of these were significantly higher than that of Corn treatment. These results indicated that conversion of cropland to perennial forage or grassland can significantly improve the SQ in the Songnen grassland. In addition, SQI-NLWA can provide a better practical, quantitative tool for assessing SQ and is recommended for soil quality evaluation under different land uses in semiarid agroecosystems.

Facilitative and Inhibitory Effect of Litter on Seedling Emergence and Early Growth of Six Herbaceous Species in an Early Successional Old Field Ecosystem

In the current study, a field experiment was conducted to examine effects of litter on seedling emergence and early growth of four dominant weed species from the early successional stages of old field ecosystem and two perennial grassland species in late successional stages. Our results showed that increased litter cover decreased soil temperature and temperature variability over time and improved soil moisture status. Surface soil electrical conductivity increased as litter increased. The increased litter delayed seedling emergence time and rate. The emergence percentage of seedlings and establishment success rate firstly increased then decreased as litter cover increased. When litter biomass was below 600 g m−2, litter increased seedlings emergence and establishment success in all species. With litter increasing, the basal diameter of seedling decreased, but seedling height increased. Increasing amounts of litter tended to increase seedling dry weight and stem leaf ratio. Different species responded differently to the increase of litter. Puccinellia tenuiflora and Chloris virgata will acquire more emergence benefits under high litter amount. It is predicted that Chloris virgata will dominate further in this natural succession old field ecosystem with litter accumulation. Artificial P. tenuiflora seeds addition may be required to accelerate old field succession toward matured grassland.