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Highlights • Biodiversity-productivity relationship in the grasslands of QTP varied along the spatial scales. • Species richness positively related to above- and below-ground biomass at landscape scale. • Shannon–Wiener index positively related to above- and below-ground biomass at landscape scale. • Pielou evenness index negatively related to above- and below-ground biomass at landscape scale. • Plant biomass partitioning between root and shoot was independent of plant diversity at all scales. Abstract There is no consensus about the relationship between plant species diversity and productivity in grasslands. Lack of consensus might be caused by different diversity metrics used and different spatial scales examined. In particular, the impacts of different biodiversity indices on the plant diversity–plant productivity relationship of alpine grasslands at different spatial scales of the Qinghai–Tibetan Plateau (QTP) require investigation. We investigated the relations of multi-dimensional diversity indices (species richness, Shannon–Wiener diversity, and Pielou evenness) with aboveground and belowground plant biomass in the alpine grasslands of the QTP by linear mixed model (LMM). We assessed the plant diversity and biomass of alpine meadow, alpine steppe, and alpine desert steppe from 5 sites across the vast landscape of the QTP by using 6 randomly placed plots in each site and 27 replicated quadrats in each plot. The species richness of the studied alpine grasslands ranged from 2 to 35, aboveground plant dry biomass ranged from 17 to 838 g m−2, and belowground plant dry biomass ranged from 398 to 3945 g m−2. The species richness and Shannon–Wiener indices were positively correlated with aboveground plant biomass and belowground plant biomass at the landscape scale, whereas the Pielou evenness index was negatively correlated with aboveground plant biomass and belowground plant biomass at the landscape scale. Less than 20% sites showed significant relationships between plant diversity indices and plant biomass at site scale. Plant biomass partitioning between the root and shoot was not correlated with the species richness, Shannon–Wiener and Pielou evenness indices at all scales. The plant diversity–biomass relationships of the alpine grassland ecosystems in the QTP depend on both the type (or dimension) of the biodiversity index and the spatial scale of sampling. Thus, the design and implementation of plant diversity conservation should consider different dimensions of plant diversity. It is not enough to increase species richness only in the process of grassland restoration and conservation, but also to reduce species evenness so as to promote productivity more fully, for example, in planting artificial grassland. [ABSTRACT FROM AUTHOR]

The plateau pika ( Ochotona curzoniae ) is considered a keystone species on the Qinghai–Tibetan Plateau (QTP). Under a moderate burrow density condition, we investigated plant community and soil properties surrounding pika's burrows in comparison to the control sites (without pika's burrows) in an alpine meadow ecosystem. The results demonstrated that plant biomass, especially aboveground biomass around pika's burrow, was improved. The contents of available soil nutrients around the pika's burrow were improved as well. The highest aboveground biomass and highest contents of NH 4 -N, available phosphorus and available potassium was detected at the back of the burrow. The compositions of plant community were not changed significantly around the pika burrow, excluding at the front of the burrow. Our findings revealed that the activities of plateau pika can improve the production of alpine meadow and increase the soil fertility at individual burrow level when the burrow density was not out of control. [ABSTRACT FROM AUTHOR]

The Qinghai-Tibet Plateau (QTP) is experiencing increasing nitrogen (N) deposition, which may have great impacts on the physical, chemical, and biological factors that determine the stabilization of soil organic carbon (SOC). However, few studies have been conducted to quantify the relative contributions of these factors to SOC stabilization at various N addition levels in alpine habitats. We established a N manipulation experiment from 2015 to 2016 in an alpine meadow on the QTP to examine the impacts of N addition gradients on SOC stabilization under different scenarios of N deposition including 8, 24, 40, 56, and 72 kg N ha−1 yr−1. Using solid-state 13C NMR spectroscopy, we assessed the changes in the chemical composition of SOC. We measured soil aggregate size fractions, iron ions, soil microbes, and soil chemicals to investigate their contributions to SOC stabilization. We found that there were response thresholds of SOC to N addition in this alpine meadow on the QTP. The critical level of N addition for the change of SOC was close to 16 kg N ha−1 yr−1 plus the natural atmospheric N deposition (approximately 8 kg N ha−1 yr−1). N addition affected SOC stabilization in this alpine meadow mainly by affecting soil aggregates and soil microbes. These results of this study suggest that an exogenous N input lower than the critical load is beneficial for C sequestration in this alpine meadow on the QTP. This is potentially important for understanding the influences of atmospheric N deposition on soil properties, with subsequent effects on SOC stabilization on the alpine meadow of QTP and similar fragile ecosystems worldwide. • There were response thresholds of SOC to N input in alpine meadows. • The critical load of N input was close to 16 kg N ha−1 yr−1 for SOC change. • N input affected SOC stability mainly by affecting soil aggregates and microbes. [ABSTRACT FROM AUTHOR]

Construction and operation of cascading dams can pose drastic effects on sediment transport and deposition, thus affecting sedimentary carbon concentrations in the riverine ecosystem. This paper examines the spatial variations of sedimentary organic carbon (OC sed ) and its potential relationship with terrestrial soil loss in two cascade reservoirs (Manwan and Dachaoshan) along the mainstream of Lancang River. During both wet and dry seasons in 2013 and 2014, 25 sampling sections were chosen to evaluate the spatial variations of sedimentary organic carbon. Generally, the contents of OC sed in the upper 5 cm of the bottom sediment in wet seasons were higher than those in dry seasons in both reservoirs. Spatially, lower reservoir (Dachaoshan) preserved higher OC sed content than the upper reservoir (Manwan), at 36.1 kg m −2 and 27.8 kg m −2 , respectively. Additionally, the contents of OC sed in the reservoir heads were higher than those in the reservoir centres and tails, this trend was also observed for terrestrial organic carbon (OC ter ) and liable organic carbon (LOC). Hillslope delivery ratio (HSDR) method are used to estimate the incoming sediment yields from the river basin. The results indicated that Dachaoshan catchment generated higher sediment stream deposits than the Manwan catchment with the high sediment loading (>40 t/ha/year) areas located within 3 km buffers encompassing a higher accumulation of farmlands. The cumulative effects of sediment transport on OC sed along the river channel were further investigated by setting sequential riverine sediment delivery ratios (0–0.55) to explore potential relationships between OC sed and total sediment delivered to stream. The results showed that in the Dachaoshan Reservoir the OC sed contents correlated with the total sediment delivered to streams when the ratios ranged from 0.10 to 0.55, in particular in delivery ratios ranging from 0.50 to 0.55. These findings emphasized the importance of direct and indirect connections between the terrestrial and riverine ecosystems, and also provided a preferable view to understand the cumulative effects of sediment transport on OC sed distributions in the reservoirs generated by cascading dams. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • FQI is a suitable index for evaluating the vegetation restoration. • Cu content had the greatest promotional effect on FQI. • Cd and TK contents had a significantly inhibitory effect on FQI. • Excessive nutrients might produce 'toxicity' to the growth of vegetation. Abstract Open-pit mining activities cause great damage to the local ecosystems. It is therefore necessary to assess and recover the vegetation status to maintain ecological stability. In this study, the Floristic Quality Index (FQI) was used to assess the vegetation habitat and the structural equation model (SEM) was applied to quantify the influences of different environmental factors on FQI in the Kunyang open-pit phosphate rock mine in Yunnan Province, China. Non-metric multidimensional scaling analyses revealed that great differences of vegetation community composition existed in the sampled plots, even those at similar distances to mining areas, which indicates that disturbing distance was not the only factor to determine the vegetation community. SEM results showed that Cu promoted the FQI most obviously (0.84), followed by Co (0.75), while the inhibition of Cd content in soil to the FQI was the most significant (−0.88), followed by TK (−0.82), and C (−0.79). Soil fertility quality and soil pollution indexes were also established to analyze the effects of comprehensive soil parameters on FQI. The results showed that the soil fertility quality index had a strong negative effect on FQI, which revealed that higher levels of TP, TN, TK, and other nutrients in the soil would produce 'toxicity' to the growth of vegetation. Findings from our study could provide a scientific method for assessing the ecological restoration results in the mining area. [ABSTRACT FROM AUTHOR]

Tree species and afforestation age can affect soil carbon (C) and nitrogen (N) sequestration as well as soil properties through different litter input and microbial activities. However, uncertainty remains because the responses vary under different climates and prior land uses. A site-specific study was conducted to investigate the dissimilarities in plant litter, soil properties, and soil microbial biomass and their influencing factors of different aged (22, 32, and 44 years) larch (Larix principis-rupprechtii) plantations and different aged (19, 30, and 43 years) Mongolian pine (Pinus sylvestris var. mongolica) plantations. In general, afforestation increased soil organic carbon (SOC), soil total nitrogen (STN), soil microbial biomass carbon (MBC), and soil microbial biomass nitrogen (MBN) contents compared with those of sparse grassland. However, there was still room for improvement in these variables compared with local natural secondary forest, which was dominated by white birch (Betula platyphylla , a deciduous broad-leaved tree species). Changes in STN, SOC, MBC, and MBN contents with afforestation age were almost insignificant in larch plantations, while significant increase can be found in STN (only in 10–20 cm soil layer), MBC and MBN in Mongolian pine plantations. The results indicated that larch was superior to Mongolian pine in soil C and N sequestration and soil fertility improvement at an early afforestation stage probably because of the higher C and N inputs from litter and higher N supply in the soil. There is an upper limit of carbon and nitrogen sequestration and soil fertility in the coniferous plantation, and mix planting of broad-leaved trees in coniferous forests may make up for this disadvantage. This study provided a reference for the selection of afforestation tree species in northern China and other areas with similar climatic conditions. • Afforestation increased SOC, STN, MBC, and MBN contents compared with those of barren land. • Changes in STN, SOC, MBC, and MBN contents with afforestation age varied in larch and Mongolian pine. • Larch was superior to Mongolian pine in soil fertility improvement at an early afforestation stage. • The higher C and N inputs from litter and N supply form soil may cause the differences between larch and Mongolian pine. [ABSTRACT FROM AUTHOR]