Summary
The continuing nitrogen (N) deposition observed worldwide alters ecosystem nutrient cycling and ecosystem functioning. Litter decomposition is a key process contributing to these changes, but ...the numerous mechanisms for altered decomposition remain poorly identified.
We assessed these different mechanisms with a decomposition experiment using litter from four abundant species (Achnatherum sibiricum, Agropyron cristatum, Leymus chinensis and Stipa grandis) and litter mixtures representing treatment‐specific community composition in a semi‐arid grassland under long‐term simulation of six different rates of N deposition.
Decomposition increased consistently with increasing rates of N addition in all litter types. Higher soil manganese (Mn) availability, which apparently was a consequence of N addition‐induced lower soil pH, was the most important factor for faster decomposition. Soil C : N ratios were lower with N addition that subsequently led to markedly higher bacterial to fungal ratios, which also stimulated litter decomposition.
Several factors contributed jointly to higher rates of litter decomposition in response to N deposition. Shifts in plant species composition and litter quality played a minor role compared to N‐driven reductions in soil pH and C : N, which increased soil Mn availability and altered microbial community structure. The soil‐driven effect on decomposition reported here may have long‐lasting impacts on nutrient cycling, soil organic matter dynamics and ecosystem functioning.
Between‐species variation in nutrient resorption is one of the mechanisms explaining the positive relationship between biodiversity and primary productivity. Yet, the role of within‐species ...variations in nutrient resorption in mediating the relationship between biodiversity and productivity remains unclear.
We examined how within‐species nutrient resorption, and ultimately productivity, respond to changes in species richness by using four traits related to nitrogen and phosphorus use in four dominant species from different plant functional groups in a biodiversity removal experiment in the temperate steppe.
Nitrogen and phosphorus concentrations in both green and senesced leaves in all species significantly decreased with increasing plant species richness, suggesting that plants used those limiting nutrients more efficiently with increasing biodiversity. Plants in higher diversity communities resorbed more nutrients during senescence, which may facilitate reproduction and vegetative regrowth in the next year.
Synthesis. Our results highlight the importance of considering within‐species variation in nutrient resorption as an important underlying mechanism explaining the positive effects of biodiversity on primary productivity and ecosystem carbon accumulation.
Plants in higher‐diversity communities resorbed more nutrients during senescence, which may facilitate reproduction and vegetative regrowth in the next year. Our results highlight the importance of considering within‐species variation in nutrient resorption as an important underlying mechanism explaining the positive effects of biodiversity on primary productivity and ecosystem carbon accumulation.
摘要
生物多样性与生产力之间存在正向相关关系， 对这一关系内在驱动机制的探讨是国际生态学研究的热点问题， 主要的科学假说包括取样效应 (Sampling effect） 和互补效应 （Complementarity effect）。以往的研究认为植物群落内不同物种对土壤资源的互补性利用 （种间作用） 是导致生物多样性和生产力存在正向关系的重要原因之一， 却忽视了单种植物的养分利用特征 （种内变化） 随着群落中生物多样性的变化会发生怎样的改变， 这种改变进而会如何作用于生产力。本研究利用位于中国内蒙古典型草原的物种去除实验平台， 分析了羊草、大针茅、细叶葱、猪毛菜等四种来自四个不同的植物功能群的代表性植物在枯萎过程中养分回收效率随群落中植物物种多样性的变化情况。研究结果表明上述四种植物夏季绿色成熟叶片和秋季枯萎叶片中的氮磷养分含量均随着群落中物种多样性的增加而降低， 这说明在高多样性的群落中植物会提高自身的养分利用效率。在枯萎过程中， 多数植物的养分回收效率随着群落中植物多样性的增加而升高， 回收的这部分养分会进入植物的繁殖器官和储藏器官从而有利于植物的繁殖生长和下一个生长季的营养生长。本研究从植物养分利用特征种内变化这一新的角度解释了为什么生物多样性与生产力之间存在正向相关关系。
Ceftriaxone(Cef) selectively increases the expression of glial glutamate transporter‐1 (GLT‐1), which was thought to be neuroprotective in some circumstances. However, the effect of Cef on glutamate ...uptake of GLT‐1 was mostly assayed using in vitro studies such as primary neuron/astrocyte cultures or brain slices. In addition, the effect of Cef on neurons in different ischemic models was still discrepant. Therefore, this study was undertaken to observe the effect of Cef on neurons in global brain ischemia in rats, and especially to provide direct evidence of the up‐regulation of GLT‐1 uptake for glutamate contributing to the neuronal protection of Cef against brain ischemia. Neuropathological evaluation indicated that administration of Cef, especially pre‐treatment protocols, significantly prevented delayed neuronal death in hippocampal CA1 subregion normally induced by global brain ischemia. Simultaneously, pre‐administration of Cef significantly up‐regulated the expression of GLT‐1. Particularly, GLT‐1 uptake assay with 3H‐glutamate in living cells from adult rats showed that up‐regulation in glutamate uptake accompanied up‐regulated GLT‐1 expression. Inhibition of GLT‐1 by antisense oligodeoxynucleotides or dihydrokainate significantly inhibited the Cef‐induced up‐regulation in GLT‐1 uptake and the neuroprotective effect against global ischemia. Thus, we may conclude that Cef protects neurons against global brain ischemia via up‐regulation of the expression and glutamate uptake of GLT‐1.
Glutamate uptake by glial glutamate transporter‐1 (GLT‐1) is the principal way to regulate extracellular glutamate homeostasis in central nervous system. Over‐accumulation of glutamate results in excitotoxicity and injures neurons after cerebral ischemia. Ceftriaxone up‐regulates GLT‐1 expression and uptake of glutamate, diminishes the excitotoxicity of glutamate and then protects neurons against global brain ischemia.
Glutamate uptake by glial glutamate transporter‐1 (GLT‐1) is the principal way to regulate extracellular glutamate homeostasis in central nervous system. Over‐accumulation of glutamate results in excitotoxicity and injures neurons after cerebral ischemia. Ceftriaxone up‐regulates GLT‐1 expression and uptake of glutamate, diminishes the excitotoxicity of glutamate and then protects neurons against global brain ischemia.
Purpose
Soil nematodes play a fundamental role in regulating ecosystem carbon and nutrient cycling. It is widely recognized that soil nematode community composition is sensitive to nutrient ...enrichment, but the linkage between community assembly processes and functional changes under nutrient enrichment condition remains poorly understood.
Methods
We examined the compositional and functional responses and quantified the role of main community assembly processes (genus losses, genus gains, and context-dependent variations of abundance) in driving the carbon budget of soil nematode communities in response to nitrogen (N) and phosphorus (P) addition in a temperate grassland.
Results
Nitrogen and P addition significantly interacted to affect nematodes abundance, biomass, and functional variables of C cycling, in that P addition increased all the variables under ambient N condition but not under N enriched condition. Soil pH, ammonium concentration, and total phosphorus concentration played important roles in driving the variations of nematode C budgets, indicating the minor role of plant community characteristics. The enhancement of all variables following P addition was caused by the increases in the abundance of common genera (e.g.
Acrobeles
,
Scutylenchus
, and
Tylencholaimus
). The variation of genus richness contributed to the P-induced increases of nematode abundance but not to the increases of carbon budgets.
Conclusions
Our results uncover the linkages between community assembly processes and the abundance and C cycling function of soil nematode community under nutrient enrichment conditions. The significant interactive effects between N and P addition highlight the complexity in predicting the compositional and functional changes in soil nematode community under a scenario of multiple-nutrient enrichment.
Glial glutamate transporter 1 (GLT‐1) plays a vital role in the induction of brain ischemic tolerance (BIT) by ischemic preconditioning (IPC). However, the mechanism still needs to be further ...explained. The aim of this study was to investigate whether peroxisome proliferator‐activated receptor gamma (PPARγ) participates in regulating GLT‐1 during the acquisition of BIT induced by IPC. Initially, cerebral IPC induced BIT and enhanced PPARγ and GLT‐1 expression in the CA1 hippocampus in rats. The ratio of nuclear/cytoplasmic PPARγ was also increased. At the same time, the up‐regulation of PPARγ expression in astrocytes in the CA1 hippocampus was revealed by double immunofluorescence for PPARγ and glial fibrillary acidic protein. Then, the mechanism by which PPARγ regulates GLT‐1 was studied in rat cortical astrocyte‐neuron cocultures. We found that IPC 45 min of oxygen glucose deprivation (OGD) protected neuronal survival after lethal OGD (4 h of OGD), which usually leads to neuronal death. The activation of PPARγ occurred earlier than the up‐regulation of GLT‐1 in astrocytes after IPC, as determined by western blot and immunofluorescence. Moreover, the preadministration of the PPARγ antagonist T0070907 or PPARγ siRNA significantly attenuated GLT‐1 up‐regulation and the neuroprotective effects induced by IPC in vitro. Finally, the effect of the PPARγ antagonist on GLT‐1 expression and BIT was verified in vivo. We observed that the preadministration of T0070907 by intracerebroventricular injection dose‐dependently attenuated the up‐regulation of GLT‐1 and BIT induced by cerebral IPC in rats. In conclusion, PPARγ participates in regulating GLT‐1 during the acquisition of BIT induced by IPC.
Cover Image for this issue: doi: 10.1111/jnc.14532.
Open Science: This manuscript was awarded with the Open Materials Badge
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Ischemic preconditioning (IPC) could induce neuron ischemic tolerance. During this process, IPC activated PPARγ in astrocytes, then the activation of PPARγ triggered the up‐regulation of GLT‐1 and contributed to the induction of neuroprotection by IPC in vivo and in vitro. It could be concluded that astrocytic PPARγ participates in the induction of neuron ischemic tolerance by IPC via regulating GLT‐1.
Cover Image for this issue: doi: 10.1111/jnc.14532.
Aims
Nutrient addition is a widely-used strategy to restore degraded grasslands. It remains unknown whether and how the number of added nutrients affects the soil nematode community in degraded ...grasslands.
Methods
We examined the immediate responses of taxonomic and functional composition of the soil nematode community to different numbers of added nutrients using factorial combinations of nitrogen (N), phosphorus (P), and potassium (K + micronutrients) in a degraded grassland of northern China.
Results
The taxonomic and functional composition of the soil nematode community generally formed a unimodal relationship with the number of added nutrients. Changes of soil pH after fertilization affected the structural stability and complexity of the soil nematode community. The magnitude of nematode functional responses to nutrient supply was driven by changes of plant aboveground biomass and soil pH.
Conclusions
Soil nematode community showed non-linear responses to the variations of the number of added nutrients in a degraded grassland, which contrasts previous findings from plant community. The number of added nutrients should be given full consideration in formulating effective restoration strategies for degraded grasslands.
Anthropogenic nitrogen (N) deposition has affected plant community composition and nutrient cycling in terrestrial ecosystems worldwide. This includes changes to the way plants use and recycle ...nutrients, including effects on nutrient resorption, which is a key process through which plants recover nutrients from tissue during senescence. Nutrient resorption has considerable adaptive and functional significance for plants and helps regulate core ecosystem processes such as decomposition. However, our understanding of how N deposition affects nutrient resorption and, in particular, of how N inputs alter ecosystem resorption via changes to existing species’ resorption compared with changes to community composition remains poor. To disentangle the role of species
versus
community composition controls driving variation in nutrient resorption responses to N inputs, we carried out an experiment with six different N addition rates in a temperate steppe. We found that species-scale nutrient resorption responses to N enrichment were variable; for example, only half of the measured species reduced both N and P resorption efficiency in response to increased N inputs. In contrast, community-scale responses consistently resulted in reduced N and P resorption. Still, N-induced changes in community composition were a weaker control on overall resorption responses than were the effects on individual species; however, it was the synergistic interaction between the two that resulted in the large total reductions of nutrient resorption in the face of increased N. Taken together, our results highlight that understanding and predicting nutrient resorption responses will be most accurately scaled by accounting not only for species’ reductions in resorption but also for changes in community composition.
Cerebral ischemic preconditioning (CIP)-induced brain ischemic tolerance protects neurons from subsequent lethal ischemic insult. However, the specific mechanisms underlying CIP remain unclear. In ...the present study, we explored the hypothesis that peroxisome proliferator-activated receptor gamma (PPARγ) participates in the upregulation of Klotho during the induction of brain ischemic tolerance by CIP. First we investigated the expression of Klotho during the brain ischemic tolerance induced by CIP. Lethal ischemia significantly decreased Klotho expression from 6 h to 7 days, while CIP significantly increased Klotho expression from 12 h to 7 days in the hippocampal CA1 region. Inhibition of Klotho expression by its shRNA blocked the neuroprotection induced by CIP. These results indicate that Klotho participates in brain ischemic tolerance by CIP. Furthermore, we tested the role of PPARγ in regulating Klotho expression after CIP. CIP caused PPARγ protein translocation to the nucleus in neurons in the CA1 region of the hippocampus. Pretreatment with GW9962, a PPARγ inhibitor, significantly attenuated the upregulation of Klotho protein and blocked the brain ischemic tolerance induced by CIP. Taken together, it can be concluded that Klotho upregulation via PPARγ contributes to the induction of brain ischemic tolerance by CIP.
Background
Manganese (Mn) is an essential nutrient for plant growth and a key factor driving litter decomposition. Nitrogen (N) deposition is expected to enhance soil Mn availability via soil ...acidification, and subsequently to increase plant Mn concentrations.
Aims
We aimed to quantify the responses of Mn concentrations in green and senesced shoots at both species and community levels to N addition, and determine whether N addition would decrease Mn retranslocation efficiency during plant senescence.
Methods
We examined the changes of Mn concentrations in soil and in green and senesced shoots of all plant species across multiple N addition rates ranging from 0 to 50 g N m−2 y−1 in a temperate steppe after six years treatments. Plant Mn retranslocation efficiency were quantified at species, life form, and community levels. The relationship between plant Mn nutritional parameters and soil Mn availability across the N addition gradient was analyzed.
Results
There were positive correlations between plant Mn concentrations and N addition rates for most species. Relative to the control plots, community‐level mean Mn concentration in green and senesced shoots in the plots received the highest level of N addition increased by 137.50% (from 0.19 mg kg−1 to 0.08 mg kg−1) and 187.50% (from 0.23 mg kg−1 to 0.08 mg kg−1), respectively. There was no correlation between Mn retranslocation efficiency and N addition rates at species, life form and community levels. Plant Mn status was weakly correlated with soil Mn concentrations for most species.
Conclusions
Plant Mn retranslocation showed conserved responses to increasing N addition rates, which would be an adaptive strategy for plants in face of N‐induced higher soil Mn availability.
Aims The responses of functional structures in plant communities to global change drivers is predicted to be driven by both species turnover and intraspecific trait variability (ITV). However, the ...relative importance of those two drivers is not well-known, which retards our ability to predict the functional changes of plant community under global change scenarios. We hypothesized that ITV rather than species turnover would drive the nutritional responses of plant community at the initial stage after nitrogen and water enrichment. Methods We measured community weighted means (CWM) and non-weighted means (CM) of foliar N and P concentrations and N:P ratio in a temperate steppe after two years factorial N and water addition. Species composition and nutrition traits of each species were recorded in each plot. Results The impacts of N addition on community level nutrition traits were highly dependent on water conditions, as indicated by significant interactive effects between N and water addition. Nitrogen addition significantly increased CWM of foliar N, but only under ambient water condition. Water addition decreased CWM of foliar P and increased that of N:P. Consistent with our hypothesis, communities responded to both N and water addition after two years treatments mainly through ITV. Conclusions Our results highlight the importance of ITV in driving short-term responses of community functional composition to the increases of nitrogen and water availability in the temperate steppe. The existence of interactive effects of N and water addition would make it more difficult to predict the impacts of N deposition on plant-mediated biogeochemical cycling under the scenarios of precipitation regime changes than previously assumed.
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