Effects of nitrogen and phosphorus additions on soil nematode community of soybean farmland

The nitrogen(N)and phosphorus(P)addition promotes the abundance of soybean soil nematodes.The addition of nitrogen can alleviate the suppression of phosphorus on nematodes.Phosphorus addition affects nematode abundance by ammonium nitrogen.

Accuracy of space-for-time substitution for vegetation state prediction following shrub restoration

Aims:Space-for-time substitution(SFT)is often used for vegetation status estimation during the recovery process of deserts.However,the evaluated accuracy of SFT remains uncertain.An eight-year located observation was used to assess the validity of SFT for vegetation state prediction.Methods:This study analyzed a chronosequence of Caragana microphylla Lam.plantings using the located observation method to test the accuracy of SFT for vegetation state prediction in the mobile sand dunes of the Horqin Sandy Land in northeastern China from July 2005 to June 2013.Important Findings:According to SFT,simple vegetation parameters(density,coverage and biomass)were found to be unstable,while sophisticated veg-etation parameters(species diversity and evenness)were relatively stable across the experimental treatments during the study period.Conversely,both the simple and sophisticated parameters were found to be relatively stable when tested using the located obser-vation method.Furthermore,most simple vegetation parameters slightly increased,while sophisticated parameters slightly decreased after eight years of field observations.Thus,long-term restoration management facilitated improvements in the simple parameters,but may have adversely impacted the sophisticated parameters in the post-restoration community.Our results suggest that sophisticated vegetation parameter states can be predicted by SFT,while simple vegetation parameter states are not well predicted by SFT.in conclusion,located observations or other effective evaluation methods must be employed to offset the deficiency of the SFT method for the prediction of vegetation parameters.

Effects of fire and nitrogen addition on photosynthesis and growth of three dominant understory plant species in a temperate forest

Aims Fire and atmospheric nitrogen(N)deposition have the potential to influence growth and productivity of forest canopy.However,their impacts on photosynthesis and growth traits of understory plants in forests remain largely unexplored.This study was conducted to examine the effects of burning and N addition on foliar N content,net photosynthesis and growth traits of three dominant shrub species(Vitex negundo,Lindera glauca and Symplocos chinensis)in a temperate forest in Central China.Methods The experiment used a pair-nested design,with four treatments(control,burning,N addition and burning plus N addition)and five replicates.Leaf mass area(LMA),area-based concentrations of foliar N and chlorophyll(N_(area) and Chl_(area)),net photosynthesis(A_(n)),stomatal conductance(g_(s)),maximum photosynthetic rate(A_(max))and maximal carboxylation rate(V_(cmax)),basal diameter,height and branch length(BL)of the three species were measured.Important Findings Across the three species,burning stimulated LMA,N_(area),Chl_(area),A_(n),g_(s),A_(max) and V_(cmax),and consequently enhanced basal diam-eter,height and BL.Nitrogen addition increased A_(n) and gs but did not affect LMA,N_(area),Chl_(area),A_(max),V_(cmax),basal diameter,height or BL.However,N addition strengthened the positive effects of burning on g_(s),V_(cmax),A_(n) and BL.The findings indicate the primary role of light resources in determining plant photosynthesis and growth of understory shrub species after fire and highlight that understory plants should be considered in projection of biomass accumulation and productivity of forests under environmental perturbations.

群落时间稳定性对刈割和养分富集的响应随时间的变化

土地利用和养分富集能对生物多样性和生态系统功能产生巨大的影响。然而,群落时间稳定性对土地利用和养分富集的响应是如何随时间变化的尚不清楚。作为历经15年(2005-2019)野外实验的一部分,本研究旨在探索在蒙古高原温带草原上,刈割、氮添加和磷添加对群落时间稳定性的效应。经过15年的实验,氮添加和磷添加均降低了群落时间稳定性,尤其是灌木和半灌木功能群的时间稳定性。刈割仅在实验早期(2005-2009)增加群落时间稳定性。氮添加在实验早期和末期(2015-2019)降低了群落时间稳定性,但在实验中期(2010-2014)反而提高了群落时间稳定性。磷添加在实验早期只轻微降低群落时间稳定性,但在实验末期显著降低群落时间稳定性。氮添加引起的群落时间稳定性变化的波动主要归因于其对物种异步性和种群时间稳定性的不同影响。我们的发现强调了植物功能群和物种异步性在调控群落时间稳定性方面的重要作用,以及仍然需要进行更长期的研究,以准确预测全球变化背景下的生态系统响应模式。

土地利用方式对黄河漫滩土壤微生物群落结构和多样性的影响

土壤微生物群落及其多样性是土壤碳和养分循环的重要生物指标。土地利用变化是影响漫滩生态系统土壤微生物群落组成的主要决定因素。然而,土壤微生物群落的结构和多样性如何响应土地利用变化,以及这些变化的主要驱动因素是什么,仍不清楚。本研究在黄河漫滩进行,以检验土地利用变化对土壤微生物群落的影响。选取了4种土地利用类型(灌丛、农田、草地和森林),其中以灌木地为对照,用磷脂脂肪酸测量了土壤微生物组成和多样性。研究结果表明,土地利用变化显著影响了总细菌、真菌和革兰氏阳性/阴性细菌。与灌丛相比,农田的总磷脂脂肪酸和细菌较高,森林的真菌较高。土壤pH值和全磷是微生物组成的最佳预测因子,分别解释了37%和26%的变异性。土壤全氮和硝态氮是影响微生物多样性的主要因素。花生农田的土壤碳含量、土壤碳储量、磷脂脂肪酸总量和微生物多样性最高,表明漫滩具有巨大的碳汇潜力。这些研究结果表明,黄河漫滩的农田对于维持土壤微生物群落和土壤碳固存至关重要。

Effects of warming on soil respiration during the non-growing seasons in a semiarid temperate steppe

尽管许多研究认为增温对陆地生态系统非生长季土壤呼吸的影响非常重要,但是关于这一问题仍缺乏充分的理解。本论文研究了非生长季增温对温带半干旱草原土壤呼吸的影响,并探讨了其影响机制。本实验位于温带半干旱典型草原,包括10对样地,每对样地包括一个对照和模拟增温处理。模拟增温样地自2014年10月开始,采用开顶箱(OTC)进行。2014年10月到2015年4月,2015年10月到2016年4月期间每月测定几次土壤呼吸、土壤温度与土壤湿度;并测定0-20 cm微生物量碳(MBC)、微生物量氮(MBN)和土壤速效氮。采用重复测量方差和成对t检验方法分析增温、时间及其交互作用对土壤呼吸的影响。采用简单回归确定各指标之间的因果关系。结果表明,对照样地非生长季平均土壤呼吸速率为0.24μmol m^(-2) s^(-1),约占当地生长季碳通量的14.4%。模拟增温在两个非生长季使土壤温度和土壤呼吸分别比对照样地提高了1.48℃(P<0.001)和42.1%(P<0.01)。2015-2016年非生长季模拟增温降低了0.66%的土壤湿度,降低幅度不显著。模拟增温处理下2015-2016年非生长季MBC和MBN分别显著提高了19.72%和20.99%(P<0.05)。此外,研究结果还表明,土壤温度、MBC和MBN的变化调控了土壤呼吸对模拟增温的响应。本结果揭示非生长季土壤呼吸变化能影响碳循环的其它组分,并可以有效促进气候变化背景下陆地生态系统碳循环的模型预测。

Carbon fluxes and species diversity in grazed and fenced typical steppe grassland of Inner Mongolia, China

Aim Grasslands are dominant vegetation of China,support outstanding biodiversity and sequester bulk amount of atmospheric CO_(2).These grasslands are highly degraded and fragmented due to remarkable anthropogenic and grazing loads.Chinese Government has made great attempt to restore by grazing exclusion.The relations of carbon fluxes with species composition and diversity in the communities sensitive to grazing by large herbivores are needed to be analysed under the global climate change scenario.The objective of present study was to comprehend the effects of grazing and fencing on the ecosystem structure and function of the typical steppe grassland.Methods To meet the objectives,overgrazed and fenced(since year 2001)sys-tems were selected in typical steppe grassland at the Duolun Restoration Ecology Research Station,Inner Mogolia,China.Within each system,three dominant communities with three replicates were selected.In each replicate community,three 1×1 m plots,were randomly located.Each plot was divided into four 50×50 cm quadrats.A total of 216,50×50 cm quadrats were sampled.From each quadrat,number of individuals and above-ground herbaceous biomass for each species,soil respiration(SR),ecosystem respira-tion(ER),net(NEE)as well as gross(GEE)ecosystem CO_(2) exchanges were recorded in June 2015.Data were well analysed using statistical software.Canonical correspondence analysis showed dif-ferential responses of communities to the structure and function of the typical steppe grassland.Important Findings Across the communities,fencing reduced the soil tempera-ture by 12%and at the same time increased the soil moisture by 44.30%,thus,increased the species richness by 28%,evenness by 21%,above-ground biomass by 19%and plant carbon by 20%.Interestingly,fencing increased NEE by 128%,GEE by 77%,SR by 65%and ER by 39%.Under fencing,species composition partially governed the CO_(2) exchange processes.Conclusions Fencing reduces soil temperature and thereby improves species diversity and more efficient CO_(2) sequestration and long-term and in-depth study is desirable for a better understanding of the relation-ship between species diversity and ecosystem carbon uptake.

Considerable impacts of litter inputs on soil nematode community composition in a young Acacia crassicapa plantation

Aboveground litter inputs and root exudates provide basal resources for soil communities,however,their relative contributions to soil food web are still not well understood.Here,we conducted a field manipulative experiment to differentiate the effects of litter inputs and living root on nematode community composition of surface and subsoils in a young Acacia crassicapa plantation in southern China.Our results showed that both litter addition and root presence significantly enhanced soil nematode abundance by 17.3%and 35.3%,respectively.Litter addition altered nematode trophic group composition,decreased fungivore to bacterivore ratio,and enhanced maturity index and structure index,which led to a bacterial-based energy channel and a more complex food web structure.However,root presence had a limited impact on the nematode community composition and ecological indices.Despite nematodes surface assembly,soil depth did not affect nematode trophic group composition or ecological index.Our findings highlight the importance of litter inputs in shaping soil nematode community structure and regulating soil energy channel.