基于生态学原理的作物品种混合种植建立

作物品种混合种植具有很多有益效应,包括抑制病原体和增加产量和产量稳定性。然而,这些效应并不一定在所有作物品种混合种植中都出现,多样性带来的效应可能会因作物异质性的增加而抵消。在田间建立作物品种混合种植,如果没有预先预测组合哪些基因型可以产生表现良好的混合种植,会导致工作量过于庞大。因此,需要有效的工具来缩减有希望的品种混合种植组合,并在实验中确定其中哪些组合会带来最大效应。在这里,我们首先综述已有的关于生态多样性实验和当前农业应用效应及其机理,然后讨论应用这些知识开发良好品种混合种植组合时出现的一些主要困难。我们还讨论了解决其中一些问题的非常规方法。我们特别强调基于性状确定好的品种混合种植伙伴的潜力和局限性,并认为非传统性状和性状衍生的指标可能需要基于性状的方法来充分发挥其潜力。具体而言,我们认为可以使用现代遗传和基因组方法确定良好的混合种植伙伴。或者,可以通过组合对环境变化做出不同反应的品种(这些品种可以在标准品种测试试验中轻松识别)来获得良好的混作组合。初步分析结果表明,解释对不同环境响应的生态位差异,可以指示功能互补性并提高混合种植组合的产量及其稳定性。

On the combined effect of soil fertility and topography on tree growth in subtropical forest ecosystems—a study from SE China

Aims The aim of our research was to understand small-scale effects of topography and soil fertility on tree growth in a forest biodiversity and ecosystem functioning(BEF)experiment in subtropical SE China.Methods Geomorphometric terrain analyses were carried out at a spatial resolution of 5×5 m.Soil samples of different depth increments and data on tree height were collected from a total of 566 plots(667 m2 each).The soils were analyzed for carbon(soil organic carbon[SOC]),nitrogen,acidity,cation exchange capacity(CEC),exchangeable cations and base saturation as soil fertility attributes.All plots were classified into geomorphological units.Analyses of variance and linear regressions were applied to all terrain,soil fertility and tree growth attributes.Important Findings In general,young and shallow soils and relatively small differences in stable soil properties suggest that soil erosion has truncated the soils to a large extent over the whole area of the experiment.This explains the concurrently increasing CEC and SOC stocks downslope,in hollows and in valleys.However,colluvial,carbon-rich sediments are missing widely due to the convexity of the footslopes caused by uplift and removal of eroded sediments by adjacent waterways.The results showed that soil fertility is mainly influenced by topography.Monte-Carlo flow accumulation(MCCA),curvature,slope and aspect significantly affected soil fertility.Furthermore,soil fertility was affected by the different geomorphological positions on the experimental sites with ridge and spur positions showing lower exchangeable base cation contents,especially potassium(K),due to leaching.This geomorphological effect of soil fertility is most pronounced in the topsoil and decreases when considering the subsoil down to 50 cm depth.Few soil fertility attributes affect tree height after 1-2 years of growth,among which C stocks proved to be most important while pH_(KCl)and CEC only played minor roles.Nevertheless,soil acidity and a high proportion of Al on the exchange complex affected tree height even after only 1-2 years growth.Hence,our study showed that forest nutrition is coupled to a recycling of litter nutrients,and does not only depend on subsequent supply of nutrients from the mineral soil.Besides soil fertility,topography affected tree height.We found that especially MCCA as indicator of water availability affected tree growth at small-scale,as well as aspect.Overall,our synthesis on the interrelation between fertility,topography and tree growth in a subtropical forest ecosystem in SE China showed that topographic heterogeneity lead to ecological gradients across geomorphological positions.In this respect,small-scale soil-plant interactions in a young forest can serve as a driver for the future development of vegetation and biodiversity control on soil fertility.In addition,it shows that terrain attributes should be accounted for in ecological research.

Positive effects of tree species diversity on litterfall quantity and quality along a secondary successional chronosequence in a subtropical forest

Aims Litterfall,as an important link between aboveground and belowground processes,plays a key role in forest ecosystems.Here,we test for effects of tree species richness on litter production and litter quality in subtropical forest.The study further encompasses a factorial gradient of secondary succession that resulted from human exploitation.Given that a large percentage of subtropical forests are in secondary successional stages,understanding the role of biodiversity on forest re-growth after disturbance appears critical.Methods From January 2009 to December 2014,we monitored forest litterfall in 27 Comparative Study Plots that spanned a gradient of tree species richness(3-20 species)and secondary successional ages(~20 to 120 years)in Gutianshan Natural Nature Reserve,Zhejiang Province,China.The experiment is part of the biodiversity-ecosystem functioning research platform‘BEF-China’.Tree litterfall was collected in monthly intervals using litter traps.Samples were separated into leaf and non-leaf components.Leaf litter was further sorted into dominant and other species.Community level monthly leaf litter C and N contents were analysed through a full year.General linear mixed-effects models were applied to test for effects of tree species richness and successional age on litter quantity and leaf litter C/N.Important Findings Litterfall increased with species richness among and within successional age and this effect was consistent across years.Successionally older stands had higher litterfall and this effect was related to increased tree species richness.However,species richness did not change the intra-and inter-annual temporal stability of litterfall.Increasing tree species richness increased leaf litter quality(decreased C/N),while successional age had no effect.Our study indicates that more diverse forest stands produce more leaf litter and that this litter has higher N concentrations,which could promote forest growth through accelerated nutrient re-cycling.

Tree diversity increases levels of herbivore damage in a subtropical forest canopy:evidence for dietary mixing by arthropods?

Aims Plant diversity has been linked to both increasing and decreasing levels of arthropod herbivore damage in different plant communities.So far,these links have mainly been studied in grasslands or in artificial tree plantations with low species richness.Furthermore,most studies provide results from newly established experimental plant communities where trophic links are not fully established or from stands of tree saplings that have not yet developed a canopy.Here,we test how tree diversity in a species-rich subtropical forest in China with fully developed tree canopy affects levels of herbivore damage caused by different arthropod feeding guilds.Methods We established 27 plots of 30×30 m area.The plots were selected randomly but with the constraint that they had to span a large range of tree diversity as required for comparative studies in contrast to sample surveys.We recorded herbivore damage caused by arthropod feeding guilds(leaf chewers,leaf skeletonizers and sap feeders)on canopy leaves of all major tree species.Important Findings Levels of herbivore damage increased with tree species richness and tree phylogenetic diversity.These effects were most pronounced for damage caused by leaf chewers.Although the two diversity measures were highly correlated,we additionally found a significant interaction between them,whereby species richness increased herbivory mostly at low levels of phylogenetic diversity.Tree species with the lowest proportion of canopy leaf biomass in a plot tended to suffer the highest levels of herbivore damage,which is in contrast to expectations based on the resource concentration hypothesis.Our results are in agreement with expectations of the dietary mixing hypothesis where generalist herbivores with a broad spectrum of food plants benefit from increased resource diversity in tree species-rich forest patches.

Leaf area increases with species richness in young experimental stands of subtropical trees

Aims Most biodiversity-ecosystem functioning research has been carried out in grassland ecosystems,and little is known about whether forest ecosystems,in particular outside the temperate zone,respond similarly.Here,we tested whether productivity,assessed as leaf area index(LAI),increases with species richness in young experimental stands of subtropical trees,whether this response is similar for early-season leaf area(which is dominated by evergreens)and seasonal leaf area increase(which is dominated by deciduous species),and whether responses saturate at high species richness.Methods We used a planted tree biodiversity experiment in south-east China to test our hypotheses.LAI was determined three times by digital hemispheric photography in 144 plots that had been planted with 400 trees each,forming communities with 1,2,4,8 or 16 tree species.Important Findings LAI increased significantly with tree species richness in the fifth year of stand establishment.Similar,but weaker,statistically non-significant trends were observed 1 year before.We did not observe leaf area overyielding and the presence of particularly productive and unproductive species explained large amounts of variation in leaf area,suggesting that selection-type effects contributed substantially to the biodiversity effects we found in this early phase of stand establishment.Effects sizes were moderate to large and comparable in magnitude to the ones reported for grassland ecosystems.Subtropical(and tropical)forests harbor substantial parts of global net primary production and are critical for the Earth’s carbon and hydrological cycle,and our results suggest that tree diversity critically supports these ecosystem services.

Opposing intraspecific vs.interspecific diversity effects on herbivory and growth in subtropical experimental tree assemblages

Aims Positive plant diversity-ecosystem function relations are ultimately driven by variation in functional traits among individuals that form a community.To date,research has largely focused on the role of species diversity for ecosystem functioning.However,substantial intraspecific trait variation is common and a significant part of this variation caused by genetic differences among individuals.Here,we studied the relative importance of species diversity and seed family(SF)diversity within species for growth and herbivory in experimental subtropical tree assemblages.Methods In 2010,we set up a field experiment in subtropical China,using four species from the local species pool.Trees were raised from seeds,with seeds from the same mother tree forming an SF.We established 23 plots containing one or four species(species diversity treatment)and one or four SFs per species(SF diversity treatment).Tree growth(stem diameter,plant height and crown expansion)and herbivory(percentage leaf loss due to leaf chewers)were monitored annually from 2011 to 2013.Important findings Tree species richness promoted growth but had no effect on herbivory.In contrast,SF diversity reduced growth and increased herbivory but only so in species mixtures.Most of the observed effects were time dependent,with the largest effect found in 2013.Our results suggest that biodiversity can affect plant performance directly via tree species-species interactions,or context dependent,via potential effects on inter-trophic interactions.Two important conclusions should be drawn from our findings.Firstly,in future studies regarding biodiversity and ecosystem functioning(BEF)relationships,intraspecific genetic diversity should be given similar weight as species diversity as it has often been neglected and its effects are not well understood.Secondly,we demonstrate opposite effects of biodiversity among and within species,stressing the importance to consider the effects of multiple levels of biodiversity simultaneously.

Effect of clear-cutting silviculture on soil respiration in a subtropical forest of China

Aims Clear-cutting is a common forest management practice,especially in subtropical China.However,the potential ecological consequences of clear-cutting remain unclear.In particular,the effect of clear-cutting on soil processes,such as the carbon cycle,has not been quantified in subtropical forests.Here,we investigated the response of soil respiration(Rs)to clear-cutting during a 12-month period in a subtropical forest in eastern China.Methods We randomly selected four clear-cut(CC)plots and four corresponding undisturbed forest(UF)plots.Measurements of Rs were made at monthly time points and were combined with continuous climatic measurements in both CC and UF.Daily Rs was estimated by interpolating data with an exponential model dependent on soil temperature.Daily Rs was cumulated to annual Rs estimates.Important Findings In the first year after clear-cutting,annual estimates of Rs in CC(508±23g C m^(−2) yr^(−1))showed no significant difference to UF plots(480±12g C m^(−2) yr^(−1)).During the summer,soil temperatures were usually higher,whereas the soil volumetric water content was lower in CC than in UF plots.The long-term effects of clear-cutting on Rs are not significant,although there might be effects during the first several months after clear-cutting.Compared with previous work,this pattern was more pronounced in our subtropical forest than in the temperate and boreal forests that have been studied by others.With aboveground residuals off-site after clear-cutting,our results indicate that the stimulation of increasing root debris,as well as environmental changes,will not lead to a significant increase in Rs.In addition,long-term Rs will not show a significant decrease from the termination of root respiration,and this observation might be because of the influence of fast-growing vegetation after clear-cutting in situ.