植物养分捕获策略随成土年龄的变化及生态学意义

自然成土过程中土壤养分的变化与植被原生演替常同时发生。随成土年龄变化的植物养分捕获策略(NASs)对植物竞争能力和演替过程具有重要影响。该文将植物NASs划分为细根、微生物、特殊根系、食虫和寄生策略等5个类型;发现植物NASs的多样性随成土年龄的增加呈哑铃型变化模式;特殊根系策略对植物捕获养分的作用在成土中期最小、后期最大,细根和微生物策略的作用随成土年龄的增加逐渐降低;分析了成土过程中NASs对植物种间关系影响的变化,发现NASs对成土早期植物的促进作用和中期的竞争关系具有重要影响,而成土后期多样和互补的NASs对植被群落的稳定共存及多样性的形成具有影响;提出应进一步探究成土过程中土壤养分与植物NASs变化之间的定量关系,开展更多研究以阐明NASs对植被原生演替、物种多样性形成和成土过程的贡献与机理。

Arsenic in Rice Soils and Potential Agronomic Mitigation Strategies to Reduce Arsenic Bioavailability： A Review

Soils used for rice （Oryza sativa L.） cultivation in some areas contain high concentrations of arsenic （As）due to irrigation with groundwater containing As and intensive use of agrochemicals or industrial residues containing As. To restrict rice uptake of As in these soils, approaches to reduce As input and bioavailability must be considered. One approach to reduce As input into rice soils or uptake by rice is cultivating rice under aerobic, intermittent flooding, or alternate wetting and drying （AWD） conditions, rather than in submerged soils, or use of irrigation water low in As. For reducing As bioavailability in soil, aerobic or AWD rice culture and application of biochar, sulfur （S）, and/or rice polish to soil are promising. Moreover, use of As-hyperaecumulating plant species （e.g., Pteris vittata L.） in rotation or combinations with favourable plant species （e.g., Azolla, Chlorella, or Nannochloropsis species） can also be promoted, in addition to using rice cultivars that are tolerant to As. Though applications of high doses of phosphorus （P）, iron （Fe）, and silicon （Si） fertilizers have shown promise in many instances, these methods have to be practiced carefully, because negative effects have also been reported, although such incidents are rare. Major factors affecting As speciation and bioavailability in soil are chemical properties such as redox status, pH, and Fe, P, Si, and S concentrations, physical properties such as texture and organic matter, and biological properties such as methylation activity by soil microorganisms. However, as many of these factors interact, long-term examination under field conditions is needed before measures are recommended for and implemented in farmers＇ fields.

Nutrient resorption from senescing leaves of epiphytes,hemiparasites and their hosts in tropical forests of Sri Lanka

Aims Epiphytes and hemiparasites do not have direct access to soil nutri-ents.Epiphytes acquire nutrients through symbiosis,foliar leachates and throughfall,whilst hemiparasites have specialized structures(haustoria)to acquire nutrients from their host.Irrespective of the green leaf nutrient concentrations of epiphytes,hemiparasites and their hosts,nutrient-resorption efficiency and proficiency are expected to be the greater in epiphytes than in their hosts and in hemiparasites.These hypotheses were tested.Methods Green and senescing leaves of epiphytes(n=23),hemiparasites(n=9)and their hosts were collected,and leaf area,leaf dry weight,nutrient(nitrogen-N,phosphorus-P,potassium-K,calcium-Ca)and sodium(Na)concentrations were measured,and resorption effi-ciency(%)and proficiency were calculated.Important Findings Concentrations of N,P,K,Ca and Na in green leaves of epiphytes and hemiparasites were either similar or greater than those of their hosts,except for lower green leaf N concentration in hemiparasites.Epiphytes resorbed N,P,K and Na,while their hosts resorbed only N,P and K.Hemiparasites and their hosts resorbed P,K and Na while N was not resorbed.Overall,resorption efficiency was great-est in epiphytes>hemiparasites=hosts,while the resorption pro-ficiencies were similar or greater for epiphytes and hemiparasites compared with their hosts,except for N in hemiparasites.Relatively high nutrient concentrations in epiphytes were associated with greater resorption efficiency.Understanding contrasting nutrient concentrations in epiphytes,hemiparasites and their hosts will be important in recognising their contribution to ecosystem nutrient cycling.

In the beginning,there was only bare regolith-then some plants arrived and changed the regolith

Pedogenesis along chronosequences has received attention from soil scientists for decades,following the pioneering work of Walker and Syers(1976),who showed a general pattern of the availability of nitrogen(N)and phosphorus(P)subsequently confirmed for a range of chronosequences(Huggett 1998;Turner and Condron 2013;Vitousek and Farrington 1997).Much more recently,changes of plant nutrient-acquisition strategies with soil development have drawn attention,first with a conceptual model(Lambers et al.2008),which was subsequently confirmed with solid experimental data collected along the Jurien Bay chronosequence in south-western Australia(Zemunik et al.2015).The original conceptual model has since been amended,to explain why presumably less-effective mycorrhizal P-acquisition strategies coexist with more-effective strategies based on the release carboxylates(organic anions)(Lambers et al.2018).Mycorrhizas may not be effective at acquiring P from severely P-impoverished soils,but they do boost the defence against pathogens,which strongly affect the growth of non-mycorrhizal carboxylate-releasing Proteaceae(Albornoz et al.2017;Lalibertéet al.2015).What has received little or no attention is the P-acquisition strategies of species that are the first to colonize the bare regolith of the earliest stage of chronosequences(Figs 1 and 2).When the soil P availability is relatively high such as along the Jurien Bay chronosequence(Turner et al.2018),there is little point searching for specialized strategies,but along many chronosequences,i.e.not the case(Egli et al.2012;Richardson et al.2004;Zhou et al.2019).

Leaf traits from stomata to morphology are associated with climatic and edaphic variables for dominant tropical forest evergreen oaks

Aims Understanding variation and coordination of leaf traits at multiscales along elevational gradients can help predict the likely responses of dominant species to climate change.We seek to determine the extent to which variation in leaf stomatal,anatomical and morphological traits is associated with environmental factors,and whether ecological strategies of Cyclobalanopsis species shift with elevations.Methods In a tropical forest landscape in Jianfengling,South China,we determined leaf traits related to stomata,anatomy and morphology of six evergreen oak species(Cyclobalanopsis bambusaefolia,C.hui,C.patelliformis,C.fleuryi,C.tiaoloshanica and C.phanera)along a long elevational gradient(400–1400 m above sea level).Important Findings We found that stomatal density and stomatal pore index increased,whereas spongy mesophyll thickness to leaf thickness ratios decreased,significantly with elevation.The leaf area and leaf dry matter content increased and decreased,respectively,with elevation.Variations in stomatal,anatomical and morphological traits were mainly correlated to the mean annual temperature,mean annual sum precipitation and soil pH.At low and high elevations,the oak species exhibited strong stress tolerance combined with competition strategy,while they shifted toward more clearly the competitive strategy at intermediate elevations.And the changes in soil phosphorus concentration and soil pH along the elevation may drive the shift of ecological strategy.The results showed that the dominant oak species in tropical forests respond to environmental change by modulating traits at multiple levels,from that of the individual cell,through tissue and up to the whole leaf scale.

Revisiting mycorrhizal dogmas:Are mycorrhizas really functioning as they are widely believed to do?

Since the discovery of mycorrhizas,dogmas have been developed regarding their function,ecology,and distribution.We explore if these dogmas are valid,and if there are research biases toward regions inhabited by most researchers and away from regions inhabited by most plant species.We found,first,that the mycorrhizal status is known in less than 1%of plant species,with few having proven mycorrhizal benefits for growth and development.Second,the mycorrhizal status of a plant species varies within families,even genera.Third,mycorrhizas are important for phosphorus acquisition only within a narrow phosphorus range.Fourth,mycorrhizal plants are not uniform in their response to environment;taxonomy,phylogeny and continental history strongly drive mycorrhizal diversity.For example,the center of diversification of Ericaceae and Orchidaceae is in the neotropics,rather than,as recently claimed,in cold and high-latitude climates.Understanding the importance of mycorrhizas at the family-wide and biome-wide level is therefore conflicted by a research bias toward research-intensive regions outside the phylogenetic hotspots of diversification.The current precepts on mycorrhizas provide important starting points for hypotheses to robustly test when and where mycorrhizas play a role in determining ecological trajectory.The time has come to move forward and revisit past assumptions and update the dogmas,rather than assume functional significance in terms of nutritional benefits from studies on extraneous regions and species.We conclude that non-nutritional benefits deserve far greater attention.

Highlights of special issue on “Sustainable Phosphorus Use in Agri-Food System”

Phosphorus(P)is an essential element for plants,and all other life on Earth including humans.However,P is a nonrenewable resource with a very uneven distribution in the world.In the agri-food system,P is supplied to agricultural land as chemical P fertilizer and/or animal manure for producing food,feed and fiber,followed by their use or consumption by animals and humans.Despite some returns of P in crop production as organic manure,large amounts of P are released into the environment,severely contributing to pollution or eutrophication(mainly surface waters like rivers,lakes and oceans).Therefore,how to close the P cycle in the agri-food system has become a major challenge for ensuring food and environmental security globally.This special issue focuses on the sustainable use of P in agriculture,and comprises 12 review and research articles covering a wide range of topics on P resources,P use in crop and animal systems,P recycling and eco-environment.

CHALLENGES PROVIDING MULTIPLE ECOSYSTEM BENEFITS FOR SUSTAINABLE MANAGED SYSTEMS

Since humans started practicing agriculture at the expense of natural forests,8000 years ago,they have affected atmospheric CO_(2) concentrations.Their impact on atmospheric CH_(4) started about 5000 years ago,as result of the cultivation of paddy rice.A challenge of modern agricultural practices is to reverse the impact cropping has had on greenhouse gas emissions and the global climate.There is an increasing demand for agriculture to provide food security as well as a range of other ecosystem services.Depending on ecosystem management,different practices may involve trade-offs and synergies,and these must be considered to work toward desirable management systems.Solution toward food security should not only focus on agricultural management practices,but also on strategies to reduce food waste,more socially-just distribution of resources,changes in lifestyle including decarbonization of the economy,as well as reducing human population growth.

SUSTAINABLE CROP AND PASTURE SYSTEMS:FROM ABOVE-AND BELOWGROUND INTERACTIONS TO ECOSYSTEM MULTIFUNCTIONALITY

Intensive agriculture, characterized by strong reliance on excessive amount of external agrochemical inputs in simplified cropping systems has contributed successfully to feeding an increasing number of humans, but at the expense of severe resource and environmental costs. Consequently, the Earth is facing multifaceted challenges, including increasing food demand both in quantity and quality, global warming associated with extreme weather events, soil degradation and depletion of natural resources.

Highlights of special issue on“Sustainable Phosphorus Use in Agri-Food System”

The original version of this article unfortunately contained a project duration mistake.The correction is given below:The duration“2009-2011”(Page 312,line 4)of Sino-German research collaboration project should be“2008-2012”。