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Planned urban form has become an important strategy to improve air quality in urban agglomerations (UAs), especially pollution due to PM

The major goal of ecological security patterns (ESPs) is to identify key ecological sources and corridors, which play an important role in achieving regional sustainability. Although an increasing number of reviews have been published on constructing ESPs, reasonably prioritizing ecological corridors to maintain vital ecological processes and landscape connectivity remains a challenge. This study aimed to provide guidance for landscape management and decision making by developing an evaluation framework to construct ESPs and further prioritize potential corridors. Taking Jiangsu Province as a study area, we identified ecological sources by considering three key ecosystem services (biodiversity, carbon storage and water yield) and three ecological sensitivity indicators (soil erosion sensitivity, water sensitivity and habitat sensitivity) using the InVEST model, RULSE model and GIS spatial overlay analysis. Then, ecological corridors were delineated with the least-cost path method, and the ESPs were obtained by combining these corridors with ecological sources. We further prioritized ecological corridors based on the gravity model and the probability of connectivity index. The ESPs of Jiangsu Province contained 51 patches and 37 corridors. The total area of the ecological patches was 15,170.51 km2, accounting for 14.61% of the study area and primarily consisting of water bodies, cropland and forestland. Ecological corridors comprised 1920.38 km and were divided into four quadrants via a precedence matrix. The sixteen ecological corridors in the first quadrant (high importance and strong connectivity) were defined as priority areas and occupied 39.50% of the total corridor length. Our methodology framework offers a valuable tool for constructing ESPs and prioritizing corridors at the regional scale. This framework incorporates targeted ecosystem services and ecological vulnerability indicators to systematically assess and identify key ecological space. The conservation of ecological corridors selected in light of their importance and contribution to enhancing connectivity is a more targeted measure. It could be applied to other landscapes and geographical contexts.

Although compact urban form plays an important role in constraining emissions of carbon dioxide (CO

Increasing levels of nitrogen (N) in aquatic ecosystems due to intensified human activities is focusing attention on N removal mechanisms as a means to mitigate environmental damage. Important N removal processes such as denitrification can resolve this issue by converting N to gaseous emissions. Here, the spatiotemporal variability of N removal rates in China's Zhongtian River, a headwater stream that contains wetlands, was investigated by quantifying gaseous emissions of the main end products, N

Formulation of suitable land use strategies for sustainable management of urban landscapes requires assessment of the potential impact of future urban expansion on ecosystem services. We assessed land use change in the rapidly urbanizing Kunshan City of China during 2006–2016 and projected future land uses in 2030 under three alternative scenarios: Business-As-Usual (BAU), Croplands Protection (CP), and Ecological Restoration (ER). Then we quantified the spatio-temporal variations of six ecosystem services (including crop production, carbon storage, habitat quality, flood regulation, and nitrogen and phosphorus retention) in response to urban land use change from 2006 to 2030 using the InVEST model. We also analyzed temporal variation of the tradeoffs and synergies among multiple ecosystem services throughout the period of study. Our estimates indicate that the urban land of Kunshan increased by 19% over the past decade and will continue to expand by 15% from 2016 to 2030 under the BAU scenario. As a result, crop production, carbon storage, habitat quality, and flood regulation capacity would all decrease tremendously. Crop production would remain stable under the CP scenario owing to the strict protection of croplands, but nitrogen and phosphorus loading would increase by 8%. In contrast, the ER scenario would decrease nutrient loading by over 35% with concomitant benefits to carbon storage, habitat quality, and flood regulation capacity. However, crop production would decrease dramatically under the ER scenario, primarily due to the transition of large areas of croplands to ecological zones. Although croplands were the major sources for nitrogen and phosphorus loading in Kunshan during the years 2006–2016, urban land would become the major source of pollution under all future scenarios. Crop production and habitat quality were not significantly correlated during the years 2006–2016, while they would be positively correlated under the BAU and CP scenarios. This implies that croplands would become increasingly important in providing habitats as urban land continues to expand by replacing ecological land from 2016 to 2030. We propose four major land use strategies, including compact urban growth, croplands protection, reforestation to build greenways, and wetlands restoration in the riparian areas of drinking water sources to improve ecosystem services in Kunshan.

The concept of water–energy–food (WEF) nexus is gaining favor as a means to highlight the functions of the three individual nexus elements as interrelated components of a single complex system. In practice, the nexus approach projects forward from the present, seeking to maximize future WEF synergies and avoid undesirable tradeoffs. A complementary approach was employed here to gain insights into how the ancients dealt with WEF relationships, whether currently relevant nexus principles were practiced long ago, and how past WEF dynamics compare to those of today. Two examples, both dating to before the common era (BCE), are considered in detail. The qanats of ancient Persia brought groundwater to the surface and directed it to clusters of agricultural fields in arid areas where crop production was not otherwise feasible. In contrast, the Dujiangyan irrigation scheme of ancient China harnessed previously destructive surface water flows to stabilize food production across a vast agricultural plain. Designed and constructed under highly uncertain conditions and with a long-term perspective, both relied on local resources and expertise to exploit the tight coupling of water and the intrinsic energy from its flows to produce food. Ingenious infrastructure combined with sound governance allowed both to achieve remarkable synergies among the WEF components with minimal apparent tradeoffs. Although both are now challenged by climate change and the increasing complexity of modern WEF relationships, qanat systems and the Dujiangyan irrigation scheme have survived for millennia and still exist in recognizable form. This is due in large part to the persistence of governance systems that devolved significant decision-making authority to those who used water and energy for food production. Although it is not feasible to roll back technology to that of an earlier time, the successful attributes of earlier WEF governance systems warrant more attention in the future.

Wetlands can improve water quality, but they are also recognized as important sources of greenhouse gases (GHG) such as nitrous oxide (N

The Qiandao Lake Basin (QLB), which occupies low hilly terrain in the monsoon region of southeastern China, is facing serious environmental challenges due to human activities and climate change. Here, we investigated source attribution, transport processes, and the spatiotemporal dynamics of nitrogen (N) movement in the QLB using the Soil and Water Assessment Tool (SWAT), a physical-based model. The goal was to generate key localized vegetative parameters and agronomic variables to serve as credible information on N sources and as a reference for basin management. The simulation indicated that the basin&rsquo, s annual average total nitrogen (TN) load between 2007 and 2016 was 11,474 tons. Steep slopes with low vegetation coverage significantly influenced the spatiotemporal distribution of N and its transport process. Monthly average TN loads peaked in June due to intensive fertilization of tea plantations and other agricultural areas and then dropped rapidly in July. Subsurface flow is the key transport pathway, with approximately 70% of N loads originating within Anhui Province, which occupies just 58% of the basin area. The TN yields of sub-basins vary considerably and have strong spatial effects on incremental loads entering the basin&rsquo, major stream, the Xin&rsquo, anjiang River. The largest contributor to N loads was domestic sewage (21.8%), followed by livestock production (20.8%), cropland (18.6%), tea land (15.5%), forest land (10.9%), atmospheric deposition (5.6%), orchards (4.6%), industry (1.4%), and other land (0.8%). Our simulation underscores the urgency of increasing the efficiency of the wastewater treatment, conserving slope land, and optimizing agricultural management as components of a comprehensive policy to control N pollution in the basin.

Kazakhstan, a former Soviet republic that is now independent, lies near the center of arid Eurasia. Its sparse hydrographic network includes a small number of large rivers, lakes, and reservoirs, many ponds and smaller streams, as well as littoral zones bordering the Caspian Sea and the Aral Sea. A diverse fisheries sector, initially based on wild fish capture and later including aquaculture, developed in these waters during the Soviet era, when animal agriculture was unable to meet the protein needs of Soviet citizens. The sector, which was originally centered on the Volga–Caspian basin, was tightly managed by Moscow and benefitted from coordinated investments in research, infrastructure, and human resources, as well as policies to increase the consumption of fish products. Independence in 1991 administered a political and economic shock that disrupted these relationships. Kazakhstan’s wild fish harvests plummeted by more than two-thirds, and aquaculture collapsed to just 3% of its previous level. Per capita consumption of fish products also declined, as did processing capacity. Favorable recent policies to define fishing rights, incentivize investments, prevent illegal fishing, and make stocking more effective have helped to reverse these trends and stabilize the sector. Continued recovery will require additional steps to manage water resources sustainably, prioritize the use of water for fish habitats, and minimize the effects of climate change. This comprehensive assessment of Kazakhstan’s fisheries sector over the past century provides the basis to understand how long-term dynamic interactions of the environment with the political economy influence fisheries in Eurasia’s largest country.

Wetlands can improve water quality, but they are also recognized as important sources of greenhouse gases (GHG) such as nitrous oxide (N2O) and methane (CH4). Emissions of these gases from wetland ecosystems, especially those in headwaters, are poorly understood. Here, we determined monthly concentrations of dissolved N2O and CH4 in a headwater stream of the Taihu Lake basin of China that contains both wetland and non-wetland reaches. Daily GHG dynamics in the wetland reach were also investigated. Riverine N2O and CH4 concentrations generally varied within 10–30 nmol L−1 and 0.1–1.5 μmol L−1, respectively. CH4 saturation levels in the wetland reach were about seven times higher than those in the non-wetland reach, but there was no difference in N2O saturation. In the wetland reach, saturation levels of CH4 peaked in July, coincident with a dip in N2O saturation to levels below its saturated solubility. This underscores that hotspots of CH4 production and sinks for N2O can occur occasionally in wetlands in mid-summer, when vegetative growth and microbial activities are high. Diurnal measurements indicated that CH4 saturation in water flows passing through the wetlands from midnight through the early morning can surge to levels 10 times higher than those detected at other times of the day. Simultaneously, saturation levels of N2O decreased by 75%, indicating a net consumption of N2O. Changes in nutrient supply determined by upstream inflows, as well as dissolved oxygen, pH, and other environmental factors mediated by the wetlands, correlate with the differentiated behavior of N2O and CH4 production in wetlands. Additional work will be necessary to confirm the roles of these factors in regulating GHG emissions in riverine wetlands.

In this chapter, we provide an overview of the social-ecological systems (SES) in the Asian Drylands Belt (ADB), a vast geographical region composed of 17 independent countries and six administrative provinces of China. The ADB, which covers 15.4 million km2 and is the home to more than 645 million people, has served as a major human migratory route across Eurasia, was the home of the earliest societal organizations around the Fertile Crescent 9500 years ago, and has long provided the base for trading connections between the East and West via the Silk Road. The ADB (also defined as Greater Central Asia in this volume) retains its strategic importance, and so for historical and contemporary reasons, the SES of the ADB are highly diverse in space and time. We summarize the variable changes in temperature and precipitation over the past six decades and identify divergent dynamics in land cover across the ADB. Taking a macrosystem approach, we also examine the interrelationships among SES indicators by comparing three sub-regions: Drylands East Asia (DEA), Central Asia Core (CAC), and the Middle East (ME). Five pressing issues facing the future sustainability of SES are: (1) worsened water scarcity; (2) intensified land use and land cover changes; (3) climatic extremes and climatic change; (4) globalization and cross-country effects; and (5) unforeseeable institutional changes and shifts. We conclude by proposing a conceptual framework for understanding and modeling the SES. It includes the institutions of the ADB as an essential foundation upon which to base the conventional three pillars of sustainability science: the social system, economic system, and ecological system.

Rapid economic development and population growth in China’s Yangtze River Delta (YRD) are exerting significant environmental pressure on the region’s land and water, especially in hilly areas where many drinking water reservoirs have been constructed. These areas, which are characterized by steep slopes and thin soils, provide critical services, including flood control, water resource supply, food production, and recreational opportunities for nearby highly developed and heavily populated areas of the delta. We contrast two of these areas—the well-studied Tianmu Lake watershed and the much larger Qiandao Lake watershed. Both face similar challenges from nitrogen and phosphorus pollution due to rapid socio-economic development, but differences in watershed size and distinctions related to political boundaries influence the range of approaches available to maintain water quality. We review experiences of controlling nutrient pollution in these watersheds as case studies, and based on that information, propose an integrated framework to minimize nitrogen and phosphorus pollution in similarly challenged watersheds. The framework, which is designed to be generalizable rather than prescriptive, emphasizes source control, delivery interception, and fate management of nutrients.

In the published article [...]

Although agriculture and aquaculture depend on access to increasingly scarce, shared water resources to produce food for human consumption, they are most often considered in isolation. We argue that they should be treated as integrated components of a single complex system that is prone to direct or indirect tradeoffs that should be avoided while also being amenable to synergies that should be sought. Direct tradeoffs such as competition for space or the pollution of shared water resources usually occur when the footprints of agriculture and aquaculture overlap or when the two practices coexist in close proximity to one another. Interactions can be modulated by factors such as hydropower infrastructure and short-term economic incentives, both of which are known to disrupt the balance between aquaculture and agriculture. Indirect tradeoffs, on the other hand, play out across distances, i.e., when agricultural food sources are diverted to feed animals in aquaculture. Synergies are associated with the culture of aquatic organisms in rice paddies and irrigation waters, seasonal rotations of crop cultivation with aquaculture, and various forms of integrated agriculture–aquaculture (IAA), including jitang, a highly developed variant of pond-dike IAA. Policy decisions, socioeconomic considerations, and technology warrant increased scrutiny as determinants of tradeoffs and synergies. Priority issues for the future include guiding the expansion of aquaculture from its traditional base in Asia, taking advantage of the heterogeneity that exists within both agricultural and aquaculture systems, the development of additional metrics of tradeoffs and synergies, and adapting to the effects of climate change.

Conflicts between agricultural intensification and the increasing demand for clean water resources are growing worldwide. This study sought to understand how the negative consequences of agricultural expansion in fragile hilly watersheds can be mitigated by ecologically based engineering practices. We analyzed long-term and seasonal water quality trends in two sub-watersheds of the Tianmu Lake watershed in Eastern China. The Zhongtian and nearby Zhucao sub-watersheds are very similar in terms of climate, topography and other features that can influence water quality. Both are experiencing rapid expansion of tea plantations, but the Zhongtian River contains an engineered system of overflow dams and cascade wetlands that is absent from the Zhucao River. The multi-year averaged reduction (2009–2018) of total nitrogen (TN) and total phosphorus (TP) from upstream to downstream reaches was 10%–15% greater in the engineered Zhongtian River compared to the non-engineered and free flowing Zhucao River, which has no interventions to reduce nutrient concentrations. Average annual reductions in TN, TP, and total suspended solids (SS) downstream of the engineered system reached 0.5%–4.0% of their multi-year averaged concentrations over this time interval. These reductions occurred despite a 2.3-fold expansion of tea plantation area in the engineered watershed, which contrasts with deteriorating water quality in the non-engineered watershed that had a 0.4-fold expansion of tea plantation area. Our results underscore the value of such engineered systems to improve water quality and help reconcile competing advantages of agricultural development and environmental protection in hilly watersheds, where there is limited in-stream processing of nutrients and the effects of human activities are substantial.

Intensive agricultural cultivation in hilly catchments is subject to significant environmental risks, because the local terrain and exceptionally fragile ecosystem usually promote high levels of nutrient loss. In order to assess such negative effects, we compared long-term (2012–2018) water quality dynamics of four ponds that are fed by runoff from agricultural hillsides with contrasting slopes and land cover near Tianmu Lake in Eastern China. Averaged total nitrogen (TN) levels in ponds increased from 7.0 mg L−1 to 10.0 mg L−1 when the cultivated slopes above them doubled from 8° to 16°. In contrast, total phosphorus (TP) levels varied modestly from 0.05 to 0.07 mg L−1 among the four ponds. Values were lower when drained hillslopes had good vegetation coverage and/or buffer strips. Redundancy analysis (RDA) indicated that relatively high precipitation is the determining factor for N loss from gentle hillsides, but as slope gradients increase, the frequency of rainfall events becomes the major influential factor. TP loss was associated with strong rainfall events and can be greatly reduced if hillsides are well covered with vegetation. When vegetation cover is removed, nutrient loss, especially N, is heightened. Our results underscore the significance of agricultural cultivation of steep hillsides in exacerbating N and P pollution and highlight the value of forests and grasslands in reducing nutrient loss from these sensitive areas. An integrated strategy that includes controlling land exploitation, source control, delivery interception, and pond management should be considered to minimize nutrient loss in hilly areas prone to rapid agricultural expansion.

Water is a scarce resource in Central Asia, and many catchments span international boundaries, among them that of the Ili River, which is shared by China and Kazakhstan. Since 1970, the natural hydrological regime of the Ili River, both absolute flow rates and cycles, has changed due to construction of reservoirs such as that at Kapchagai, as well as natural climatic cycles and the growth of water consumption in the basin. Using data from Kazhydromet, we calculated that flow rates below Kapchagai dam averaged 468 m3/sec before construction of the dam, 366 m3/sec while the reservoir was being filled, and 489 m3/sec between 1988 and 2013. The dam has profoundly altered the annual cycle of flows in the river, with reductions in the summer and increases in the winter, when water is released to produce hydropower. The effects of these changes are being heightened by China’s increasing diversion of the river’s water. The sustainable use of decreasing water resources to conserve the biodiversity of the Ili-Balkhash basin’s ecosystems mandates a solution to the water allocation challenge between China and Kazakhstan. This will require a basin-wide approach that includes modernization of water distribution systems and careful consideration to relative priority needs for food, hydropower, and communal uses in both countries.

Although PM2.5 poses a serious threat to public health, the role of urban form in influencing concentrations of this air pollutant is unresolved. Ridge regression was employed to investigate relationships between satellite-derived estimates of PM2.5 concentrations and the urban form of 350 cities in the rapidly urbanizing Yangtze River Delta (YRD) of eastern China. The cities were stratified by population into small ( 1,000,000), and urban circularity, fragmentation, and compactness were measured from 1998 to 2015. Circularity was not a statistically significant predictor of PM2.5 concentrations, except for maxima in large cities. Although fragmentation was strongly negatively correlated with mean and maximum PM2.5 concentrations for all cities, compactness was positively associated with mean and maximum PM2.5 concentrations only in small and medium-sized cities. Urban form thus had a relatively stronger impact on PM2.5 concentrations in cities that were not yet large. After controlling for population, land area, and climate, more sprawled cities had lower PM2.5 concentrations than their more spatially compact counterparts. These findings indicate that planning agencies in the YRD should encourage moderately scattered and polycentric urban development rather than compact, monocentric growth.

The Ili River originates in the mountains of Xinjiang, China, and flows across an increasingly arid landscape before terminating in Kazakhstan’s Lake Balkhash, which has no outlet to the ocean. The river has been extensively impounded and diverted over the past half century to produce hydroelectric power and food on irrigated land. Water withdrawals are increasing to the extent that they are beginning to threaten the ecosystem, just as it is becoming stressed by altered inflows as glaciers retreat and disappear. If the Ili River ecosystem is to be preserved, it is crucial that we thoroughly understand the spatial and temporal nuances of the interrelationships between water, energy, and food—and the vulnerability of these components to climate change. The ecosystem has all of the characteristics of a classically-defined “wicked problem”, and so it warrants treatment as a complex and dynamic challenge subject to changing assumptions, unexpected consequences, and strong social and economic overtones. Research should thus focus not just on new knowledge about the water, energy, or food component, but on advancing our understanding of the ecosystem as a whole. This will require the participation of interdisciplinary teams of researchers with both tacit and specialized knowledge.

Lake Balkhash is the largest water body in Central Asia. More than three-quarters of its inflow comes from the Ili River, which is under increasing strain due to the diversion of water for energy and food production. Commercial fishing in Lake Balkhash began in 1929 and is currently in a state of crisis. The construction of the Balkhash dam and reservoir in the late 1960s reduced Ili River flows into the lake and upset the natural cycle of spring floods, which greatly reduced spawning and feeding areas for carp (Cyprinus carpio). Carp populations were consequently reduced by more than 90% during the filling of the reservoir and have not recovered, even though the lake’s level subsequently rose. Catches of carp and freshwater bream (Abramis brama orientalis) have shown an inverse relationship since the 1960s, and the age structure of freshwater bream is changing. Historically, most captured fish of this species were 4- to 7-years-old, but smaller, 3- to 5-year-old fish have dominated recent catches. The total fish harvest from Lake Balkhash is currently at near historical lows, not just because of environmental factors, but also because of structural changes triggered by the collapse of the Soviet Union. Poaching, government disinterest, lack of enforcement of fishing regulations, and the economic challenges faced by today’s small fishing enterprises all contribute to the problem.

Central Asia’s arid lowland ecosystems are dependent on water that originates in nearby mountains and is carried by rivers to terminal lakes and freshwater seas with no outlets to the ocean. Fish traditionally thrived in these waterways, but they have become increasingly jeopardized by water impoundment and diversion for energy and crop production. Fish capture in the five new Central Asian republics consequently entered a period of long decline, a trend that was accelerated by removal of the centralized controls imposed by the former Soviet Union. Production levels have recovered during the past decade, but only in some countries. A similar trend is evident with aquaculture, which reached its lowest production levels in 2003–2008 but now is partially recovering. In both cases, progress is most evident in water-deficient Uzbekistan. Fish capture in Kazakhstan’s Ili River ecosystem, including Kapchagay Reservoir and Lake Balkhash, is now dropping precipitously. Effects on the lake’s fisheries have been magnified by the disproportionate rates of disappearance of valuable carp and pike-perch. The interrelationships between water, energy, and food underlie these threats to Central Asia’s fish and define a classic “wicked problem” that must be addressed regionally with explicit attention given to fish as important components of the ecosystem. Recent developments, although not all positive, give reason for cautious optimism that the region’s fisheries and aquaculture industries can be stabilized.

The water-energy-food (WEF) nexus has become a hotspot in the field of sustainability science, and researchers and policymakers are now considering the theoretical underpinnings of the concept and its implications for policy practice. This requires an integrated method for assessing the sustainability of a region's WEF nexus. Here we evaluate the sustainability trends of an important regional WEF nexus using Jiangsu Province, China, as a case study. Using statistical data from 2000 to 2016, we propose a step-by-step methodological approach to evaluate sustainability and carry out empirical research to examine it. The methodology constructs a composite index, combining single WEF sector indicators and WEF linkage indicators that reflect the characteristics of the nexus. This enables exploration of differences in assessment results based on the concept of strong and weak sustainability. Such differences are obvious in the evaluation results based on sustainability surplus compensation (SSC) and sine sustainability surplus compensation (SSSC) methods. The analysis confirms that Jiangsu Province is following a path of unsustainable development of the WEF nexus. This is mainly due to substandard indicators of the water and energy systems, some of which are declining. The general approach provides a timely and useful means for the sustainability assessment of the WEF nexus. It can be easily applied in practice and provides policy intervention signals to stakeholders and policymakers in resource and sustainable development management.

Central Asia’s Ili River is fed by mountain streams that flow down into an isolated and arid basin that today is shared by Kazakhstan and China. Agriculture in the basin is dependent upon irrigation, which was practiced as long ago as the Iron Age, when early pastoralists constructed ditches to channel water from streams onto nearby fields. Irrigation had become much more common by the 18th century, when the region was controlled by the Dzungarian Khanate. The khanate was toppled by the Qing Chinese in the 1750s in the first of a series of confrontations that destroyed and then rebuilt the basin’s agricultural economy. The region has since been dominated by a succession of Chinese and Russian (and later Soviet and independent Kazakh) governments, each of which recognized the essential role of irrigated agriculture in maintaining control. Thus every cycle of destruction led to reclamation of new lands, resettlement of farmers and upgrading of infrastructure to expand irrigation. This allowed an impressive diversity of fruits, vegetables and field crops to be grown, especially on loess soils of the more fertile upper basin, where tributaries could be easily tapped by gravity flow. Many of these tributaries were entirely diverted by the 19th century, so that they no longer reached the Ili. Large scale irrigation commenced in the 1960s, when the Soviets built Kapchagai dam and reservoir in the lower part of the basin and installed pumps to raise water from the Ili River onto nearby reclaimed sierozem soils, mostly for cultivation of rice. China later constructed a cluster of small- and medium-sized dams that enabled expansion of agriculture in the upper part of the basin. Many irrigated areas along the lower reaches of the Ili in Kazakhstan have been abandoned, but irrigation in the upper basin continues to expand. Declining soil fertility, salinization, pollution, insufficient inflows and adverse economic conditions currently challenge irrigation across the entire basin. Investments are being made in new technologies as a means to sustain irrigated agriculture in the basin, but it remains to be seen if these strategies will be successful.

Transgenic Bt maize that produces less than a high-dose has been widely adopted and presents considerable insect resistance management (IRM) challenges. Western corn rootworm, Diabrotica virgifera virgifera LeConte, has rapidly evolved resistance to Bt maize in the field, leading to local loss of efficacy for some corn rootworm Bt maize events. Documenting and responding to this resistance has been complicated by a lack of rapid diagnostic bioassays and by regulatory triggers that hinder timely and effective management responses. These failures are of great concern to the scientific and agricultural community. Specific challenges posed by western corn rootworm resistance to Bt maize, and more general concerns around Bt crops that produce less than a high-dose of Bt toxin, have caused uncertainty around current IRM protocols. More than 15 years of experience with IRM has shown that high-dose and refuge-based IRM is not applicable to Bt crops that produce less than a high-dose. Adaptive IRM approaches and pro-active, integrated IRM-pest management strategies are needed and should be in place before release of new technologies that produce less than a high-dose. We suggest changes in IRM strategies to preserve the utility of corn rootworm Bt maize by 1) targeting local resistance management earlier in the sequence of responses to resistance and 2) developing area-wide criteria to address widespread economic losses. We also favor consideration of policies and programs to counteract economic forces that are contributing to rapid resistance evolution.

nolX, a nod box-independent nodulation gene from the nitrogen-fixing symbiont, Sinorhizobium fredii, regulates cultivar-specific nodulation of soybean. Expression of this gene is triggered by isoflavonoid cues from host roots but is not mediated by a typical cis-acting nod box promoter. We have found that two isoflavonoids, daidzein and coumestrol, induce expression of a nolX-lacZ gene fusion at pH values between 5.5 and 8.5, with an optimum at 6.5. Expression of nolX is highly dependent on nutritional status but insensitive to salinity. Methionine and casamino acids, amendments that enhance expression of hrpF, a homologous gene from the plant pathogen Xanthomonas campestris biovar vesicatoria, have no and strongly negative effects, respectively, on expression of nolX. Growth of S. fredii on rhamnose, galactose, xylose, or myo-inositol as carbon source greatly elevates inducibility in comparison to a standard yeast extract-mannitol medium. None of the tested variables, however, released nolX from its dependence on isoflavonoids as inducers.

nodD1 of Sinorhizobium fredii HH103, which is identical to that of S. fredii USDA257 and USDA191, repressed its own expression. Spontaneous flavonoid-independent transcription activation (FITA) mutants of S. fredii HH103 M (=HH103 RifR pSym::Tn 5-Mob) showing constitutive expression of nod genes were isolated. No differences were found among soybean cultivar Williams plants inoculated with FITA mutants SVQ250 or SVQ253 or with the parental strain HH103M. Soybean plants inoculated with mutant SVQ255 formed more nodules, and those inoculated with mutant SVQ251 had symptoms of nitrogen starvation. Sequence analyses showed that all of the FITA mutants carried a point mutation in their nodD1 coding region. Mutants SVQ251 and SVQ253 carried the same mutation, but only the former was symbiotically impaired, which indicated the presence of an additional mutation elsewhere in the genome of mutant SVQ251. Mutants SVQ251 and SVQ255 were outcompeted by the parental strain for nodulation of soybean cultivar Williams. The symbiotic plasmids of mutants SVQ251 and SVQ255 (pSym251 and pSym255, respectively) and that (pSymHH103M) of the parental strain were transferred to pSym-cured derivatives of S. fredii USDA192 and USDA193 (USDA192C and USDA193C, respectively). Soybean responses to inoculation with S. fredii USDA192C and USDA193C transconjugants carrying pSym251 and pSymHH103M were not significantly different, whereas more nodules were formed after inoculation with transconjugants carrying pSym255. Only transconjugant USDA192C(pSym255) produced a significant increase in soybean dry weight.

The ability to accomplish some fancy biology underlies the current dialogue on the social and economic impacts of biotechnology. Using crop plant models, this article sets the scientific context for the discussion that follows in this issue. There are three key messages: Changing plants to suit human needs is an ancient and ongoing process, biotechnology makes this process faster and more precise, and the emphasis for biotechnology is increasingly whole genomes and not jsut genes. Scientists can enrich the discussion of impacts and acceptance, but as the accompanying articles confirm, science alone is insufficient to provide answers to complex societal questions.

Sinorhizobium fredii strain USDA208 is a nitrogen-fixing bacterium that forms nodules on roots of soybean and other legume plants. We previously found that the Tn5-containing mutant 208T3, which was derived from strain USDA208, is both deficient in production of exopolysaccharides and more competitive than the wild-type strain in competing against other rhizobia for nodulation of soybean. We now demonstrate that the transposon insertion of the mutant lies in a locus that is highly homologous to a portion of the exo region, which functions in exopolysaccharide biosynthesis by Sinorhizobium meliloti. We sequenced 2906 bp surrounding the insertion site and identified three genes: exoA, exoM, and exoO. The transposon lies within exoM, a glucosyl transferase. A cosmid containing exoHKLAMONP of S. meliloti restores exopolysaccharide production by mutant 208T3 to wild-type levels. Although exo mutants of S. meliloti are defective in their abilities to form indeterminate nodules, the capacities of mutant 208T3 and its wild-type parent to form such nodules on five legume species are indistinguishable. Thus the symbiotic function of exopolysaccharide in S. fredii appears to differ fundamentally from that in S. meliloti.

Sinorhizobium meliloti is a well-known symbiont that fixes nitrogen with plants of three genera of the family Leguminosae, Tribe Trifolieae: Medicago, Melilotus, and Trigonella. We have found that S. meliloti strain RCR2011 forms ineffective nodules on a distantly related legume species, Sesbania macrocarpa. Nodules are indeterminate and lack leghemoglobin. Although S. meliloti deformed root-hairs of S. macrocarpa, infection threads were not detected in these cells. Instead, cells of S. meliloti were found in infection pockets between cortical cells and within infection threads that had penetrated into these cells. Bacteria eventually were released and gave rise to symbiosomes, which contained large quantities of an amorphous matrix with parallel arrays of electron-dense striations. Mutants of strain RCR2011 lacking nodA or nodH failed to nodulate S. macrocarpa, inactivation of nodG or nodE resulted in smaller nodules, while inactivation of region IIa, which contains nodIJ, had no apparent effect on nodulation.

Sinorhizobium frediistrain USDA191 forms N-fixing nodules on the soybean (Glycine max L. Merr.) cultivars (cvs) McCall and Peking, but S. fredii strain USDA257 nodulates only cv Peking. We wondered whether specificity in this system is conditioned by the release of unique flavonoid signals from one of the cultivars or by differential perception of signals by the strains. We isolated flavonoids and usednodC and nolX, which arenod-box-dependent and -independent nodgenes, respectively, to determine how signals activate genes in the microsymbionts. Seeds of cv McCall and cv Peking contain the isoflavones daidzein, genistein, and glycitein, as well as their glucosyl and malonylglucosyl glycosides. Roots exude picomolar concentrations of daidzein, genistein, glycitein, and coumestrol. Amounts are generally higher in cv Peking than in cv McCall, and the presence of rhizobia markedly influences the level of specific signals. Nanomolar concentrations of daidzein, genistein, and coumestrol induce expression of nodC and nolX in strain USDA257, but the relative nolX-inducing activities of these signals differ in strain USDA191. Glycitein and the conjugates are inactive. Strain USDA257 deglycosylates daidzin and genistin into daidzein and genistein, respectively, thereby converting inactive precursors into active inducers. Although neither soybean cultivar contains unique nod-gene-inducing flavonoids, strain- and cultivar-specific interactions are characterized by distinct patterns of signal release and response.

Sinorhizobium fredii strain HH103, a nitrogen-fixing bacterial symbiont of plants, contains an insertion sequence (IS) that cantranspose into plasmid pMUS248 and activate a promoterless TcR gene that is normally not expressed. We have cloned andcharacterized this element, which we designate IS Rf1. The IS is 1002 bp in length, contains a single 513-bp open reading frame(ORF), is flanked by imperfect 36-bp terminal inverted repeats, and creates 5-bp target duplications. Two copies of IS Rf1 arepresent in the genome of HH103, but it is absent from 12 other Sinorhizobium and Rhizobium strains. The element transposes ata frequency of 2.7×10−6per generation per cell. © 1997 Elsevier Science B.V. Keywords: Insertion sequence; Legume– Rhizobium symbiosis; Tetracycline resistance; Tn 5403 1. Introduction 1987), but also as agents of horizontal gene transfer toand from bacteria residing in the soil (Deng et al., 1995;Rhizobia, e.g. bacteria of the genera Rhizobium , Ponsonnet et al., 1995). Although a transposon (Tn)

Rhizobium (now Sinorhizobium) fredii is a symbiotic nitrogen-fixing bacterium that can nodulate soybean in a cultivar-specific manner. This process is governed by a set of negatively acting nodulation genes termed noIXWBTUV. These genes prevent R. fredii strain USDA257 from infecting soybean cultivars such as McCall, but they do not block nodulation of cultivar Peking. R. fredii strain USDA191 contains DNA sequences that hybridize to noIXWBTUV, yet it forms normal nitrogen-fixing nodules on both McCall and Peking soybean. These sequences were isolated and their structure and function examined in comparison to noIXWBTUV of strain USDA257. Restriction maps of the two loci are identical, as is a 2∙4 kb DNA sequence that corresponds to noIX and its promoter region. Expression of noIX by strain USDA191 is flavonoid-dependent in culture and readily detectable in nodules. The gene is not inducible in a mutant of strain USDA191 that lacks the regulatory nodD1 gene, and its expression is greatly attenuated in a nodD2 mutant. noIX is also present and flavonoid-inducible in HH103, a second R. fredii strain that nodulates McCall soybean normally. Inactivation of noIX in strain HH103, USDA191 or USDA257 leads to retardation of initial nodulation rates on soybean cultivars such as Peking and to acquisition of the capacity to form nitrogen-fixing nodules on two species of Erythrina. noIX is thus of symbiotic significance in all three strains, even though it regulates soybean cultivar specificity only in strain USDA257.

The transcripts of nolW and nolB, two divergently oriented cultivar specificity genes of Rhizobium fredii strain USDA257, are known to be initiated 14 bp apart from promoters that face one another. We show here that expression of nolB is dependent both on induction with flavonoid signals and on the regulatory gene, nodD1. Expression of nolW is constitutive and independent of flavonoids and nodD1. Normal expression of nolB is retained with a promoter that extends only 61 bp upstream of the transcript start site, but it is lost if an additional 24 bp are removed. Substantial expression of nolW is retained with a promoter that contains only 34 bp of DNA upstream from the transcript initiation site. The dual control region for the two genes is thus only about 109 bp in length.

Summary We have examined six fast-growing Rhizobium strains isolated from nodulated soybean [Glycine max (L.) Merr.] plants growing in Vietnam, with special emphasis on two of them, SMX11 and SMH12. The abilities of strains SMX11 and SMH12 to utilize 11 carbon sources were indistinguishable from that of control Sinorhizobium fredii strains USDA257 and HH103, but their growth rates in standard media were considerably more rapid. The Vietnamese strains also were more salt-tolerant and antibiotic-resistant than the S. fredii reference strains, and their LPS banding patterns were less complex. Weak immunological cross-reactivity between the Vietnamese strains and S. fredii was evident. RFLP patterns of a series of nodulation genes and a repetitive sequence from S. fredii matched those of the Vietnamese strains, as did the sequence of a portion of a 16S rRNA gene. Analysis of cellular fatty acids was consistent with the assignment of strain SMH 12 and four other Vietnamese strains to S. fredii, but it aligned strain SMX11 more closely to other related groups of rhizobia. The Vietnamese strains have broad host ranges for nodulation of legumes, and their abilities to fix nitrogen in association with five soybean cultivars are equivalent to or surpass that of S. fredii.

Genistein and other flavonoids from host legumes are known to stimulate cells of the nitrogen-fixing soybean symbiont Rhizobium fredii to synthesize Nod factors, which function as signals during nodule initiation. Flavonoids also trigger R. fredii to secrete a set of signal-responsive (SR) proteins into the environment. By insertion mutagenesis, we showed that secretion of SR proteins by this organism has an absolute dependence on the regulatory gene nodD1. We isolated and sequenced nodD1 and nodD2 of R. fredii USDA257 and constructed strains containing additional, plasmid-borne copies of these genes. Extra copies of nodD1 had no effect on secretion of SR proteins, but extra copies of nodD2 rendered the process constitutive. Extracts from seeds of the soybean cultivars McCall and Peking can substitute for purified flavonoids as inducers of SR proteins. The nolXWBTUV locus is known to control cultivar-specific nodulation of McCall soybean in a negative, flavonoid-dependent manner. Inactivation of any of these genes prevented SR proteins from accumulating in culture fluids. Protein secretion in response to host signals was a characteristic of nine out of ten R. fredii strains tested. Immunological probes failed to detect SR3 or SR5 in mature soybean or cowpea nodules. Although the functions of these proteins remain unknown, their potential role in symbiosis is strengthened by the discovery that their accumulation depends on nodD1, nodD2 and nolXWBTUV.

We have isolated and characterized the extracellular Nod factors of Rhizobium fredii USDA257, a nitrogen-fixing symbiont of soybean [Glycine max (L.) Merr.] and several other legume species. These signals are produced upon exposure to the isoflavone genistein and consist of a series of substituted, beta 1,4-linked tri-, tetra-, and pentamers of N-acetylglucosamine. N-Vaccenic acid replaces acetate on the nonreducing residue, and the reducing residue contains alpha-linked 2-O-methylfucose on carbon 6. Small amounts of a fucose-containing tetramer also were present. The Nod factors elicit root-hair deformations on soybean and two other plants at concentrations ranging from 10(-6) to 10(-12) M.

Symbiotic interactions between rhizobia and legumes are largely controlled by reciprocal signal exchange. Legume roots excrete flavonoids which induce rhizobial nodulation genes to synthesize and excrete lipo-oligosaccharide Nod factors. In turn, Nod factors provoke deformation of the root hairs and nodule primordium formation. Normally, rhizobia enter roots through infection threads in markedly curled root hairs. If Nod factors are responsible for symbiosis-specific root hair deformation, they could also be the signal for entry of rhizobia into legume roots. We tested this hypothesis by adding, at inoculation, NodNGR-factors to signal-production-deficient mutants of the broad-host-range Rhizobium sp. NGR234 and Bradyrhizobium japonicum strain USDA110. Between 10(-7) M and 10(-6) M NodNGR factors permitted these NodABC- mutants to penetrate, nodulate and fix nitrogen on Vigna unguiculata and Glycine max, respectively. NodNGR factors also allowed Rhizobium fredii strain USDA257 to enter and fix nitrogen on Calopogonium caeruleum, a nonhost. Detailed cytological investigations of V. unguiculata showed that the NodABC- mutant NGR delta nodABC, in the presence of NodNGR factors, entered roots in the same way as the wild-type bacterium. Since infection threads were also present in the resulting nodules, we conclude that Nod factors are the signals that permit rhizobia to penetrate legume roots via infection threads.

Symbiotic rhizobia enter roots of their hosts via infection threads in root-hairs and invade the cortex, where nodules are initiated. We have transferred a cloned cellulase (Cel) gene from Erwinia carotovora subsp. carotovora into rhizobia and examined both the production of the enzyme and its impact on nodulation. Acquisition of a Cel + plasmid allowed cultured cells of Rhizobium fredii ,R. meliloti , and R. tropici to produce extracellular enzymes that degrade carboxymethylcellulose. The Cel + plasmid was retained by R. fredii during nodulation of cowpea, and analysis of a gene fusion confirmed that the Cel promoter was active in planta. Cellulase levels in nodules nevertheless were low, and infection and nodulation were unaffected by the presence of the Cel + plasmid.

Rhizobiumfredii USDA257 is a Gram-negative soil bacterium from China that fixes nitrogen in symbiosis with primitive soybean (Glycine max [L.] Merr.) cultivars such as Peking, but not with advanced cultivars such as McCall. Mutation of either of two bacterial loci, nolBTUVWX or no1C, removes this cultivar-specificity constraint, allowing the bacterium to nodulate advanced cultivars. We have discovered that USDA257 forms nodules on Erythrina costaricensis M. Micheli, but not on six other species of this genus, which includes trees and shrubs from the tropics. Inactivation of nolBU or nolC broadensA4he symbiosis to include other Erythrina species. Whereas nolBU-mutants acquire the capacity to nodulate E. fusca Loureiro, E. variegata L., and E. vespertilio Benth., nolC-mutants could nodulate only E. variegata. Nodules are determinate and often clustered in root axils near the root crown. E. variegata nodules containing a nolBU-mutant consist of well-developed inner and outer cortical layers, as well as a bacteroid zone. The cortical layers are separated from one another by a meristematic region that is associated with large darkly staining cells, and cells of the inner cortex contain numerous starch grains. Histochemical staining of E. variegata roots inoculated with a strain containing a nolB-lacZ gene fusion confirms that nolB and nolC are expressed during the initial stages of bacterial interaction with the host. R. fredii enters elongated root-hairs via infection threads, which ramify within root-hairs and are associated with meristematic activity