Rongzhong Ye

Land‐Use Effects on Soil Nutrient Cycling and Microbial Community Dynamics in the Everglades Agricultural Area, Florida

Soil subsidence has become a critical problem since the onset of drainage of the organic soils in the Everglades Agricultural Area (EAA), which may impair current land uses in the future. The objectives of this study were to characterize soil microbial community‐level physiology profiles, extracellular enzymatic activities, microbial biomass, and nutrient pools for four land uses: sugarcane, turfgrass, pasture, and forest. Long‐term cultivation and management significantly altered the distribution and cycling of nutrients and microbial community composition and activity in the EAA, especially for sugarcane and turf fields. The least‐managed fields under pasture had the lowest microbial biomass and phosphorus (P) levels. Turf and forest had more microbial metabolic diversity than pasture or the most intensively managed sugarcane fields. Land‐use changes from sugarcane cropping to turf increased microbial activity and organic‐matter decomposition rates, indicating that changes from agricultural to urban land uses may further contribute to soil subsidence.

Sulfur Distribution and Transformations in Everglades Agricultural Area Soil as Influenced by Sulfur Amendment

Nutrient export from the Everglades Agricultural Area (EAA) has been implicated in causing sulfur (S) enrichment of Everglades wetlands. However, quantification of the S budget and transformations in EAA soils is inadequate. The objective of this study was to quantify various S fractions and investigate how elemental S amendment affects S dynamics in EAA soils. Reduced S compounds were not detected in soil before elemental S application. Organic S was the major form of S, comprising 87% of total S, followed by extractable SO4-S (13%). Extractable SO4-S for soils receiving 448 kg S ha−1 was 36%, 131%, 201%, and 270% higher than for unamended soils at 2, 6, 9, and 13 months, respectively. Elemental S was significantly higher in soils receiving 448 kg S ha−1 (482 mg kg−1) than in soils receiving 224 (111 mg kg−1) and 112 kg S ha-1 (55 mg kg−1) and unamended soil (0 mg kg−1) at 2 months after S application. Similar to extractable SO4-S, elemental S significantly decreased during the growing season. Sulfur application did not affect the sulfatase activity, however, mineralizable S increased concurrently with S application rate, and the effects continued throughout the growing season. This result was largely attributed to the oxidation of the applied elemental S. Our results suggest that large-scale S application in the EAA soils is likely to increase SO42− concentrations in soils, which poses a potential risk of SO42− export to sensitive Everglades wetlands.

SEASONAL CHANGES IN NUTRIENT AVAILABILITY FOR SULFUR-AMENDED EVERGLADES SOILS UNDER SUGARCANE

The objective of this study was to evaluate effects of elemental sulfur (S) addition on soil pH and availability of macro- and micronutrients during the sugarcane growing season. Sulfur application did not significantly reduce soil pH when applied at 0 to 448 kg S ha−1 due to the high soil buffering capacity. Water extractable phosphorus (P) and potassium (K) for soils receiving the highest S rate were 188% and 71% higher than for unamended soils only at two months after application, indicating a short-term enhancement of macronutrient availability. Soil amended with 448 kg S ha−1 contained 134% more acetic acid-extractable zinc (Zn) than unamended soil, although stimulatory effects did not extend beyond two months. Sugar yield was not affected by S addition, averaging 17 Mg sugar ha−1. The failure of S to enhance nutrient availability throughout the growing season indicates the limited benefit of applying elemental S to reduce pH and increase nutrient availability to sugarcane.

Higher yields and lower methane emissions with new rice cultivars

Breeding high-yielding rice cultivars through increasing biomass is a key strategy to meet rising global food demands. Yet, increasing rice growth can stimulate methane (CH4 ) emissions, exacerbating global climate change, as rice cultivation is a major source of this powerful greenhouse gas. Here, we show in a series of experiments that high-yielding rice cultivars actually reduce CH4 emissions from typical paddy soils. Averaged across 33 rice cultivars, a biomass increase of 10% resulted in a 10.3% decrease in CH4 emissions in a soil with a high carbon (C) content. Compared to a low-yielding cultivar, a high-yielding cultivar significantly increased root porosity and the abundance of methane-consuming microorganisms, suggesting that the larger and more porous root systems of high-yielding cultivars facilitated CH4 oxidation by promoting O2 transport to soils. Our results were further supported by a meta-analysis, showing that high-yielding rice cultivars strongly decrease CH4 emissions from paddy soils with high organic C contents. Based on our results, increasing rice biomass by 10% could reduce annual CH4 emissions from Chinese rice agriculture by 7.1%. Our findings suggest that modern rice breeding strategies for high-yielding cultivars can substantially mitigate paddy CH4 emission in China and other rice growing regions.

A genomic perspective on stoichiometric regulation of soil carbon cycling

Similar to plant growth, soil carbon (C) cycling is constrained by the availability of nitrogen (N) and phosphorus (P). We hypothesized that stoichiometric control over soil microbial C cycling may be shaped by functional guilds with distinct nutrient substrate preferences. Across a series of rice fields spanning 5–25% soil C (N:P from 1:12 to 1:70), C turnover was best correlated with P availability and increased with experimental N addition only in lower C (mineral) soils with N:P⩽16. Microbial community membership also varied with soil stoichiometry but not with N addition. Shotgun metagenome data revealed changes in community functions with increasing C turnover, including a shift from aromatic C to carbohydrate utilization accompanied by lower N uptake and P scavenging. Similar patterns of C, N and P acquisition, along with higher ribosomal RNA operon copy numbers, distinguished that microbial taxa positively correlated with C turnover. Considering such tradeoffs in genomic resource allocation patterns among taxa strengthened correlations between microbial community composition and C cycling, suggesting simplified guilds amenable to ecosystem modeling. Our results suggest that patterns of soil C turnover may reflect community-dependent metabolic shifts driven by resource allocation strategies, analogous to growth rate–stoichiometry coupling in animal and plant communities.

Modeling the Effects of Phosphate Mining on Groundwater at Different Stages of Mine Development

In this study, a three-dimensional hydrogeological conceptual model was developed and a numerical model was calibrated with Visual MODFLOW to predict groundwater flow and evolution of groundwater field at different developmental stages at a large phosphate mine in Leibo, China, the Baku mine. ArcGIS was used to quantify changes in groundwater flow direction. The development of the cone of depression in the surrounding mining areas was predicted and the associated environmental impacts were discussed. At the beginning of mining, the cone of depression is limited to near each mining subarea and the drawdown is relatively small. The cone spreads out to the Liutong River as excavation proceeds. The model also estimated groundwater inflow rates into the different mining tunnels. The greatest inflow rate occurred in mining subarea M1.2 due to its large scale of mining and low elevation of the bottom of the tunnel. The results of this study can be used to plan optimal groundwater pumping and mine dewatering for safe mining at different mine development stages.抽象建立中国雷波县巴库(Baku)磷矿三维水文地质概念模型和Visual MODFLOW数值模型以预测地下水流和各采矿阶段流场演化。ArcGIS用以量化地下水流方向。预测了矿坑周围水位降落漏斗和相关环境问题。开采初期,水位降落漏斗集中于采区附近,漏斗范围较小。随开采面积扩展,水位降落漏斗将扩展到流通河(Liutong)。模型也可用于预测开采区涌水量。井田2号盘区将由于开采面积大和开采水平低而形成最大涌水。研究可用于指导地下水泵水方案优化和各采矿阶段安全疏水规划。ZusammenfassungGegenstand der vorliegenden Arbeit sind die Erstellung eines dreidimensionalen hydrogeologischen Konzeptmodells und die Kalibrierung eines numerischen Modelles auf Basis von Visual MODFLOW mit dem Ziel, Grundwasserströmung sowie Veränderungen des Grundwasserströmungsfeldes während unterschiedlicher Entwicklungsstadien des bedeutenden Phosphatbergwerks von Baku in Leibo, China zu prognostizieren. Veränderungen der Grundwasserfließrichtung wurden mit ArcGIS quantifiziert. Weiterhin wurden die Entwicklung des Grundwasserabsenkungstrichters in den umgebenden Baufeldern vorhergesagt sowie die damit verbundenen Umweltauswirkungen betrachtet. Zu Beginn des bergbaulichen Eingriffs bleibt der Absenktrichter auf den Nahbereich der einzelnen Baufelder beschränkt und die Absenkung relativ gering. Mit fortschreitendem Abbaustand erreicht die Absenkfront den Liutong-Fluss. Auch ist das Modell in der Lage, Grundwasserzutritte zu den einzelnen Grubenbauen abzuschätzen. Die größten Zuflussmengen wurden für das Teilgrubenfeld M1.2 abgeleitet wegen des beträchtlichen Umfangs der dort vorhandenen bergbaulichen Auffahrungen sowie aufgrund der großen Teufenlage der Streckenauffahrung. Die Studienergebnisse können zur Ableitung einer optimalen Entwässerungs- und Grundwasserabsenkungsplanung verwendet werden und dienen somit der Gewährleistung eines sicheren Grubenbetriebes in den unterschiedlichen Betriebsphasen.ResumenEn este estudio se desarrolló un modelo hidrogeológico tridimensional y se calibró un modelo numérico con Visual MODFLOW para predecir el flujo de aguas subterráneas y la evolución de las mismas en diferentes estadíos del desarrollo de la minería de fosfatos en una mina en Leibo, China: la mina Baku. Se usó ArcGIS para cuantificar los cambios en la dirección del flujo de aguas subterráneas. Se predijo el desarrollo del cono de depresión en los alrededores de las áreas mineras y se discutieron los impactos ambientales. Al comienzo de las actividades mineras, el cono de depresión estaba limitado a la subárea de actividad minera y la reducción era relativamente pequeña. El cono se extendió hacia el río Liutong a medida que la excavación continuó. El modelo también estimó las velocidades de los influentes dentro de los diferentes túneles de la mina. La mayor velocidad tuvo lugar en la subárea M1.2 debido a la gran escala de la minería en ese lugar y la baja elevación del fondo del túnel. Los resultados de este estudio pueden ser usados para planear un óptimo bombeo de las aguas subterráneas y el desagote para una minería segura en diferentes estadíos del desarrollo de la mina.