为探明宁夏菜心产生连作障碍的原因，本研究以种植1年菜心及其根际土壤为对照，测定连作3、6和9年菜心根际土壤的理化性状、酶活性和微生物群落变化以及菜心的农艺性状和品质。结果表明，长期连作（连作9年）导致菜心土壤容重、电导率、全氮、速效钾含量显著升高，在连作9年时土壤容重达1.33 g·cm^-3，与对照相比，电导率和全氮含量上升了34.21%和54.29%，速效钾含量升高了2.41倍；而pH值、总有机碳、全磷、碱解氮、有效磷含量显著下降，连作9年时，全磷和有效磷含量分别下降了26.55%和26.07%。长期连作菜心根际土壤蔗糖酶、碱性磷酸酶、过氧化氢酶和纤维素酶活性均较对照显著降低，连作9年时最低，分别下降了55.43%、59.28%、33.73%、52.37%，而脲酶活性在连作6年土壤中最高。此外，长期连作改变了菜心根际土壤微生物群落的丰富度和多样性，细菌群落丰富度下降，多样性上升，而真菌群落丰富度和多样性均下降。随着连作年限增加，菜心薹长、茎粗、地上部干鲜重、根干鲜重以及产量均有不同程度的下降，在连作9年时分别较对照下降了39%、18%、26%、22%、28%、41%和22.97%；随着连作年限的增加，菜心可溶性糖、可溶性蛋白、维生素C含量均下降，连作9年时显著下降了20%、22%和27%。综上所述，长期连作导致菜心土壤环境恶化，引起菜心产量下降，品质变劣。本研究初步探明了宁夏地区菜心长期连作后的生长状况及其根际土壤环境的变化情况，可为后续缓解菜心连作障碍研究提供参考。

水稻-长梗白菜轮作模式作为嘉兴市桐乡当地一种特色新型稻菜轮作种植模式,在稳定粮食面积和提高种粮效益方面具有重要的意义。通过大田试验,以传统水稻-油菜轮作模式为对照,研究在水稻-长梗白菜特色新型稻菜轮作模式对农田土壤养分、活性炭、氮库的影响,并对其效益进行分析。结果表明,水稻-长梗白菜轮作模式和水稻-油菜轮作模式均可以增加土壤速效钾和速效磷含量,而土壤全氮、铵态氮和硝态氮含量均有所降低。同水稻-油菜轮作模式相比,水稻-长梗白菜轮作模式的微生物量有机碳含量增加,微生物量有机氮、可溶性有机碳和可溶性有机氮含量均减少。在肥料用量方面,同常规水稻-油菜轮作模式相比,水稻-长梗白菜轮作模式的肥料用量有所减少。在经济效益方面,每667 m²水稻-长梗白菜绿色高效循环农业模式的经济效益为4 802元,较常规水稻-油菜轮作模式增收95.20%。

A major challenge in rice (Oryza sativa L.) production is to achieve the dual goal of increasing food production and saving water. This study aimed to investigate if alternate wetting and drying regimes could improve root and shoot growth and consequently increase grain yield and water use efficiency (WUE). Two rice varieties were field‐grown at Yangzhou, China in 2005 and 2006. Three irrigation regimes, alternate wetting and moderate soil drying (WMD, re‐watered when soil water potential reached −15 kPa at 15–20 cm depth), alternate wetting and severe soil drying (WSD, re‐watered when soil water potential reached −30 kPa), and a conventional irrigation (CI, continuously flooded), were imposed during the whole growing season. Compared with the CI, the WMD regime significantly increased, whereas the WSD regime reduced, root oxidation activity, cytokinin concentrations in roots and shoots, leaf photosynthetic rate, and activities of key enzymes involved in sucrose‐to‐starch conversion in grains. Grain yield of the two varieties, on the average, was increased by 11% under the WMD regime, and was reduced by 32% under the WSD regime when compared with that under the CI regime. Averaged WUE of the two varieties was increased by 55% under the WMD regime and 36% under the WSD regime. We conclude that a moderate wetting and drying regime can enhance root growth which benefits other physiological processes and result in higher grain yield and WUE.

\n One of our current challenges is to quantify the mechanisms, capacity, and longevity of C stabilization in agricultural lands. The objectives of this study were to evaluate the long‐term (10 yr) role of C input in soil organic carbon (SOC) sequestration and to identify underlying mechanisms of C stabilization in soils. Carbon input and SOC sequestration, as governed by crop management strategies, were assessed across 10 Mediterranean cropping systems. Empirically derived relationships between yield and aboveground plus belowground crop biomass as well as estimates of C contributions from crop residues and manure amendments were used to quantify cumulative C inputs into each cropping system. Soil samples were separated into four aggregate size classes (>2000, 250–2000, 53–250, and <53 μm) and into three soil organic matter (SOM) fractions within the large (>2000 μm) and small (250–2000 μm) macroaggregates. Aggregate stability increased linearly with both C input (\n r\n 2\n = 0.75,\n p\n = 0.001) and SOC (\n r\n 2\n = 0.63,\n p\n = 0.006). Across the 10 cropping systems, annual soil C sequestration rates ranged from −0.35 to 0.56 Mg C ha\n −1\n yr\n −1\n We found a strong linear relationship (\n r\n 2\n = 0.70,\n p\n = 0.003) between SOC sequestration and cumulative C input, with a residue‐C conversion to SOC rate of 7.6%. This linear relationship suggests that these soils have not reached an upper limit of C sequestration (i.e., not C saturated). In addition, C shifted from the <53‐μm fraction in low C input systems to the large and small macroaggregates in high C input systems. A majority of the accumulation of SOC due to additional C inputs was preferentially sequestered in the microaggregates‐within‐small‐macroaggregates (mM). Hence, the mM fraction is an ideal indicator for C sequestration potential in sustainable agroecosystems.\n

The soil microbiome is highly diverse and comprises up to one quarter of Earth's diversity. Yet, how such a diverse and functionally complex microbiome influences ecosystem functioning remains unclear. Here we manipulated the soil microbiome in experimental grassland ecosystems and observed that microbiome diversity and microbial network complexity positively influenced multiple ecosystem functions related to nutrient cycling (e.g. multifunctionality). Grassland microcosms with poorly developed microbial networks and reduced microbial richness had the lowest multifunctionality due to fewer taxa present that support the same function (redundancy) and lower diversity of taxa that support different functions (reduced  functional uniqueness). Moreover, different microbial taxa explained different ecosystem functions pointing to the significance of functional diversity in microbial communities. These findings indicate the importance of microbial interactions within and among fungal and bacterial communities for enhancing ecosystem performance and demonstrate that the extinction of complex ecological associations belowground can impair ecosystem functioning.

以“西兰花-空闲”轮作为对照,研究西兰花种植前和收获期,“西兰花-南瓜”轮作、“西兰花-早稻”轮作1 a和“西兰花-早稻”轮作2 a对土壤微生物和酶活性的影响。西兰花种植前,“西兰花-南瓜”轮作土壤细菌、放线菌和真菌数量最多;西兰花收获期,“西兰花-早稻”轮作2 a土壤细菌和真菌数量最多,“西兰花-早稻”轮作1 a土壤放线菌数量最多。西兰花种植前,“西兰花-早稻”轮作1 a土壤微生物生物量氮最高;西兰花收获期,“西兰花-早稻”轮作2 a土壤微生物生物量碳和土壤微生物生物量氮均最高。西兰花种植前,“西兰花-早稻”轮作2 a土壤脲酶活性最高;西兰花收获期,“西兰花-早稻”轮作2 a土壤脲酶和蔗糖酶活性均最高。上述结果表明,与其余3种轮作模式相比,“西兰花-早稻”轮作2 a可更有效地改善西兰花耕作土壤微生物环境,提高土壤酶活性。

Studying the obstacles associated with continuous cropping is necessary for sustainable agricultural production. Phenolic acids play an important role in continuous cropping systems, although their mechanism of action in these systems remains unclear. Using High-performance Liquid Chromatography, we characterized the changes in phenolic acid contents in soils that had been continuously cropped with tobacco for different time periods and evaluated the interactions between soil physicochemical properties, bacterial community structure and diversity, and phenolic acids. Prolonged continuous cropping was associated with a significant increase in the content of phenolic acids and a significant decrease in soil pH and bacterial diversity. A significant negative correlation between pH and phenolic acids content was observed, suggesting that soil acidification potentially leads to the accumulation of phenolic acids. The Mantel test indicated that phenolic acids were positively associated with relative bacterial abundance (R = 0.480, P < 0.01), signifying that the accumulation of phenolic acids is a potential factor leading to changes in bacterial community structure. Continuous cropping lowered the soil pH, which stimulated phenolic acid accumulation and consequently altered the bacterial community structure and diversity, ultimately impacting tobacco plant growth.

Soil-related obstacles resulting from continuous monoculture have limited the sustainable development of the tomato industry in China. An experiment on tomatoes with seven continuous monoculture treatments (the 1st, 3rd, 5th, 7th, 9th, 11th, and 13th crops, respectively) was conducted in a solar greenhouse, to investigate the influence of monoculture on soil quality. Most soil quality indicators first increased and then decreased with increasing continuous monoculture crops, and significant differences among crops were observed. Indicators at the 13th crop were significantly lower than those at the other crops in terms of average well color development (AWCD), substrate richness (S), the Shannon diversity index (H), and the McIntosh index (U) of the soil microbial community (SMC), soil urease (UR), and neutral phosphatase (N-PHO) activities, and available nitrogen (AN) and potassium (AK). However, fungal abundance (FUN) at the 13th crop was significantly higher than that at the other crops. As principal component analysis (PCA) revealed, SMC functional diversity at the 1st, 11th, and 13th crops were similar, and were obviously distinguished from those at the other crops. Moreover, the tomato yield was significantly and positively correlated with soil-available potassium and SMC functional diversity indexes. Our findings indicated that short-term continuous monoculture, e.g., for fewer than seven or nine crops, was beneficial for soil quality improvement. However, continuous monoculture for greater than 11 crops had adverse effects on soil enzyme activities, soil microbial abundances, soil chemical properties, soil SMC functional diversity, and the tomato yield, particularly at the 13th crop.