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Employing elevated CO2 (eCO2), similar to increasing atmospheric CO2 in a greenhouse, is a common practice used to increase vegetable crop yields. However, the responses of nutrient availability, nutrient uptake and use efficiency in leafy vegetables to eCO2 remain largely unknown. The plant biomass production, nitrogen (N), phosphorus (P) and potassium (K) contents, nutrient uptake, and soil enzymatic activities of three Brassica chinensis varieties of 'Longpangqing', 'Heimeiren' and 'Qingjiangbai' were thus assessed under ambient CO2 (C0, 420/470 ppm, day/night) and eCO2 (C1, C0 + 33.3%C0; C2, C0 + 66.7%C0; and C3, C0 + 100%C0) for 4 months. Biomass production was significantly enhanced in these three tested B. chinensis varieties along with eCO2 gradients, with the highest biomass production under C3. Moreover, the eCO2 significantly increased plant N and K uptake, P and K use efficiency, soil saccharase, urease, and phosphatase activities, but decreased plant P content, soil available N and K, and catalase activity. Under eCO2, 'Qingjiangbai' exhibited higher biomass production and P and K uptake, without a decrease in soil available N and P. Consequently, more external fertilizer supplementation (especially N, followed by K) is required to maintain or promote Brassica chinensis yield under eCO2, while these management strategies must be carefully considered for different crop varieties. [ABSTRACT FROM AUTHOR]

Few studies have examined if perennial leguminous cover crops are able to transfer nitrogen (N) via common mycorrhizal networks (CMNs) to neighboring fruit trees; the gradient of such N transfer could affect the N nutrition of both plants. Using separated three-column chambers to grow plants in a greenhouse, 99 atom% 15N as (15NH4)2SO4 was applied to leaves of white clover (Trifolium repens L.) and 15N was then traced in neighboring citrus (Citrus sinensis (L.) Osbeck) seedlings interconnected by an arbuscular mycorrhizal fungus (AMF, Rhizophagus intraradices). A range of 66.85–68.74% mycorrhizal colonization in white clover (mycorrhizal and/or Rhizobium trifolii inoculated) and 19.29–23.41% in citrus (non-mycorrhizal inoculated) was observed after 12 months of AMF inoculation in the white clover, indicating a successful CMN linkage was established between these two plant species. This CMN establishment resulted in significant increases in biomass, N accumulation, and 15N content of citrus when accompanied with nodulated and mycorrhizal fungus colonized white clover. N transfer from white clover to citrus was significantly greater under nodulation plus mycorrhization (46.23 mg N per pot, 1.71% of N transferred) than under non-inoculated control (4.36 mg N per pot, 0.21% of N transferred), and higher than sole mycorrhization (36.34 mg N per pot, 1.42% of N transferred). The percentage of N in citrus derived from white clover under nodulated/mycorrhization was 1.83–1.93%, and was highest in leaves (3.31%), moderate in stems (2.47%), and lowest in roots (0.41%) of citrus. In summary, results from this experiment demonstrated that nearly 2.0% of N transferred from white clover to citrus via CMN. Further studies are needed to quantify N transfer between white clover and citrus by other routes, including soil or root exudation pathways. [ABSTRACT FROM AUTHOR]

With increasing application of nitrogen (N), phosphorus (P), and potassium (K) fertilizers, especially in China's fruit crops, the agronomic responses of fruit crops to fertilization may be reduced with time. Thus, the quantification of these responses would be useful for establishing nutrient recommendation and fertilizer management for fruit crops. Here, a meta-analysis including 552 paired data for agronomic response and 1283 sets for amounts of optimal fertilization from 293 field studies in China were performed to systemically quantify these variations of yield response (YR), relative yield (RY), agronomic efficiency (AE), and partial factor productivity (PFP) in response to the application of N, P, or K fertilizer under different groups including fruit crop types, time, and regions. The results showed that the average YRs to N, P or K fertilizer were 7.6, 5.2, or 5.9 t ha−1, indicating related RYs of 78.0%, 82.9%, or 82.4%, respectively. All of the RYs for N, P, or K application in studies after 2000 were higher and less variable than those before 2000. Higher RYs were also shown for deciduous fruit trees when compared with evergreen fruit trees. The average AEs of N, P, and K fertilizer in China's fruit crops were 29.1, 32.4 and 20.2 kg kg−1, all of them were negatively correlated with fertilizer rate. Due to a higher yield response and less fertilizer rate, annual crops (mainly watermelon and melons) had significantly higher AE than that of perennial crops. The average PFPs of N, P, and K fertilizer in China's fruit crops were 129, 205, and 113 kg kg−1, all of which showed a declining trend with time. These findings demonstrated that the building-up of soil indigenous nutrient supply (indicated by RY) together with improving fruit varieties, as well as pest management and other forms of management could make external fertilization less important for increasing the yield of fruit crops in China. A rational nutrient management is therefore crucial for balancing yield and environmental concerns in countries like China, India, and other countries where fertilizers are often overused. [ABSTRACT FROM AUTHOR]