氮肥运筹对免耕水稻根系生长、根际土壤特性及产量的影响

为探索氮肥运筹对免耕条件下水稻根系生长以及对根际土壤特性、产量的影响,以金优253为材料进行试验。结果表明：平衡施肥显著提高单株根系干重、根长、单株生物量、根半径、单株根表面积、根长密度及根系活力,实收单产高于重穗肥和重基肥处理,且与重基肥差异达95％的显著水平,主要是有效穗数、结实率的增加。平衡施肥显著提高0~10 cm土层的0~2 mm根际土壤有机质、碱解氮含量及脲酶、蔗糖酶活性。因此平衡施肥能明显促进免耕水稻根系生长和有效穗数的增加,对提高水稻产量具有促进作用。     

减氮配施稻秆生物炭对稻田土壤养分及植株氮素吸收的影响

通过2018年早稻和晚稻田间试验,研究化学氮肥减量及配施稻秆生物炭对稻田土壤养分特性及植株氮素吸收的影响。试验包括6个处理:不施氮(CK)、常规施氮(N₁₀₀)、减氮20%(N₈₀)、减氮20%配施生物炭(N₈₀+BC)、减氮40%(N₆₀)、减氮40%配施生物炭(N₆₀+BC)。结果表明: 与常规施氮相比,单纯减氮20%和40%或配施生物炭对早晚稻不同生育期土壤pH、有机质、全氮、铵态氮、全磷、有效磷、全钾、速效钾无显著影响;减氮20%配施生物炭显著增加晚稻分蘖期的土壤阳离子交换量(CEC),而减氮40%配施生物炭则显著增加晚稻抽穗期的电导率(EC)值。与单纯减氮相比,N₈₀+BC的土壤速效钾含量在早晚稻抽穗期均显著升高,土壤pH值、全氮在晚稻成熟期显著增加;N₆₀+BC的土壤全钾含量在早稻成熟期显著升高。不同处理早稻土壤硝态氮含量随生育进程逐渐降低,与分蘖期相比,抽穗期和成熟期的常规施氮土壤硝态氮含量分别降低50.0%和71.6%,而配施生物炭处理则降低6.3%～45.5%,减氮配施生物炭显著降低了硝态氮的流失。在晚稻抽穗期,减氮配施生物炭植株吸氮量显著高于常规施氮和单纯减氮,增加幅度为34.8%～52.4%。综上,适度的减氮或配施稻秆生物炭能有效保持土壤养分,促进水稻对氮素的吸收,提高氮素利用率。     

Long‐term research avoids spurious and misleading trends in sustainability attributes of no‐till

Agricultural management recommendations based on short‐term studies can produce findings inconsistent with long‐term reality. Here, we test the long‐term environmental sustainability and profitability of continuous no‐till agriculture on yield, soil water availability, and N₂O fluxes. Using a moving window approach, we investigate the development and stability of several attributes of continuous no‐till as compared to conventional till agriculture over a 29‐year period at a site in the upper Midwest, US. Over a decade is needed to detect the consistent effects of no‐till. Both crop yield and soil water availability required 15 years or longer to generate patterns consistent with 29‐year trends. Only marginal trends for N₂O fluxes appeared in this period. Relative profitability analysis suggests that after initial implementation, 86% of periods between 10 and 29 years recuperated the initial expense of no‐till implementation, with the probability of higher relative profit increasing with longevity. Importantly, statistically significant but misleading short‐term trends appeared in more than 20% of the periods examined. Results underscore the importance of decadal and longer studies for revealing consistent dynamics and emergent outcomes of no‐till agriculture, shown to be beneficial in the long term.     

Long‐term antagonistic effect of increased precipitation and nitrogen addition on soil respiration in a semiarid steppe

Changes in water and nitrogen (N) availability due to climate change and atmospheric N deposition could have significant effects on soil respiration, a major pathway of carbon (C) loss from terrestrial ecosystems. A manipulative experiment simulating increased precipitation and atmospheric N deposition has been conducted for 9 years (2005–2013) in a semiarid grassland in Mongolian Plateau, China. Increased precipitation and N addition interactively affect soil respiration through the 9 years. The interactions demonstrated that N addition weakened the precipitation‐induced stimulation of soil respiration, whereas increased precipitation exacerbated the negative impacts of N addition. The main effects of increased precipitation and N addition treatment on soil respiration were 15.8% stimulated and 14.2% suppressed, respectively. Moreover, a declining pattern and 2‐year oscillation were observed for soil respiration response to N addition under increased precipitation. The dependence of soil respiration upon gross primary productivity and soil moisture, but not soil temperature, suggests that resources C substrate supply and water availability are more important than temperature in regulating interannual variations of soil C release in semiarid grassland ecosystems. The findings indicate that atmospheric N deposition may have the potential to mitigate soil C loss induced by increased precipitation, and highlight that long‐term and multi‐factor global change studies are critical for predicting the general patterns of terrestrial C cycling in response to global change in the future.     

Long‐term nitrogen addition modifies microbial composition and functions for slow carbon cycling and increased sequestration in tropical forest soil

Nitrogen (N) deposition is a component of global change that has considerable impact on belowground carbon (C) dynamics. Plant growth stimulation and alterations of fungal community composition and functions are the main mechanisms driving soil C gains following N deposition in N‐limited temperate forests. In N‐rich tropical forests, however, N deposition generally has minor effects on plant growth; consequently, C storage in soil may strongly depend on the microbial processes that drive litter and soil organic matter decomposition. Here, we investigated how microbial functions in old‐growth tropical forest soil responded to 13 years of N addition at four rates: 0 (Control), 50 (Low‐N), 100 (Medium‐N), and 150 (High‐N) kg N ha^?1 year^?1. Soil organic carbon (SOC) content increased under High‐N, corresponding to a 33% decrease in CO₂ efflux, and reductions in relative abundances of bacteria as well as genes responsible for cellulose and chitin degradation. A 113% increase in N₂O emission was positively correlated with soil acidification and an increase in the relative abundances of denitrification genes (narG and norB). Soil acidification induced by N addition decreased available P concentrations, and was associated with reductions in the relative abundance of phytase. The decreased relative abundance of bacteria and key functional gene groups for C degradation were related to slower SOC decomposition, indicating the key mechanisms driving SOC accumulation in the tropical forest soil subjected to High‐N addition. However, changes in microbial functional groups associated with N and P cycling led to coincidentally large increases in N₂O emissions, and exacerbated soil P deficiency. These two factors partially offset the perceived beneficial effects of N addition on SOC storage in tropical forest soils. These findings suggest a potential to incorporate microbial community and functions into Earth system models considering their effects on greenhouse gas emission, biogeochemical processes, and biodiversity of tropical ecosystems.     

OsMOGS is required for N‐glycan formation and auxin‐mediated root development in rice (Oryza sativa L.)

N‐glycosylation is a major modification of glycoproteins in eukaryotic cells. In Arabidopsis, great progress has been made in functional analysis of N‐glycan production, however there are few studies in monocotyledons. Here, we characterized a rice (Oryza sativa L.) osmogs mutant with shortened roots and isolated a gene that coded a putative mannosyl‐oligosaccharide glucosidase (OsMOGS), an ortholog of α‐glucosidase I in Arabidopsis, which trims the terminal glucosyl residue of the oligosaccharide chain of nascent peptides in the endoplasmic reticulum (ER). OsMOGS is strongly expressed in rapidly cell‐dividing tissues and OsMOGS protein is localized in the ER. Mutation of OsMOGS entirely blocked N‐glycan maturation and inhibited high‐mannose N‐glycan formation. The osmogs mutant exhibited severe defects in root cell division and elongation, resulting in a short‐root phenotype. In addition, osmogs plants had impaired root hair formation and elongation, and reduced root epidemic cell wall thickness due to decreased cellulose synthesis. Further analysis showed that auxin content and polar transport in osmogs roots were reduced due to incomplete N‐glycosylation of the B subfamily of ATP‐binding cassette transporter proteins (ABCBs). Our results demonstrate that involvement of OsMOGS in N‐glycan formation is required for auxin‐mediated root development in rice.     

Soil hydrological properties as influenced by long‐term nitrogen application and landscape positions under switchgrass seeded to a marginal cropland

Switchgrass (Panicum virgatum L.) has the potential to recover the soil hydrological properties of marginal lands. Nitrogen (N) and landscape position are the key factors in impacting these soil properties under switchgrass. The specific objective of this study was to investigate the responses of N rate (low, 0 kg N/ha and high, 112 kg N/ha) and landscape positions (shoulder and footslope) on near‐surface soil hydrological properties that included: infiltration rate (q_s), saturated hydraulic conductivity (K_sat), bulk density (ρ_b), penetration resistance (SPR), water retention (SWR), pore‐size distribution (PSD), and carbon (C) and nitrogen (N) fractions under switchgrass production. Data showed that, in general, the N and landscape position significantly influenced soil hydrological properties. Higher N rate decreased ρ_b (1.23 and 1.36 g/cm³ at 0–5 and 5–15 cm, respectively) and SPR (1.06 and 1.53 MPa at 0–5 and 5–15 cm, respectively) at both depths and increased the q_s, K_sat and Green–Ampt estimated sorptivity (S) and hydraulic conductivity (K_s) parameters, and SWR (0–5 cm depth) at 0 and ?0.4 kPa matric potentials (ψ_m). Furthermore, footslope position significantly decreased ρ_b, SPR at 0–5 and 5–15 cm depths, and increased the q_s, K_sat, S, K_s, and SWR (0–5 cm depth) at every ψ_m ranged from 0 to ?30.0 kPa. The higher N rate increased the coarse mesopores (60–1,000 μm) and total pores, whereas, footslope position increased the coarse mesopores, micropores (<60 μm), and total pores. Data from this study showed that planting switchgrass with 112 kg N/ha under footslope position helped in improving the soil hydrological properties, those can be beneficial in enhancing the biomass yield under marginal lands.     

A critical review of the impacts of cover crops on nitrogen leaching,net greenhouse gas balance and crop productivity

Cover crops play an increasingly important role in improving soil quality, reducing agricultural inputs and improving environmental sustainability. The main objectives of this critical global review and systematic analysis were to assess cover crop practices in the context of their impacts on nitrogen leaching, net greenhouse gas balances (NGHGB) and crop productivity. Only studies that investigated the impacts of cover crops and measured one or a combination of nitrogen leaching, soil organic carbon (SOC), nitrous oxide (N₂O), grain yield and nitrogen in grain of primary crop, and had a control treatment were included in the analysis. Long‐term studies were uncommon, with most data coming from studies lasting 2–3 years. The literature search resulted in 106 studies carried out at 372 sites and covering different countries, climatic zones and management. Our analysis demonstrates that cover crops significantly (p < 0.001) decreased N leaching and significantly (p < 0.001) increased SOC sequestration without having significant (p > 0.05) effects on direct N₂O emissions. Cover crops could mitigate the NGHGB by 2.06 ± 2.10 Mg CO₂‐eq ha^?1 year^?1. One of the potential disadvantages of cover crops identified was the reduction in grain yield of the primary crop by ≈4%, compared to the control treatment. This drawback could be avoided by selecting mixed cover crops with a range of legumes and non‐legumes, which increased the yield by ≈13%. These advantages of cover crops justify their widespread adoption. However, management practices in relation to cover crops will need to be adapted to specific soil, management and regional climatic conditions.     

Nonlinear root-derived carbon sequestration across a gradient of nitrogen and phosphorous deposition in experimental mesocosms

Enhanced sequestration of plant‐carbon (C) inputs to soil may mitigate rising atmospheric carbon dioxide (CO₂) concentrations and related climate change but how this sequestration will respond to anthropogenic nitrogen (N) and phosphorous (P) deposition is uncertain. We couple isotope, soil C fractionation and mesocosm techniques to assess the sequestration of plant‐C inputs, and their partitioning into C pools with different sink potentials, under an experimental gradient of N and P deposition (0, 10, 30, 60 and 100 kg N ha^?1 yr^?1; and 0, 2, 6, 12 and 20 kg P ha^?1 yr^?1). We hypothesized that N deposition would increase sequestration, with the majority of the C being sequestered in faster cycling soil pools because N deposition has been shown to accelerate the turnover of these pools while decelerating the turnover of slower cycling pools. In contrast to this hypothesis, sequestration into all soil C pools peaked at intermediate levels of N deposition. Given that P amendment has been shown to cause a net loss of soil C, we postulated that P deposition would decrease sequestration. This expectation was not supported by our data, with sequestration generally being greater under P deposition. When soils were amended simultaneously with N and P, neither the shape of the sequestration relationship across the deposition gradient, nor the observed sequestration at the majority of the deposition rates, was statistically predictable from the effects of N and P in isolation. The profound nonlinearities we observed, both for total sequestration responses and the partitioning of C into soil pools with different sink potentials, suggests that the rates of N and P deposition to ecosystems will be the critical determinant of whether they enhance or decrease the long‐term sequestration of fresh plant‐C inputs to soils.     

Putative zeatin O‐glucosyltransferase OscZOG1 regulates root and shoot development and formation of agronomic traits in rice

As a ubiquitous reaction, glucosylation controls the bioactivity of cytokinins in plant growth and development.Here we show that genetic manipulation of zeatin-Oglucosylation regulates the formation of important agronomic traits in rice by manipulating the expression of OscZOG1 gene,encoding a putative zeatin O-glucosyltransferase. We found that OscZOG1 was preferentially expressed in shoot and root meristematic tissues and nascent organs. The growth of lateral roots was stimulated in the overexpression lines, but inhibited in RNA interference lines. In shoots, knockdown of OscZOG1 expression by RNA interference significantly improved tillering, panicle branching, grain number per panicle and seed size, which are important agronomic traits for grain yield. In contrast, constitutive expression of OscZOG1 leads to negative effects on the formation of the grain-yielding traits with a marked increase in the accumulation levels of cis-zeatin O-glucoside(c ZOG) in the transgenic rice plants. In this study,our findings demonstrate the feasibility of improving the critical yield-determinant agronomic traits, including tiller number, panicle branches, total grain number per panicle and grain weight by downregulating the expression level of OscZOG1. Our results suggest that modulating the levels of cytokinin glucosylation can function as a fine-tuning switch in regulating the formation of agronomic traits in rice.     

Long‐term dynamics of mycorrhizal root tips in a loblolly pine forest grown with free‐air CO2 enrichment and soil N fertilization for 6 years

Large‐scale, long‐term FACE (Free‐Air CO₂ enrichment) experiments indicate that increases in atmospheric CO₂ concentrations will influence forest C cycling in unpredictable ways. It has been recently suggested that responses of mycorrhizal fungi could determine whether forest net primary productivity (NPP) is increased by elevated CO₂ over long time periods and if forests soils will function as sources or sinks of C in the future. We studied the dynamic responses of ectomycorrhizae to N fertilization and atmospheric CO₂ enrichment at the Duke FACE experiment using minirhizotrons over a 6 year period (2005–2010). Stimulation of mycorrhizal production by elevated CO₂ was observed during only 1 (2007) of 6 years. This increased the standing crop of mycorrhizal tips during 2007 and 2008; during 2008, significantly higher mortality returned standing crop to ambient levels for the remainder of the experiment. It is therefore unlikely that increased production of mycorrhizal tips can explain the lack of progressive nitrogen limitations and associated increases in N uptake observed in CO₂‐enriched plots at this site. Fertilization generally decreased tree reliance on mycorrhizae as tip production declined with the addition of nitrogen as has been shown in many other studies. Annual NPP of mycorrhizal tips was greatest during years with warm January temperatures and during years with cool spring temperatures. A 2 °C increase in average late spring temperatures (May and June) decreased annual production of mycorrhizal root tip length by 50%. This has important implications for ecosystem function in a warmer world in addition to potential for forest soils to sequester atmospheric C.     

Oryza sativa Lysine‐Histidine‐type Transporter 1 functions in root uptake and root‐to‐shoot allocation of amino acids in rice

In agricultural soils, amino acids can represent vital nitrogen (N) sources for crop growth and yield. However, the molecular mechanisms underlying amino acid uptake and allocation are poorly understood in crop plants. This study shows that rice (Oryza sativa L.) roots can acquire aspartate at soil concentration, and that japonica subspecies take up this acidic amino acid 1.5‐fold more efficiently than indica subspecies. Genetic association analyses with 68 representative japonica or indica germplasms identified rice Lysine‐Histidine‐type Transporter 1 (OsLHT1) as a candidate gene associated with the aspartate uptake trait. When expressed in yeast, OsLHT1 supported cell growth on a broad spectrum of amino acids, and effectively transported aspartate, asparagine and glutamate. OsLHT1 is localized throughout the rice root, including root hairs, epidermis, cortex and stele, and to the leaf vasculature. Knockout of OsLHT1 in japonica resulted in reduced root uptake of amino acids. Furthermore, in ¹⁵N‐amino acid‐fed mutants versus wild‐type, a higher percentage of ¹⁵N remained in roots instead of being allocated to the shoot. ¹⁵N‐ammonium uptake and subsequently the delivery of root‐synthesized amino acids to Oslht1 shoots were also significantly decreased, which was accompanied by reduced shoot growth. These results together provide evidence that OsLHT1 functions in both root uptake and root to shoot allocation of a broad spectrum of amino acids in rice.     

Fruit production is influenced by tree size and size‐asymmetric crowding in a wet tropical forest

In tropical forest communities, seedling recruitment can be limited by the number of fruit produced by adults. Fruit production tends to be highly unequal among trees of the same species, which may be due to environmental factors. We observed fruit production for ~2,000 trees of 17 species across 3 years in a wet tropical forest in Costa Rica. Fruit production was modeled as a function of tree size, nutrient availability, and neighborhood crowding. Following model selection, tree size and neighborhood crowding predicted both the probability of reproduction and the number of fruit produced. Nutrient availability only predicted only the probability of reproduction. In all species, larger trees were more likely to be reproductive and produce more fruit. In addition, number of fruit was strongly negatively related to presence of larger neighboring trees in 13 species; presence of all neighboring trees had a weak‐to‐moderate negative influence on reproductive status in 16 species. Among various metrics of soil nutrient availability, only sum of base cations was positively associated with reproductive status, and for only four species. Synthesis Overall, these results suggest that direct influences on fruit production tend to be mediated through tree size and crowding from neighboring trees, rather than soil nutrients. However, we found variation in the effects of neighbors and nutrients among species; mechanistic studies of allocation to fruit production are needed to explain these differences.