Fanqiao Meng

Investigation of photosynthate-C allocation 27 days after 13C-pulse labeling of Zea mays L. at different growth stages

AimsPulse labeling of crops using 13C is often employed to trace photosynthesized carbon (C) within crop-soil systems. However, few studies have compared the C distribution for different labeling periods. The overall aim of this study was to determine the length of the monitoring interval required after 13C-pulse labeling to quantify photosynthate C allocation into plant, soil and rhizosphere respiration pools for the entire growing season of maize (Zea mays L.).MethodsPot grown maize was pulse-labeled with 13CO2 (98xa0at.u2009%) at the beginning of emergence, elongation, heading and grainfilling growth stages. The routing of 13C into shoot and root biomass, soil CO2 flux and soil organic carbon (SOC) pools was monitored for 27xa0days after 13C-pulse labeling at the beginning of each growth stage.ResultsThe majority of the 13C was recovered after 27 d in the maize shoots, i.e., 57xa0%, 53xa0%, 70xa0% and 80xa0%, at the emergence, elongation, heading, and grainfilling stages, respectively. More 13C was recovered in the root biomass at elongation (27xa0%) compared to the least at the grainfilling stage (3xa0%). The amount recovered in the soil was the smallest pool of 13C at emergence (2.3xa0%), elongation (3.8xa0%), heading and grainfilling (less than 2xa0%). The amount of 13C recovered in rhizosphere respiration, i.e. 13CO2, was greatest at emergence (26xa0%), and similar at the elongation, heading and grainfilling stages (~16xa0%).ConclusionsAt least 24xa0days is required to effectively monitor the recovery of 13C after pulse labeling with 13CO2 for maize in plant and soil pools. The recovery of 13C differed between growth stages and corresponded to the changing metabolic requirements of the plant, which indicated labeling for the entire growth season would more accurately quantify the C budget in plant-soil system.

Agricultural sustainable intensification improved nitrogen use efficiency and maintained high crop yield during 1980-2014 in Northern China

Global population increase will require rapid increase of food production from existing agricultural land by 2050, which will inevitably mean the increase of agricultural productivity. Due to agricultural sustainable intensification since the 1990s, crop production in Huantai County of northern China has risen to 15tha-1yr-1 for the annual wheat-maize rotation system. We examined the temporal dynamics of nitrogen (N) budget, N losses, and N use efficiency (NUE) during the 35years (1980-2014) in Huantai. The results revealed that atmospheric N deposition increased 220% while reactive N losses decreased by 21.5% from 1980s to 2010s. During 1980-2002, annual N partial factor productivity (PFPN), apparent NUE and N recovery efficiency (REN) increased from 20.3 to 40.7kggrainkg-1Nfert, from 36.5% to 71.0%, and from 32.4% to 57.7%, respectively; meanwhile, reactive N losses intensity, land use intensity and N use intensity decreased by 69.8%, 53.4%, 50.0%, respectively, but without further significant changes after 2002. Overall increases in NUE and decreases in N losses were largely due to the introduction of optimized fertilization practice, mechanization and increased incorporation of crop straw in Huantai. Straw incorporation was also significant in soil N stock accrual and fertility improvement. By 2030, northern China may reach the lowest end of PFPN values in developed countries (>45kggrainkg-1Nfert). These agricultural sustainable intensification practices will be critical in maintaining high grain yields and associated decreases in environmental pollution, although water use efficiency in the region still needs to be improved.

Environmental impacts and production performances of organic agriculture in China: A monetary valuation.

Organic agriculture has developed rapidly in China since the 1990s, driven by the increasing domestic and international demand for organic products. Quantification of the environmental benefits and production performances of organic agriculture on a national scale helps to develop sustainable high yielding agricultural production systems with minimum impacts on the environment. Data of organic production for 2013 were obtained from a national survey organized by the Certification and Accreditation Administration of China. Farming performance and environmental impact indicators were screened and indicator values were defined based on an intensive literature review and were validated by national statistics. The economic (monetary) values of farming inputs, crop production and individual environmental benefits were then quantified and integrated to compare the overall performances of organic vs. conventional agriculture. In 2013, organically managed farmland accounted for approximately 0.97% of national arable land, covering 1.158 million ha. If organic crop yields were assumed to be 10%-15% lower than conventional yields, the environmental benefits of organic agriculture (i.e., a decrease in nitrate leaching, an increase in farmland biodiversity, an increase in carbon sequestration and a decrease in greenhouse gas emissions) were valued at 1921 million RMB (320.2 million USD), or 1659 RMB (276.5 USD) per ha. By reducing the farming inputs, the costs saved was 3110 million RMB (518.3 million USD), or 2686 RMB (447.7 USD) per ha. The economic loss associated with the decrease in crop yields from organic agriculture was valued at 6115 million RMB (1019.2 million USD), or 5280 RMB (880 USD) per ha. Although they were likely underestimated because of the complex relationships among farming operations, ecosystems and humans, the production costs saved and environmental benefits of organic agriculture that were quantified in our study compensated substantially for the economic losses associated with the decrease in crop production. This suggests that payment for the environmental benefits of organic agriculture should be incorporated into public policies. Most of the environmental impacts of organic farming were related to N fluxes within agroecosystems, which is a call for the better management of N fertilizer in regions or countries with low levels of N-use efficiency. Issues such as higher external inputs and lack of integration cropping with animal husbandry should be addressed during the quantification of change of conventional to organic agriculture, and the quantification of this change is challenging.

Allocation of photosynthesized carbon in an intensively farmed winter wheat–soil system as revealed by 14CO2 pulse labelling

Understanding the rhizodeposited carbon (C) dynamics of winter wheat (Triticum aestivum L.), is crucial for soil fertility and C sequestration. Pot-grown winter wheat was pulse labelled with 14CO2 at the key growth stages. 14C in the shoots, roots and soil was measured at 5 or 2 days after 14C-labelling (DAL 5/2) at each growth stage and at harvest. The 14C in the shoots increased from 4% of the net 14C recovered (shootsu2009+u2009rootsu2009+u2009soil) during tillering to 53% at harvest. Approximately 14–34% of the net 14C recovered was incorporated into the soil. Allocation of photosynthesized C was extrapolated from the pot experiment to field condition, assuming a planting density of 1.8 million plants ha−1. The estimated C input to the soil was 1.7 t C ha−1, and 0.7 t C ha−1 of root residues was retained after wheat harvest; both values were higher than those previously reported (0.6 and 0.4 t C ha−1, respectively). Our findings highlight that C tracing during the entire crop season is necessary to quantify the temporal allocation of photosynthesized C, especially the contribution to soil carbon in intensified farming system.

Impacts of natural factors and farming practices on greenhouse gas emissions in the North China Plain: A meta-analysis

Abstract Requirements for mitigation of the continued increase in greenhouse gas (GHG) emissions are much needed for the North China Plain (NCP). We conducted a meta‐analysis of 76 published studies of 24 sites in the NCP to examine the effects of natural conditions and farming practices on GHG emissions in that region. We found that N2O was the main component of the area‐scaled total GHG balance, and the CH 4 contribution was <5%. Precipitation, temperature, soil pH, and texture had no significant impacts on annual GHG emissions, because of limited variation of these factors in the NCP. The N2O emissions increased exponentially with mineral fertilizer N application rate, with y = 0.2389e0.0058x for wheat season and y = 0.365e0.0071x for maize season. Emission factors were estimated at 0.37% for wheat and 0.90% for maize at conventional fertilizer N application rates. The agronomic optimal N rates (241 and 185 kg N ha−1 for wheat and maize, respectively) exhibited great potential for reducing N2O emissions, by 0.39 (29%) and 1.71 (56%) kg N2O‐N ha−1 season−1 for the wheat and maize seasons, respectively. Mixed application of organic manure with reduced mineral fertilizer N could reduce annual N2O emissions by 16% relative to mineral N application alone while maintaining a high crop yield. Compared with conventional tillage, no‐tillage significantly reduced N2O emissions by ~30% in the wheat season, whereas it increased those emissions by ~10% in the maize season. This may have resulted from the lower soil temperature in winter and increased soil moisture in summer under no‐tillage practice. Straw incorporation significantly increased annual N2O emissions, by 26% relative to straw removal. Our analysis indicates that these farming practices could be further tested to mitigate GHG emission and maintain high crop yields in the NCP.

Change in the abundance and community composition of ammonia-oxidizing bacteria and archaea at soil aggregate level as native pasture converted to cropland in a semiarid alpine steppe of central Asia

PurposeThe study aimed to improve understanding of the transformation of N in the Ili River Valley by investigating the abundance and community composition of ammonia-oxidizing bacteria (AOB) and archaea (AOA) under different land uses at bulk soil and aggregate levels.Materials and methodsSoil samples were collected from plots of three types of land use, i.e., native pasture (NP), conventional farming (CF), and organic farming (OF). Soil aggregates were separated using wet-sieving method. The abundance and structure of AOB and AOA communities were assessed by qPCR and DGGE, respectively.Results and discussionCompared with CF, OF and NP both increased soil TN and SOC stock but via contrasting mechanisms. The abundance of AOB under cropland usesxa0(CF and OF) was higher than those of NP. The AOB sequences, belonging to Nitrosospira cluster 1, which is adaptable to high mineral N content in cold region, increased in CF than in other land uses. Conversion of NP to cropland did not affect the abundance, but the community structure of AOA. The abundance of AOB and AOA in large macroaggregate and silt and clay aggregate were significantly lower than those in small macroaggregate under cropland uses. In cropland, the small macroaggregate provided the microenvironment for the growth of AOB and AOA, thereby serving as a potential hotspot for ammonia oxidation.ConclusionsReclamation of grassland to cropland significantly increased the AOB abundance, and shifted the community structure and spatial distribution variation of AOB and AOA at the soil aggregates. The results indicated that soil N cycle could be substantially altered and this should be well integrated in the improvement of regional land utilization.