Land management policy shift influenced seasonal variation of erosion-induced nitrogen and phosphorus outputs from intensive agricultural catchment.

A shift in policy to intensive agricultural production and land management often leads to excessive fertilizer application and accelerated erosion with consequent detrimental effects to water bodies. We investigated the impact of that shift by quantifying the spatial and temporal change in sediment sources and associated total nitrogen (TN) and total phosphorus (TP) pollutants output loads in an intensive agricultural catchment in North China across one year (November 2021-November 2022). We describe the implications of this work for intensive agriculture elsewhere in China and other countries. Seasonal sediment source apportionment was estimated at the catchment outlet using Berillium-7 (7Be) combined with compound-specific stable isotope (CSSI) signatures from sources and sediments. Diagnostic 'fingerprints' in MixSIAR were used to discriminate sediment sources between forest and crop farmland converted from forest (F + C(F)), crop farmland (C), and vegetable farmland (V). Our study identified F + C(F) as the dominant sediment source (mean 55.24 ± 2.91 %), intermediate on V (mean 30.06 ± 2.20 %), and least on C (mean 14.70 ± 2.13 %). Sedimentation ranged from 37.98 ± 3.02 to 89.60 ± 12.68 t·ha-1·event-1 and coincided with shifted land use policy and rainfall distribution. The TN and TP in sediment were both mainly derived from F + C(F) (averaged 22.27 ± 4.26 t·event-1 and 11.62 ± 2.28 t·event-1) and least from V (averaged 1.63 ± 0.29 and 2.09 ± 0.33 t·event-1). Despite being a significant sediment source, V contributed little sediment TN and TP input for eutrophication. Our findings imply that F + C(F) are diffuse sources of catchment pollution over the short term. These results describe the successful use of CSSI and 7Be to cost-effectively quantify the seasonal variation of sediment TN and TP loads from land-use-specific sources in the catchment under shifting land management policy in China with potential for use elsewhere. These findings enable soil conservation strategies and land management practices optimized for implementing targeted pollutant abatement initiatives in intensive agriculture in China and elsewhere.

Disentangling nitrate pollution sources and apportionment in a tropical agricultural ecosystem using a multi-stable isotope model.

Fertilizers increase agricultural productivity and farmers' income. However, intensive agriculture frequently overuses fertilizers, which in turn can contaminate surface and groundwater. In this study, hydrochemical and multi-isotope (δ15NNO3, δ18ONO3 and δ18OH2O) data have been combined to identify nitrate pollution sources in Ghana's Densu River Basin, trace the Nitrogen (N) biogeochemical processes in the basin and apportion the contribution of each pollution source. Surface water NO3- ranged from 0.3 to 10.6 mg/L (as N), while groundwater NO3- ranged from 0.9 to 34 mg/L. Hierarchical cluster analysis classified the water samples into three spatial categories: upstream, midstream, and downstream, reflecting river and land use patterns. The multi-isotope model considered five primary NO3- sources: atmospheric deposition, manure/sewage, NH4+ in fertilizers, other NO3- based fertilizers and soil N. Nitrification was identified as the major biogeochemical process upstream, whereas mixing of sources and denitrification dominate the midstream to downstream sections of the basin. Nitrate source apportioning using a MixSIAR model reveal that N fertilizers (40 %) and soil N (34 %) contribute the most to nitrate pollution upstream of the river. From the midstream to downstream sections, manure/sewage (43 %) become the dominant nitrate source, reflecting the transition from agriculture to peri-urban and urban land use. This study has shown that soil erosion and runoff contribute to nitrate pollution in the Densu River, at levels comparable to N fertilizers, and groundwater across the basin is impacted mainly by manure/sewage. The multi-isotope analyses allowed the partitioning of N sources in other ways not possible using only classical hydrochemical methods.

Uptake of (14)C-atropine and/or its transformation products from soil by wheat (Triticum aestivum var Kronjet) and their translocation to shoots.

Plant uptake of toxins and their translocation to edible plant parts are important processes in the transfer of contaminants into the food chain. Atropine, a highly toxic muscarine receptor antagonist produced by Solanacea species, is found in all plant tissues and can enter the soil and hence be available for uptake by crops. The absorption of atropine and/or its transformation products from soil by wheat (Triticum aestivum var Kronjet) and its distribution to shoots was investigated by growing wheat in soil spiked with unlabeled or (14)C-labeled atropine. Radioactivity attributable to (14)C-atropine and its transformation products was measurable in plants sampled at 15 d after sowing (DAS) and thereafter until the end of experiment. The highest accumulation of (14)C-atropine and/or its transformation products by plants was detected in leaves (between 73 and 90% of the total accumulated) with lower amounts in stems, roots, and seeds (approximately 14%, 9%, and 3%, respectively). (14)C-Atropine and/or its transformation products were detected in soil leachate at 30, 60, and 90 DAS and were strongly adsorbed to soil, with 60% of the applied dose adsorbed at 30 DAS, plateauing at 70% from 60 DAS. Unlabeled atropine was detected in shoots 30 DAS at a concentration of 3.9 ± 0.1 µg kg(-1) (mean ± SD). The observed bioconcentration factor was 2.3 ± 0.04. The results suggest a potential risk of atropine toxicity to consumers.

High temperature effects on photosynthate partitioning and sugar metabolism during ear expansion in maize (Zea mays L.) genotypes.

Short hot and dry spells before, or during, silking have an inordinately large effect on maize (Zea mays L.; corn) grain yield. New high yielding genotypes could be developed if the mechanism of yield loss were more fully understood and new assays developed. The aim here was to determine the effects of high temperature (35/27 degrees C) compared to cooler (25/18 degrees C) temperatures (day/night). Stress was applied for a 14 d-period during reproductive stages prior to silking. Effects on whole plant biomass, ear development, photosynthesis and carbohydrate metabolism were measured in both dent and sweet corn genotypes. Results showed that the whole plant biomass was increased by the high temperature. However, the response varied among plant parts; in leaves and culms weights were slightly increased or stable; cob weights decreased; and other ear parts of dent corn also decreased by high temperature. Photosynthetic activity was not affected by the treatments. The (13)C export rate from an ear leaf was decreased by the high temperature treatment. The amount of (13)C partitioning to the ears decreased more than to other plant parts by the high temperature. Within the ear decreases were greatest in the cob than the shank within an ear. Sugar concentrations in both hemicellulose and cellulose fractions of cobs in sweet corn were decreased by high temperature, and the hemicellulose fraction in the shank also decreased. In dent corn there was no reduction of sugar concentration except in the in cellulose fraction, suggesting that synthesis of cell-wall components is impaired by high temperatures. The high temperature treatment promoted the growth of vegetative plant parts but reduced ear expansion, particularly suppression of cob extensibility by impairing hemicellulose and cellulose synthesis through reduction of photosynthate supply. Therefore, plant biomass production was enhanced and grain yield reduced by the high temperature treatment due to effects on sink activity rather than source activity. Heat resistant ear development can be targeted for genetic improvement.

Partitioning of 13C-labelled photosynthate varies with growth stage and panicle size in high-yielding rice.

A super-high-yielding rice (Oryza sativa L.) cultivar, Takanari, and a traditional japonica rice cultivar, Nakateshinsenbon, were grown under field conditions to compare partitioning of 13C-labelled photosynthate to different plant organs during the period of reproductive development. The flag leaf and the two leaves immediately below it on the main culm were exposed individually to 13CO2 and the movement of the heavy carbon isotope to grains, hull, panicle branches and vegetative parts of plant was assessed. Also, the effect of a reduction of sink size on the partitioning of 13C to different organs was studied by removing some of the primary branches of the panicle. 13C taken up by the three leaves in the post-heading period, moved mostly to the grains and hull of the panicle. At this stage, the uppermost three leaves and the panicle consisted of a single source-sink unit. Partitioning of 13C to the rest of the vegetative structures of the plant was minimal. In the case of Nakateshinsenbon, the flag leaf supplied most of the carbon assimilates for the grains and contributions from the other two leaves were much smaller. However, in Takanari, the contribution of 13C to grains from the second leaf was equivalent to that of the flag leaf. In Takanari, removal of more than one third of the primary branches of the panicle significantly reduced partitioning from the third leaf of the culm, but partitioning from the flag leaf was not significantly changed. In contrast, branch removal treatment significantly depressed transport of carbon assimilates from the flag leaf in Nakateshinsenbon. The obligatory nature of the source-sink relationship in rice is discussed. It is concluded that in lower-yielding traditional rice, photosynthesis in the flag leaf supplies carbon assimilates to the developing grains. But in the super-yielding rice Takanari, the main source area is extended to include the two leaves below the flag leaf so as to sustain an extra large panicle. Even greater grain-filling is possible in super-yielding rice, if the source area is increased further.