Yong Tao

Carbon Dioxide Flux from Rice Paddy Soils in Central China: Effects of Intermittent Flooding and Draining Cycles

A field experiment was conducted to (i) examine the diurnal and seasonal soil carbon dioxide (CO2) fluxes pattern in rice paddy fields in central China and (ii) assess the role of floodwater in controlling the emissions of CO2 from soil and floodwater in intermittently draining rice paddy soil. The soil CO2 flux rates ranged from −0.45 to 8.62 µmol.m−2.s−1 during the rice-growing season. The net effluxes of CO2 from the paddy soil were lower when the paddy was flooded than when it was drained. The CO2 emissions for the drained conditions showed distinct diurnal variation with a maximum efflux observed in the afternoon. When the paddy was flooded, daytime soil CO2 fluxes reversed with a peak negative efflux just after midday. In draining/flooding alternating periods, a sudden pulse-like event of rapidly increasing CO2 efflux occured in response to re-flooding after draining. Correlation analysis showed a negative relation between soil CO2 flux and temperature under flooded conditions, but a positive relation was found under drained conditions. The results showed that draining and flooding cycles play a vital role in controlling CO2 emissions from paddy soils.

Straw Mulching Reduces the Harmful Effects of Extreme Hydrological and Temperature Conditions in Citrus Orchards

Extreme weather conditions with negative impacts can strongly affect agricultural production. In the Danjiangkou reservoir area, citrus yields were greatly influenced by cold weather conditions and drought stress in 2011. Soil straw mulching (SM) practices have a major effect on soil water and thermal regimes. A two-year field experiment was conducted to evaluate whether the SM practices can help achieve favorable citrus fruit yields. Results showed that the annual total runoff was significantly (P<0.05) reduced with SM as compared to the control (CK). Correspondingly, mean soil water storage in the top 100 cm of the soil profile was increased in the SM as compared to the CK treatment. However, this result was significant only in the dry season (Jan to Mar), and not in the wet season (Jul to Sep) for both years. Interestingly, the SM treatment did not significantly increase citrus fruit yield in 2010 but did so in 2011, when the citrus crop was completely destroyed (zero fruit yield) in the CK treatment plot due to extremely low temperatures during the citrus overwintering stage. The mulch probably acted as an insulator, resulting in smaller fluctuations in soil temperature in the SM than in the CK treatment. The results suggested that the small effects on soil water and temperature changes created by surface mulch had limited impact on citrus fruit yield in a normal year (e.g., in 2010). However, SM practices can positively impact citrus fruit yield in extreme weather conditions.

Impact of fertilizing pattern on the biodiversity of a weed community and wheat growth.

Weeding and fertilization are important farming practices. Integrated weed management should protect or improve the biodiversity of farmland weed communities for a better ecological environment with not only increased crop yield, but also reduced use of herbicides. This study hypothesized that appropriate fertilization would benefit both crop growth and the biodiversity of farmland weed communities. To study the effects of different fertilizing patterns on the biodiversity of a farmland weed community and their adaptive mechanisms, indices of species diversity and responses of weed species and wheat were investigated in a 17-year field trial with a winter wheat-soybean rotation. This long term field trial includes six fertilizing treatments with different N, P and K application rates. The results indicated that wheat and the four prevalent weed species (Galium aparine, Vicia sativa, Veronica persica and Geranium carolinianum) showed different responses to fertilizer treatment in terms of density, plant height, shoot biomass, and nutrient accumulations. Each individual weed population exhibited its own adaptive mechanisms, such as increased internode length for growth advantages and increased light interception. The PK treatment had higher density, shoot biomass, Shannon-Wiener and Pielou Indices of weed community than N plus P fertilizer treatments. The N1/2PK treatment showed the same weed species number as the PK treatment. It also showed higher Shannon-Wiener and Pielou Indices of the weed community, although it had a lower wheat yield than the NPK treatment. The negative effects of the N1/2PK treatment on wheat yield could be balanced by the simultaneous positive effects on weed communities, which are intermediate in terms of the effects on wheat and weeds.

The Structural Adaptation of Aerial Parts of Invasive Alternanthera philoxeroides to Water Regime

Alternanthera philoxeroides has successfully invaded diverse habitats with considerably various water availability, threatening biological diversity in many parts of the world. Because its genetic variation is very low, phenotypic plasticity is believed to be the primary strategy for adapting to the diverse habitats. In the present paper, we investigated the plastic changes of anatomical traits of the aerial parts of A. philoxeroides from flooding to wet then to drought habitat; the results are as follows: A. philoxeroides could change anatomical structures sensitively to adapt to water regime. As a whole, effects of water regime on structures in stem were greater than those in leaf. Except for principal vein diameter and stoma density on leaf surfaces, all other structural traits were significantly affected by water regime. Among which, cuticular wax layer, collenchyma cell wall, phloem fiber cell wall, and hair density on both leaf surfaces thickened significantly with decrease of water availability, whereas, pith cavity and vessel lumen in stem lessened significantly; wet habitat is vital for the spread of A. philoxeroides from flooding to drought habitat and vice versa, because in this habitat, it had the greatest structural variations; when switching from flooding to wet then to drought habitat, the variations of cuticular wax layer, collenchyma cell wall, phloem fiber cell wall, pith cavity area ratio, diameter of vessel lumen, and hair density on both leaf surfaces, played the most important role. These responsive variables contribute most to the adaptation of A. philoxeroides to diverse habitats with considerably various water availability.

Adaptive Phenotypic Differences to Low Potassium Soil of Two Cotton Genotypes with Various Potassium-Use Efficiencies

Cotton (Gossypium hirsutum L.) is one of the most important cash crops in the world, and potassium (K) is an important limiting factor for cotton farming. Therefore, it is critical to improve K-use efficiency by selecting or breeding cotton genotypes with high K-use efficiency. Through a pot experiment with low-K soil, this article documentes the differences in vessel element anatomy and root hair traits between two cotton genotypes with different K-use efficiencies at both seedling and boll stages. Experimental results showed that at the seedling stage both frequency and length of root hair in the genotype with high K-use efficiency were significantly greater than those of the genotype with low K-use efficiency, but the frequency and diameter of vessels were not significantly different between the two genotypes. In the boll stage, the vessel frequencies in root, stem, petiole, and carpophore; root hair frequency, and length of high K-use-efficiency genotype were all significantly greater than those of the low K-use-efficiency genotype. The denser and longer root hairs were often found and accompanied by thicker vessel elements in the genotype with high K-use efficiency. This means the genotype had greater nutrient uptake and transportation capacity. The root hairs, vessel elements in root, stem, petiole, and carpophore, formed a complete system for nutrient uptake and translocation. The results from this study provide valuable information for the breeding of high K-use-efficiency cotton.

A plant nutrition strategy for ex-situ conservation based on “Ecological Similarity”

This paper reviewed a large scale conservation work of rare and endangered plants currently conducted in main botanical gardens in China, and the existed, predictable and neglected problems on plant growth and reproduction in ex-situ conservation process. Considered the status quo in plant ex conservation, a nutritional strategy on the plant conservation was proposed based on ‘Ecological Similarity’. Its main idea was that the ex-situ conservation plants coming from natural ecosystem were compulsively allocated in the agro-ecosystems and would return to natural ecosystem ultimately. Therefore, research on plant nutrition of the ex-situ conservation plants should neither just pursue yield and quality as that in agro-ecosystems nor merely stay on intrinsic natures without human intervening. We should give attentions to both of their attributes as in natural ecosystems and in agro-ecosystems, i.e., taking full advantage of plant nutritional measures as in agro-ecosystems to solve actual survival problems of the ex-conservation plants, and ensuring the final goal of returning to nature and playing its ecological role.