Soil physical and chemical properties (0−10 cm) of the study site prior to the land conversion.

<p>Soil physical and chemical properties (0−10 cm) of the study site prior to the land conversion.</p

Cumulative N₂O emissions under rice and vegetables with or without fertilization during the study period.

<p>Treatments are RF, rice with fertilization; NRF, rice with no fertilization; VF, vegetables with fertilization, and VNF, vegetables with no fertilization.</p

Rice and vegetables yields as affected by treatment in each growing season.

<p>The different superscript letters within the same column between different treatments indicate significant differences.</p

Seasonal dynamics of: (a) relative CPC deficits at QYZ station from 2003 to 2010; (b) mean relative CPC and Ta deficits

<p><strong>Figure 4.</strong> Seasonal dynamics of: (a) relative CPC deficits at QYZ station from 2003 to 2010; (b) mean relative CPC and Ta deficits. Error bars denote the standard deviation of deficits in each season. The subtropical coniferous forest ecosystem at Qianyanzhou station was divided into four seasons: spring (March, April and May); summer (June, July and August); autumn (September, October and November); winter (December, January and February) in regard to episodic summer drought attributable to the Asian monsoon climate.</p> <p><strong>Abstract</strong></p> <p>Increasing occurrences of climate extreme events urge us to study their impacts on terrestrial carbon sequestration. Ecosystem potential productivity deficits could characterize such impacts and display the ecosystem vulnerability and resilience to the extremes in climate change, whereas few studies have analyzed the yearly dynamics of forest potential productivity deficits. Based on a perfect-deficit approach, we used <em>in situ</em> eddy covariance flux data and meteorological observation data at Qianyanzhou station from 2003 to 2010 to explore the relationship between potential productivity and climate extremes, such as droughts in 2003 and 2007, ice rain in 2005, and an ice storm in 2008. We found (1) the monthly canopy photosynthetic capacity (CPC) deficits could be mainly explained by air temperature (Ta) deficits (<em>R</em>² = 0.45, <em>p</em> < 0.000 01); (2) a significant correlation was noted between seasonal CPC deficits and co-current Ta deficits (<em>R</em>² = 0.45, <em>p</em> < 0.000 01), especially in winter (<em>R</em>² = 0.79, <em>p</em> = 0.003); (3) drought in summer exerted a negatively lagged effect on potential productivity (<em>R</em>² = 0.59, <em>p</em> = 0.02), but at a short time scale; and (4) annual CPC deficits captured the impacts of climate extremes on the forest ecosystem potential productivity, and the two largest potential productivity deficits occurred in 2003 (relative CPC deficits = 0.34) and in 2005 (relative CPC deficits = 0.35), respectively. With the perfect-deficit approach, the forest ecosystem vulnerability to extremes was analyzed in a novel way.</p

The relationship between relative CPC deficits in a specific month and P/ET in previous months

<p><b>Table 1.</b>  The relationship between relative CPC deficits in a specific month and P/ET in previous months. In general, summer droughts lasted from June to August, and we will focus only on the monthly CPC deficits in those three months. </p> <p><strong>Abstract</strong></p> <p>Increasing occurrences of climate extreme events urge us to study their impacts on terrestrial carbon sequestration. Ecosystem potential productivity deficits could characterize such impacts and display the ecosystem vulnerability and resilience to the extremes in climate change, whereas few studies have analyzed the yearly dynamics of forest potential productivity deficits. Based on a perfect-deficit approach, we used <em>in situ</em> eddy covariance flux data and meteorological observation data at Qianyanzhou station from 2003 to 2010 to explore the relationship between potential productivity and climate extremes, such as droughts in 2003 and 2007, ice rain in 2005, and an ice storm in 2008. We found (1) the monthly canopy photosynthetic capacity (CPC) deficits could be mainly explained by air temperature (Ta) deficits (<em>R</em>² = 0.45, <em>p</em> < 0.000 01); (2) a significant correlation was noted between seasonal CPC deficits and co-current Ta deficits (<em>R</em>² = 0.45, <em>p</em> < 0.000 01), especially in winter (<em>R</em>² = 0.79, <em>p</em> = 0.003); (3) drought in summer exerted a negatively lagged effect on potential productivity (<em>R</em>² = 0.59, <em>p</em> = 0.02), but at a short time scale; and (4) annual CPC deficits captured the impacts of climate extremes on the forest ecosystem potential productivity, and the two largest potential productivity deficits occurred in 2003 (relative CPC deficits = 0.34) and in 2005 (relative CPC deficits = 0.35), respectively. With the perfect-deficit approach, the forest ecosystem vulnerability to extremes was analyzed in a novel way.</p

Seasonal variations in the CH₄ fluxes and the amount of irrigation for rice and vegetables (a) and the water depth under rice and daily precipitation from May 2012 to July 2013 (b).

<p>Seasonal variations in the CH₄ fluxes and the amount of irrigation for rice and vegetables (a) and the water depth under rice and daily precipitation from May 2012 to July 2013 (b).</p

Effects of Land-Use Conversion from Double Rice Cropping to Vegetables on Methane and Nitrous Oxide Fluxes in Southern China

<div><p>Compared with CO₂, methane (CH₄) and nitrous oxide (N₂O) are potent greenhouse gases in terms of their global warming potentials. Previous studies have indicated that land-use conversion has a significant impact on greenhouse gas emissions. However, little is known regarding the impact of converting rice (<i>Oryza sativa</i> L.) to vegetable fields, an increasing trend in land-use change in southern China, on CH₄ and N₂O fluxes. The effects of converting double rice cropping to vegetables on CH₄ and N₂O fluxes were examined using a static chamber method in southern China from July 2012 to July 2013. The results indicate that CH₄ fluxes could reach 31.6 mg C m⁻² h⁻¹ under rice before land conversion. The cumulative CH₄ emissions for fertilized and unfertilized rice were 348.9 and 321.0 kg C ha⁻¹ yr⁻¹, respectively. After the land conversion, the cumulative CH₄ emissions were −0.4 and 1.4 kg C ha⁻¹ yr⁻¹ for the fertilized and unfertilized vegetable fields, respectively. Similarly, the cumulative N₂O fluxes under rice were 1.27 and 0.56 kg N ha⁻¹ yr⁻¹ for the fertilized and unfertilized treatments before the land conversion and 19.2 and 8.5 kg N ha⁻¹ yr⁻¹, respectively, after the land conversion. By combining the global warming potentials (GWPs) of both gases, the overall land-use conversion effect was minor (<i>P</i> = 0.36) with fertilization, but the conversion reduced GWP by 63% when rice and vegetables were not fertilized. Increase in CH₄ emissions increased GWP under rice compared with vegetables with non-fertilization, but increased N₂O emissions compensated for similar GWPs with fertilization under rice and vegetables.</p></div

Results from the linear mixed model on the effects of land use and fertilization on the CH₄ and N₂O fluxes.

<p>Results from the linear mixed model on the effects of land use and fertilization on the CH₄ and N₂O fluxes.</p

Global warming potentials under rice and vegetables with or without chemical fertilization.

<p>Treatments are RF, rice with fertilization; NRF, rice with no fertilization; VF, vegetables with fertilization, and VNF, vegetables with no fertilization. Bars with different letter at the top are significantly different at <i>P</i> = 0.05 by the least significant difference test.</p

Variation of relative monthly CPC deficits and relative monthly air temperature (Ta) deficits

<p><strong>Figure 2.</strong> Variation of relative monthly CPC deficits and relative monthly air temperature (Ta) deficits. CPC deficits monthly dynamics (black line) and Ta deficits monthly dynamics (blue line). Ta deficits were calculated by corresponding half-hourly meteorological data with the perfect-deficit approach. The relative deficits were the values of CPC and Ta deficits normalized by the total area of their perfect curve integrated over each month, respectively.</p> <p><strong>Abstract</strong></p> <p>Increasing occurrences of climate extreme events urge us to study their impacts on terrestrial carbon sequestration. Ecosystem potential productivity deficits could characterize such impacts and display the ecosystem vulnerability and resilience to the extremes in climate change, whereas few studies have analyzed the yearly dynamics of forest potential productivity deficits. Based on a perfect-deficit approach, we used <em>in situ</em> eddy covariance flux data and meteorological observation data at Qianyanzhou station from 2003 to 2010 to explore the relationship between potential productivity and climate extremes, such as droughts in 2003 and 2007, ice rain in 2005, and an ice storm in 2008. We found (1) the monthly canopy photosynthetic capacity (CPC) deficits could be mainly explained by air temperature (Ta) deficits (<em>R</em>² = 0.45, <em>p</em> < 0.000 01); (2) a significant correlation was noted between seasonal CPC deficits and co-current Ta deficits (<em>R</em>² = 0.45, <em>p</em> < 0.000 01), especially in winter (<em>R</em>² = 0.79, <em>p</em> = 0.003); (3) drought in summer exerted a negatively lagged effect on potential productivity (<em>R</em>² = 0.59, <em>p</em> = 0.02), but at a short time scale; and (4) annual CPC deficits captured the impacts of climate extremes on the forest ecosystem potential productivity, and the two largest potential productivity deficits occurred in 2003 (relative CPC deficits = 0.34) and in 2005 (relative CPC deficits = 0.35), respectively. With the perfect-deficit approach, the forest ecosystem vulnerability to extremes was analyzed in a novel way.</p